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Geology of the country north of Derby. Memoir for 1:50 000 sheet 125

By D. V. Frost and J. G. O. Smart

Bibliographical reference: Frost, D. V. and Smart, J. G. O. 1979. Geology of the country north of Derby. Mem. Geol. Surv. G.B., sheet 125.

• Authors
• D. V. Frost and J. G. O. Smart
• Contributors
• Stratigraphy N. Aitkenhead
• Geophysics J. D. Cornwell
• Palaeontology M. Mitchell W. H. C. Ramsbottom M. A. Calver and J. Pattison
• Micropalaeontology M. J. Reynolds and G. Warrington
• Petrography R. K. Harrison K. S. Siddiqui and N. G. Berridge

Geological Survey of Great Britain England and Wales, Institute of Geological Sciences  Natural Environment Research Council

London Her Majesty's Stationery Office 1979 © Crown copyright 1979 ISBN 0 11 884119 X.

Authors

D. V. Frost, Bsc, PhD and J. G. O. Smart, BSc

Contributors

N. Aitkenhead, BSc, PhD, N. G. Berridge, BSc, PhD, M. A. Calver, MA, PhD, J. D. Cornwell, MSc, PhD, M. Mitchell, MA, J. Pattison, MSc, W. H. C. Ramsbottom MA, PhD, M. J. Reynolds, BSc, MPhil, K. S. Siddiqui, MSc and G. Warrington, BSc, PhD Institute of Geological Sciences, Ring Road Halton, Leeds LS15 8TQ R. K. Harrison, MSc Institute of Geological Sciences, London

Typeset for the Institute of Geological Sciences by Raithby, Lawrence & Company Ltd, Leicester and London

Illustration films by U.D.O. Jenn Ltd, London

Printed in England for Her Majesty's Stationery Office by Ebenezer Baylis and Son, Limited, The Trinity Press, Worcester, and London. Dd 696803 K16

(Front cover)

(Rear cover)

(Dust jacket front) A portion of a typical geological map SK44SW (1:10,560) of the Coal Measues (Westphalian) near Smalley, south-east Derbyshire showing the complex stratigraphy and structure of the area. It gives some indication of the amount of detailed information which has to be assessed from surface exposures and features, underground mines and archival records, before the geology can be interpreted and a geological map produced.

(Dust jacket rear)

Other publications of the Institute dealing with the geology of this and adjoining districts

Books

• British Regional Geology
• The Pennines and adjacent areas, 3rd Edition 1954, reprinted 1978
• Memoirs
• Geology of the country around Buxton (in preparation)
• Geology of the country around Chesterfield, Matlock and Mansfield, 1967
• Geology of the country around Ollerton, 1967
• Geology of the country around Ashbourne (in preparation)
• Geology of the country around Burton upon Trent, Rugeley and Uttoxeter, 1955

Maps

• 1: 625 000
• Sheet 2 Geological
• Sheet 2 Quaternary
• Sheet 2 Aeromagnetic
• 1: 50 000 (and one inch to one mile)
• Sheet 111 (Buxton) 1978
• Sheet 112 (Chesterfield) 1963
• Sheet 113 (Ollerton) 1966
• Sheet 124 (Ashbourne) in preparation
• Sheet 126 (Nottingham) 1974
• Sheet 140 (Burton upon Trent) 1953
• Sheet 141 (Loughborough) 1976
• Sheet 142 (Melton Mowbray) 1977
• 1: 25 000
• Matlock

Preface

This memoir describes the geology of the district covered by the Derby (125) Sheet 1: 50 000 Geological Map of England and Wales. The district was originally surveyed on the scale of one-inch to one mile by W. W. Smyth, A. C. Ramsay, E. Hull, W. T. Aveline and T. R. Polwhele and the results published on Old Series sheets 71 NW and 71 NE between 1855 and 1858. Subsequent additions by A. H. Green, W. T. Aveline and J. R. Dakyns resulted in further publication in 1867 to 1878. A six-inch survey was carried out by W. Gibson, T. I. Pocock, C. B. Wedd, R. L. Sherlock, G. W. Lamplugh and C. Fox-Strangways between 1902 and 1907: the uncoloured one-inch sheet with drift lines was published in 1907 and completed in colour in 1908.

During the 1939–45 war Mr W. N. Edwards carried out a reconnaissance survey of the exposed coalfield areas of the district, based upon mining information compiled by himself and Mr A. J. Butler. Dr J. Shirley recorded information from opencast operations during this period. The northern margin of the Derby sheet was resurveyed on a six-inch scale by Messrs E. G. Smith, G. H. Rhys, P. McL. D. Duff and R. A. Eden during their work on the adjoining Chesterfield sheet from 1952 to 1960. Systematic fieldwork on the Derby sheet was started in 1960 by Dr D. V. Frost to be joined in 1961 by Mr J. G. 0. Smart and later, by Dr N. Aitkenhead in 1965, with whose help the sheet was completed in 1966. The resurvey was under the supervision of Mr D. R. A. Ponsford as District Geologist. The six-inch maps covered by the various surveyors are listed on p. xi. The solid with drift edition of the 1: 50 000 map was published in 1972. Part of the Derby district is covered by a special 1: 25 000 sheet (Matlock) published in 1970.

The writing and compilation of the present memoir has been shared equally by Mr Smart and Dr Frost. Mr Smart was largely responsible for the Namurian, Westphalian (A and B), Quaternary and structural chapters. Dr Frost has written much of the Dinantian, Westphalian (C), Permo-Triassic and Economic products and water supply chapters. Dr Aitkenhead has contributed towards many of the chapters and in particular that on the Namurian. The memoir was edited by Mr D. R. A. Ponsford.

Mr M. Mitchell identified the fossils from the Dinantian and contributed an account of the stratigraphical palaeontology. Dr W. H. C. Ramsbottom and Dr M. A. Calver, assisted by Miss D. M. Gregory, identified fossils from the Namurian and Westphalian respectively and contributed to the relevant stratigraphical chapters. Mr M. J. Reynolds has provided micropalaeontological information from the Namurian. Mr J. Pattison has identified the Permian macrofossils and Dr G. Warrington has supplied palynological data. Mr R. K. Harrison, Dr N. Berridge and Mr K. S. Siddiqui have supplied mineralogical and petrological data for several chapters, and Dr J. D. Cornwell has written a geophysical account of the area. Mr M. Lock, Coal Scientist/Deputy Regional Geologist, of the National Coal Board has contributed an account on the properties of the coals and Mr J. E. Metcalfe, formerly Regional Opencast Manager (Development), has written a short history of opencast mining in the district.

Grateful acknowledgement is made to numerous organisations and individuals for generous help, advice and information, in particular to Mr R. E. Elliott and his staff of the Regional Geological Services of the National Coal Board, to Mr Metcalfe and his staff of the Opencast Executive and to the survey staff of the now superseded Nos. 4, 5 and 6 Areas of the National Coal Board, East Midlands Division. BP Limited has kindly sanctioned the inclusion of records of oil bores.

The stratigraphical details, shaft and borehole sections, etc., relative to the district are so numerous that it has been necessary to present them in 'miniprint' although they were originally prepared for full publication. This has resulted in some duplication between the two sections particularly in Chapters 4 and 10. The miniprint section is listed on p. vi and appears at the back of the memoir. Page-sized copies of this material can be provided by the Institute of Geological Sciences on application.

Austin W. Woodland Director, Institute of Geological Sciences, Exhibition Road, London. SW7 2DE. 26 January 1979

Six-inch maps

Published geological maps included wholly or in part in 1:50 000 Sheet 125 (Derby) are listed below with the names of the surveyors and dates of survey. The surveyors were N. Aitkenhead, P.McL. D. Duff, R.A. Eden, D.V. Frost, G. H. Rhys, J.G.O. Smart and E.G. Smith. All the maps are published.

Notes

• Throughout the memoir the word 'district' refers to the area covered by the Derby (125) Sheet.
• National Grid references are given in square brackets. Unless otherwise stated all lie within the 100 km square SK.
• Numbers preceded by L refer to photographs in the Institute's collections.
• Letters preceding specimen numbers refer to Institute collections as follows:
• E English sliced rocks; GSM Leeds; Za Leeds

Geology of the country north of Derby—summary

The Derby district lies at the south-eastern tip of the Pennines and includes areas of unspoilt beauty in the west, contrasting markedly with the industrial landscape of the East Midlands Coalfield to the east.

The importance and prosperity of the district is due largely to its mineral wealth. Lead has been exploited since Roman times; other economic products include coal, ironstone, limestone, moulding sands and refractory and building materials.

After an introductory chapter, the general stratigraphy of the Carboniferous, Permian and Triassic rocks is described and illustrated with numerous plates and figures. A brief account of the Neogene deposits is followed by chapters on the Quaternary era, the structure and the economic products of the area. A special chapter on geophysical investigations interprets basement structures of the district and places it in an overall regional setting.

Local details of the stratigraphy and palaeontology of the Carboniferous, Permo-Triassic, and Quaternary rocks, together with further information on their structure and geophysical aspects, are included in a miniprint section in an attempt to reduce the size and cost of this publication.

Appendices, also in miniprint, contain comprehensive summaries of boreholes, shafts and drifts, detailed recordings of sections of Westphalian strata, the locations of opencast sites and a complete list of Geological Survey photographs of the district.

Geological sequence

The rocks summarised below are present in the district

Chapter 1 Introduction

Physical features and drainage

This memoir describes the Derby (125) Sheet of the 1: 50 000 (formerly One-inch) Geological Map of England and Wales. It completes the resurvey of the exposed part of the Yorkshire and East Midlands Coalfield, the southern limit of which is within this district (Figure 1).

The district lies chiefly in Derbyshire but includes part of Nottinghamshire to the east of the River Erewash, which forms the county boundary (Figure 2).

The highest ground, composed of the oldest rocks of the district (Dinantian limestone), lies to the north-west near Wirksworth at a little over 1000 ft. The lowest ground is in the south-east near Beeston where alluvium of the River Trent overlies Triassic rocks at an altitude of a little under 100 ft.

The two major rivers are the Derwent and Erewash, which drain southwards to join the Trent just beyond the southern margin of the district. The River Derwent and its tributary, the Ecclesbourne, drain the western hills, composed of Namurian rocks, including thick sandstones such as the Ashover Grit, which reaches a height of 1032 ft at Alport Hill. The River Erewash, in the east, traverses the gentler landscapes of the Westphalian rocks.

Along the southern and eastern margins of the district the Permo-Triassic rocks, cropping out in a belt some 3 miles wide, produce a varied topography of limestone dip-slopes, undulating heavy clay lands and well-drained, elevated sandy areas.

The south-eastern corner of the Derbyshire Dome is included in the district near Wirksworth in the north-west. Here the Dinantian outcrop is given over largely to upland pastures, and the once flourishing lead/zinc mining industry centred on Wirksworth has now been replaced by limestone quarrying. The village of Crich, 4 miles E of Wirksworth, stands on limestone which crops out on the southern flank of an anticlinal inlier.

Further beds of Dinantian age crop out in the Ecclesbourne Valley, west of Duffield, but they are composed of mudstones, siltstones and thin limestones so the topography is comparable with that of the Westphalian outcrop.

The Namurian rocks of the Derwent catchment are of little economic importance, their outcrop comprising an area of small farms, some of which are being replaced by low-density housing for the commuters of the large towns to the east and south. The Derwent Valley has for many years been a major road and rail route, with Ambergate an important junction. It is now better known for the numerous factories and mills strung along its length.

The exposed coalfield has been extensively exploited for its coal, ironstone, seatearth and brick clay since the beginning of the industrial revolution. Much of the ground is covered by buildings, tips and excavations, though pockets of mixed farming still remain.

The Permo-Triassic outcrops are extensively farmed, the Lower Magnesian Limestone producing the most fertile • soil in the district. Some areas are covered by large tips and housing estates associated with deep mining in the concealed coalfield. Sand and clay have been quarried locally.

The large spreads of terrace gravels and alluvium in the Trent Valley have provided level and desirable sites for the spread of the large cities of Derby and Nottingham.

Historical

The importance and prosperity of the district is due largely to its mineral wealth. Pigs of smelted lead showing Latin inscriptions prove that lead ore was worked near Wirksworth during the Roman occupation. In 1086 Wirksworth possessed a church and a priest and was already a place of industrial prosperity. Its population of about 1000 was chiefly engaged in lead mining. The ores were placed in wood fires on the surrounding hills, such as Bole Hill, for smelting. They were then brought to the Moot Hall where the courts for the regulation of trade were, and still are held. The importance of lead has since declined, but the network of old workings and drainage levels, the hundreds of shafts and the lines of spoil heaps indicate the extent of this former mining industry (Rieuwerts, 1972).

In 1204 Derby (possibly derived from Derventio–the Roman Camp nearby) was granted privileges similar to those afforded to Nottingham but including the monopoly of dyeing cloth (Pendleton, 1886). The town was noted for its wool, malt marts and its Darby Ale. The brewing industry, now well established farther south at Burton, was probably attracted to the area by the excellent water supply from wells in the Permo-Triassic rocks.

The main industrial development of the region began with the discovery of coal and its allied deposits. The coal was first used by the smiths and lime-burners and later as a domestic fuel. Impetus was given to the coal production by the introduction of machines for shaft and underground haulage, the improvement of ventilation, and the extension of railways to convey the coal more rapidly and cheaply to the markets.

Cinderhill Colliery was one of the first Nottinghamshire collieries to adopt ventilation furnaces at the top of shafts in 1843. Despite such improvements, coal production was retarded by many explosions such as that at Annesley in 1877. By this date most large collieries had gone over to fan ventilation. Better ventilation removed the dangers of 'black damp', a concentration of carbon dioxide and nitrogen, and 'fire-damp', which was a particular problem at Pinxton Colliery (Griffin, 1971).

Willey Lane Pit, near Underwood, had the first winding engine in the district in 1838 and by 1841 engines had replaced 'whin gins' at most of the collieries, Swanwick being a notable exception. Here, however, mechanical means of haulage were first used underground to extract coal from workings in a 2 ft 7 in seam, which were too low even for the employment of children.

The first definite references to rail transportation in connection with coal mining were in 1597. Rails were laid from the pits at Wollaton and Strelley to the River Trent to ease and speed the passage of coal from the mine to the barge, for the 'Strelley Cartway is so fowle as few cariadges can pass'. A 'plateway' built by the Derby Canal Company in 1797 from Little Eaton to Kilburn and Denby remained in use until 1908 and was known as the Little Eaton gangway.

Such technological advances resulted in greatly improved productivity in the twenty years after 1840 but as the workings extended the distances from the shafts and the depths increased. More pits were sunk and more men employed to work longer hours during day and night shifts to maintain output, particularly as the best and thickest seams such as the Top Hard were by then largely worked out.

In the 1939–45 war, production of coal from the collieries was supplemented by opencast mining, and millions of tons were extracted by this means.

Although 70 collieries were working within the Derby district in 1811, only two remain open in the exposed coalfield at the time of writing. Even in the more prosperous concealed coalfield the higher thicker seams, such as the High Main, are rapidly being worked out and further exploration of the deeper coals may become necessary. There are still many millions of tons of coal left in some abandoned areas of the Derby district, but modern sophisticated machinery is unable to operate in seams that are thin, variable or faulted.

Farey, in his General View of the Agriculture and Minerals of Derbyshire of 1811, lists 18 localities where ironstone 'rakes' had been worked. Remnants of this type of ironstone working, which paid little regard to replacing or levelling the ground afterwards are still visible at Morley Park and near Stanton. Later, the ore was worked at depth by bell pits. Most of the ironstones were smelted by charcoal furnaces until about 1770 when the country's timber was exhausted. The close proximity of coal to the ironstone deposits commonly resulted in a colliery being established near the iron furnaces and mines. By 1811 all the iron made in Derbyshire was smelted in coal or coke furnaces blown by steam-driven bellows. The first such furnace installed by Francis Hurt at Morley Park, made 700 pigs of iron annually. Gradually, however, the working of Westphalian ironstone became uneconomic and ceased, and Ironville was built on levelled tips dating from the days of local iron smelting.

The declining lead, iron and coal mining industries have been replaced by the extraction of sand and gravels and limestones for aggregates, and by pottery clays such as those at Denby. The industrial landscape is correspondingly changing. Old pit tips are being levelled and used as fill, and rows of terraced houses built for miners are being demolished. The railway lines at Ambergate and Annesley, now uneconomic, are being removed. The exposed coalfield is thus slowly returning to its former agricultural state except in those areas selected for housing employees of industries peripheral to coal mining. In the west of the district there remains much unspoilt open country–a valuable recreational outlet for the population.

Basement (pre-Carboniferous) rocks

No borings have penetrated the base of the Carboniferous rocks within the district, so the nature of the underlying rocks has to be inferred from outcrops and boreholes in surrounding areas. The information available at the time was summarised by Kent (1966, 1967, 1968), who envisaged that in Carboniferous times there was a shallow basement composed of crystalline rocks similar to those now exposed in Charnwood Forest; it formed part of the Midland Barrier, lying mainly south of the Derby district and extended across the East Midlands to north Norfolk (Kent, 1967, fig. 1, p. 131). The crystalline massif is flanked to the north by a belt of quartzitic conglomerates of possible Old Red Sandstone age, found underlying the Carboniferous rocks in oil boreholes at Eakring in Nottinghamshire and in Lincolnshire. At Eakring, Kent noted (1968, ix–142) 'heavily sheared mudstone which might be older Palaeozoic or (less probably) Pre-Cambrian' underlying the conglomerates.

A more recent borehole to the north-west of the district at Eyam, Derbyshire (Dunham, 1973), proved thick Lower Carboniferous rocks overlying steeply dipping Ordovician ( ?Llanvirn) mudstones. These sediments are more closely allied to the rocks at depth at Eakring than to the shallow basement of the English Midlands.

It is therefore inferred that the basement of the major part of the Derby district consists of folded Lower Palaeozoic rocks, possibly overlain in the east by a wedge of Old Red Sandstone which could account for the easterly decrease in Bouguer anomaly values discussed on p. 117. In the extreme south of the district Carboniferous rocks may rest directly on crystalline Pre-Cambrian rocks.

Dr Cornwell (Chapter 10) discusses geophysical evidence for the presence, within the Lower Palaeozoic and possible Precambrian basement sequences, of a belt of volcanic rocks extending south-eastwards from Wirksworth through Nottingham. The Aeromagnetic Map (Figure 65) shows a broad magnetic high in this area. More localised magnetic anomalies, east of Belper and at Hucknall, may indicate intrusions, possibly penetrating the Lower Carboniferous.

Geological history

Following the Caledonian earth movements, the Dinantian Sea transgressed over the eroded basement rocks into the Derby district. No Tournaisian rocks are known but their presence may be inferred at depth in the district. The oldest rocks seen at outcrop are Dinantian limestones which are exposed near Wirksworth; they were deposited slowly on a 'shelf', in relatively shallow seas rich in animal life. At the same time, greater thicknesses of mudstones, thinly bedded, dark grey limestones and thin sandstones were being laid down to the south-west around Duffield and Derby in deeper muddier waters of a basinal area known as the Widmerpool Gulf. Sedimentation here was at times so rapid that the deposits became unstable and, perhaps triggered off by earthquakes, slumped down the slopes of the Gulf to form turbidites. These are thought to have come mainly from the south.

Between basin and shelf deposition was a reef belt, in which sedimentation kept pace with subsidence. At times local uplift along this margin upset the delicate balance and erosion of the reefs gave rise to non-sequences and unconformities within the limestone formations.

Periodically during Dinantian times volcanic activity resulted in the extrusion of lavas from vents like that at Hopton and the formation of tuffs in both the Widmerpool Gulf and the Derbyshire shelf areas.

In late Dinantian times the rate of subsidence increased and basinal conditions extended northwards until, in the early Namurian, shales were deposited against the eroded limestone cliffs of the reef margin and eventually spread over them on to the shelf itself. However, deposition in the shelf area was still slow compared with the turbidite deposition which continued in the Widmerpool Gulf. Later in the Namurian, the pattern of sedimentation changed with the establishment of a large delta resulting in the deposition of the Ashover Grit. Carboniferous sedimentation for the first time outpaced subsidence and a coal swamp was established which is now represented by a coal seam overlying the Ashover Grit. Subsequent fluctuations in the rate of subsidence are reflected in distinct cycles of sedimentation, each beginning with the deposition of marine shales which pass up through mudstones into deltaic siltstones and sandstones.

In Westphalian times the Namurian pattern continued but with increasing dominance of shallow-water deposits of argillaceous composition. The cycles increased in number—but became generally thinner. Emergence, with the establishment of land floras, became more frequent and in many cases prolonged, resulting in coal complexes. Volcanic activity, which persisted to the east, resulted in sporadic showers of fine ash falling in the Derby district.

The oncoming of the Hercynian Orogeny was heralded by the intrusion of dolerite sills into the Dinantian rocks. Regional uplift and increased erosion is reflected by fewer coals and more sandstones in the Westphalian C sequence. Eventually the whole of the Pennine area was uplifted, folded and faulted, much of the fracturing following old lines of weakness established in Caledonian times. A long period of denudation followed during the late Carboniferous and early Permian when many thousands of feet of Carboniferous rocks were removed. The resulting land surface was subjected to tropical weathering and the truncated Carboniferous rocks were superficially reddened to a depth of 30 ft or so.

In Upper Permian times the sea returned from the east and calcareous sediments were laid down on a peneplain in a south-western extension of the Zechstein Sea during a long period of desiccation and slow deposition under arid conditions. This ended with a period of fluvial activity and deposition of Triassic sands over a wider area than that covered by the Zechstein Sea.

There followed a period of minor uplift, when the Triassic deposits were locally removed and in some places the old Carboniferous surface was again laid bare. Further subsidence occurred and the later Triassic rocks were deposited in another period of increasing aridity.

During Permo-Triassic times, deep-seated migratory fluids invaded the rocks of the district, particularly the well-jointed and fractured Dinantian limestones and left ore deposits of lead, zinc and copper.

Most of the post-Triassic rocks of the district were removed by prolonged erosion during the Tertiary, but isolated remnants of reworked Triassic sands, dating from Neogene times, were preserved in hollows in the Dinantian limestone surface. The Alpine Orogeny produced only a slight easterly and southerly tilt, associated with minor faulting along pre-existing Hercynian fractures.

During the Pleistocene, a Wolstonian ice sheet overrode the district from the north-west; it met ice advancing from the east along the southern margin of the district and later melted, probably after a long period of stagnation. It left deposits of boulder clay and sand and gravel now found as isolated patches mainly on the higher ground.

Terraces of the River Trent were formed probably during the waning of the Wolstonian ice sheet and during the subsequent Ipswichian Interglacial. The succeeding Devensian ice sheet did not reach the district, which suffered periglacial conditions with the formation of frost wedges, valley bulges and cambering and the deposition of head, and further river gravels.

The Flandrian Stage saw the final evolution of the landscape into its present form with the deposition of the recent alluvium of rivers and streams. However, the earthquake activity which still continues on a small scale in the Derby district is a reminder of its instability in the past.

Chapter 2 Dinantian (Carboniferous Limestone Series)

Introduction

The Dinantian limestones of Derbyshire may be regarded as belonging to three main facies (Edwards and Trotter, 1954) all of which are represented within the district. They comprise a 'massif' or 'shelf' facies of beds deposited over an ancient relatively stable block, a 'basin' facies developed in more rapidly subsiding areas around the block, and a 'marginal' facies, usually associated with 'reef' beds, deposited between the block and the basin. This facies classification provides a convenient way of describing the palaeogeography and the related lithological types but is probably an oversimplification of the complex interrelationships of the processes of sedimentation. Availability and proximity to source of sediments, depth of water and strength of currents may be as important as the implied structural controls.

Limestones of the 'shelf' and 'marginal' facies crop out in the Wirksworth–Hopton area, where they form the south-eastern margin of the main limestone outcrop of the 'Derbyshire Dome'. Beds of 'shelf' facies also crop out in a small area around Crich and were proved at depth in Ironville oil bores Nos. 1 and 3 drilled through Westphalian and Namurian rocks farther east (see (Figure 3) and Figure 4)).

The 'basin' facies is developed to the south of Wirksworth in the Widmerpool Gulf (Falcon and Kent, 1960, p. 18), where the Dinantian beds comprise a thick turbidite sequence of mudstones, siltstones, sandstones and dark impure limestones for which the name Widmerpool Formation is here introduced. South of Wirksworth (Figure 3) the Widmerpool Formation is concealed below Namurian beds, but farther south towards Derby it crops out over some six square miles in inliers surrounded by Triassic rocks. The information from these scattered surface exposures is supplemented by the Duffield Borehole [SK 3428 4217], drilled in 1967 (Institute of Geological Sciences, 1968, p.82; Aitkenhead, 1977), and it is now possible to trace the changes from 'shelf' to 'basin' facies over a distance of 8 miles from Wirksworth to Duffield and to interpret the complex geological history of the 'marginal' area between these two facies. Further information on the gulf was obtained from the Trusley Borehole [SK 2548 3588] drilled in 1969 by the Institute of Geological Sciences. This borehole, sited in the south-western corner of the district some 11 miles S of Wirksworth, proved a reddened facies of the Widmerpool Formation.

General account

The Wirksworth–Derby area provides a cross-section through a range of typical 'block' and 'basin' sediments in the Carboniferous of northern England.

The Widmerpool Gulf is characterised by a thick monotonous sequence of successive graded units of calcareous mudstones, siltstones and sandstones contrasting faunally and lithologically with intercalated darker fissile mudstones. There is a complete absence of sedimentary structures and fossils positively indicative of a shallow-water environment, and the graded units are thought to have been deposited by turbidity currents in a marine environment deeper than that of the 'shelf' areas.

In the 'shelf' facies near Matlock, the Hoptonwood Limestone (D₁) and Matlock Limestone (D₂) comprise grey, massive, standard limestones, but southwards to Wirksworth the top of the sequence thins and passes into irregularly bedded dark-coloured limestones associated with non-sequences and breccias. A 'reef' facies, confined to the highest beds (Cawdor Limestone = P₂) at Matlock, is also present in the upper part of the Hoptonwood Limestone farther south in the Wirksworth–Hopton marginal area. Distinct knoll-reefs are uncommon, presumably due to the erosion to which limestones of D₁ and D₂ age were subjected. Unconformities are locally present between the various mapped subdivisions, i.e. between beds of D₁ and D„ D₂ and P, and P₂ and E ages, as well as within P₂ beds.

The transition from 'shelf' to 'basin' facies through the 'marginal' reef belt probably occurs rapidly over a narrow zone which is commonly faulted and/or folded. The fourfold increase in thickness of Dinantian sediments into the Widmerpool Gulf is a measure of both the greater subsidence and the more rapid deposition in the gulf compared with the positive stable 'block' or 'shelf' area.

Using the criteria listed by Kent (1966, p. 325) it is possible to indicate the limits of the Widmerpool Gulf within the district. Assuming that the presence of thick Namurian sediments is a continuation of a thick Dinantian development beneath, then the north-eastern limits of the Widmerpool Gulf can be delineated as shown in (Figure 3). The Hopton Borehole proved Namurian (E₂) shales at least three times thicker than the equivalent strata at Ashover some 6 miles to the north-east. Ramsbottom and others (1962, fig. 1) show the thinning of Namurian shales across the axes of the Ashover and Crich anticlines, suggesting that these areas remained positive throughout most of Namurian times. Conversely, in the intervening syncline there is a south-westwards thickening of some 200 ft towards Wirksworth and this may be accounted for by the small embayment on the northern edge of the 'gulf' (Figure 3).

The juxtaposition of Namurian thickening together with important fault lines, e.g. near Smalley (SK 44 SW), Ripley (SK 44 NW) and Wirksworth (SK 25 SE) facilitates further delineation.

It is assumed that Duffield Borehole occupies a central position in the Widmerpool Gulf, but little information is available regarding the gulf's south-western limits. Trusley Borehole, drilled for 177 ft below the base of the Trias, showed a Carboniferous sequence of reddened turbiditic sandstones and siltstones with interbedded pelagic mudstones. The sediments are of 'basin' facies but occupy a more distal position than those in Duffield Borehole and the Kirk Langley area. The sediments were unusual in containing thin horizontal beds and irregular discordant veinlets of gypsum.

The northernmost exposure, at Flower Lilies (see locality 4, (Figure 3) and p. 130c), contains more limestone than any other recorded sequence in the Widmerpool Formation (Green and others, 1887, p. 88). This may indicate either a position nearer the margin of the gulf than Duffield, so that the gulf was less extensive in Dinantian than in Namurian times, or some local facies change within the gulf.

The north-westerly trend of the gulf in the present district compares well with that of the Edale Gulf and Gainsborough Trough. This and other evidence supports Kent's (1966) postulate that the gulfs originated as down-warped and/or faulted belts along Charnian lines of weakness.

Shelf and marginal facies

The main outcrop

Subdivisions erected by Eden and others (1959, p. 33) in the adjacent Matlock area are here modified in conformity with current stratigraphical practice so as to give the following classification:

Smith and others (1967, pp. 11–12) noted that in the Matlock area the Hoptonwood and Matlock limestones consist largely of grey massive beds typical of the 'shelf' facies, but that towards Wirksworth the Matlock Limestone thins and passes into irregularly bedded dark-coloured limestones with non-sequences and breccias. They infer that the latter form part of an apron-reef complex largely hidden beneath the Cawdor and Namurian shales to the south and east. Shirley (1959, p. 420) noted that south-west of Wirksworth, reef-like limestones occur in D₁ (Hoptonwood Limestone) and reef-like mounds, possibly of Cawdor Limestone, project through the overlying Namurian shales [SK 2800 5300]. The present survey has confirmed these strati-graphical changes which occur as the limestone margin is approached. Boreholes beyond this margin, e.g. at Hopton, prove thick Namurian (E₂) shales which between Hopton and Carsington overstep westwards on to successively lower horizons of the Hoptonwood Limestone. There is therefore good evidence of a significant break or breaks within the sequence in P Zone or post-P Zone times with the removal or non-deposition of some 300 ft of sediments in this marginal area. The concealed apron-reef postulated to the south-east of Wirksworth (Smith and others, 1967, p. 13) may have been partly or wholly removed by late Dinantianearly Namurian erosion, following local uplift, as in the area to the south-west of Wirksworth.

Instability in the Wirksworth–Hopton area during much of early Carboniferous times is implied therefore by the transition from block to basinal deposition, by the upper Dinantian erosional breaks and associated lavas and tuffs (p. 96), and by the later ore mineralisation. The area shows many of the facies changes present in the Castleton area some 20 miles to the north-north-west (Eden and others, 1964).

Hoptonwood Limestone

This formation, consists of up to 280 ft of limestones which are pale grey to off-white, fine-grained to porcellanous, partly oolitic and massively bedded. Macrofossils are not common but shelly concentrations occur along the southern margin of the outcrop and a small knoll-reef [SK 2610 5332] near Hopton contains a D₁ assemblage. The Hoptonwood Limestone crops out over a large area to the north of Carsington and Hopton, where extensive dolomitisation often masks the original lithology and fauna. Its base is not exposed within the district although the limestones in the floor of Stone Dene [SK 2580 5369] near Hopton must be close to the underlying Griffe Grange Bed (Smith and others, 1967, p. 8).

Beds at the top of the Hoptonwood Limestone crop out on a 'promontory' south of Godfreyhole and are also exposed as inliers in quarries on the west or upthrow side of the Gulf Fault north-west of Wirksworth. In these quarries the highest beds pass south-eastwards into disturbed and brecciated strata associated with the reef margin.

Interbedded with the limestones are lavas and at least seven clay bands or wayboards, some of which may be lateral equivalents of lavas. An agglomerate, which probably occupies a volcanic neck, is present at Hopton.

The Hoptonwood Limestone contains limited coral and brachiopod faunas including Carcinophyllum vaughani, Dibunophyllum bourtonense, Palaeosmilia murchisoni and Davidsonina septosa, an assemblage which is characteristic of the Lower Dibunophyllum (D₁) Zone. Outcrops of the reefs along the southern margin of the limestone yield rich brachiopod faunas typical of this zone including Overtonia fimbriata, Proboscidella proboscidea, Pugnax pugnus [small form] and Pugnoides triplex, forms which are restricted to beds of this age in the reef limestones at Treak Cliff, Castleton (Mitchell in Stevenson and Gaunt, 1971, p. 149). Information is insufficient however to indicate which part of the zone the fauna represents.

The Hoptonwood Limestone represents the Fifth Group of Minor Cycles of Ramsbottom (1973) and is of Asbian age (George and others, 1976, fig. 8). The general thickness and presence of unconformities suggest that parts of the sequence are probably missing.

Matlock Limestone

This formation comprises limestones with the Matlock Lower Lava at the base.

The Lava is not exposed but it forms a well-marked feature 200 yd W of Hopton Tunnel and can be traced for one mile southwards to the Yokecliffe Rake where it apparently ends, but may possibly continue and be connected to a feeder down the Rake. Soft green clay some 7 in thick was proved in a borehole [SK 2730 5434] near Four Lane Ends and is considered to be at the horizon of the Lava.

To the north, on the Chesterfield (112) Sheet, the Matlock Lower Lava, an amygdaloidal olivine-basalt, is an accumulation of flows up to 380 ft thick, but west of Wirksworth it has a maximum thickness of 15 ft and may be a single flow.

The overlying beds comprise variable dark grey and grey limestones up to 140 ft thick, with fossiliferous bands and locally much chert. The top shows sharp lithological changes.

A small patch of fossiliferous reef limestone is preserved in Stonycroft Quarry [SK 2862 5431] at the top of the formation.

Traced south-eastwards over a distance of about 100 yd through the quarries north and west of Wirksworth, the whole of the Matlock Limestone (i.e. 140 ft) is progressively cut out so that in Baileycroft Quarry, Wirksworth (Plate 2); (Figure 5) dark, thinly bedded Cawdor Limestone rests directly on the massive Hoptonwood Limestone. An unconformity is also present within the Matlock Limestone. In Dale Quarry, 300 yd W of Baileycroft Quarry, dark grey cherty Matlock Limestone is again present. Most of the quarry faces are inaccessible.

In Middlepeak Quarry, a 'Girvanella' band (possibly equivalent to the Upper 'Girvanella' Band of north Derbyshire) lies some 18 ft from the top of the Matlock Limestone, here totalling 80 ft. The band has not been found in Stonycroft Quarry 200 yd to the south, where 60 ft of D₂ beds were measured. 'Girvanella' nodules are present near the base of the Matlock Limestone in a small quarry [SK 2729 5362] near Godfreyhole. This may be the correlative of the Lower 'Girvanella' Band of North Derbyshire (Eden and others, 1964, fig.1), and if so shows that the lower part of the sequence is complete.

The Matlock Limestone crops out north-west of Wirksworth and is well exposed in the approaches to Hopton Tunnel and in the Yokecliffe Rake fault scarp. It is dark grey and well-bedded but sporadic massive pale greyish brown beds provide valuable marker horizons. Bedded chert as well as irregular chert nodules are common, and there are several coral and shelly bands. Limestone breccias occur at the top of the sequence. Only a small part south of Hopton Tunnel has been dolomitised.

The eastern side of the Godfreyhole 'promontory' comprises some 50 ft of dark grey, well-bedded limestones which appear to be directly overlain by low Namurian (E) shales.

The fauna of the Matlock Limestone is more varied than that of the Hoptonwood Limestone and includes Aulophyllum fungites pachyendothecum, Dibunophyllum bipartitum bipartitum, Diphyphyllum lateseptatum, Lonsdaleia floriformis, Palaeosmilia regia, Megachonetes siblyi, Pugilis pugilis and Striatifera striata–all diagnostic of the Upper Dibunophyllum (D₂) Zone. The Matlock Limestone represents the Sixth Group of Minor Cycles of Ramsbottom (1973) and is of Brigantian age (George and others, 1976, fig. 8).

Cawdor Group

This group consists of fossiliferous thinly bedded cherty limestones with shale partings (Cawdor Limestone) totalling 60 ft in thickness, overlain by Cawdor Shale some 20ft thick. In the Derby district the basal 20 ft or so of Cawdor Limestone are well exposed, but the top is missing due to unconformable overlap by Namurian shales. The basal beds crop out north and west of Wirksworth and comprise grey and dark grey thinly bedded cherty limestones with shale partings. Most of these limestones have been extracted in the Wirksworth quarries (Middlepeak, Stonycroft and Bailey-croft), but a few remaining isolated pillars and pockets provide excellent collecting grounds for the shelly reef-type faunas. In the accessible north-western corner of Dale Quarry the Matlock Limestone–Cawdor Limestone junction is well displayed.

South-west of Wirksworth and south of the Yokecliffe Rake the Cawdor Limestone is missing owing to Namurian overlap, but near Millers Green [SK 2793 5305] a topographical knoll, some 120 yd by 100 yd, of poorly bedded massive pale grey-cream limestone protrudes through the surrounding shales, and contains a reef fauna of the Cawdor Limestone (Shirley, 1959, p. 420). Traced north-eastwards, up dip, the limestone passes into pale grey brachiopod-rich and partly oolitic limestone. South-eastwards, a few feet of thinly bedded dark grey limestone are poorly exposed [SK 2797 5300]. Apparently overlying the pale grey 'knoll' limestone, they are in turn overlain by laminated shales which have yielded E_2a goniatites some 10 ft above the limestone.

There is a rich fauna of zaphrentoid corals and reef brachiopods in the Cawdor Limestone and Ramsbottom (in Smith and others, 1967, p. 52) has described the lithologies and faunas of the several distinctive facies that can be distinguished. No goniatites have been collected from the present district, but the age of the Cawdor Limestone is established by the records of Goniatites (Mesoglyphioceras) granosus and Lyrogoniatites aff. georgiensis from the Cawdor Limestone of Cawdor Quarry. These indicate an upper Posidonia (P₂) age–within the range P_2a-c, (Ramsbottom op. cit.).

Volcanic rocks

The toadstones' in this part of Derbyshire were described by Arnold-Bemrose (1894, 1907), Geikie (1897) and Pocock (in Gibson and others, 1908) (Figure 6). More recently, Harrison (in Smith and others, 1967, p. 261) has discussed the petrography of the Matlock Lower Lava. Its apparent isotopic age of 185 ± 5 million years relates to intense hydrothermal alteration subsequent to its formation (Fitch and others, 1970). Its true age must exceed that of the Ible Sill (Smith and others, 1967, p. 26), emplaced in the Hoptonwood Limestone 4 miles N of the present district, and dated at 309 ± 21 million years (op. cit).

The Hopton Agglomerate, which is exposed along the east side of the Hopton–Middleton road, was originally mapped by the Geological Survey in the 1850s as interbedded with the limestones, and was estimated to be 1000 ft below the Lower Lava. Geikie (1897) considered it was a vent with transgressive relationships to the limestone. Pocock, during the resurvey of the area in 1903, pointed out that the limestone thicknesses were exaggerated and separated the agglomerate and the limestone from the 'Yoredales' (Namurian Shales) to the south by a fault. Arnold-Bemrose (1907) discovered agglomerate to the south of Pocock's fault and suggested that the vent cut across both the limestone and overlying shales so that a fault was unnecessary.

The present survey has found no evidence for a fault south of the vent and has confirmed the northern and eastern boundaries of the agglomerate as transgressive.

The agglomerate is cut off to the north by the Yokecliffe Fault. Between Newclose and Quickset Mine [SK 2625 5379], however, 'toadstone' is commonly incorporated in the dry-stone walls of nearby fields. If this material was excavated from deep workings along the Rake, the latter may have acted as a feeder for the Matlock Lower Lava, the outcrop [SK 2752 5384] of which appears to end at the Yokecliffe Rake near Godfreyhole. Moreover, the location of this possible feeder between the vent, now filled by the Hopton Agglomerate, on the west, and the lava on the east, suggests that the three features belong to the same volcanic episode.

The agglomerate is a breccia composed of small lapilli and subangular blocks of dolerite and basalt up to 2 ft across. The basalt contains augite and feldspar, often fresh; olivines are altered and set in a black glassy base.

Crich

The northern half of this periclinal dome was described by Smith and others (1967, p.35) who give the following section:

The unexposed beds were proved in shafts now abandoned.

The village of Crich is built almost entirely on limestone, which is faulted against Ashover Grit along the Southern Crich Fault in the west. The limestone dips at angles of 4 to 20° under the Cawdor and Namurian shales to the east. To the south it plunges even more steeply, but the overlying beds are concealed by drift.

The 20 to 30 ft of Cawdor Shale overlying the limestones are not exposed, their presence being inferred from boreholes to the north.

Provings in deep boreholes

Dinantian limestone of the shelf facies has been reached in two deep boreholes within the district–Ironville Nos. 1 and 3–which were drilled into anticlines in the exposed Westphalian rocks, in the hope of finding oil.

Ironville No. 1 Oil Bore was sited on the southern end of the Ironville Anticline and the top of the Dinantian was reached at 2035 ft. Examination of the chipping samples by Mr K. S. Siddiqui showed concentrations of tuffaceous fragments at 2105 to 2220 ft, 2295 to 2300 ft and 2385 to 2390 ft. Olivine-dolerite was recorded between 2300 and 2355 ft.

The upper 70 ft of limestones are dark grey and contain a 5-ft shale band at 2075 ft—features comparable with the Cawdor Group. The beds associated with the tuffs and dolerites are probably the Matlock Limestone. Below 2390 ft the limestone is generally whitish in colour and suggestive of the Hoptonwood Limestone. Below 3000 ft the beds are more variable, dark grey alternating with pale grey-brown and white limestones which may be correlatives of the Griffe Grange Bed (p. 7).

Ironville No. 3 Oil Bore on the eastern flank of the anticline reached Dinantian limestone at 2200 ft. Spot cores of the top of the limestone showed dark grey limestones associated with black calcareous shales. Zaphrentites sp. and Diphyphyllum lateseptatum, genera recorded from the Cawdor Limestone at outcrop, occurred at 2250 ft. 'White trap' (bleached basic volcanic rock) was encountered at 2300 ft, and green and mottled tuff and agglomerate extended between 2400 and 2700 ft. The limestone beneath the volcanic rocks was pale brown to off-white and finely crystalline. The hole was completed at a depth of 2742 ft.

As at outcrop, darker limestones are common in the upper part of the succession, and paler grey or brown crystalline limestones occur towards the base. In Ironville No. 3 Oil Bore, the 300 ft of tuff and agglomerate separate the two types of limestone. Whilst accurate correlation is impossible, it seems reasonable to consider these extrusives as the approximate equivalents of the Matlock Lower Lava (see (Figure 6)) which separates the pale Hoptonwood Limestone from the Matlock and Cawdor limestones at outcrop.

Basin facies

The Widmerpool Formation outcrop borders that of the Lower Namurian in the Turnditch, Quarndon and Weston Underwood districts and forms poorly exposed inliers in the valley of Mackworth Brook near Kirk Langley, at Wildpark Wood, one mile east of Brailsford, and in a valley immediately south of Brailsford (Figure 3).

Sporadic exposures in streams such as Blind Brook, Kedleston, and Cutler Brook, Weston Underwood, show that the formation consists of thin beds of dark grey argillaceous limestone and grey calcareous siltstone; sole markings are commonly present. The beds contain plant fragments, with occasional poorly preserved bivalves (see also Gibson and others, 1908, p. 24). A few of the coarser limestones contain conspicuous crinoid and brachiopod debris. An extensive microflora obtained from a sequence near Mackworth [SK 3137 3768] included no diagnostic species. The Duffield Borehole [SK 3428 4217] was therefore drilled to establish a detailed succession of the formation. This proved Dinantian rocks belonging to the Upper Beyrichoceras (B₂), Lower Posidonia (P₁) and Upper Posidonia (P₂) zones, totalling some 2100 ft of fine-grained sediments together with igneous rocks and tuffs corresponding to the top 500 ft or so of the 'shelf' limestones north of Wirksworth. The borehole demonstrated therefore not only the complete change in facies but also a four-fold increase in the thickness of the beds (Figure 4).

Apart from igneous rocks and two relatively thin calcareous mudstone sequences the succession consists largely of turbiditic graded silty mudstone/sandstone and muddy limestone units with dark grey mudstone intercalations. Further details are given by Aitkenhead (1977).

Provisional thicknesses of strata (excluding igneous rocks) attributed to the various zones are shown below:

Six tuff bands and two dolerite sills were encountered. Details of the tuffs are as follows:

The tuffs range from fine to coarse-grained and vary in colour from pale blue to greenish grey (p. 167d). They usually contain pumice fragments and in some beds lapilli are present. Some intermixing of tuff with calcareous mud has been noted, particularly in the thickest band.

At outcrop, white, tuffaceous, calcareous clay bands 3 ft and 24 ft occur in Blind Brook [SK 3097 4233] and a temporary exposure [SK 3037 4352] respectively. They are of volcanic origin but some reworking as well as mineral replacement seems to have occurred.

Two dolerite sills are 27 ft 9 in and 220 ft 3 in thick, their bases occurring at 1779 ft 7 in (P₁) and 3337 ft 3 in (B₂) respectively. Both have chilled upper and lower margins and have baked the adjacent sediments.

A second borehole [SK 2548 3588] at Trusley in the south-west corner of the district passed through 331 ft of Triassic rocks into a sequence of purplish red sandstones, siltstones and mudstones of Dinantian age. This sequence, like Duffield, was composed largely of graded turbidite units and confirmed a southerly extension of the Widmerpool Formation. The turbidite sequence of red and purple sandstones, siltstones and silty mudstones showed grading, slumping and sole markings. The lower part of the sequence is calcareous. Interbedded with the turbidite units are red, brown and purple mudstones interlaminated with pale grey-green mudstones.

Detailed examination of representative lengths of Trusley core show that the sandstone-bearing turbidites have a proximality index (R. G. Walker, 1967) of 20 per cent compared with 96 per cent in the B₂ Zone sandstone-bearing turbidites of similar age in Duffield Borehole. Thus both sequences are of distal turbidites, but that in Duffield Borehole appears to be more distal than that in Trusley (p. 174c).

In thin sections made from the lowest and most calcareous parts of the sequence (504 ft) Dr W. H. C. Ramsbottom identified bryozoa and crinoid fragments and the following D₁ Zone algae and foraminifera–Koninckopora inflata, Archaediscus krestovnikovi, A. moelleri, Endothyra spp.and Tetrataxis sp.

Sub-Trias secondary reddening was detected throughout the 177 ft of strata proved. This is in marked contrast to surface exposures of the formation, in which reddening is restricted to patchy staining. At Trusley the Pebble Beds are absent and the Waterstones overlie the Widmerpool Formation; the thickness therefore of reddened beds may be partly a reflection of the large time interval between the Dinantian and the Anisian.

Both the Carboniferous and Triassic rocks in the Trusley Borehole are intruded by numerous gypsum veins and stringers, the thickest of which (up to 3.5 in) were usually found along the bedding planes. Whilst the presence of penecontemporaneous gypsum and anhydrite is known within the Carboniferous of the Widmerpool Gulf (Llewellyn and others, 1969, p. 85), a Triassic origin for the sulphate minerals at Trusley is considered most likely. The numerous fault planes and fractures present in the Carboniferous rocks would have provided easy access for the migrating fluids.

Miscellaneous rock-types associated with Dinantian limestones

Dolomite

Dolomite is present mainly in parts of the Hoptonwood and Matlock limestones. The contact between dolomite and limestone is sometimes sharp, but the line on the published six-inch and 1:50 000 maps mostly represents a zone of gradual transition. The dolomitic limestone weathers into characteristic 'tors' the most prominent of which occur just outside the present district, north-west of Hopton, i.e. the Harborough Rocks.

Dunham (1952, p. 402) considered the dolomite to be a product of secondary alteration which preceded the ore-mineralisation. The field relationships were discussed in detail by Parsons (1922), who considered the dolomitisation to be pre-Triassic, a view reiterated by Kent (1957).

The identification of Triassic pebbly sandstones at an elevation of about 800 ft near Blackwall [SK 2561 4959] adds weight to the conclusion that much of the Dinantian limestone in this district was once covered by Triassic sands–the deposits in the Brassington silica sand-pits being relics of this former cover (Kent, 1957). Purple-staining of the Namurian sandstones cropping out at high elevations, e.g. Black Rocks, Cromford, and the Kirk Ireton synclinal plateau together with remanie deposits of clay and Bunter-type pebbles over much of the limestone and shale outcrop near Hopton is additional evidence to support this view.

No Permian deposits are preserved, and it is unlikely that the Zechstein transgression reached this area. The Dinantian limestones may therefore have been altered by the action of the magnesium-rich Triassic waters percolating down from the sea floor. Evidence in favour of this theory is:

1. That the areas of maximum dolomitisation usually occur in regions of maximum elevation. The boundary between the dolomite and underlying limestone in Golconda Mine [SK 2437 5505], just north-west of the present district, is in the form of an irregular dome, although the bedding in the limestones is roughly horizontal (Shirley, 1959). The 'dome' may therefore be the reflection of a local elevation in the Triassic sea floor.
2. The absence of dolomitisation below the Matlock lavas, e.g. at [SK 2653 5405], suggests that they operated as a protective cap which prevented downward percolation. Similarly, notable areas of undolomitised limestone in other elevated areas may be due to the barrier afforded by local patches of Namurian shale, since removed.
3. The association of the silica-sand deposits with the dolomitisation in elevated areas.
4. Extrapolation from the area of outcrop near Turnditch suggests that the base of the Trias lay close above the dolomitised zone in the Brassington–Carsington–Yokecliffe Rake area (Figure 63).

Chert and silicified limestone

Chert is commonest in the Matlock and Cawdor limestones, where it occurs as bedded tabular sheets of limited lateral extent and as layers of irregular nodules. It decreases in importance towards the gulf margin. Pocock (in Gibson and others, 1908, p. 12) described black chert from the Cawdor Limestone in Dale Quarry and noted an abundance of foraminifera and sponge spicules. Crinoid debris is common.

The formation of chert predates the dolomitisation, and according to Sargent (1921) was an inorganic process which occurred penecontemporaneously with the formation of the surrounding limestones. The introduction of the silica was attributed to contemporary vulcanism.

Pettijohn (1957, pp. 439–440) preferred a post-depositional origin with an early segregation into nodules and bands of initially diffuse silica. Orme (1973) found that the majority of Derbyshire cherts were formed by replacement of carbonate prior to consolidation, and suggested that in many cases segregation of the inorganic silica may have been penecontemporaneous with sedimentation.

Silicified limestones or quartz rocks result from a later more intense replacement of the limestone, but are of restricted occurrence, usually associated with faults and/or mineral veins. They are considered to be products of low temperature metasomatism by hydrothermal fluids.

One large boulder of silicified limestone was noted near Sprink Wood [SK 2732 5300] south-west of Wirksworth. It was partly hematitised and contained large quantities of fluorite. Smith and others (1967, p. 39) suggested that in mineralised rocks silicification probably post-dated fluoritisation. Orme (1973) considers the process to precede fluoritisation. Such conflicting views probably result from the silicification being associated with a complex and prolonged mineralising phase ranging from the Triassic to the Jurassic.

Bituminous limestone

Pocock (in Gibson and others, 1908, p. 13) noted the local occurrence of bitumen in limestone near Hopton and Wirksworth. It is common in the pale grey massive limestone which forms a small 'knoll' near Pittywood Farm [SK 2790 5310] south-west of Wirksworth. In thin section the dull-black bituminous material is seen to form secondary impregnations filling the pore spaces, and dense localised concentrations completely obliterate and mask the host-rock. Tests with various solvents proved negative and no aromatic compounds were observed.

Fragments of black bitumen were common in the Hoptonwood Limestone proved in the site investigation borehole [SK 2652 5340] near Hopton.

Minerals associated with Dinantian strata

The Dinantian limestone exposed in the Wirksworth area is extensively mineralised, its anticlinal structure being favourable for ore deposition below the Namurian shale cover now partly removed by erosion. Orebodies may exist below the Upper Carboniferous cover, for fluorite veining was recorded at depths of 2300 to 2400 ft in Ironville No. 3 Oil Bore. Large areas of the outcrop are dolomitised and there are patches of silicification. The orebodies, principally of galena and fluorite with calcite and baryte as the main gangue minerals, were once of considerable economic importance (pp. 104–109).

Gypsum veining has been recorded at depth in the Widmerpool Formation at Trusley Borehole.

Chapter 3 Namurian (Millstone Grit Series)

Introduction

The outcrop of Namurian strata is between 5 and 7 miles wide and extends from Wirksworth in the north-west of the district south-eastwards to Breadsall. It forms ground rising to over 1000 ft at Alport Hill between the rivers Derwent and Ecclesbourne. The alternating sandstones and shales in the upper part of the sequence form an upland area to the west of the coalfield and have weathered into a series of impressive scarps or 'edges', particularly along the Derwent valley north of Duffield. The lowest part, consisting largely of shales, floors much of the Ecclesbourne valley in the west of the district.

The Namurian rocks of the Derby district, as elsewhere in Britain, reflect an upward transition from the wholly marine environment of the Dinantian to the paralic environment of the Westphalian. The 'block' or 'massif' and 'gulf' controls on Dinantian sedimentation continued to influence deposition in the Namurian though they are apparent only in the thickness variations shown by the upper part of the sequence, where the predominantly arenaceous rocks are of deltaic origin.

Previous research

Whitehurst (1778, p. 147) introduced the term 'Millstone Grit' for a coarse sandstone separated by shales from the Dinantian limestone in the Derwent valley. Farey (1811) called this sandstone the 'First Grit Rock' in the Matlock area and calculated that it was separated from the limestone by 420 ft of 'Limestone Shale'.

The primary geological survey by Green and others (1869, 1887) grouped the strata now assigned to the Widmerpool Formation and the lower part of the Namurian into a lower division consisting of black shales with thin beds and nodules of earthy limestone, and the upper of shales with thin beds of hard close-grained sandstone (Yoredale Sandstones). Gibson and others (1908), unable to sustain this distinction or to determine a demarcation between Lower and Upper Carboniferous, named the beds 'Limestone Shales' up to the horizon of the lowest sandstone (now a lower leaf of the Ashover Grit) which they termed 'Shale Grit'. For the latter and the succeeding 'Kinderscout Grit' (also now Ashover Grit) they followed the terminology of Green and others (1869), but for the higher sandstones they used the local names Belper Grit (now Chatsworth Grit), Coxbench Grit (now Rough Rock) and Rough Rock (now Crawshaw Sandstone, of Westphalian age).

Classification

Based upon the work of Hind (1909) and Bisat (1924), the base of the Namurian is defined by the first entry of the goniatite Cravenoceras leion and the top is drawn at the base of the Gastrioceras subcrenatum Marine Band. It is therefore chronologically synonymous with the Millstone Grit Series, as used extensively in publications of the Geological Survey dealing with the southern Pennines. Because of poor exposures some of the detailed palaeontology, particularly in the upper parts of the sequence, remains unproved within the district. The zonation already established in the adjacent Chesterfield district (Smith and others, 1967) is applicable however, and is shown in (Figure 7) relative to the generalised vertical section of the Namurian of the Derby district. Borehole sections in the district and adjacent areas are shown graphically on (Plate 4), which includes the probable correlation of sections lacking palaeontological control.

Some modern sedimentological work in the district has been published in outline by Mayhew (1967).

Lithologies

Two general sedimentary environments are reflected in the lithologies of the succession, with the main change appearing near the base of the Marsdenian Stage. The underlying predominantly argillaceous sequence is widely, but poorly exposed and most of the information on it relates to the 'basin' sequence proved in the Duffield Borehole (Aitkenhead, 1977).

In the borehole, the pre-Marsdenian beds consist largely of mudstones with eleven separate sequences of predominantly thin quartzose sandstone–siltstone–silty mudstone units. Each unit displays irregular graded bedding, usually with a basal sandstone division which is massive except for faint parallel lamination at its base. Less commonly sandstone with strong parallel lamination, and even more rarely massive sandstone, underlies a ripple-laminated division. The bases of the unit are always sharp and often show sole-structures. These features are characteristic of the deposits of waning turbidity currents which are henceforward referred to as turbidites (Bouma, 1962, pp. 49–50). The turbidite units are normally less than 1 ft thick but may reach 4 ft. They usually contain poorly preserved plant debris, but are otherwise unfossiliferous. Dark grey fissile mudstone intercalations between individual turbidite units commonly contain fish-scales and represent slow background deposition in quiet bottom waters. Chemical and spectrographic analyses have been published by Read and others (1973).

The mudstones between the turbidite sequences in the E_1a to E_2b zones are generally calcareous, particularly in the goniatite bands, and are mainly unlaminated and silty with fissile intercalations in which fossils, if any, are concentrated. The unlaminated beds may also be turbiditic in origin.

Above E_2b the mudstones are mainly shaly, non-calcareous and pyritic, but become increasingly silty above the R. gracile Marine Band, heralding the incoming of deltaic deposition that was to continue during the remainder of the Namurian and into the Westphalian.

There are no complete sections within the district of the mudstones deposited in the 'massif' or 'block' environment. The nearest are those described in the Tansley, Uppertown and Highoredish boreholes in the Chesterfield district (Ramsbottom and others, 1962), where the sequence is largely composed of grey mudstones which are either calcareous or pyritous.

'Bullions' in the form of thin beds or concretions of hard calcareous siltstone with well-preserved goniatites are present in the fossiliferous mudstones of both 'massif' and 'gulf' environments. The concretions are normally discoid and may be several feet in diameter. Holdsworth (1966) described similar bullions from Staffordshire as calcite ferroan dolomite with an apparent complete absence of clay minerals. Besides goniatites, Holdsworth found they contained small sponges, abundant Radiolaria and spat of bivalves and gastropods.

Laminae of potassium bentonites rich in kaolinite are present in the mudstones of both environments. These have been identified by Trewin (1968) in Staffordshire and north Derbyshire as altered wind-blown volcanic ash; the laminae are brown or pale grey when unweathered or pale grey to white in surface exposure. Eleven such bands (Figure 7) proved by the Duffield Borehole can be correlated with those described by Trewin (Aitkenhead, 1977). None has been detected at outcrop within the district.

Ironstone nodules and bands are relatively rare in the 'gulf' facies sediments, although many of the turbiditic sandstones have a ferruginous cement.

The change to deltaic conditions during the Marsdenian and Yeadonian produced a rhythmic form of sedimentation. Cycles, which are not always complete, are typically as follows (Smith and others, 1967, p. 5):

• Coal
• Seatearth
• Sandstone or siltstone
• Grey mudstone becoming silty at top
• Dark mudstone, commonly marine at or near base

The darker marine mudstones are very fossiliferous and pyritous and form discrete bands up to 1 or 2 ft thick. They also display a cyclic arrangement of their fauna (Rams-bottom and others, 1962, pp. 114–117). The grey mudstones contain rare bivalve horizons; plant remains are common as are ironstone nodules and bands. The mudstones normally grade upwards through silty strata to become inter-banded with the basal parts of the overlying sandstones. Sharp contacts with the sandstones are indicative of erosion or 'washout' conditions.

There are three thick sandstone sequences in the district, i.e. the Ashover Grit, the Chatsworth Grit and, close to the top of the Namurian, the Rough Rock. Only the Ashover Grit is coarse enough to merit the term 'grit' but the name Chatsworth Grit, dating from Green and others (1869), is retained for historical reasons.

The Ashover Grit sequence comprises an uppermost persistent sandstone called the Main Bed because of its thickness, extensive outcrop and strong topographic expression, and at least three major lower sandstones of a less presistent nature. Lithologically the Ashover Grit is a coarse arkosic sandstone, pebbly in places, and of a pale grey to brown colour blotched with pink. The pebbles are mainly of vein quartz and less than 1 inch in size. Mayhew (1967, p. 94) has recognised two major facies–'a lower non-pebbly facies characterised by trough-shaped sets of cross-strata which accumulated under delta distributary channel-mouth bar conditions' and a 'transgressive, more coarse-grained pebbly facies dominated by planar sets of cross-strata which was deposited within fluvial channels'. Both facies are present in the Main Bed in this district, but the less persistent lower sandstones are characterised by the non-pebbly facies.

The Chatsworth Grit and Rough Rock are similarly arkosic, but less coarse than the Ashover Grit and with only rare pebbles; cross-bedding is common as are micaceous flaggy and shaly beds. Slumping, locally on a large scale, is present in the Rough Rock. There are commonly two leaves to the Chatsworth Grit.

Harrison (in Smith and others, 1967, pp. 267–276) has described and discussed petrographical and modal analyses of the Ashover and Chatsworth Grits from the Chesterfield area. He found broad similarities in the major and minor mineral suites with ubiquitous orthoclase and microcline and minor acid plagioclase. Altered muscovite and biotite are fairly constant minor constituents. Heavy minerals include zircon, rutile, apatite, tourmaline, ilmenite and monazite. The modal analyses show little difference between the ratios of quartz to feldspar in the two grits.

The deltaic deposits were laid down without any significant lithological differentiation in both 'gulf' and 'massif' areas, the locations of which are revealed only by thickness increases in the 'gulf' areas.

The coal seams which cap at least five of the Namurian cycles of the district are all impersistent and normally less than 1 ft thick. However near Alderwasley one unnamed coal above the R. superbilingue Marine Band is 2 ft thick (Wedd in Gibson and others, 1908, p. 42) and was formerly worked underground. Seatearths or ganisters are generally more persistent than the overlying coals.

Sedimentation

The Central Province area of Dinantian deposition which extended from the Craven Fault belt of Yorkshire to the Wales–Brabant Island (now the English Midlands) continued to receive sediment during Namurian times (Rams-bottom, 1970). A large river system draining from the north and north-east deposited deltaic sediments up to 6000 ft thick. Deposition of thick deltaic sandstones began in early Namurian times in the north, but did not move southwards to reach the Derby district until the Marsdenian Stage. Until then, the southern part of the province was receiving sediments derived from the Wales–Brabant Island and transported largely by turbidity currents (Holdsworth, 1963; Trewin and Holdsworth, 1973; Aitkenhead, 1977) into the Widmerpool Gulf (Falcon and Kent, 1960). Although its exact limits are difficult to define (pp. 5 and 25), the 'gulf' continued to have a marked influence on sedimentation in the Namurian.

The sediments in the 'gulf' are interpreted by Aitkenhead (1977) as mainly distal turbidites alternating with sequences of mudstones containing most of the goniatite marker bands which occur extensively throughout the Central Province. Aitkenhead (ibid.) has also tentatively suggested that the source of the turbidites was to the south-west of Duffield around which, and as far east as the Derwent valley and Breadsall, the turbidite sequences form mappable features, shown on the geological maps as 'sandstone/shale interbedded'. This distribution suggests proximity to a turbidite feeder channel.

The Duffield Borehole sequence shows that deposition from turbidity currents continued intermittently through much of the Pendleian, Arnsbergian and Chokierian. There is no evidence, however, that such deposition continued in the district during the Alportian and Kinderscoutian.

There is less evidence of the 'block' or 'massif' sequences in the district. The Ironville oil bores provide little detail, but the sequence below the Ashover Grit appears to be similar to that of the Tansley Borehole (Ramsbottom and others, 1962). Ironville is considered therefore to lie on the 'block' or 'massif' area beyond the area dominantly influenced by turbidite flows from the Wales–Brabant Island. In (Table 1) the Tansley–Ashover area is included to illustrate the probable thickness variations of the Kinderscoutian and lower stages for which only an overall figure is ascertainable for the Ironville oil bores. It shows that rocks of the early Namurian stages are thin and fairly constant over some 50 square miles of the 'block' between Ashover, Ironville and Ambergate. The increase in sediment thickness in the Widmerpool Gulf occurs largely in E_1a to H_1a strata, which are expanded by a factor of 5.

(Table 1) provides an indication of the relative amounts of subsidence between 'block' and 'gulf' in the Derby district. It also demonstrates the weakening influence of the Widmerpool Gulf during Namurian times.

During the Marsdenian and Yeadonian the district received sediments from the advancing delta, but the overall thickening into the 'gulf' was most evident in the former stage. This thickening is largely expressed in the sandstone beds of the Ashover Grit, the combined thickness of which expands from 100 to 600 ft and is illustrated by isopachs of the interval between the R. bilingue and R. superbilingue marine bands (Figure 8). The measured cross-bedding directions in the Ashover Grit (Figure 9) indicate that the depositing currents were in general flowing towards the north-west. In the Chatsworth Grit (p. 135b) cross-bedding directions so far measured indicate depositional currents flowing towards the south-west (Mayhew, 1967, p. 100) yet the sandstone is thickest in the 'gulf' areas compared with the Ironville oil bores on the 'block'.

The overall thickness of the Yeadonian rocks (Table 1) and (Table 3) shows little variation between 'block and 'gulf' yet the Rough Rock itself appears to be thickest in the 'gulf'.

Since the completion of the Derby resurvey Chisholm (1977) has identified growth faulting in the Ashover Grit near Stanton to the north-west of this district. Similar growth faulting appears to be present in the Ashover Grit near Little Eaton and may also occur in the vicinity of Alport Hill.

General stratigraphy

Pendleian (E₁)

These beds are thickest in the Widmerpool Gulf sequence of Duffield Borehole where they consist of 566 ft of mudstones with turbidite mudstones, siltstones, sandstones and/ or limestones. There are three main suites of turbidites, of which the uppermost in the C. malhamense Zone (E_1e) spans about 175 ft of strata. A thin K-bentonite band was proved near the base of this Zone. In the 'gulf' marginal area to the north, near Wirksworth, the E₁ Stage is thin or absent due either to non-deposition or to subsequent erosion.

Arnsbergian (E₂)

Beds of this stage vary from 655 ft of mudstones with turbidites proved in Duffield Borehole to 200 ft of grey silty mudstones and calcareous siltstones bordering the Dinantian limestone in the north. As in other parts of Derbyshire, mudstones of the E₂ stage overlap the lowest Namurian sediments to rest directly on the limestone. In the present district E₂ shales are considered to rest on limestones ranging in age from D₁ (Hoptonwood Limestone) to P₂ (Cawdor Formation). K-bentonites were recorded in rocks of this stage in the 'gulf' facies (Figure 7).

Chokerian (H₁) and Alportian (H₂)

Few details are known of the H Zone sequence in the Derby district. A three-fold thickening of measures between the Ashover 'block' facies and the Duffield 'gulf' facies is indicated from borehole data. Much of this thickening would appear to be in the Chokerian which probably includes the uppermost turbidite suite proved in Duffield Borehole, where some 109 ft are assigned to the H_ia Subzone.

An estimate of the maximum thickness of the entire H Zone from surface observations is of the order of 130ft.

Kinderscoutian (R₁)

Borehole evidence from Ashover (Ramsbottom and others, 1962) and thickness estimates from scattered exposures in the Franker Brook and near Breadsall show that the rate of deposition was fairly constant over a large area of Derbyshire. The measures of the Kinderscoutian Stage at outcrop are probably less than 100 ft thick in the Derby district and differ from the Chesterfield and other Pennine areas to the north in the absence of any sandstone representative of the Kinderscout Grit. Its recognition in Ironville No. 2 Oil Bore (Smith and others, 1967, fig. 7) seems doubtful, for the lowest sandstone here is now considered to be the Ashover Grit.

Marsdenian (R₂)

The Marsdenian Stage consists of 500 to 1100 ft of strata lying between the base of the Reticuloceras gracile Marine Band and the base of the Gastrioceras cancellatum Marine Band (p. 134b). The following upward sequence of beds is known to be present in the district; the Reticuloceras gracile Marine Band, known only in the vicinity of Wirksworth and Shottlegate although its horizon can be inferred from the gamma logs of Ironville No. 3 Oil Bore (see also Downing and Howitt, 1969, fig. 3), is succeeded by argillaceous rocks, containing the Reticuloceras bilingue Marine Band. The interval between these marine bands however is not known. Early to late forms of R. bilingue have been found at outcrop below the Ashover Grit, but the information is too indefinite to enable separation into discrete bands. The Ashover Grit is divided into lower leaves of variable persistence and an upper persistent Main Bed. An unnamed and impersistent coal closely overlies the Main Bed and the succeeding argillaceous and arenaceous sequence contains Lingula beds (Plate 4) and is topped by the Reticuloceras superbilingue Marine Band. The overlying argillaceous rocks, which include another unnamed and impersistent coal, extend up to the Chatsworth Grit. This grit is in two leaves, with the upper capped by the Baslow or Ringinglow Coal (Smith and others, 1967; Stevenson and Gaunt, 1971). The overlying mudstones are in turn overlain by thin Redmires Flags, at least in boreholes remote from the outcrop. At the top of the stage a thin coal correlated with the Simmondley Coal of Stevenson and Gaunt (1971) is present.

The thicknesses of these individual beds are shown in (Table 2).

Yeadonian (G₁)

The lower, argillaceous, part of the Yeadonian rocks include the inferred Gastrioceras cancellatum Marine Band, marking the base of the stage, and the G. cumbriense Marine Band. The upper sandy part contains the Rough Rock capped by a few feet of strata comprising the thin Pot Clay Coal and its seatearth or ganister. (Table 3) illustrates the thickness variations of the Yeadonian strata in boreholes in this district; their locations are given in the 'Details'; thicknesses are to the nearest foot.

Within the present district the G. cancellatum and G. cumbriense marine bands have been proved in Ironville No. 4 Oil Bore and Nether Heage Borehole. The G. cancellatum Marine Band yields only Lingula. The Rough Rock is ubiquitous but varies markedly in thickness and in its sedimentation. The Pot Clay Coal is known only in two boreholes in the south-east of the district, but its seatearth or ganister is widespread.

The Rough Rock has been confused with the Crawshaw Sandstone of the Westphalian A by Stephens (1952) who described the 'peculiar lithological development of the Rough Rock' emphasising the upper coarse division and the finer lower division, separated at Ridgeway [SK 3585 5154] by 20 ft of shale. It is in the basal part of this shale that the Pot Clay Marine Band has been discovered (p. 136b) thus identifying Stephens' upper division as the Crawshaw Sandstone.

Chapter 4 Westphalian (Coal Measures)

Introduction and classification

Westphalian (Coal Measures) strata rest conformably upon the Namurian and are unconformably overlain by Permo-Triassic rocks in the east and south-east of the district. They crop out in a central belt some 8 miles wide and, with their extension below the Permo-Triassic rocks, comprise the south-western part of the Yorkshire and East Midlands Coalfield.

The maximum thickness of measures proved in this part of the Pennine Province is some 3700 ft. Westphalian A rocks (Lower Coal Measures), some 1600 ft thick, contain several important workable coals, mainly in the top 500 ft; Westphalian B rocks (in large part the Middle Coal Measures) are about 1400 ft thick and contain the majority of the economically important seams; Westphalian C (700 ft) is a sequence largely devoid of useful seams apart from the High Main Coal.

The measures consist chiefly of mudstones with subordinate siltstones, sandstones, seatearths and coals in repetitive sequences or cycles, commonly in that upward order and each usually between 30 and 50 ft thick. The thickest cycles are usually dominated by sandstone and are mainly of Westphalian C age.

The lithologies are closely comparable with those found elsewhere in the Pennine Province, comprehensive accounts of which have been given by Trueman (1954, pp. 1–29), Smith and others (1967, pp. 80–83) and Murchison and Westoll (1968, pp. 71–85).

The strata in Britain are subdivided into Lower, Middle and Upper Coal Measures with the boundaries at marine bands (Stubblefield and Trotter, 1957). Correspondence with the Westphalian classification is shown in (Figure 10). Further subdivisions are based on the non-marine bivalves (mussels) (Trueman and Weir, 1946–56; Weir, 1960–68) and these have been divided further into faunal belts (Calver, 1956; Eagar, 1947, 1952, 1954, 1956) which facilitate more detailed correlation, particularly in Westphalian A and B. Plants have long been employed as broad zonal indicators, and recently Smith and Butterworth (1967) have established seven miospore zones of value for coal seam identification and the wider aspects of inter-coalfield correlation. The main features of the palaeontology of the Westphalian have been described by Calver (in Smith and others, 1967, pp. 87–97; 1973, pp. 42–46).

Westphalian rock-types

Coals

The coals form about 3.5 per cent^‡1  of the Westphalian A and B measures. In this account their classification follows that of the former Coal Survey Laboratory, which separated the following types of coal:

1. Brights (Softs)—layered, generally brittle coal formed mainly from the large Lycopod floras.
2. Dull (Hards)—less obviously banded, harder coal formed by decomposition of smaller herbaceous floras or a mixture of herbaceous and arborescent floras.
3. Banded dull and brights–a mixture of 1 and 2.
4. Cannel—finely comminuted plant debris with a variable content of mud, devoid of lamination.
5. Dirty coal—inferior admixture of bright and/or dull coals and dirt, with an ash content of 15 to 40 per cent.
6. Dirt—mudstone, commonly carbonaceous or with interbedded coal streaks and an ash content over 40 per cent.

Some of the diagrams that follow show the relative importance of the various coal types in the major seams and that the pattern of coal types within a seam is an important guide to its correlation. Typical 'bright' coals are the Blackshale, Deep Soft, High Hazles and Mainbright; '1^-lards' or dull coal is present as thick bands in the Low Main, Deep Hard and Top Hard seams.

The coals are considered to have been formed from vegetation which grew in situ in water which, though shallow, was deep enough and sufficiently de-oxygenated for the preservation of vegetable matter (Elliott, 1968, p. 359).

The phenomenon of split seams has been discussed by, among others, Raistrick and Marshall (1939, p. 63), and Elliott (1968, p. 366). In the present district there are two prevalent types. The first involves interdigitation on a regional scale with sediment derived mainly from the north and east and less commonly from the south and west. The second is local and linear in form due to local subsidence and sedimentation, possibly along a pre-existing water course.

Coal seams are subject to another facies-controlled variation known as swilleys. These take the form of linear hollows filled with coaly material; they occur at the base of seams and locally increase their thickness. Elliott (1965, p. 137) visualises levees of a river which ponded back a shallow lake in which cannel lenses were formed. Swilleys therefore record the course of rivers across the coal swamps. Good examples from the Derby district are known in the Deep Hard, Deep Soft and Top Hard coals of the Hucknall area and in the Lowbright Coal at Cinderhill Colliery.

Seatearths

The seatearths include all grades of sediment from sandstone to mudstone, but are distinguished by the general absence of bedding and the presence of rootlets. Once thought to be the soils in which the coal-forming forest grew, they are now believed to represent a sub-aqueous soil accumulation on which vegetation flourished without being preserved as coal. Coal formation normally took place later under more stagnant swamp conditions (Moore in Murchison and Westoll, 1968, pp. 113–122).

Elliott (1968, fig. 2 and p. 359) has shown that the seatearths between the Blackshale and Mainbright coals are of two main types–grey mudstones with nodular siderite, and brown mudstones and sphaerosiderite. The brown seatearths are usually overlain by thin coals. Elliott attributes the different coloration to varying groundwater conditions. The green colours noted in seatearths above the Mansfield Marine Band are a reflection of increased subaerial reaction in areas of better drainage.

Mudstones

Sediments of this grade form over 50 per cent of the Westphalian sequence and have been referred to as shales or bind, etc. by early workers. Mudstones devoid of any silt fraction are rare in this district and even the marine mudstones are slightly silty though darker grey than most of the non-marine beds.

Most mudstones contain evidence of bottom-living faunas, thus indicating a rate of sedimentation sufficiently gentle for living organisms to flourish, with bottom currents too slight to disturb the fine laminations now preserved. By an increase in silt content mudstone grades into siltstone or passes by intercalation and interlamination of sandy beds (striped beds) into sandstone.

Sandstones and siltstones

These sediments form up to 45 per cent of the total sequence and represent deposition in an increased energy environment. They range from rapidly deposited siltstones, locally containing upright tree trunks presumably swamped by sediment-laden floodwater, to washout sandstones, beneath which the underlying mudstones and coals have been removed, giving rise to breccio-conglomerates. Within this range there is a complex relationship between the sand and silt fractions, reflecting the varied conditions of deposition (Elliott, 1968, p. 355).

Miscellaneous rocks

Tonsteins are unlaminated layers or lenses of pale brown-grey to black kaolinitic mudstone usually associated with seatearths and coals. Strauss (1971), working mainly to the east and south of this district, has extended the earlier work of Eden and others (1963) and recognised tonsteins at 16 horizons within the Westphalian of the East Midlands. Of these only three have been located in the Derby district–within the First Piper and Deep Hard coals and below the High Main Coal. A fourth horizon–above the Brown Rake Coal–is now considered to be the related Fragmental Clayrock (see below). Tonsteins have diverse origins varying from diagenetic to pyroclastic (see e.g. Williamson, 1970).

The diagenetic process, according to Moore (1964) working on the Erda Tonstein from the Westphalian B rocks of Germany, involves microbiological degradation of organic matter in a soil or upon a surface below shallow and temporary water. This produces the necessary conditions, varying from anaerobic to aerobic, for the formation of kaolinite. The German theory of the pyroclastic origin of tonsteins in which ash fall-out into a peat bog environment is broken down into kaolinite, is supported in Scotland by the lateral passage from tonstein to tuff (Francis, 1961, pp. 199–201) and nearer this district by the presence of pumice within the First Piper Coal in the Nottingham district (Eden and others, 1963, p. 53). In support of a pyroclastic origin for the East Midlands tonsteins Francis (1969) emphasised the presence of suitable sources of material from vents within the Westphalian volcanic field proved in oil and coal boreholes east of Nottingham which, for example, gave rise to the closely related rock known as the Black Rake Tuffaceous Siltstone (see below).

Rocks related to tonsteins include Kaolin coolith' bands, Fragmental Clayrocks and the Black Rake Tuffaceous Siltstone.

Kaolin 'oolith' bands are widespread but discontinuous, thin (up to 2 in) beds of red-brown siderite with tiny spherules or irregular masses of pale kaolinite. They have been described in detail by Deans (1935) and Strauss (1971), the latter listing their horizons within the East Midlands Westphalian rocks. Hemingway (in Murchison and Westoll, 1968, p. 63) interprets them as late replacements of chamosite oolites. The most widespread band within this district is in the roof of the First Ell Coal, and others occur in the roofs of the First Piper and Clown coals.

Fragmental Clayrocks (Richardson and Francis, 1971), consisting of pale brown-grey disrupted and wispy kaolinitic mudstones up to about inch in thickness, are known within the district in the roofs of the Brown Rake and High Main coals. They differ from true tonsteins in their disrupted nature and restricted distribution (although the above authors describe one extending over 500 square miles in north-east England). Mineralogically they contain the clay mineral Mite' which is missing from true tonsteins and they may also contain sporadic ostracods.

The Black Rake Tuffaceous Siltstone, some 23 to 50 ft below the Clay Cross Marine Band, has been described by Francis and others (1968). It is a hard, banded and graded siltstone containing basaltic glass shards and pumice. There is a high proportion of carbonates, mainly dolomite and kaolinite, the latter replacing the basaltic glass. It was formed from fall-out dust from at least three volcanic vents situated to the east and north-east of Nottingham and takes its name from the associated Black Rake Ironstone.

Ironstones

Ironstones are found in all parts of the cycle but are most common in the mudstones as nodules, lenses and bands, some of which are very fossiliferous. Some nodules are septarian, others occur in the grey seatearths, often occupying the irregular cavities left by decomposed root structures. Sphaerosiderite is also present in many seatearths. Some iron is present as pyrite in the coal or overlying dark grey marine shales, but it occurs most commonly in coal as siderite and to a lesser extent as ankerite, particularly as an infilling in the cleat.

The source of iron in the Westphalian is considered by Hemingway (in Murchison and Westoll, 1968, p. 63) to be the pre-Carboniferous land masses surrounding the depositional basins. The manner in which the transported oxides were concentrated into their present forms is not clearly understood, but the early diagenesis is considered to be a reduction process caused by the presence of faunal and floral matter in shallow water and subsequent concentration of the products.

Sedimentation

The cyclic repetition of coal measure lithologies and its mechanism of formation has been the subject of a voluminous literature, which has been summarised by Westoll (in Murchison and Westoll, 1968, pp. 71–103).

Thickness variations of Westphalian A strata (Figure 11) show marked similarities to those of the Namurian rocks presented by Howitt (in Kent, 1966, p. 334) and reveals the continued influence of the Widmerpool and Edale gulfs during the Westphalian, as noted by Kent (1966, p.338). That influence is also apparent from thickness variations shown by some individual cycles, but the pattern is not consistent. Many cycles show variations apparently unrelated to the gulfs, though there is some evidence that gulf influence might still be detectable in Westphalian B rocks.

Sedimentary processes affect the thickness of the measures between the Deep Hard and Deep Soft coals which, over most of the district, form a single cycle. These measures show marked thickening towards a major sandstone 'washout' in the Deep Hard Coal, which was probably a main 'feeder' channel for the supply of sediment.

The coal isopach plans presented in the 'Details of Stratigraphy' show, with the notable exception of the Yard/ Blackshale Coal, that many seams are thicker in the west and south-west than in the east and north-east. Other coals deteriorate in quality or split to the east or north-east.

The isopach plans of five seams, the Belperlawn, Alton, Kilburn, Low Main and Brown Rake, reveal a relationship between coal thicknesses and the main axes of folding within the district. The relationship is by no means perfect, but these seams are thicker in the Shipley and Ripley synclines than on the axes of the Breadsall, Erewash, Crich and Ironville anticlines. Five more seams, the Deep Hard, Deep Soft, Bottom and Top Second Waterloo and Dunsil, show less well defined thickening in the synclines. It is thus evident that at times coal accumulation was influenced by precursory movements along Hercynian fold axes.

Stratigraphy

Westphalian A (Lower Coal Measures)

Base of Westphalian strata to Kilburn Coal

Measures between the Pot Clay Marine Band and Kilburn Coal

The measures between the Pot Clay Marine Band and Kilburn Coal range in thickness from about 590 ft near Bond-land Colliery to about 800ft S of Denby Colliery (Figure 12). In the east they are 625 ft thick in Beechdale Road Borehole.

Of the twelve component cycles within the district only that above the Belperlawn Coal and that capped by the Kilburn Coal lack marine or near-marine horizons at their bases. The highest marine horizon known to occur in these measures to the north and near Nottingham (Smith and others, 1967, p. 116)—the Burton Joyce Marine Band—remains unproved.

Within these measures are two principal sandstones–the Crawshaw Sandstone and Wingfield Flags—and three coals that have been worked underground—the Belperlawn, Alton and to a lesser extent, the Norton. Ganisters, present within the seatearths of many of the lower coals, were formerly worked in the north of the district.

The distribution of the marine and near-marine horizons was given by Eden (1954) and the faunal sequence is similar to that described by Smith and others (1967, 1973) in the Chesterfield and East Retford districts. The mussel beds between the Belperlawn and Alton coals contain the distinctive Carbonicola fallax/C. protea faunas described by Eagar (1947, 1952) from above the Soft Bed Coal in Yorkshire. Another distinctive horizon is the Norton Mussel-band with Carbonicola proxima which overlies the Norton Marine Band.

The Pot Clay Marine Band

The dark grey marine mudstones at the base of the Westphalian have been proved in Nether Heage, Park Brook and Beechdale Road boreholes. The characteristic goniatite, Gastrioceras subcrenatum, is present and the associated fauna consists of a further species of Gastrioceras, together with Dunbarella papyracea, Lingula mytilloides, Orbiculoidea sp., conodonts including Hindeodella sp.and fish debris (see also Eden, 1954, p. 106).

The measures between the Pot Clay Marine Band and the Belperlawn Coal

The measures between the Pot Clay Marine Band and the Belperlawn Coal range from about 100 to 145 ft. Below the Crawshaw Sandstone they comprise largely argillaceous strata with a few feet of dark grey mudstones containing fish debris overlying the marine band. Wedd (in Gibson and others, 1908, p. 50) noted these strata to be '12 or 14 yards thick and composed of blue sandy micaceous shale' in a well [SK 3634 4363] ¹ near Coxbench. In the Ambergate area a thin layer of penecontemporaneously contorted mudstone, similar to those described by Cope (1946), has been noted a few inches above the marine band.

The Crawshaw Sandstone ranges up to 112 ft in thickness and reflects a resumption of Namurian conditions of sedimentation. Its cross-bedding suggests derivation from the south. The sandstone is mainly medium to coarse-grained, gritty and arkosic; its colour is buff at outcrop, but grey to white when encountered in boreholes; pink and red staining is common both at outcrop and in boreholes and a green coloration has been sporadically recorded. Except at Ridgeway Quarry and in Beechdale Road Borehole the base of the sandstone is gradational into the underlying argillaceous strata: the lowest beds are either fine-grained for a thickness of up to 24 ft or interbedded with siltstone and mudstone. Within the main mass of sandstone, beds of siltstone and mudstone have been proved, and similar beds reach mappable proportions in the outcrop near Holbrook. Towards the top of the sequence the rock usually becomes finer grained and contains beds of siltstone and mudstone. At the top, below the Belperlawn Coal, there is a ganisteroid sandstone about 2 ft thick and mudstone seatearth up to about 1.5 ft thick.

The Belperlawn Coal

The Belperlawn Coal (Figure 13) has been proved to be 66 in thick at Nodinhill Site and is 38 to 50 inches in the type area north-east of Belper, where it has been extensively worked, mainly by opencast methods.

Away from the western outcrop the thickness of coal only exceeds 30 in within the 'take' of Denby (Drury-Lowe) Colliery. Near Heanor it is less than 20 in, but at Ilkeston the 27-in seam^‡2  is split by 9 in of dirt; at Oakwell Staple Pit the dirt parting is 18 in thick, separating two 9-in leaves of coal; the Ironville oil bores did not prove coal at this horizon.

The measures between the Belperlawn and Alton coals

The measures between the Belperlawn and Alton coals (Figure 14), which have a maximum thickness of 78 ft at Denby (Drury-Lowe) Colliery, thin northwards to 30 ft at Ridgeway Site. They comprise up to four cycles with three thin and impersistent coals, in ascending order the Holbrook, Second and First Smalley coals (Eden, 1954). The lowest beds of each cycle, except those immediately overlying the Belperlawn Coal, are normally mudstones with Lingula mytilloides and, commonly, mussels. Fish debris, which does occur in the roof measures of the Belperlawn Coal, is intermittently recorded from the remaining cycles. It tends to be associated with, or replaces, the Lingula bands. Mussels are very rare in the cycle above the Second Smalley Coal and there is no record within this district of the mussels described from the Yorkshire equivalent of the roof of the Belperlawn Seam. The distinctive mussel fauna of this sequence has been described by Eagar (1952, 1954) and by Smith and others (1967, 1973). In Denby (Drury-Lowe) Colliery Underground Borehole it includes Carbonicola haberghamensis above the Holbrook Coal and C. declinata, C. fallax, C. limax and Curvirimula sp., together with Geisina arcuata above the First Smalley Coal.

Each cycle contains variable amounts of sandstone and siltstone, and ganisteroid sandstone seatearths frequently underlie the coals. Sandstone in the uppermost cycle has been called the Sub-Alton Sandstone by Smith and others (1967, p. 105). The lithologies and faunas observed at most localities within the district are shown diagrammatically in (Figure 14) and by Eden (1954, pl. 2A).

The Holbrook Coal is impersistent, ranging in thickness from 4 to 14 in of shaly coal, and is represented only by seatearth in places.

The Second Smalley Coal is a variable seam up to 18 in thick and composed of coal and batt in Smalley Mill Well (Gibson and others, 1908, p. 74), more usually it is less than 10 in thick (Figure 14). It may also be composed of split thin coals or represented by seatearth only.

The First Smalley Coal ranges in thickness up to 29 in of shaly coal at West Hallam Colliery Borehole. Over parts of the district the seam consists of two coal leaves separated by sandstone (Figure 14), (Figure 67). At Smalley Mill Well (Gibson and others, 1908, p. 74), for instance, the whole was 3 ft 11 in thick and included a 1-ft rock parting.

The Sub-Alton Sandstone is an impersistent sandstone lying in the uppermost cycle of these measures.

The Alton Coal

The Alton Coal ranges from 10 in on Chestnut Site and up to 54 in on Ridgeway Site, both near Ambergate. The isopachs shown in (Figure 15) represent only a regional tendency and exclude abrupt local variations in thickness; for instance other recordings on Chestnut Site range up to 31 in. The quality of the coal is good to medium with variable ash and high to very high sulphur contents; the latter originate from the many pyritised fusain partings.

The measures between the Alton and Forty-Yards coals

The measures between the Alton and Forty-Yards coals (Figure 16) vary between 59 and 112 ft in thickness and, as described by Eden (1954), are composed of two cycles. The lower, 16 to 39 ft thick, commences with the Alton Marine Band and is largely argillaceous with significant sandstone or siltstone beds only locally recorded. A 2-in seatearth at the top of the lower cycle has been recorded in Wiremill Bridge Borehole; elsewhere the base of the upper cycle can be recognised only by the presence of the Parkhouse Marine Bands. This upper cycle, which is 43 to 96 ft thick, with variable thicknesses of sandstone and siltstone comprising the Loxley Edge Rock near the top, is capped by the sea tearth or ganister below the Forty-Yards Coal.

The Alton Marine Band directly overlies the Alton Coal and consists of fossiliferous dark grey pyritous shales with 'bunions' of ironstone containing uncrushed goniatites. It is only a few inches thick in the Denby (Drury-Lowe) Colliery district, but reaches 7 ft 10 in in Beechdale Road Borehole. In the thicker sequences the marine band is split (Eden, 1954), the upper part consisting of dark mudstones with Lingula sp.and microfossils which may be separated from the lower part by up to 3 ft 8 in of mudstone without marine fossils, as in Beechdale Road Borehole.

The marine band was first noted in the Ambergate area by Wedd (1903, p. 12) and described, but not named, by Gibson and others (1908, pp. 64–67, 100, 185). The fauna includes Dunbarella papyracea, Posidonia gibsoni, Caneyella multirugata, turreted gastropods, Anthracoceratites sp., Gastrioceras listeri, orthocone nautiloid, Hindeodella sp.and fish remains.

Fish debris and mussels have been recorded in the mudstones above the marine band.

The Lower and Upper Parkhouse Marine Bands occur at the base of the uppermost cycle below the Forty-Yards Coal and yield Ammodiscus sp., Glomospira sp., Lingula mytilloides and fish remains. Over parts of the district only one band is present.

The Loxley Edge Rock is a fine micaceous sandstone with siltstone and mudstone partings, lying in the upper part of the cycle which commences with the Parkhouse Marine Bands (Eden, 1954). It rarely exceeds 30 ft and is locally absent.

The Forty-Yards Coal

The Forty-Yards Coal commonly comprises two thin seams on average below 12 in thick separated by up to 15 ft of measures, which consist largely of seatearth, but may include mudstone, siltstone, sandstone and ganister. Most records of ganister come from below the lower, least persistent, leaf of the seam.

The measures between the Forty-Yards and Norton coals

The measures between the Forty-Yards and Norton coals comprise one cycle normally about 30 ft thick, but ranging from 18 to 39 ft. The cycle consists largely of mudstone with ironstone bands and nodules (the 'Dale Moor Rake' of Smyth, 1856, p. 59) and is now marked by extensive old excavations at outcrop near Stanton Ironworks [SK 4630 3880]. Fish remains are plentiful (see Gibson and others, 1908, p. 101) and include Diplodus sp., Elonichthys sp., Rhabdoderma sp.and Rhizodopsis sp.The arenaceous part of the cycle is thin and impersistent, but the seatearth at the top is up to 14 ft thick.

The Forty-Yards Marine Band lies at the base of the cycle (Smith and others, 1967, p. 114) and contains Ammodiscus sp., Lingula mytilloides, Hindeodella sp., Elonichthys aitkeni and an acanthodian spine. The non-marine mudstones of this cycle contain fish and plant debris.

The Norton Coal

The Norton Coal, which varies in thickness from 3 to 27 in, has been worked only in the south of the coalfield, near Stanton Gate (Gibson and others, 1908, p. 68).

The measures between the Norton Coal and the Upper Band horizon form an argillaceous sequence ranging from 25 to 53 ft in thickness (Beechdale Road and Wiremill Bridge boreholes). The sequence is composed of up to two cycles, although the evidence for this division has been found only in three sections (Figure 16).

The Norton Marine Band at, or very close to, the base of the sequence, consists of a thin bed of pyritous shale containing Ammodiscus sp., Glomospira sp., Lingula mytilloides, Caneyella aff. multirugata, Dunbarella aff. papyracea, and a conodont assemblage including Hindeodella sp.and Ozarkodina sp. The overlying mudstone and silty mudstones contain fish debris, plants and the Norton Mussel-band (Eden, 1954, p. 97; Eagar, 1956). The mussels are commonly preserved in calcitic material over a thickness of 5 to 20 ft, and comprise Carbonicola crispa, C. proximo, Curvirimula belgica and Naiadites sp., in association with Geisina arcuata, Rhabdoderma sp., Rhadinichthys sp.and Rhizodopsis sp.

Measures between the Upper Band horizon and Kilburn Coal

The Measures between the Upper Band horizon and Kilburn Coal range in thickness from 306 to 395 ft, and consist of two cycles. The lower, thicker, cycle, much of it sandstone, extends up to a seatearth lying some 20 to 60 ft below the Kilburn Coal. The upper cycle, largely argillaceous, extends from the top of this seatearth to the top of the Kilburn Coal.

Arenaceous measures of both cycles are assigned to the Wingfield Flags, although their main development lies in the upper part of the lower cycle.

The Upper Band Marine Band is known only from New Langley Colliery Borehole, the type locality (Godwin, 1960, p. 33; Calver, 1968b, p. 34). It consists of dark mudstones with Ammodiscus sp., Lingula mytilloides, and abundant fish remains including Elonichthys sp.The principal horizon with Lingula was 4 ft 6 in above the Upper Band seatearth. Fucoids only were recorded from this horizon in Wiremill Bridge Borehole. Up to 195 ft of mudstones with fish remains and mussels separate the Upper Band seatearth and the Wingfield Flags.

The Burton Joyce Marine Band (Smith and others, 1967, p. 116), which is present about 25 ft above the Upper Band seatearth in the Chesterfield and Nottingham districts, has not been proved within this district.

The Wingfield Flags are a sequence of pale grey flaggy sandstones, siltstones and silty mudstones in variable proportions up to about 200 ft in thickness. The top of the lower cycle (see above) is marked by a thin seatearth which, although not proved at outcrop, is present in most boreholes. A 3-in 'batt' in Bailey Brook Colliery Drift and a 3-in coal in Annesley Colliery (Deep Hard) Underground Borehole are the only records of coal at this horizon.

The upper cycle, normally 45 to 80ft thick, consists largely of dark grey to black mudstones with ironstones; fish debris and ostracods have been recorded and mussels are common. The presence of the fauna serves to identify the cycle in sections such as Moor Farm Borehole where the underlying seatearth is missing; its sandstones tend to be generally thin.

Kilburn Coal to Threequarters Coal

The measures between the Kilburn and Threequarters coals (Figure 17) and (Figure 18) are thickest in the north, where they reach a maximum of 661 ft. They exceed 600 ft in the south-west of the district. Eastwards and south-eastwards they thin to less than 500 ft. The sequence includes the Kilburn Coal, which was extensively worked for house coal; other important seams are the 'Ashgate', Blackshale, Yard and Threequarters. With the exception of the Yard and Blackshale, the coals tend to thin in an easterly direction.

The fauna of these measures consists largely of mussels of the Carbonicola pseudorobusta group, with fish debris present in the roofs of the coals up to and including the Mickley Thin; marine fossils are unknown in this district.

Kilburn Coal

Ranges from 30 to over 70 inches in thickness in the south-western part of the exposed field, but in the north-east it is thin (Figure 19). The maximum proved thicknesses are at outcrop in the south-west, where 761in of coal (including 5i in of dirt) and 74 in of coal were recorded in Hollies Farm and Mary sites respectively. The seam is composed predominantly of bright coal with subordinate dull bands, and is of good to medium quality with a low to moderate ash content.

Measures between the Kilburn and Mickley Thin coals

Ranges in thickness from 198 to 288 ft (Figure 20) and are composed of five main cycles. To the south-east of an irregular line from Swanwick to Stapleford the lowest cycle can be identified only by the presence of arenaceous measures at its top. Each cycle locally includes coal, but the seams are thin or of poor quality and have little economic value. The cyclic sequence of these measures is relatively uniform throughout the district except in the two Ironville oil bores and Moorgreen Loco Road Underground Borehole. The latter encountered additional seatearths, interpreted as splits of the two cycles above the Morley Muck Coal.

The lowest cycle, found only in the north-east of the district, ranges from 25 to 80 ft in thickness, its top commonly formed by a seatearth and with coal sporadically recorded. The upper cycle at Eastwood Hall Borehole is predominately arenaceous but Spirorbis sp., Carbonicola cf. browni and C. cf. pseudorobusta, Curvirimula subovata, Carbonita humilis, C. pungens and fish remains were present in interbedded mudstone and siltstone.

The Morley Muck Coal may contain over 50 in of coal in up to three leaves of poor to very inferior quality; the seam is therefore of no economic value. The coal or its seatearth lies between 50 and 130 ft above the Kilburn Coal.

The cycle overlying the Morley Muck Coal varies from 36 to 56 ft. The coal, cannel or seatearth at the top can be recognised in many provings throughout the district; the coal is unnamed and, discounting a dubious record of 24 in in the chippings from the Ironville No. 1 Oil Bore, has a maximum thickness of 10 in. It is absent over wide areas in the east and north. The cycle includes up to about 50 ft of arenaceous measures, with Spirorbis sp., Carbonicola cf. polmontensis, C. pseudorobusta, Curvirimula sp., Geisina arcuata and fish remains including Rhabdoderma sp.in the underlying argillaceous beds above the Morley Muck Coal.

The succeeding cycle, ranging in thickness from 25 to 50 ft, is also widely recognised and has the Lower Brampton Coal at its top. Sandstones are less prominent than in the underlying cycle and the mussels less abundant.

The Lower Brampton Coal (Smith and others, 1967, p. 121) has a maximum thickness of 21 in including 12 in of cannel and is of very poor quality. Provings between Mapperley and West Hallam collieries show this seam to be split into two very thin leaves, each under 9 in thick, up to 63 in apart. The upper leaf is locally canneloid. In the north of the district the Lower Brampton is under 4 in thick; it is absent in the east and 9 to 12 in thick in the south-east.

The remaining cycle, that with the Mickley Thin Coal at the top, ranges in thickness from 46 to 67ft and is almost wholly composed of argillaceous strata, locally bearing a mussel fauna; at Eastwood Hall Borehole Carbonicola sp.and Curvirimula subovata were recorded. Sandstones are only a few feet thick in the floor measures of the coal.

The Mickley Thin (or Upper Brampton) Coal

The Mickley Thin (or Upper Brampton) Coal is thickest at Morrells Wood Site, where 20 in were recorded. As at Chalfont Site (19 in) and Beechdale Road Borehole (3 in) the coal is of good to moderate quality, but it deteriorates to poor in two analyses from Moses Lane Site (9 to 12 in). The thickness is 18 in or less in the remaining provings within the district, the thinnest recordings being in the east.

The measures between the Mickley Thin and 'Ashgate' coals

The measures between the Mickley Thin and 'Ashgate' coals form one cycle ranging from 41 to 68ft. The roof measures of the Mickley Thin contain fish, ostracods and sporadic mussels.

The 'Ashgate' Coal

The 'Ashgate' Coal consists of two leaves of coal each showing rapid variations in thickness up to a maximum of 54 in and lying up to 62 ft apart. Washouts are common. The upper and lower leaves were originally called the Ashgate and Mickley coals respectively and they have been extensively worked underground near Denby, Heanor and Trowell Moor under these names. The seam is not the correlative of the Ashgate Coal of the Chesterfield district, which lies slighty higher in the sequence; instead the two leaves of the 'Ashgate' Coal of the present district are equivalent to the two thin coals present above the Mickley Thin Coal in Cotespark No. 1 Underground Borehole (Smith and others, 1967, fig. 11, p. 119).

The lower leaf of the seam is washed out within a sinuous belt of sandstone which extends from north-east of Eastwood to Ilkeston and thence south-east towards Wollaton, the upper leaf fails on the crest of this sandstone.

The measures between the 'Ashgate' and Blackshale

The measures between the 'Ashgate' and Blackshale coals are largely arenaceous and range from 60 to 146 ft. They contain up to two main coal horizons, which are probably the representatives of the Ashgate Coal of Smith and others (1967, p. 124). Each coal is itself split into up to three leaves, all thin and of no economic importance; the maximum thickness recorded is 28 in of 'batty coal' in Ormonde Colliery Shaft.

The Blackshale and Yard coals

The Blackshale and Yard coals (Figure 21) and (Figure 22) are a complex sequence of up to six main leaves of coal lying within strata varying in thickness from 8 to 110 ft. The Blackshale Coal consists of the lowest three main leaves of the sequence plus, in this account, the two overlying leaves, here called the upper and lower Denby leaves after their striking development in Denby Hall Colliery Shaft (Figure 22). The three lowest leaves are the Top Softs, Middle Dirt with Tinkers Coal and Bottom Softs of the old miners' terminology, which together form the Blackshale Coal of the Chesterfield district (Smith and others, 1967, p. 125). The Low 'Estheria' Band, which to the north-east occurs above the Bottom Softs (or Low Silkstone) is absent in the Derby district.

Each of the six areas shown in (Figure 21) and (Figure 22) contains a different combination of the seams. In Area A all the coal leaves are present in close proximity to form the Yard/ Blackshale, a seam which is equivalent with or approximates to the Silkstone of Yorkshire and which can be 96 in thick, including 18 in of dirt and dirty coal in partings. In Area B a thick Yard Coal is separated from the Blackshale Coal, which includes a variable sequence of the Denby leaves and ranges from a total of 65 in including 13 in of dirt to 155 in including 67 in of dirt. The Denby leaves attain a maximum in a single 54-in coal at Salterwood Site. Measures some 10 to 76 ft divide the Denby leaves from the Yard Coal, which itself ranges up to 59 in thick.

In areas C and D the Yard Coal is widely separated from insignificant Denby leaves which in turn are remote from the Top Softs–Middle Dirt–Bottom Softs sequence. In area C the Top Softs–Middle Dirt–Bottom Softs sequence varies between 33 and 54 in of which up to 10 in may be dirt partings; in area D it is generally 40 to 60 in thick with up to 13 in of dirt, but thick sections of 115 in (including 11 in of dirt) and 99 in (23 in of dirt) have been recorded.

In area C the Top Softs are separated from the Denby leaves by mainly arenaceous strata ranging in thickness from 13 to 80 ft. The Denby leaves are represented by seatearths up to 17 ft apart. The Yard Coal, lying 7 to 13 ft above the Denby leaves, is thin.

In area D a single Denby leaf was encountered only in Swanwick Colliery, New Pit, where 14 in of coal and dirt were encountered 44 ft above the Top Softs. Elsewhere the leaves appear to be absent or unrecorded.

The Denby leaves horizon is separated from the Yard Coal by sandy measures ranging in thickness from 7 to 85 ft. The Yard Coal, variable in quality, ranges from 17 to 38 in and has been extensively worked.

The centre line of area E coincides with the greatest thickness of sandy measures, which lie between an impoverished Yard Coal and the Top Softs–Middle Dirt–Bottom Softs sequence throughout the area. The Denby leaves are not proved; they may be merged with the Yard Coal or washed out by the sandy measures. Where wholly represented in the area, the Top Softs–Middle Dirt–Bottom Softs sequence varies from 39 in, including 7.5 in of dirt to 78.5 in, including 26 in of dirt. The Denby leaves are only recorded with certainty from within this area at Pippinhill Site, where some provings show the Lower Denby leaf within 18 in of the Top Softs. The Yard Coal is represented mainly by a seatearth horizon.

Area F lies south of the thick belt of sandy measures and consequently a variable sequence of the Yard Coal and Denby leaves reappears. Moderately thick measures overlie a variable Top Softs–Middle Dirt–Bottom Softs sequence –a feature which, apart from its location on the opposite side of the thick arenaceous measures, distinguishes this area from area C.

The Top Softs–Middle Dirt–Bottom Softs sequence, except in that part of the area near Cinderhill and Hucknall colliery provings, is characterised by an increase in the thickness of dirt partings compared with the rest of the district. The Top Softs of this area do not exceed 33 in and the Bottom Softs 20 inches in thickness. The thickest overall sequence of 101 inches in Stanley Colliery Shaft includes 51 in of dirt and dirty coal while the thinnest, of 48 inches in Cinderhill 19's Left Gate Underground Borehole, includes only 7 in of dirt.

The Denby leaves are 21 to 78 ft above the Top Softs but are represented only by a single seatearth or thin coal over much of the area. Measures ranging in thickness from 8 in to 30 ft separate the Denby leaves from the Yard Coal, which itself is mainly a single seatearth horizon or very thin coal.

The measures between the Yard and Threequarters coals

The measures between the Yard and Threequarters coals range in thickness from 47 to 123 ft and normally form a single cycle containing variable arenaceous and argillaceous strata. The roof of the Yard Coal yields fish and plant debris and, more rarely, mussels; ironstones higher in the argillaceous measures form, in ascending order, the Striped Rake of Kirk Hallam, Blackshale Rake and Nodule Rake of the Morley Park district (Smyth, 1856, p. 38). The overlying sandstone is the 'Silkstone Rock' of the country to the north of this district.

The Threequarters (Tupton Threequarters or Dogtooth) Coal

The Threequarters (Tupton Threequarters or Dogtooth) Coal ranges in thickness from 3 inches in Trowell Moor Colliery Shaft to 49 in at Salterwood Site. These figures exclude the thickness of a floor coal, the distribution of which is shown on (Figure 23).

Threequarters Coal to Clay Cross Marine Band

These measures range in thickness from 304 to 455 ft (Figure 24) and (Figure 25), and include the Low Main, First Piper, Deep Hard and Deep Soft coals, which were extensively mined as sources of household and steam coals throughout the district and have also been widely exploited by opencast methods. The Deep Soft group of coals is combined over a restricted area near Smalley to form the thickest coal sequence in the district. Other rock types in the sequence include the thin Black Rake Tuffaceous Siltstone which is an important lithological marker at the top of the Deep Soft group of coals. The two widespread and important sandstones of the measures are the 'Tupton Rock', found in the west and also within a broad channel in the eastern part of the district, and the 'Deep Hard Rock' which occupies a narrow belt extending north-eastwards from its outcrop at Salterwood.

Boreholes in the east of the district illustrate the manner in which the Cockleshell and Hospital coals thin or disappear on the crests of thick sandstones. In contrast, however, the individual thicknesses of the coals of the Deep Soft group appear to be little related to the thickness of underlying sandstone, although the splitting of the coal sequence was controlled by the influx of sand at various times and locations. This group therefore resembles the Blackshale and Yard coal sequence (p. 35) though the area of maximum coal thicknesses is different.

The Carbonicola cristagalli mussel fauna (Smith and others, 1967, pp. 134–135) occurs above the Cockleshell Coal and passes upwards into the Anthracosia regularis fauna at about the horizon of the Deep Soft Coal (Smith and others, 1967, p.96; 1973, p. 44).

The measures between the Threequarters and Low Main coals

The measures between the Threequarters and Low Main coals range in thickness from 6 to 23 ft and are mainly argillaceous with ironstone nodules; much of the sequence is composed of the seatearth of the Low Main Coal.

The Low Main (Low Tupton or Furnace) Coal

The Low Main (Low Tupton or Furnace) Coal has a maximum thickness of 66 in at Salterwood Site and is generally of good to very good quality. The seam thins irregularly and gradually from its outcrop to less than 36 inches in the south-east of the district. In the north-east (Figure 26) the top of the seam lies about 9 in below the Cockleshell Coal and together the two form the Tupton Coal. Within this area of union the Low Main element ranges in thickness from 36 to 42 in. A second and poorly defined area of union with the Cockleshell Coal exists near Swanwick, Birchwood and Pinxton collieries where the Tupton Coal is 45 to 50 in thick. The structure of the Low Main is frequently distinctive, particularly the basal 12 in, which are composed of bright coal with hard bands or interbedded hard and bright coal (Figure 28). The central portion of the seam in most records comprises soft bright coal, and the upper part is variable with hard coal, bright coal and cannel.

A dirt parting up to 2 in thick or a band of hard coal within this upper part of the seam can be correlated over wide areas. The ash content of the whole seam is low, the average of 138 analyses from the district being 4.4 per cent. Sulphur content is also low. The seam is frequently washed out within the eastern area of arenaceous roof measures (Figure 27).

The measures between the Low Main and First Piper coals

The measures between the Low Main and First Piper coals range in thickness from 101 to 187 ft. The variation is directly related to the thickness of sandstones within the four major component cycles (Figure 29). The three lowest cycles are locally crowned by thin coals named, in ascending order, the Cockleshell, Hospital and Second Piper; the fourth is capped by the First Piper Lower Coal or First Piper Coal.

Washouts are present in these measures and, as both the Cockleshell and Hospital coals are split and the Second Piper Coal and seatearth are unrecorded in a number of the provings, the detailed correlation is not always certain. The sub-Hospital sandstone ('Tupton Rock') is thickest within the takes of Cinderhill and Wollaton collieries and crops out between Shortwood Site and Trowell Moor Colliery. Where this rock is thickest the Cockleshell Coal is absent as a result of erosion and/or non-deposition. The Hospital Coal also fails or is reduced on the 'crest' of this sandstone. In the west of the district, only the sub-Cockleshell sandstone is important, as displayed by Ormonde Colliery Shaft (Figure 25) and (Figure 29), where it is about 70 ft thick. This sandstone is marked by only minor ground features at outcrop except on the flanks of the Ironville Anticline. In the north-east of the district a thick sub-First Piper sandstone is the dominant sandstone; its sinuous line of maximum thickness enters and leaves the district within Annesley Colliery take. Its base falls to 14 ft above the Tupton Coal in Annesley Deep Soft G.4's Underground Borehole to the north of this district, and along part of the line ofmaximum thickness the Hospital Coal is reduced or washed out and the Second Piper Coal and seatearth are absent. Elsewhere in the district the sequence below the First Piper Coal includes only minor sandstones.

The Cockleshell Coal (Figure 27) lies up to 76 ft above the Low Main Coal and is united with it in the north and north-east of the district. Most of the intervening measures are sandy but 'cocklebeds' have frequently been recorded where mudstones form the roof of the Low Main Coal. The Cockleshell Coal may be composed of bright coal, dirty coal, cannel and/or interbedded coal and mudstone (batt) (Figure 28). Multiple sequences of coal and dirt, each a few inches thick, may range through several feet of measures. The thickest record of the unsplit seam, 28 inches in Cinderhill 6's Underground Borehole, includes laminae of dirt.

The measures between the Cockleshell and Hospital coals range in thickness from 8 to 75 ft. Widespread mussels in the roof of the Cockleshell Coal are frequently preserved in carbonate and include Carbonicola cristagalli, C. cf. rhomboidalis and Naiadites flexuosus. Sandstones are generally thin, except near Cinderhill and Wollaton collieries, where the top of the 'Tupton Rock' extends close to the base of the Hospital Coal (Figure 29) and the Cockleshell Coal is washed out along the line of maximum sandstone thickness.

The Hospital Coal is thickest, an exceptional 43 inches, in Seagrave Borehole. It ranges from 21 to 31 in at the outcrop in the west; elsewhere it is thinner or irregularly split into two or more leaves. Analyses of this coal are wholly from opencast provings; it is of good to medium quality in the west with low ash and sulphur contents, but the quality deteriorates in the south of the district.

The measures between the Hospital and Second Piper coals range in thickness from 12 to about 30 ft. Carbonicola cristagalli, Geisina arcuata and fish remains are present in the more argillaceous part of this cycle.

The Second Piper Coal attains a maximum thickness of 12 in of 'coaly shale' in Selston Colliery No. 2 Drift. There are only seven other records of a carbonaceous bed in deep provings; however the underlying seatearth is widespread, though locally impersistent.

The measures between the Second Piper Coal and the Lower Coal of the First Piper or First Piper Coal range in thickness from 16 to 84 ft, the increase being directly proportional to the thickness of the sub-First Piper sandstone in the north-east of the district (Figure 29).

The First Piper Coal

The First Piper Coal (Figure 30) is composed of up to three main elements which comprise the lower and upper parts of the Lower Coal of the First Piper and the Upper Coal of the First Piper as figured by Smith and others (1967, fig. 18) for the Chesterfield district. Over a large part of the district they are combined in a single seam, up to 60 in thick, as in Bennerley Colliery Shaft. Many records of the combined seam show the tripartite subdivision, though a bipartite sequence of Upper and Lower coals is more widespread and important. The three elements of the seam divide irregularly so that they may be distributed through up to 43 ft of measures in two areas (Figure 30). In the north-easterly area the division is largely into two rather than three leaves. The Lower Coal of the First Piper is unimportant and usually of poor quality. The dirt parting between the lower and upper parts is normally a few inches in thickness, but increases rapidly to as much as 22 ft in the extreme north-west of the district (the 3-ft isopach is shown on (Figure 30)). The individual thicknesses of the two parts rarely exceed 12 in except west and south-west of Denby Hall Colliery, where analyses in opencast records show high ash contents.

Within the north-eastern area of split the Lower Coal is 10 in thick (including dirt partings) 6 in below the Upper Coal at Annesley 204's, 1 in (of batt) 3 ft 9 in below the Upper Coal at Annesley 10's, and 20 in at Cinderhill 2's Heading underground boreholes (Figure 30).

The Upper Coal of the First Piper within the northwestern area of split varies from 15 to 40 in. Isopachs are shown on (Figure 30). The coal is of variable quality, the thicker sequences being usually poor with high ash contents. In the north-eastern area of split it varies from 12 to 21 in and may contain up to 2i in of cannel at the top.

The combined First Piper seam ranges from 11 in (with 2-in cannel overlying) to 60 in.

The measures between the First Piper and Deep Hard coals

The measures between the First Piper and Deep Hard coals are between 30 and 40ft thick over much of the district but range from 29 to as much as 80 ft. They are thickest in the north and east. Eastwards there are two component cycles divided by the Deep Hard Floor Coal or its seatearth. The Floor Coal appears to separate from the Deep Hard Coal east of the sinuous north–south line shown on (Figure 31).

The Deep Hard Coal

The Deep Hard Coal is composed of three principal elements, the Floor Coal, the main seam and the Roof Coal, which may extend through up to 27ft of strata. The main seam in turn can be divided into three parts.

The Floor Coal and the main Deep Hard seam are together in the west of the district, where their combined thickness ranges from 85 to 45 in. The Floor Coal never exceeds 12 in where the seam is combined. North of Openwood Site, the Floor Coal itself is split into two or three thin coals. The line of split between the Floor Coal and the main Deep Hard shown on (Figure 31) is imprecise because most sections which record the separate seams lie well to the east of it. The Floor Coal is usually composed of dirty coal and may lie up to 19 ft below the main Deep Hard. East of the line of split most sections show only its seatearth.

The main Deep Hard Coal comprises the 'Bottom Brights', 'Hards' and 'Top Brights'– names used by the early miners (Anon., 1933). These terms are a simplification, for the composition of the seam is variable. The thickness of the main Deep Hard averages about 40 in but ranges from 14 to 76 in. The latter, in Hucknall Colliery No. 5 Shaft, is an abnormally thick swilley sequence.

The Roof Coal in the north-east of the district may lie up to 24 ft above the main Deep Hard and has a maximum thickness of 13 in of cannel.

A washout sandstone about 300 yd wide cuts out the main seam along a linear belt trending north-north-eastwards from the outcrop near Denby Hall Colliery.

Measures between the Deep Hard Coal or the Deep Hard Roof Coal and the Deep Soft Coal

The measures between the Deep Hard Coal or the Deep Hard Roof Coal and the Deep Soft Coal vary from 20 to 100 ft and are composed of up to three cycles; the lowest two are capped by thin, impersistent coals. The lowest cycle is composed largely of silty measures which may be up to 35 ft thick. The 'Deep Hard Rock' (Smith and others, 1967, p. 146) is only of local significance within this district, its most important outcrop lying near the washout described above. The Foot Coal at the top of this cycle is never thicker than 12 in. The second cycle either finishes at an impersistent thin coal or cannel lying up to about 2 ft below the Deep Soft Coal or extends upwards to include the Deep Soft Coal. The third cycle if present, therefore, includes these 2 ft of measures and the Deep Soft Coal. The measures are partly arenaceous but include thick seatearths of varying lithology. The underclay below the Deep Soft Coal was of considerable value as raw material for the ceramics industry.

The Deep Soft group of coals

The Deep Soft group of coals comprises in ascending order the Deep Soft, Roof Soft, Top Soft and Black Rake coals. Over a restricted area (A on (Figure 32)) near Smalley these coals lie within 25 ft of strata. Elsewhere they may be distributed in up to 96 ft of strata.

In area B of (Figure 32) the Top Soft Coal splits off the combined seam. The Black Rake Coal, not recognised in area A, probably a split off the Top Soft, is present in this area. To the east, in area E, the sequence is further divided. There are two, or sporadically three, leaves of the Roof Soft, a thinner Top Soft and, locally, a Black Rake Coal. Only the Deep Soft remains as a persistent seam of importance.

In area c the Roof Soft and Top Soft seams, with or without the topmost Black Rake element, are close together, but are widely separated from the Deep Soft Coal. The combined Roof Soft and Top Soft coals, which may contain up to four separate leaves, was originally called the Ell Coal (Gibson and others, 1908, p. 69); latterly this name was altered to False Ell to avoid confusion with the Ell coals of Westphalian B. Type sections of the False Ell are provided by Grammer Street Borehole, where the sequence probably includes the Black Rake at the top (Figure 34), and Stoneyford Borehole, where the Black Rake is a separate seam.

In area D, as in area E, the higher coals of the group are divided and remote from the Deep Soft. There is a thick Roof Soft ( ?lower leaf) in Birchwood Colliery Shady Shaft and Pinxton No. 3 Pit, but elsewhere the topmost coal is the principal seam. It is not certain if the latter is the Black Rake Coal or a combination of that seam with lower elements. It is however the Sitwell Coal (Smith and others, 1967, p. 149) of the south-west of the Chesterfield district.

The Deep Soft Coal itself (Figure 33) has a maximum thickness of 66 inches in Heanor Gate Borehole and thins irregularly towards the north-east. One or sometimes two thin floor coals or cannels, up to 7 in thick, lie as much as 2 ft below the main coal sequence.

The measures between the Deep Soft and Roof Soft coals (Figure 34) consist of up to 11 in of dirt over the major part of areas A and B; this increases in the north of these areas to between 24 and 57 in. Northwards into area c the sequence up to the base of the False Ell Coal consists of silty and sandy measures ranging in thickness from 27 to 71 ft. In the part of area D where the Roof Soft Coal or its seatearth is recognisable, these measures range in thickness from 28 to about 41 ft. Near the northern margin of the district, where the Roof Soft Coal is unrecognisable, the measures between the Deep Soft Coal and ?Black Rake Coal are as much as 91 ft thick and include mudstone and siltstone with 24 ft of seatearth at their top. Near the south-west margin of area E, where they are largely argillaceous, these measures can be as thin as 12 ft, but over the rest of this area the incoming of arenaceous measures increases this interval to as much as 67 ft.

The Roof Soft Coal is thickest–up to 60 in–where combined with the Deep Soft Coal in areas A and B (Figure 32).

The Roof Soft is split in most places within area E into two leaves which are variable in thickness and distance apart.

Measures ranging in thickness from 8 ft at Turkey Field Colliery to 34 ft at Cotmanhay Colliery separate the lower and upper leaves of coal in area E, the thinner sequences being composed of argillaceous rocks and/or seatearth.

The Roof Soft Coal in area c is described below as part of the False Ell Coal. In area D, where much of the correlation is tentative, it is thought to be split in Birchwood Shady Shaft, where the lower 36-in leaf is separated by 21 ft of measures from the upper 6-in leaf and also in Swanwick Colliery

New Pit (Figure 34). Where the horizon has been recognised elsewhere within this area, the Roof Soft is either of insignificant thickness or represented only by seatearth.

The False Ell Coal in area c comprises the Roof Soft and Top Soft coals in three or four leaves in up to 16 ft of strata. Over part of area c it probably contains the Black Rake Coal at the top. The lowest leaf of the seam is everywhere the thickest and reaches a maximum of 37 inches in Grammer Street Borehole. The second leaf (the upper leaf of the Roof Soft) is never more than 14 in thick and lies up to 16 in above the lowest leaf. Exceptionally, as at Brands and

Portland No. 1 collieries, there are three thin leaves to the Roof Soft component of the seam.

The Top Soft Coal is thickest, 32 to 52 in, in area A. Elsewhere within the Derby district the seam is of importance only as part of the False Ell Coal described above. In area B it is 8 to 39 in thick and lies up to 47 ft above the Roof Soft Coal, though over most of the district this interval is less than 15 ft. In area E the seam is usually thinner than 14 in but it is locally as much as 30 in. In the north-west (area D, (Figure 32)) the Top Soft is unrecognisable within the thick seatearths recorded below the Black Rake Coal, or it is incorporated within that coal.

The Black Rake Coal is the least important member of the Deep Soft group and is recognisable, mainly in a narrow central belt which widens towards the north-west (Figure 32), up to 27 ft above the Top Soft Coal. The coal varies from 6 to 24 in and is thickest in the north-west of the district. It is known locally in the eastern part of the district.

The measures between the Top Soft or Black Rake coals

The measures between the Top Soft or Black Rake coals and the Brown Rake Coal range in thickness from 13 to 43 ft. Dark grey mudstones near the base of the cycle contain ironstone nodules of the Black Rake Ironstone (Smyth, 1856, p. 37) which have been worked both opencast and underground as a source of ore. Within these mudstones and forming a roof to underground workings is a widespread bed called the Black Rake Tuffaceous Siltstone described by Francis and others (1968).

A few feet of mudstone with ironstone nodules normally overlie the tuffaceous siltstone, the remainder of the cycle comprising arenaceous measures and seatearth. In Manchester Wood Borehole Spirorbis sp., Anthraconaia sp., Anthracosia regularis, Carbonicola cf. venusta, Naiadites sp.and Geisina arcuata were present in the mudstones of this cycle.

The Brown Rake Coal

The Brown Rake Coal, which is up to 38 in thick at Club Room Site, thins rapidly towards the east where, over wide areas, it is under 12 in. In the north the seam is divided into two and sometimes three leaves, with up to 7 ft of measures between. The thickest single leaf is 18 in.

The measures between the Brown Rake Coal and the Clay Cross Marine Band

The measures between the Brown Rake Coal and the Clay Cross Marine Band vary in thickness from 8 to 35 ft and are wholly argillaceous in the district apart from a 3-ft sandstone in the vicinity of Linby Colliery.

The measures, including some of the ironstones, contain abundant Anthracosia regularis, Naiadites sp.and Geisina arcuata; Spirorbis sp.is common and Planolites montanus also occurs. Near the top, the fossils tend to be pyritised.

Westphalian B

Clay Cross Marine Band to Top Hard Coal

The measures between the Clay Cross Marine Band and Top Hard Coal (Plate 5) are about 460 ft thick at Heanor Gate Borehole and about 450 ft near Swanwick Colliery; they thin eastwards to about 330 ft at Hucknall No. 2 and Broxtowe collieries, though an incongruous record from Hempshill Heading in the east shows about 406 ft. Approximate isopachs are shown on the inset map of (Plate 5). The measures comprise twelve or more cycles, most of which contain both arenaceous and argillaceous strata. There are ten named coals. Marine fossils are confined to the Clay Cross Marine Band. Mussels are present in the roof measures of all the coals except the Bottom First and Bottom Second Waterloo coals; the Anthracosia aquilina/ovum fauna lying below the Second Ell Coal grades upwards into the A. phrygiana fauna, which continues to the Top Hard Coal.

The named coals have been exploited mainly by opencast means, but the Second Waterloo Coal has also been extensively worked underground. The measures associated with the Second Waterloo Coal are worked for brickmaking.

The Clay Cross Marine Band

The Clay Cross Marine Band consists of up to about 9 ft of dark grey mudstone with thin ironstone lenses. The marine fossils and their distribution within the marine band have been described by Edwards and Stubblefield (1948, p. 215) and Calver (in Smith and others, 1967, pp. 157–159; and 1968a, pp. 163–173). The 1 ft 10 in of mudstone between the Joan Coal seatearth and the Dunbarella/goniatite-bearing mudstones in Eastwood Hall Borehole contain Lioestheria at their base with Lingula and foraminifera above. They are indicative of an increasing marine influence on the conditions of deposition, but there is no clear separation of the foraminifera and Lingula phases. The Dunbarella and goniatite-rich horizons near or at the base of the sequence occur in dark mudstone, tougher and more fissile than the overlying Lingula-rich horizons. As noted by Gibson and Wedd (1913, p. 71) and Edwards and Stubblefield (1948, p. 216) the upper Lingula-bearing horizons alternate with mudstones containing stunted mussels.

The measures between the Clay Cross Marine Band and Second Ell Coal

The measures between the Clay Cross Marine Band and Second Ell Coal form part of a single cycle and range in thickness from 48 ft in the east to 95 ft, the thicker sequences being found mainly in the western and south-eastern parts of the district. Sandstones occur in the uppermost third of these measures; the most persistent is found to the west of Heanor. The mudstones are rich in mussels, which may be pyritised within 40 ft of the marine band, but may also be preserved in calcareous and ferruginous material. Many of the mudstones display worm tracks and burrows, and there are plants at the higher levels. Ironstones are common and frequently exhibit cone-in-cone structure.

The Second Ell Coal

The Second Ell Coal is extremely variable both in thickness and composition. Near outcrop in the north-west, and as far south as Upper Hartshay Colliery, it is a split seam similar to that described by Smith and others (1967, p. 158) in the Alfreton area to the north. The upper leaf (Tanyard Coal) is of medium quality and ranges in thickness from 18 to 28 in; it is separated from the 1-in to 8-in lower leaf of dirty coal by up to 26 in of seatearth.

Within a wide area in the north and west of the district the seam is composed wholly or largely of cannel. Two leaves are frequently present, up to 14 ft apart near Heanor. Cannel is also locally present in the upper part of the seam in the eastern part of the district. Elsewhere, the Second Ell is a single or split coal in which the lower leaf or the lower part of the single seam is commonly composed of dirty coal. The thickest known section is 19 in of coal underlying 48 in of dirty coal, and the maximum proved separation of the two leaves is 6 ft.

The measures between the Second and First Ell coals

The measures between the Second and First Ell coals average about 50 ft over much of the district, with a minimum of 31 ft and a maximum of 65 ft.

The First Ell Coal

The First Ell Coal shows great variations both in quality and thickness. It is thickest to the south-west of Heanor and in the Erewash Valley, east of Ilkeston. South-west of Heanor it is mainly 30 to 42 in thick, although locally only 23 in. Analyses from opencast sites show that it is rather poor to very poor in quality in this area.

North and north-west of Heanor the First Ell is of medium to very poor quality. It is 18 to 27 in thick at the northern boundary of the district, thickening to 36 in at Bailey Brook Colliery Shaft. Dirt partings, 5 in or less in thickness, are recorded from several localities.

The measures between the First Ell and Fourth Waterloo coals

The measures between the First Ell and Fourth Waterloo coals are about 40 ft thick over most of the district. They are thickest near Heanor, where they total 56 ft, and thinnest in the south-east of the district, where they are only 10.5 to 16 ft thick. In most sections they comprise only one cycle with, in the immediate roof of the First Ell, a lenticular ironstone, usually up to about 2 in thick with kaolinite ooliths and pyrite, which forms a useful lithological marker.

The Fourth Waterloo Coal

The Fourth Waterloo Coal is variable both in thickness and in quality and may comprise up to three leaves of coal of which the middle leaf is the most persistent and important. It is 15 to 29 in thick in the north-west of the district, where it is medium to rather poor in quality. Elsewhere it ranges from 6 to 34 in.

The measures between the Fourth and Third Waterloo coals

The measures between the Fourth and Third Waterloo coals are usually 30 to 45 ft thick, but vary from 27 to 76 ft. Thicknesses are related to the proportion of sandstone present. The two component cycles cannot be separately distinguished, though 19 widely distributed provings in the district record a thin coal or seatearth 12 to 20 ft (exceptionally 38 ft) below the Third Waterloo Coal.

The argillaceous roof measures of the Fourth Waterloo Coal contain fish debris, ostracods, cf. Planolites and plants. Anthracosia cf. beaniana and A. disjuncta are also recorded from mudstones within a sequence of interbedded sandstone, siltstone and mudstone near the top of these measures.

The Third Waterloo Coal

The Third Waterloo Coal ranges from 12 in to a multiple sequence of coal and dirt, 48 in thick. In the north and north-east the seam is about 2 ft thick over wide areas, and dirt partings are recorded only locally. Well south of Heanor, at outcrop near Mapperley Colliery, there is a dirt parting near the top of the seam.

The measures between the Third and Second Waterloo coals

The measures between the Third and Second Waterloo coals vary in thickness from 16 to 46 ft and locally include a thin coal which is usually about 3 in thick, but may be thicker when close to the Second Waterloo Coal. The measures include a variable amount of sandy strata and the mudstones contain many mussels, some of which may be pyritic, together with fish debris, Spirorbis sp., Planolites montanus, worm tracks and borings.

The Second Waterloo Coal

The Second Waterloo Coal consists of two principal elements which, where they constitute separate seams, are named the Bottom Second Waterloo and Top Second Waterloo coals (Figure 35). This split is irregular and the two leaves are locally re-united in the south-west of the district. The Top Second Waterloo Coal itself divides in the south-east of the district. The interpretation of the Second Waterloo Coal sequence is based upon a report by the former Nottingham Coal Survey Laboratory (Turner, 1961b).

Away from the line of split, the Second Waterloo Coal is 49 to 57 in thick with two dirt partings totalling up to 10 in. The lower parting divides the Bottom and Top Second Waterloo elements, but the upper parting is also conspicuous and can be widely traced in sections of both the Second Waterloo and Top Second Waterloo.

The Bottom Second Waterloo, up to 31 ft below the Top Second Waterloo in the west of the district, is generally between 12 and 18 in thick (Figure 35), though it ranges from 10 to 25 in. The few analyses show it to be of medium quality, but to the north-west of Ripley Colliery it is composed wholly of cannel up to 18 in thick. Deep mine provings at the eastern margin and in the north-east of the district show the seam to be not more than 17 ft below the Top Second Waterloo and under 13 in thick, but it varies from 8 to 271 inches in opencast sites on the eastern side of the Erewash Valley to the east of Ilkeston.

The measures between the Bottom and Top Second Waterloo coals are largely argillaceous, but include appreciable amounts of sandy strata near Heanor. Mussels occur at the base of the cycle.

The Top Second Waterloo Coal is thickest, up to 64 in, in the extreme north-west of the district, where it may include a basal cannel up to 42 in thick. Elsewhere in the west the thickness ranges from 24 to 57 in. The detailed sequence of the seam is variable, including many dull coal bands and sometimes two dirt partings some 8 to 12 in above the base. Its quality is medium with a moderately low sulphur content. It has been worked underground from Coppice and Woodside collieries and has extensive opencast workings.

At the eastern margin of the district, at Hucknall and Linby collieries, the Top Second Waterloo Coal is 22 to 33 in thick; and over an area in the south-east it divides into two leaves along a line slightly north and west of the split between the Top and Bottom Second Waterloo coals. The line of split on (Figure 35) is drawn approximately at the 18-in isopach of the separating measures and, as emphasised by Turner (1961b), it occurs at a higher horizon in the seam than the prominent dirt parting which can be widely traced in the district (Figure 74). The maximum proved separation of the two leaves is 15 ft in an outline record of Cinderhill Colliery No. 2 Shaft.

The measures between the Second and First Waterloo coals

The measures between the Second and First Waterloo coals are reduced in thickness from 65 ft in the north to only 23 ft in the south, thereby continuing a trend mentioned by Smith and others (1967, p. 164). The attenuation is irregular. The measures comprise two main cycles divided by the Waterloo Marker Coal, plus, locally, a third thin cycle caused by splitting of that coal. There are mussels at the base of both the main cycles, and sineoids have been frequently recorded, mainly, however, from the lower cycle. Anthracosia phrygiana and Spirorbis sp. have been recorded from the roof of the Second Waterloo and A. aquilina, A. beaniana, A. phrygiana, Naiadites quadratus and Carbonita humilis from the mudstones overlying the Waterloo Marker Coal.

The Waterloo Marker Coal is a persistent thin coal or cannel which serves as an indicator horizon between the First and Second Waterloo coals. It rarely exceeds 12 inches in thickness and is of no economic importance.

The First Waterloo Coal

The First Waterloo Coal forms a single seam over two large areas in the east of the district (Figure 36) as described by Turner (1961a). These two areas are separated by a narrow corridor within which the seam is split into the Bottom and Top Waterloo coals and which extends north-eastwards from Greasley Castle Borehole to Linby Colliery. The corridor opens at both ends into wide areas covering the northern and western parts of the district where the seam is similarly split.

In the northern area of undivided coal the minimum thickness of the First Waterloo is 34 in with a prominent dirt parting, normally 1.5 to 6 in thick, but reaching a maximum of 12 in. The lower leaf varies from 16 to 25 in and the upper leaf from 14 to 27 in.

In the southern area of undivided coal, the First Waterloo reaches a maximum of 59 in, thinning eastwards to 21 in.

Over the remainder of the district, that is in the north and west, the seam is divided into Bottom and Top First Waterloo coals; the line of splitting shown on (Figure 36) is drawn at the 12-in isopach of the dirt parting at which the split occurs. The maximum division of the leaves is in the north-west of the district, where it amounts to 39 ft. The dividing measures are composed of a single cycle.

The Bottom First Waterloo Coal is recorded as comprising 30 in of cannel in Swanwick Colliery, Common Pit, although this maximum thickness must be regarded as doubtful because-only 12 to 15 in of coal were recorded in nearby shafts of the same colliery. The seam is mainly 18 to 24 in thick, but thicknesses of 27 and 28 in have been recorded locally.

The Top First Waterloo Coal is thickest adjacent to the lines of split in the First Waterloo Coal. It is 30 in thick in Moor-green Colliery 10's workings, of which 15 in are dirty coal or dirt and 19 inches in Bentinck W1 Underground Borehole, of which 5.5 in are dirty coal. Away from the lines of split, the seam is frequently recorded as cannel, usually about 12 in thick, but reaching 23 inches in Brinsley Colliery shafts.

The measures between the First Waterloo and Dunsil coals

The measures between the First Waterloo and Dunsil coals form a single cycle normally about 30 ft in thickness, but ranging up to 57 ft. The measures are variable in lithology and many sections show an unusually thick seatearth below the Dunsil Coal. Small specimens of Anthracosia cf. phrygiana, A. disjuncta and Naiadites sp.have been recorded from the roof measures of the First Waterloo Coal. Plant debris is present throughout the measures; sineoids and worm tracks have also been noted.

The Dunsil Coal

The Dunsil Coal usually consists of a main leaf 18 to 34 in thick and a thin floor coal a few inches below. Over large parts of the district (Figure 37) the floor coal is not recorded separately and it appears from detailed sections that it is locally united with the main leaf. Elsewhere, particularly at Cromford Canal Site and over most of the eastern part of the district, less reliable evidence suggests that it has^-died out.

The quality of the Dunsil is good to medium, with low to medium ash content and low to moderately low sulphur content. The seam has been mined locally, but it has mostly been worked by opencast means.

The measures between the Dunsil and Top Hard (or Top Hard Floor) coals

The measures between the Dunsil and Top Hard (or Top Hard Floor) coals form a single cycle about 40 ft in thickness, but ranging from 24 to 54 ft. Mussels and ostracods are recorded (p. 144d) from the roof of the Dunsil Coal and sineoids and worm tracks are also known. Ironstones are prominent in the mudstones, though in places, the cycle is mainly composed of sandstone.

Top Hard Coal to Mansfield Marine Band

The general thickness and lithological characteristics of this group of strata are shown on (Figure 38) and (Figure 46). Thicknesses range from a maximum of about 590 ft in the High Park Colliery area to a minimum of 520 ft at Hempshill Colliery. The chief coals mined underground are the Top Hard–Comb at the base, and the Cinderhill, High Hazles, Lowbright and Mainbright higher in the sequence. Coals of lesser importance are the Mainsmut, Brinsley Thin and Two-Foot. Sandstones are common and locally prominent above the Cinderhill coals and between the Lowbright Coal and Haughton Marine Band. Washouts occur in the Top Hard and Clown seams.

The Two-Foot Marine Band is found throughout the area but the Manton 'Estheria' Band and Haughton Marine Band are impersistent.

The Top Hard is a convenient boundary to take between the A. modiolaris and Lower similis-pulchra zones for it separates the characteristic A. phrygiana fauna below, from the equally distinctive Anthraconaia pulchella fauna above. The lowest distinctive fauna of the Lower similis-pulchra Zone occurs above the ?Second St John's Coal and includes Anthraconaia pulchella, Anthracosia cf. planitumida and A. simulans. Slightly higher in the sequence, above the Cinderhill Coal, representatives of the Anthracosia caledonica fauna were found. In addition to this species the assemblages included A. sp. cf. fulva. The mussel-bands between the High Hazles and Two-Foot coals are notable for the first appearance of the Anthracosia atra group. The associated species include Anthracosia simulans and Naiadites cf. obliquus. The A. atra group attains its acme in the beds overlying the Clown Coal. In the higher beds up to the Mansfield Marine Band mussels are not common but include Naiadites aff. angustus.

The Top Hard–Comb Coal

The Top Hard–Comb Coal consists of four elements, namely, the Top Hard Floor Coal, the main part of the Top Hard Coal and the Lower and Upper Comb coals, which occur in a variety of combinations in strata ranging in thickness from 12 to 87 ft (Figure 39), (Figure 40), (Figure 41).

Over most of the outlier at Heanor all four seams are united and the dirt partings in the sequence may total as little as 10 in. The various lines of split in the composite seam are shown on (Figure 39)A.

The Top Hard Floor Coal is separately identified north-east of Eastwood ((Figure 39)A). It is derived from the Top Hard seam by a split off the Bottom Brights (see below) and is of variable quality.

The Top Hard Coal itself consists of bright coal at the base and top of the seam, the Bottom Brights and Top Brights, separated by a variable thickness of hard coal, the Hards (Figure 40). The hard coal provided an excellent locomotive and steam fuel and the 'brights' a house coal. The overall high quality made it one of the principal economic seams in the coalfield and it was the first to be exhausted in the present district. In many early workings only the 'hards' were removed leaving the 'brights' as a roof and floor; these remnants have been exploited by opencast means in recent years and are still eagerly sought.

Variations in thickness of the Top Hard are shown in (Figure 41). In Hucknall Nos. 1 and 2 collieries there is cannel at the base of the seam, 27 in thick in No. 2 Colliery, No. 5 Shaft. According to Elliott (1965, pp. 133–141) the cannel was formed in a pool flanking a 'swilley' which is present to the east of this district.

The Comb Coal in the Heanor outlier is usually less than 9 in above the Top Hard, but locally as much as 15 in. The seam contains a dirt parting which expands gradually southwards and is 3 ft thick at the line of split shown on (Figure 41). In Shipley Lake Site the dirt has passed into argillaceous measures about 40 ft thick. Cromford Canal Site exposed a 40-ft trunk of Lepidodendron in position of growth, with its base in the Top Hard Coal and its top close to the base of the Comb seam (Plate 6).

The measures between the Comb and Mainsmut coals

The measures between the Comb and Mainsmut coals range in thickness from 21 to 71 ft (Figure 75). The Comb Coal is closely succeeded over wide areas by sandstone or interbedded sandstone, siltstone and mudstone, locally referred to as the 'Top Hard Rock'. This is thickest (over 50 ft) in the Hucknall area, and over much of the exposed coalfield forms a pronounced feature or is part of a composite feature upon which Swanwick, Ripley and Heanor are sited.

Mainsmut Coal

The Mainsmut Coal in the type area around Shipley, Kimberley and Watnall, is generally 24 to 36 in thick (Figure 75). A maximum of 39 in was recorded at Shipley Park Borehole, where the seam was composed of two 17-in bands of bright coal separated by 5 in of 'hards'. North-eastwards the seam splits into two leaves, up to 27 ft apart, and deteriorates both in quality and thickness. The ash content of the seam in the south and west is usually moderately high (7 to 10 per cent), but in the north and east it is very high (29.8 per cent at Delves Site near Swanwick). The sulphur content is typically low.

The Mainsmut Coal is unusual because of the presence of inclusions within the upper part of the seam. They vary from sandy laminae to lenses of quartzitic sandstone.

The measures between the Mainsmut and Cinderhill coals

The measures between the Mainsmut and Cinderhill coals range in thickness from 41 to 106 ft and contain, in the areas of thickest sedimentation, several cycles and two thin coals (up to 9 in thick) or seatearths. These coals may equate with the Second St John's Coal of the Chesterfield district to the north.

Sandstone, up to 50 ft thick, is common and forms good features in the Pinxton–Brinsley area. Mussels are recorded at various horizons, notably some 30 and 60 ft above the Mainsmut Coal. They are usually found either in black shale or preserved in ironstone nodules or bands.

The Cinderhill Coal

The Cinderhill Coal, sometimes referred to as the Cinderhill Main, is 44 in thick in Cinderhill Colliery No. 4 Shaft and consistently a little under 4 ft in the surrounding area. It was mined in the 1920's on both sides of the Cinderhill Fault.

This belt of thick coal trends west-north-westwards through Nuthall and Kimberley and has been worked opencast in synclinal outliers south of Heanor, at Poplar Farm and Johnson Farm sites (Figure 76). In these thick sections the coal is composed essentially of 'brights' with banded dull and bright coal forming a thin parting in the middle of the seam. Ash content is low to moderate and sulphur percentages are moderate to moderately high.

North-east of a line through Strelley, Kimberley and Eastwood, the Cinderhill splits and may be represented to the north and east by up to three coals ((Figure 76)B) i.e. an upward sequence of Cinderhill Coal, an Upper Leaf and a split from the Upper Leaf.

Smith and others (1967, p. 174) state that the Cinderhill Coal cannot be recognised with certainty in the shaft sections east of Alfreton, but infer from its position relative to the High Hazles that it may be the correlative of the First St John's Coal of districts to the north.

The measures between the Cinderhill and High Hazles coals

The measures between the Cinderhill and High Hazles coals vary between 105 ft in the south to 48 ft in the north, although leaves of the two coals are only 27 ft apart at Moorgreen Colliery. The succession in the areas of maximum deposition is dominated by sandstone, which is over 80 ft thick at Hempshill Colliery. At Newstead this sandstone was recorded as 'exuding grease'.

The High Hazles Coal

The High Hazles Coal is an economically important seam which has been worked in the past from Linby, Bulwell and Cinderhill (Babbington) collieries. It has promising reserves in the north-east of the district, where it is well documented from over 50 provings. The main seam has a maximum thickness of 36 inches in the north-east, but it splits and thins to the south and west beyond Hucknall and Annesley (Figure 42).

The High Hazles Coal consists largely of bright coal, but both the top and bottom of the seam are dirty. The ash content varies considerably; it is lowest in the areas of thickest coal at Linby (3.7 per cent) and Allens Green Site (2.9 per cent) and high to very high in the Swanwick Syncline. Sulphur content is moderately low.

The Brinsley Thin Coal

The Brinsley Thin Coal is separated from the High Hazles Coal by largely argillaceous measures ranging in thickness from 20 ft at Hempshill Colliery to 45 ft at Portland Colliery No. 2 Shaft. In the type area near Brinsley village, 2 miles N of Eastwood, the Brinsley Thin consists of up to 48 in of coal and dirt, but its average thickness is 2 ft at outcrop between Selston and Watnall and it decreases to under 6 inches in the north-east of the district (Figure 77). In this north-eastern area a thin coal, the Brinsley Thin (Upper Leaf), is present up to 16 ft above the main seam.

The Brinsley Thin Coal is variable in quality with ash content ranging from good to very inferior (3.6 to 27.0 per cent). Sulphur content varies from low to moderately high (0.5 to 2.4 per cent). It has never been an economic proposition for deep mining.

The measures between the Brinsley Thin (Upper Leaf) and Lowbright Floor coals

The measures between the Brinsley Thin (Upper Leaf) and Lowbright Floor coals range in thickness from 50 ft at Selston Colliery in the north-west to 25 ft at Hempshill Colliery in the south-east. They comprise largely argillaceous strata containing sporadic mussels including Naiadites cf. obliquus, particularly common in the roof of the Brinsley Thin, together with plant fragments and Planolites. The mudstones contain ironstone bands up to 8 in thick.

The Lowbright (Furnace or Abdy) Coal

The Lowbright (Furnace or Abdy) Coal is over 30 in thick in much of the district, reaching a maximum of 46 inches in the south-west at Lambclose House Site (Figure 43). It has been worked underground to a limited extent at Newstead, Watnall and Cinderhill (Babbington) collieries, but has been extensively exploited by opencast workings between Pinxton and Kimberley.

The Lowbright is composed largely of 'brights' with a persistent band of 'hards' about the middle of the seam, where the splits tend to occur.

The ash content varies from very low (2.5 per cent) in the Hucknall– Watnall area to high (over 15 per cent) in the Portland area. Sulphur percentages range from low to moderate.

The Floor Coalusually occurs less than 10 ft beneath the Lowbright. In the north-east of the district it closely approaches the main seam and in Newstead N1 Underground Borehole a separation of only 5 in is recorded.

The measures between the Lowbright and Two-Foot coals

The measures between the Lowbright and Two-Foot coals consist predominantly of interlaminated and interbedded sandstone and siltstone and are thickest, up to 44 ft, in Kennel Wood Borehole. The sandstone occurring at this locality is unusual. It contains two thin breccia horizons made up of siltstone fragments and ferruginous nodules, and shows many sedimentary structures such as current ripples, disturbed laminae, crumpled bedding and rib and furrow development. The sequence is thinnest (26 ft) in the vicinity of Selston Colliery, where the roof measures of the Low-bright Coal contain mussels.

The Two-Foot (Sough or Middlebright) Coal

The Two-Foot (Sough or Middlebright) Coal exceeds 18 in over much of the district, but varies from 29 in at Rap Site in the south-west to about 6 inches in the extreme north-east (Figure 78). In the Swanwick Syncline it averages 24 in. The seam is of little economic value for deep mining, but its close proximity to the Mainbright Coal along most of the outcrop has led to the extraction of both seams from the same opencast workings. The seam consists largely of 'brights', but many analyses show the upper half to be rather dirty. The ash content varies widely, from low to very high in under two miles, and sulphur percentages similarly range from low to very high.

A thin floor coal, 2 to 9 in thick, is present some 2 to 10 ft below the Two-Foot between Cinderhill and Selston.

The measures between the Two-Foot and Mainbright coals

The measures between the Two-Foot and Mainbright coals range between 19 ft in the east and 10 ft in the west. The Two-Foot Coal is invariably overlain by dark grey mudstone 'black bind' in the old shaft records. It is slightly silty, rather fissile and contains ferruginous laminae, some with a speckled appearance, possibly due to kaolinisation, whilst others are oolitic. The mudstone is richly fossiliferous, containing fish debris, 'Estheria' sp., mussels and ostracods, together with pyritised and carbonised plant fragments.

The Two-Foot Marine Band forms a reliable marker horizon and has been proved to be of wide lateral extent throughout the district. It comprises that part of the above-mentioned fossiliferous mudstones which contains Lingula and foraminifera, commencing immediately or close above the Two-Foot Coal and extending up to 5 ft 2 in above.

The dark grey mudstones in the lower half of this cycle pass up into silty mudstones with sporadic siltstone laminae containing a few mussels including Anthraconaia cymbula and scattered plant fragments.

The Mainbright Coal

The Mainbright Coal is an economically important seam, which has been worked from Hucknall, Watnall, Bulwell, Hempshill and Cinderhill collieries, but its best reserves lie beyond the eastern limits of the present district. The type section of the seam is at Hucknall No. 2 Colliery, No. 5 Shaft, where it consists of 34 in of bright coal containing a 5.5-in parting of banded 'dull' and 'brights'.

In the main area of outcrop, the Mainbright Coal is thickest in the south and west with a maximum of 49 in recorded in a temporary section near Broxtowe Wood (Figure 44). It thins northwards to 36 inches in the Hucknall–Watnall– Selston area and to 24 in near Annesley Park and Mexborough. The coal deteriorates in the north-east corner of the district, where it splits into thin seams with dirt partings or is represented by cannel and inferior coal as at Newstead.

The seam generally is of good quality with low ash and sulphur contents. It is composed largely of 'brights', with subsidiary partings of dull or banded bright and dull coal throughout (Figure 44).

The measures between the Mainbright Coal and the Mansfield Marine Band

The measures between the Mainbright Coal and the Mansfield Marine Band vary from 246 ft at Annesley in the north. to 185 ft at Cinderhill in the south. They include several thin coals of no economic value such as the Clown and ?Swinton Pottery. Marine bands and marker horizons proved in these measures in the Chesterfield and Ollerton districts to the north tend to be less persistent and only the Haughton Marine Band has been proved with certainty in the present district. The measures are rich in ironstone nodules and ferruginous patches; sphaerosiderite is common locally, as in the seatearth of the Clown Coal. Worm burrows are much in evidence and are often lined by ferruginous residues; root-structures in the seatearths are replaced by ironstone.

'Estheria' has been found in the roof of the Mainbright Coal in many recent boreholes. The fossil is preserved mostly as irridescent films in a grey mudstone, and is associated with ostracods, small mussels and fish remains.

Distorted roof measures have been observed on the Mainbright Coal. Shirley (1955, p. 274) recorded near-vertical 'dykes' of hard sandstone, 2 to 5 ft thick, in roof measures at Bagthorpe Site. He attributed this phenomenon to earthquake tremors, the effects of which he has traced in other parts of the coalfield at this horizon (Shirley in Eden and others, 1957, p. 112).

The Manton 'Estheria' Band horizon occurs in Annesley Park Borehole, where 'Estheria' associated with fish scales is present in 8 in of black mudstone.

The strata between the ?Manton 'Estheria' Band and the Clown Coal range from 78 ft in the west at High Park Colliery to 12 ft in the east at Annesley Park Borehole. South of Hucknall the absence of the Manton 'Estheria' Band and presence of washout sandstones at the Clown horizon make correlation uncertain.

The Clown Coal is thickest in the west, amounting to 78 inches in Wansley Hall Site, but thinning rapidly eastwards. Beyond Watnall and Newstead it is either washed-out, thin or represented by a seatearth (Figure 45).

The coal commonly contains many dirt partings which render the seam economically worthless.

The dark grey to black mudstone intermittently forming the roof of the Clown Coal contains variable amounts of fish and carbonaceous plant debris in the lowest few inches. In the Chesterfield district to the north, the mudstone also contains large specimens of Lingula and forms the Clown Marine Band.

The mudstones above the horizon of the Clown Marine Band contain numerous mussels typical of the Anthracosia atra fauna, together with pyritic plant fragments and ferruginous bands showing evidence of boring organisms. Some 20 ft above the Clown Coal in Mapplewells Borehole, such mudstones and siltstones are of a distinctive pale greenish grey colour. This colouring may be penecontemporaneous, for the Permo-Triassic unconformity is some 440 ft above.

There are a number of coals or seatearths between the Clown Coal and the Haughton Marine Band. The thickest seam is 29 in at Cinderhill Colliery No. 4 Shaft. At Hucknall Colliery No. 1 Shaft, a group of coals and dirts has an overall thickness of 139 in. It is not clear whether the first coal or seatearth below the Haughton Marine Band is the Swinton Pottery of districts to the north, or whether several or all of the coal horizons between the Marine Band and the Clown represent a split Swinton Pottery.

The Haughton Marine Band consists of dark grey mudstone with marine fossils. It is characterised by gastropods and Tomaculum sp. which occur together with Lingula and fish debris. The marine band is not seen at outcrop. In Felley Lane Borehole the assemblage included Euphemites anthracinus. Bellerophontoid gastropods were also recorded in Kennel Wood Borehole, where Lingula mytilloides, Serpuloides stubblefieldi and fish debris were found near the base of the marine band. The mudstones are particularly rich in ironstone and pyrite, and listric surfaces, some of which are associated with the zone of compression around ironstone nodules, are common.

The measures between the Haughton Marine Band and the Mansfield Marine Band comprise two main cycles totalling 57 to 78 ft in thickness. They are largely mudstones with subordinate arenaceous strata; sphaerosiderite is common. The top of the first cycle is marked by a thin, but persistent, coal which has a maximum thickness of 15 in at Cinderhill Colliery No. 4 Shaft.

This coal is overlain by the ?Sutton Marine Band in Mapplewells Borehole. The marine band may also be present in Hucknall Colliery High Main 27's Underground Borehole, but it is apparently missing over the greater part of the Derby district. At Mapplewells Borehole the possible marine band consists of 9 in of dark mudstone with pyrite and phosphatic nodules, its fauna consisting largely of fish debris.

The top of the cycle containing the Sutton Marine Band is invariably marked by a coal and/or seatearth. The coal is thickest (7 in) in Cinderhill Colliery No. 2 Shaft. This horizon is in places separated from the overlying Mansfield Marine Band by a few inches of mudstone or siltstone with pyritised and coaly plant fragments and non-marine bivalves.

Westphalian C

Mansfield Marine Band to Top Marine Band

These strata, some 350 ft thick, contain only one economically important coal, the High Main (Figure 49). They are concealed by Permo-Triassic rocks except for a narrow strip cropping out between Greasley and Pinxton. The general characters of the strata are shown in (Figure 47).

Above the Mansfield Marine Band, the mussel fauna is less varied than in the lower beds, with Naiadites as the dominant genus. Between the Mansfield Marine Band and the Edmondia Band the species include Naiadites melvillei and N. cf. productus. Above the Edmondia Band, N. cf. hindi is common. The lowest occurrence of Lioestheria vinti in this part of the sequence is in the roof measures of the first coal above the Edmondia Band, and this fossil recurs in several bands up to the Top Marine Band. Ostracods in these measures include Geisina subarcuata and Carbonita pungens.

The Mansfield Marine Band

The Mansfield Marine Band consists of up to 15 ft of dark grey mudstone with an abundant and varied fauna. A bed of fossiliferous 'cank' (hard ankeritic siltstone) occurs in the lower part and provides a reliable and persistent lithological marker horizon which is recognisable even in the records of old shafts and sinkings. The 'cank', which is 6 to 32 in thick, has a distinctive conchoidal fracture and is irregularly veined by calcite. Its petrography was described by Dunham (in Edwards and Stubblefield, 1948, pp. 249252). Chonetoid brachiopods and small Lingula are commonly present (see also p. 147c).

The measures between the Mansfield Marine Band and High Main Coal

The measures between the Mansfield Marine Band and High Main Coal vary from 158 ft in the north-west to 115 ft in the south-east, and contain up to four coals. The measures crop out just to the west of the Permo-Triassic escarpment in the Annesley Woodhouse–Selston Underwood areas, but are concealed by the younger rocks south of Watnall.

The variations of thickness in the measures are related to the presence of sandstones, particularly in the lowest and highest cycles.

Eden and others (1963, p. 54) record the sporadic occurrence of a kaolinite-rich band below the High Main Coal in various East Midlands localities. Boreholes indicate that this bed is widespread in the present district also, but because of the difficulty of differentiating such tonstein-like bands from normal ironstones and ferruginous mudstones it may have been missed in many of the records.

The measures between the Mansfield Marine Band and the High Main Coal are rich in ferruginous concretions, and sphaerosiderite is particularly common in the seatearths. Ironstone bands are locally oolitic and often have kaolin-filled centres. Kaolin patches and spots have been recorded below all the minor coal seams within these measures. The lowest of these minor coals is considered to be the probable equivalent of the Wales Coal of the East Retford district (Smith and others, 1973, p. 88). It is not known whether the overlying coals are splits from the Wales or represent higher seams including the Sharlston Low of Yorkshire.

The ?Wales Coal is about 12 in thick in the north-west of the district, where it lies some 85 ft above the Mansfield Marine Band. Traced south-eastwards this interval is halved and the seam deteriorates until, in the Cinderhill area, it is represented solely by seatearth. Analysis of this coal obtained from Newstead N1 Underground Borehole, just north of the district boundary, shows a medium ash content and low sulphur percentage.

The thickest single seam recorded in the measures up to the High Main Coal is 23 in at Hucknall Colliery No. 2 Pit, No. 3 Shaft, in the second cycle above the Mansfield Marine Band. Analysis of this seam from Babbington Pit Yard Boring showed poor quality (13 per cent ash) and high sulphur content (3.6 per cent).

The highest coal in these measures occupies a fairly persistent position some 40 ft below the High Main. An analysis from Linby 36's Slane Underground Borehole showed it to consist of bright coal which becomes inferior towards the middle and base of the seam. Overall quality is poor, with an ash content of 7.7 per cent and 0.93 per cent of sulphur.

Fish scales and associated debris have been recorded above this coal.

Sporadic mussels occur in the measures between the Mansfield Marine Band and the High Main including Naiadites melvillei and N. cf. productus.

The seatearth below the High Main Coal and most of the seatearths above this horizon have a distinctive grey-green, creamy grey or pale brown coloration. Similar colours commonly occur in the stained measures below the Permo-Triassic; those found in the High Main seatearth are some 300 ft below the stained zone in this district and are considered to be a reflection of the changing conditions of deposition in the upper part of the Westphalian sequence.

The High Main Coal

The High Main Coal is commonly 4 ft thick, but ranges from 43 to 62 in (Figure 48). It is mined in Newstead and Linby collieries at depths ranging from the 150-ft cover line in the west to 500 ft in the south and east. The seam consists of two major divisions (Figure 48)–a thin upper 'brights' and a thick lower 'brights' separated by a variable but generally thin dull coal or 'bluestone'. Between Annesley Woodhouse and Greasley the seam is split above the 'bluestone' over a zone some 600 to 1200 yd wide, comparable in plan with a meandering north–south channel (Figure 48). A detailed section across the split zone is afforded by Brookshill Farm Site, where some 200 trial boreholes were drilled. (Figure 79) shows isopachs of the measures, largely seatearth and mudstone, separating the two leaves. A longitudinal section A-B illustrates the present configuration of the coals. The lower 'brights' have been partially washed out in only one borehole (Whyburn South) and the upper 'brights' are fairly uniform in thickness.

If it is assumed that the configuration of the coals in section A-B is largely of penecontemporaneous origin, then at the end of the formation of the High Main Coal, when the upper leaf should have been nearly horizontal, the lower 'brights' seam would have the profile a–b. Such a profile suggests a NE–SW belt of rapid subsidence along a preexisting channel and/or tectonic line.

The quality of the coal varies from good to rather poor with ash content, less dirt, ranging between 4.6 and 9.6 per cent. Sulphur content is low.

Eden and others (1963) recorded a tonstein within the High Main Coal at several widely spaced localities in the East Midlands Coalfield. In the present district no definite occurrences are known.

The measures between the High Main Coal and Edmondia Band

The measures between the High Main Coal and Edmondia Band are some 30 to 40 ft thick and consist largely of mudstone though a washout siltstone, some 23 ft thick, overlies the High Main Coal in the Whyburn South Borehole and a 10-ft sandstone overlies the same seam at crop in the Beauvale Abbey area [SK 490 490]. They contain up to two thin coals. The lower coal, present only in the south-east of the district, where the two cycles are clearly defined in the Linby, Hucknall and Watnall areas, is possibly a split from the High Main Coal. This coal lies 10 to 20 ft below the higher coal, which is up to 11 in thick. Mussels occur locally above both coals, and they lie generally 5 ft, but up to 17 ft, below the Edmondia Band.

The Edmondia Band

The Edmondia Band has been found in 33 boreholes and shafts in the present district. It ranges in thickness from 2 to 24 ft, being thickest in a restricted belt of country which corresponds closely to the zone of split in the High Main Coal (Figure 48). This belt seems to have been liable to increased subsidence intermittently throughout this short period of geological time. Edwards (1967, p. 110) noted that the Band included a distinctive pale grey mudstone in the Ollerton area. Whilst pale mudstones are present within the Band in this district they are variable in both thickness and position. Foraminifera are found in both pale and dark grey mudstones and were particularly well preserved in the Whyburn House Borehole.

In Annesley Lodge Borehole the Edmondia Band contained abundant foraminifera including Glomospira, Glomospirella and Tolypammina. In the middle of the Band Myalina and Hollinella occur, an assemblage typical of the Myalina facies which is the usual development shown by this Band throughout the Yorkshire and East Midlands Coalfield. In Kennel Wood Borehole Curvirimula was found in association with Myalina cf. compressa. Curvirimula does not occur above the top of the C. communis Zone except in the retreat phases of some of the Westphalian B marine bands (Calver, 1968a, p. 151). The basal part of the Band contains cf. Planolites ophthalmoides and pyritised strap-like markings (fucoids). Thin bands and small nodules of ironstone occur throughout and pyrite is common as grains, clusters, concretions, coatings and infillings and replaces many of the plant fragments, worm burrows and fossils. The Edmondia Band contains galena in Misk Farm, Whyburn South and Kitty's Wood boreholes.

The measures between the Edmondia Band and the Shafton Marine Band

The measures between the Edmondia Band and the Shafton Marine Band are normally about 100 ft thick, though a maximum of 156 ft was recorded at Cavendish Crescent Borehole. They include up to six variable coals. The measures are particularly sandy and are broadly equivalent to the Mexborough Rock of south Yorkshire. They are nowhere exposed, being almost wholly concealed beneath the Permo-Triassic rocks.

The lowest cycle, commonly arenaceous and averaging 50 ft in thickness, is normally topped by a thin coal. The two succeeding thin cycles contain thin coals which are overlain by mudstones with Lioestheria.

The lower of these bands, which may be the "Main 'Estheria' Band" of Edwards and Stubblefield (1948, p. 231), consists of 1 in to several feet of grey mudstone. It is rich in Lioestheria sp.together with fish debris and ostracods. Pyrite is common, often replacing plant and shell fragments and infilling worm burrows. The carapaces are distinctive, appearing as abundant irridescent blotches in the mudstone. The size of the carapaces both within the band and throughout the district is variable. The coal underlying this "Main 'Estheria' Band" has been appropriately called the 'Bug Coal' by miners in the Ollerton area (Edwards, 1951, p.110).

The higher of the Lioestheria-bearing bands up to 23 ft 5 in above the lower, is from 3 in to a few feet thick, and is restricted in its distribution to the areas where the High Main Coal is split and the Edmondia Band is thick. Whatever the cause of this localised increase in thickness of sediment (p. 148c), it affects over 100 ft of strata.

The first cycle above the higher Lioestheria band is usually between 20 and 30 ft thick with a seatearth and/or coal, up to 25 in thick, at the top. This coal, unnamed in the Nottingham area, may be the Shafton of south Yorkshire, though Edwards (1967, p. 111) correlates the coal close below the Shafton Marine Band in the Ollerton district with the Shafton Coal. In this memoir the seam is referred to as the ?Shafton Coal (Figure 80).

The cycle succeeding the ?Shafton ranges from 5 ft 8 inches in Annesley Hall Borehole to 25 ft 10 inches in Kitty's Wood Borehole. The cycle is topped by a coal which underlies the Shafton Marine Band and is apparently the equivalent of the seam in a comparable position in south Yorkshire, though evidence from the Ollerton district (see above) raises the possibility that it is the Shafton or a leaf of that seam. This coal is thickest in the Annesley Park area (Figure 80) and thins northwards, passing into batt and cannel in Mapplewells Borehole. The overall quality is poor with high ash and sulphur contents.

The Shafton Marine Band

The Shafton Marine Band, recorded at 15 localities within the district, ranges in thickness from 8 in to 11 ft 7 in. The fauna includes Anthraconaia spathulata, ostracods such as Paraparchites, fish fragments, fucoids and worm burrows. Lingula has been recorded in three boreholes. The band usually closely overlies a coal or seatearth (see above), but may be separated by up to 14 ft 8 in of measures.

The measures between the Shafton Marine Band and Top Marine Band

The measures between the Shafton Marine Band and Top Marine Band vary from 46 to 64 ft and contain up to three cycles with locally associated coals. Mussels occur sporadically in all three cycles, but are most common in the lowest, where they include Naiadites daviesi.

The Top Marine Band

The Top Marine Band is a valuable and persistent marker horizon which has been proved throughout the district from Annesley Woodhouse in the north to Bulwell in the south. It usually comprises 2 to 7 ft of grey to dark grey mudstone containing a varied fauna of foraminifera, goniatites, brachiopods including Lingula, productoids, and Dunbarella gastropods, ostracods, fish, fucoids, Planolites and Lioestheria. Pyrite is common, replacing and coating plant and organic debris.

Measures above the Top Marine Band (Upper Coal Measures)

Some 500 ft of measures above the Top Marine Band are calculated to have been preserved in the extreme north-east part of the district, but westwards they are overstepped by the Permo-Triassic rocks. The maximum thickness proved is 350 ft at Linby Colliery. In the past 10 years many boreholes have been drilled by the National Coal Board in the east of the district, but these measures are rarely cored because they lack workable coals.

The measures comprise two thick and persistent cycles near the base, overlain by many thinner and variable cycles. One of the highest cycles, some 220 ft above the Top Marine Band, contains a coal about 2 ft thick known as the Manor Coal (Edwards, 1951, p. 75).

The measures are commonly arenaceous and mussels occur only sporadically in the argillaceous beds. A change in the mussel fauna takes place near the base of the Upper Coal Measures with the loss of Naiadites and the incoming of Anthraconauta. The dominant form is A. phillipsii.

The Top Marine Band cycle reaches a maximum thickness of 78 ft in Washdyke North Borehole and is the thickest single cycle in Westphalian C. Sandstone and siltstone, containing scattered plant fragments, form a large proportion of the total, but a 15-in seatearth was recorded in Washdyke North Borehole some 19 ft below the top of the cycle. A coal, here named the Annesley Coal, is commonly present at the top of the cycle. It is 9 to 16 in thick in a localised east–west belt between Annesley and Watnall, but elsewhere variations are considerable. It is represented by a ganister at Linby and a cannel at Hucknall.

The Annesley Coal is overlain by dark grey mudstones containing Lioestheria and fish debris. Ostracods and phosphatic fragments have also been recorded. Mussels, including Anthraconauta phillipsii, are also present in the lower part of this cycle. It may well be that the Annesley Coal is the correlative of the Scofton Coal of the East Retford district, which is similarly overlain by mudstones with 'Estheria', mussels and ostracods (Smith and others, 1973, p. 94).

The second cycle above the Top Marine Band ranges in thickness from 42 ft at Springfield Hosiery Borehole to 56 ft at Annesley Park Borehole. Above it there is a complex series of seatearths, coals, batts and carbonaceous shales spread over up to 40 ft of measures. One of these coals is 30 in thick in Hucknall No. 2 Colliery, No. 5 Shaft.

Fish fragments were recorded at two horizons between these coals at Annesley Park Borehole and at one horizon in Washdyke North Borehole. Ostracods are also present in both boreholes but at slightly different levels. Sphaerosiderite is a common constituent of the seatearths in Springfield Hosiery, Washdyke North and Whyburn East boreholes.

Above these coals are siltstones and sandstones 30 to 90 ft thick. They are succeeded by a group of eight minor impersistent cycles, which in Linby Colliery No. 1 Shaft comprise 120 ft of measures.

The Manor Coal at the base of this group, reaches a maximum of 27 inches in Hucknall No. 2 Colliery, No. 5 Shaft, where it is overlain by 36 in of cannel. In the Hucknall–Linby area the coal is generally over 2 ft thick but it thins northwards to 21 in at Newstead.

At Linby Colliery the Manor Coal is overlain by 110 ft of largely argillaceous strata, extending up to the unconformable Permo-Triassic cover. Sandstones are common in the Newstead and Hucknall areas. Primary red measures have not been recorded in the district.

Stained measures

The Westphalian strata underlying the Permo-Triassic rocks (Figure 49) are normally stained to about 50 ft below the unconformity, but range from 10 ft at Annesley and Hucknall collieries to 115 ft at Whyburn East Borehole. Red, brown, pink, purple and green coloration is common in the mudstones and sandstones.

Seatearths show purple mottling, although in the measures above the Mansfield Marine Band they are commonly a pale grey or cream colour, contrasting with the darker seatearths of lower horizons (p. 24). Ironstone nodules, normally pale brown or buff, are markedly reddened. Sandstones often show staining to greater depths than do other lithologies. Staining is considered to be due to subaerial weathering and oxidation of the Westphalian land surface in late Carboniferous and possibly Lower Permian times (Anderson and Dunham, 1953; Trotter, 1953; Smith and others, 1967). Because argillaceous rocks are as highly coloured as other lithologies, percolating solutions are probably less important than weathering, though the increased depths of staining in areas of porous strata would suggest that the former process took place penecontemporaneously with the denudation. Where the Permo-Triassic rocks are present, staining affects measures above the Mansfield Marine Band, but evidence from the west of the present district (p. 26) shows that the lowest sandstone in the Westphalian, i.e. the Crawshaw Sandstone, is similarly stained although the Permo-Triassic strata have long since been eroded.

The measures immediately below the unconformity are often leached to a depth of a few inches.

The approximate positions of the coal crops beneath the Permo-Triassic rocks are shown in (Figure 50).

Chapter 5 Permo-Triassic

Introduction

Rocks of the Permian and Triassic systems, originally classified by Sedgwick (1829), were considered by early workers such as Aveline (1877, 1879) and Irving (1882) and later by Trechmann (1930) to be separated by an unconformity. This was questioned by Wilson (1876, 1881), who described the main divisions of the succession in north-east England, and Sherlock (1911, 1926, 1947), who suggested that there was a lateral passage between the Permian and the lower part of the Triassic. The usual practice of the Geological Survey since has been to group the two systems together.

Apart from the early papers of Wilson (1876, 1881) and Shipman (1889), Hickling (1906), Vernon (1910), Swinnerton (1910) and Smith (1910, 1912, 1913), the first comprehensive account of the present district was by Sherlock (in Gibson and others, 1908) in the memoir accompanying the primary 6-in survey of Sheet 125 (Derby). Further details have been added by Swinnerton (1914, 1918, 1948), Edwards (1951), Elliott (1961), Taylor (1964a and b, 1965, 1966, 1968, 1973), Taylor and Elliott (1971) and Smith (1968).

The strata unconformably overlie the Carboniferous rocks in the south-western, southern and eastern parts of the Derby district. Because of erosion and marked lateral thickness variations the thickest recorded sequence at any one locality is 450 ft near Chilwell, west of Nottingham. Thickness variations are exemplified by the Upper Permian strata, which are 140 ft thick in the north-east of the district and absent 8 miles to the south, near Nottingham. The lithostratigraphical subdivision of the Permo-Triassic sequence is shown in (Figure 51), and the relationship between this sequence and the underlying Carboniferous rocks is depicted in (Figure 52). Boreholes near Newstead in the north-east of the district proved Lower Marl overlying Westphalian C rocks whereas at Strelley the Lower Marl rests on Westphalian B rocks; at Breadsall, Pebble Beds rest on the Namurian Ashover Grit, and at Weston Underwood in the south-west of the district Waterstones overlie the Widmerpool Formation of Dinantian age.

Classification and correlation

The Permian rocks above the Basal Breccia were proved to be Upper Permian on the basis of miospore taxa in the 'Lower Permian Marl' (Clarke, 1965). Thus the use of 'Lower' and 'Middle' in the nomenclature of the various divisions is illogical and though they are retained on the published maps for the sake of continuity with adjoining areas, the modified terms, Permian Basal Breccia, Lower Marl and Middle Marl are used in this memoir.

As compared with over 1000 ft of Permian strata proved in County Durham (Smith and Francis, 1967), the maximum thickness in the present district is only some 200 ft, and in the south and west they are absent.

In north-east England, Smith (1970a) has described five evaporite cycles, but only the lowest (EZ1) is represented with certainty in the Derby district. Thin bands of dolomite in the Middle Marl may be local representatives of the second cycle carbonates (EZ2).

Smith (1968) recognised the Hampole Beds in the Lower Magnesian Limestone of the present district. The beds form a distinctive marker horizon between the lower and upper subdivisions of the formation.

The Middle Marl is overlain by 'Bunter Sandstone', which Sherlock (1911) divided in the Nottingham area into a fine-grained, predominantly red marly lower division the Lower Mottled Sandstone—and a coarser, pebbly, predominantly yellowish brown upper division—the Bunter Pebble Beds. His conclusion that there is a lateral passage of the Lower Magnesian Limestone into Lower Mottled Sandstone implied that the latter is partly of Permian age. This lateral passage was supported by the resurvey. The Lower Mottled Sandstone is therefore a sandy facies of the Upper Permian continental red beds and represents fluviatile activity on an increasingly important scale.

Smith and others (1973, p. 105) in the East Retford district have taken the base of the Trias at the base of the Pebble Beds–an arbitrary lithological boundary. This boundary in the south and east of the present district is gradational. In the west of the district a basal conglomeratic formation assigned to the Pebble Beds, but of uncertain age, transgresses on to an old land surface of Carboniferous rocks.

Recent palynological investigations (Warrington, 1967; Geiger and Hopping, 1968) have shown that the European stages of the Trias can be extended into the British Isles, and Smith and Warrington (1971) have thus been able to demonstrate that the Green Beds, Waterstones and Keuper Marl are diachronous formations to the north-east of the present district. No palynomorphs have been obtained from surface exposures in the Derby district, but in Trusley Borehole Dr Warrington reports Anisian miospore assemblages from the Waterstones and Anisian and probable Ladinian assemblages from the Radcliffe Formation; probable late Ladinian to early Carnian miospores occur some 20 ft above the Plains Skerry.

No distinct evaporite horizons are known in the present district. The well known Tutbury gypsum which is worked south of Derby occurs in the Trent Formation–above the highest rocks at outcrop in the present district. Gypsum is rarely seen in surface exposures. Elliott (1961, p. 228) has shown that gypsum is removed by solution in a zone which is up to 100 ft deep in the vicinity of faults. Fibrous gypsum was common below 62 ft in the Trusley Borehole in the south-west of the district. It occurs in veins as well as along bedding planes and is considered to be of a secondary origin.

Because of the repetitive nature of the Keuper Marl succession, detailed correlation of small exposures is particularly difficult, even with the aid of the various diagnostic sedimentary structures. Numerous old clay and skerry pits worked in the last century are flooded, grassed over, or in-filled. The resurvey was fortunate therefore to have the results of a series of major roadworks and pipe-line schemes, the cuttings and excavations of which provided almost continuous sections through the Keuper rocks.

Conditions of deposition

The Permian sediments accumulated in a broad basin which extended eastwards to the Baltic and which on paleomagnetic and paleoclimatological evidence is considered to have lain in tropical and sub-tropical latitudes.

Following the Armorican Orogeny and associated uplift, the Carboniferous rocks in the east of the district were eroded into an eastward-sloping peneplain interrupted by minor irregularities of up to 10 ft amplitude. The sub-Permian peneplain was reddened by surface oxidation under desert-like conditions, usually to depths of 30 ft or so, depending on the porosity and fracture of the underlying beds. In many areas such reddening is the only evidence of a former cover of Permo-Triassic rocks. North-west of Wirksworth, a mantle of younger, probably Triassic rocks, overlay the Dinantian limestone and remnants of this cover are preserved in old pot-holes in the limestone surface despite a long history of re-working. The dolomitisation of the limestone has been attributed to downward percolation of magnesium-rich solutions from a once extensive Triassic sea (p. 12; (Figure 56)).

The Permian and younger rocks rest therefore with pronounced unconformity and progressive overlap on a planed surface of negligible relief in the east. To the south and west they were deposited on a land surface of considerable relief (Figure 56).

The Permian Basal Breccia was laid down on the Carboniferous peneplain under continental conditions as a piedmont breccia by intermittent fluviatile activity and was derived from local as well as distant sources. There followed a rapid southward transgression of the Zechstein Sea reaching almost to Nottingham (Figure 71).

It is convenient to think of Permian sedimentation in terms of desiccation cycles (Dunham, 1948; Stewart, 1954; Smith and Francis, 1967), each ideally consisting of a basal elastic member followed by carbonate and sulphate precipitates, and ending with salt and potash deposits. In marginal areas such as the present district these cycles are rarely complete, the bulk of the Permian succession being formed by the carbonate phase of the lowest (EZ1) cycle (Lower Magnesian Limestone and Lower Marl) ((Figure 51); Smith, 1970b).

In this district much of the Lower Magnesian Limestone is recrystallised and dolomitised and the original textures have been destroyed. By analogy with the areas to the north, the rocks were deposited along the margins of a shallow sea which, judging from the restricted faunas, must have been highly saline. The Hampole Beds are considered to have accumulated intermittently on an extensive intertidal or supratidal coastal flat (Smith, 1968).

The overlying Middle Marl represents the silting up of the Zechstein basin and was deposited in playa-like depressions on a wide coastal plain. It indicates the establishment of arid continental conditions which were to persist into Triassic times.

In the rocks above the Middle Marl, differences between eastern and western lithologies reflect the palaeogeography of the period. In the east, the Zechstein basin persisted and the Bunter reveals a change in the energy environment from slow deposition in a shallow saline shelf sea to rapid accumulation in delta fans fed by fast-flowing rivers from the south. In the west, delta fans were deposited on uneven topography at the north-eastern margin of the Staffordshire or Needwood Basin (Figure 56). These two depositional basins were divided by an upland region formed by the outcrops of Namurian and Westphalian sandstone of the Morley area and called the Pennine–Charnwood Sill by Wills (1970). Moira Breccia formed here as a scree deposit, possibly from early Permian times. The upland area north of Morley village was not transgressed until the Waterstones were laid down; the underlying Pebble Beds were banked against the scarp face of Ashover Grit over much of its length (Wedd in Gibson and others, 1908, p. 120).

In the eastern basin, the Lower Mottled Sandstone thins westwards towards the Morley barrier and is probably banked against the dip-slope of the Crawshaw Sandstone (Westphalian A). The later Waterstones rocks overlap the Pebble Beds (Gibson and others, 1908, p. 124) and north of Morley rest either upon Moira Breccia or directly upon Carboniferous. They overlie a broad plateau feature in the older rocks, which appear to continue north-westwards as a planation surface linking the summits of the hills.

Wills (1970, p. 229) has divided the Bunter into cycles of sedimentation of a flood deposit type, in each of which there is an upward decrease of grain size.

During the deposition of the Keuper rocks the district was part of an area of relatively slow sedimentation lying across the Pennine–Charnwood ridge (Wills, 1970, p. 274). The dominant lithology is a massive red silty mudstone. Sedimentary structures (Elliott, 1961; Klein, 1962) show that deposition took place in water, although the sporadic silt and sand grains may have been wind-borne from nearly, land. Some authors consider transportation of the 'marls' to have been largely aeolian. At times climatic changes promoted an inflow of coarser detritus into the region, resulting in the formation of skerries. At other times aridity prevailed and evaporation led to the precipitation of soluble salts. Since the work of Shearman (1966) these evaporite sequences have been compared with the present-day sabkha environment of the Trucial Coast.

The origin of the red coloration of the Keuper rocks has provoked much discussion and controversy. The red colour is considered by Dunham (in Stevenson and Mitchell, 1955, p. 61) to be due to the even dissemination of minute granules of hematite through the rock. The green colour he considered is due to a magnesian clay mineral of the chlorite or montmorillonite group. The green rocks contain far less ferric oxide than red rocks, but the difference in the ferrous oxide content is not significant, so he ruled out the reduction of hematite in situ. Hematite is virtually absent in green rocks and Dunham (op. cit.) concluded that either it was not deposited or has been removed in solution; the latter possibility appears unlikely.

Clark (1962) has emphasised that the origin of red beds may be complex and result from the influence of more than one environment. Recent work by T. R. Walker (1967) and Norris (1969) provides evidence that the hematite pigment in many red beds, particularly those associated with evaporites and aeolian sandstones, has been formed in situ by alteration of non-red sediments in hot arid or semi-arid climates. The role of subsequent alteration however is considered to be a minor factor in the Keuper rocks of this district. In the finely laminated beds of the Harlequin Formation, for example, there is no diffusion of colour from one layer to another as might be expected from in situ alteration. Instead each colour shows lateral persistence and restriction to one layer. It is therefore concluded that the Keuper red beds are derived from sediments reddened at source during periods of aridity and the green beds are formed in less arid periods from green muds, which possibly owe their colour to reduction by bacteria either at source or during transport. The reducing role of bacteria has been emphasised in recent studies of Keuper-type beds in the Persian Gulf.

Permian

Permian Basal Breccia

The basal breccias, probably of Lower Permian age, represent the rapid accumulation and resorting of the products of erosion of the post-Carboniferous land surface. They include breccio-conglomerates which are rich in ironstone nodules derived from the Westphalian. The breccias are usually present throughout the district, though represented locally by only a few quartzite pebbles at the base of the Lower Marl or Lower Magnesian Limestone. In a large area south of Newstead, roughly coinciding with sub-Permian crops of thick Westphalian sandstones which were resistant to erosion, the breccia is less than 6 in thick (Figure 81). In the Annesley Woodhouse district and between Kimberley and Strelley accumulations of 48 in or more are not uncommon, the maximum thickness for the district of 5 ft 9 in being recorded in the Mapplewells Borehole. In Whyburn West Borehole, west of Hucknall, there is a 5-in sandstone at the horizon of the breccia.

The breccia is composed of rounded fragments of quartz and quartzite, with Westphalian ironstones, mudstones, siltstones and sandstones, and with angular fragments of igneous and metamorphic rocks of probable Charnian age, set in a grey-green sandy calcareous and/or dolomitic matrix. The fragments vary in size up to 12 in and the predominance of red-brown stained quartzites and dark red ironstones gives rise to local names such as 'plumcake rock' in the Kimberley area. The larger fragments occur in vaguely defined bands which occasionally show cross-lamination.

Lower Marl

The rocks now referred to as Lower Marl were described by Wilson (1876, p. 534) in a railway cutting near Hempshill as 'a series of thin-bedded slate-coloured sandstones and shales' which he considered representative of the Marl Slate of County Durham. They were noted by Farey (1811, p. 157) as a possible source of lime. These beds were mapped by Sherlock during the original survey of 1908 and included in the Lower Magnesian Limestone. He subsequently referred to them as 'Grey Beds' in his more extensive work (1926, p. 14) on the Permo-Triassic deposits of Britain. The present resurvey has shown that the Lower Marl forms an outcrop some 100 yd wide at the bottom of the Lower Magnesian Limestone escarpment from Annesley Woodhouse in the north to Strelley in the south with a narrow extension for over one mile to the east up the deep railway cuttings of the Kimberley–Nuthall area. There is an inlier at Broxtowe and a small outlier near Beauvale. In the north the formation is up to 80 ft thick but is only 50 ft at Hucknall and thins out rapidly in the five miles between Hucknall and Strelley, being absent south of a line approximately through Strelley, Bilborough and Radford (Figure 53). The beds are composed essentially of mudstones with siltstone, limestone and dolostone (dolomite of siltstone grade) bands. In general, dolostone bands are more abundant in the north where the overlying Lower Magnesian Limestone is thickest and decrease in importance to the south and east (see below). The more resistant carbonate lithologies are most common in the top part of the formation and mudstones increase in importance towards the base, but the mudstones comprise less than 50 per cent of the rock in most areas.

The beds are grey to pale grey when fresh but weather to a yellow-brown colour. In the top few feet they are irregularly red-brown in colour, and there is an upward passage into similarly coloured dolomitic Lower Magnesian Limestone by the intercalation of dolomite bands. Carbonaceous plant fragments are common, including leaves of cf. Ullmannia bronni, U. frumentaria, Callipteris martinsi, a young shoot of ?Pseudovoltzia liebeana and undetermined conifer leaves and cone scales. Spores from the Lower Marl were listed by Clarke (1965). Lingula is rare in the present district except in the extreme north-east near Newstead.

Calcareous bands within the formation are commonly shelly but have an impoverished fauna, with Bakevellia ceratophaga, Schizodus obscurus, and other (indeterminate) bivalves and crinoids.

The Lower Marl was deposited in a shallow sea–a low energy environment but with a nearby land source of plant material. When traced north-eastwards there is an increase in thickness of the Lower Marl accompanied by a greater abundance and variety of fauna, indicating an approach to the main area of Zechstein deposition.

Lower Magnesian Limestone

In the north, the Lower Magnesian Limestone forms a marked westward-facing scarp some 100 ft high, forming the watershed between the Rivers Leen and Erewash. This feature decreases in prominence southwards and at Strelley is only some 30 ft high. The eastward-inclined dip-slope is about three miles wide and covers a large area (14 square miles) of outcrop which is disproportionate to the thickness of the formation. It forms gently rolling country modified by elongate dry hollows leading to narrow river valleys and covered by a rather thin red-brown sandy and marly loam suited to arable farming. The formation has been extensively quarried in the past and has been penetrated by some 40 boreholes and shafts extending into the Westphalian strata beneath. There is, in addition such a wealth of railway and motorway cuttings, together with natural exposures, opencast sites, and numerous temporary sections provided by new development schemes in the outskirts of Nottingham that this chapter necessarily contains only a selection and condensation of the available information. Most of the surface exposures are shown on published six-inch maps SK 44 NE, SK 44 SE; SK 45 SW; SK 54 NW, SK 54 SW; and SK 55 SW.

The thickness of the formation varies between 20 and 40 ft over most of the outcrop, but generally thins southwards, and the southern limit of outcrop extending between Catstone Hill, Old Radford and Nottingham approximates to the depositional margin. That margin lies approximately one mile to the south of the depositional limit of the underlying Lower Marl. The southward thinning is accompanied by a change of colour from the pale greys and yellows of the northern area, through yellow-browns, to reddish browns and purples along the southern outcrop.

The formation consists of a flaggy, granular-textured dolomite or calcareous dolomite resembling a sandstone in appearance. The term 'limestone', used for convenience throughout the chapter, denotes dolomitic rock or dolomitic limestone.

Numerous red-brown silty micaceous mudstone bands, normally less than 1 in thick, accentuate the bedding-planes, which are commonly wavy, and at times, stylolitic. The Hampole discontinuity (Smith, 1968), noted in quarries and railway cuttings between Annesley and Bulwell, was located in Annesley Hall Borehole some 14 ft from the bottom of the limestone.

Because of the rather open granular texture produced by the dolomite rhombs, the rock tends to weather into dolomitic sand along the major joint planes, and isolated pockets of softened brown limonitic dolomite occur at depth. Hard finely crystalline calcareous dolomite commonly forms thin pinkish massive layers, particularly towards the base of the formation, and also occurs elsewhere as irregular nodules. Sherlock (in Gibson and others, 1908, p. 107) noted this concretionary phenomenon at the top of the Lower Magnesian Limestone at Cinderhill. Sporadic veinlets, cavity fillings up to 1 inch in diameter and small irregular patches of calcite occur within the formation. Pyrite associated with calcareous nodules and galena, both disseminated and in thin 'stringers', have also been recorded. Dendritic patterns and irregular speckling of black manganese dioxide are present along bedding and joint planes.

The transition from Lower Marl to Lower Magnesian Limestone involves changes in lithology and texture. The proportion of mudstone decreases upwards, and the grain size increases from fine silt grade in the Lower Marl to the coarse granular and saccharoidal textures of the Lower Magnesian Limestone. Accurate demarcation of the two formations is often difficult, particularly in the records of old borings and sinkings. The transition beds commonly contain calcite-filled cavities and veining.

The boundary of the Lower Magnesian Limestone with the overlying Middle Marl is usually a distinct lithological break. The top few inches of the limestone are commonly silicified, forming a hard pinkish finely crystalline dolomite. At many localities this top bed contains irregular concentrations of galena, and it was at this horizon that Deans (1961) proved the presence of wulfenite and uraniferous hydrocarbons including asphaltite. These deposits may have been carried in solution and trapped by the Middle Marl, acting as a cap-rock.

Sporadic sand grains occur throughout the Limestone; two distinct sandy bands, both about 2 in thick, occur in the Hucknall area, one 15 ft from the top and the other 8 ft from the base of the limestone. They thicken southwards until at Strelley the top half of the formation is largely a breccio-conglomeratic sandstone, representing a shoreline facies of the Lower Magnesian Limestone. Breccias have been recorded in Whyburn House Borehole, north-west of Hucknall, where a grey 'marly' band up to 2 in thick contained Magnesian Limestone pebbles approximately at the base of the Lower Magnesian Limestone. Gibson and others (1908, p. 106) recorded breccias in old quarries near Beauvale Abbey, and noted that the underlying 'marl slates' (Lower Marl) appear to be locally absent. Waring (1966, p. 207) came to similar conclusions and postulated an approach to a western shoreline in this northern area west of Hucknall. The present survey produced no evidence to support Waring's view.

The Lower Magnesian Limestone commonly shows cross-laminated units with foreset dips, normally some 10°, suggesting palaeocurrents from all quadrants except the north-east. Large areas of bedding planes showing assymmetrical and oscillatory ripple marks are common in the Linby area (Plate 9). The steepest slopes of the former variety are to the west, suggesting that the direction of wave movement was mainly from the east, i.e. the prevailing Permian wind direction.

Dome structures described by Smith and others (1967, p. 201) in the Pleasley–Mansfield area to the north of the present district occur towards the top of the Lower Magnesian Limestone, and are considered to be depositional in origin.

Fossils are not common in the formation as a whole and are usually present as solitary valves of Bakevellia, Liebea and Schizodus. At certain horizons they are concentrated into distinct bands as at Bulwell, where a 12-in shell band near the top of the Limestone contained Bakevellia cf. binneyi, B. cf. ceratophaga, Liebea squamosa and Schizodus obscurus. In addition Permophorus costatus has been found at Nuthall. Finely comminuted carbonaceous plant debris is sporadically present.

The Lower Magnesian Limestone was laid down in shallow saline water, largely as an oolite. Subsequent recrystallisation has destroyed most of its original structure in the present district. There is evidence in the Durham and East Retford areas that some of the beds formed under supratidal-sabkha conditions (Smith and Francis, 1967; Smith and others, 1973). In the Derby district the presence of large scale cross-bedding suggests fairly deep water.

Preferred dip orientations of the cross-bedded units are from the north-west and south, confirming the likelihood of shorelines in those directions. Concentration of shell debris occurs at various horizons within the Lower Magnesian Limestone.

Whilst numbers of individuals are large, the number of species is small (see p. 80), and it is inferred that conditions were not conducive to active marine growth in this marginal area of the Zechstein Sea. The present district was rarely beyond the reach of detrital sand grains which were either blown in from the nearby shorelines, or transported by currents. Where the Lower Magnesian Limestone is the basal unit of the Permo-Trias the lowest few inches often contain conglomeratic fragments and coarse sand grains which probably represent a period of local erosion and reworking in Upper Permian times, which was distinct from the erosion producing the main Permian Basal Breccia, a bed largely consolidated and compacted in Lower Permian times.

At Strelley the top half of the Lower Magnesian Limestone is composed entirely of sand and small pebbles washed in from land adjacent to this shoreline. Onlap of the Lower Magnesian Limestone is about 1 mile to the south of the Lower Marl.

The Lower Magnesian Limestone is well jointed (see p. 159d), and cambering on valley sides has resulted in considerable widening of the joints which have been infilled subsequently with glacial debris. The jointing facilitates quarrying and throughout the Nottingham–Mansfield area the Limestone has been used extensively in the past for building stone, e.g. at Linby, Hucknall and Bulwell, and has also been burnt for lime. Its use for building has declined in recent years, but it is still in demand as an ornamental and rockery stone.

Middle Marl

The Middle Marl is confined to irregular outliers on the Lower Magnesian Limestone dip-slope west of the River Leen. A protective cap of Lower Mottled Sandstone usually overlies the Marl. Many small pockets of marl preserved in depressions in the dip-slope are too small to show on the map. Joints, widened by cambering, and glacial frost wedges in the top part of the Lower Magnesian Limestone contain a mixture of sand, derived Middle Marl and quartzite pebbles.

The formation weathers into a heavy, poorly drained, red-brown clay which is locally modified by a surface layer of sand and pebbles of Bunter origin to produce a light clay loam soil. The top soil is invariably rich in rounded quartzite pebbles and the Middle Marl outcrop contains Pleistocene erratic's (see p. 158a), commonly attaining a length of between 2 and 3 ft.

The Middle Marl base marks the end of continuous carbonate deposition. Mud and silt are the dominant lithologies, but thin impersistent sandstone bands also occur, probably representing periods of excessive rainfall. Sporadic dolomitic layers indicate quiescent periods with a reversion to carbonate deposition. The limit of Middle Marl deposition lay to the north of the Lower Magnesian Limestone shoreline reflecting contraction, due to silting up, of the Zechstein depositional area.

In the present district the base of the Middle Marl is invariably sharply defined but there is upward as well as lateral passage into the overlying Lower Mottled Sandstone. The thickness of marl is therefore open to interpretation, but generally it does not exceed 25 ft in the north; a maximum of 34 ft was recorded in Mapplewells Borehole. The Middle Marl thins rather irregularly southwards, in which direction there is also a decrease in the clay content.

The Middle Marl consists of red clay or mudstone in beds up to 5 ft thick, interbedded with red-brown and green silty, sandy or sandstone bands. The harder sandstone bands have a dolomitic cement and are variable in thickness and extent. Thin beds of buff and yellow dolomitic limestone, lithologically comparable with the underlying Lower Magnesian Limestone, occur less commonly. The basal few inches of the marl overlying the Magnesian Limestone are invariably pale grey-green in colour, which is presumably due to the reducing action of migrating fluids in the limestone.

Deposition of the Middle Marl is considered to have occurred in the shallow land-locked remnants of the Zechstein Sea. The supply of elastic sediment, water borne as well as possibly wind borne, was normally too great to allow the formation of limestone. The thicker sandstone bands show current structures and probably represent rapidly accumulated sediments, following 'flash' floods. Such sandstones are not ideal for correlation, but in the absence of other markers have been so used with related breccia beds at Hempshill (Wilson, 1876) and beyond the limits of the district at Harworth (Mackintosh, 1937) and Calverton (Edwards, 1967, p.121).

The Middle Marl was formerly extracted for brick-making at Linby, Watnall, Hucknall, Bulwell and Cinderhill. The outcrop supports numerous artificial lakes and fish ponds in the grounds of Annesley, Papplewick, Bulwell, Basford and Strelley Halls and Newstead Abbey. The lake at Nuthall is only partly floored by the Marl and the clay was puddled to provide a watertight seal where permeable strata such as the Lower Magnesian Limestone form the base.

The marl has been exploited for the manufacture of plant pots at Bulwell but material suitable for firing is limited and production is tending to decrease in the face of competition from plastic pots.

Triassic

In the south and east of the district the Middle Marl passes up into the Lower Mottled Sandstone, which may be wholly or in part of Permian age (p. 74). Where present, Pebble Beds are overlain by Waterstones, which, beyond the northern limits of the district, have been proved to be diachronous ranging in age from late Scythian in the north to Anisian in the south (Smith and Warrington, 1971). In the south-west of the present district beds of Waterstones lithology have yielded Anisian miospores.

Moira Breccia

According to Mitchell and Stubblefield (1948, p. 24) 'the Moira or Hopwas Breccia at the base of the New Red Sandstone is a basal breccia which may equally well occur at the base of the Keuper Marl (where that has overlapped the lower beds) or at the base of the Bunter Pebble Beds'. This adequately describes its restricted occurrences in the Derby district.

Only the large outcrop at Morley underlying transgressive sandy rocks of Waterstones lithology has been shown on the map; the occurrences of breccia near Breadsall, originally noted by Wedd (in Gibson and others, 1908, pp. 110–112), are too thin or have too patchy a distribution to be shown separately from the overlying Pebble Beds. As Wedd pointed out, the Moira Breccia shows distinct affinities with the Permian Basal Breccia (pp. 150b and 152c).

In the field, the matrix of the breccia is normally a red or ochreous calcareous sand, but may be clayey in some sections; the fragments, which are up to about 6 in across, are of quartzitic rocks, hard and soft sandstones, siltstones, reddened ironstones, igneous rocks and soft mudstones. The rock is usually softer at outcrop than the Permian Basal Breccia.

The Moira Breccia is probably a scree deposit laid down in an area of high relief, but its age, whether Permian or Triassic, is uncertain.

Lower Mottled Sandstone

The largest area of outcrop of the Lower Mottled Sandstone, some 3 square miles, is a down-faulted block in the north-east of the district near Annesley. In the south-east the outcrop is a narrow belt marginal to the more extensive outcrop of the thicker overlying Pebble Beds. In the intervening ground the Lower Mottled Sandstone occurs as scattered small outliers on the Lower Magnesian Limestone dip-slope west of the River Leen. The sandstone gives rise to undulating, easily worked but not particularly fertile agricultural land, which readily reverts to birch scrub. Many acres have now been planted with conifers by the Forestry Commission.

A total thickness of about 100 ft is present in the north-east near Newstead Abbey and Robin Hood Hills. It thins southwards at crop to 50 ft in the Strelley area, but boreholes near Bulwell and Nottingham have proved red sandstone up to 100 ft thick. Farther south, between Wollaton and Dale Abbey, the thickness of the Lower Mottled Sandstone decreases to about 25 ft; farther west it appears to be overlapped by yellow Pebble Beds. At Morley, dolomitic Lower Mottled Sandstone is exposed near the western limits of deposition.

Despite its name, the sandstone is not obviously mottled in the present district except at the top, where there is an upward passage into the yellow to buff Pebble Beds. The base of the sandstone is usually gradational with the Middle Marl, though locally there is a basal breccia as in the Hempshill–Kimberley railway cutting, where a band up to 5 ft thick persists for at least 50 yd (Wilson, 1876, p. 533).

In the south-east near Bramcote, the Lower Mottled Sandstone is used as a moulding sand and in the past many pits were dug to supply Stanton Iron Works. To the north, in the Mansfield area (Smith and others, 1967, p. 209), the highest beds of the formation are the most important source of moulding sands, but in the present district it is the lowest 50 ft or so that contains the necessary 10 per cent clay fraction. Here the highest beds are used as building sand.

The formation is a red fine-grained friable sandstone, commonly argillaceous and locally pebbly. It contains red, grey and pale green mudstone partings and bands up to 4 ft thick together with angular fragments, inclusions and pellets of red, yellow and grey mudstone. The presence of sun cracks, contemporaneous clay-flake breccias, rounded and etched sand grains, rare dolomitic bands and pebbly horizons indicates semi-arid continental conditions of deposition. The Lower Mottled Sandstone appears to be a basin-edge facies of the Zechstein.

Petrographical analysis shows a bimodal grain size pattern, one of fine sand, the other of a clay fraction, which would suggest a reworking of the underlying marls. Cross-bedding is common and preferred orientations of the foreset beds suggest a northerly and westerly provenance for beds north of the Bulwell area, whilst southerly origins are indicated in the south of the district. From the study of numerous thin sections Dr N. Berridge reports that the Lower Mottled Sandstone consists of fine-grained, iron-stained sandstone with dominantly sub-angular, rather loosely packed, poorly sorted and weakly cemented grains. The feldspar content is variable, so that the sandstones include subarkoses and protoquartzites, of which the former are probably predominant. Many feldspar grains are highly altered to microcrystalline aggregates of other minerals and are then difficult to distinguish from compact siltstone. Other grains include true siltstone, chert, quartzite, gneiss, schist and hornfels and, rarely, igneous rocks. Accessory detrital minerals include opaque oxide ores, zircon, tourmaline, and rutile often intergrown with quartz; more rarely present are apatite, staurolite, andalusite, garnet and epidote.

Grains are characteristically coated by pellicles of limonite and locally ferric oxide is sufficiently abundant to act as a cement. Commonly the interstices of the sandstone are partly filled by calcite and dolomite, the latter typically in rhombic form with growth zones delineated by limonite inclusions. Scattered accessory patches of well crystallised kaolinite also occupy interstitial spaces in a majority of the thin sections examined. These are distinct from the small proportions of probably primary interstitial clay mineral aggregates that coat grains in many specimens and fill minor intergranular spaces.

The evidence provided by regional variation in composition, though limited, suggests provenance from a metamorphic terrain lying to the south and west, i.e., probably the Charnwood Forest area, or a former extension of it, but local sources were also available as shown by the presence of chert, siltstone and Magnesian Limestone particles. The upper part of the formation is not significantly richer in clay than the lower as is the case farther north (Smith and others, 1967, pp. 209–210).

The occurrence of baryte cementation at both Stapleford and Dale Abbey coincides with the presence of the same mineral in the overlying Pebble Beds. This supports the conclusions of Taylor and Houldsworth (1973) that the baryte is related to fault-controlled mineralisation and that strati-graphical control is limited to the availability of suitable host rocks.

Pebble Beds

The Pebble Beds crop out over some 8 square miles, largely in a belt between Nottingham in the south-east and Turnditch in the west. North of Nottingham they are present only as outliers or westerly extensions of the main crop which lies to the east of the district. They occupy some of the highest ground, for example to the north-west of Nottingham, and in the Dale Hills area, where they form northward-facing scarps capped by Keuper rocks.

The Pebble Beds are thickest in the south-east, where they average 150 ft, but they thin westwards to half that figure at Dale Abbey. Farther west near Turnditch, however, the thickness ranges up to 130 ft, though they are absent south of Weston Underwood. The sandstone consists predominantly of subangular, rather poorly sorted and loosely packed grains of quartz and feldspar mainly medium-grained but with bands of fine-grained argillaceous sandstone as well as coarser pebbly horizons. Lithic clasts are abundant and predominantly composed of metamorphic rocks, especially quartzite and mica-schist, as well as fine-grained, mainly acidic, igneous rocks. Provenance from a metamorphic terrain is further suggested by the occurrence of poorly rounded grains of accessory garnet (E36489) and staurolite (E36488). The sandstones are generally weakly cemented by illite and limonite, but some contain spots of more concentrated ferruginous welding of clasts and the accessory occurrence of poikiloblastic baryte (e.g. Stapleford Hill and the Hemlock Stone.) At the top of the formation the sandstone is partially cemented by coarsely crystalline calcite that has poikiloblastically engulfed and partly replaced the affected sand particles. Irregular weathering at the top of the Pebble Beds is partly due to this calcite mineralisation and partly to analogous cementation and replacement by dolomite. The dolomite occurs as aggregates of small rhombohedra (0.02 mm diameter) which are engulfed by large crystals of calcite where both carbonate minerals are present together.

Mudstone is common as lenses, inclusions, and as a coating to the pebbles. There is much lateral variation, particularly in the west, where the beds are generally coarser, more pebbly and contain a greater proportion of argillaceous material. The highest beds are usually coarser than those low in the sequence. Cross-lamination is common, but foreset orientation is very variable. Derivation of sediments was predominantly from the north and north-west, but there is also an important element derived from the south.

Some pebbles came from the Charnwood area but the rest are mostly quartzites which seem to have been derived from sources to the south-west (Bonney, 1900; Matley, 1914; Campbell Smith, 1963). There is a northward and eastward decrease in size and abundance of pebbles, but the variations in the cross-bedding directions indicate considerable reworking and channelling in a complex deltaic area. The sandstones are coarser than the underlying Lower Mottled Sandstone and contain many more mudstone fragments, features indicating increased erosive activity. The Pebble Beds also have a wider distribution than the Lower Mottled Sandstone, which they overlap in the western half of the district.

Patches of pebbly sand between Turnditch and Wirksworth, originally mapped as glacial deposits (Gibson and others, 1908, p. 152), are now considered to be outliers of an original widespread Pebble Beds cover, e.g. at Blackwall [SK 2540 4980]. The Triassic beds rest on a peneplained surface of Carboniferous rocks which rises northwards at some 3°. The extrapolation of this surface would carry the Pebble Beds outcrop over the Dinantian rocks north-west of Wirksworth–an area noted for secondary dolomitisation of the limestone (p. 12) and the Brassington pocket deposits (Walsh and others, 1972). The present authors therefore maintain (p. 90) that these pocket deposits are of Triassic origin although partially reworked in Tertiary times.

Waterstones and Keuper Marl

The outcrop of these rocks, forming the upper part of the Trias, is two to four miles wide and covers 30 square miles. It is confined to the southern part of the district where, outside Derby city, it gives rise to pleasant undulating country suited to mixed farming.

In the Burton district to the south-west, these rocks are about 1000 ft thick (Stevenson and Mitchell, 1955), but only the lowest part of the succession, 400 ft around Derby and 270 ft in the Nottingham area, are preserved in the present district. The classification erected by Elliott (1961) is applicable in the ground between Derby and Nottingham but difficulties were found to the west of Derby as the Midland basin of Triassic deposition is approached. The Water-stones contain a preponderance of laminated, silty and sandy beds; the Keuper Marl comprises predominantly blocky red-brown mudstones, with sporadic green beds and patches and interlaminated and interbanded pale grey siltstones. Some of the thicker more persistent siltstones coalesce to form 'skerries' which are more resistant to erosion and form mappable features. Some 'skerries' are ofsand grade and cemented by dolomite. Superimposed upon this overall pattern are repetitive cycles of sedimentation of various scales discerned by Elliott (1961, p. 225) and Wills (1970, p. 225). During the deposition of the Waterstones and Keuper Marl influxes of water became progressively less common and evaporation correspondingly more effective. In the present district, however, evaporites (gypsum and anhydrite) in the Keuper Marl are confined to secondary veins, stringers and nodules.

Sulphate solution in the surface beds leaves numerous small cavities and collapse-structures so that it is difficult to obtain good borehole cores from this part of the sequence. Elliott (1961, p. 228) has shown that the depth of the solution zone increases in the vicinity of faults.

Trusley Borehole (Appendix 1, p. 174a) was drilled through some 330 ft of Keuper rocks. Miospores of Anisian age were obtained from the lowest 98 ft, and probable Ladinian miospores to some 98 ft higher (Plate 10). The uppermost beds are inferred to be of Carnian age though no miospores have been found in them (see p. 156c). Dr Warrington reports that the borehole has provided the most abundant assemblage of mircroplankton so far recovered from the British Keuper. The occurrence in the Trusley assemblages of Dictyotidium with small Micrhystridium, abundant Tasmanites and some Veryhachium may indicate deposition in a somewhat turbulent environment near to a shoreline or in an area of shallow water.

In the east of the district the Waterstones overlie the Woodthorpe Formation (Elliott, 1961). In the west, the Woodthorpe Formation has not been recognised and the Waterstones are represented by an arenaceous facies. Trusley Borehole proved some 90 ft of Waterstones, the basal 50 ft of which are composed essentially of red-brown massive sandstone with a few laminae of siltstone and silty mudstone.

The thickness of the Waterstones in the east can only be estimated from the logs of old, inadequately described boreholes. The Waterstones and Woodthorpe formations together are considered to attain a maximum thickness of 150 ft in the Beeston area (Ericsson's Borehole) and to average 100 ft over much of the south-eastern part of the district. Sections [SK 474 376] near Stanton show the Water-stones Formation to rest with angular unconformity upon the Woodthorpe Formation. A minor unconformity is also present within the Waterstones Formation.

Thicknesses of Waterstones are irregularin the west, with 70 ft proved at Weston Underwood, 90 ft at Trusley Borehole, 30 ft at outcrop near Kirk Langley and Mackworth and 90 ft inferred in boreholes in Derby city.

On the map the Keuper Marl is not subdivided, but this account follows the subdivisions of Elliott (1961), which are, in upward sequence, the Radcliffe, Carlton, Harlequin and Edwalton formations. The overlying Trent and Parva formations crop out beyond the margins of the district.

Woodthorpe Formation

This formation is the southern Nottinghamshire equivalent of the Keuper Basement Beds–an omnibus term used by Lamplugh and Gibson (1910) for the variable coarse-grained basal Keuper rocks of the English Midland Province. Swinnerton (1918) considered these basal beds to be detritus derived from the erosion of the underlying Bunter rocks and redeposited in shallow water nearshore. Northwards from Nottingham the formation passes into the Green Beds (Smith, 1912; Smith and Warrington, 1971); westwards it thins and has not been recognised west of the Derwent Valley.

At the base of the formation there is a pebble bed apparently consisting of recycled quartzite pebbles from the underlying Pebble Beds. The bulk of the formation, as Elliott (1961) has shown, comprises rhythmic alternations of sandstone and mudstone in units up to 8 ft thick. Six such units were recognised in cuttings for the M1 Motorway near Stanton. Channelled sandstones also occur.

Waterstones Formation

This formation consists typically of fine-grained sandstone with bands and laminae of mudstone and siltstone. The mudstones are predominantly red-brown in colour with micaceous partings, and the sandstones range from pale grey through buff to red-brown. The formation is generally well laminated throughout in contrast with the underlying Woodthorpe Formation and the overlying Keuper Marl. Ripple-marks, sun cracks, salt pseudomorphs, mudstone pellets and clay-flake breccias, are common.

The top of the Waterstones Formation is gradational and particularly difficult to determine without detailed knowledge of the overlying strata. Elliott (1961) defines the junction as lying below the lowest skerry typical of the Keuper Marl and above the highest pale brown micaceous sandstone commonly found in the Waterstones. In the Sandiacre–Stapleford area a prominent sandstone, some 30 ft thick, occurs near this junction, the top of which acts as a useful marker and mapping horizon for delineating the top of the formation. In the west of the district the sequence is sandier throughout and the term 'Waterstones Formation' as defined by Elliott (1961) is not directly applicable.

The Waterstones Formation has been shown by palynological means to be of Anisian age in the present district, where it is therefore synchronous with Muschelkalk deposits of the North Sea Basin and Europe. The formation has yielded more macrofossils than any other unit in the Trias (except the Rhaetic) in the Nottingham–Derby area. Inarticulate brachiopods (Lingula) are recorded from the Waterstones near Eakring to the north (Rose and Kent, 1955) and numerous fish were discovered at Nottingham (Newton, 1887; Swinnerton, 1925, 1928). The record of plant remains (Wilson in Newton, 1887) from the fish-bearing horizon is doubtful however (Elliott, 1961). The Waterstones have yielded an extensive ichnofauna in the Nottingham–Derby area (Swinnerton, 1912; Sarjeant, 1967, 1970); the majority of these traces (of land vertebrates) occurred at Mapperley, Nottingham, but one (Deuterotetrapous plancus) was discovered within the present district at Dale Abbey, Stanton-by-Dale, Derbyshire (Sarjeant, 1967).

Radcliffe Formation

The Radcliffe Formation has a gradational base drawn below the lowest skerry but above the micaceous thinly bedded sandstones of the underlying Waterstones (Elliott, 1961, p. 216). It comprises evenly bedded, thinly laminated, red mudstones containing pale pink siltstone and silty mudstone layers with clearly defined salt pseudomorphs and hopper crystal outlines. Dolomitic slip layers were not observed at outcrop, but were recorded in Trusley Borehole and are reported to be common in the formation to the south and east of Nottingham. Purple mudstones are also a characteristic feature. The formation marks a change in deposition from dominantly quartzose and current-deposited rocks to beds which are primarily fine-grained and partly evaporitic.

The average thickness of the Radcliffe Formation in the type area is 40 ft (Elliott, 1961, p. 210). Some 45 ft were measured in exposures [SK 471 371] on the M1 motorway near Sandiacre, west of Nottingham. In the south and west of the district it is about 30 ft thick in Trusley Borehole and in a pipe trench [SK 2910 4142] near Weston Underwood.

Carlton Formation

This formation, which comprises massive or poorly bedded marly red mudstones with flow breccias and several skerries, including the Plains Skerry towards the top, is well displayed in Chilwell Brick Pit [SK 5130 3585] west of Nottingham (Plate 11), where its thickness of some 73 ft corresponds closely with that of the type area to the south-east of Nottingham. Farther west in cuttings of the M1 Motorway [SK 471 365] and in Trusley Borehole it is about 60 ft thick. The purple ramifying structures which occur some 9 ft beneath the Plains Skerry (Elliott, 1961, p. 218) appear to be of considerable lateral extent for they have been detected in the present district at Chilwell Brick Pit, Sandiacre motorway cuttings and in Trusley Borehole.

Penecontemporaneous breccias similar to those in the formation have been found in Keuper rocks of the Cheshire Basin (Dr A. A. Wilson, personal communication 1977), where they are attributed to the former presence of salt, the solution of which disrupted the original laminae.

Harlequin Formation

The Harlequin Formation is defined by Elliott (1961, pp. 218–219) as overlying all beds with flow-type brecciation but underlying beds containing a high proportion of even thin laminae and especially paper-thin laminae. The lower boundary lies some 15 ft above the Plains Skerry; the upper boundary is the base of the Cotgrave Skerry. The formation is over 130 ft thick in the M1 Motorway sections, and some 180 ft thick in the Trusley area.

The formation is characterised by repetitive cycles, each comprising red massive silty mudstone below and green laminated siltstone above. Interlamination and inter-banding of the two lithologies in the middle of cycles is common. Red, brown and pink siltstone, as well as green mudstones, also occur in the sequence. A typical cycle recorded from the Harlequin Formation exposed in a cutting [SK 4715 3585] for the M1 Motorway near Sandiacre is as follows

The proportion of green and laminated beds increases upwards in each cycle, representing an increasing energy environment and/or nearness to a shoreline. The laminated part of the cycle may be missing, when the massive mudstone is capped only by a siltstone.

Edwalton Formation

The Edwalton Formation extends from the base of the Cotgrave Skerry to the top of the Hollygate Skerries and is 150 ft thick in the type area (Elliott, 1961, p. 210). In the present district only the lowest 20 ft of the formation are represented, of which some 6 ft are exposed. The Trent and Parva formations are not preserved in the district.

Chapter 6 Tertiary (Neogene)

Pocket deposits

Around Brassington, immediately to the north-west of the district, is an area of Dinantian limestone in which solution hollows are filled with silica sands and clays.

The area extends into this district to the north of Hopton and Wirksworth, where small scattered hollows [SK 2600 5470] and [SK 2627 5453] are filled with sand and pebbles (Early and Dyer, 1964). The pocket deposits, first noted by Green and others (1887, p. 163) and Howe (1896), were thought by Yorke (1961, p. 22) to represent Triassic sediments originally spread over the Derbyshire Dome and trapped in pre-existing limestone hollows–in part solution cavities and in part surface watercourses. Kent (1957) also assumed a Triassic age for the sand, but considered that intermittent solution subsidence persisted through Mesozoic and Tertiary times. Ford and King (1969) thought that the distribution of the pockets was controlled by the form and position of the base of the dolomitised zone of the Dinantian limestone and that their age is post-mineralisation, in part Triassic, for they contain Pliocene plant remains and are post-faultingprobably late Tertiary. The sands are overlain by boulder clay. Boulter and others (1971) proposed the name Brassington Formation for these pocket deposits. Walsh and others (1972) thought that the formation represents a single cycle of sedimentation of Neogene age and noted that detached blocks of Namurian E₂ shales, in contact with the lowest sands found in the pockets, are stained lilac and thus represent a pre-subsidence land surface. Similar lilac staining was recorded during the present resurvey^-in the Namurian sediments that crop out south of Wirksworth and are, in places, overlain by Triassic sands. The present authors believe therefore that the origin of the pockets was by solution and subsequent collapse into limestone caverns in post-Triassic–pre-Pliocene times. The minor differences in grade and heavy mineral content between the Triassic Pebble Beds and the Brassington Formation are largely a result of reworking and resorting.

Chapter 7 Quaternary

Introduction

The distribution of the Quaternary deposits of the Derby district is shown on (Figure 57). The glacial deposits, consisting of Boulder Clay and Glacial Sand and Gravel occur mainly on the higher ground, and are the eroded remnants of once larger sheets. The Post-Glacial deposits consist of: Head, mantling slopes and filling valleys cut in the solid rocks and earlier drift deposits; River Terraces, present in the valleys of major rivers and streams; Alluvium and its underlying Flood-plain Terrace, which occur along the water courses; and Peat, locally present in the west of the district. Also described under this heading are landslips, periglacial features, including cambering and the formation of dolomite tors, and the development of the drainage system.

The ages of the Quaternary deposits are summarised as follows:

There are no deposits in the district known to have been laid down between the Neogene (see p. 90) and the Wolstonian boulder clay. High-level gravels previously assigned to the Anglian glaciation (called Berrocian or Lowestoft Gravels) are now included within the Permo-Triassic rocks (p. 84).

During the Wolstonian, ice crossed the district from the north-west, but later in that glaciation it impinged against ice advancing from the east along the southern margin of the district. Very little evidence exists of the waning phases of this composite sheet of Wolstonian ice; there are no marginal drainage features within the district and it is assumed that the ice melted in situ in a stagnant condition.

The high undifferentiated terraces of the Derwent and the Hilton Terrace (p. 92) are assigned to this waning period and represent the re-establishment of the pre-Wolsaniton drainage system. According to Straw (1963) the high base level of the Trent, and hence that of the Derwent, during Hilton Terrace times was controlled by ice blocking the Humber mouth.

Posnansky (1960), on the evidence of warm-climate mammalian remains from Allenton (p. 301) to the south of the district, referred the Beeston or First Terrace to the Ipswichian (Eemian) Interglacial. This has been confirmed by Jones and Stanley (1974, 1975) who found an Ipswichian mammalian fauna in this terrace at Boulton Moor to the south of the district.

During the Devensian (Weichsel) glaciation ice failed to reach the district, but lay in the head-waters of the Trent to the west and also dammed the natural drainage outlet through the Humber to the north-east. The Flood-plain Terrace was probably deposited during this period. The periglacial climate during the Devensian Stage gave rise to a period, probably the main period, of Head formation and of landslipping.

During the succeeding Flandrian Stage alluvium was deposited.

Boulder clay and glacial sand and gravel

The boulder clay consists of stiff to sandy clay containing numerous boulders and fragments of local Dinantian, Namurian, Westphalian and Permian rocks and the almost ubiquitous quartzitic pebbles from the Trias. Coal fragments are common; far-travelled erratics include flints from the Chalk and volcanic rocks from the Lake District. When unweathered, the clay matrix is predominantly a similar grey colour to the Carboniferous mudstones from which it is largely derived. Red clays, probably derived from the Trias, are also present locally. The sands and gravels underlie, overlie and are interbedded with the boulder clay, and may be interpreted either as outwash deposits during local advances and retreats of the ice or as englacial deposits.

The boulder clay is discontinuously spread throughout the district. As in the Chesterfield district to the north (Smith and others, 1967), the spreads are the eroded remnants of more extensive deposits which were formed mainly as ground moraine of a composite ice sheet which covered the district. Because boulder clay drapes many of the valley sides it is likely that the main features of the present-day drainage pattern existed in pre-glacial times. The deposit is nevertheless so eroded as to indicate that it is of Older Drift (i.e. pre-Devensian) age. In the south-east Pennine uplands such deposits are assigned to the Wolstonian (Saalian) glaciation.

It has been known since early in the century (Wedd in Gibson and others, 1908, pp. 153–154) that the movement of ice near Crich (p. 157b) was parallel to the Derwent Valley and the presence of Lake District erratics indicate that the ice must have crossed the Derbyshire limestone massif. This ice flowed southwards into the Midlands (Posnansky, 1960, p.289), where it deposited boulder clay with Pennine erratics (Pennine Drift). In the Midlands this drift is overlain by more widespread, easterly derived boulder clay containing Mesozoic erratics, principally chalk and flint. On the evidence of these erratics, Clayton (1953), Posnansky (1960), King (1966) and Rice (1968) show that the eastern ice reached the southern margin of the Derby district, where it overrode or impinged against the Pennine-derived ice somewhat north of the valley of the Trent. The limits of the Eastern Ice depend upon the recognition offlints in the glacial deposits and should perhaps now include Turnditch (see (Figure 84)), Breadsall [SK 3691 4052] (p. 157c) and Heanor (Farey, 1811, p. 138). In all probability there was considerable fluctuation and intermingling of the two ice sheets.

In the north-eastern part of the district the glacial deposits contain Permian limestone erratics and thicken eastwards, indicating probable derivation from the north-east. They were deposited from ice sweeping south-westwards along the broad Trent Valley, and mounting the eastern flank of the Pennines until it encountered the Pennine Ice.

River terraces

Terrace deposits have been preserved above many of the flood-plains of the rivers of the district, but are most extensive in the valleys of the Trent, the Derwent and its right-bank tributaries, and the lower reaches of the Erewash.

The highest deposits, lying up to 140 ft above the flood-plain of the Derwent, usually form well marked terrace features, but their heights relative to the flood-plain are too irregular for classification simply as a Third Terrace and they are shown on the maps as Terrace, undifferentiated. Two lower terraces have been identified and are shown as Second and First terraces on the maps. Their bases lie about 35 ft and up to about 10 ft respectively above the flood-plain. Each terrace, however, appears to be an aggradation of sand and/or gravel.

The Derwent terrace system is analogous to that of the River Trent, of which only a very small tract lies within the district. The Trent terraces have been extensively studied (Deeley, 1886; Pocock, 1929; Swinnerton, 1935; Clayton, 1953; Stevenson and Mitchell, 1955; Posnansky, 1960; Straw, 1963 and extensive review accounts by King, 1966 and Rice, 1968). A tripartite sequence, named in descending order the Hilton, Beeston and Flood-plain Terraces, has received near general agreement, at least in respect of the nomenclature. There is disagreement in respect of the chronology of the sequence and of the mode of origin of the Hilton Terrace, but neither dispute can be resolved by a study restricted to the present district.

The flood-plain terrace is included with the alluvium on the maps of the Derby district. The Beeston Terrace, the type area of which lies within the district, is the First Terrace of the Derby sequence, and the Hilton the Second.

The chronology of the Trent terraces is controversial. Clayton (1953) named the Hilton Terrace and assigned it to the Ipswichian Interglacial. The terrace includes gravels mapped by Stevenson and Mitchell (1955, p. 92) as fluvioglacial and which they considered to be younger than the Chalky Boulder Clay (of probable Wolstonian age). Posnansky (1960, p. 300) agreed that part of the Hilton Terrace was fluvioglacial and dated it on the evidence of included artifacts to the waning phase of the Wolstonian Glaciation. Straw (1963, pp. 187–188) also referred the Hilton Terrace to this phase with the Trent ponded against ice in its lower reaches.

The Beeston Terrace was assigned both by Clayton (1953) and Posnansky (1960, p. 301) to the Eemian (Ipswichian) Interglacial' (Ipswichian) and Straw (1963) to a late remains (Plant, 1859; Arnold-Bemrose and Deeley, 1896). Straw (1963) considered the Beeston Terrace aggradation to be of early Devensian age but Jones and Stanley (1974, 1975), on the basis of mammalian remains, place it in the Ipswichian.

There is agreement that the Flood-plain Terrace is Devensian but Clayton (1953) assigned it to the 'Acheulian Interglacial, (Ipswichian) and Straw (1963) to a late Devensian glacial episode when an ice readvance blocked the Humber.

The present authors accept the chronology presented by Shotton (1973), i.e. Hilton Terrace, Wolstonian; Beeston Terrace, Ipswichian; Flood-plain Terrace, Devensian.

Some doubt exists on the correlation of low terraces in the middle reaches of the River Ecclesbourne and the Markeaton (Cutler, Mercaston) Brook because of the presence of two knickpoints which can be traced in the long profiles of these two streams. Knickpoints occur at 500 ft OD near Wirksworth and 325 ft OD near Idridgehay in the Ecclesbourne and at 400 ft OD near Mercaston and about 250 to 275 ft OD (within the ornamental lakes of Kedleston Park) in the Markeaton Brook. The terraces in question lie between the knickpoints in both streams and may therefore be older than their relationship to the adjacent flood plains would suggest; they are shown therefore as undifferentiated.

The age of the high undifferentiated terraces of the Derwent are problematical. They rest on well-marked bench features below the level of adjacent Wolstonian boulder clay, which they therefore presumably post-date. They are higher than the Hilton Terrace, but may also date from the waning period of the Wolstonian ice sheet.

Head deposits

The Head deposits (Andersson, 1906; Dines and others, 1940) of the district consist of accumulations on slopes or valley floors of material derived by solifluction from drift deposits or solid rock. Their Ethology therefore varies according to the source of the material. They were largely formed under Devensian periglacial conditions, but recent down-wash deposits are included locally.

Alluvium (including flood-plain terrace)

Alluvial deposits consisting of sandy loam, clay, sand and gravel border the rivers and streams of the district. Gravels at depth in these deposits are assigned to the flood-plain terrace. The near-surface deposits tend to reflect the parent rock of the rivers, for instance the Ecclesbourne alluvium tends to be more clayey than that in the Derwent Valley.

Peat

Mappable peat is found only near Ravensdale Park in the west of the district; it has formed where drainage of springs from the Pebble Beds is impeded, and locally [SK 262 437] overlies head deposits. Bridges (1966, p. 45) noted a patchy thin surface peat on some poorly drained head deposits in the upland regions.

Landslips

The commonest landslips of the district occur where thick Namurian sandstone overlies mudstone on steep valley sides. Water from the sandstone lubricates the underlying mudstones, facilitating the development of shear planes along which the slip moves. The displacement may be rotational and, where the dip is into the valley, down the bedding planes. Faults and joints are additional factors in the origin of slips. Other slips are triggered off by undercutting of valley sides by rivers. Related mudflows are initiated in exceptionally wet periods on slopes underlain by mudstones and superficial deposits.

Periglacial and solution phenomena

These are best displayed in the Permo-Triassic rocks, in particular in the Lower Magnesian Limestone and the Pebble Beds. Crycturbation structures are preserved in the Pebble Beds in the western part of the district between Hulland and Brailsford. They vary from crenulations, convolutions and small faults, well depicted by thin marl partings and laminae, to frost-wedge structures, a small example of which near Muggington has been described by Bridges (1964, p. 262).

An isolated structure (Figure 84) about 1 mile S of Turnditch [SK 2814 4549] in the Pebble Beds is of such proportions that its formation solely by ice is considered unlikely. The structure, lying at about 700 ft OD, is a vertical parallel-sided fissure some 60 ft deep, and 15 ft wide, which is 'V' shaped in the basal 5 ft. It has an east-north-easterly trend and a mapped length of over 200 yd. It contains red-brown clayey sand on the north side and friable fine buff sand on the south, and is traversed by red mudstone laminae which depict a synclinal or collapse structure in the centre. Scattered irregularly throughout are erratics of sandstone (red fine-grained and yellow coarse-grained, of Ashover Grit type), Dinantian limestone and flint. Near the walls of the fissure the deposit contains numerous 'Bunter' quartzite pebbles commonly coated with black manganese oxide, with their long axes aligned along the margin. The regular geometrical form of the fissure suggests initiation along a plane of structural weakness. The internal structure is comparable with that produced by subsidence simulation experiments (Walsh and others, 1972), used to explain the formation of the Brassington 'pocket deposits' in the Dinantian limestone. Its abrupt termination downwards suggests that it originated as a 'gull' due to the gravitational movement to the north-west of a large area of Pebble Beds. Despite the extensive sand and gravel workings in this area, only one such structure is known and it seems to be the result of a rare set of circumstances.

Valley bulge and camber structures

Most of the stream exposures in the Namurian rocks show anomalous disturbed and disrupted strata. These structures, also found in the Permo-Triassic rocks, are believed to result from local pressure of overlying competent beds on the valley sides squeezing the incompetent argillaceous strata in the load-free valley bottom. These bulge structures–compressional folds, faults and thrusts–were described by Jones and Weaver (1975) in Namurian strata near Derby and by Hollingworth and others (1944) in the Mesozoic rocks of the Midlands. They are known to decrease in magnitude downwards and to die out at depths of 100 ft or so (see, for instance, Stevenson and Gaunt, 1971, p. 338). Ideal conditions for such superficial movement occurred during the Pleistocene Period when the argillaceous strata were softened at surface during the thawing of ground ice. However, in order to account for the association of large bulges with low relief on certain valley sides, even when allowing for unloading of the bulge by erosion, Kellaway (1972) has suggested that the movements were assisted by the weight of ice on the valley sides. These conditions he considered would be effective during deglaciation, where erosion of the bulge occurs within a subglacial drainage channel along the valley floor.

Cambering (Hollingworth aml others, 1944) consists of a lowering of the competent rocks on interfluves and valley sides associated with valley bulging. In the competent rocks, joints approximately at right-angles to the direction of slope are widened to form fissures or 'gulls'.

The formation of the valley bulges and the cambering of the district cannot be dated accurately, but probably occurred under periglacial conditions as well as during deglaciation.

General geomorphology and drainage

Fearnsides (1932, p. 177) recognised a vestigial peneplain in the Peak District–a relic of the post-Hercynian sub-Permo-Triassic surface. The present survey confirmed the existence of this surface, which is an important geomorphological feature of the Derby district. The base of the Pebble Beds rises westwards from some 400 ft near Weston Underwood and Brailsford to 800 ft at Kirk Ireton and once lay close above the existing dolomitic limestone surface near Brassington, Hopton and Wirksworth (Figure 56).

Linton (1951, p. 452) considered that the higher reaches of the Welsh Dee were the headwaters of a proto-Trent which flowed eastwards across the south of the district. Supporting evidence for this is present in the southern Pennines where deeply incised upland streams flow in a south-south-easterly direction. He noted Fearnsides' comment that the Derwent is a subsequent or strike stream, but emphasised the discordant nature of the river, which cuts indiscriminately across different rocks and structures. Since they are clearly superimposed, Linton was of the opinion that the

Derwent and Erewash were tributaries of a proto-Trent established on a pre-Eocene down-fold of the Chalk, all traces of which have since been removed by erosion.

Clayton (1968, p. 324) suggested the presence of a 1000-ft subaerial surface cut wholly in Carboniferous rocks, maintaining that many relics of it are still present. Assuming that this 1000-ft surface existed, its attempted reconstruction suggests that the Derwent then followed a syncline in the Westphalian rocks. However at Ridgeway Quarry [SK 3587 5150] near Ambergate the Crawshaw Sandstone, at between 300 and 500 ft OD, shows red and purple staining, pointing to the proximity of a Permo-Triassic cover.

In the west of the Derby district the drainage trends south-south-eastwards towards the River Ecclesbourne. Many of the streams were initiated on Triassic rocks and have subsequently been incised into Carboniferous strata, e.g. Cutler, Sherbourne and Alton brooks. There is also close parallelism in this western area between the stream pattern and the trend of the faulting.

Farther north an east-south-easterly drainage trend is preserved on the surface of the Dinantian limestone north and west of Wirksworth. The limestone has been eroded into a series of valleys which are now largely without streams for most if not all of the year. Smith and others (1967, p. 233) assumed that the main valleys were in existence before the glaciation.

(Figure 58) shows the probable sequence of events leading up to the present drainage system in this north-western part of the district. The earliest drainage is thought to have been by the Dale, Warmbrook and Eniscloud valleys, which formerly linked up with three valleys to the east of Wirksworth now occupied by Pendleton Brook, Peatpits Brook and a channel north of Alport Hill.

The linear nature of these channels suggests that they are part of a superimposed drainage system originally formed on a Triassic sandstone dip-slope, prior to the development of the Ecclesbourne Valley.

The depth and length of these channels suggest that large quantities of water flowing from the limestone uplands rapidly eroded the softer Namurian shales below the Ashover Grit of the area south of Wirksworth.

The Derwent Valley was deepened and the Ecclesbourne Valley enlarged and cut back, resulting in the capture of the Dale, Warmbrook and Eniscloud streams. Minor modifications to these channels also occurred. The Eniscloud stream cut a deep gorge known as Stone Dene and its flow was diverted southwards through Hopton and into Scow Brook assisted possibly by the relative softness of the weathered Hopton Agglomerate. Similarly a southern tributary of the Dale channel was captured and a major valley created trending southwards through Godfreyhole into Scow Brook. The south-eastern part of the Eniscloud channel was therefore beheaded and the lower part of the valley is now much too large for the brook flowing in it.

As the ice sheets diminished and the water table was lowered by progressive downcutting, the drainage of the limestone area moved underground. Subsequent attempts to de-water the lead mines of the Wirksworth basin by soughs have re-established the link with the Derwent. The River Ecclesbourne, however, is still deprived of much of its source water, which drains to the north and east, and it appears a paltry river for the size of the valley.

Clayton (1968) recognised subaerial surfaces at 560 to 580 ft, 460 to 595 ft and 280 to 360 ft OD, which he considered were stages in the excavation of the river valleys formed before the principal glaciation, which left a thin sheet of drift upon them. The present survey has shown that some of these surfaces are planar because of a thick cover of drift masking irregularities at a lower level, and others can be explained by near horizontal outcrops of sandstone.

Chapter 8 Structure

Introduction

The Derby district lies at the southern end of the Pennines. The main period of folding is of Hercynian age, but the district was subsequently uplifted during the Alpine Orogeny during the Tertiary period. The Alpine movements resulted in an easterly dip of 1° to 2° over most of the East Pennine coalfield, but in the Derby district the dip swings to the south as part of the southward plunge of the main Pennine upfold. Not all the movements within the district occurred during these two orogenies; there were precursory movements during deposition of the Carboniferous rocks and there is also evidence of contemporaneous tilting within the Permo-Triassic rocks.

The main structural elements of the Derby district are shown on (Figure 59) and structural contours on selected horizons in the Carboniferous rocks are shown on (Plate 12).

Intra-Carboniferous movements

Direct evidence of earth movements during deposition of the Carboniferous rocks is found in the Dinantian limestones and Namurian shales of the Wirksworth area, where the order of events may be summarised as follows:

Zone

• D₁ Local uplift and concomitant formation of knoll reefs. Folding and probable early movements along the Yokecliffe Rake. Outpouring of the Matlock Lower Lava from the Hopton vent. Erosion and reworking of the D₁ limestone top as evidenced by rolled and rounded corals of D₁ age in the lowest beds of D₂.
• D₂ Strong local movements in D₂ times, giving unconformities (Plate 2.1). Complete erosion and/or non-deposition of D₂ limestones in the west; progressive erosion in the south and east. Reefs were formed in the south and subsequently eroded with only patches remaining. Breccia formation in the highest beds north of Wirksworth. Silicification and chert formation.
• P₂ Deposition of Cawdor Limestone on an irregular surface of Hoptonwood (D₁) and Matlock (D₂) limestones. Formation of numerous patch reefs. Penecontemporaneous folding and thrusting (Dale Quarry). Continued erosion or non-deposition in the west.
• Late P₂ to early E₁ Renewed subsidence with transgression of shales on to eroded limestone. Reactivated movement along Yokecliffe and Gulf faults.

Elsewhere within the district, insofar as is known, there is a conformable sequence throughout the Carboniferous rocks, but thickness variations show the effects of contemporaneous earth movements. For instance precursory movements of the anticlines, particularly that at Breadsall, during deposition of Namurian sediments and Westphalian coals resulted in slight thickness variations. Much more significant, however, was the differential subsidence in the Edale and Widmerpool gulfs, which dominated Dinantian and Namurian sedimentation in the Derby district and continued at least into Westphalian B times. This subsidence represents a down-folding of greater magnitude than the subsequent Hercynian folding (Kent, 1966, p. 339). The Edale Gulf (ibid.) lies to the north of the Derby district and the centre line of the south-eastward-trending Widmerpool Gulf (Falcon and Kent, 1960, p. 18) crosses the district north of Derby.

The Carboniferous succession in the central part of the Widmerpool Gulf has been proved by Duffield Borehole, but the only indications of the positions of the margins are the gravity and magnetic observations (p. 117), certain sedimentological observations discussed on p. 5 and structural evidence. The last depends upon the recognition of adjustment faults in overlying strata (Kent, 1966, p. 325) and suggests that the north-eastern margin of the gulf corresponds with the Ridgeway–Pentrich–Porter Barn–Parkgate–Smalley–Hagg fault belt or the Ridgeway–Pentrich–Godkin–Aldercar–Cinderhill fault belt (Figure 59). Because the first-mentioned belt lies south of Little Hallam Water Borehole, which proved a thick gulf sequence of Namurian rocks (Falcon and Kent, 1960, figs. 8 and 9, pp. 18–19), it is suggested tentatively that it marks the gulf margin during the Dinantian, and that the Ridgeway–Cinderhill belt delineates the margin during the Namurian and Westphalian. The position of the south-western margin of the gulf has not been recognised and may lie to the south of the Derby district.

On the block some 200 ft of limestone overlying tuff in Ironville No. 3 Oil Bore are equated with 1740 ft of D₂ and P strata in Duffield Borehole. Such an eight-fold increase in thickness into the 'gulf' is unlikely to apply to the whole of the Dinantian; probably subsidence was very irregular, and overall figures for thickness increases from 'block' to 'gulf' are speculative. In the construction of the sketch-sections in (Figure 61) the overall thickness of Dinantian rocks proved in the Eyam Borehole (Dunham, 1973) has been applied (perhaps somewhat generously) to the Ironville area. The two-fold increase in thickness of D₂ Zone sediments from the Eyam area^‡3  to the Duffield area has been applied to the remainder of the Dinantian at Duffield.

The variation in thickness of the Namurian rocks is based on the borehole evidence at Duffield and Ironville together with the field mapping; the thicknesses are tabulated on p. 18 and indicate a three-fold increase into the 'gulf'. The thickness variations in the Westphalian rocks are based on an extension of thickness variations in Westphalian A strata (Figure 11) to the remainder of the sequence below the Top Marine Band; they may err somewhat upon the conservative side (see Howitt in Kent, 1966, p. 334). The sections (Figure 60) show a total subsidence at Duffield of about 19 000 ft from the beginning of the Carboniferous until the deposition of the Top Marine Band; the equivalent figure for Ironville is 9500 ft. The amounts of subsequent uplift, including the effects of the Hercynian and Alpine orogenies, are a minimum of 6500 and 2000 ft respectively.

The Hercynian Orogeny and later movements

The Hercynian Orogeny affected the rocks of the district from late in the Westphalian until early in the Permian (Edwards,1951, pp. 76–77). Early folding and faulting in response to east–west compressional forces was followed by normal faulting. The main trends of the faulting ((Figure 59), inset A) lie between north and west with a minor trend in a south-west direction. The throws of these faults, including later Alpine movements, are generally 100 to 200 ft but the maximum known is more than 800 ft (p. 160c). The folding and the major faults of the district are described in the detailed account (p. 160b). Towards the close of the Hercynian Orogeny the district was subjected to erosion, which removed 7000 ft more strata from the uplifted south-west of the district than from the north-east prior to the deposition of the Permo-Triassic rocks.

Differential movements apparently took place during the deposition of the Permo-Triassic rocks and continued up to the Waterstones; thereafter, i.e. from Anisian times, subsidence was more or less equal throughout the district.

Mesozoic rocks younger than the Trias are unrepresented in the district but the tectonic history is likely to have been one of continued subsidence until the end of the epoch. There followed uplift and erosion, and in the Miocene the district was subjected to renewed faulting and gentle folding representing the Alpine Orogeny.

The Alpine Orogeny and later movements

The main Alpine fold is a south-easterly trending anticline or monocline crossing the south-east of the district; it gives rise to different regional dips of the Permo-Triassic rocks in the east and south.

Structural contours on the base of the Permo-Triassic strata are shown on (Figure 60). In the western and south-central parts of the district these contours reflect irregularities of the original dissected surface upon which the Triassic rocks were deposited. In the east the sub-Permian surface was peneplained.

In the west of the district there is additional gentle folding along axes aligned north-west–south-east and north–south. Re-activation of Hercynian faults is displayed by lesser displacements in the Permo-Triassic rocks than in the Carboniferous. Displacements were greatest in the south-east of the district. In the east a few weak anticlinal structures were formed in the Permo-Triassic rocks along lines of faults in the underlying Carboniferous.

The Alpine Orogeny was followed by subsidence and the deposition of the Neogene sediments now found in pockets to the north-west of the district (p. 90). The district was subsequently uplifted to its present form. renewed compression and folding, passing finally into a regime suitable for normal faulting. Moseley and Ahmed (ibid., p. 80) also stated that the pattern of faulting in the Carboniferous rocks in the north of England is inherited from that in underlying Lower Palaeozoic strata. The north-north-west and south-west fault trends of the Derby district agree closely with the fault pattern of Charnwood Forest (Figure 59) and, although some of the steeply dipping faults may have resulted from shearing stress associated with the folding, the majority of the normal faults are believed to have been controlled by pre-existing faults in the basement rocks of the district. Similarly the Permo-Triassic structures reflect the Carboniferous faults.

Origin of the faults

The folding in the Carboniferous rocks appears to have resulted from compressional forces acting in an east–west field. It was followed by faulting with a dominant north-north-west (Charnian) trend and subsidiary trends which are west-north-west and south (see insets, Figure 59). The majority of these faults are normal, with dips of their planes averaging 60° although showing considerable variation, and are apparently of tensional origin. The mechanics of vertical displacement following horizonal stress, a general association in northern England, has been investigated by Moseley and Ahmed (1967). They considered that the faults were controlled by earlier shear fractures, and described their formation as commencing with folding and wrench faulting under stress, followed first by a diminution of stress during which joints were formed and secondly by

Earthquakes

There have been twelve earthquakes of an intensity of 5 or more (Davison Scale) in central England since 1900 (Hains and Horton, 1969, p.119), of which several were located near Derby. A map by De Rance (1896) which showed the occurrence of earthquakes since 1248 also emphasised the importance of the Derby area in British seismic activity.

Known seismic foci in the vicinity of Derby fall into three groups. There is a north-western group with epicentres 1 mile E of Ashbourne and 3 miles W of Wirksworth. The Wirksworth focus corresponds closely with the westerly surface termination of the Yokecliffe Rake Fault–an important east–west boundary fault on the southern end of the Derbyshire limestone block (see p. 160c). A second group of foci occur south-west of Nottingham, near Beeston, again associated with long and important westerly trending faults affecting Carboniferous and Permo-Triassic strata. The third group lies south-east of Derby with some foci in north-west Leicestershire (Dollar, 1957). Here structural lines are obscured by Permo-Triassic rocks, but strong north-west trending faults are known.

According to Davison (1924) the strongest of all recorded earthquakes in Derbyshire occurred in 1795. Other earthquakes in the district were recorded in 1084, 1180, 1678, 1734, 1738, 1784, 1857, 1865, 1872, 1873, 1903–6, 1956 and 1957.

The foci of the earthquakes of 1903–6 were in the Ashbourne–Wirksworth area. Slight tremors were felt on 2nd March 1903. The shock of 3rd May 1903 with a maximum intensity of 5 was widely felt north-west of Derby. The next reported seismic event was on 3rd July 1904 with an intensity of 7. On 27th August 1906 a shock of intensity 5 was centred around Ashbourne. Tremors at Winster 17 miles NNW of Derby in 1952 and 1954 are possibly associated with the focus near Wirksworth.

The most recent and important earthquake in the district was on 1 1 th February 1957 and has been studied in detail by Dollar (1957) and Lees (1958). Its epicentral region included Derby, Ilkeston and Nottingham and the damage to chimneys, masonry and brickwork indicated an intensity of 8 (Davison Scale). The initial quake was felt as a double shock, which may indicate two points of origin. The area of country disturbed was at least 30 000 square miles, stretching from Doncaster and Preston to the north, Oakham to the east, Nuneaton to the south and Shrewsbury and Chester to the west. Its focus is considered to be near Diseworth, a small village south of the Trent and roughly mid-way between Derby and Nottingham.

Davison (1924) suggested that there had been a westerly migration of the foci of earthquakes from Northampton (1750 and 1768), through Leicester (1893 and 1904) to Derby 1905–6. It appears that such foci lie on a northwesterly trending fault–a dominant structural direction in the area south of Derby. As noted by Dollar (1957), however, the 1954 earthquake with its epicentre at Diseworth does not fit this progression. An investigation by Lees (1958) into the effects of this earthquake on vibration-sensitive relays at local power stations in the Trent and Erewash valleys showed that the relays which tripped were always those sited on the river side of the power station and consequently over the maximum thickness of alluvial deposits. This factor appeared more significant than the orientation of the relays. Most of the macroseismic evidence concerning the direction of fall of chimneys, etc. suggested that although the epicentre was south-east of Derby the shock waves travelled through the town from a more easterly direction, i.e. along the Derwent Valley. A similar rough parallelism between the shock waves and the trend of the Erewash Valley deposits was also noted.

The importance of the configuration of the Widmerpool Gulf (see p. 5) has, however, not been considered in relation to the epicentral areas. There was considerable crustal distortion and volcanic activity along the margins of the Widmerpool Gulf during Carboniferous times and evidence of downwarping in post-Liassic strata. The southern boundary of the gulf is particularly sensitive to changes of stress since it is the northern limit of the old resistant block of St George's Land in the Charnwood area. Kent (1966) has drawn attention to the presence of large and important faults as indicators of the margins of such gulfs. Whilst the limits of the Widmerpool Gulf are known only in outline, the three groups of seismic foci known in the present district correspond to its estimated margins. Thus Diseworth, situated near Breedon Cloud, is on the southern margin of the gulf, Beeston near Nottingham lies on the northern margin and the Ashbourne–Wirksworth area forms the north-eastern edge. The influence of valley deposits, causing refraction of the earthquake waves, is therefore considered to be a surface modification of deep-seated faulting along the margins of the Widmerpool Gulf.

The district has evidence of past instability in the form of tuffs and sills in the Dinantian of the Duffield area, turbidites perhaps triggered off by earthquakes, in the Dinantian and Namurian rocks north of Derby, disturbed coal seams and roof strata in the Westphalian north of Nottingham and tuffaceous siltstones interpreted as 'fallout' of volcanic ash in the Westphalian north-east of Nottingham. These phenomena probably represent response to the imbalance brought about in this part of the earth's crust by the differential sedimentation rates between Wirksworth and Derby. The sulphurous and warm waters of Wirksworth and Matlock are indications of the continuing links between the deep-seated structures and the surface.

Chapter 9 Economic products and water supply

Introduction

The present wealth and importance of the district owes much to the underlying rocks and over the years every formation represented on the map has provided something of economic use. As early as Roman times the Dinantian limestones were being exploited for the lead deposits they contained. Recently other minerals associated with the lead, such as fluorite, have attained importance. The limestones have been quarried for roadstone and for lime for agricultural and smelting purposes. The Namurian sandstones have supplied millstones and grindstones and have been an abundant source of excellent building stone. Every rock type in the Westphalian sequence has been used, coal, for heating and a multitude of by-products, the mudstones for brick-making, the sandstones for building, roofing and paving, the ironstones for smelting and the seatearths and Banisters for heat-resistant bricks for use in the steel industry.

In the Permian, the Lower Magnesian Limestone has been quarried for lime and for building and ornamental stone, the Middle Marl was dug for manufacturing bricks and plant pots, and the Lower Mottled Sandstone provides a valuable source of moulding sand. The Pebble Beds yield building sands and a pebbly fraction which is ideal for aggregates. The Keuper Marl provides material for brick-making as do the boulder clays. Glacial, fluvioglacial and riverine sands and gravels are now of great importance in the Trent Valley.

The economic products both past and present are described below, followed by an account of the water supply of the district.

Coal

When the resurvey of the Derby district began in 1961 there were some 30 working collieries. Today, as a result of closure and amalgamations, there are only seven, of which five are on the concealed part of the coalfield. In addition the district has been extensively exploited for opencast coal and, although the scale has recently been reduced, two major sites were producing in 1973 and the present trend is one of expansion.

A description of the physical and chemical properties of the coals of the district was given by Dawe and Coles (1948), and the following up-to-date account, including (Table 4), has been provided by Mr M. Lock of the National Coal Board.

The south-western part of the Nottinghamshire and North Derbyshire Coalfield, covered by Sheet 125, contains Annesley, Newstead, Linby, Hucknall, Cinderhill (Babbington), Pye Hill and Moorgreen collieries. The seams currently being deep-mined are the High Main, First Waterloo, Second Waterloo, Deep Soft, Deep Hard, Tupton and Blackshale. The following notes on the properties of these seams are based on analyses of in situ seam less dirt samples.

The Deep Soft, Deep Hard and Tupton are the cleanest of the above coals, with an ash range of 3 to 7 per cent. Of slightly poorer quality, with an ash range of 5 to 9 per cent, are the High Main and First Waterloo seams. The Second Waterloo has 8 to 11 per cent ash and the Blackshale a range of 6 to 14 per cent.

The amount of sulphur in the seams worked is generally low to moderately low (0.5 to 1.5 per cent) with the exception of the Blackshale, which has high values ranging from 2 to 5 per cent. Chlorine, an important minor constituent, shows a general easterly increase in this part of the coalfield, with values ranging from a trace to 0.70 per cent and normally 0.30 to 0.60 per cent.

The rank of the seams being worked shows a general increase towards the north-east; seams currently mined are non-caking (rank code 900) to medium caking (rank code 600), the High Main having the lowest rank and the Blackshale the highest. Calorific values (d.a.f.) of the coals are of the order of 13 900 to 14 900 B.T.U./lb. and volatile matter contents (d.m.m.f.) 35 to 42 per cent, but normally 36 to 40 per cent.

The coals being worked are suitable for household and industrial purposes, depending on the size of the product. Larger sizes are utilised for house coal and domestic purposes; the smaller sizes are used mainly for electricity generation, but also for industrial steam raising.

Seams worked at collieries now exhausted produced good, medium and variable quality coals. The Mainbright, Lowbright, Top Hard, Deep Soft, Deep Hard, Tupton, Mickley and Kilburn seams gave ash values ranging from 2 to 6 per cent, the First Waterloo, Brown Rake, Top Soft and Alton seams values ranging from 5 to 10 per cent and the High Hazles, First Piper, Blackshale and Ashgate seams, values ranging from 4 to 18 per cent. Sulphur in the Mainbright, Lowbright, High Hazles, Top Hard, Top Soft, Deep Soft, Deep Hard and Tupton seams was generally under 1.5 per cent, but higher values–up to 5 per cent–were encountered in the First Piper, Blackshale and Alton seams. The extremely high sulphur content of the Alton is associated with the presence of the overlying marine band.'

The following account concerning opencast coal operations, with special reference to prospecting has been provided by Mr J. E. Metcalfe, formerly Regional Opencast Manager (Development), National Coal Board.

Official opencast coal activity in Great Britain was instituted in 1942, when the Directorate of Opencast Coal Production (DOCP), was established. Control passed to the National Coal Board in 1952, when the responsible body became the Opencast Executive. In the Derbyshire and Nottinghamshire exposed coalfield the whole sequence of workable seams from the Belperlawn to the High Main has been explored.

At the time of publication, there are about 300 prospected sites within the confines of the Derby Sheet. Of these, slightly over half have been worked and restored, and of the remainder, many have been proved to be economically workable but are not yet worked. Some sites which were prospected and abandoned in earlier years have been subsequently revived, profitable working having been made possible by improved economic circumstances and the introduction of sophisticated plant.

Sites have varied in size from those yielding a few thousand tons to some yielding a million tons or more, but in some cases adjacent prospecting sites have been combined to form single working sites. Some areas have been especially prolific, such as that between Loscoe and Denby, where 12 sites produced 2.5 million tons from seams from the Waterloo group to the Threequarters. There are substantial quantities of proved coal still unworked near Denby.

South of the Loscoe–Denby area lies the Shipley area, where opencast production has been spectacular. Of all the seams worked, from the Mainsmut to the Second Ell, the most rewarding has been the Top Hard, which with the two Combs, forms a thick seam with partings. In spite of old workings in the Top Hard, and the considerable excavation depths reached, opencast production has been profitable and ratios of overburden to coal have been relatively low. At the time of writing production in the Shipley area is still in progress, but from 23 sites completely worked and restored the total production was 5.4 million tons.

North-east of the Shipley area there is a complex of sites, now restored, occupying land formerly owned by the Butterley Company. Here, all seams from the Waterloo group to the Blackshale were worked, the most productive being the Deep Soft in combination with the Top Soft and Roof Soft. Six sites (including combined sites) produced 1.9 million tons. One site, Corfield, was notable in consisting mainly of a nine-hole golf course which after excavation was satisfactorily returned to its former use. North of these sites, at Swanwick, there was Tramway Site, where 946 000 tons were recovered from the High Hazles, Comb, Top Hard and Dunsil seams.

In recent years there has been a general policy, where practicable, of associating opencast coal production with reclamation or landscaping of derelict or unsightly areas of land. Obvious cases for treatment are disused collieries, with their waste heaps, slurry ponds, abandoned buildings and railway sidings, and both the Opencast Executive and licensed operators have carried out projects in the Region in consultation with the County Councils. In the area of the Derby Sheet one of the first schemes was the grading of two high colliery tips in association with the working of Cromford Canal Site and adjacent sites, the seams involved being all those from the Mainsmut to the Second Ell. A somewhat more ambitious project embraces the derelict area around Woodside and Coppice collieries at Shipley, where the principal seams are the Combs and Top Hard. Large waste heaps and many disused buildings were involved, and an extensive country park is taking shape. The scheme includes the recovery of over 1 million tons of coal, some of which lay under a lake which has been drained and will be reinstated. A smaller reclamation scheme has been completed by a licensed operator at Stanley Colliery, West Hallam, where extraction of the Low Main and Threequarter seams enabled a massive waste heap to be partly removed and reshaped. Shilo Site in the Awsworth–Eastwood area includes a number of derelict features, and the estimated production of about 500 000 tons will be from the Deep Soft, Deep Hard, Piper and associated seams.

In the route-planning of the M1 Motorway cooperation between the consulting engineers and the Opencast Executive Prospecting Department was essential. The contractors were warned of hazards such as old workings, and where it was known that excavations would cut coal seams recovery contracts could be arranged in advance. In cases where the motorway was to affect sites proposed for contract, liaison was organised between the motorway contractors and the Opencast Executive's contractors. Such a case was Catstone Hill Site between Trowell and Nuthall, where working of the Top Hard, Waterloo and Ell seams, in conjunction with the motorway construction, provided 466 000 tons. An important example of motorway liaison was provided at Trowell. Here, the proposed service area roughly coincided with the Opencast Executive's Shortwood Site, where the Deep Soft and Deep Hard seams had been extensively worked but there was enough coal left for economic production. The site was duly excavated, the replaced overburden was compacted in 4-ft layers, and the resultant surface formed a firm foundation for the service area.

In conclusion, it can be stated that coal resources suitable for economic opencast working, even within the well-worked area of this district, are by no means exhausted. Considerable tonnages have been proved which are not yet worked, and there are probably workable sites still to be discovered and assessed.

The writer is obliged to the National Coal Board Opencast Executive for permission to publish this contribution, and in particular he is grateful to Mr G. Jago for his constructive interest.'

Lead

The earliest records of lead mining in Derbyshire date from 81 AD based on Roman inscriptions upon pigs of smelted lead. Mining at Wirksworth was active in Saxon times, in the 9th century, but there are few records until many centuries later when the district became an important lead producing and administrative centre with Wirksworth as 'the Westminster of the Peak'. Detailed records have been kept for many hundreds of years by the Barmaster of the King's Field in the Soak and Wapentake of Wirksworth. The Barmote Court for the regulation of trade sat in the Moot Hall, where the famous Miners' Standard Dish made in the reign of Henry VIII is still in use today.

In 1842 the local Barmaster informed a Royal Commission that there were 70 to 80 small mines in the Wirksworth–Cromford area, nearly all of which were worked by their owners.

The mediaeval mining laws, administered by the Barmote Court at Wirksworth, gave the Derbyshire miners legal rights over the landowners in the King's Field to win the lead. This system, established to promote a pioneer expansion of the industry, was not conducive to 19th century capitalist methods. Parliamentary bills in 1857 did little to rectify the situation and the old pattern of mining lingered on. Floatations of lead mining companies were often unsuccessful despite the speculation of thousands of pounds on underground drainage and sough construction (see p. 114.)

The peak years of lead production for Derbyshire were between 1850 and 1870 when the county produced some 9 per cent of the country's total (i.e. 7000 to 11 000 tons of lead). The southern area of the Peak, south of the Wye Valley, proved to be the most important half of the county's lead producing area. Up till 1861 the number of men in Derbyshire lead mines was fairly stable at around 2000, but it declined rapidly to only 281 in 1901. In 1851 there were only twice as many Derbyshire coal miners as lead miners, but ten years later the coal miners were four times as numerous. The technical advances of the Industrial Revolution made little impact on the Derbyshire lead mining industry and output per man remained very low. After 1900 the industry was maintained against all economic odds by miners having part-time jobs in agriculture and in the rapidly expanding textile industries at Matlock, Belper and Duffield.

The industry survives today mainly by virtue of the associated minerals such as fluorite, with lead ore produced only as a by-product. There is little mining activity within the district at the present time.

The history and development of the lead mining industry has attracted a voluminous literature. Contributions by Pilkington (1789), Farey (1811), Green and others (1887), Varvill (1959) and Fuller (1965) provide valuable details and list references for further reading and research into an industry second only to coal in past importance.

Future prospects

Varvill (1959, p. 200) noted that the future working of lead-zinc ores is likely to prove economic only when carried out in conjunction with gangue mineral mining. The example of Millclose Mine (Smith and others, 1967, p. 244), where exploration of the deeper levels proved so fruitful, was not followed by the deepening of any of the old mines in the Wirksworth area. Ford and Ineson (1971, p. 205) suggest that attention be paid to the areas of limestone at shallow depth surrounding the Wirksworth area.

The present survey has revealed a gentle anticline trending south-south-eastwards from the Wirksworth limestone massif with the base of the Namurian lying at an estimated depth of 600 ft, some 12 miles south of Wirksworth (Plate 12). Geophysical prospecting has confirmed this estimate and geochemical sampling across mapped faults nearby on the sides of the Ecclesbourne Valley has indicated statistically significant enrichment of lead and zinc at surface.

Orebodies

The Wirksworth area is a continuation of the Matlock mineralised belt, the mining and mineral deposits of which have been described by Smith and others (1967, p. 39).

The primary metallic ores are galena (lead sulphide) and sphalerite or blende (zinc sulphide); the principal gangue minerals are calcite, baryte and fluorite. Secondary alteration of the ores resulted in the formation of small pockets of ochre (limonite), wad (manganese oxide) and calamine (zinc carbonate or silicate). Maximum exploitation of lead ore has been concentrated along the veins with an approximate east-west trend (see (Figure 62)), but veins of another set trending north-west-south-east have been worked on a smaller scale.

There are three main areas of mineralisation and past mining in the Wirksworth district:

1. A main east-west vein–The Yokecliffe Rake
2. The 'Gulf' area north-east of Wirksworth
3. The Dream Mine area, south-west of Wirksworth

The Yokecliffe Rake

The Yokecliffe Rake trends westwards from Wirksworth for 2 miles, passing north of Hopton and Carsington before petering out some 700 yd W of St Margaret's Church outside the present district. Its course is clearly marked on the ground by a series of spoil heaps which are distinctly larger than those associated with the north-east trending veins. The Rake is exposed sporadically along its length and occupies the plane of a fault having a downthrow to the south of between 50 and 150 ft. It is best exposed in Yokecliffe Wood [SK 2760 5382] 2 mile W of Wirksworth, where it produces a spectacular fault scarp of Matlock Limestone overlooking the Namurian shales to the south. The fault hades at about 30° to the south and the vein rock, some 5 in thick, consists of radiating aggregates of crystalline calcite, together with disseminated galena. Farther west, in an adit entrance [SK 2697 5383] near Boulderflats Mine, the calcite crystals are arranged normal to the fault plane and the vein is up to 10 ft wide. The Rake was reported to be some 30 ft wide in excavations beneath the dining room of the Gatehouse [SK 2853 5387], Wirksworth (Gibson and others, 1908, p. 175). The calcite-baryte-galena mineralisation of the Yokecliffe Rake accords with the statement by Dunham (1952, p. 83) that the present area lies within the baryte-calcite zone, Wirksworth marking the western limit of the zone with predominant fluorite.

Gibson and others (1908, p. 176) noted that wad (manganese oxide) was dug from a hollow in the 'toadstone' on the Yokecliffe Rake north of Hopton. The Ochre Mine, to which it is assumed they were referring, is north of the Rake and walled by dolomitic limestone, and appears to be the weathered top of a north-trending vein.

The 'Gulf' area north-east of Wirksworth

The 'Gulf' area north-east of Wirksworth comprises a topographical hollow of down-faulted Namurian shale and Dinantian limestone between the Gulf Fault and the Ash-over Grit scarp. The limestones contain numerous veins trending north-west parallel with the Gulf Fault; some are also fault-planes, e.g. the Rantor Vein. These veins were worked in the 19th century but the combination of a high water table and low structural position gave rise to exceptional problems of underground drainage in the mines. To overcome these a network of soughs, or underground drainage channels, were made in the area and its extension towards Matlock. The Hannage Sough, which was started about 1663, was probably the earliest construction. Others followed, including the Cromford Sough and finally Meer-brook Sough (Figure 63), which empties into the River Derwent near Whatstandwell. According to Farey (1811, p. 330), the Meerbrook Sough was started in 1773 and not completed until 1889. It is over 22 miles long, up to 600 ft below surface and was large enough for the use of boats (idem).The cost was over £45 000.

Many of the springs encountered in the mines in this region were of warm water obviously derived from considerable depth.

The most important mines, e.g. Bage and Ratchwood, in the 'Gulf' are just north of the present district. Smaller mines such as Sitch, George, Merebrooksough and Twenty-lands were less economic owing to smaller size of veins and greater working depths. A zone of mineralisation often occurred below the limestone/shale junction, where the shale had acted as a cap rock to the rising mineralising solutions.

Two veins trending north-west have been worked under Wirksworth itself–the Bailey Croft, and the Blackman Croft–the latter passing under the west end of the church (Figure 62).

The 'promontory' of limestone south of the Yokecliffe Rake

The 'promontory' of limestone south of the Yokecliffe Rake contains numerous old shafts and workings, the most successful of which was the Dream Mine. Here an important vein trending WSW–ENE was worked for 140 yd to the west 'before the shale comes on' (Gibson and others, 1908, p. 175). The present survey suggests that the shale is brought down by a fault and it is possible that the vein continues at a greater depth in the underlying limestone.

The Sandhole Vein runs parallel to the Yokecliffe Rake through the Foxhole—an open chasm from which calamine (smithsonite, ZnCO₃) and ochre have been extracted. Buckland found a rhinoceros skeleton in the early 19th century in a cavern discovered in the mine workings referred to as the Dream Cave by Arnold-Bemrose (1910a, p. 48). The intensity of mining on the 'promontory' seems to have been greatest at the southern end, where the structure is anticlinal. Approximately on the axis of the fold in Sprink Wood [SK 2725 5295] fluorite was extracted on a small scale in about 1960. This locality is one mile west of the suggested periphery of fluorite mineralisation. Small fluorite crystals also occur in parts of the pale grey reefy Hoptonwood Limestone on the crest of the 'promontory'. As suggested by Shirley (1959, p. 420), the maximum mineralisation is often associated with the anticlinal areas.

Details

Mines associated with the Yokecliffe Rake

This rake follows the line of a major fault from about 70 yd S of Wirksworth Church westwards for over 2 miles to Carsington beyond the western margin of the sheet.

The vein has been extensively worked throughout its length and has yielded galena and much smithsonite. In one place the ore was found in the top of the vein, scattered under the soil, over a field known as California, 750 yd west by south of Wirksworth Church (Carruthers and Strahan, 1923, p. 7).

Yokecliffe Mine [SK 2757 5381] (1)^‡4  was situated at the foot of the Yokecliffe Rake scarp. Vein calcite and galena are still attached to the scarp face, which dips southwards at 70°. Several shafts were sunk through Namurian shales to intersect the vein at depth. The main Engine Shaft [SK 2757 5381] was 342 ft deep. The mine yielded galena and smithsonite, and the main gangue mineral was calcite.

Windmill Lane [SK 2733 5380] (2) Two shafts were sunk on the south side of Yokecliffe Rake to intersect it at depth; no details are known.

Boulderflats Mine [SK 2715 5382] (3) No details known.

Oldgell's Mines [SK 2682 5381] (4) No underground details are known, but extensive surface tips and the presence of several shafts in addition to the main one suggest that the mine was as large and important as Yokecliffe Mine. It differs from mines farther east (see above) in that the mineralisation was associated with dolomitised limestone. An old level [SK 2701 5384] near the Godfreyhole–Middleton Road still shows the Yokecliffe Rake some 10 ft wide, hading at 20° to the south. Calcite commonly occurs as gangue. The main vein is crossed by a north-westerly vein which is of importance south of Godfreyhole (see (Figure 62)). A possible extension of this vein north-westwards was worked from Foxcloud Mine [SK 2661 5393] (5) and Nile Mine [SK 2650 5422] (7).

Several scrins leave the Rake in a north-westerly direction, but have usually been worked for only a few yards.

Smithycove Mine [SK 2651 5383] (9) No underground details are known, but many old shafts and a large area of spoil are present. Between Oldgell's Mine and Smithycove Mine a north-westerly vein of some importance has been worked for up to 700 yd in Foxcloud Mine and Shiningcloud Mine.

Shiningcloud Mine [SK 2645 5414] (6), 360 ft deep, is situated on a pipe at the junction of three veins. It produced galena, baryte, and hemimorphite. The mine was dry.

Quickset Mine [SK 2635 5377] (9) No details are available. Boulders of toadstone incorporated in nearby dry-stone walls may be erratics but it is more likely that they came from a lava associated with the fault plane of the Yokecliffe Rake.

Newclose Mine [SK 2613 5376] (10) No underground information is available but the surface tips are extensive. Where the Rake is partially exposed [SK 2595 5369] west of the mine, it consists of calcite and baryte.

Old Jacob's Mine [SK 2590 5367] (11) No details are known. North of Old Jacob's and Newclose mines a small north-west-trending vein 400 yd long was worked from Hewitstone Mine [SK 2604 5394] (12).

Doglow Mine [SK 2564 5360] (13) No details are known. Some 100 yd to the north [SK 2563 5370] ochre was worked at surface from a north-trending excavation.

There are many old shafts to the north of the Yokecliffe Rake which worked small veins and scrins trending north-westwards.

Unnamed mines and shafts to the south of the Rake appear to have worked veins more or less parallel to it.

Mines North-West of Wirksworth

Much of this area has now been quarried for limestone on such a large scale that the old pattern of rakes and mine workings has been obscured. The two main north-westerly trending veins, Burton Vein and Blackman Croft or Dale Veins were worked from the Shovel and Toby Mines [SK 2761 5463] (14) and Dalefield Mine [SK 2740 5446] (15) respectively. The Blackman Croft Mine was situated at the junction of these two veins. Dale Quarry was restricted in its working by the presence of Burton's Vein which passes through the middle of the quarry; the adjacent limestone was left as a pillar owing to the unstable and irregular nature of the workings. A southerly extension of this mineralisation, the Lees Vein, passes under Wirksworth Church [SK 2875 5395]. The Little Glory Vein is parallel to but some 150 yd to the south of the Lee's Vein.

A group of small veins approximately at right angles to the main veins were also worked such as the Pinfold Vein from Hawleys Garden Shaft [SK 2847 5399], Pulpit Scrin (beneath the church) from Bright's Mine [SK 2884 5406] (16), and Good Luck Vein from Meerbrook sough Mine [SK 2885 5457] (17) east of the Gulf Fault.

Mines North-East of Wirksworth

Most of the mines in this area on the downthrow side of the Gulf Fault are north of the Derby district and were described by Eden (in Smith and others, 1967, p. 45). The veins have a dominant north-westerly trend parallel to the Gulf Fault and were worked from the following mines:

Jenny Shaft [SK 2865 5438] on the Northcliffe Vein.

Twentylands Mine [SK 2852 5462] (18) and Captain Mine [SK 2862 5456] on numerous veins between the Gulf Fault and the Rantor Vein. Meerbrook sough Mine [SK 2885 5457] on the Rantor and Greymare Veins and the Goodluck Vein (north-easterly trend). The Goodluck Shaft was some 258 ft deep; the water level fluctuated from 192 to 242 ft below surface.

George Mine [SK 2908 5477] (19) on George Vein; the mine, linked to the Cromford Sough, was dry.

Hallam's Mine [SK 2925 5475] (20) on Bage Vein; Hallam's Shaft was 357 ft deep with the water level varying from 309 to 367 ft.

Sitch Mine [SK 2935 5464] (21) on veins east of Bage Vein; lead and fluorite are present in its tips.

Mines South of Godfreyhole

The southerly promontory of limestone is anticlinal and surrounded on three sides by shale. A number of veins have been worked in the limestone at crop and for some distance beneath the shale cover, particularly to the east. The veins trend north-north-west or east-north-east and contain galena, baryte, calcite and fluorite.

Dream Mine (or Stafford's Dream) [SK 2726 5322] (23) according to Carruthers and Strahan (1923, p. 80) was very profitable to a depth of 360 ft. Farey (1811, p. 267) noted that the mine yielded much lead and ochre. The vein runs east-north-eastwards and passes under shale.

Sandhole Mine [SK2735 5307] The Sandhole Vein runs east–west and has been confused with the Dream Mine on some Ordnance Maps. The mine was drained by Jewlows Sough, driven 900 yd from the stream near Speedwell Mill to the workings. An openwork known as the Foxhole [SK 2728 5308] 75 yd W of the shaft yielded lead, smithsonite and ochre (Farey, 1811, p.258). From its name it can be surmised that the Foxhole was a pot-hole in the limestone containing sand like that farther north at Brassington (see p. 90).

Bells Scrin is an east-north-east vein some 100 yd to the south of Dream Vein. Sweenclose Vein is a north-east-trending vein and fault extending from Sandhole Vein 130 yd E of Sandhole Mine to Blobber Vein, a distance of some 700 yd.

Blobber Mine [SK 2809 5327] worked lead from two shafts, each said to be 135 ft deep. An unsuccessful attempt was made to reopen the mine in 1924–25. An old plan by W. M. Else, dated 1917, shows two north-easterly trending veins, both called Blobber. The workings however run north-west–south-east between the two shafts, and plans dated 1925 show the main Blobber Shaft to reach 176 ft. A 90-ft level, now silted up, which ran into the Mill Pond at Millers Green, was used by the miners as a sough. The water in summer stood at about 144 ft below the surface without pumping but in winter rose to 90 ft. Lead was found in lumps weighing 4 cwt in 1925 at the 144-ft level some 60 yd north of the shaft.

In Namurian and Westphalian rocks

Lead was worked at Alport Hill Spout (Farey, 1811, p. 252) in the Alport Mine.

Minor occurrences Mineralisation of a minor nature has also been noted in the Westphalian rocks. In 1954 Mr A. V. Priest of the National Coal Board noted galena in a small fault [SK 4210 4270] 0.5 mile S of Mapperley Colliery (Craven, in discussion and contributions to Schnellmann, 1955, p. 626). Galena was also said to occur in masses up to 12 in thick in the floor of the First Piper Coal at the same locality. This is the locality 'a few miles west of Ilkeston' mentioned by Varvill (1959, p. 202). A specimen (MI29837) from this locality is on display in the Geological Museum, Exhibition Road. Another specimen which cannot be located more accurately than from 'Mapperley Colliery (brought out by the manager)' was described by Dr J. Phemister in 1943 (E20377) as 'an argillaceous sandstone cut by veins of zinc blende and calcite'. The horizon of the specimen is not known but if it came from the floor of the First Piper Coal then the locality must have been close to the shafts of the colliery on account of the known dates of workings in that coal.

Varvill (ibid.) also recorded lead ore at an opencast site near Ambergate and Mr J. Scarborough of the National Coal Board Opencast Executive noted traces of lead ore in the roof of the First Ell Coal at Godbers Lum Site [SK 405 486] near Denby and in the Second Waterloo Coal at Cromford Canal Site [SK 452 491] in the Erewash Valley.

Other minerals associated with lead

The production of lead has in the past overshadowed that of associated minerals, but recently the position has changed.

Zinc

In 1720 the production of zinc in Derbyshire was only 1500 tons. Between 1850 and 1949 Derbyshire produced a total of 80000 tons, nearly half of which came from Mill-close Mine to the north of the present district (Smith and others, 1967, p. 243). Zinc is not mined in the district at present, but is the main product of the separation process carried out by C. E. Giulini (Derbyshire) Ltd at Hopton, who are re-working the old tailing dumps from Millclose Mine.

Silver

The percentage of silver in Derbyshire lead averages only 2 to 4 oz a ton, which makes recovery uneconomic.

Baryte

In Derbyshire the mineral is mostly discoloured and of low grade. It has been produced at Upper Golconda Mine just beyond the north-west corner of the district.

Fluorite

As a result of introduction of the basic open-hearth process for steel manufacture, fluorite has become an important mineral.

Wirksworth lies on the western edge of the zone of pyrite-fluorite concentrations (Dunham, 1952), but a small deposit in Sprink Wood [SK 2726 5295] was dug about 1960. It occurs in pale grey limestone of D₁ age in the crest of the anticline forming the promontory. Fluorspar veining was recorded in Dinantian limestone at depths of 2300 to 2400 ft in Ironville No. 3 Oil Bore some 5 miles from the nearest outcrop.

Wad

Manganese ores, known locally under the collective term 'wad', have been extracted in the past at Doglow Wood [SK 2563 5369] near Hopton. Wad was used as a black pigment and delivered to paint mills at Bonsall and Matlock. Wad associated with ochre was also dug in a shallow working [SK 2741 5309] at Foxhole, near Godfreyhole.

Limestone

In recent years owing to increased demand for roadstone and aggregate the output of Dinantian limestone from the Wirksworth area has increased rapidly. The low value of raw limestone restricts the market area. However, the shortage of competing aggregates in the areas to the south and east makes road transport economic even as far as London, 140 miles from Wirksworth. Where there is a steady demand for large quantities, as at Corby, it is economic to use rail transport. A new bunker is proposed at Wirksworth to allow liner trains to carry the products farther afield.

The principal quarries are Stoneycroft [SK 285 543] now closed, and Middlepeak [SK 282 547] which has been described in detail in the Quarry Managers' Journal for December, 1967 (Vol. 51, No. 12). The latter quarry originally produced lime and stone for use as flux in the steel industry, but it is now extensively modernised and produces road aggregate with a capacity well in excess of 400 000 tons annually. The quarry is now operated by Tarmac Road-stone Holdings Ltd. Dale Quarry [SK 284 541] has closed since the completion of the survey due to the increasing height of the faces and the lack of space within the quarry for tipping. Analysis of the white limestone from the bottom of the quarry (Hoptonwood Limestone, D₁) in per cent was as follows: SiO₂ 0.36; Fe₂0₃ 0.07; Al₂O₃ 0.05; CaO 55.00; MgO 0.43. Percentages for the dark blue limestone from the top of the quarry (Matlock Limestone, D₂) were SiO₂ 2.04; Fe₂O₃ 0.26; Al₂O₃ 2.18; CaO 52.70; MgO 0.72 (see also Smith and others,1967, p. 241).

In the Crich area, some quarries are now abandoned and used for tipping. Crich Cliff Quarry, north of Crich village (Smith and others, 1967, p.35), supplied the limeworks at Ambergate until 1959. The works were erected over 100 years ago by George Stephenson's Clay Cross Company and used a steeply graded tramway to transport the limestone from the quarry at 750 ft OD to the works almost 2 miles due south at 300 ft OD. After 1959 the works obtained limestone by road from Cromford but increasing costs and falling markets caused their closure in 1965. The Ambergate site has now been taken over by the East Midlands Gas Board.

Quarrying of dolomitic Dinantian limestone was carried out in recent years by Magnesium Elektron Ltd at Hopton. The quarry [SK 2570 5465] aimed to provide some 80 000 tons of dolomite annually and this was expected to yield 5000 tons of magnesium by a thermal process using over 20 000 tons of fuel oil, 5000 tons of ferrosilicon and a small quantity of fluorspar. Unfortunately the dolomitisation of the limestone was too variable and the works are now closed. Parsons (1922, p. 114) gives two analyses of the dolomitic limestone at Hopton. The percentages of CaCO₃ were 56.8 and 62.2 and of MgCO₃ 40.5 and 34.3 respectively. Iron content was 0.9 and 1.1.

The Lower Magnesian Limestone has been extensively worked in the past, and quarries near Linby [SK 534 522] are said to have been used by monks from Newstead Abbey in the 12th century. It has been quarried for building stone, road metal and agricultural lime. It is a particularly attractive building stone, with a yellow-brown colour and coarse texture, which has withstood the years of industrial atmosphere particularly well. Many of the older houses and terrace rows in Hucknall and Bulwell are constructed of the stone. Linby village was built almost entirely from the local stones. The rather friable nature and open texture of the Lower Magnesian Limestone makes it less suitable for motorway construction, for which Dinantian limestone has been preferred. It is however still used locally as hard-core. The stone is also in demand as rockery, walling and ornamental material. The principal working quarries are at

Quarry Banks [SK 537 525], Linby, and at Bulwell [SK 533 455]. The following chemical analysis (percentage figures) from the quarry at Linby is of limestone about 12 ft up in the quarry face (E15986) (analyst, Mr I. G. Evans of the Building Research Station): SiO₂ 6.38; Al₂O₃ 0.93; Fe₂O₃ 1.28; MgO 18.78; CaO 28.40; Na₂O 0.07; K₂O 0.12; TiO₂ 0.04; Mn₂O₄ 0.13; SO₃ 0.07; loss on ignition 43.86-total 100.06.

Ironstone

Ironstone in the form of nodules, either dispersed or concentrated in bands or ('rakes'), are present in the Westphalian mudstones. Most of the horizons that have been worked lie between the Top Hard and Kilburn coals. They were mined in the past by means of closely spaced bell-pits or by opencast pits; at least one, the Black Rake (p. 48), was also worked extensively underground.

Yields were up to 6000 tons of ore per acre with up to 33 per cent metallic iron content. The annual output in 1873 from the Derbyshire–Nottinghamshire Coalfield reached almost 500 000 tons, but after that date the industry went rapidly into decline.

Smyth (1856) and Gibson and others (1908) list the 'rakes' of the district and their positions in the Westphalian sequence. There is however confusion of the naming in some working plans, for ironstones of similar character but at different horizons have been given the same name. Some of the more important ironstone horizons are indicated in the detailed account of the Westphalian rocks. Smyth and Gibson and others quote analyses of several 'rakes' from within the district. The following are the percentage range of the results of the seven available analyses from six 'rakes': Protoxide of iron' 33.31 to 40.01; 'Peroxide of iron' 1.04 to 2.71; Protoxide of manganese' 0.96 to 2.18; 'Alumina' 0.41 to 1.14; 'Lime' 2.32 to 4.53; 'Magnesia' 2.44 to 5.43; 'Carbonic acid' 24.83 to 29.92; 'Phosphoric acid' 0.34 to 1.12; 'Bisulphide of iron' 0.05 to 0.26; 'Water hygroscopic' 0.45 to 0.74; 'Water in combination' 0.87 to 1.87; 'Organic matter' 0.36 to 1.85; 'insoluble residue' 15.8 to 27.42. Of the insoluble residues, 'Silica' ranged from 10.04 to 17.24; 'Alumina' 4.51 to 7.9; 'Peroxide of iron' 0.45 to 1.22; 'Lime' trace to 0.07; 'Magnesia' 0.03 to 0.27; 'Potash' 0.34 to 0.74. The total amount of iron ranged from 26.79 to 33.20 per cent.

Sandstone

All the major Namurian and Westphalian sandstones have been worked at various times for building, walling and paving stones, but none are exploited on a large scale at present. Gibson and others (1908, pp. 177–179) described the quarrying of the Namurian sandstones of the district, an industry which is today virtually defunct.

The Ashover Grit is the thickest Carboniferous sandstone and has been quarried in the past at Alport Hill [SK 304 516] and Crich [SK 346 530]. The quarries at Shiningcliff Wood and Crich Chase produced millstones.

The largest quarries have worked the Main Bed of the Ashover Grit particularly between Milford and Little Eaton (p. 134c). Small quarries also worked the thinner sandstones beneath this Main Bed, which in the Callow area are stained pink and purple due to a former cover of Triassic rocks. The village of Kirk Ireton is notable for buildings made from this coloured stone.

The Rough Rock is quarried at Ridgeway [SK 3585 5150] for building and ornamental stones. The topmost beds are pale coloured, fine-grained and particularly hard and well cemented. The same quarry has yielded greater quantities of the coarser grained Crawshaw Sandstone, largely for walling purposes. This is the only quarry in the district regularly worked at the present time for the supply of building stone.

The Wingfield Flags are, as their name implies, too thinly-bedded to be of much use in building. They were used in the past however to build Wingfield Manor [SK 374 547] on the northern margin of the district. On the outcrop are many small quarries once worked for paving and walling stones.

Sandstone in the measures above the Morley Muck Coal near Rowson Green [SK 376 470] is sporadically worked for ornamental purposes. The sandstone overlying the Blackshale Coal was once worked for house building from Pentrichcommon Quarry [SK 3830 8385]. The 'Tupton Rock' used in the construction of Codnor Castle [SK 4335 4995] came from thin flaggy beds in the nearby quarries [SK 4333 5180], but the stone has weathered badly and the castle walls are now in ruins.

Numerous sandstones higher in the Westphalian, notably those above the Deep Soft, Top Hard and Cinderhill and those below the Clown and High Main seams, were once worked in small quarries.

Moulding and building sands

An old quarry in the Lower Mottled Sandstone at Catstone Hill [SK 5075 4145] was once worked to provide moulding sand for Stanton Ironworks but has now been filled in. The same beds have been quarried at Bramcote Hills [SK 503 389] and are now worked by British Industrial Sand Ltd for both moulding and building sand. The company has kindly provided the following analysis of saleable sand for foundry use (percentages figures): SiO₂, 87.5; Al₂O₃, 4.41; Fe₂O₃, 2.51; CaO, 1.00; Na₂O, 0.08; K₂O, 1.41; loss on ignition 2.16. Grading data for the two types of sand are as follows:

Many other quarries in the district have worked the Lower Mottled Sandstone for building and moulding sand, e.g. Stanton by Dale [SK 460 382] and [SK 452 366] Dale Abbey [SK 4355 3882] and [SK 4305 3930], Nottingham [SK 546 388] and Nuthall [SK 5275 4430].

The Pebble Beds have also been extensively quarried in the past for building sand. The principal quarries were Sandiacre [SK 478 372], Dale Abbey [SK 4355 3882], the Flourish [SK 4285 3870] and Dunnshill [SK 4220 3846]. Sands from the Pebble Beds near Muggington worked by Blue Circle Aggregates Ltd are extensively quarried (see below) and utilised for brick-making, plastering and for concrete, including spun concrete pipes.

Aggregates

The use of Dinantian limestones for aggregate has already been noted (p. 109).

In the west of the district the Pebble Beds are variable in lithology but in general pebbles are abundant and provide a valuable supply of aggregate. The beds thin and show an increase in the clay content southwards. The largest quarries are north of Mugginton [SK 2785 4520], [SK 2670 4440] and [SK 2920 4840], where up to 130 ft of friable pebbly sandstones are present. They are worked by Blue Circle Aggregates Ltd, who produce about 8000 tons per week of aggregates and sands for the building industry after multiple crushing and screening processes. The aggregates range from 1/16 in to 7/8 in and the small sizes are sold to firebrick manufacturers and for potting compost; 0.25 in aggregate is used locally for concrete products and, with 3/8 in, as road chippings. The larger sizes are utilised as concrete aggregates.

A large outlier of Pebble Beds has been removed almost entirely by quarrying at Hulland Ward [SK 2600 4570]. The site is now occupied by Charcon Products Ltd, who make concrete slabs and kerbstones using imported raw materials.

Aglite (Midlands) Ltd of Denby [SK 478 390] produce a low-density cellular aggregate from local Westphalian mudstones by means of a sintering process to 1250°C. The end product after crushing and grading is utilised in the construction industry for lightweight concrete with good thermal insulation and fire resistant properties. It is also made up into concrete blocks and slabs.

Refractory materials

Ganister

A mine [SK 3583 5202] belonging to Mr H. Glossop at Ridgeway, Ambergate, worked in the 1920's a very fine, hard, siliceous and ferruginous cemented sandstone about 3 ft 9 in thick (Wedd in Strahan, 1920, p. 75) immediately beneath the Pot Clay Marine Band. It was also worked by opencast methods. The stone was sold for making ordinary silica bricks for Sheffield.

Farther south a trial excavation was made in ganister at the same horizon and Wedd (op. cit., p. 76) quotes the following upward sequence: ganister, 2 ft+; coal smut, 1 in; ganister 6 in. The stone dries to almost white and is comparable in appearance with the best Durham ganisters, but not so compact and quartzitic as the best Sheffield ganister. Wedd (idem.) gave a petrographic description of the lower ganister (E11789), and an analysis is shown in (Table 5).

In 1920 Litchfield's Ganister Mine [SK 359 505] (Wedd, op. cit., p. 77) was no more than a trial shaft some 24 ft deep through the base of the Crawshaw Sandstone into the underlying shale and the ganister at the top of the Rough Rock. The ganister was similar to that at the previous two localities but was apparently unworked.

Sabine, Guppy and Sergeant (1969) have petrographically described the Glossop's and Litchfield's ganisters as follows:

Glossop's Ganister (E11792) A grey sandstone impregnated with hematite along joint faces and containing some plant remains. The rock is composed of angular quartz grains mainly 0.06 to 0.15 mm across with ferruginous and quartzose cement. There are scattered muscovite flakes and plentiful heavy mineral grains.

Litchfield's Ganister (E11791) A greyish brown fine-grained sandstone with very small plant remains. The rock is composed of angular quartz grains commonly 0.05 to 0.1 mm across, scattered muscovite flakes and some heavy mineral grains, with interstitial iron-stained clay minerals, iron ore granules, carbonaceous material and a siliceous cement.

Chemical analyses of these rocks from the same source are given in (Table 5).

A ganister said to have been recognised by Mr F. Russell as Glossop's Ganister in the railway cutting north of Wingfield Park (Wedd in Strahan, 1920, p. 70) is in fact a higher bed below the Norton Coal. A ganister beneath the Forty-Yards Coal was worked in two pits nearby [SK 3705 5305] and [SK 3665 5255] by the Derby Silica Brick Company in 1942. The ganister, some 3 ft thick, underlay a 7-in coal and rested on fireclay.

Other old ganister pits [SK 3698 5372] and [SK 3713 5352] in the Wingfield Park area worked the ganister, 30 to 33 in thick, beneath the Alton Coal. This ganister was also worked in the Bullbridge Pit [SK 362 519] near Ambergate (Wedd in Strahan, 1920, p. 74).

Chemical analyses of the 'White Clay' and 'Bottom Clay' presumably respectively overlying and underlying the ganister and taken from Ennos and Scott (1924, p. 50) are tabulated below ((Table 5)). These authors quote one further analysis of fireclay from the Pyebridge area but its horizon is not known.

Wedd (in Strahan, 1920, p. 69) noted the presence of workings in fireclay below the Deep Hard Coal and in silica rock in a sandstone above the Tupton Coal in mines near Riddings. The silica rock was mixed with the fireclay to make bricks for boilers, coke ovens, cement and pipe kilns. The company, James Oakes and Company (Riddings) Ltd, have kindly provided the following information on their activities together with analyses of their clays. 'Brick-making continued until about five years ago (i.e. 1968), but the main development has been in the manufacture of vitrified clay pipes and fittings. Originally the clay used was won in the deep mine and adjacent to the pipeworks (Pye Hill) but since the 1930's the source of clays has been from opencast sites in the area.

The clays used are low-grade fireclays, principally those below the Deep Hard and Main [SK Deep] Soft coals but clays below the Piper, Yard, Threequarters and Dunsil seams have also been used.

In addition to the fireclays the shale overlying the coal seams has been used for brickmaking and to a lesser extent for pipemaking.

The clays are dry ground after blending and are tempered to about 15 per cent moisture content to make them suitable for extrusion from vertical auger type presses. At this works both traditional intermittent kilns and tunnel kilns are used to fire the product to over 1100°C to achieve the low porosity needed for drainage purposes. The consumption of clay is currently about 75000 tons per annum, but a considerable increase in usage is envisaged in the near future.'

Typical analyses of three of the fireclays mentioned are given in (Table 6).

Other ganisters were noted in the Kilburn Shaft deepening, some 22 and 50ft below the Alton Coal and 52 ft below the Norton Coal (Wedd in Strahan, 1920).

Joseph Bourne and Co. Ltd of the Denby Pottery, who make high quality ceramic ware for kitchen use, originally utilised fireclays within the Deep Soft group of coals from the Denby area, but now obtain their raw material from elsewhere.

Brick clay

Carboniferous rocks

Large quarries exist near the Ambergate Brick Works [SK 3600 5182], where a variety of house bricks are made from the shales and associated strata above the Pot Clay Marine Band. The quarries were formerly worked for ganister (p. 176a).

Large areas of excavated ground are present in the Riddings–Lower Somercotes area, where James Oakes and Co. have removed Westphalian A strata for brick-making. A large field [SK 4315 5225], now largely composed of made ground, was once worked for clay, the measures extracted being between the First and Second Piper coals. At Lower Somercotes [SK 434 533] the measures between the Deep Soft and Roof Soft coals have been extracted. New trial excavations [SK 4375 5328] made to the south during the resurvey proved that suitable mudstones continue along the strike.

Measures which include the Waterloo group of coals are worked at Waingroves [SK 408 488] near Ripley by the Butterley Co. Ltd for class B engineering and facing bricks; production is about 960 000 bricks per week. The Manners Brick Co. Ltd near Eastwood [SK 469 458] also work measures at the same horizon for building bricks.

The Loscoe Brickworks Ltd [SK 426 471] near Heanor utilises the measures between the Bottom Second Waterloo and Top First Waterloo coals for the production of bricks for most types of building work including good quality facing bricks. Production in 1972 was of the order of 1 200 000 bricks.

Messrs G. S. Langton and Co. excavate [SK 374 470], near Rowson Green, up to 2000 tons per week of the measures overlying the Morley Muck Coal for use in local pipe and brickworks, and the Denby Mining Co. at Ryefields [SK 393 470] (New Winnings Colliery) intermittently work the measures between the Deep Hard and Deep Soft coals.

An analysis of the brickclay from Birchwood Quarry [SK 435 533], Lower Somercotes, in the Deep Soft group of coals has been provided by James Oakes and Co. (percentage figures): SiO₂ 62.80; Al₂O₃ 20.00; Fe₂O₃ 3.75; MgO 1.20; CaO 0.45; Na₂O 1.60; K₂O 2.14; TiO₂ 1.36; loss on ignition 6.42.

Permo-Triassic rocks

The largest brickworks in operation at the time of the resurvey was at Chilwell Brick Pit [SK 513 357]. The works, which have since closed, used the Keuper Marl for its raw material. The Plains Skerry formed the highest beds of the pit and the marl below was massive and relatively free from the siltstone bands and laminae detrimental to the colour and strength of the bricks. Keuper Marl at a similar horizon was formerly used extensively in Derby [SK 334 358] for the manufacture of bricks.

Good quality bricks were made from the Middle Marl at Watnall [SK 510 480]. The Watnall Brick Yard is now used by the National Coal Board who import clay from elsewhere. At Bulwell the main use for the clay was for the manufacture of flower pots by Richard Sankey and Son Ltd. As the maximum workable thickness of marl was about 20 ft the old clay workings have left large areas of waste ground. Recently plastic pots have been manufactured at the same site.

Oil and gas

Attention was first drawn to the Alfreton area in 1847 by seepage of oil into colliery workings in the New Deep Pit near Riddings (Marshall, 1875). The workings were in the Kilburn Coal some 720 ft below surface and the 'spring' produced 300 gallons of oil daily for over 12 months before drying up. It is perhaps significant that the explosion which occurred during the sinking of the New Deep Pit was probably a result of gas seepage from the Kilburn Sandstone some 120 ft above the Kilburn Coal.

Ironville No. 1 Oil Bore was sited on the southern end of the Ironville Anticline, near the region of previously known seepage and close to the Riddings Fault which, it was assumed, had acted as a feeder tapping oil from the Dinantian limestone. Drilling commenced in March 1919. At 2031 ft there was a show of residual heavy oil and at 2405 ft an artesian head of water was encountered. The Dinantian limestone was drilled for some 1600 ft and further traces of oil were found at 2500 and at 3600 ft, 30ft from the bottom of the borehole. Large quantities of salt water at 3500 ft could not be shut-off; this made attempts to 'shoot' the well very difficult. A 180-lb dynamite charge failed to initiate an oil flow and the hole was abandoned in September 1920. Ironville No. 2 Oil Bore, drilled to the north in the Chesterfield district, also found traces of oil (Smith and others, 1967, p. 38).

Ironville No. 3 Oil Bore commenced drilling in October 1956 at a site on the eastern flank of the anticline, well clear of known surface faults. The top of the Dinantian limestone was reached at 2220 ft. Despite penetration of 522 ft of limestone, no oil was tapped and the hole was abandoned at a depth of 2742 ft. It was cemented back to about 1800 ft to preserve a head of gas originating from the Ash-over Grit. In 1958 Ironville No.4 Oil Bore was drilled about 450 yd SSW of No. 3 in a final but unsuccessful attempt to locate an oil accumulation.

The results of the Carboniferous oil bores were disappointing in view of the promising structures. The presence of oil traces at many horizons suggests that most of the original oil had escaped upwards along faults with only the heavy fraction remaining. The Hardstoft Borehole farther north (Smith and others, 1967, p. 249) was fortunate in penetrating a small reservoir which had an effective seal.

There still appears to be an escape of gas in the Riddings area, for an inflammable vapour was recorded in cellars and manholes in 1966.

During the resurvey a seepage of oil was observed from sandstone at the top of the Waterstones near Stapleford [SK 493 361]. Some 30 ft of the sandstone had been excavated for the new Sandiacre–Stapleford By-pass, revealing a gentle anticlinal structure which had trapped this local pocket of oil. British Petroleum drilled an exploratory hole, Stapleford No. 1 [SK 4905 3596], nearby in 1966 through some 300 ft of Triassic strata (p. 173c) into the Westphalian but without tapping any further oil.

Other oil 'shows' have been encountered, as in Newstead Colliery shaft some 1180 ft below the surface in a sandstone below the High Hazles Coal. There may be many pockets of residual oil in the district, but the chances that an effective trap containing high grade oil of economic dimensions is present are remote.

Miscellaneous

The 'smudge' of the Belperlawn Coal was worked [SK 3595 5120] near Ambergate in 1943–44 for sale to the Via Gellia Colour Co. for making the dye known as vandyke brown. Under an overburden some 3 ft thick the weathered seam was between 24 and 36 inches in thickness.

Water supply

Until the late 19th century the upper reaches of the Derwent and its tributaries were only of local importance and were used mainly as sources of power and soft water for the textile industries. In 1899 the Derwent Valley Water Board was created to develop the water resources of this highly favourable area and to supply Derby, Nottingham, Leicester and Sheffield. With effect from April 1974 the Severn-Trent Water Authority is responsible for the public water supplies of the district.

The rainfall of the district varies from 35 inches in the north-west to 25 inches in the south-east. There are no large reservoirs but supplies are obtained from wells and boreholes in the Carboniferous, Permian and Triassic strata and from old mine workings in the Dinantian limestone and Westphalian rocks. There is also abstraction from shallow wells, large diameter boreholes and tunnels in the river deposits of the main valleys of the Trent, Derwent and Erewash.

A comprehensive account of the groundwater hydrology of Derbyshire was given by Stephens (1929) and of the Trent River Basin by Downing and others (1970). More detailed work on specific aquifers has been undertaken by Land (1966) on the Bunter Sandstone of Nottinghamshire and by Downing and Howitt (1969), who reported on the saline groundwaters in the Carboniferous rocks of the East Midlands.

The following account considers sequentially each geological formation of the district. Acknowledgement is made for the help of the former Trent River Authority and the South Derbyshire Water Board in providing the modern statistical data upon which much of the account is based.

Dinantian

The Dinantian limestone has a low intergranular porosity and permeability contrasting with a high fissure flow. Because of the presence of numerous joints, infiltration is rapid and normally surface run-off is nil. Impervious beds within the limestone such as clay bands, tuffs and lavas cause perched water tables. Mining has interfered with the natural flow of underground water and much of the limestone in the district is artificially drained by the Meerbrook Sough (p. 106 and (Figure 86)) which takes the limestone groundwater eastwards into the Derwent Valley.

Well yields in limestone aquifers tend to show considerable variation depending on the abundance of fissures (Downing and others, 1970, p. 36). Groundwater temperature is normally between 9° and 13°C but warmer temperatures are known locally, e.g. Matlock Bath (20°C) north of the present district and Warmbrook Sough [SK 286 537] south of Wirksworth. The temperature of the water at the outfall of the Meerbrook Sough varies between 13.5°C and 15°C. Such occurrences of thermal water are thought to be due to local meteoric waters circulating to considerable depths before emergence (Edmunds, 1971).

In the early part of the century there was little correspondence between the flow of Meerbrook Sough and the rainfall amounts. Recently however there has been a 3 months' interval between maximum rainfall and maximum outfall. Water abstracted from Meerbrook Sough during the year ending March 1973 totalled 3611 m.g.

Water from the disused Ladyflatts Mine is pumped from Blobber Shaft (72 in diam.) [SK 2811 5322] at a licensed annual rate of 183 m.g. for public use. Attempts were made to pump the workings dry preparatory to re-opening the mine but powerful pumps had little effect on the water levels. Analysis of the water compares closely with that of water from the Meerbrook Sough (Table 8).

There are two chemical types of groundwater, i.e. a calcium bicarbonate type and a calcium sulphate/bicarbonate type, which show no regular regional pattern. Total hardness of shallow groundwater varies between 148 and 400 mg/1 as CaCO₃.

The Widmerpool Formation, composed largely of impermeable strata, is an unimportant aquifer. Annual licensed abstraction from springs for public supply is 10 m.g. whilst that from shallow boreholes is 2 m.g.

Namurian

The two principal aquifers of the Namurian are the Ashover and Chatsworth grits. They are separated by impervious shales and normally there is no hydraulic continuity between them. The Ashover Grit is coarse-grained and some intergranular flow occurs near the surface, but the largest yields are obtained from fissured strata. Springs commonly occur at or near the base of sandstones and the water is collected and stored in tanks such as those at Kirk Ireton which supply the needs of the village. Farther south at Millington Green [SK 2647 4775] a spa 'well' provides a constant flow of cold sulphurous water formerly sought after as a cure for rheumatism.

The natural flow from springs in the district is subject to considerable seasonal variations and ranges between 7000 and 240 000 gallons per day (g.p.d.). Yields from boreholes in the Namurian range from a few thousand to 40000 g.p.d. The most reliable supplies come from boreholes penetrating more than one sandstone and some have an artesian flow. Total hardness varies between 23 and 236 mg/l.

The total annual licensed abstraction from Namurian strata is 752 m.g. Most of the supply is from boreholes and 727 m.g. are from public undertakings. Agriculture uses 9 m.g. and industry only some 4 m.g.

Analysis of water from a spring at Whatstandwell [SK 332 543] is shown in (Table 8).

Westphalian

The thicker beds of sandstone in the Westphalian sequence, such as the Crawshaw Sandstone, 'Tupton Rock' and 'Top Hard Rock', provide aquifers of local importance. They are commonly well jointed but faulting breaks them into separate blocks between which there may or may not be hydraulic continuity. Most blocks therefore possess only limited^, outcrop areas over which surface recharge can take place and for this reason yields from boreholes are poorly sustained.

Mining, by making artificial connections between aquifers has disturbed many of the natural rest water levels. Large areas of backfilled opencast sites have effectively sealed off many square miles of permeable outcrop from possible surface recharge. Thus underground workings originally troubled by water have sometimes become dry after the same seam, up-dip, has been removed by opencast methods. The Derbyshire pits are some of the wettest in the country, largely due to their location in synclinal belts. Large quantities ofwater are impounded in old workings of the Top Hard, Dunsil, Second Waterloo, Deep Soft, Deep Hard, Tupton and Blackshale coals, which are overlain by fissured water-bearing sandstones. The concealed part of the coalfield is drier because the impervious Lower Marl of the Permian seals off the Westphalian 'crops' and the underground workings from the Permo-Triassic water. Workings also tend to be deeper with less associated fissuring.

The chemical nature of groundwater in abandoned mine workings is very variable. Considerable treatment is necessary in most cases to render the water usable, with frequent checks on chemical and bacterial quality.

The typical hardness of water from colliery workings ranges from 397 to 578 mg/l. High figures obtained from Cinderhill (Babbington) No. 6 Shaft and Annesley Colliery may reflect seepage of Permo-Triassic water.

Table 7 shows the volume of water drained annually from mines in the district since 1970.

As in the Namurian, borehole yields in Westphalian rocks are more reliable where several sandstone aquifers are penetrated. In general 200 ft x 12 in diameter boreholes in the Westphalian rocks yield up to 6000 g.p.h. Slack Lane Waterworks [SK 3948 5028], Ripley, produced some 20 000 g.p.d. from an 8-ft diameter 180-ft water bore in 1923; nearby mining was blamed for a decrease in supply and eventual abandonment of the borehole. Comparison of the analyses (Table 8) shows that the borehole water from the Westphalian rocks is softer than that from the old workings.

Permo-Triassic

The Lower Magnesian Limestone is confined both above and below by impervious 'marls' and where the Lower Magnesian Limestone/Lower Marl junction is exposed in the old railway cuttings at Kimberley (p. 150d) there is a continual seepage of water. Although the Lower Magnesian Limestone is a coarsely granular rock composed largely of dolomite rhombs, its porosity and intrinsic permeability are low and its transmissivity is related to the number of open discontinuities. Yields for boreholes up to 8 in diameter rarely exceed 800 g.p.h. The water is excessively hard with a range of 400 to 1000 mg/l. Sulphate values are also particularly high. The total annual licensed abstraction of water from the Lower Magnesian Limestone is some 127 m.g., most of which is for industrial use.

The Lower Mottled Sandstone and Pebble Beds together form the most important aquifer, generally known as the Bunter Sandstone of the East Midlands. In the Derby district the water table reaches a maximum elevation of about 550 ft near Annesley Woodhouse in the north-east and near Turnditch to the west. The annual range of water levels is only of the order of a few feet (Land, 1966). Excessive abstraction ofgroundwater around Nottingham has reversed the natural water flowage from the Bunter into the River Trent, with resultant groundwater contamination. The Lower Mottled Sandstone is finer in grain size and a 10 per cent clay fraction reduces its porosity compared with the coarser, 'cleaner' Pebble Beds.

The Pebble Beds are highly permeable and bores with diameters of 24 to 36 in commonly yield between 1 and 2 m.g.d. Variations in yield are due largely to differing degrees of cementation and fissuring of the sandstone. The isolated outcrops of Pebble Beds in the west of the district yield up to 3000 g.p.d. from boreholes of 100 ft or so. Total hardness is usually above 100mg/l. Replenishment of the aquifer is restricted by a cover of boulder clay to the west.

The total annual licensed abstraction from Triassic sandstones is 350 m.g., of which 40 m.g. are derived from the Pebble Beds west of the River Derwent. Some 300 m.g. are used by industry, particularly the National Coal Board. (Table 8) shows a typical analysis of water from the Sandi-acre and Stapleford Station boreholes [SK 4821 3658]; [SK 4820 3659]; twin boreholes, 30 in in diameter and 203 ft deep, yield 25 m.g. per annum.

Groundwater from the Keuper Marl and Waterstones, usually extremely hard, owes its non-carbonate hardness to solution of gypsum bands and nodules. Total annual abstraction is 11 m.g., over half of which is derived from springs and used for agricultural purposes.

Quaternary deposits

River terraces and alluvium are important sources of water, particularly where they are in hydraulic continuity with the river. In the case of the Trent alluvium there is only limited connection between the river and the groundwater of the alluvium. This is probably due to a high proportion of clay in the alluvium and some degree of puddling of the river bed.

The iron content is very high in water from gravels in the Trent Valley. Molyneux (1869) suggested that the iron is associated with organic deposits in old channels of the Trent. Such gravels are however rich in ironstone (p. 158c) which may be largely responsible for the concentration.

Twin boreholes [SK 5372 3670] of 48 in diameter and 16 and 19 ft deep in the Trent alluvium at Beeston Lane have an annual licensed abstraction of 40 m.g. for industrial use. Similar quantities are taken from shallow boreholes in the River Derwent alluvium, but only 8 m.g. per annum are used by industry from the Erewash valley deposits. The South Derbyshire Water Board extracted 2471 m.g. in the year ending March 1973 from an extensive tunnel system in the Derwent alluvium between Little Eaton and Allestree.

Excavations [SK 4935 5166] for the M1 Motorway showed that where glacial sand and gravel overlie, or are interbedded with boulder clay, springs and seepages are common.

The chemistry of the groundwaters of superficial deposits is very variable and supplies of water from all such deposits are liable to chemical and bacterial pollution.

Future development

Downing and others (1970) concluded that the development of groundwater resources in the district will be ultimately at the expense of river flow. Further extraction from the Bunter is possible, except in the Nottingham area. The other aquifers should only be developed locally and left to maintain base flows, to dilute sewage effluents and as a source of water for artificial recharge of the Bunter Sandstone.

The main prospect of meeting the future demands of the district appears to be by improving the quality of the River Trent water, one of the recommendations in the Report on the Water Resources in England and Wales (Anon., 1973).

Chapter 10 Geophysical investigations

The association in the Derby district of low density Westphalian and Permo-Triassic sediments with older, higher density limestones of Dinantian age would be expected to produce pronounced Bouguer anomalies due to near-surface density contrasts. While this is generally true the Bouguer anomaly map also reflects more deeply buried structures such as the thick Namurian sequence in the Widmerpool Gulf and a largely unproven ridge of Lower Carboniferous, or older, rocks which extends southwards from the Derbyshire Dome.

Magnetic surveys reveal extensive zones of magnetic material at depth beneath a cover of non-magnetic sediments. The magnetic zones bear little overall relationship to the structures revealed by the gravity data, although there is a certain correspondence in minor features; they probably represent magnetic bodies at a deeper level in the crust.

Physical properties of the main rock types

(Table 9) contains a summary of the physical properties of the main rocks in the Derby district, using both published information and the results of surveys carried out by the Institute. The data are based on sample measurements, ground surveys and, in the case of resistivity results, geophysical borehole logs.

Susceptibility determinations on samples indicate values of about 4 x 10⁻⁴ emu for the dolerite intrusion at Ible, some 3 miles NW of Wirksworth, and 1 x 10⁻⁴ emu for the Hopton agglomerate, some 2 miles W of Wirksworth. Sedimentary rocks in the area would be expected to be practically non-magnetic, with susceptibilities less than 1 X 10⁻⁵ emu.

Sonic velocity data for the main rock types in the Nottingham area have been obtained from well velocity surveys, mostly in oil boreholes, including those at Eakring and Widmerpool (Wyrobeck, 1959).

Gravity surveys

The Bouguer anomaly map of the Derby district is dominated by two elongated highs which merge near Wirksworth where the maximum value reaches +23 mGal (Figure 64). The north-south high passing through Trusley has an anomaly level only about 3 mGal lower than the value over the main area of Dinantian rocks in Derbyshire and it would be most convenient to explain the feature as being due to a buried limestone ridge, forming the western boundary of the Widmerpool Gulf. However the northern part of the high north of Trusley coincides with an area of shaly limestones of the Widmerpool Formation, and a borehole at Mickleover Hospital, 4.5 miles SW of Derby, encountered similar strata below a depth of −69 m OD (Stephens, 1929). This shaly limestone facies should be less dense than the main massive limestone sequence and it seems likely that it is underlain by denser limestone or older rocks responsible for the Bouguer anomaly high.

South of the Derby district this elongated Bouguer anomaly changes direction to the south-south-east and passes between the Leicestershire and South Derbyshire coalfields, coincident with the Ashby Anticline. The north-south line can be traced southwards as a Bouguer anomaly feature in the Burton upon Trent area.

In the northern part of the Derby district the regional decrease in Bouguer anomaly values to the east (Figure 64) is largely due to the increasing thickness of low density Westphalian rocks and, farther east, to the appearance of Permo-Triassic sediments.

South of a line from Wirksworth to Nottingham, Westphalian rocks are largely absent and the Bouguer anomaly low in the Derby–Long Eaton area is thought to be due to the thick Namurian sequence in the Widmerpool Gulf (Falcon and Kent, 1960; Kent, 1966) for the thickness of Trias is inadequate to explain the anomaly and the Bouguer anomaly gradient values exclude the possibility of any deep-seated origin. The full extent of this anomaly is difficult to judge but it would seem that the amplitude must be at least 11 mGal (Figure 89), assuming that the regional anomaly continues southwards to a level of about +10 mGal near Charnwood Forest. With a density contrast against the Dinantian limestone of –0.25 g/cm³, an additional thickness of at least 1.05 km (3450 ft) of Namurian sediments is necessary to explain this anomaly. As the Namurian sequence is about 0.3 km (1000 ft) thick at Ironville (Kent, 1966) away from the gulf development, the total depth to the base of the Namurian would have to be at least 1.4 km (4600 ft), allowing for the comparatively thin Trias. The estimate of 1.4 km (4600 ft) exceeds the Namurian thickness of 0.8 km(2600 ft) at Widmerpool and 0.8 km (2600 ft) in the Duffield area. The southward decrease in Bouguer anomaly values in this area is therefore probably not due solely to the thickening of lower density sediments in the Namurian but probably also to a thickening of the shaly facies in the upper part of the Dinantian. In both Widmerpool (Kent, 1966) and Duffield boreholes the Widmerpool Formation is considerably thicker than equivalent strata in the Ironville area, containing mudstones and sandstones which are less dense than the massive limestone and therefore tending to cause Bouguer anomaly lows. Any gravitational effect of the igneous intrusion which is presumably responsible for the magnetic anomaly west of Nottingham (Figure 65) is obscured by the steep Bouguer anomaly gradient.

The Wirksworth–Nottingham Bouguer anomaly high can be traced from near Wirksworth through the limestone inlier of Crich (Figure 64) and the Ironville Anticline. In the extreme south-east the high coincides with an abrupt change in the direction of the Bouguer anomaly contours from north-south (reflecting the increasing thickness of Westphalian strata) to east-west through Ilkeston (largely reflecting the increased thickness of Namurian strata in the Widmerpool Gulf). The small Bouguer anomaly peak along the crest of the high of about 1 or 2 mGal can be explained in places by structures such as the Ironville Anticline. The belt of faults in the Westphalian (Plate 12) also coinciding with the Bouguer anomaly high may reflect the presence of a buried limestone ridge.

The highest Bouguer anomaly value (+23 mGal) in the area is located over the main outcrop of limestone north-west of Wirksworth at the intersection point of the trends of the two elongated highs described above. The amplitude of the closure in this area may be exaggerated by local features such as a thicker development of dolomite in the Dinantian sequence or high density basic intrusions similar to that at Ible [SK 252 575].

Superimposed on the broad, major anomalies in (Figure 64) are local small-amplitude Bouguer anomalies which can usually be related directly to mapped features at the surface. These are not easily recognisable in (Figure 64) but more detailed measurements across the Dinantian–Namurian boundary in the Wirksworth area, for example, revealed step-like anomalies of 2 to 3 mGal which are due to the density contrast between the shales and limestones. Interpretations of these profiles generally show that the limestone surface dips at angles of up to 20° near the mapped contact but then levels off to a more gentle slope.

Magnetic surveys

The Derby district was included in the aeromagnetic survey flown in 1955 with a mean terrain clearance of 1000 ft (308 m). The map shown in (Figure 65) is taken from the 1:625 000 scale aeromagnetic map (Sheet 2) of Great Britain (Geological Survey, 1965). The total field measurements were made with a fluxgate magnetometer along east to west flight lines 1.61 km (1 mile) apart and north to south tie lines 9.65 km (6 miles) apart.

The magnetic field in the Derby district is dominated by a broad magnetic high, about 30 km wide and at least 80 km long, trending south-eastwards from Wirksworth through Nottingham. The smooth, widely spaced magnetic contours in the south-west suggest that the structure causing the anomaly probably lies at a considerable depth.

Superimposed on the main magnetic high are several sharply defined anomalies suggesting smaller magnetic bodies at comparatively shallow depths of 1 or 2 km (3300–6600 ft). The pronounced circular anomaly at Hucknall is the most obvious of these, but other examples are the circular feature some 6 miles E of Belper and the ridge trending north-west from near the Hucknall anomaly. Broader magnetic highs west of Nottingham and north-west of Wirksworth suggest magnetic bodies at intermediate depths (3 to 4 km or 10000–13000 ft).

The main north-west-trending magnetic zone in (Figure 65) can be interpreted as a broad horizontal slab extending from a depth of −3 km (10 000 ft) down to −6 km (20 000 ft) with a susceptibility of 2 x 10⁻⁴ emu. The depth extent however can be varied without invalidating the interpretation and the susceptibility changed accordingly, but it seems that the south-west margin must be inclined in all cases to account for the low gradient west of Derby. The steeper north-eastern margin crosses the corner of the area shown in (Figure 65) north of Hucknall but it is necessary to postulate the existence of some magnetic material at depth north-east of this line to reproduce the higher background value in this area. The depth and shape of this model, its elongate form and the lack of corresponding structures in the Carboniferous rocks suggest that it could be due to a belt of volcanic or metamorphic rocks without an unusually high density in Lower Palaeozoic or Precambrian basement rocks.

Superimposed on the broad magnetic belt are more localised anomalies of shallower origin which may be due to intrusions, some of which may rise through the Lower Carboniferous strata. The shallowest of these is the anomaly 9 km E of Belper (Figure 65) which is probably due to a plug-like intrusion rising to less than –0.7km (-2300 ft) OD. The anomaly lies on an extended belt of faulting on the northern flank of the south-east-trending Bouguer anomaly high, but the slightly larger and deeper source of the anomaly at Hucknall lies beneath Permian sediments and has no surface indication. The east–west anomaly west of Nottingham coincides in position and direction with the Bouguer anomaly gradients associated with the northern margin of the Widmerpool Gulf (Figure 64). The positive magnetic anomaly near the north-west corner of the area shown in (Figure 65) coincides with the outcrop of Dinantian limestones on the south-east corner of the Derbyshire Dome and represents a broad rise in the magnetic material.

A comparison of the structures suggested by the magnetic map with those deduced from the main Bouguer anomalies (Figure 64) reveals little in common. The broad magnetic zone appears to lie below the Carboniferous rocks responsible for almost all the Bouguer anomaly features, but its north-west to south-east trend is repeated by the Bouguer anomaly high interpreted as a ridge in the Lower Carboniferous.

The broad magnetic zone has a Charnian trend and a Precambrian or Lower Palaeozoic age is suggested. Farther to the south, outside the Derby district, a distinct group of magnetic anomalies, probably due to intrusions related to the Caledonian Mountsorrel granodiorite, occur within the broad magnetic zone. From this evidence it would appear that the zone has been the scene of repeated igneous activity extending from Lower Palaeozoic or even Precambrian times through to the late Carboniferous.

North–south-trending structures of Hercynian age are prominent on the Bouguer anomaly map, which mainly reflects density contrasts within the Carboniferous. There are only two places where this trend can be seen on the magnetic map. One is the slight bulge in the contours west of Wirksworth, which is the only magnetic feature correlating with the pronounced north–south Bouguer anomaly high. The other is the north–south-trending western margin of the shallower magnetic anomalies west and north-west of Nottingham which coincides at the surface with the eastern flank of the anticline beneath Denby [SK 398 462]. On the Bouguer anomaly map this feature is shown only as a weak local anomaly of −1 mGal.

Seismic surveys

A seismic reflection and refraction survey was carried out by the Applied Geophysics Unit to trace the continuation of the Dinantian limestones beneath the Namurian shales in the Ecclesbourne Valley area south of Wirksworth. The contact of the shale with the limestone was expected to be a good reflecting horizon, but it was found that several, poorly defined, reflectors existed, making correlation difficult in an area without any borehole control. The survey produced some evidence to support the existence of the small anticlinal structure trending south-south-east from near Wirksworth (Plate 12), but it appeared that the mean velocity of the Namurian shales could not be greater than 2.5 km/s if depths consistent with the gravity and geological evidence were to be produced.

From refraction data obtained in the same survey, drift thicknesses were found to be mostly less than 12 m in the area and the bedrock velocities varied between 1.5 and 3.5km/s with an average of 2.46 km/s for the Namurian shales. Sandstone (Ashover Grit) horizons in the sequence gave a slightly higher mean velocity of 2.71 km/s.

Chapter 2 Dinantian (Carboniferous Limestone Series). Details

Hoptonwood Limestone

North of the Yokecliffe Rake

The Hoptonwood Limestone crops out on high ground between Carsington and Hopton in the south, and the lble valley to the north. Exposures are common often occurring as isolated crags or 'tors' of flat-lying, pale yellow and brown dolomitic limestone, e.g. at Foxcloud Plantation [SK 2665 5394]. Despite dolomitization, destruction of fossils is not always complete and lithostrotionoids, gigantoproductoids and crinoid ossicles are recognisable in places.

In the type section at Hoptonwood Quarries (Smith and others 1967, p. 15), on the southern edge of the Chesterfield district, the Hoptonwood Limestone is 250 ft thick and is unaltered, but dolomitization in the Hopton–Carsington area precludes detailed correlation. Sargent (1912) quotes an analysis by E. Sinkinson of the clay from the Matlock Lower Lava in Hoptonwood Quarry as follows: SiO₂ 47.83%, Al₂O₃ 22.74%, Fe₂O₃ and FeO 4.76%, FeS₂ 5.02%, MgO 2.50%, CaO 1.19% Na₂O and K₂O₃.30%, H₂O 12.66%. Boreholes three miles east of Hoptonwood Quarries and just beyond the north-western corner of the Derby district, proved limestones with up to seven clay horizons and with oolite bands which were particularly common towards the base. One bore penetrated a greenish grey siliceous rock at least 24 ft thick which may be tuffaceous and related to the Hopton Agglomerate and the Matlock Lower Lava.

In the now disused Magnesium-Electron quarry [SK 2560 5480] the formation consists of up to 50 ft of massive grey-brown dolomite and dolomitic limestones which are strongly but irregularly jointed. Bedding is vague but one variable plane contains up to 6 in of pale green, possibly tuffaceous clay. The top surface of the dolomite is very irregular with joints widened to form pockets up to 10 ft at the top and containing brown sand stratified with clays pebbles and chert. This area is on the fringe of the well-known Braasington pocket deposits (Early and Dyer 1964; Ford 1967, p. 70), the origin of which is discussed on p.90.

Quarries north-west of Wirksworth

The Hoptonwood Limestone is exposed as inners in the lower benches of the Middlepeak, Stonycroft, Baileycroft and Dale quarries. It is thickest in Stonycroft Quarry (locs. 1 and 2)^‡5  [SK 286 543], where 120 ft or so of limestones have been excavated in close proximity to the Gulf Fault. The limestones are massive, pale grey and grey-brown, weathering to off-white. Fossils are rare and largely comprise fine crinoid debris.

The limestone is largely inaccessible, but displays a uniformity of bedding and colour. The top is marked by a 6-in dark grey shale band [SK 2850 5431] with rolled brachiopods and corals, including Dibunophyllum bipartitum bipartitum and Carcinophyllum vaughani, which have probably been derived from the Hoptonwood Limestone. In the Middlepeak (loc. 3) [SK 282 546] and Dale [SK 283 542] quarries the massive nature and uniform bedding of the Hoptonwood Limestone is again well displayed. The maximum thickness of the limestone in Dale Quarry is estimated at a little over 100 ft.

The Baileycroft Quarry [SK 287 542] is now disused and has been partially obscured by tipping. The generalized succession is;

The Hoptonwood Limestone is overlain by 19 ft of Matlock Limestone (loc. 23). Both limestones are truncated by thinly bedded dark grey Cawdor Limestone (loc. 38) showing an undulating base (See (Plate 2.1), (Plate 2.2) and (Figure 5)).

In the access tunnel [SK 2870 5410] to Dale Quarry some 60 yd S of Baileycroft Quarry, typical pale grey massive limestones lying some 80 ft below the top of the Hoptonwood Limestone are exposed.

South of the Yokecliffe Rake

The Hoptonwood Limestone is in the main undolomitized, comprising pale grey to off-white fine-grained massive limestones. The topmost bed, some 4 ft thick, is particularly rich in gigantoproductoids and colonial corals and is exposed in the small quarries (loc. 5) [SK 2709 5372] south-east of Godfreyhole. The limestones bordering the Hopton Agglomerate are richly fossiliferous and of a reefy nature (locs. 6 and 7).

A distinct reef-knoll north of the Almshouses at Hopton (loc. 8) [SK 2608 5333] yielded a rich assemblage, typical of D, reef limestones, including; Fenestella sp., Acanthoplecta mesoloba, Aliteria cf. panderi, Antiquatonia cf. antiquate A. hindi, A. insculpta, Avonia youngiana, Dielasma hastatum, Echinoconchus punctatus, Eomarginifera sp. lobata group, Fluctuaria sp., Gigantoproductus sp., G.? sp. nov.[wrinkled concentric ornament], Martinothyris cf. lineata, Overtonia fimbriata, Pleuropugnoides pleurodon, Plicatifera plicatilis, Plicochonetes cf. buchianus, Pugnas acuminates platylobatus, P. pugnus [small form], Pugnoides Spirifer cf. grandicostatus, S. trigonalis, orthocone nautiloids, Cyclus sp. and ostracods.

Similar assemblages were obtained from limestones on the western side of the Hopton Agglomerate e.g. at Carsington Wood (loc. 9) [SK 2542 5340]. An old quarry [SK 2625 5340] east of Hopton is largely inaccessible, but appears to comprise about 50 ft of massive, pale grey, fine-grained to porcellaneous limestone without obvious fossil concentrations.

A site investigation borehole (loc. 10) [SK 2652 5340] drilled on the extreme edge of the limestone outcrop some 200 yd east of the above quarry proved 131 ft of pale grey to grey-brown fine-grained massive Hoptonwood Limestone. Thin shelly bands in bioclastic limestone contained a D₁ fossil assemblage including Dibunophyllum bourtonense (at 129 ft 7 in). The limestones were intersected by numerous fault planes and associated minor fractures.

The most southerly outcrops of limestone [SK 2723 5302], in the vicinity of Dream Mine (loc. 11) and Sprink Wood (loc. 12), form an elevated promontory surrounded on three sides by Namurian shales. They lie within the top 50 ft or so of the Hoptonwood Limestone and are of reef facies. They are richly fossiliferous, and brachiopods often with red coatings of algal material are particularly common. Shirley (1959, p. 420) noted the reef-like fauna from this locality and recorded the characteristic D₁ fossil Davidsonina septosa. A collection during the present resurvey from near Dream Mine (loc. 8) yielded a D₁ reef assemblage including the following, Koninckopora inflata, Lithostrotion martini, L. pauciradiale, Athyris cf. Chonetipustula carringtoniana, D. hastatum, Echinoconchus punctatus, Eomarginifera sp. lobate group, Gigantoproductus, sp. nov. [wrinkled concentric ornament], Leptagonia analoga. Overtonia sp. [juv.], Pugnax pugnus [small form], Schizophoria resupinata, Spirifer cf. grandicostatus, S. trigonalis, S. bisulcatus, Straparella fallax, Straparollus dionysii, Turbonitella biserialis, Conocardium alaeforme, Girtypecten? tessellate, Griffithides? and ostracods.

The margin of the promontory is complicated by faulting and mineralization, but the structure appears anticlinal near Dream Mine. On the nose of the 'promontory' southerly dips up to 65° carry the beds down the slope, at the base of which they pass below Namurian shales of estimated E₁ age.

This folding possibly accentuates already existing depositional dips.

Matlock Limestone

North of the Yokecliffe Rake

The outcrop of the Matlock Limestone is only about half the area of that of the Hoptonwood Limestone. North-west of Wirksworth at the base of the Matlock Limestone, a ledge-like feature is considered to be the outcrop of a thin representative of the Matlock Lower Lava, the only evidence of which was noted [SK 2646 5475] 140 yd W of the Hopton Tunnel entrance where it is marked by fragments of greenish weathered clay. The succession in the cuttings in the approaches to the Tunnel is:

The passage from dolomite to limestone occurs approximately to the middle of the tunnel. The Yokecliffe Rake Fault scarp (locs, 13–15), some 60 ft high, provides an excellent section of Matlock Limestone, which is massive, grey and crinoidal with sporadic shelly bands. At the top of the scarp [SK 2807 5391] the junction with the overlying Cawdor Limestone can be seen.

Quarries between Middleton and Wirksworth

In Middlepeak Quarry (locs. 16–19) [SK 282 546] a maximum thickness of 140 ft of Matlock Limestone was recorded in 1956. Subsequent quarrying has extended the face by some 100 yd south-westwards and by 300 yd north-westwards. Eden (in Smith and others 1967, p. 22) noted that, when traced southwards, the Matlock Limestone becomes progressively darker, less cherty and more thinly bedded. It includes a prominent unconformity; lenticular bedding and beds of breccia are particularly common at the top.

The following succession was measured in the south-western corner of the quarry [SK 2815 5441];

In Stonycroft Quarry (locs 20–22), 300 yd SE of the Middlepeak section, the thickness of the Matlock Limestone is reduced to 62 ft. The overlying Cawdor Limestone has overlapped the uppermost part and rests on limestones below the Upper 'Girvanella' Band. The Matlock Limestone is thinly bedded, individual beds lensing out south-eastwards.

On the north-eastern face of Baileycroft Quarry, the Matlock Limestone comprises some 19 ft of mostly massive, grey to dark grey beds which contain breccias towards the base. In the basal 7 ft, beds wedge out southwards but contain a rich fauna (loc. 23) including Aulophyllum fungites, Dibunophyllum bipartitum, Diphyphyllum lateseptatum, Lithostrotion junceum, L. martini, L. pauciradiale, Lonsdaleia floriformis, Palaeosmilia murchisoni and P. regis. The beds continue to thin southwards (p.129b) and 120 yd along the quarry face they are overlapped completely by the Cawdor Limestone. Some 80 ft of Matlock Limestone are therefore cut out in 200 yd. Between Middleton and Wirksworth some 140 ft of Matlock Limestone are removed in a distance of 1000 yd.

When traced south-westwards from Stonycroft Quarry to Dale Quarry (locs 24, 25) [SK 282 540] the Matlock Limestone again shows a decrease in thickness. The succession in the southern end of Dale Quarry is:

In this southern part of the district the Matlock Limestone is generally dark grey and thinly bedded and difficult to differentiate from the overlying Cawdor Limestone where angular discordance is not pronounced.

South of the Yokecliffe Rake

The eastern side of the Godfreyhole promontory (locs 26–29) comprises a maximum of about 50 ft of Matlock Limestone, though on the southern part of the promontory the thickness is estimated to be less than 25 ft. This may be due to overlap by the Namurian or to thinning across a penecontemporaneous anticline (p.96).

The basal beds of Matlock Limestone exposed south-east of Godfreyhole (p.129b are massive, grey and partly oolitic. In a small quarry, some 100 yd to the north-east (loc. 30) [SK 2729 5363], 21 ft of massive, grey, evenly bedded, crinoidal limestone are exposed. The discovery of 'Girvanella' nodules in these beds may indicate an equivalence with the Lower 'Girvanella' Band of the Castleton area which there lies some 6 ft above the boundary between the D₁ and D₂, zones (Stevenson and Gaunt 1971, p. 73).

The fauna includes; 'Girvanella' nodules, foraminifera, Aulophyllum fungites, Dibunophyllum bipartitum, Lithostrotion pauciradiale, Palaeosmilia murchisoni, Gigantoproductus sp. [latissimoid], Spirifer bisulcatus, Sulcatopinna flabelliformis and ostracods.

Some 150 yd E of Dream Mine (loc. 31) [SK 2741 5308] grey thinly bedded limestone, about 10 ft above the base of the Matlock Limestone, is exposed. The northern face of the quarry is rather rubbly bedded and coarsely crinoidal; it yielded a fauna including: Dibunophyllum bipartitum, Eomarginifera sp. lobata group, Gigantoproductus sp., Megachonetes sp. papilionaceus group and M. siblyi.

The dip increases eastwards and the Matlock Limestone plunges beneath the overlapping presumed Namurian shales at an angle of 33°.

Cawdor Group

The Cawdor Limestone is mainly exposed north-east of Wirksworth. In Middlepeak Quarry most of it has been worked out, but the remaining isolated patches are readily accessible. The limestone is predominantly grey and dark grey, thinly bedded and cherty with shaly partings. Crinoidal debris is common, associated with rich reefy patches of brachiopods. The basal beds are invariably irregular and reflect the undulations of the eroded and channelled top surface of the underlying Matlock Limestone. Some pockets are coarsely crinoidal and often contain broken brachiopod shells and brecciated fragments of limestone.

The following fauna was obtained from the lowest 15 ft of Cawdor Limestone in Middlepeak Quarry (locs.34 and 35): Caninia juddi, zaphrentoid. Aliteria panderi. Antiquatonia insculpta, Avonia davidsoni, A. youngiana, 'Brachythyris' planicostata, Dielasma hastatum, Eomarginifera lobate aff. laquea., E. longispina, Gigantoproductus crassiventer, orthotetoids, Productus concinnus, Rugochonetes Schellwienella sp., Schizophoria sp., smooth spiriferoids, Spirifer trigonalis, S. bisulcatus, Naticopsis sp., Aviculopecten?, Edmondia,, Leiopteria sp. [juv.]. Griffithides sp., Weberides sp., ostracods, fish tooth and plate. In the east of Baileycroft Quarry (see p. 129b) for section) thinly bedded dark grey limestones with shales show considerable undulation and are overlain W the south by dark laminated shales which contain abundant Caneyella membranacea (McCoy), characteristic of the highest beds of P₂ (See locs.36, 37 and 38 for Baileycroft Quarry, west side). In Dale Quarry (loc. 39) similar shales of Cawdor age rest unconformably on the Matlock Limestone. This is the most southerly outcrop of the Cawdor Shales; farther south [SK 2800 5300] they are overlapped by the Namurian shales of low E₂ or E₁ age which rest on successively lower horizons within the Cawdor Limestone.

South of the Yokecliffe Rake, the Sweenclose Vein separates the main outcrop of Hoptonwood and Matlock limestones to the north-west from an irregular patch of poorly exposed and variable limestone, near Pittywood Farm (locs. 40 to 45). This limestone, partly exhumed from beneath the Namurian shale cover, has an irregular surface with it relief of up to 25 ft. Its western boundary, straight over a distance of 300 yd, suggests a fault. The beds vary from pale grey, partly oolitic limestones to grey and dark grey limestones. Shirley (1959) refers them to the Cawdor Limestone. A 'knoll'of massive pale grey limestone is bordered on the south by thinly bedded fine-grained dark grey limestones which may be remnants of it once more extensive Cawdor Limestone outcrop. The present survey has confirmed that the faunas are of D₁ age and include typical Cawdor reef forms from the vicinity of the knoll. The fauna recorded from limestones between Sweenclose Vein and Pittywood Farm includes: Dibunophyllum bipartitum bipartitum, Syringopora cf. ramulosa, Antiquatonia antiquata, cf. 'Brachthyris'. Echinoconchus punctatus, Gigantoproductus cf. edelburgensis, orthotetoid, Phricodothyris cf. insolita, Pleuropugnoides pleurodon, Plicochonetes sp., Productus sp., Schizophoria sp., Spirifer trigonalis, S. bisulcatus, Striatifera striata, Bellerophon sp., Straparollus sp. and Weberides sp.

Crich

The best exposures are at Hilts Quarry [SK 3530 5425], south-east of the village. The general succession is:

A 6-in brown clay band (First Clay Band see p.130b) with limestone partings occurs some 11 ft below thetop of the Matlock Limestone, and may be the lateral extension of a bed of toadstone (Alsop 1845). Farther north, it 2-ft clay band (Second Clay Band, see below) some 70 ft below the top of the Matlock Limestone, has been regarded as the lateral equivalent of the Matlock Upper Lava (Smith and others 1967, p. 36), but this horizon is unfortunately now obscured in Hilts Quarry. Recent excavation in Cliff Quarry [SK 343 557], north of Crich, exposed it 2-ft mudstone some 70 ft below the top of the Matlock Limestone. The mudstone was grey silty and pyritic and contained bryozoa and shell fragments. It extended throughout the quarry, which is on the axis of the Crich Anticline (p.10). The basal few inches comprised green and purple-stained clay and the top 3 in or so were altered to it dark grey and ferruginous brown colour.

This description confirms that of Arnold-Bemrose (1899, p. 77) and modifies the observations of Sargent (1912) who considered such it lithology to be limited to one small exposure.

Such evidence indicates that not all clay wayboards are decomposed lavas or tuffs and that in the Crich area, limestone sedimentation was interrupted towards the end of D₂ times by an influx of argillaceous material which compares with that found in the overlying Cawdor Limestone and Shale. The shale rests on a weathered limestone surface which together with the altered shale margins indicates local periods of emergence.

Sargent (1912, p. 412) quotes the following analyses by E. Sinkinson of two clay bands:

Basin facies

In the following account it is convenient first to summarize the borehole results and Wen to pass on to the surface exposures of the district.

Duffield Borehole [SK 3428 4217]

This proved upper Visean rocks belonging to the Upper Beyrichoceras (B₂), Lower Posidonia (P₁) and Upper Posidonia (P₂) zones, the succession being broken by faults which probably cut out only it small thickness of strata. Apart from igneous rocks and two relatively thin calcareous mudstone sequences of 13 ft and 13 ft 6 in at depths of 1406 ft 4 W and 1443 ft 11 in respectively, the succession consists largely of graded silty mudstone/sandstone and muddy limestone units with dark grey mudstone intercalations, comprising the Widmerpool Formation.

Graded Units

The graded units range in thickness from less than an inch to 4 ft but are normally under 2 ft Wick. They all have sharp contacts with the underlying mudstone and the soles often show linear structures such as groove and bounce casts or small, irregular, knobbly structures, some of which are probably the sand-filled burrows of bottom-dwelling animals.

In general, the graded units show two distinct divisions, a lower grey to pale grey arenaceous division and an upper dark grey calcareous silty mudstone or pelitic division. An intervening poorly delineated, relatively this third division of silty or sandy calcareous mudstone with faintly developed parallel lamination is also present in most units.

The arenaceous division consists mainly of quartz sand and silt or of bioclastic debris. Graded units with quartz sand in the lower divisions predominate in the top 34 ft of P₂ immediately below the Cravenoceras leion Band, between 2633 ft and 3030 ft in the lowest 400 ft of P₁ and between 3353 ft 3 in and 3436 ft 10 in in B₂. In this last sequence sandstone makes up about 57 per cent of the total thickness and 65 per cent of the turbidite beds with the sandstone divisions averaging 4.5 in. These sandstones usually show this sets of ripple lamination. In it few thicker graded twits one or two additional lower divisions show strong parallel laminations or massive sandstone, but sedimentary structures are often masked by diagenetic calcium carbonate recrystallization. The arenaceous divisions in which bioclastic debris predominates usually show parallel lamination with alternating pale and dark laminae. In it significant proportion of units the arenaceous division is absent.

The pelitic divisions form the major proportion of the succession except between 3353 ft 3 in and 3436 ft 10 in, in the lowest 84 ft of the B₂ sequence (see above). They are usually massive with it slight upwards decrease in grain size, and the calcium carbonate content (qualitatively estimated from the amount of effervescence with dilute HCl) is generally high, where the arenaceous division of the unit is rich in bioclastic debris. One exceptional unit at 1717 ft 3 in is 7 ft-8 in thick and grades unevenly upwards from limestone conglomerate to dark grey calcareous mudstone. The conglomerate contains angular phenoclasts of muddy limestone up to 4 in across, set in a dark grey muddy limestone matrix with coarse crinoidal and broken shelly debris.

Fossils in the graded units are restricted to small shells and bioclastic debris and to finely divided plant debris which mainly occurs in the laminated silty mudstone and sandstone divisions.

Mudstone Beds

The mudstones between thegraded units are normally less Wan 1 in thick; some are merely films which adhere to the soles of the overlying graded units. In it few cases they are absent, presumably removed by the current depositing the succeeding graded unit. In the strongly calcareous sequences their presence may be masked by recrystallization They are then distinguished by sharp contacts with the pelitic top of the underlying graded units, their darker colour (often nearly black), their its silt content and their fissility. Fossils, particularly goniatites and bivalves, are common in the mudstone beds.

Igneous rocks

Six tuff bands and two dolerite sills were encountered. The tuffs range from fine- to coarse-grained and vary colour from pale blue to greenish-grey (p.1674). They usually contain pumice fragments and in some beds lapilli are present. Some intermixing of tuff with calcareous mud has been noted, particularly in the thickest band.

The two dolerite sills are 27 ft 9 in and 220 ft 3 in thick, their bases occurring at 1779 ft 7 in (P₁) and 3337 ft 3 in (B₂) respectively. Both have chilled upper and lower margins and have baked the adjacent sediments.

Trusley Borehole [SK 2548 3588]

The Dinantian rocks in this borehole comprise a turbidite sequence of red and purple sandstones, siltstones and silty mudstones which show grading, slumping and sole markings. The lower part of the sequence is calcareous. Mterbedded with the turbidite units are red, brown and purple mudstones interlaminated with pale grey-green mudstones.

Detailed examination of representative lengths of Trusley core (330 ft 9 in to 340 ft 8 in, 368 ft 11 in to 380 ft 7 in, 410 ft to 420 ft, 455 ft 2 in to 465 ft 6 in and 496 ft 7 in to 507 ft 2 in) indicates that graded sandstone- mudstone (turbidite) units comprise about 84 per cent of the core and interturbidite or pelagic shale about 16 per cent. Sandstone makes up about 49 per cent of the turbidites or 42 per cent of the total core with individual sandstone divisions averaging 2.8 inches in thickness. The sandstone-bearing turbidites have a proximality index(R.G. Walker 1967) of 20 per cent compared with 96 per cent in the B₂ Zone sandstone-bearing turbidites of similar age in Duffield Borehole. Thus both sequences are of distal turbidites, but that in the Duffield Borehole appears to be more distal than that in Trusely. However, there is no evidence that the two sequences are stratigraphically equivalent and sedimentological comparisons are of doubtful validity.

The Trusley Borehole sequence is sparsely fossiliferous but contains enough to justify its classification as the Widmerpool Formation. Fragments of orthotetoid brachiopods have been identified from 503 ft. In this sections made from the lowest and most calcareous parts of the sequence (504 ft) Dr W. H. C. Ramsbottom identified bryozoa and crinoid fragments and the following D₁ Zone algae and foraminifera — Koninckopora inflata, Archaediscus krestovnikovi, A. moelleri, Endothyra spp. and Tetrataxis sp.

A typical section with turbidite units from the Trusley Borehole is shown on the next page.

At outcrop

The Widmerpool Formation outcrop borders that of the lower Namurian in the Turnditch, Quarndon and Weston Underwood districts and forms inliers in the valley of Mackworth Brook near Kirk Langley, at Wildpark Wood, one mile east of Brailsford, and in a valley immediately south of Brailsford (Figure 3).

In general, the formation consists of thin beds of dark grey argillaceous limestone and grey calcareous siltstone exposed sporadically in streams such as Blind Brook, Kedleston and its tributaries [SK 3088 4199] and [SK 3159 4194], Cutler Brook, Weston Underwood [SK 2908 4188] Black Brook, Ravensdale Park [SK 2730 4454], Waterlaggs Brook, Hulland Ward [SK 2765 4597], Flagshaw Brook (see below) and a stream near Windley [SK 3058 4438]. Similar hard beds have also been noted in old pits, temporary sections and road banks. They commonly contain plant fragments, with occasional poorly preserved bivalves (see also Gibson and other s 1908, p. 24). A few of the coarser limestones contain conspicuous crinoid and brachiopod debris). An extensive microflora obtained from a sequence near Mackworth [SK 3137 3768] included no diagnostic species. In the details listed below the numbers correspond to the locations shown on (Figure 3).

Turnditch (4)

In an old limestone quarry at Flower Lilies [SK 2946 4550], south-west of Turnditch, 30 ft of alternating dark grey limestones, calcareous siltstones and grey fossiliferous mudstones are poorly exposed and-largely inaccessible. The limestones contain crinoid debris and brachiopods including Buxtonia sp., Dielasma sp., productoid fragments [costate] and Spirifer sp. The shale tips [SK 2933 4563] near the quarry entrance yielded specimens of Posidonia corrugate indicative of a P₂ age. The same age is indicated by Neoglyphioceras spirale (Phillips), found near this locality by Ford (1968a).

At the only exposure of the basal Namurian Cravenoceras leion Band in the Derby district a stream section and its nearby tributary near Champion Farm [SK 3243 4328] — the underlying Dinantian rocks are thinly bedded quartzitic sandstones and siltstones. Similar sandstones, probably belonging to the same sequence, have been worked in shallow pits in Park Nook Wood [SK 3254 4142].

White tuffaceous calcareous clay bands, 3 ft and 2.5 ft thick in Blind Brook [SK 3097 4233] and a temporary exposure [SK 3037 4352] respectively, are the only exposed representatives of the upper P₁–lower P₂ tuffaceous sequence recorded in Duffield Borehole. Microscopic examination by Mr R.K. Harrison shows a distinct pyroclastic assemblage altered to clay consisting predominantly of a mixed-layer mineral (E34597). Differential thermal analysis confirmed the presence of a mixed montmorillonite-illite clay mineral but with no detectable sepiolite. The clay bands are therefore of volcanic origin, though some reworking as well as mineral replacement seems to have occurred.

Wild Park Inlier [SK 2726 4127] (2)

Some 4 ft of purple and buff-stained calcareous sandstone and siltstone are poorly exposed in the banks of Wild Park Brook. The colouration here and in other exposures (see above) is due to secondary alteration close beneath a former cover of Triassic beds. Farey (1811, p. 159) described patches of yellow limestone from this locality and mistakenly thought them to be Magnesian Limestone overlying Westphalian rocks.

Kirk Langley Inlier (1)

Exposures in an old quarry [SK 2919 3891] comprise about 12 ft of red and red-brown sandstone in beds up to about 2 ft thick, with sole structures aligned east-west and east-north-east–west-south-west, and with thin intercalations of red and green clays and silty clays (see also Green and others,1887, p.88). Crinoids and Fenestella sp. have been recorded. This sequence is more arenaceous than any other recorded either at outcrop or in the Duffield and Trusley boreholes, but its stratigraphic level is uncertain.

Mr K. S. Siddiqui described a thin section (E38065) from this locality as a 'well-consolidated feldspathic sandstone lightly stained with red-brown iron oxide. The elastics are coarse-to medium-grained (0.8 x 0.6 mm-0.4 x 0.3 mm), mainly angular to subangular though a few are subrounded, very poorly sorted, much fragmented and scattered with aggregated patchy cement. Polygranular quartz (average 0.3 mm), angular in places is the predominant minerals, pitted with numerous inclusions and cracks and showing secondary overgrowths, Orthoclase (average 0.3 mm), plagioclase (0.2 mm), and a few grains of microcline (0.2 mm) make up the bulk of the section. Rarer scales of muscovite and chlorite, mostly orientated along the bedding, occur and dispersed aggregates of illite, kaolinite, dusty carbonates and well-crystallized dolomite (in places etching the silicates) are common. Cherty grains of cherty sillica (0.6 mm), particles of siltstone and sandstone and quartzite (0.6 mm), grains of pyrite, and leucoxene and a few granules of red-brown iron oxide and red organic matter are also present. A microchemical test confirmed the presence of ferric radical. A heavy mineral analysis showed the predominance of opaque ferric grains followed by perfect to broken prisms of zircon (some with zonal growth), tourmaline (O = dark brown, E = colourless to light yellow) anhedral grains of garnet (some step-etched) and rounded an prismatic grains of apatite'.

The presence of plagioclase suggests a B₂ age for the beds, the mineral have only been recorded from the B₂ Zone in the Duffield and Trusley boreholes.

In Flagshaw Brook, interbedded mudstones, siltstones and sandstones are exposed sporadically for nearly a mile, and at one locality [SK 2977 3894] Sudeticeras sp. and Posidonia corrugata, indicative of the P₂ Zone, have been collected from 6 ft of grey silty mudstones containing bands up to 6 in thick, of hard grey siltstone with sole structures.

In a road cutting [SK 3137 3768] at Mackworth, faulted against Waterstones, are 3 ft 7 in of laminated grey and dark-grey mudstone containing bands, up to 4 in thick, of grey-brown slightly calcareous siltstone and one band, 8 in thick, of brown and red-tinged fine calcareous sandstone. Dr B. Owens refers the extensive microflora from this sequence (Sample SAL 1247) to the upper Dinantian or Namurian A. Since siltstone and fine sandstones are absent from the lowest 150 ft of the Namurian in Duffield Borehole, the sequence at Mackworth is assigned to the top part of the Widmerpool Formation.

There are no exposures in the Brailsford Inlier (3).

A typical section with turbidite units from the Trueley Borehole is as follows:

Palaeontology of the Dinantian limestones

The stratigraphical palaeontology of the Dinantian limestones is similar to that already described by Ramsbottom (in Smith and others 1967, pp. 47–57) from the adjacent Matlock district and is therefore not described here. The available palaeontological data for the various limestone divisions in the district is summarized below in two lists, the first giving the fossil determinations in biological order with cross-references to the numbered localities where they were collected, the second giving the complementary list of localities. Brief notes on the fauna and age of the limestones is given in the general account (p.5).

Fossils collected from the limestones

The names of the fossils are followed by the numbers of the localities from which each has been recorded. The use of '?', 'cf.' or 'aff. ' before a locality number in these lists respectively indicates doubt as to the identification of, similarity to, or departure from the genus or species named.

Hoptonwood Limestone

• Koninckopora inflata (de Koninck) 11
• Algal nodules 11
• Foraminifera 4
• Aulophyllum fungites (Fleming) 4
• Caninia cf. densa Lewis (of Hudson & Cotton 1945, p. 306] 4
• Caninia sp. 3, 4, 75, 7
• Carcinophyllum vaughani Salle 4
• Chaetetes depressus (Fleming) 4
• Chaetetes septosus (Fleeting) 4
• Dibunophyllum bipartitum bipartitum (McCoy) 4
• Dibunophyllum bourtonense Garwood & Goodyear 4, 10
• Diphyphyllum sp. 4
• Konickophyllum cf. proprium Sibly 4
• Lithostrotion martini Milne Edwards & Haime ?3, 11
• Lithostrotion pauciradiale (McCoy) 4, 11
• Palaeosmilia murchisoni Milne Edwards & Haime 4, 7
• Syringopora sp. 4, 5
• Zaphrentoid 4
• Serpula sp. 11
• Fenestella sp. 6, 8
• Acanthoplecta mesoloba (Phillips) 8
• Aliteria cf. panderi (Muir-Wood & Cooper) 8
• Antiquatonia antiquata (J. Sowerby) 8, cf. 8, 9
• Antiquatonia hindi (Muir-Wood) 8, 12
• Antiquatonia insculpta (Muir-Wood) 8
• Antiquatonia sp. 7
• Athria cf. expanse (Phillips) 11
• Avonia youngiana (Davidson) 8
• Avonia sp. (juv.) 11
• Brachythyris p. 11
• Buxtonia sp.8, 9
• Chonetipustula carringtoniana (Davidson) 11
• Chonetipustula sp. ?8, 11
• Davidsonina septosa (Phillips) 7
• Davidsonina ?2b
• Dictyoclostus pinguis (Muir-Wood) 8
• Dielasma hastatum (J. de C. Sowerby) 8. 11
• Dielasma sp. 7, 9
• Echinoconchus punctatus (J. Sowerby) 8, 11, cf. 11
• Echinoconchus sp. 7
• Eomarginifera sp. lobate (J. Sowerby) group, 5, 8, 11
• Eomarginifera sp. 11
• Fluctuaria sp. 8
• Georgethyris cf. acutiloba (George) 7
• Gigantoproductus spp. 1, 2a, 2b, 3, 7, 8, 9, 11
• Gigantoproductus? spp. nov. [wrinkled concentric ornament; Mitchell in Stevenson and Gaunt 1971, pl. 14, fig. 2], 8, 11
• Gigantoproductus sp, (latissimoid) 4
• Krotovia? [juv.] 8
• Leptagonia analoga (Phillips) 11
• Linoprotonia sp. ?1, 2a, 8, 9
• Martinia 3, 6
• Martinothyris cf. lineata (J. Sowerby) 8
• Megachonetes ap. 5
• Orthotetoid 5, 6, 7, 9
• Ovatia sp, 6
• Overtonia fimbriata (J. de C. Sowerby) 8
• Overtonia sp., [juv.] 11
• Phricodothyris sp. 11
• Pleuropugnoides pleurodon (Phillips) 6, 8
• Pleuropugnoides sp. [juv.] 9
• Plicatifera plicatilis (J. de C. Sowerby) 8
• Plicatifera sp. 8, 11, ?12
• Plicochonetes cf. buchianus (de Koninck) 8
• Plicochonetes sp. [juv, ] 11
• Proboscidella proboscides (de Verneuil) 6, 9
• Productus? 8
• Pugnax acuminates (J. Sowerby) platylobatus (J. de C. Sowerby)
• Pugnax pugnus (Martin) [small form] 8, 11
• Pugnoides triplex (McCoy) 8
• Reticularia cf. mesoloba (Phillips) 9
• Schizophoria connivens (Phillips) 7
• Schizophoria resupinata (Martin) 7, 11
• Schizophoria sp. 6, 8, 12
• Smooth spiriferoid 5, 6, 7, 8, 9, 11
• Spirifer bisulcatus J. de C. Sowerby 11
• Spirifer cf. granicostatus McCoy 8, 11
• Spirifer trigonalis (Martin) 8, 11, 12
• Spirifer sp. 4
• Bellerophon sp. [juv.] 8
• Euomphalus? 2b, 11
• Naticopsis sp. juv. 9
• Straparella fallax (de Koninck) 11
• Straparollus dionsii de Montfort 11
• Straparollus sp. 8, 11
• Turbonitella biserialis (Phillips) 11
• Conocardium alaeformis (J. de C. Sowerby) 11
• Edmondia sp. 6, ?8, 11
• Girtypecten tessellatus (Phillips) 11
• Pectinoid 8
• Sangutholites sp. [juv.] 8
• Streblopteria laevigata (McCoy) 6
• Bivalve indet. 11
• Orthocone nautiloid 8
• Cyclus sp. 8
• Griffithides? 11
• Ostracods 8, 11

Matlock Limestone

• 'Girvanella' nodules 30c
• Saccamminopsis sp 27
• Foraminifera 19b, 20, 23, 24b, 30a, 31, 32a
• Amplexizaphrentis enniskilleni (Milne Edwards & Haime) 1913
• Aulophyllum fungites (Fleming) 20, 23, 24b, 30c
• Aulophyllum fungites pachyendothecum Thomson 19
• Caninia benburbensis Lewis 32a
• Caninia juddi (Thomson) ?18a, 18b, ?19d, 20
• Caninia sp., 19b, 23, ?24a
• Carcinophyllum vaughani Sallée 17, 21
• Chaetetes depresses (Fleming) 23
• Clisiophyllum keyserlingi McCoy 19a
• Clisiophyllum sp. 32a
• Dibunophyllum bipartitum bipartitum (McCoy) 13, 18a, 18b, 21, 23, 30a, 30c, 31
• Diphyphyllum lateseptatum McCoy 16, 18b, 23, 24b, aff. 33
• Diphyphyllum sp. 13, ?31
• Koninckophyllum proprium Sibly 32a
• Koninckophyllum sp. 13
• Lithostrotion junceum (Fleming) 23
• Lithostrotion martini Milne Edwards & Haime 19a, 20, 23
• Lithostrotion pauciradiale (McCoy) 14, 18b, 23, 30a, 30c, 32a
• Lonsdaleia floriformis floriformis (Mart.) 23
• Palaeosmilia murchisoni Milne Edwards & Haime 23, 30c
• Palaeosmilia regia (Phillips) 17, 23
• Syringopora cf..geniculata Phillips 23
• Syringopora cf. ramulosa Goldfuss 18b, 20
• Zaphrentites sp. 33
• Fistulipora incrustans (Phillips) 23
• Antiquatonia cf. muricata (Phillips) 25
• Antiquatonia sp. 13, ?14, 19c, 28
• Avonia davidsoni (Jerosz) 31
• Avonia youngiana (Davidson) 25
• Avonia sp. [juv.] 30a
• 'Brachythyris' planicostata McCoy 31
• Brachythyris sp. 31
• Dielasma sp. 31, 32b
• Echinoconchus sp. 26, 31
• Eomarginifera sp. lobate (J. Sowerby) group 31
• Eomarginifera sp. 24c, 26
• Gigantoproductus crassiventer (Prentice) 24c
• Gigantoproductus cf. edelburgensis (Phillips) 15, 27
• Gigantoproductus aff. gigantoides (Paeckelmann)
• Gigantoproductus inflatus (Sarycheva) 20
• Gigantoproductus sp. [latissimoid] 18a, 19b, 30a
• Gigantoproductus spp. 13, 14, 16, 18b, 19a, 19d, 20, 21, 24a, 24b, 25, 27, 28, 30a, 30c, 31, 32a, 32c
• Linoprotonia sp. 19c, 28
• Martinia sp. 19b, 24b, 26
• Megachonetes cf. papilionaceus (Phillips) 26
• Megachonetes siblyi (I. Thomas) 20, 22, 31
• Megachonetes sp. 31
• Orbiculoidea? 19c
• Orthotetoid 13, 20, 31
• Phricodothyris 20
• Pleuropugnoides cf. greenleightonensis Ferguson 32b
• Plicatifera? 25
• Productus productus (Martin) 19c, 28, 32b
• Productus sp. 19b, 24b, 24c, 30a, 31, 32a
• Pugilis pugilis (Phillips) 15, 20, ?25
• Pustula sp. 26
• Rhynchonelloid 27
• Rugosochonetes p. 30c
• Schizophoria resupinata (Martin) 20
• Schizophoria sp. 13, 19b, 24b, 25, 26, 30c, 31
• Smooth spiriferoid 13, 19a, 19b, 19c, 20, 25, 26, 27, 30a, 30c
• Spirifer bisulcatus J. de C. Sowerby 14, 18a, 19b, 24b, 24c, 25, 30a, 30c, 32c
• Spirifer trigonalis? (Martin) 27
• Spiriferoid 27
• Striatifera striata (Phillips) 27
• Bellerophon sp. 29
• Eoptychia? 31
• Euphemites sp. 32b
• Straparollus [juv.] 20
• Pectinoid 26
• Sanguinolites? 20
• Sulcatopinna flabelliformis (Martin) 30a
• Griffithides sp. 25
• Ostracods 20, 30c
• Fish tooth and plate

Cawdor Limestone

• Foraminifera 47a, 47b
• Amplexizaphrentis enniskilleni (Milne Edwards & Haime) 37a
• Aulophyllum fungites (Fleming) 47a
• Caninia benburbensis Lewis 47a
• Caninia aff. cornucopiae Michelin 37a
• Caninia juddi (Thomson) 34b, cf. 35
• Caninia sp. 37a, ?46, 48a, 48b, 49
• Chaetetes depressus (Fleming) 47a
• Clisiophyllum keyserlingi McCoy 48c
• Clisiophyllum sp.?46, 48b
• Clisiophylloid 37a, 48d
• Cyathaxonia cornu Michelin/rushiana Vaughan group 37a, 38, 46, 48d
• Dibunophyllum bipartitum bipartitum (McCoy) 38, 45
• Dibunophyllum bipartitum craigianum (Thomson) 47a, 47b
• Diphyphyllum sp. 47a, 48c, 48d
• Fasciculophyllum densum (Carruthers) 38, 46
• Fasciculophyllum sp. 47a, 48c
• Koninckophyllum interruptum Thomson & Nicholson 47a
• Koninckophyllum sp. 48b
• Lithostrotion junceum (Fleming) 47b, 48c, 48d
• Lithostrotion pauciradiale (McCoy) 47b, 48a
• Rhopalolosma aff. bradbournense (Wilmore) 46
• Rotiphyllum costatum (McCoy) 37a, 47a
• Rotiphyllum sp. 38
• Syringopora cf. geniculata Phillips 48b
• Syringopora cf. ramulosa Goldfuss 45, 47a, 47b
• Zaphrentites? sp. [juv.] 37
• Zaphrentoid 34b
• Fenestella sp. 36, 47b
• Alitaria panderi (Muir-Wood & Cooper) 34b
• Antiquatonia antiquate (J. Sowerby) 36, 38, 40
• Antiquatonia hindi (Muir-Wood) cf. 35, 38
• Antiquatonia insculpta (Muir-Wood) 34b, 36
• Antiquatonia cf. muricata (Phillips) 48d
• Antiquatonia sp 34a
• Athyris sp. 37a
• Avonia davidsoni (Jarosz) 34a
• Avonia youngiana (Davidson) 34a, 34b, 38
• 'Brachthyris' planicostata McCoy 34b, 36, cf. 40
• Brachthyris sp. 38, 45
• Buxtonia p. 34b, 35, 37a, 38
• 'Camarotoechia' sp. 36
• Chonetoid 35, 36, 37a
• Dictyoclostus sp. 34b
• Dielasma hastatum (J. de C. Sowerby) 34b
• Dielasma sp. 34a, 36, 38
• Echinoconchus elegans (McCoy) cf. 37b, 48d
• Echinoconchus punctatus (J. Sowerby) 38, 41
• Echinoconchus sp. 37a
• Eomarginifera lobata (J. Sowerby) off. laqueata (Muir-Wood) 34b, 38
• Eomarginifera cf. lobata 34a, 34b
• Eomarginifera cf. longispina (J. Sowerby) 34a
• Eomarginifera cf. setosa (Phillips) 35
• Eomarginifera cf. 36, 47b, 48d
• Gigantoproductus crassiventer (Prentice) 34b
• Gigantoproductus crassus (Fleming) 47b
• Gigantoproductus cf. edelburgensis (Phillips) 44
• Gigantoproductus giganteus (J. Sowerby) 35, aft. 35
• Gigantoproductus cf. tulensis (Bolkhovitinova) 35
• Gigantoproductus sp. [latissimoid] 34b
• Gigantoproductus spp. 34a, 34b, 36, 40, 41, 42, 45, 46, 47a, 48c, 48d
• Krotovia spinulosa (J. Sowerby) 35
• Linoprotonia sp. 43, 45
• Martinia sp. 35, 37a, 47b
• Orthotetoid 34a, 34b, 38, 42, 44, 46, 47b
• Phricodothyris cf. insolita George 41. 46
• Phricodothyris sp. 37
• Pleuropugnoides pleurodon (Phillips) 44
• Plicochonetes cf. crassistria (McCoy) 40, 46
• Plicochonetes sp. 38, 40, 45, ?46
• Productus concinnus J. Sowerby 34b
• Productus productus (Martin) 48c, 48d
• Productus sp. ?34a, 38, 42, 48a
• Pugilis pugilis (Phillips) 34a, 34b
• Pugilis ?36
• Pustula sp. 38
• Rugicostella? 46
• Rugosochonetes sp. 34a, 34b
• Schizophoria sp. 34b, 36. 40, 42, 45
• Smooth spiriferoids 34a, 34b, 35, 36, 37a, 38, 40, 42, 43, 47b, 48d
• Spirifer bisulcatus J. de C. Sowerby 34b, 35, 36, 38, 40, 45, 47b, 48c, 48d
• Spirifer trigonalis (Mart.) 34b, 37a, cf. 37a, ?38, 41
• Spirifer sp. 46, 47b
• Striatifera striata (Phillips) 42, 43
• Striatifera sp. 45
• Tylothyris sp. 38
• Bellerophon sp. 42, 43, 47b
• Naticopsis sp. 34b, 47b
• Pleurotomarian 43
• Straparollus sp. 40
• Turreted gastropod 46
• Aviculopecten? 34b
• Caneyella membranacea (McCoy) 37b
• Edmondia? 34b
• Leiopteria squamosa (Phillips) 47b
• Leiopteria sp. [juv.] 34b
• Streblopteria sp. 47b
• Bivalve indet. 36, 48d
• Griffithides sp. 346
• Weberides sp. 34a, 34b, 37a, 39, 41
• Trilobite fragments 36, 38
• Ostracods 34b
• Archaeocidaris sp. [plate] 47b
• Fish teeth and plates 34b, 35, 36, 37a, 47b

List of localities

Where more than one face in a quarry is listed, the first-mentioned yielded the most comprehensive assemblage. Each item includes the 105 registered numbers of the specimens. The fossil assemblage at a particular locality is found by searching the faunal. lists (p. 131).r entries bearing the locality number.

Hoptonwood Limestone (1–11)

Matlock Limestone (ML)

Cawdor Limestone (CL)

Chapter 3 Namurian (Millstone Grit Series). Details

Pendleian (E₁)

The maximum thickness of this stage where complete over the 'block' areas is estimated at about 50 ft. In the Widmerpool Gulf some 566 ft were proved in the Duffield Borehole.

The Cravenoceras leion band, marking the base of the stage, is exposed at only one locality in the district, in a stream [SK 3243 4328] near Farnah House, Duffield, where it occurs in about 4 ft of dark grey weathered shale with a decalcified limestone band 1 ft above the base. Both lithologies have yielded Cravenoceras cf. leion (p. 14). Since the mapping was completed, C. leion together with Posidonia cf, membranacea have been found in fragments of brown decalcified limestone ploughed up at Windley [SK 3057 4547]. The conjectural position of the Namurian–Dinantian boundary shown on the first published editions of 1 10 560 sheet SK 34 NW and 1 50,000 sheet therefore requires correction. Shale tips [SK 2710 4435] on the Dinantian outcrop near Black Burn yielded a single specimen of Eumorphoceras tornquisti and an orthocone nautiloid (E_1a), but the source of the debris is not known.

South-west of Duffield, a series of scarp and dip-stops features trending north-north-west to south-south-east are the surface expression of unexposed sequences of graded mudstonesandstone turbidite beds of E_1b, to H_1a age proved in the Duffield Borehole.

Arnsbergian (E₂)

The lowest E₂ fossiliferous horizon seen during the resurvey was poorly exposed in a shale bank [SK 2802 5305] 0.75 mile SW of Wirksworth Church and yielded Eumorphoceras bisulcatum (E_2a). The locality is some 10 yards east of the Dinantian limestone/Namurian shale contact. The E₁ stage is therefore this or missing, with E₂ shales resting directly on Cawdor Limestone (p. 000). Steep dips and poor core recovery in the Hopton Borehole [SK 2677 5334] indicate disturbances in these lowest shales of the Namurian.

Cravenoceratoides (E_2b) was identified at 43 ft in Hopton Borehole, where the sequence consisted predominantly of grey silty mudstone with subordinate calcareous siltstone. The fossils, which were confined to certain horizons, proved that the E₂ stage continues to the bottom of the borehole at 149 ft. This thickness is double that in the Ashover area (Ramsbottom and others 1962) and suggests that the margin of the limestone 'massif' was dose to the margin of the Widmerpool Golf in early Namurian times. There were no indications from the cores of a true 'gulf' facies.

In a temporary excavation [SK 2872 5340] 0.33 mile S of Wirksworth, finely laminated shales and ferruginous orange-coloured rottenstone contained Posidonia corrugate, suggesting an E₂ or older age. The same species was recorded some 1000 yd SW of Wirksworth in temporary exposures [SK 2812 5326] made for house foundations. Ford (1968b) recorded fossils of E₂ age in shales near Wirksworth station ?[SK 2894 5442]. The over-all thickness of the Arnsbergian Stage around and south of Wirksworth is therefore probably between 150 and 200 ft.

In sporadic stream exposures near Kirk Ireton, grey silty mudstones and dark grey calcareous shales predominate. This limestone (calcareous siltstone) bands up to 12 in thick contain goniatites, bivalves and gastropods. Ferruginous, fine-grained, hard sandstone bands and laminae often exhibit groove, flute and tool marks, typical of turbiditic sedimentation.

In the Ridgeway Brook [SK 2924 4694] north-east of Turnditch dark grey shales with calcareous siltstone bands yielded P. corrugata together with indeterminate goniatites and gastropods considered to be E₂ or older.

In Biggin Brook [SK 2576 4777] the following section was recorded:

The lower calcareous beds yielded Nuculoceras nuculum (E_2c). Sporadic exposures in the stream [SK 2572 4779] to [SK 2634 4766] yielded the following E_2c fauna: Eumorphoceras bisulcatum, Dimorphoceras sp. [s.l.] orthocone nautiloid, P. corrugata, Posidoniella variablis, Actinopteria regularis.

Nearby, at Millington Green [SK 2646 4779], tough calcareous mudstone contained Cravenoceratoides fragilis, palaeoniscid fish scales and carbonised plant fragments probably from the N. nuculum Zone (E_2c).

A 10-ft scar [SK 3178 4508] on the left bank of the River Ecclesbourne shows this alternations of brown and grey mudstone containing Ct. edalensis (E_2b) and Posidonia corrugata in the lowest 4 ft. A band with Ct. edalensis occurring some distance upstream [SK 3165 4521], is probably at the same horizon.

The next scar upstream [SK 3137 4555] consists of variegated shale with N. stellarum and Posidonella aff, vetusta 8 ft 5 in above the bottom of the section, marking the base of the E_2c Zone. These shales overly 5 ft 7 in of tough cherty interlaminated dark mudstones and pale siltstones containing Ct. nititoides, E. rostratum, crinoid columnals and a pectenoid. The benthonic fauna and associated cherty lithology of these beds constitute a distinctive marker band in the Namurian of the Central Province (Stevenson and Gaunt 1971, pp. 189–190).

There are few exposures in the Franker Brook of the beds between the N. atellarum band and the goniatite band with N. nuculum and Eumorphoceras [SK 3082 4729]. However, the sequences with-alternations of mudstone and thin quartzose sandstones (formerly known asCrowstones) proved in the E₂ succession in the Duffield Borehole are represented by minor scarps, aligned sub-parallel to the Ecclesbourne Valley, north-north-west and south-south-east of Postern Lodge. Temporary trench exposures across these features showed the beds to be folded with axial trends in the same direction as the scarps. A small exposure of mudstone with thin quartzose siltstones, 50 yd downstream from the N. nuculum band noted above, probably belongs to this sequence. The Franker Brook section provides exposures of several of the many goniatite bands in the E_2c to R_1c sequence (Figure 66). The dip, generally to the north-east, varies from 0 to 19° with a few minor reversals, which, together with the many gaps between exposures, allow only approximate estimation of thickness. The N. nuculum band occurs in a 10-in grey carbonate siltstone and probably correlates with a bed with a similar lithology and fauna at a depth of 123 ft 2 in in Duffield Borehole which forms part of the highest of three N. nuculum bands occurring extensively in the Central Province. N. nuculum was recovered from bunions in the bed [SK 3738 4053] of the Boosemoor Brook, Breadsall (Figure 66). It could not be established whether or not the bullions were in place and since H. subglobosum Zone sediments are present both in the adjacent bank and downstream (p.133c). it is inferred that the top of the Arnsbergian is here raised to stream level by a superficial structure.

In Ferriby (or Dam) Brook, Breadsall (Figure 66), N. nuculum was found [SK 3758 3954] in a 10-in siltstone band underlain by about 15 ft of soft grey mudstone with darker more shaly bands exposed low in the stream bank; the horizon is probably low in the H. subglobosum Zone.

Chokierian (H₁)

Homoceras cf. beyrichianum and H. beyrichianum (H_1b) together with Anthracoceras or Dimorphoceras have been discovered in the Scow Brook [SK 2537 5238] some 2 miles SW of Wirksworth. H. beyrichianum was also recorded [SK 2618 4763] in Biggin Brook nearly 2 miles south of Kirk Ireton, but is not considered to be in situ for surrounding strata are of the Arnsbergian Stage (p. 133b).

A gap in Franker Brook between the N. nuculum band and the H. beyrichianum band [SK 3059 4761], representing about 116 ft of strata, is referred to the H. subglobosum (H_1a) Zone; it contains only a few small exposures of black carbonaceous shaly mudstone. As well as H. beyrichianum present in a bullion, the latter band has yielded Caneyella semisulcata, an orthocone nautiloid and H. cf. subglobosum. A badly preserved fauna exposed higher up the brook [SK 3060 4778] includes H. cf. subglobosum and H. sp. nov, and possibly represents an horizon slightly lower than the H. beyrichianum band noted above, The stream section may therefore contain unexposed faults and minor folding to cause this reversal in the succession. A higher H_1b band occurs in a 6-ft exposure [SK 3057 4774] of mudstone containing H. sp. aff. beyrichianum and H. sp. of the subglobosum group.

A temporary section [SK 3725 3970] for school playing-fields at Breadsall exposed about 30 ft of decalcified dark grey mudstone with weathered (limonitic) bullions and, near the top, sporadic thin (up to 3 in) sandstone ribs. H. subglobosum was plentiful.

In Boosemoor Brook north-east of Breadsall H. subglobosum was collected from a few feet of weathered greymudstone in the bank [SK 3738 4053] adjacent to the bullions with N. nuculum in the stream bed (p.133c). H. subglobosum also occurs in a large bullion about 35 yd downstream. No other diagnostic fossils were collected from this stream section which includes a 20 ft section [SK 3748 4060] showing iron-stained and weathered grey mudstone.

In Mill Plantation [SK 3759 3955] near Breadsall the following section is exposed low in the bank of Ferriby (Dam) Brook over a distance of about 20 yd:

The section has yielded H. subglobosum in quantity. Mr M.J. Reynolds has examined the bullions from this section (including those in the Arnsbergian strata) for their conodont fauna and found the following species to be present; Euprioniodina microdenta, Gnathodus girtyi, Hibbardella acuta, H. ortha, Hindeodella ibergensis, H. subtilis, H. uncata, Idiognathoides minutus, Idiognathoides noduliferus, Neoprioniodus cf. armatus, Ozarkodina cf. macer, Prioniodina subaequalis. Adjacent exposures upstream show poor sections, up to about 17 ft, of mudstone with interbedded sandstones up to 2.5 ft thick, dipping towards the east. These are probably the representatives of the highest turbidite sequence in the Duffield Borehole (Aitkenhead, in press). Near the eastern end of Mill Plantation sections of unfossiliferous mthistones are referable to either this stage or the overlying Alportian.

Alportian (H₂)

Shales of the Hudsonoceras proteus zone (H_2a) are exposed in Scow Brook [SK 2540 5240] 0.5 mile S of Hopton Hall. The goniatites are concentrated in large calcareous bullions. The basal H_2a band of H. proteus is not exposed in Franker Brook, but a bullion containing this fossil was found in a temporary exposure [SK 3135 4714], 830 yd SE of Shottle Hall. The Hornoceras undulatum Zone (H_2b) is probably represented in Franker Brook by an exposure [SK 3055 4782] containing badly preserved fossils, including H. cf. undulatum obtained from 2 ft of grey mudstone containing a bullion. Another exposure [SK 3058 4785], some 6 ft higher in the sequence yielded H. sp. (eostriolatum group), probably from the Ht. prereticulatus Zone (H_2c). The stage has not been established in the Ferriby Brook, but is probably represented by the scattered small sections showing mudstones and this grey sandstones, the latter with sole-marks, in the banks for 200 yd E of Mill Plantation. Caneyella sp. is the only fossil recovered from this part of the stream [SK 3781 3962].

Kinderscoutian (R₁)

Shales containing goniatites of the Reticuloceras nodosum group have been seen at two localities [SK 2898 5354] and [SK 2755 5209] near Wirksworth in a small tributary stream of the River Ecclesbourne. The fauna included Homoceratoides aff. divaricatus, Dimorphoceras sp., Homoceras sp. as well as Caneyella sp.

R. coreticulatum has been identified in Callow Borehole [SK 2665 5282] at depths between 61 and 90 ft, together with the following fauna: C. rugata, Dunbarella sp. Posidonia sp. juv., Anthracoceratites sp., Reticuloceras spp. The Franker Brook exposes two goniatite bands in the R. circumplicatile (R_1a) Zone. The lowest [SK 3056 4788], probably about 9 ft above the H_2c band noted above, consists of 5 ft 9 in of grey mudstone with a bullion band. The fauna obtained from the mudstone includes H. henkei, Homoceratoides sp. and R. circumplicatile. About 9 ft of unexposed strata separate this band from a small exposure of mudstone [SK 3059 4796] which has yielded Dimorphoceras sp. and R. subreticulatum. About 15 ft of mainly unexposed mudstone separates this band from the only exposure [SK 3060 4805] of the R. nodosum (R_1b) Zone band in the section, comprising poorly exposed mudstone with a bullion band. The fauna from the mudstone includes H. cf. striolatum and R. stubblefieldi. Above are about 10 ft of poorly exposed mudstone overlain by grey mudstone containing Dimorphoceras sp., and R. cf. reticulatum, the only exposure in the R. reticulatum (R_1c) Zone [SK 3051 4812].

In the Ferriby Brook section Kinderscoutian rocks, in disturbed condition, are intermittently exposed between localities [SK 3787 3966] and [SK 3808 3978] in the 5-ft banks of the stream. Over the western 50 yd of this outcrop R. circumplicatile and H. henkei have been collected from up to 5 ft of dark grey and ochreous mudstones containing a 4 to 5-in band of siltstone and a bullion. R. cf. subreticulatum (R_1a) is present in westerly dipping grey mudatone [SK 3797 3972] containing cooly laminae, plants and ferruginous bands; at one locality [SK 3800 3973] mudstones which are overturned both to the east and west contain a hard grey saptarian siltstone which yielded R. cf. stubblefieldi and R. sp. (nodosum group) (R_1b). At least two horizons of bullions (up to 3 ft x 1 ft in size) within 5 ft of gently dipping dark grey mudstones [SK 3802 3975], are of R_1b or R_1c age since they contain R. cf. reticulatum, Dimorphoceras Posidonia sp. and a fragmentary orthocone natitiloid. The remaining exposures [SK 3804 3977] and [SK 3808 3978] of Kinderscoutian age include this sandstone and siltstone ribs and lenses. Hudsonoceras ornatum, and Reticuloceras sp., collected from bullions, are indicative of the R. nodosum Zone. The presence of the highest zone (R_1c) is not definitely established'on the available material.

The total thickness of Kinderscoutian rocks in this brook section is of the order of 70 ft.

Mr M. J. Reynolds found the following conodonts in the bullions from the Kinderscoutian sections in this stream. In one section [SK 3800 3973] he records Hindeodella sp. fragments, Idiognathoides corrugates, I. sulcatus, Lonchodina furnishi, Neoprioniodus sp. and Ozarkodina roundyi; at another [SK 3802 3975] Hindeodella sp. fragments, I. noduliferus, I. sinutatus, I. sulcatus, Ligonodina sp. fragments Lonchodina cf. furnishi and Streptognathodus lateralis; and at another [SK 3808 3978] Euprioniodina microdenta, Neognathodus bassleri, H. ibergensis, H. subtilis, H. uncata, H. noduliferus, O. hindei, Prioniodina stipans S. elegantulus and S. lateralis.

Namurian Beds below the Marsdenian in Ironville Nos. 1 and 3 Oil Bores

Downing and Howitt (1969, p. 246, fig. 3) have recognised the R. gracile horizon in Ironville No. 3 Oil Bore at about 1894 ft depth on the gamma log. It lies immediately above a light brown sandy limestone overlying a this sideritic sandstone. The whole sequence, about 15 ft thick, is about 380 ft above the Dmantian limestone. No sandy limestone or sideritic sandstone was recorded in the Ashover boreholes at this level, though their gamma logs through the R. gracile sequence are similar to that of No. 3 Bore.

The late C. E. N. Bromehead noted 'fine brown micaceous calcareous grit' probably representing the same horizon, in chipping samples from 1715 to 1735 ft in Ironville No. 1 Oil Bore, again lying about 300 ft above the Dinantian limestone. The approximate depths of 1814 ft No. 3 Bore and 1715 ft in No. 1 are therefore taken to mark the base of the Marsdenian.

The underlying sequence down to the top of the Dinantian limestone is recorded in No. 3 Bore as largely black, pyritic mudstone, slightly silty near the top with thin 'fine-grained white sandstones' noted at about 2010, 2020, 2030, 2118 and 2165 ft, the lowest being shelly. The top of the Dinantian limestone has been recognised from the gamma log at about 2220 ft (Howitt in litt.). In No. 1 Bore predominantly argillaceous rocks are recorded. The top of the Dinantian limestone is at 2035 ft.

The similarities of the gamma log of No. 3 Bore to those of the Ashover boreholes (Cosgrove in Ramsbottom and others 1962) is the evidence on which the stage boundaries shown in (Plate 4) are based. The base of R₁ is thought to lie at about 2057 ft, the base of H at about 2108 ft and the base or E₂ probably at about 2184 ft.

Marsdenian

Beds below the Ashover Grit

In Callow Borehole a ferruginous band in fragmentary cores at 20 ft depth yielded Reticuloceras gracile. At outcrop this horizon is some 30 ft below the lowest mapped sandstone in the Wirksworth district, proving the absence of the Kinderscout Grit is south Derbyshire. The basal goniatite band of the R. gracile Zone was found in a temporary excavation [SK 3137 4741] near Shottlegate, where weathered grey mudstone yielded Dunbarella sp. and R gracile.

In Franker Brook, the R. gracile and R. bilingue bands are probably out out by a fault [SK 3058 4833] crossing the stream. Upstream to a locality [SK 3063 4931] near Carrbrook Farm, there are numerous exposures of grey silty mudstone and siltstone with bands of ironstone nodules and a few hard grey or grey-brown sandstone beds up to 5 ft thick. These sporadically exposed and variably dipping beds, which are about 250 ft thick, probably represent an early pro-delta intermittent arenaceous phase preceding the major sand influxes of the Ashover Grit.

Similar rocks are exposed in streams west and south of Blackbrook where the Blackbrook Water Borehole [SK 3308 4775], sunk towards the end of the last century (Wedd in Gibson and others 1908, p. 37), proved alternations of shale and sandstone to a depth of 231 ft 2 in. The deeply incised streams near Lumb Grange below the Ashover Grit escarpment are mainly in grey silty mudstones, siltstones and fine sandstone, but 2 ft above the base of one 10-ft section [SK 3314 4675] is a 2-in rottenstone band from which R. bilingue was collected. The Blackbrook Water Borehole probably started near the crop of this band. A lower band is poorly exposed in a roadside bank at Hazelwood [SK 3327 4549], where weathered mudstone has yielded R. cf. bilingue. A specimen of R. bilingue late form was collected during the first 6-in survey (Wedd in Gibson and others 1908, p. 25) from the north side of the railway cutting at Duffield [SK 3429 4364], The fossil was found in a 'thin band of pyritous shale' at the top of the cutting and was then identified as Glyphioceras bilingue (Salter). A fossiliferous band, 4 in thick, was excavated here during the present survey, but no diagnostic fauna was found. The R. bilingue late form band, the defined base of strata containing the Ashover Grit (Smith and others 1967, p. 68) is about 50 ft below the lowest mappable Ashover Grit sandstone at Duffield.

R. bilingue late form occurring with Caneyella sp., Posidonia pp. nov. and fragmentary Dunbarella sp., in small sections of dark grey mudstones with silty bands in the river bank [SK 3808 3978], marks the lowest Marsdenian horizon proved in the Ferriby Brook. A few yards upstream are intermittent exposures of micaceous mudstones with siltstone bands, some containing plant remains and one, 2.5 in thick, with a vertical dip [SK 3811 3976]. Farther upstream, dips become more orderly towards the east in grey micaceous silty mudstone with siltstone bands, and near the top of the sequence are this ferruginous sandstone bands indicative of a passage upwards into the lowest sandstone of the Ashover Grit. Calculations of thickness of these deposits are unreliable because of the variations in dip; it is possible that the R. bilingue band noted above may lie some 300 ft below the lowest mapped leaf of the Ashover Grit in this area.

The base of the Marsdenian in Ironville No. 3 Oil Bore is drawn at a gamma peak at about 1894 ft and above a "sandy limestone" (Downing and Howitt 1969, p. 246). The overlying strata up to the base of the Ashover Grit (1738 ft on the gamma log) is recorded as'dark grey-black micaceous silty mudstone with white silt and tight very fine-grained sandstone'.

Ashover Grit below the Main Bed

Wirksworth and Ecclesbourne Valley

North of Wirksworth and near Crich, the Ashover Grit Math Bed is underlain by silty laminated mudstones with subordinate siltstone and sandstone horizons. To the south of Wirksworth, between Shottle Hall and Duffield, however, these beds give way to sandstones, which vary from isolated lenses, up to 20 ft thick, to continuous fine-grained, cross-laminated beds up to 140 ft thick, forming good features on the sides of the Ecclesbourne Valley.

The lowest thick sandstone, some 500 ft below the base of the Main Bed, is exposed in the disused Stainsbro' Quarry [SK 2660 5265] 0.25 mile N of Callow. It comprises some 20 ft of light brown fine-grained sandstone with mudstone inclusions in the basal 8 ft and with shaly micaceous bands up to 2 in thick containing carbonaceous plant fragments.

Some 20 ft of sandstone, about 150 ft below the Main Bed, are exposed in Callow Quarry [SK 2660 5120], 0.5 mile S of Callow. Shaly micaceous bands within the sandstone show purple and pink colorations which suggest post-Carboniferous staining related to a Triassic cover since removed.

These sandstones and shales are exposed in many places along the sides of the Ecclesbourne Valley (See 6-in geological map SK 25 SE). The shales are predominantly silty with ironstone nodules and bands: apart from scattered plant fragments, fossils are rare.

Calculations based on information obtained from the old plans of the Meerbrook Sough together with recent details from the Mines Research and Exploration Group led by Mr Nash, indicate that the base of the Main Bed is some 600 ft above the top of the Dinantian limestone in the area east of Wirksworth. A further sandstone of the Ashover Grit some 100 ft thick occurs about 100 ft below the Main Bed (Figure 7).

West of the River Derwent

In an old quarry [SK 3343 4471] in a garden at Hazelbrow, Duffield. 10 ft of pale brown fine-grained cross-bedded sandstone with poorly delineated soft-weathering ferruginous concretions are exposed. Similar cross-bedded sandstone, but without concretions, occurs in the railway cutting at Duffield.

The overlying sandstones are thicker, coarser and more continuous at outcrop, particularly to the north-west and east of Shottle. Here an old quarry [SK 3121 4988] exposes about 30 ft of coarse, pale brown sandstone with lens-shaped cross-bedded units up to 3 ft thick which commonly contain bands with pebbles up to I in diameter. A few incomplete casts of fossil trees are present on bedding planes. Smaller exposures of similar sandstone in old quarries near Hollyseat [SK 3200 4876] and Holly House [SK 3302 4823] represent the most important leaf of the Ashover Grit below the Main Bed. In Belper Meadows Water Borehole [SK 3399 4776] 112 ft of grit were recorded below the Main Bed (Wedd in Gibson and others 1908, p. 40) the only proved thickness of this lower leaf. The leaf is best exposed in the base of an old quarry near Milford [SK 3466 4501] where 30 ft of pale brown medium-grained sandstone with cross-bedded sets 1 in to 3 ft thick are seen. At the northern end of the Milford railway tunnel 25 ft of the same sandstone are exposed.

Derwent Valley

A lower leaf of the Ashover Grit forms an inner in the valley of the Derwent between Whatstandwell and Ambergate. A temporary exposure at the works near Oak Hurst [SK 3404 5230] revealed 25.5 ft of pale brown fine to coarse-grained cross-bedded sandstone, in beds up to 2 ft thick, interbedded with fine ripple-laminated sandstone.

The strata, undivided on the maps, which lie between the mapped Ashover Grit sandstones, are generally poorly exposed. They probably consist mainly of grey to grey-brown laminated shaley siltstones, very silty mudstones and fine micaceous sandstones. They are best seen in the cutting at the southern end of the Milford railway tunnel [SK 3446 4468] and are sporadically exposed in the stream west of Oak Hurst [SK 336 521]. Fossils other than small plant fragments have been found only near Milford [SK 3438 4525], where a specimen of the non-marine bivalve Anthraconaia angulosa was collected from an 8-ft section of purplish grey very silty mudstones with carbonaceous partings (Aitkenhead 1966). Strata underlying the Math Bed were temporarily exposed on the roadside [SK 3544 4251] near Outwoods, where below 4 ft of soil and wash (p.158c) they comprised some 5 ft of grey-brown, ochreous-stained and banded sandy micaceous mudstones with thin (up to 2 in) sandstone ribs.

Little Eaton to Breadsall

A section within the lower leaves of the Ashover Grit seen in an old quarry [SK 3607 4166] near the Vicarage at Little Eaton comprises 5 ft of coarse laminated red and red-brown micaceous clayey sand with 6-in bands of sandstone, overlain by 6 ft of brown and pale brown speckled coarse sandstone. East of Little Eaton equivalent beds are seen in a roadside section [SK 3673 4163], where they consist at the base of 25 ft of medium to coarse cross-bedded khaki and red speckled sandstone with large brown and red friable ovoid patches up to 6 ft in diameter. This is overlain by 18 ft of thin and wedge-bedded, medium to coarse, red, red-brown and khaki micaceous sandstone locally containing fragments of angular red silty mudstone in the basal few feet.

In Camp Wood, south of Little Eaton, a section [SK 3668 4115] in the lowest mapped sandstone shows 25 ft of cross-bedded (towards the south-west) medium to coarse-grained brown and red-stained micaceous sandstone with friable patches. This sandstone was not encountered, according to Wedd (in Gibson and others 1908, pp. 44–45) in the well at the Paper Mill about [SK 354 423] and has probably died out below the cover of the Derwent alluvium. To the east of Camp Wood it dies out, or is cut out by the Math Bed (see p.134d) before Breadsall Priory is reached. However, it may be represented by the lowest mapped leaf of Ashover Grit in the Ferriby Brook (see below). There is little doubt that the sandstone forming Burley Hill on the west side of the Derwent near Little Eaton is the Ashover Grit. Wedd (in Gibson and others 1908, p. 32), although calling it Shale Grit, implied correctly that it is a continuation of the sandstone cropping out in Duffield and correlated by the presence of R. bilingue late form about 50 ft below. Debris of black mudstone with Dunbarella sp. from a roadside excavation [SK 3500 4135] near Burley is assigned to this marine horizon. Exposures at the Hill itself are poor; a few feet of khaki and pale grey speckled sandstone are seen on the north side, and in the bank of the River Derwent about 20 ft of steeply dipping brown micaceous medium-grained sandstone with harder nodules containing plant remains are underlain by 3 to 4 ft of coarser sandstone with similar nodules and overlain by 3 ft of grey silty micaceous mudstones. This sandstone dies away to the east of Burley Hill, but it is perhaps represented by siltstones proved in trial boreholes for roadworks on the hill at the Water Works [SK 367 407], south of Little Eaton. It is absent in the stream section at Breadsall where the lowest sandstone is some 300 ft above the R. bilingue Marine Band.

There are poor sections of the lowest mapped leaf of the Ashover Grit in the Ferriby Brook [SK 3838 3978] where 10 ft+ of soft bedded micaceous silty sandstone with 1-ft harder ferruginous bands are exposed near the base of the mapped sandstone; 15 ft of similar beds with thin sandstone bands are exposed some 10 to 15 yd upstream. This sandstone, which may correlate with the sandstone leaf in Camp Wood, near Little Eaton, is about 75 ft thick and its top lies a calculated 300 ft below the base of the Math Bed; only a few feet of the intervening mudstones are exposed in the stream banks.

Ashover Grit (Main Bed)

East of Wirksworth to the Derwent Valley The Ashover Grit (Math Bed) forms the main part of the thterfluve between the Ecclesbourne and Derwent valleys. At levels above 900 ft it is often stained a purplish red colour by percolation of ground waters and by weathering below a Permian land surface which was eventually overlain by Triassic rocks. There are small sections [SK 2974 5313] and [SK 2980 5355] on the scarp overlooking Wirksworth.

The full thickness of the Main Bed has been proved in boreholes at Wigwell [SK 3170 5465] and Hanson Farm [SK 3233 5459], where 163 ft and 170 ft 6 in respectively were recorded. A similar thickness (171 ft) was proved at Belper Meadows Water Borehole [SK 3399 4776], but this borehole started in a shaly sandstone slack within the Main Bed and did not prove the full thickness. Exposures of the Main Bed are small and scattered in the extensive outcrops west of the Derwent valley, the best befog in the old quarry at Alport Hill [SK 3038 5157]. Here, a column of sandstone, known as the Alport Stone, left standing in the middle of the quarry, shows 17 ft of coarse-grained sandstone with dispersed pebbles up to 0.75 in diameter, resting discordantly on a single set of cross-bedded coarse pebbly sandstone (Plate 3.1), (Plate 3.2). The upper bed here probably represents a restricted channel fill similar to those described by Mayhew (1967, pp. 96–97) at Cocking Tor [SK 348 540] in the Chesterfield district.

Crich area

The Math Bed forms the lowest mappable feature east of the Dthantian limestone inlier. Where completely exposed in a temporary trench [SK 3564 5334], near Mill Green, its thickness totalled some 160 ft, the basal 15 ft being coarse-grained, and in places conglomeratic. Coaly partings were common and cross-bedding was well displayed in the central portion. It was immediately overlain by a 20-in coal.

Sporadic exposures of massive, buff, cross-laminated sandstone occur along the outcrop at Fritchley [SK 3555 5303]. In the Amber Valley near Bullbridge some 500 ft of predominantly arenaceous measures were seen in excavations [SK 3546 5207] below the top of the Ashover Grit.

The extensively quarried east-facing escarpment extending south from The Tors near Crich also has good exposures, though in general the cross-beddthg is not well weathered out. At the highest (50-ft) quarry face Mayhew (1967, p. 97) has recognised the upper pebbly planar cross-stratified facies lying with a transgressive base on the lower non-pebbly trough cross-stratified facies.

The Derwent Valley

The escarpments flanking the Derwent valley from Whatstandwell to Ambergate show numerous craggy exposures. The best sections are found in disused quarries on the west flank of the valley [SK 3291 5465] near Hankin Farm, at Shththg Cliff Woods [SK 3332 5227] to [SK 3332 5285] and on the east flank at Dukes Quarries [SK 3344 5467] and Chase Cliff [SK 3415 5370], where thicknesses of up to 70 ft, 45 ft, 40 ft and 60 ft respectively are seen. The sandstone is buff to pale purple-brown, cross-bedded and coarse-grained except in the Dukes Quarries where it is fine- to medium-grained and more micaceous, probably representing a fining-upwards facies near the top of the Math Bed similar to that exposed at the Ambergate railway cutting (see below). Small pebbles, up to 0.75 in across, are more common in the lower beds seen in the south-facthg 45-ft exposure at Shining Cliff Woods [SK 3350 5230]. The planar cross-beddthg which appears to characterise most of the lower two thirds of the Math Bed is here particularly well displayed with individual sets up to 6 ft thick truncated by thin interbedded units showing indistinct current-ripple lamination. There are small sections in the Main Bed near Thackers Wood [SK 352 513] and extensive exposures of the pebbly cross-bedded facies by the math A6 road at Ambergate [SK 3481 5115] and [SK 3504 5160], near Belper [SK 3884 4837], in the old quarry above Blackbrook [SK 3363 4768], in the railway cutting at Chevthside [SK 3468 4594] and at the old quarry west of Milford [SK 3480 4525].

The uppermost part of the Main Bed is well exposed only in the railway cutting at Ambergate [SK 3467 5080], where about 50 ft of sandstone are seen with sporadic exposures of the overlying sequence (p.135a). About 20 ft below the top of the Grit the cross-bedding appears to pass upwards from planar to broad lenticular sets. The top 6 ft are flaggy bedded and micaceous with parallel and current-ripple lamination. There is an overall fining upwards.

Two local exceptions to the prevailing planar cross-bedded facies are exposed at quarries on Firestone Hill. The first [SK 3359 4650] shows 18 ft of coarse cross-bedded sandstone, soft and micaceous in the basal 2 to 3 ft, overlying 10 ft of coarse massive sandstone. The second, to a disused quarry 200 yd to the south [SK 3368 4587], shows 70 ft of coarse sandstone with unusually thick cross-bedded sets, some exceeding 10 ft. The cross-bedding dip directions indicate current supply from the north-west, which is quite contrary to those for the Math Bed as a whole (p.18).

A shale slack has been mapped within the Math Bed at Crossroads Farm, where a small temporary exposure revealed grey-brown silty mudstone with carbonaceous micaceous partings. Other small temporary excavations suggest that this slack contains a thin coal seam.

Duffield to Breadsall

The Main Bed is almost continuously exposed in old quarries on the escarpment between Milford and Breadsall. Most of the quarries lie today within private gardens. The sandstone is largely pebbly, and medium- to coarse-grained, its basic pale grey colour frequently brown-speckled and reddened; soft friable limonitic patches are commonly present and the planar cross-bedding, which is inclined largely towards the north-west (Figure 9) at angles of 15 to 20°, may reach inclinations as high as 33° [SK 3563 4243] when coincident with the dip of the beds. Cross-bedding units up to 30 ft thick have been observed. The following is a list of the principal quarries in the Main Bed and the estimated thicknesses exposed:-

Roadside at Milford [SK 352 452], 85 ft; quarry near Makeney Lodge [SK 3534 4440], 60 ft; quarries at Thrpins [SK 353 437], three faces totalling about 70 ft; Bank Wood Quarry [SK 3532 4354], 25 ft; Manor Quarry [SK 3538 4329] 80 ft; quarry near Manor Farm [SK 3530 4317], 32 ft; quarry [SK 3536 4292], 60 ft with, near the base, 12 ft of lenticular sandstones, interbedded with red micaceous flaggy sandstone with clay laminae—probably the lower facies of Mayhew (1967)—underlain by 10 ft of brown medium to coarse-grained cross-bedded sandstone; quarry near Outwoods [SK 3551 4260], 25 ft; Blue Mountains Quarry [SK 3563 4243], 50 ft; Outwoods Quarry [SK 358 421], 70 ft; Hathering Wood Quarry [SK 360 420], 75 ft; quarry at Eaton Hill [SK 3637 4215], 75 ft; Little Eaton Quarries [SK 366 420], 100 ft (Mayhew (1967) records his lower facies here); old quarries in Horsley Carr [SK 3708 4241], 12 ft.

The Main Bed, comprising brown coarse sandstone, is exposed for 11 ft below Head (p.158c in an old quarry [SK 3843 4139] near Breadsall Priory and includes 2.5 ft of laminated brown and purple sandstone. In Ferriby Brook, east of Breadsall, the poorly exposed Main Bed is softened and reddened due to close proximity to the unconformity at the base of the Permo-Triassic.

Some discussion is necessary on the total thickness and sequence of the Ashover Grit in the vicinity of Little Eaton and Breadsall. Wedd (in Gibson and others 1908, pp. 29–30) gives a figure of 'of quite 500 ft. thick' of which the now-named Main Bed would account for '300 feet or more'. Outwoods Borehole (p. 172a) entered the Main Bed sandstone a calculated 40 ft below the top and continued to the total depth of 320 ft without encountering shale. It is estimated that it reached the bottom of the Main Bed which must therefore be about 360 ft thick. Wedd also noted that a water well at the Paper Mills about [SK 354 423] was sunk 80 ft without proving any sandstone, although some of this thickness is in alluvium. This thickness together with a further 200 ft of shale and sandstone mapped as lying below the Main Bed near the Paper Mills brings the total to about 640 ft and there is still the unproved thickness of the sandstone on Burley Hill to be added. This suggests an overall thickness of about 700 ft for the Ashover Grit, and therefore a minimum of 800 ft for the interval between the R. bilingue and R. superbilingue marine bands is credible.

There is confirmation of the thickness of the Math Bed from the Little Eaton Water Bores [SK 3684 4249] which penetrated Ashover Grit from 73 ft to 427 ft. The overall thickness of Ashover Grit here therefore appears to be similar to that of the Outwoods–Paper Mills area.

Only the Main Bed appears to be represented at outcrop east of the faults near Breadsall Priory. However a lower leaf of sandstone is present in the Ferriby Brook section about one mile to the south. The low leaves of sandstone appear to be missing over the axial line of the Breadsall Anticline, but it is not known if this is due to non-deposition or erosion.

In the north of the district most of the Ashover Grit was cored in Ironville No. 4 Oil Bore (Appendix 1, p. 169c and (Plate 4)), where 116 ft 2 in of fine- to medium-grained sandstones with two mudstone beds were proved. The sequence in the Ironville Nos. 1 and 3 bores are shown graphically on (Plate 4).

Little Hallam Water Bore is interpreted as entering Ashover Grit at 1406 ft and continuing in the Main Bed to 1792 ft, 9 ft above the bottom of the bore. The succession, recorded by Stephens (1929, pp. 97–98) includes a 'trace of coal', at about 1504 ft.

Strata between the Ashover Grit and the Chatsworth Grit

West of Hankin Farm [SK 3214 5448]

R. superbilingue occurs only a few yards upstream from the exposed flaggy top of the Ashover Grit (Smith and others 1967, p. 72), whereas in the Ambergate railway cutting the following composite section was measured:

A soft weathered coal up to 33 in occurred 10 ft or so above the top of the Main Bed of the Ashover Grit in an excavation [SK 3546 5207] in the Amber Valley near Bullbridge.

A sequence of coal-bearing strata overlying the Ashover Grit was recorded by Wedd (in Gibson and others 1908, p. 48) from a trial borehole and quarry section north of Crich Carr, just beyond the boundary of the district.

In the same part of the succession, 9 in of weathered coal are exposed in a ditch [SK 3092 5367] near Lanehead, 2 ft of coal and dirt on clayey seatearth were recorded in a temporary exposure at Wiggonlee Farm and 2 ft of coal overlying 2 ft of seatearth, mudstone and ailtstone are exposed in the right bank of the River Derwent [SK 3428 4802] near Belper. Coal was formerly worked along the foot of the Ashover Grit (Main Bed) dip slope near Belperlane End. R. superbilingue was found in shale dug out of a house foundation [SK 3428 4830] on the hillside about 60 ft above the coal.

A higher coal and its underlying fireclay were formerly mined from an edit [SK 3210 5425] beneath the outlier of Chatsworth Grit north of Alderwasley village. The coal appear to lie about 45 ft above the R. superbilingue Marine Band at [SK 3214 5448] (see p. 00), but R. superbilingue has also been found in old shale tips on the slope below the old shaft [SK 3151 5412]. A borehole record nearby, not precisely located, gives the following section from the base of the Chatsworth Grit (Wedd in Gibson and others 1908, p. 42):

A thin bed full of Lingula mytilloides formerly exposed in an old brickpit [SK 3226 5431] about 20 ft above the top of the Ashover Grit is also recorded by Wedd.

The coal seam in the above section was proved recently in a trench [SK 3170 5345] near Alderwasley where it was 2 ft 0.5 in thick overlying 3 ft of seatearth clay.

The Reticuloceras superbilingue Marine Band was proved some 85 ft above the Main Bed of the Ashover Grit in Amber Dye Works Nos. 1 and 2 boreholes (Plate 4) and named by Swinnerton (1946) the Belper Grit Marine Band. He recorded Carbonicola cf. recta and C. aff. lenicurvata some 30 ft below. The latter species was then considered to be the lowest record of a non-marine bivalve from the Namurian. The R. superbilingue Marine Band was discovered in a temporary exposure [SK 3551 5201] for a gas holder at Bullbridge, where it also contained numerous specimens of and was recorded by Mr R. A. Eden in a temporary exposure [SK 3548 5184] near Hag Wood, in black carbonaceous shale.

Between Milford and Little Eaton there are no significant exposures. The thickness of the sequence appears to increase from about 120 to 160 ft between these two localities. Wedd (in Gibson and others 1908, p. 45) recorded an unsuccessful attempt to prove the coal overlying the Ashover Grit near Milford. A section is provided by water bores at Little Eaton (p.170b

The 148 ft 8-in sequence lying between the Ashover and Chatsworth Grits and consisting mainly of mudstone was cored in Ironville No. 4 Oil Bore (p.169c). The base of the R. superbilingue Marine Band is taken at 1321 ft, with Lingula and poorly preserved goniatites present, sporadically, in the cores for about 40 ft above this level. The sequences in Ironville No. 1 and No. 3 Oil bores are shown on (Plate 4). In the latter bore, gamma peaks indicate the assumed position of the R. superbilingue Marine Band (Downing and Howitt 1969, p. 246) at about 1578 ft.

Little Hallam Water Bore proved 'sandy shales' 38 ft, on 95 ft 'blue shale containing a few very small Lingulae' (Stephens 1929, p. 97) overlying 11 ft of sandy shale at 1406 ft 0.5 in. The 'Lingulae' are assumed to represent the R. superbilingue Marine Band.

The Chatsworth Grit

West of its main outcrop the Chatsworth Grit forms several outliers flanking the Derwent Valley near Whatstandwell and Alderwasley. The full thickness is not proved and the only significant exposures are in two old quarries [SK 3157 5415] and [SK 3163 5420] near Knob Farm, where up to 15 ft of pale brown and partially red-stained fine- to coarse-grained sandstone are seen.

In another outlier, on the west side of the Derwent Valley north-west of Belper, the grit le estimated to be at least 90 ft thick. An old quarry [SK 3400 4936] to the north-east corner of this outlier shoes 30 ft of thin-bedded fine- to medium-grained pale and purple-brown sandstone with numerous ripple-laminated micaceous partings; it is croas-bedded in sets up to 6 in thick.

Similar sandstone is exposed in faces up to 25 ft high in old quarries above the main A6 road about 830 yd N of Broadholm. A shale slack in the outcrop of the Chatsworth Grit indicates a split into upper and lower leaves about 70 ft, and over 100 ft thick respectively.

The grit forms a pronounced feature in the Crick–Fritchley–Ambergate area and comprises some 65 ft of tine- to medium-grained sandstone with shaly partings and lenses, the base of which lies some 40 ft above the R. superbilingue Marine Band.

In temporary sections in the gas pipe trench at Mill Green [SK 3576 5336] the highest beds of the grit were (leggy, micaceous and purple-stained. Sporadic exposures in the Ambergate–Toadmoor area show a brown, fine- to medium-grained sandstone up to 20 ft thick. It is cross-laminated and commonly exhibits ripple structures. Pink weathering affects the rock along its joints. The best exposures are at Hag Wood Railway cutting [SK 3557 5194] and at Thackers Wood [SK 3559 5152]. The upper leaf of the Chatsworth Grit is about 60 ft thick and is exposed in old quarries north of Helper. One quarry [SK 3536 4889] shows 25 ft of pale brown, ochreous and pink mottled sandstone with friable patches and with cross-bedding dipping towards the south-east. The some leaf is seen in old quarries high on the scarp face at Belper [SK 3531 4810] to [SK 3538 4761], where up to 20 ft of cross-bedded units (up to 5 ft thick) of pale brown sandstone with softer pink micaceous sandstones (as bottom-set beds) are exposed. In the southemmost quarry there are pipe-like masses of incoherent sand 5 ft wide in which only vague traces of the original bedding are preserved.

Near Milford the division of the grit into upper and lower leaves is well displayed by ground features; the only section [SK 3567 4506] shows 4 ft of flaggy fine-grained sandstone. South-eastwards the grit is nowhere exposed. It is calculated to be about 60 ft thick north of Little Eaton.

In Ironville No. 4 Oil Bore the Chatsworth Grit is only 20 ft 9 in thick composed of sandstone with interbedded mudstones (p. 169c). The sequences in Nos. 1 and 3 oil bores are illustrated graphically on (Plate 4).

In Little Hallam Water Bore strata between 1158 ft 4.5 in and 1262 ft 0.5 in are assigned to the Chatsworth Grit (Stephen. 1929, p. 97). There is an upper sandstone 25 ft 8 in thick overlying 'sandy shale', below which is a lower leaf comprising 3 ft of 'hard close-grained sandstone'.

Trowell Moor Colliery Underground Borehole proved 66 ft of hard, grey or variegated sandstone without reaching the base of the Chatsworth Grit.

Beds above the Chatsworth Grit

There are no significant exposures of this sequence, but it is well recorded in borehole, In Nether Heage Borehole (p.171c) the Chatsworth Grit is overlain successively by 13 ft 4 in of mudstone, 3 ft 2 in of siltstone and 7 ft 6 in of ganisteroid sandstone. This sandstone is taken to represent the Redmires Flags (Smith and others 1967, p. 75) at the top of the Marsdenian. In Ironville No. 4 Oil Bore the cores of this sequence (p.169c) 19 ft 7 in thick, included 4 ft 10 in of gritstone at 1202 ft 10 is also thought to represent the Redmires Flags.

Sandstones above the Chatsworth Grit mapped locally near Ambergate and Milford may represent these flags at outcrop, but in the absence of palaeontological control they are not named on the geological maps.

Overlying the Chatsworth Grit in Trowell Moor Colliery Underground Borehole are some 40 ft of grey sandy shales overlain by 15 ft 6 in of grey sandstone (including 2 ft of sandy shale) assigned to the Redmires Flags. At the inferred top of the Marsdenian is 6 in of 'Simmondley Coal'.

In Little Hallam Water Bore, Stephens (1929, p. 97) recorded some 8 in of coal 4 ft 9 in above the Chatsworth Grit. This coal is thought to be the representative of the Baslow Coal (Smith and others 1967, p. 54) or Ringinglow Coal (Stevenson and Gaunt 1971). A 4 in coal 55 ft 8 in higher in the borehole marks the assumed top of the Marsdenian and probably represents the Sirnmondley Coal.

Coaly debris above the Chatsworth Grit outcrop was noted on the northern edge of the district east of Culland Farm [SK 3657 5384].

Yeadonian

Beds below the Rough Rock

Nether Heage Borehole and Ironville No. 4 011 Bore (pp 171c and 169c) provide the only significant records of the Yeadonian beds below the Rough Rock in the district. Their respective sequences are 140 ft 2 in and 111 ft 2 in thick and each proved the G. cumbriense Marine Band. In both borehole, the base of the Yeadonian is marked by Lingula bands which are taken to represent the G. cancellatum Marine Band. This interpretation is supported by a comparison of the gamma logs with that of Calow No. 1 Oil Bore in the Chesterfield district, in which both the G. cumbriense and G. cancellatum marine bands were proved (Smith and others 1967, fig. 7, p. 62). Bivalve and Lingula beds are known elsewhere in the Central Province both between the marine bands and also below the G. cancellatum Marine Band (Smith and others 1967, pp. 74, 77).

The lithological correlation of the Trowell Moor Colliery Underground and Little Hallam Water boreholes [SK 4621 4048] is shown on (Plate 4). The Simmondley Coal is respectively 6 in and 4 in thick.

The Rough Rock and overlying beds

The Rough Rock was exposed in a trench [SK 3650 5326] north-west of Beech Hill Farm, where it consisted of brown cross-bedded fine-to medium-grained sandstone some 60 ft thick.

At the top of the Rough Rock, in an old quarry [SK 3590 5251] near Bullbridge, a 4-in ganister overlies some 18 in of pale grey fireclay. Exposures in the railway cutting nearby [SK 3595 5213] show the following section;

The Rough Rock has a gradational base down into mudstone. The section does not accord with the report by Neve. (1967, p. 44) that in the Crich area the Rough Rock is reduced to a few feet of siltstone, but agrees with that proved in Nether Heage Borehole.

Ten feet of flaggy fine-grained sandstone forming part of the Rough Rock were seen in temporary exposures for extensions to the Brick Works [SK 3584 5196], Ambergate.

The top of the Rough Rock together with overlying beds are exposed in Ridgeway Quarry [SK 3585 5145];

In Ironville No. 4 Oil Bore the Rough Rock is 44 ft thick with its base at about 1086 ft; the lowest 14 ft is recorded as sandy micaceous siltstone, the main mass of the rock as fine-grained whitish sandstone, finer and micaceous at the base, and the top as a 3-ft bed of ganister. The Cromford Fault (p.160b) intersects the borehole at approximately the top of the Rough Rock. In No. 3 Bore the Rough Rock (about 1325 to about 1378 ft) was cored over the greater part of its thickness and is recorded as silty fine-grained cemented sandstone, micaceous and laminated, increasingly silty towards the base. The Rough Rock at Pinchom's Hill, to the south of the Horsley Fault, has a mapped thickness of about 110 ft. Discontinuous exposures in the quarries [SK 3604 4693] and [SK 3595 4689] show up to 30 ft of cross-bedded sandstones in units or 'posts' about 3 ft thick; rippled and laminated micaceous sandstones, probably formed as bottom-set beds, are also present. Towards the summit of the hill, a separate low feature with ganister fragments in the soil is taken to represent the Pot Clay seatearth. There is no palaeontological evidence of the age of these rocks.

At Shawlane Quarry [SK 3592 4559] the uppermost 11 ft of the Rough Rock there exposed are composed of laminated and foggy sandstone in which weak cross-bedding is apparent in places; the cross-bedding is truncated by the flagstone bedding. Underlying are some 20 ft of medium to coarse-grained, brown to red-brown cross-bedded (towards the north-west) sandstone. A large ferruginous mass, 8 ft long and 1.5 ft thick, was noted.

The Rough Rock is well exposed in quarries east and west of Coxbench in the Bottle Brook valley and is about 100 ft thick. West of the old Coxbench–Little Eaton road [SK 3701 4320] about 40 ft of medium-grained micaceous sandstone coloured in various shades of brown are exposed, parts of the face being in a very friable condition. Immediately south-west of this pit a quarry-face nearly 300 yd long and up to 75 ft high exhibits similar but harder sandstone with irregular and often curved fractures. Clear bedding-planes are rarely seen and although westerly dipping cross-bedding was observed in one place, the few parts of the face which are suitably weathered exhibit extreme contortions of the bedding with amplitudes of up to 10 ft (Plate 3.1), (Plate 3.2). It is apparent that the irregular fractures are the result of quarrying the contorted or slumped sandstone which comprises the entire face. A further quarry [SK 3657 4297] 300 yd SW of the above face shows about 60 ft of cross-bedded pale grey to brown medium- to fine-grained sandstone; the cross-bedding dips slightly west of south. On the west side of the valley the lower 30 ft in the Coxbench Quarry [SK 374 433] is cross-bedded (towards the west-north-west) sandstone in units up to 15 ft thick; there is some red staining mainly on the bottoinset beds and ferruginous concretions up to 5 ft by 8 ft occur. In the uppermost 20 ft of the quarry the rock is brown and red-stained and contains small hard nodules, small-scale cross-bedding and slump structures. The base of the Rough Rock is exposed among quarry waste in the adjacent yard of Castle Farm [SK 3738 4317]. It is underlain by 1 ft 3 in of purple mudstone on grey micaceous mudstone. Cross-bedding in the sections in old quarries near Horsley Castle dip mainly towards the west-north-west, but units dipping west and west-south-west were also measured; up to 60 ft of the rock is exposed.

On the east side of the Horsley Fault system the Rough Rock has a thickness of little more than 50 ft in old quarries near Morley Moor Farm. At Morley Moor Farm [SK 388 425] the lower part of the north face of the quarry shows 10 to 18 ft of brown and purple mottled sandstone with slump structures; cross-bedding, some of which dips towards the south-east, is best seen in the lowest 5 ft exposed. At the west end of this face there is a passage between slump and cross-bedding and convolutions are present in the laminated foreset beds of the latter. The upper part of the face shows 12 ft of cross-bedded medium-grained brown and purple mottled sandstone with softer purple micaceous bands. At the top of the quarry 4 to 6 ft of inaccessible, red and grey mottled clays are assumed to include the Pot Clay horizon.

No detailed sedimentological study of the Rough Rock has been attempted, but it is concluded that in the Coxbench–Morley Moor Farm area, instability during deposition was responsible for the slump structures. These and the differential subsidence revealed by local thickness changes are interpreted as evidence of precursory movements associated with the formation of the Breadsall Anticline (Figure 59).

In Park Brook Borehole [SK 3830 4385] the following sequence was proved below the Pot Clay Marine Band base at 505 ft 8 in;

The Pot Clay Coal, 2 in thick, was encountered in Trowell Moor Colliery Underground Borehole and was separated by 7 in. of 'grey sandy 'clunch' from the top of the Rough Rock. The latter, 79 ft 6 in thick, is recorded as follows:

Mr R.A. Eden placed the base of the Westphalian in Little Hallam Water Bore at 939 ft 7.5 in. The Rough Rock is 112 ft thick with base at 1051 ft 7.5 in. The detailed section, recorded by Stephens (1929, pp. 95–98), is from the top: sandy shale, 4 ft; grey mudstone, 16 ft; sandy shale, 3 ft 6 in; variegated sandstone, 11 ft; grey sandstone ('dark streak.), 67 ft 6 in; strong sandy shale, 10 ft.

In Beechdale Road (Robin's Wood) Borehole, the base of the Pot Clay Marine Band is at 2068 ft 8 in. The underlying downward sequence is dark grey silty mudstone with fish debris, 4 in; Pot Clay Coal. 2 in; ganister, 4 in. This rested on Rough Rock composed of pale greenish grey fine-grained sandstone with dark greenish grey coarse siltstone bands at base, 8 ft 6 in; on greyish white micaceous sandstone, 12 ft.

Chapter 4 Westphalian (Coal Measures). Details

Westphalian A (Lower Coal Measures)

Base of Westphalian to Kilburn Coal

The measures between the Pot Clay Marine Band and Kilburn Coal range in thickness from about 590 ft near Bondland Colliery to about 800 ft south of Denby Colliery (Figure 12). In the east they are 625 ft thick in Beechdale Road Borehole.

Of the twelve component cycles within the district only that above the Belperlawn Coal and that capped by the Kilburn Coal lack marine or near-marine horizons at their bases. The highest marine horizon known to occur in these measures to the north and near Nottingham (Smith and others 1967, p. 116)—the Burton Joyce Marine Band—remains unproved.

Within these measures are two principal sandstones—the Crawshaw Sandstone and Wingfield Flags—and three coals that have been worked underground—the Belperlawn, Alton and, to a lesser extent, the Norton. Ganisters, present with, the seatearths of many of the lower coals, were formerly worked in the north of the district.

The distribution of the marine and near-marine horizons was given by Eden (1954) and the faunal sequence is similar to that described by Smith and others (1967, 1973) in the Chesterfield and East Retford districts. The mussel beds between the Belperlawn and Alton coals contain the distinctive Carbonicola fallax/C. protea faunas described by Eagar (1947, 1952) from above the Soft Bed Coal in Yorkshire. Another distinctive horizon is the Norton Mussel-band with Carbonicola proxima which overlies the Norton Marine Band,

The quality of coal mentioned in this section is assessed according to a scale used by the Coal Survey Laboratory for the ash and sulphur contents as follows:

The Pot Clay Marine Band

The dark grey marine mudstones at the base of the Westphalian have been proved in three boreholes. The characteristic goniatite, Gastrioceras subcrenatum, is present and the associated fauna consists of a further species of Gastrioceras, together with Dunbarella papyracea, Lingula mytilloides, Orbiculoidea sp., conodonts including Hindeodella sp. and fish debris (see also Eden 1954, p. 106).

Strata inferred to represent the marine band are exposed near Ambergate at Bullbridge Brickworks Quarry [SK 3602 5203], and at Ridgeway Quarry [SK 3583 5146]; they may occur also as reddened mudstones at Brackley Gate. At Ridgeway Quarry, the ganister at the top of the Namurian is overlain by some 12 in of laminated grey silty and listric mudstones containing fish scales and foraminifera; within the basal 1 in are rare specimens of Lingula sp. and Orbiculoidea sp. This thin sequence of the marine band is unusual in view of the sparse fauna and the presence of foraminifera (see Calver 1968, p. 26; Smith and others 1967, p. 102). In the nearby Nether Heage Borehole both goniatites and Lingula were present in 1 ft 2 in of dark grey mudstone.

Posidonia sp., Anthracoceras sp. and G. subcrenatum were collected from 4 ft 8 in of dark grey mudstone in Park Brook Borehole; in Beechdale Road (Robin's Wood) Borehole the marine band was 2 ft 4 in thick (Eden 1954, p. 84). The position of the marine band is marked by a 'high' between 1304 and1308 ft depth in the gamma log of Ironville No. 3 Oil Bore. Smalley Mill Well, Little Hallam Borehole and Trowell Moor Colliery Underground Borehole also penetrated the horizon, but yielded insufficient evidence to establish its precise position.

The Measures between the Pot Clay Marine Band and the Belperlawn Coal

The Measures between the Pot Clay Marine Band and the Belperlawn Coal range from about 100 ft in Beechdale Road and Nether Heage boreholes to 145 ft in Park Brook Borehole. Below the Crawshaw Sandstone they comprise largely argillaceous strata with a few feet of dark grey mudstones containing fish debris overlying the marine band. Wedd (in Gibson and others 1908, p. 50) noted these strata to be '12 or 14 yards thick and composed of blue sandy micaceous shale' in a well [SK 3634 4363] near Coxbench. in the Ambergate area a thin layer of penecontemporaneously contorted mudstone similar to those described by Cope (1946) has been noted a few inches above the marine band. These argillaceous measures are exposed in the Bullbridge Brickworks Quarry and adjoining rail cutting and in Ridgeway Quarry (see Appendix 2).

The Crawshaw Sandstone ranges up to 112 ft on thickness in Little Hallam Borehole and reflects a resumption of Namurian conditions of sedimentation. Its cross-bedding suggests derivation from the south. The sandstone is mainly medium to coarse, gritty and arkosic; its colour is buff at outcrop, but grey to white when encountered in bores; pink and red staining is common both at outcrop and in boreholes and a green coloration has been sporadically recorded. Except at Ridgeway Quarry (Appendix 2) and in Beechdale Road Borehole the base of the sandstone is gradational into the underlying argillaceous strata; the lowest beds are either fine-grained for a thickness of up to 24 ft as at Beechdale Road Borehole or interbedded with siltstone and mudstone, as in the vicinity of Ambergate. Within the main mass of sandstone, beds of siltstone and mudstone (about 3 ft at Coppice Colliery Underground Borehole and 7 ft at Stapleford No. 1 Oil Bore have been proved, and similar beds reach mappable proportions in the outcrop near Holbrook. Towards the top of the sequence the rock usually becomes finer grained and contains beds of siltstone and mudstone. At the top, below the Belperlawn Coal, there is a ganisteroid sandstone about 2 ft thick and mudstone seatearth up to about 1.5 ft thick.

North of Ridgeway, silty bands occur in both the highest and lowest parts of the sandstone, and at the southern end of the Brick Works Quarry the sandstone is entirely fine-grained and silty. Southwards from Ambergate the bold escarpment of the Crawshaw Sandstone is broken by faulting. Between Howson Green (south-east of Belper) and Holbrook there are several small exposures of coarse pebbly sandstone.

Subangular brown ferruginous sandstone fragments and quartz pebbles (up to 1 in diameter) were seen in 5 ft of coarse brown feldspathic sandstone near Holbrook Moor [SK 3622 4580] and 18 ft of cross-bedded and shattered coarse sandstone are exposed south of the roadway to Rowson Green [SK 3678 4606].

From Holbrook to Coxbench, and also near Brackley Gate, the outcrop is divided by an argillaceous bed near the base of the sandstone. At Portway^‡6  Site, it is believed that the Crawshaw Sandstone is locally united with a sandstone lying below the Alton Coal (see p. 136d); similarly to coal, presumably the Belperlawn, was proved up to 24 in thick within sandstone at Beechhill Farm Site, 0.5 mile east of Fritchley. The Crawshaw Sandstone is exposed locally between Stanton (or Stanton by Dale) and Dale in the south-east of the district. It has been quarried [SK 4715 3783] immediately east of Stanton, where 50 ft of massive brown to off-white micaceous medium- to coarse-grained sandstones are seen. The quartz grains are angular and well cemented, and cross-lamination suggests a southerly origin. West of Stanton, in an old sand pit [SK 4604 3833], a section of a fault plane in the Crawshaw Sandstone shoots grain variations from fine to medium sandstone to coarse grit.

The Belperlawn Coal (Figure 13) has been proved to be 66 in thick at Nodinhill Site and is 38 to 50 in in the type area north-east of Belper, where it has been extensively worked, mainly by opencast methods.

The following section, recorded by N. A. Eden at Far Lawn Site [SK 3665 4901] prior to working, typifies the seam at outcrop near Belper;

Away from the western outcrop the thickness of coal only exceeds 30 in with the 'take' of Denby (Drury-Lowe) Colliery. Near Heanor it is less than 20 in., but at Ilkeston (Manners Colliery Borehole) the 27 in. seam is split by 9 in of dirt; at Oakwell Staple Pit the dirt parting is 18 in thick, separating two 9-in leaves of coal; the Ironville oil bores did not prove coal at this horizon.

In many sections^‡7  the seam is divided by a bed of dirt or dirty coal. Above this parting the seam is variable and frequently of poor quality; below the parting it is of medium to poor quality with, on average, a moderately high ash content. A number of bell pits have been sunk to the seam between Ridgeway and Heage, including Bowman's Colliery [SK 3590 5087], where the Belperlawn was recorded as 5 ft thick at 18 ft depth. A quarter of a mile to the north [SK 3594 5122] the weathered crop ('smudge') of the seam was once worked for dye-making. A small area of Belperlawn Coal up to 32 in thick was mined near Sawmill from Bullbridge Colliery. The seam, 2 ft 10 in thick, is exposed in the adjacent railway culling [SK 3621 5212], where it is overlain by unfossiliferous shale and underlain by 8 in of grey seatearth.

The Measures between the Belperlawn Coal and Alton Coal

The Measures between the Belperlawn and Alton Coals (Figure 14), which have a maximum thickness of 78 ft on Denby (Drury-Lowe) Colliery Alton No. 1 Underground Borehole, thin northwards to 30 ft at Ridgeway Site and eastwards to 42 ft in Trowell Moor Colliery Underground Borehole. They comprise up to four cycles with three thin and impersistent coals, in ascending order the Holbrook, Second and First Smalley coals (Eden 1954). The lowest beds of each cycle, except those immediately overlying the Belperlawn Coal, are normally mudstones with Lingula mytilloides and, frequently, mussels. Fish debris which occurs in the roof measures of the Belperlawn Coal and is intermittently recorded from the remaining cycles tends to be associated with, or replaces, the Lingula bands. Mussels are very rare in the cycle above the Second Smalley Coal and there is no record within this district of the mussels described from the Yorkshire equivalent of the roof of the Belperlawn seam. The distinctive mussel fauna of this sequence hail been described by Eager (1952, 1954) and by Smith and others (1967, 1973), In Denby (Drury-Lowe) Colliery Underground Borehole it includes Carbonicola haberghamensis above the Holbrook Coal and C. decliata, C. fallax, C. limax and Curvirimula sp. together with Geisina arcuate above the First Smalley Coal.

Each cycle contains variable amounts of sandstone and siltstone, and ganisteroid sandstone seatearths frequently underlie the coals. Sandstone in the uppermost cycle has been called the Sub-Alton Sandstone by Smith and others (1967, p. 105). The lithologies and faunas observed at most localities within the district are shown diagrammatically in (Figure 14) and by Eden (1954, pl. 2A) and sections near Ambergate and Holbrook are described in Appendix 2.

The Holbrook Coal is impersistent, ranging in thickness up to 14 in (of shaly coal) in Manners Colliery Borehole. It is only 4 on thick at Browns Road Site near Holbrook in the west (Eden 1954. p. 89) and is represented only by seatearth at, for instance, Moor Farm Borehole. Twin seatearths however separated by 6 ft of sandstone and siltstone in Fritchley No. 1 Borehole and 'sandstone with dark markings' 18 ft above the Belperlawn Coal. Bailey Brook Colliery Drift further illustrate the variable nature of this horizon. Eden (1954, p. 87) also observed a non-sequence cutting out a 2-in coal (probably the Holbrook) lying 8 ft above the Belperlawn Coal on part of Ridgeway Site.

The Second Smalley Coal is a variable seam up to 18 in thick and composed of coal and batt in Smalley Mill Well (Gibson and others 1908, p. 74); more usually it is less than 10 in thick (Figure 14). It may also be composed of split thin coals such as in Mapperley Colliery Underground Borehole where the downwards sequence is coals0.5 in seatearth and mudstone 17.5 in, coal 3 on or it may be represented by seatearth only.

The First Smalley Coal where developed as a single seam ranges in thickness up to 29 in (of shaly coal at West Hallam Colliery Borehole), but over parts of the district the seam consists of two coal leaves separated by sandstone (Figs. 14, 67). tn Smalley Mill Well (Gibson and others 1908, p, 74) for instance, the whole was 3 ft 11 in thick and included a 1-ft rock parting.

The Sub-Alton Sandstone is an impersistent sandstone lying in the uppermost cycle of these measures. In the west it becomes important on part of Portway Site where, on the evidence of a few boreholes, it is united with or rests upon the Crawshaw Sandstone with none of the intervening coals proved. The sandstone–siltstone sequence between the Belperlawn and Alton coals at Trowell Moor Colliery Underground Borehole and in Moor Farm Borehole where it is faulted against the Holbrook horizon are considered to be this sandstone (Figure 14). It is less certainly recognised at Foreclose Farm and Farlawn sites near Belper where, as in other opencast sites, the thin coals are difficult to correlate because of splits and non-sequences.

The Alton Coal

The Alton Coal is only 10 in thick in Fritchley No. 1 Borehole (on Chestnut Site) and also near Heanor (Bailey Brook Colliery Drift) but ranges up to 54 in at Ridgeway and Spanker sites near Ambergate. The isopachs shown in (Figure 15) represent only a regional tendency and exclude abrupt local variations in thickness; for instance other recordings on Chestnut Site range up to 31 in. The quality of the coal is good to medium with variable ash and high to very high sulphur contents; the latter originate from the many pyritised fusain partings.

The seatearth has been worked for ganister at Wingfield Park [SK 3700 5370] and for fireclay at Sawmill [SK 3625 5195]. The coal, ranging from 30 to 45 in on thickness, has been extensively worked by underground and opencast means in the area east of Belper. It has also been worked at outcrop at Rykneld Covert Site [SK 387 430] near Brackley Gate and in the south-east of the district at Beal Site, where the thickness varied between 33 and 36..

Away from the outcrop the Alton Coal was recorded as 27 and 36 in in the uncored Ironville Nos. 3 and 1 oil bores respectively. It is thin near Fleenor, where 16 in of coal were encountered in New Langley Colliery Borehole; in Beechdale Road Borehole only a trace of coal was recorded, but a maximum thickness of 41 in was proved in Trowell Moor Colliery Underground Borehole. A 10-in'smut or coal'at 1721 ft 1 in in Wollaton Colliery No. 3 Shaft Boring is only doubtfully correlated with the Alton. In concealed measures along the southern margin of the district A Dale Abbey No. 2 Borehole, the coal was 39 in thick at 227 ft.

A motorway proving hole [SK 4764 3789] showed 27 in of coal underlain by light grey mudstone seatearth with ganister at the base.

The measures between the Alton Coal and Forty-Yards Coal

The measures between the Alton and Forty-Yards Coals (Figure 16) vary between 59 and 112 ft on thickness and, as described by Eden (1954), are composed of two cycles. The lower, 16 to 39 ft thick, commences with the Alton Marine Band and is largely argillaceous with significant sandstone or siltstone beds only in Bondland Colliery Shaft, Wiremill Bridge Borehole and also, probably, at Stanton Sinking, where all but 5 ft of the 87 ft of these measures are recorded arerock'or 'stone bind'. A 2-in seatearth at the top of the lower cycle has been recorded in Wiremill Bridge Borehole; elsewhere the base of the upper cycle can be recognised only by the presence of the Parkhouse Marine Band. The upper cycle, which is 43 to 96 ft thick, with variable thicknesses of sandstone and siltstone comprising the Loxley Edge Rock near the top, is capped by the seatearth or ganiater below the Forty-Yards Coal.

The Alton Marine Band directly overlies the Alton Coal except in New Langley Colliery Borehole (see below) and consists of fosailiferous dark grey pyritous anales with'bullions'of ironstone containing uncrushed goniatites. It is only a few inches thick in the Denby (Drury-Lowe) Colliery district, but reaches 7 ft 10 in in Beechdale Road Borehole. In the thicker sequences the marine band is split (Eden 1954), the upper part consisting of dark mudstones with Lingula sp. and microfosslls which may be separated from the lower part by up to 3 ft 8 in of mudstone without marine fossils, as in Beechdale Road Borehole.

The marine band was first noted in the Ambergate area by Wedd (1903, p. 12) and described, but not named, by Gibson and others (1908, pp. 64–67, 100, 185). The fauna includes Dunbarella papyracea, Posidonia gibsoni, Caneyella multirugata, turreted gastropods, Anthracoceratites sp., Gastrioceras listeri, orthocone nautiloid, Hindeodella sp. and fish remains.

There are no in situ exposures, but tips near Sawmill [SK 3630 5195], Ridgeway [SK 3617 5142] and Denby (Drury-Lowe) Colliery Engine Pit [SK 3836 4734] and slipped debris on Rykneld Covert Site near Brackley Gate [SK 3915 4294] contain fossiliferous shales and bullions. Detailed provings of the marine band are as follows:

Wiremill Bridge Borehole, 5 in; Fritchley No, 1 Borehole, 6 ft 2 in; Bondland Colliery Shaft, 2 ft 1 in; Ridgeway Site and vicinity, 5 ft; Colliers' Rest Borehole, 4 in; Denby (Drury-Lowe) Colliery Kilburn Shaft, thin; Denby (Drury-Lowe) Colliery Underground Borehole, 8 in (see Eden 1954, p. 93 for details); Rykneld Covert Site near Brackley Gate, 4 ft (see Appendix 2); Park Brook Borehole, 6 ft 10 in; Mapperley Colliery Underground Borehole, 4 ft 3 in including 2 ft of shale between the two parts (see Eden 1954, p. 93 for details); Coppice Colliery Underground Borehole, 3 ft; New Langley Colliery Borehole, 4 ft 3 in including 9 in of siltstone between the marine band and the coal; Bailey Brook Colliery Drift, 1 in; West Hallam Colliery Borehole, 1 ft 5 in; Manners Colliery Borehole, 2 ft 7 in; Oakwell Colliery Staple Pit, 1 ft 4 in (Vernon 1909, p. 295); Moor Farm Borehole, 7 ft 8 in, including 2 ft 5 in between the upper and lower parts; Beechdale Road Borehole, 7 ft 10 in. including 3 ft 8 in between the upper and lower parts; and a motorway proving east of Stanton [SK 4764 3789], 9 in. Twin peaks on the gamma log of Stapleford No. 1 Oil Bore represent the bipartite nature of the marine band and spot cores yielded Lingula sp. and fish debris. A gamma 'high' at about 1180 ft in Ironville No. 3 Oil Bore is also correlated with this marine band.

Fish debris occurs in the mudstones above the marine band and mussels (Eden 1954, pp. 94, 100) have been recorded in Denby (Drury-Lowe) Colliery Underground Borehole, New Langley Colliery Borehole, Beechdale Road Borehole, Manners Colliery Borehole and, abundantly, in Coppice Colliery Underground Borehole. At Denby Carbonicola prisca and palaeoniscid scales occurred and at Coppice Curvirimula belgica, Geisina arcuata and Rhadinichthys sp. were present with Carbonicola prisca. Examples of the latter species were described and figured by Eager (1954, pp. 60–61; 1956, p. 345) who noted its value as a horizon marker.

A sandstone 25 ft thick, lying close above the Alton Coal, forms a feature in Wingfield Park and in the Nether Heage area [SK 3620 5100].

The Upper and Lower Parkhouse marine bands occur at the base of the uppermost cycle below the Forty-Yards Coal and yield Ammodiscus sp., Glomospira sp., Lingula mytilloides and fish remains. Over parts of the Derby district only one bend is present. At Wiremill Bridge Borehole in the north of the district 4 ft of dark silty mudstone, with fish and mussels, separate the seatearth at the top of the lower cycle from further mudstones containing two thin Lingula bands, 1 ft apart; presumably these are the Upper and Lower Parkhouse marine bands.

A gamma 'high' at 1147 ft in Ironville No. 3 Oil Bore is correlated with this marine band. In Collier's Rest Borehole there was only one 6-in band with Lingula and 'Estheria' (note also Eden 1954, p. 95), some 16 ft above the Alton Coal. In Denby (Drury-Lowe) Colliery Underground Borehole the Lower Parkhouse Marine Band lies 17 ft above the Alton Coal and contains Lingula at three levels within 7 ft 6 in of shale and siltstone (Eden 1954, p. 94): the Upper Parkhouse Marine Band, consisting of 2 ft 9 in of carbonaceous shale with Lingula, lies 49 ft 4 in above the Alton Coal.

Mr R.A. Eden (1954, p. 95) found a micro-fauna 16 ft above the Alton Coal and 'Estheria' in a 2-in ironstone band some 18 in higher at Rykneld Covert Site. Lingula, was found at Mapperley Colliery Underground Borehole, in a 19-in band within dark shale, 25 ft 6 in above the Alton Coal and in 5 ft 11 in of pyritous mudstones, 27 ft 11 in above this coal in Coppice Colliery Underground Borehole. Two bands of black mudstone with Lingula, separated by 9 in of micaceous mudstone, lie 25 ft 2 in above the Alton Coal in New Langley Colliery Borehole, and two bands, 3 ft apart within grey mudstone, lie 26 ft 10 in above the Alton Coal in Manners Colliery Borehole.

In Moor Farm Borehole, Lingula is present through 1 ft 4 in of the Lower Parkhouse Marine Band 27 ft 5 in above the Alton Coal, and in two thin beds 4 ft 4 in apart, representing the Upper Parkhouse Marine Band 39 ft 5 in above the coal. Both bands lie within grey mudstone with ironstone bands and minute pyritic nodules and 'tubes', In Beechdale Road Borehole the marine bands are apparently united to form a single 3 ft 8 in band within grey mudstone some 27 ft 4 in above the Alton Coal.

The mudstones between the Parkhouse Marine Band and the Loxley Edge Rock contain sporadic fish remains and mussels.

The Loxley Edge Rock comprises a fine micaceous sandstone with siltstone and mudstone partings, variable in thickness, lying in the upper part of the cycle which commences with the Parkhouse Marine Band (Eden 1954). The sandstone exceeds 30 ft only in New Langley Colliery Borehole and Stanton Sinking. The rock was absent in the Denby (Drury-Lowe) Colliery Underground Borehole, Dale Abbey No. 2 Borehole and from one of the records of the Smalley Mill Well. East of Belper the Loxley Edge Rock forms a topographic feature which appears to merge locally with that of a sandstone close above the Alton Coal within Whitemoor Site and near Holbrook; it forms a gentle feature between Dale and Stanton; in a motorway borehole [SK 4779 3798] it consisted of 20 ft of massive, light grey, fine-grained micaceous sandstone with carbonaceous partings.

The Forty-Yards Coal

The Forty-Yards Coal commonly comprises two thin seams separated by up to 15 ft of measures, which consist largely of seatearth, but may include mudstone, siltstone, sandstone and ganister. Most records of ganister, however, come from below the lower leaf of the seam. This lower leaf is the least persistent and is represented solely by seatearth or ganister in Denby (Drury-Lowe) Colliery Underground Borehole, New Langley Colliery Borehole and Stanton Sinking. In those sequences where only one leaf of coal and seatearth are recorded, the rock succession and interval to the Alton Coal indicate that it is the lower leaf which is missing.

At Stanton Sinking the split is threefold with the lowest leaf represented by 1 ft 3 in of ganister; a 6-in coal lies 7 ft above and a 12-in coal a further 8 ft 9 in higher in the sequence.

The thickness of coal quoted for Stanton Sinking are near average for the district and the seam is therefore not of economic importance. The lower leaf has a maximum proved thickness of 27 in in Dale Abbey No. 2 Borehole. The upper leaf, contains dirt partings, 2.5 in thick, in an over-all 21 in of coal and 'batt' in Denby (Drury-Lowe) Colliery Kilburn Shaft and 6 in of dirt within an over-all 16-in in Dale Abbey No. 3 Borehole.

Old ganister pits [SK 3710 5310] and [SK 3660 5248], now overgrown, occur south and east of Beech Hill Farm where dip and slope coincide and shallots workings are extensive. Some 9 in of 'smut' were recorded in a trench near Beech Hill Farm [SK 3721 5315], and 8 in of 'smutty' coal on 14 in of ganister were proved at Chestnut Site. Old opencast workings in Wingfield Park [SK 3720 5366] proved 6 in of coal overlying 4 in of ganister, on fireclay.

Wedd (in Gibson and others 1908, p. 75 and ms. map) recorded 12 in of coal, probably the Forty-Yards, in a temporary section near Holbrook [SK 3697 4489], and in a drive cutting east of Brackley Gate [SK 3934 4279] the coal is 7 in thick, overlain by 3 in of black canneloid mudstone and underlain by 2 to 3 in of silty mudstone resting on ganisteroid sandstone.

The measures between the Forty-Yards Coal and Norton Coal

The measures between the Forty-Yards and Norton Coals comprise one cycle normally about 30 ft thick, but ranging from 18 ft in Bondland Colliery Shaft to 39 ft in Trowell Moor Colliery Shaft. The cycle consists largely of mudstone with ironstone bands and nodules (the 'Dale Moor Rake' of Smyth 1856, p. 59) and is now marked by extensive old excavations at outcrop near Stanton Ironworks [SK 4630 3880]. Fish remains are plentiful (see Gibson and others 1908, p. 101) and include Diplodus sp. Elonichthys sp., Rhabdoderma sp. and Rhizodopsis sp. The arenaceous part of the cycle is thin and impersistent, but the seatearth at the top is up to 14 ft thick.

At the base of the cycle the Forty-Yards Marine Band (Smith and others 1967, p. 114), containing Ammodiscus sp, Lingula mytilloides, Hindeodella sp., Elonichthys aitkeni and an acanthodian spine has been found in the following boreholes, Denby (Drury-Lowe) Colliery Underground (1 in thick); Mapperley Colliery Underground (1 in); Coppice Colliery Underground (3 ft 1 in); New Langley Colliery (3 in); West Hallam Colliery (trace); Manners Colliery (trace); Moor Farm (0.5 in); and Beechdale Road (5 ft 4 in).

The non-marine mudstones of this cycle contain fish and plant debris.

The Norton Coal

The Norton Coal which varies in thickness from 27 in in Little Hallam Water Borehole and Stanton Sinking to 3 in in Beechdale Road Borehole, has only been worked in the south of the coalfield, near Stanton Gate (Gibson and others 1908, p. 68).

In the north, in Wiremill Bridge Borehole, the section consists of 8 in of camel on 22 in of coal. Other records are; Bondland Colliery, 19 in of coal; Ridgeway Site, 22 in of bright coal containing dirt partings in the uppermost 3.5 in and a 1-in fusain parting. A coal presumed to be the Norton, varying between 5.5 and 10.5 in is exposed in the cutting of the Ambergate–Ironville Railway on either side of the tunnel [SK 3710 5300] south-east of Beech Hill Farm. Poorly exposed dark shales overlie the seam and it is underlain by fireclay with lenses of ganister up to 12 in thick. Trenches nearby [SK 3728 5311] showed 13 in of coal underlain by pale grey ganister.

In Denby (Drury-Lowe) Colliery Kilburn Shaft the Norton Coal is 20 to 22 in thick plus 1 to 3 in of 'batt' in the roof. Other records are Colliers' Rest Borehole, 26.5 in; Denby (Drury-Lowe) Colliery Underground Borehole, 16 in; Smalley Mill Well, 3 in or 22 in according to different records; Mapperley Colliery Underground Borehole, 6 in. In five provings near Heanor and Ilkeston the Norton Coal is 16 to 19 in thick and it is 21 to 27 in in deep mine provings in the south-east of the coalfield; with the exception of Wollaton Colliery No. 3 Shaft, where a seatearth at 1651 ft 4 in depth is assigned to the Norton horizon. The coal has been proved to be up to 26 in thick in opencast boreholes on Dale Moor Site and 17 in along the line of the motorway [SK 4799 3798], east of Stanton.

The Measures between the Norton Coal and the Upper Band

The Measures between the Norton Coal and the Upper Band horizon form an argillaceous sequence ranging from 25 ft to 53 ft in thickness in Beechdale Road and Wiremill Bridge boreholes respectively. The sequence is composed of up to two cycles although the evidence for this division has been found only in Denby (Drury-Lowe) Colliery Underground Borehole, Beechdale Road Borehole and Bailey Brook Colliery Drift (Figure 16).

The Norton Marine Band, at or very close to the base of the sequence, consists of a thin bed containing Ammodiscus sp., Glomospira sp, Lingula mytilloides, and a conodont assemblage including Hindeodella sp. and platforrned conodonts lying within pyritous shale in Denby (Drury-Lowe) Colliery and Mapperley Colliery Underground boreholes. In Coppice Colliery Underground Borehole the band, 1 ft 11 in thick, includes terebelloid worm tubes, Danbarella aff, papyracea, Caneyella aff. multirugata, the conodont Ozarkodina sp., and Elonichthys The overlying mudstone and silty mudstones contain fish debris, plants and the Norton Mussel-band (Eden 1954, p. 97; Eager 1956, 1962). The mussels are commonly preserved in calcitic material over a thickness of 5 to 20 ft, and comprise Carbonicola crisps, C. proxima, Curvirimula belgica and Naiadites sp., in association with Geisina arcuate, Rhabdoderma sp. Rhadinichthys sp., and Rhizodopsis sp. The mussels were exceptionally well preserved in Mapperley Colliery Underground Borehole and the holotypes of both C. crispa Eager and C. proxima Eager came from this borehole. The mussel-band is absent in Moor Farm and Beechdale Road boreholes. A seatearth, its top 28 ft 3 in above the Norton Coal, divides these measures in Denby (Drury-Lowe) Colliery Underground Borehole. The seatearth by near the base of the mussel band and contained Carbonicola cf. extenuate, Curvirimula, Geisina sp., and Rhadinichthys sp. (Eden 1954, p. 97). The equivalent seatearth in Beechdale Road Borehole is separated from the seatearth at the summit of the upper cycle by only 2 ft 6 in of dark grey silty mudstone with green Mottling.

Seatearth up to 12 ft thick marks the top of these measures, the Upper Band Coal being absent from every proving although coaly traces seen at the surface [SK 3641 4745] east of Belper may have come from this horizon.

The Measures between the Upper Band Horizon and Kilburn Coal

The Measures between the Upper Band Horizon and Kilburn Coal range in thickness from 306 ft in Trowell Moor Colliery Shaft to 395 ft in Denby (Drury-Lowe) Colliery Kilburn Shaft, and consist of two cycles. The lower thicker cycle, much of it sandstone, extends up to a seatearth lying some 20 to 60 ft below the Kilburn Coal. The upper cycle, largely argillaceous, extends from the top of this seatearth to the top of the Kilburn Coal.

Arenaceous measures of both cycles are assigned to the Wingfield Flags, although their main sequence lies in the upper part of the lower cycle.

The Burton Joyce Marine Band (Smith and others 1967, p. 116), which is present about 25 ft above the Upper Band seatearth in the Chesterfield and Nottingham districts, has not been proved within this district.

The Upper Band Marine Band is known only from New Langley Colliery Borehole, the type locality (Godwin 1960, p. 33; Calver 1968b, p. 34). It consists of dark mudstones with Ammodiscus sp Lingula mytilloides, and abundant fish remains including Elonichthys sp. The principal horizon with Lingula was 4 ft 6 in above the Upper Band seatearth. Fucoids only were recorded from this horizon in Wiremill Bridge Borehole.

Up to 195 ft of mudstones separate the Upper Band seatearth and the Wingfield Flags. The mudstones are dark and pyritous in the lowest 30 to 40 ft, suggestive of near-marine conditions; fish debris is plentiful and includes Elonichthys sp., Megalichthys sp., Rhabdoderma sp., and Rhadinichthys sp., while Carbonicola sp., and Naiadites sp. are also present. The upper part of the mudstone (with Carbonicola cf. subconstricta in Denby (Drury-Lowe) Colliery Underground Borehole) is interbedded with silty mudstones and passes gradually upwards into the Wingfield Flags. Ironstones are present which, together with those in the Norton-Upper Band cycle, form the Civilly Rake of Smyth (1856, p. 39). Fossils in the upper cycle include Carbonicola sp., Geisina arcuate and fish remains including Rhadihichthys sp., and an acanthodian spine.

The Wingfield Flags are a sequence of pale grey flaggy sandstones, siltstones and silty mudstones in variable proportions up to about 200 ft in thickness. This account is largely concerned with their outcrop while (Figure 68) depicts them in boreholes and shafts.

The Wingfield Flags form the first Marked feature in the Westphalian rocks above the Crawshaw Sandstone. On the east bank of the River Amber, near Amberley Farm, a trench temporarily exposed 40 ft of brown fine-grained sandstone dipping to the south-east at 10 to 20°. Up to 20 ft of finely laminated sandstone are sporadically exposed near Lodge Hill Farm [SK 3717 5274], where the Wingfield Flags feature is split into a main scarp below and a smaller scarp above.

In the railway cutting at Buckland Hollow Branch Junction [SK 370 520] over 70 ft of brown fine-grained sandstone are excellently exposed. The overall massive bedding is split up into 2-foot 'posts' containing a finer lamination which weathers into typical 'flags'. The base of the math body of sandstone is irregular, and sandstone balls completely enclosed within the underlying silty shales suggest slumping,

The sandstone is commonly cross-bedded and an exposure in Graves Wood [SK 3684 5151] suggests a current direction from the south-east. North of Heage, 10-ft lenses of sandstone are common at the top of the Wingfield Flags and increase in importance northwards. South of Heage shale separates the Flags into two halves, but there is a single marked escarpment as far south as Morrel Wood Farm [SK 3722 4830]. There, shale 'slacks' separate the upper leaf of sandstone from lower sandstones which increase in thickness southwards. Some 5 ft of laminated fine sandstone is exposed in the roadside at Openwoodgate [SK 3682 4739].

In the Stanton district temporary excavations for the 'Ironwork' [SK 4675 3909] exposed 11 ft of brown fine-grained sandstone, foggy at the top, and showing sporadic purple staining.

The top of the lower cycle is marked by a this seatearth which, although not proved at outcrop, is present in most boreholes. A 3-in 'batt' in Bailey Brook Colliery Drift and a 3-in coal in Annesley Colliery (Deep Hard) Underground Borehole are the only records of coal at this horizon.

The upper cycle, normally 45 to 80 ft thick, includes part of the Wingfield Flags, but consists largely of dark grey to black mudstones with ironstones; fish debris and ostracods have been recorded and mussels are common. The presence of the fauna serves to identify the cycle in sections such as Moor Farm Borehole where the underlying seatearth is missing. Sandstones tend to be this except in Selston Colliery Staple Pit and Underground Borehole, where they lie close below the Kilburn Coal and apparently continue downwards into the math body of Wingfield Flags.

Beechdale Road Borehole the upper cycle is abnormally thick, comprising 125 ft of largely arenaceous strata.

Kilburn Coal to Threequarters Coal

The measures between the Kilburn and Threequarters coals (Figure17) and (Figure 18) are thickest in the north, where they reach a maximum of 661 ft in Pinxton Colliery No. 2 Shaft. They exceed 600 ft near Stanley and Mapperley collieries in the south-west of the district and in an isolated area near Cossall Colliery. Eastwards and south-eastwards they thin to about 550 ft at Trowell Moor Colliery, 489 ft in Beechdale Road Borehole and 486 ft in Annethey (Deep Hard) Underground Borehole. The sequence includes the Kilburn Coal, which was extensively worked for house coal, and other important seams are the 'Ashgate', Blackshale, Yard and Threequarters. With the exception of the Yard and Blackshale, the coals tend to thin in an easterly direction.

The fauna of the measures consists largely of mussels of the Carbonicola pseudorobusta group, with fish debris present in the roofs of the coals up to and including the Mickley Thin; marine fossils are unknown in this district.

The Kilburn Coal

The Kilburn Coal ranges from 30 to over 70 in in thickness in the south-western part of the exposed field, but in the north-east it is thin (Figure 19). The maximum proved thicknesses are at outcrop in the south-west, where 76.5 in of coal (including 5.5 in of dirt) and 74 in of coal were recorded in Hollies Farm and Mary sites respectively. The seam is composed predominantly of bright coal with subordinate dull bands, and is of good to medium quality with a low to moderate ash content. Much in demand for house coal, it was originally one of the more important worked seams of the coalfield and one of the first to be exhausted by underground workings. The top and bottom parts of the seam are frequently recorded as inferior coal (Figure 19). In the north-west a floor coal included in the seam section has a distribution approximately complimentary to that of the uppermost cycle within the Wingfield Flags. In Moor Farm Borehole the seam was split.

The measures between the Kilburn Coal and Mickley Thin Coal

The measures between the Kilburn and Mickley Thin Coals range in thickness from 198 ft in Moorgreen Loco–Road Underground Borehole to 288 ft in Swanwick No. 1 Underground Borehole (Figure 20) and are composed of five main cycles. To the south-east of an irregular line from Swanwick to Stapleford the lowest cycle can be identified only by the presence of arenaceous measures at its top. Each cycle locally includes coal, but the seams are thin or of poor quality and have little economic value. The cyclic sequence of these measures is relatively uniform throughout the district except in the two Ironville oil bores and Moorgreen Loco-Road Underground Borehole. The latter encountered additional seatearths, interpreted as splits of the two cycles above the Morley Muck coal.

Gibson and others (1908, p. 101) have described the fish remains in dark grey mudstones within the roof measures of the Kilburn Coal at Denby (Drury-Lowe) Colliery, and similar remains have since been proved locally throughout the district with scales of Strepsodus sp. present in Eastwood Hall Borehole. The fish remains are sometimes associated with cf. Planolites, but Lingula, known to the north (Smith and others 1967, p. 121), has not been found.

Sandstones are present, in variable proportions and at various levels. They form the 'Kilburn Rock' of Gibson and others (1908, p. 70) in all recordings of the measures below the Morley Muck except New Langley Colliery Borehole, Little Hallam Water Borehole, Lodge Colliery Shaft, and Beechdale Road Borehole. The sandstones are generally thicker in the south-west of the coalfield, where the thin coal and seatearth of the lowest cycle is absent; even here, however, the sequence up to the Morley Muck Coal commonly displays sandstones at two distinct levels. These latter sandstones form a minor escarpment feature in the west, at the lower limits of the dip-slope of the Wingfield Flags, but they are less important in the south of the coalfield. Sections of the overburden of the Kilburn Coal near Rowson Green and Stanley are described in Appendix 2.

The lowest cycle, found only to the north-east of the district, ranges from 25 to 80 ft in thickness, its top commonly formed by a seatearth; coal is sporadically recorded as follows: Pinxton Colliery No. 2 Shaft, 12 in; Swanwick Colliery No. 1 Underground Borehole, 11 in; Bailey Brook Colliery Shaft, 3 in batt; Lodge Colliery Shaft, 5 in; Cossall Colliery No. 2 Shaft, trace; Trowell Moor Colliery Shafts, 27 to 30 in; Moor Farm Borehole, 1 in; Beechdale Road Borehole, 7 in; Wollaton Colliery No. 3 Shaft, 2 inbatt. In Annesley Colliery (Deep Hard) Underground Borehole, where the coal and seatearth are missing, the presence of two cycles up to the Morley Muck Coal is revealed only by the sandstones. The upper cycle at Eastwood Hall Borehole is predominately arenaceous but Spirorbis sp. Carbonicola cf. browni and C. cf. pseudorobusta, Curvirimula subovata, Carbonita humilis, C. pungens, and fish remains were present in interbedded rnudstone and siltstone.

The Morley Muck Coal may contain over 50 in of coal in up to three leaves of poor to very inferior quality; the seam is therefore of no economic value. The coal or its seatearth lies between 50 and 130 ft above the Kilburn Coal. In the north and north-east of the district it is up to 11 in thick, including 2.5 and 4 in of cannel in its roof in Cotespark No. 3 Underground Borehole and Birchwood Colliery Upcast Shaft respectively. Near Denby the 59 in of 'Batty Coal' recorded from the Denby Hall Colliery Shaft is the thickest single record of the district; a more typical sequence to Denby Colliery, New Winnings Shaft, comprises coal 3 in, dirt 3 in, coal 9 in on 'Batty Coal and Clunch' 19 in. At Rowson–Ireton Site the 19 in of coal included 4.5 in of dirt. Two leaves of the seam are exposed in the clay pit at Rowson Green [SK 3751 4688], where the roof measures contain fine specimens of Carbonicola pseudorobusta. The section is:

The full three-leaf sequence is present between Mapperley and Trowell Moor collieries, but near Heanor this sequence is reduced.

The cycle overlying the Morley Muck Coal varies from 36 ft in Stoneyford Borehole to 56 ft in Denby Colliery, New Winnings Shaft. The coal, cannel or seatearth at the top can be recognised in many provings throughout the district; the coal is unnamed and discounting a dubious record of 24 in in the chipped Ironville No. 1 Oil Bore, it has a maximum thickness of 10 in in Stanley Colliery Shaft. It is absent over wide areas in the east and north. The cycle includes up to about 50 ft of arenaceous measures, with Spirorbis sp., Carbonicola cf. polmontensis, C. pseudorobusta, Curvirimula sp., Geisina arcuata and fish remains including Rhabdoderma sp. in the underlying argillaceous bans above the Morley Muck Coal.

The succeeding cycle, ranging in thickness from 25 ft in New Langley Borehole to 50 ft in Little Hallam Water Bore, is also widely recognised and has the Lower Brampton Coal at its top. Sandstones are less prominent than in the underlying cycle and the mussels less abundant.

The Lower Brampton Coal (Smith and others 1967. p. 121) has a maximum thickness of 21 in including 12 in of cannel in Denby (Drury-Lowe) Colliery Shaft and, on the evidence of an analysis taken in the nearby Morrells Wood Site, is of very poor quality. Provings between Mapperley and West Hallam collieries show this seam to be split into two very thin leaves, each under 9 in thick, up to 63 in apart. The upper leaf is locally canneloid. In the north of the district the Lower Brampton is under 4 in thick; it is absent in the east and 9 to 12 in thick in the south-east.

The remaining cycle, that with the Mickley Thin Coal at the top, ranges in thickness from 46 ft in Eastwood Hall Borehole to 67 ft in Denby (Drury-Lowe) Colliery Shaft and is almost wholly composed of argillaceous strata, locally bearing a mussel fauna; at Eastwood Hall Borehole Carbonicola sp. and Curvirimula subovata were recorded. Sandstones are only a few feet thick in the floor measures of the coal.

The Mickley Thin (or Upper Brampton) Coal

The Mickley Thin (or Upper Brampton) Coal is thickest at Morrells Wood Site, where 20 in were recorded. As at Chalfont Site (19 in) and Beechdale Road Borehole (3 in) the coal is of good to moderate quality, but it deteriorates to poor in two analyses from Moses Lane Site (9 to 12 in). The thickness is 18 in or less in the remaining provings within the district, the thinnest recordings being to the east. The coal is exposed in the clay pit near Rowson Green [SK 3783 4725] (see Appendix 2). Washouts, which also affect the Blackshale group of coals, were encountered in Eastwood Colliery and Lodge Colliery shafts. This coal is the same as the ?Mickley Thin Coal of the Chesterfield area which Smith and others (1967, p. 122) found difficult to correlate with the Mickley Thin of the Sheffield area.

The measures between the Mickley Thin Coal and 'Ashgate' Coal

The measures between the Mickley Thin and 'Ashgate' Coals form one cycle ranging from 41 ft in Cotespark No. 2 Underground Borehole to 68 ft in Pinxton Colliery No. 2 Shaft. The roof measures of the Mickley Thin contain fish, ostracods and sporadic mussels. A section near Howson Green is descfibed in Appendix 2.

The 'Ashgate' Coal

The 'Ashgate' Coal (Figure 69) consists of two leaves of coal throughout most of this district. The upper and lower leaves were originally called the Ashgate and Mickley coals respectively and they have been extensively worked underground near Denby. Heanor and Trowell Moor under these names. The seam is not the correlative of the Ashgate Coal of the Chesterfield district, which lies slightly higher in the sequence; instead the two leaves of the "Ashgate" Coal of the present district are equivalent to the two thin coals present above the ?Mickley Thin Coal in C otespark No. 1 Underground Borehole (Smith and others 1967, fig. III, p. 119).

At Starvehimvalley Site and in the area between Denby and Heanor the two leaves lie close together, while in Awsworth Colliery Shaft they are combined with a total thickness of 81 in, the thickest known section in the district. The two leaves divide rapidly from the Heanor area to the north, west and south, with a maximum known separation of 62 ft 2 in in Mapperley Colliery shafts. The leaves are close together again at outcrop between Horsley Woodhouse and Morley Hayes Site and near Trowell Moor Colliery and were exposed, some 3 ft apart, in motorway cuttings near Trowell, a separation which is maintained until their outcrop is concealed beneath Permo-Triassic rocks near Stapleford.

A sinuous belt of sandstone which affects the 'Ashgate' Coal extends from north-east of Eastwood to Ilkeston and thence south-east towards Wollaton. It probably represents a major watercourse along which coarse material was transported into the district and which widened and became increasingly active during deposition of the upper leaf of the seam. As a result the lower leaf of the coal is apparently cut out over a restricted area of this watercourse, and in Cossall Colliery Shaft, Moor Farm Borehole and Wollaton Colliery Shaft this erosion removed measures almost down to the horizon of the Mickley Thin Coal and has even removed this coal in Eastwood No. 3 and Lodge Colliery shafts. Deposition along the watercourse affected the formation of the upper leaf of the 'Ashgate' over a wider area than the lower leaf. Where the two leaves are separated the intervening measures are sandstone except in the area between Heage and Horsley Woodhouse. The coal of the upper leaf as it 'rides' the sandstone tends to die away to cannel or is represented only by its seatearth. Sandstone is also widely distributed in the roof measures of the coal and its deposition continued so as to affect the formation of the overlying Blackshale group of coals.

The provings of sandstone in the watercourse and the first underlying recognisable horizon at each are as follows: Eastwood Hall Borehole, lower leaf of 'Ashgate' Coal present; Moorgreen Loco Road Underground Borehole, seatearth of lower leaf preserved; Eastwood Colliery No. 3 Shaft and Lodge Colliery Shaft, extends to below Mickley Thin horizon; West Hallam Borehole and Colliery Shaft, lower leaf of 'Ashgate' Coal present (as cannel); Kimberley Colliery Shaft, lower leaf of 'Ashgate' Coal present; Cossall Colliery Shaft, Moor Farm Borehole and Wollaton Colliery Shaft, roof measures of Mickley Thin Coal.

The lower leaf of the seam (discounting Awsworth Colliery Shaft, where the distinction between the two leaves fails) is thickest at Avenue Site [SK 401 439], where it includes 41 in of coal. It shows rapid variations in thickness; for instance it ranges from 24 to 36 in at Morley Hayes Site [SK 402 418]. It is 20 to 30 in thick between Heanor and the outcrop in the west, but thins in the northern part of the district, where some provings (Cotespark No. 2 Underground Borehole and Birchwood Upcast Shaft) encountered cannel. Cannel was also present in Stanley Colliery Shaft (18 in), Weet Hallam Borehole (14 in) and West Hallam Colliery Shaft (17 in). To the east of the line of the watercourse the lower leaf was 19 in of coal in Kimberley Colliery Shaft, 4 in at Cinderhill Colliery No. 4 Shaft (where the correlation is doubtful) and at Cossall 40's Underground Rebore (including 2 in of cannel). In Beechdale Road Borehole it is represented by seatearth only and in Annesley (Deep Hard) Underground Borehole by 2 in of coal.

The thickness of the upper leaf is related to the presence of sandstone below and in the roof. Like the lower leaf it shows rapid local variation; at Morrells Wood Site it varies from 14 to 54 in, the latter being the thickest record in the district. It is 20 to 24 in thick near Heanor but thins north-east of that town to 4 in in New Langley Colliery Borehole and 10 in in Ormonde 70's Underground Borehole. In Annesley (Deep Hard) Underground Borehole it is 2 in thick. In the north of the district the upper leaf 'rides' a relatively constant thickness of sandstone and is consistently 9 to 12 in thick except at Cotespark No. 2 Underground Borehole, where it is represented only by seatearth.

Between Horsley Woodhouse and Heage the thickness of the upper leaf varies inversely with the thickness of the measures in the seam split, which in this area contain little sandstone. The great coal thickness at Morrells Wood Site is the notable exception to the above. On part of Bottle Site, between Kilburn and Horsley Woodhouse, the upper leaf is cut out by an overlying sandstone which is widely distributed in the vicinity. South of Horsley Woodhouse the upper leaf varies between 33 and 36 in Gypsy, Avenue and Rose and Crown sites. Farther south, on the evidence of Morley Hayes and Moses Lane sites, the split of the two leaves is again abrupt and the upper leaf has only been proved and worked adjacent to the line of the split. This leaf again 'rides' arenaceous measures and dies away to leave only a seatearth horizon as shown by Stanley Colliery Shaft. It is also probably subject to washouts, which may only be local, at the outcrop from Moses Lane Site to near Trowell Moor Colliery, but it is not known whether the leaf has been eroded as in West Hallam Colliery Shaft and Borehole, or whether it was an area of non-deposition as in Stanley Colliery Shaft. Near Trowell Moor Colliery its thickness in the shafts and in opencast sites varies from 24 to 44 in. It was exposed in an M1 cutting [SK 4857 3912] 800 yd S of Trowell Church, (see Appendix 2) where the washout sandstone cuts down to within 5 ft of the top of the coal.

To the east of the sinuous washout deposits (Figure 69) the leaf is represented only by seatearthe in Cossall 40's Underground Rebore and Beechdale Road Borehole, by 2 in of coal in Cinderhill Colliery No. 4 Shaft, where the correlation is doubtful, and by 5 in and 11 in in Hucknall C's Heading and Math Outbye underground boreholes respectively.

The Measures between the 'Ashgate' Coal and Blackshale Coal

The Measures between the 'Ashgate' and Blackshale Coals are largely arenaceous and range from 60 ft in Pinxton No. 2 Shaft to 146 ft in Stanley Colliery Shaft. They contain up to two main coal horizons, which are probably the representatives of the Ashgate Coal of Smith and others (1967, p. 124). Each coal is itself split into up to three leaves, all thin and of no economic importance; the maximum thickness recorded is 28 in of 'batty coal' in Ormonde Colliery Shaft.

The Blackshale Coal and Yard Coal

The Blackshale and Yard Coals (Figure 21) and (Figure 22) are a complex sequence of up to six main leaves of coal lying within strata varying in thickness from 8 ft in Annesley 204's Underground Borehole to 110 ft in Coppice Colliery No. 2 Shaft. The Blackshale Coal consists of the lowest three main leaves of the sequence plus, in this account, the two overlying leaves here called the upper and lower Denby leaves after their striking development in Denby Hall Colliery Shaft (Figure 22). Where combined or not separately identified they are known as the Denby leaf, The three lowest leaves are the Top Softs, Middle Dirt with Tinkers Coal and Bottom Softs of the old millers' terminology, which together form the Blackshale Coal of the Chesterfield district (Smith and others 1967, p. 125). The Low 'Estheria' Band, which to the north-east occurs above the Bottom Softs (or Low Silkstone) is absent in the Derby district. The sequence of coal leaves appears to be controlled by deposition of sandy and silty measures below, between and above the Denby leaves. As to result the Denby leaves may be associated with the Top Softs or the Yard or may lie in the measures between and widely separated from these seams.

The correlation of the Denby leaves is somewhat arbitrary and there is also the possibility of additional splitting of the base of the Yard Coal, although this appears to be restricted to the area of the underground boreholes at Hucknall and Cinderhill collieries. In this account, however, splitting of the Yard Coal refers to minor splitting of the uppermost of the six leaves of coal of the standard sequence.

The Top Softs–Middle Rirt–Bottom Softs sequence has been extensively mined and the Yard Coal has been worked in the north, where it is thickest. The quality of the coal in all the leaves is extremely variable, but it is rarely better than medium quality, and then only in the Top Softs.

To simplify description of this coal complex, six areas, each containing a different development of the seams, have been selected and are shown in (Figure 21).

Area A is known only from underground provings; all the coal leaves are present in close proximity to form the Yard/Blackshale, a seam which is equivalent or approximates to the Silkstone of Yorkshire. In the table below, Annesley 204's Underground Borehole is an example of a virtually dirt-free sequence while Brookhill 5's section in underground workings shows a more expanded sequence typical of the area margin.

In area B the Yard Coal is thick and separated from the Blackshale Coal, which includes a variable sequence of the Denby leaves and ranges from a total of 65 in including 13 in of dirt (Selston Colliery underground workings) to 155 in including 67 in di, (Denby Hall Colliery underground workings). The Denby leaves were not recorded in Selston B 80's Underground Borehole and Pye Hill–Selston Colliery Drift, where they may be washed out; elsewhere they lie within 23 in of the Top Sofia, but are variable. They are thickest in the west where both leaves are usually present; to the east there is a single thin coal, which is either the lower leaf or represents both leaves. The Denby leaves attain a maximum in a single 54-in coal at Salterwood Site. Measures some 10 ft thick at Selston Colliery No. 1 Drift to 76 ft at Selston Colliery, Brinsley Drift, divide the Denby leaves from the Yard Coal, which itself ranges up to 59 in in thickness at Pye Hill Colliery Shafts.

In areas C and D, the Yard Coal is widely separated from insignificant Denby leaves which in turn are remote from the Top Softs–Middle Dirt–Bottom Softs sequence. In area C the Top Softs–Middle Dirt–Bottom Softs sequence varies between 33 and 54 in of which up to 10 in may be dirt partings; in area D it is generally 40 to 60 in thick with up to 13 in of dirt, but thick sections of 115 in (thcluding 11 dirt) and 99 in (23 dirt) were recorded at Bacon Lane [SK 3835 5293] and Devonshire sites [SK 3785 5182] respectively. These appear to be due to local thickening of the Bottom Solis at Bacon Lane Site and of the Top Softs at Devonshire Site.

In area C the Top Softs are separated from the Denby leaves by mainly arenaceous strata ranging in thickness from 13 ft at Moorgreen Colliery Underground Borehole to 80 ft at Cinderhill 14's Main Gate Underground Borehole. The Denby leaves are represented by seatearths up to 17 ft apart as at Moorgreen Colliery Underground Borehole, but there is only one seatearth in the Cinderhill underground borehole mentioned above. The Yard Coal lying 7 to 13 ft above the Denby leaves is thin with the possible exception of the 45 in of 'Batty Shale' recorded in Moorgreen Main Dips Underground Borehole.

In area D a single Denby leaf was encountered only in Swanwick Colliery New Pit, where 14 in of coal and dirt were encountered 44 ft above the Top Softs. Elsewhere the leaves appear to be absent or unrecorded, but the is a seatearth at this horizon, 15 ft above the Top Softs, in Pinxton Colliery No. 3 Shaft.

The Denby leaves horizon is separated from the Yard Coal by sandy measures ranging in thickness from 7 ft at Swanwick New Pit to 85 ft at Pinxton No. 3 Shaft. The Yard Coal ranges from 17 in in Pinxton Colliery No. 3 Shaft to 38 in in Swanwick Colliery New Pit and has been extensively worked from Cotespark and Pinxton collieries, where analyses show it to be of very variable quality. The splitting from Area A to Area D occurs between the Top Softs and Denby leaf, as demonstrated by the section in Bentinck Colliery Drift, just north of the district boundary, where the Denby leaf lies 32 ft above the Top Softs but is separated from the Yard Coal by only 2 in of dirt. This is followed by further splitting between the Dtnby leaves and the Yard Coal.

The centre line of area E coincides with the greatest thickness of sandy measures which lie between an impoverished Yard Coal and the Top Softs–Middle Dirt–Bottom Softs sequence throughout the area. The Denby leaves are not proved; they may be merged with the Yard Coal or washed out by the sandy measures.

These sandy measures, which probably follow a former watercourse, have cut out all the Top Softs–Middle Dirt–Bottom Softs sequence in Manchester Wood Borehole and parts of that sequence in Woodside No. 1 Underground Borehole. Oakwell Colliery Shaft, and Cinderhill 27's Main Inbye Underground Borehole and perhaps also at Denby Colliery, New Winnings Shaft and Cossall Colliery Shaft. Where wholly represented in the area the Top Softs–Middle Dirt–Bottom Softs sequence varies from 39 in, including 7.5 in dirt, in Cinderhill 6's Main Gate Underground Borehole to 78.5 in, including 26 in of dirt, in Coppice Colliery workings. The sequence was exposed in the motorway cutting near Trowell (Appendix 2). No certain Denby leaves are recorded from within this area except at Pippinhill Site, where some provings show the lower Denby leaf within 18 in of the Top Soft.

The Yard Coal is represented mainly by a seatearth horizon, but up to 12 in of coal have been encountered in West Hallam Colliery Shaft. The Yard horizon was not recorded in Bennerley, Awsworth and Kimberley colliery shafts.

Area F lies south of the thick belt of sandy measures and consequently a variable sequence of the Yard Coal and Denby leaves reappears, mainly in association. Moderately thick measures overlie a variable Top Softs–Middle Dirt Bottom Softs sequence—a feature which, apart from its location on the opposite side of the thick arenaceous measures, distinguishes this area from area C.

The Top Softs–Middle Dirt–Bottom Softs sequence, except in that part of the area near Cinderhill and Hucknall colliery provings, is characterized by an increase in the thickness of dirt partings compared with the rest of the district. The Top Softs of this area do not exceed 33 in and the Bottom Softs 20 in in thickness. The thickest overall sequence of 101 in Stanley Colliery Shaft includes 51 in of dirt and dirty coal while the thinnest, of 48 in in Cinderhill 19's Left Gate Underground Borehole, includes only 7 in of dirt. There is no coal (Tinkers) between the Bottom Softs and Top Softs in Smalley Green Borehole, Cat and Fiddle Site, Bunkerhill Site, and Wollaton Colliery No. 3 Shaft. The thickest dirt, 6 ft 9 in, between the Bottom Softs and Top Softs is found in Smalley Green Borehole.

At Cinderhill Colliery No. 4 Shaft Underground Borehole the Top Softs–Middle Dirt–Bottom Softs sequence is probably washed out and represented by seatearth only. In a small part of the area, near Shortwood and Moor Farm boreholes, this sequence contains up to four thin leaves of coal, none of which exceeds 18 in thickness.

The Denby leaves are 21 ft and 78 ft above the Top Softs in Cossall 40's Underground Borehole (Rebore) and Smalley Green Borehole respectively. They are represented only by a single seatearth or thin coal over much of the area. Exceptions are in Manners Colliery Shaft and Borehole, where the lower of two leaves is 25 and 22 in thick respectively, and between Trowell Site and Wollaton Colliery, where each leaf may exceed 20 in of dirty coal. At Cinderhill 1's Underground Borehole the Denby leaf is only 3 ft 3 in above the Top Softs, an anomalous section for the area.

Measures ranging in thickness from 8 in at Shortwood Borehole to 30 ft in Manners Colliery Shaft separate the Denby leaves from the Yard Coal. The Yard Coal is mainly a single seatearth horizon or very thin coal; however up to three thin leaves have been proved in Moor Farm Borehole.

The Measures between the Yard and Threequarters Coal

The Measures between the Yard and Threequarters Coal range in thickness from 47 ft in the Cinderhill 10's Main Gate Underground Borehole to 123 ft in Mapperley Colliery Shafts and normally form a single cycle containing variable arenaceous and argillaceous strata. Exceptionally, at Stoneyford Borehole, a weak rootlet bed 11 ft above the Yard Coal indicates the presence of a second cycle. This seatearth is perhaps the correlative of one recorded by Edwards (1967, p. 80) in the Ollerton district. The roof of the Yard Coal yields fish and plant debris and more rarely mussels; ironstones higher in the argillaceous measures form, in ascending order, the Striped Rake of Kirk Hallam, Blackshale Rake and Nodule Rake of the Morley Park district (Smyth 1856, p. 38). The overlying sandstone is the 'Silkstone Rock' of the country to the north of this district, but it forms prominent ground features only near Smalley; elsewhere it is subordinate to those of the unnamed rocks which lie between the 'Ashgate' and Blackshale coals and between the Blackshale and Yard coals.

The Threequarters (Tupton Three-Quarters or Dogtooth) Coal

The Threequarters (Tupton Three-Quarters or Dogtooth) Coal ranges in thickness from 3 to 4 in in Trowell Moor Colliery Shaft to 49 in at Salterwood Site. These figures exclude the thickness of a floor coal (see below). However, the section at Salterwood Site includes an 8-in dirt parting which itself is the thickest recorded within the main sequence of the seam. This parting is ubiquitous at outcrop between High Bank and Mill Farm sites and is present in many deep mine provings in the central part of the district. The coal above the parting is generally of good quality with a low ash content and is composed largely of bright coal with sporadic bands of hards. Below the parting, the quality of the coal is poor and variable; some analyses show dirty coal. This is epitomised by the section at Salterwood Site where the whole 19-in leaf contained over 20 per cent ash. In provings where the dirt parting is absent there is, in general, an upwards improvement of the quality of the coal, though the overall quality of the seam is medium to poor.

The Threequarters Coal has been worked underground in small areas near Ripley Colliery and near the northern margin of the district, its main attraction however lies in its close proximity to the Low Main/Tupton Coal and it has been extensively won with that coal by opencast methods.

A floor coal is present some 2 to 11 ft below the main seam. The distribution of this floor coal is indicated on (Figure 23) and its maximum known thickness is 21 in, proved in Hucknall C's Heading Underground Borehole.

Threequarters Coal to Clay Cross Marine Band

These measures range in thickness from 304 ft in Seagrove Borehole to about 455 ft in Swanwick Colliery New Pit (Figs.24 and 25). They include the Low Main, First Piper, Deep Hard and Deep Soft coals, which were extensively mined as sources of household and steam coals throughout the district and have also been widely exploited by opencast methods. The Deep Soft group of coals is combined over a restricted area near Smalley to form the thickest coal sequence in the district. Other rock types in the sequence include the this Black Rake Tuffaceous Siltstone which is an important lithological marker at the top of the Deep Soft group of coals. The two widespread and important sandstones of the measures are the 'Tupton Rock', found in the west and also within a broad channel in the eastern part of the district, and the 'Deep Hard Rock' which occupies a narrow belt extending north-eastwards from its outcrop at Salterwood.

Boreholes in the east of the district illustrate the manner in which the Cockleshell and Hospital coals this or disappear on the crests of thick sandstones. In contrast, however, the individual thicknesses of the coals of the Deep Soft group appear to be little related to the thickness of underlying sandstone, although the splitting of the coal sequence was controlled by the influx of sand at various times and locations. This group therefore resembles the Blackshale and Yard coal sequence (p. 139b) though the area of maximum coal thicknesses is different.

The Carbonicola cristagalli mussel fauna (Smith and others 1967, p. 134–135) occurs above the Cockleshell Coal and passes upwards into the Anthracosia regularis fauna at about the horizon of the Deep Soft Coal (Smith and others 1967, p. 96 and 1973, p. 44).

The measures between the Three-Quarters Coal and Low Main Coal

The Measures between the Three-Quarters and Low Main Coals range in thickness from 6 ft in Seagrove Borehole to 23 ft in Pentrich Colliery, Hartington Shaft. They are mainly argillaceous with ironstone nodules; much of the sequence is composed of the seatearth of the Low Main Coal. The measures are well exposed in an old quarry at Little Matlock [SK 4345 5137] near Ironville (Appendix 2 ).

The Low Main (Low Tupton or Furnace) Coal

The Low Main (Low Tupton or Furnace) Coal has a maximum thickness of 66 in at Salterwood Site and is generally of good to very good quality. From its outcrop the seam thins irregularly and gradually to less than 36 in in the south-east of the district. In the north-east (Figure 26) the top of the seam lies about 9 in below the Cockleshell Coal and together the two form the Tupton Coal. Within this area of union the Low Main element ranges in thickness from 36 in in Annesley 204's Underground Borehole to 42 in in Hucknall C's Heading Underground Borehole. A second and poorly defined area of union with the Cockleshell Coal exists near Swanwick, Birchwood and Pinxton collieries where the Tupton Coal is 45 to 50 in thick. In the north-central part of the district the Cockleshell Coal is recorded only in Brookhdl Colliery (Smith and others 1967, p. 308), where its lower leaf lies 50 in above the Low Main Coal, and in Agnes and Exhibition sites where it lies about 25 ft above that coal. To the west, in Brands, Western, Pentrich and Pye Hill collieries the Cockleshell horizon is inferred to lie at about the latter distance above the Low Main Coal.

The Low Main Coal is known to be split only in New Langley Colliery Shaft, where the section is coal 39 in, dirt 15 in, on coal 16 in, and in Moor Farm Borehole where the respective thicknesses were 33, 9 and 16 in.

The structure of the Low Main is frequently distinctive, particularly the basal 12 in, which are composed of bright coal with hard bands or interbedded hard and bright coal. The central portion of the seam in most records comprises soft bright coal, and the upper part is variable with hard coal, bright coal and cannel, the latter being 21 in thick in Bentinck Colliery workings. A dirt parting up to 2 in thick or a band of hard coal within this upper part of the seam can be correlated over wide areas. The ash content of the whole seam is low, the average of 138 analyses from the district being 4.4 per cent. Sulphur content is also low.

The seam is frequently washed out within the eastern area of arenaceous roof measures (Figure 27), as exemplified by Cinderhill Colliery No. 4 Shaft and 2's Left Gate Iobye underground boreholes and Model Farm No. 2 Borehole. The edge of the washout was observed in Shortwood Site (p.179c).

The measures between the Low Main Coal and First Piper Coal

The measures between the Low Main and First Piper Coals range in thickness from 101 ft in Wollaton Colliery D. H. 21's Underground Borehole to 187 ft in Wollaton Colliery, junction of South Main and South Dips Underground Borehole. The variation is directly related to the thickness of sandstones within the four major component cycles (Figure 29). The three lowest cycles are locally crowned by thin coals named, in ascending order, the Cockleshell, Hospital and Second Piper: the fourth is capped by the First Piper Lower Coal or First Piper Coal.

Washouts are present in these measures and, as both the Cockleshell and Hospital coals are split and the Second Piper Coal and seatearth are unrecorded in a number of the provings, the detailed correlation is not always certain. Additionally some of the coals recorded in boreholes have no underlying seatearths and are probably washout rafts. The sub-Hospital sandstone ( 'Tupton Rock' is thickest within the takes of Cinderhill and Wollaton collieries and crops out between Shorewood Site and Trowell Moor Colliery. Where this rock is thickest the Cockleshell Coal is absent as a result of erosion and/or non-deposition, The Hospital Coal also fails or is reduced on the "crest" of this sandstone. In the west of the district, only the sub-Cockleshell sandstone is important, as displayed by Ormonde Colliery Shaft (Figs.25 and 29), where it is about 70 ft thick. This sandstone is marked by only minor ground features at outcrop except on the flanks of the Ironville Anticline. In the north-east of the district a thick sub-First Piper sandstone is the dominant sandstone; its sinuous line of maximum thickness enters and leaves the district within Annesley Colliery take. Its base falls to 14 ft above the Tupton Coal in Annesley Deep Soft G4's Underground Borehole to the north of this district, and along part of the line of maximum thickness the Hospital Coal is reduced or washed out and the Second Piper Coal and seatearth are absent. Elsewhere in the district the sequence below the First Piper Coal includes only minor sandstones.

Nodular ironstones are a common feature of the more argillaceous part of these measures, They were once worked locally under names such as Wallis's Rake and Whetstone Rake (Smyth 1856, p. 41). Wedd (in Gibson and others 1908, pp. 79 and 171) records an oolitic ironstone in the roof of the Furnace (Low Main) Coal at Marehay and Salterwood collieries, near Denby. In Eastwood Hall Borehole Carbonicola sp. and Naiadites sp. were present about 19 ft above the Low Main Coal.

Sections in these measures near Denby, Codnor. Heanor and Smalley Common are described in Appendix 2.

The Cockleshell Coal (Figure 27) lies up to 76 ft above the Low Main Coal in Ormonde Colliery Shaft and is united with that coal in the north and north-east of the district. Most of the intervening measures are sandy but 'cocklebeds' of the Low Main Coal have frequently been recorded where mudstones form the roof. The Cockleshell Coal may be composed of bright coal, dirty coal, cannel and/or interbedded coal and mudstone (ban). Multiple sequences of coal and dirt each a few inches thick may range through several feet of measures, The thickest record of the unsplit seam, 28 in in Cinderhill 6's Underground Borehole, includes laminae of dirt. There are the distinct elements to the seam at Ford's Pit, Brookhill Colliery, Agnes Site and the Pye Hill–Selston Colliery area, separated by up to 28 ft of measures. These two elements can be traced into the north-east of the district where they unite with the Low Main Coal, but it is not known how they are related to the single seam found between West Hallam and Cinderhill collieries and in boreholes in the east of the district. The seam is unproved over wide areas within the washout in the south-east and also near the western outcrop.

The measures between the Cockleshell and Hospital coals range in thickness from 8 ft in Cinderhill 2's Heading Underground Borehole to 75 ft in Wollaton 114's Main Outbye Underground Borehole. The widespread mussels in the roof of the Cockleshell Coal are frequently preserved in carbonate and include Carbonicola cristhgalli, C. cf. rhomboidalis and Naiadites flexuosus. Sandstones are generally thin, except near Cinderhill and Wollaton collieries, where the top of the 'Tupton Rock' extends close to the base of the Hospital Coal (Figure 29), and the Cockleshell Coal is washed out along the line of maximum sandstone thickness. This sandstone is interbanded and interbedded with siltstone and includes conglomeratic layers with pebbles and derived ironstones up to 6 in long. About 9 ft of cross-bedded ferruginous sandstone are exposed on the roadside near Shortwood [SK 4913 4005]. The cross-bedding dips mainly to the east, but both north- and south-dipping units were also observed. In the nearby Shortwood Site the lowest 25 ft of the washout measures consisted of silty mudstones with poorly defined bedding features arranged in a channel, of which only the eastern margin was exposed. These mudstones cut across the Low Main Coal to rest upon the Threequarters Coal and contained large rafts and masses of derived seatearth which both transgressed and inter-fingered with the bedding of the mudstone. Within the seatearth were large ironstone nodules with kaolin. Fine khaki-coloured sandstones overlay the mudstones and, away from the channel margin itself, cut out the Low Main Coal in part of the site.

Mr R. E. Elliott (in litt.) recorded the washout in the adjacent Swancar Farm Site [SK 491 397]; the Low Main was washed out and the irregular base of the 'Tupton Rock' contained much coal debris. The underlying 12 ft of measures down to the Threequarters Coal are disrupted siltstones, seatearths and ironstone; the siltstones appear to be rafts within derived seatearth and they interfinger with overlying mudstones.

The Hospital Coal is thickest, an exceptional 43 in, in Seagrove Borehole. It ranges from 21 to 31 in at the outcrop in the west; elsewhere it is thinner or irregularly split into two or more leaves. The split is most commonly recorded near Pentrich, Cinderhill and Wollaton collieries and near the Ironville Anticline. Individual leaves of the split seam may be up to 32 ft apart, as at Brands Colliery, but this is exceptional as are also the 15-ft split in Cinderhill 6's Main Gate Underground Borehole and the 17-ft split in Radford 5's Slant Underground Borehole. The seam thins away on the crest of the 'Tupton Rock' near Wollaton Colliery. Analyses of this coal are wholly from opencast provings; it is of good to medium quality in the west with low ash and sulphur contents, but the quality deteriorates in the south of the district.

The measures between the Hospital and Second Piper coals range in thickness from 12 ft in Beechdale Road Borehole to about 30 ft in Cinderhill 9's Left Gate Heading Underground Borehole. Carbonicola cristagalli, Geisina arcuata and fish remains are present in the more argillaceous part of this cycle.

The Second Piper Coal attains a maximum thickness of 12 in of 'coaly shale' in Selston Colliery No. 2 Drift. There are only seven other records of a carbonaceous bed in deep provings; however the underlying seatearth is widespread, though locally impersistent.

The measures between the Second Piper Coal and the Lower Coal of the First Piper or First Piper Coal range in thickness from 16 ft in Cinderhill 9's Left Gate Underground Borehole to 84 ft in Annesley No. 3 Underground Borehole, the increase being directly proportional to the thickness of the sub-First Piper sandstone in the north-east of the district (Figure 29). The full thickness of this sandstone however may be as much as 120 ft in Annesley 10's Underground

Borehole, where it extends from a few feet above the Hospital Coal up to the seatearth of the First Piper. The sandstone contains bands of breccia and fine- and coarse-grained units of both sandstone and siltstone. Bands with a hard ferruginous cement (cask) up to about 1.5 ft thick are also present.

In the remainder of the district these measures are about 35 ft thick and contain a variable amount of arenaceous material. The roof of the Second Piper Coal may contain mussels of the criitagalli fauna and plants.

The First Piper Coal

The First Piper Coal (Figure 30) is composed of up to three main elements which comprise the lower and upper parts of the Lower Coal of the First Piper and the Upper Coal of the First Piper as figured by Smith and others (1967, fig. 18) for the Chesterfield district. Over a large part of the district they are combined in a single seam, up to 60 in thick, as in Bennerley Colliery Shaft. Many records of the combined seam show the tripartite subdivision, though a bipartite sequence of Upper and Lower coals is more widecipread and important. The three elements of the seam divide irregularly so that they may be distributed through up to 43 ft of measures in two areas (Figure 30). One area in the north-west includes Denby Hall, Pentrich, Ripley, Brands, Western, Birchwood, Swanwick and Pye Hill collieries and the second in the north-east lies within the takes of Annesley and Hucknall collieries. In this latter area the division of the seam is largely into two rather than three leaves. The three leaves in Hucknall C's Heading Underground Borehole are distributed through 10 it of measures.

The irregular nature of the splitting is most evident at Pye Hill Colliery, where the shaft and adjacent workings show a 22-ft division between the lower 4-in and upper 6-in parts of the Lower Coal, while only 2 in separate the Lower Coal from the 28-in Upper Coal (Figure 30). The main value of this section and also that at Swanwick New Pit, however, lies in the presence of both the Second Piper and First Piper horizons, thus facilitating the correlation of the latter within the north-western area of split.

The Lower Coal of the First Piper is unimportant and usually of poor quality. The dirt parting between the lower and upper parts is normally a few inches in thickness, but increases rapidly in the extreme north-west of the district (the 3-ft isopach is shown on (Figure 30)) to 12 ft in Pentrich Colliery Speedwell Shaft and 22 ft at Pye Hill Colliery. The individual thicknesses of the two parts rarely exceed 12 in except in opencast records west and south-west of Denby Hall Colliery, where analyses show high ash contents. The greatest thickness recorded is 27 in for the lower part in Denby Hall Colliery workings, though much of it was dirty coal.

Within the north-eastern area of split the Lower Coal is 10 in thick (including dirt partings) 6 in below the Upper Coal at Annesley 204's, 1 in of batt 3 ft 9 in below the Upper Coal at Annesley 10's, and 20 in thick and 21 in below the Upper Coal at Cinderhill 2's Heading underground boreholes. In the more divided sequence at Hucknall C's Heading

Underground Borehole the two parts of the Lower Coal are 2 ft 11 in apart and each 4 in thick. The Upper Coal of the First Piper within the north-western area of split varies from 15 in at Swanwick New Pit to 40 in at Salterwood Site. Isopachs are shown on (Figure 30). The coal is of variable quality, the thicker sequences being usually poor with high ash contents. In the north-eastern area of split it varies from 12 in at Hucknall C's Heading Underground Borehole to 21 in at Annesley 204's Underground Borehole and may contain up to 21 in of cannel at the top. The combined First Piper seam ranges from 11 in (with 2-in cannel overlying) in Annesley No. 3 Underground Borehole to 60 in at Bennerley Colliery. Two dirt partings divide the seam in the northern part of the district. They are seldom recorded above the 'Tupton Rock' crest in the south, where the seam is reduced to 14 in at Cinderhill Colliery No. 4 Shaft and to 22 in at Model Farm No. 2 Borehole, and where a bipartite subdivision is apparent.

Apart from a few inches of cannel at the top in some analyses, the Upper Coal part of the combined seam consists of bright coal containing variable quantities of ash and sulphur ('Top Brights'), the basal few inches being mainly dirty coal. The elements composing the Lower Coal are variable and, as in the areas of split, are frequently composed of dirty coal, although some units of banded bright and dull coal are recorded. A rock less than 2 in thick and having a close affinity to tonstein occurs 31 in above the base of the seam at Lodge Colliery. Eden and others (1963, p.52) described it as a quartzitic silty rock containing lenses of mudstone composed of variable amounts of kaolinite and illite. They also described a correlative of this rock from Clifton Colliery in the Nottingham district as tuffaceous.

The measures between the First Piper Coal and Deep Hard Coal

The measures between the First Piper and Deep Hard Coals are between 30 and 40 ft thick over much of the district but range from 29 ft in Eastwood Hall Borehole to as much as 80 ft in Birchwood Shady Shaft. They are thickest in the north and east. There are one or two component cycles divided by the Deep Hard Floor Coal or its seatearth. The Floor Coal appears to separate from the Deep Hard Coal east of the sinuous north-south line shown on (Figure 31). There are few records of the overlying cycle up to the floor of the Deep Hard Coal, but it can be up to 19 ft thick as in Cinderhill 10's Main Gate and 10's Inbye Underground boreholes. This cycle and the Floor Coal are described with the Deep Hard Coal below.

The roof measures of the First Piper Coal contain mussels and some fish debris, but the fauna is mainly recorded in the eastern part of the district. Plant debris and nodular ironstones have been noted. Sandy measures are comparatively thin and are largely restricted to the uppermost 10 or 20 ft except near Kimberley and Cinderhill collieries, where they are dominant. Temporary sections near Codnor, Heanor and West Hallam are described in Appendix 2.

The Deep Hard Coal

The Deep Hard Coal is composed of three principal elements, the Floor Coal, the main seam and the Roof Coal, which may extend through up to 27 ft of strata. The main seam in turn can be divided into three parts (see below). The Floor Coal and the main Deep Hard seam are together in the west of the district, where their combined thickness ranges from 85 in at Openwood Site to 45 in in Cotmanhay Colliery Shaft and workings. Of these only 8.5 and 2 in respectively represent the Floor Coal, which never exceeds 12 in where the seam is combined. North of Openwood Site the Floor Coal itself is split into two or three this coals. The line of split between the Floor Coal and the main Deep Hard shown on (Figure 31) is imprecise because most sections which record the separate seams lie well to the east of it. Exceptions are Moorgreen No, 1 and Bailey Brook Colliery shafts, where the interval is 1 ft 7 in and 2 ft respectively, and near Shilo Site, where it varies up to 6 ft. The Floor Coal is usually composed of dirty coal except where it is a persistent seam up to 18 in thick, as in Shilo Site and Bennerley Colliery Shaft, and 6 in to 6 ft below the main Deep Hard. East of the 1.e of split most sections show only its seatearth. This is separated by up to 19 ft (Cinderhill 10's Main Gate and 10's Inbye Underground borehole.) of argillaceous and arenaceous measures from the main Deep Hard. The main Deep Hard Coal comprises the 'Bottom Brights', 'Herds' and 'Top Brights' names used by the early miners (Anon 1942). These terms are a simplification, for the composition of the seam is variable. The thickness of the main Deep Hard ranges from 14 in in Cinderhill Colliery No. 4 Shaft to 76 in in Hucknall Colliery No. 5 Shaft. The latter is an abnormally thick swilley sequence which varies in the shaft down to 25 in. The seam averages about 40 in for the district, but it thins rapidly in the extreme east. In the north-east thicknesses include the Roof Coal—recognised as a separate seam only in the area shown on (Figure 31) and two adjacent sections.

The detailed seam sections (Figure 31) show the variable composition of the seam; the 'Bottom Brights' in the west include part or all of the Floor Coal element and are mainly of very poor quality. The 'Hards' have been the main unit worked underground and consist of a variable sequence of hard coal overlying interbanded hards and heights, all of good quality with low to very low ash and sulphur contents. Bright coal is common in the 'Top Brights' in many sections within the eastern third of the district, where it may be capped by a this cannel (up to 24 in). Bright coal is however rare in the remainder of the district, where 'scuds' (an inferior coal) predominate, capped by up to 12 in of 'gees' (carbonaceous shale) or 'jays' (inferior cannel); the last two terms appear to have been used indiscriminately. The Roof Coal element is made tap of all or part of this sequence of 'scuds' and 'jays'; a dirt parting between the Roof Coal and main Deep Hard is found only at New Selston Colliery and in one record from Agnes Site. Strauss (1971, pp. 1526–1527) has recorded and described a this tonstein lying at or near the top of the 'Herds' in Cossall Colliery 43's workings.

The same tonstein is noted in the log of Stoney Street Borehole and from Wollaton Colliery (Eden and others 1963, p.53) as illustrated by Strauss (1971, pp. 1526–1527). It appears to extend only into the south-eastern part of this district.

The Roof Coal in the north-east of the district may lie up to 24 ft above the main Deep Hard, as in Brookhill Colliery (Smith and others 1967, p. 308). Here its thickness is 7 in, of which the uppermost 3 in are cannel. Its maximum thickness is 13 in of cannel, in Annesley 204's Underground Borehole. Carmel may also occur at the top of the 'Hards' even within the area of division from the Roof Coal.

A washout sandstone about 300 yd wide cuts out the Deep Hard Coal along a linear belt trending north-north-eastwards from the outcrop near Denby Hall Colliery. The northern continuation has been noted by Smith and others (1967, p. 144). According to Gibson and others (1908, pp. 79–80), the coal thickens as the washout is approached, but sections in clay pits at Salterwood [SK 3888 4750] show that the abnormally thick coals are derived and lie within the sandstone; one such coal was 9 ft thick and died out within a few yards. This coal contained this sandstone lenses.

Elliott (1965, p. 138) has described a swilley in the Deep Hard Coal in Hucknall Colliery shafts and mentions a second in workings at Moorgreen Colliery. The swilley at Hucknall enters this district from the north-east and has been proved in No, 5 Shaft (see above) and in No. 3 Shaft, whence it turns southwards and its course is lost.

The measures between the Deep Hard Coal or the Deep Hard Roof Coal and the Deep Soft Coal

The measures between the Deep Hard Coal or the Deep Hard Roof Coal and the Deep Soft Coal vary from 20 ft in Lodge Colliery Shaft to about 100 ft in Denby Hall Colliery Shaft and are composed of up to three cycles; the lowest two are capped by thin, impersistent coals. The lowest cycle is composed largely of silty measures which may be up to 35 ft 1 in thick, as in Manners Colliery Shaft, where 7 in of batt at the top represent the Foot Coal. In Eastwood Hall Borehole Naiadites and Carbonita sp., were present in the roof of the Deep Hard Coal. The 'Deep Hard Rock' (Smith and others 1967, p. 146) is only of local significance within this district, its most important outcrop lying near the washout described above. The Foot Coal is never thicker than the 12 in recorded in Bennerley Colliery Shaft. (It is sporadically represented in sections near Ilkeston and Hucknall Deep Soft C's junction Underground Borehole to the east of this district). In the absence of the Foot Coal, the top of the cycle is drawn at the summit of the silty measures. The second cycle either finishes at an impersistent this coal or cannel lying up to about 2 ft below the Deep Soft Coal or extends upwards to include the Deep Soft Coal. The third cycle therefore, if present, includes these 2 ft of measures and the Deep Soft Coal. The measures are partly arenaceous but include thick seatearths of varying lithology. In Denby Hall Colliery Shaft for instance, 'clunch' and principally, 'stone clunch' was recorded for 35 ft below the Deep Soft Coal and comprised all but 3 ft of the second cycle. The underclay below the Deep Soft Coal was of considerable value as raw material for ceramics.

The Deep Soft Group of coals

The Deep Soft Group of coals comprises in ascending order the Deep Soft, Roof Soft, Top Soft and Black Rake coals. Over a restricted area (A on (Figure 32)) near Smalley these coals lie within 25 ft of strata, the most condensed sequence being at Club Room Site, where there were only 4 ft 6 in of dirt in 19 ft 5 in of coal-bearing strata. Elsewhere these coals may be distributed in up to 96 ft of strata, as in Pentrich Colliery, Speedwell Shaft.

In area B of (Figure 32) the Top Soft Coal splits off the combined seam. The Black Rake Coal, not recognised in area A, probably a split off the Top Soft, is present in this area.

To the east, in area E, the sequence is further divided. There are two, or sporadically three, leaves of the Roof Soft, a thinner Top Soft and, locally, a Black Rake Coal. Only the Deep Soft remains as a persistent seam of importance.

In area C the Roof Soft and Top Soft seams, with or without the topmost Black Rake element, are close together, but are widely separated from the Deep Soft Coal. The combined Roof Soft and Top Soft coals which may contain up to four separate leaves was originally called the Ell Coal (Gibson and others 1908, p. 69); latterly this name was altered to False Ell to avoid confusion with the Ell coals of Westphalian B. Type sections for the False Ell are provided by Grammer Street Borehole, where the sequence probably includes the Black Rake at the top (Figure 34) and Stoneyford Borehole where the Black Rake is a separate seam.

In area D, as in area E, the higher coals of the group are divided and remote from the Deep Soft. There is a thick Roof Soft (?lower leaf) in Birchwood Colliery Shady Shaft and Pinxton No. 3 Pit, but elsewhere the topmost coal is the principal seam. It is not certain if the latter is the Black Rake Coal or a combination of that seam with lower elements. It is however the Sitwell Coal (Smith and others 1967, p. 149) in the south-west of th[Chesterfield district.

The Deep Soft Coal itself (Figure 33) has a maximum thickness of 66 in in Heanor Gate Borehole and thins irregularly towards the north-east, being only 304 in in Linby Colliery (Pit Bottom) Underground Borehole. One, or sometimes two, this floor coals or cannel, up to 7 in thick, lie as much as 2 ft below the main coal sequence. The main coal consists largely of 'heights' with, in the middle of the thicker sequences, banded bright and dull coal. A this hard coal parting has been widely recorded near the base of the seam. This parting is probably the representative in the undivided seam, of the dirt interval which separates off the floor coal elsewhere. A second hard coal parting near the top of the seam is also widely recorded. The seam is generally of good quality with low ash and sulphur contents.

The measures between the Deep Soft and Roof Soft coals consist of up to 11 in of dirt over the major part of areas A and B; this increases in the north of these areas to between 24 in in Woodside Colliery Shaft and 57 in in Shipley Colliery Deepfields Pit. See also the section in Top Dumbles Site near Heanor (Appendix 2).

Northwards into area C the sequence up to the base of the False Ell Coal consists of silty and sandy measures ranging in thickness from 27 ft in Butterley Park Engine Shaft to about 71 ft in Ford's Borehole. In the part of area D where the Roof Soft Coal or its seatearth is recognisable, these measures range in thickness from 28 ft in Swanwick New Pit to about 41 ft in Birchwood Shady Shaft. In sections near the northern margin of the district, where the Roof Soft Coal is unrecognisable, the measures between the Deep Soft Coal and ?Black Rake Coal are as much as 91 ft thick in Pentrich Colliery Speedwell Shaft and include mudstone and siltstone with 24 ft of seatearth at their top. Near the south-west margin of area E, where they are largely argil, access, these measures can be as thin as 12 ft (^‡8 Rutland Colliery in Ilkeston), but over the rest of this area, the incoming of arenaceous measures increases this interval to as much as 67 ft, as in Wollaton Colliery No. 2 Shaft.

The Roof Soft Coal is thickest where combined with the Deep Soft Coal in areas A and B (Figure 32); it is 51 in at Tinklers Site and 60 in at Woodside Colliery Shaft. Analyses from opencast sites in these areas show the seam to be composed of bright coal at the base, with a banded bright and dull sequence in the centre. The top of the banded sequence is frequently marked by a this dirt parting which separates off the uppermost 8 to 13 in of bright coal. One or two this roof coals may be present close above the seam. The Roof Soft is split into two leaves in every record within area E with the exception of Hucknall No, 2 Colliery No. 1 Pit and Linby Colliery Engine House and Pit Bottom Underground boreholes, where it was represented by a few inches of coal or cannel. The leaves of the seam are very variable in thickness and in distance apart, with the upper leaf frequently near the Top Soft Coal. The lower leaf is thickest near the line of split which apparently takes place along the same line as that of the seam split from the Deep Soft and False Ell coals, The maximum known thickness of the lower leaf is 30 in in Cotmanhay Colliery Shaft, thinning northwards to 18 in at Pollington Colliery and eastwards and southwards to 12 in or less.

Measures ranging in thickness from 8 ft at Turkey Field Colliery to 34 ft at Cotmanhay Colliery separate the lower and upper leaves of coal in area E, the thinner sequences being composed of argillaceous rocks and/or seatearth. Except in the north-east of this area, the sandstones within this interval are concentrated in two belts, one along the line of splitting and the other along the eastern margin of this district. The sandstones in the region of the split appear to have been deposited from currents moving towards the north. The upper leaf of coal is normally thin, but reaches an exceptional thickness of 43 in of coal and dirt at Manners Colliery; the 18 in recorded at Turkey Field Colliery is also above average for the area.

The Roof Soft Coal in area C is described below as part of the False Ell Coal. In area D, where much of the correlation is tentative, it is thought to be split in Birchwood Shady Shaft, where the lower 36-in leaf is separated by 21 ft of measures from the upper 6-in leaf and in Swanwick Colliery New Pit (Figure 34). Where the horizon has been recognised elsewhere within this area the Roof Soft is either of insignificant thickness or represented only by seatearth.

The False Ell Coal in area C comprises the Roof Soft and Top Soft coals in three or four leaves in up to 16 ft of strata. Over part of area C it probably contains the Black Rake Coal at the top (See Append. II for such a section near Codnor). The lowest leaf of the seam is everywhere the thickest and reaches a maximum of 37 in in Grammer Street Borehole. The second leaf (the upper leaf of the Roof Soft) is never more than 14 in thick and lies up to 16 in above the lowest leaf. Exceptionally, as at Brands and Portland No. 1 collieries, there are three thin leaves to the Roof Soft component of the seam; in Ford's Borehole the lowest of the three is 24 in thick, all but 51 in being either dirty coal or dirt. The Top Soft component ranges from 18 to 30 in thick and is separated from the Roof Soft components by up to 44 in of seatearth. Analyses of deep borehole province show the Roof Soft components to be poor in quality with high ash and moderately high to high sulphur contents and the Top Soft component to be of good quality with low ash and moderately low sulphur contents.

The Top Soft Coal is thickest, 32 to 52 in, in area A. In structure, this coal displays a banded bright and dull coal sequence in the middle of the seam and is of medium quality with moderate ash content and moderately low to low sulphur content. Elsewhere within the Derby district the seam is of importance only as part of the False Ell Coal described above. In area B it is 32 to 39 in thick in Shipley Colliery Deepfields Shaft, West Hallam Colliery No. 1 and Coppice Colliery shafts and Shipley Park Borehole, but thins to 8 in and 18 in in Nutbrook Air and Woodside Colliery shafts respectively. At the last locality the seam lies some 47 ft above the Roof Soft Coal, and this is the thickest interval between these coals in the district. Over most of the district this interval is less than 15 ft. The seam in Shipley Park Borehole was of poor quality. In area E the seam is usually thinner than 14 to but it thickens to 18 in in Turkey Field Colliery, 24 in at Manners Colliery and to a maximum of 30 in at Plumtree Colliery. In the north-west (area 13, (Figure 32)) the Top Soft is unrecognisable within the thick seatearths recorded below the Black Rake Coal, or it is incorporated within that coal.

The Black Rake Coal is the least important member of the Deep Soft group and is recognisable, mainly in a narrow central belt which widens towards the north-west (Figure 32) up to 27 ft (Stoneyford Borehole) above the Top Soft Coal. The coal is thickest in the north-west of the district and varies from 6 in in Birchwood Shady Shaft to 24 in in Pentrich Colliery, Hartington Shaft. The seam is known locally in the east of the district, at Hucknall No. 1 and No. 2 collieries and Linby Colliery and also near Wollaton Colliery No. 2 Shaft. On (Figure 32) the Black Rake Coal is shown as a split off the Top Soft seam, but this is based upon little evidence and the seam could be part of an impersistent cycle distinct from that of the Top Soft. Apart from the records in the north-west of the district the coal is only a few inches thick and frequently the horizon is represented by a seatearth; there are however 24 in of 'batt' recorded in West Hallam Colliery. This seam has been worked opencast at the outcrop in the north-west of the district, where analyses show it to be of medium to rather poor quality.

The measures between the Top Soft Or Black Rake Coals and the Brown Rake Coal

The Measures between the Top Soft or Black Rake Coals and the Brown Rake Coal vary from 13 ft at Greenhill Lane Colliery, Riddings to 43 ft in Orrnonde Colliery Shaft. Dark grey mudstones near the base of the cycle contain ironstone nodules of the Black Rake Ironstone (Smyth 1856, p. 37) which have been worked both opencast and underground as a source of ore. Within these mudstones and forming a roof to underground workings is a widespread bed called the Black Rake Tuffaceous Siltstone by Francis and others (1968). Previously called the Black Rake Carbonate Rock (Edwards 1951, pp. 33, 147), it is a striped, hard bed of flinty rock up to 15 in thick with up to 50 successive pale grey graded layers which in places contain basaltic glass shards and pumice. At many localities the rock is dolomitic. It is formed from volcanic fall-out emanating from vents lying to the east of the present district; in Stoneyford Borehole it contains sufficient basaltic glass to merit the name vitric tuff while at Hucknall Colliery No. 2 Drift the bed includes layers of tuff with accretionary lapilli (Francis and others 1968, p. 399). The following petrographical description of this rock is by Dr E. H. Francis... 'a graded, partly carbonated rock with layers 1.0 to 10.0 mm thick. The coarser elements include quartz grains up to 0.3 mm diameter, together with fragments of shale, coal and abundant basaltic debris. Most of the basaltic debris is elongate and sharp-shaped. It is mainly altered to turbid brown decomposition products or, less commonly, it has been kaolinized, but there remain a few fresh, yellow, isotropic vesicular fragments. The finer elements at the tops of graded units are silty mudstone without any recognisable volcanic debris'.

A few feet of mudstone with ironstone nodules normally overlie the tuffaceous siltstone, the remainder of the cycle comprises arenaceous measures and seatearth. In Manchester Wood Borehole Spirorbis sp., Anthraconaia sp.. Anthracosia regularis, Carbonicola cf. venusta, Naiadites sp. and Geisina arcuate were present in the mudstones of this cycle.

The Brown Rake Coal

The Brown Rake Coal (Figure 71), which is up to 38 to thick at Club Room Site, thins rapidly towards the east where, over wide areas, it is under 12 in. In the north the seam is divided into two and sometimes three leaves, as in Swanwick New Pit, with up to 7 ft of measures between. The thickest single leaf is 18 in at Greenhill Lane Colliery.

The quality of the coal at outcrop is variable, but on average it is poor with high ash and moderate sulphur contents; in two analyses from deep-mine boreholes it was medium in quality with moderate ash and moderately high sulphur. The seam has been extensively exploited by opencast means, usually to conjunction with the underlying coals of the Deep Soft group.

The measures between the Brown Rake Coal and Clay Cross Marine Band

The measures between the Brown Rake Coal and Clay Cross Marine Band vary in thickness from 8 to in Stoneyford Borehole to 35 ft in Ford's Borehole, and are wholly argil, aceous in the district apart from a 3-ft sandstone in the vicinity of Linby Colliery. Temporary sections near Smalley, Codnor (Agnes Site) and Strelley (Catstone Hill Site) are described in Appendix 2.

At the base of the measures a kaolinitic rock, now considered to be a Fragmental Clayrock (Richardson and Francis 1971), of doubtful persistence, has been noted in Ford's Borehole. This correlates with one of the tonsteth horizons described by Strauss (1971, p. 1525). The grey mudstones everywhere contain nodules of the Brown Rake Ironstone (Smyth 1856). Some of these are calcareous and exhibit cone-in-cone structure. The measures, including some of the ironstones, contain abundant Anthracosia regularis, Naiadites sp. and Geisina arcuate; Spirorbis sp. is also common and Planolites montana is present. Near the top, the fossils tend to be pyritised. A sporadic seatearth, a few inches thick, at the summit of the measures has been recorded, mainly to the eastern part of the district. It is the only representative of the Joan Coal horizon; in Eastwood Hall Borehole the rootlets were pyritised.

Westphalian B

Clay Cross Marine Band to Top Hard Coal

The measures between the Clay Cross Marine Band and Top Hard Coal (Plate 5) are about 460 ft thick at Heanor Gate Borehole and about 450 ft near Swanwick Colliery; they thin eastwards to about 330 ft at Hucknall No. 2 and Broxtowe collieries, though an incongruous record from Hempshill Heading in the east shows about 406 ft of these measures. Approximate isopachs are shown on the inset map of (Plate 5). The measures comprise twelve or more cycles, most of which contain both arenaceous and argillaceous strata. There are ten named coals. Marine fossils are confined to the Clay Cross Marine Band. Mussels are present in the roof measures of all the coals except the Bottom First and Bottom Second Waterloo coals; the Anthracosia aquilina/ovum fauna lying below the Second Ell Coal grades upwards into the A. phrygiana fauna which continues to the Top Hard Coal.

The named coals have been exploited mainly by opencast means, but the Second Waterloo Coal has also been extensively worked underground. Extensive temporary sections in these measures at Catstone Hill Site near Strelley are described in Appendix 2. The measures associated with the Second Waterloo Coal are worked for brick-making.

The Clay Cross Marine Band

The Clay Cross Marine Band consists of up to about 9 ft of dark grey mudstone with thin ironstone lenses. The marine fossils and their distribution within the marine band have been described by Edwards and Stubblefield (1948, p. 215) and Calver (in Smith and others 1967, pp. 157–159 and 1968a, pp. 163–173). The 1 ft 10 in of mudstone between the Joan Coal Seatearth and the Dunbarella and goniatite-bearing mudstones in Eastwood Hall Borehole contain Lioestheria at their base with Lingula and foraminifers above. They are indicative of an increasing marine influence on the conditions of deposition, but there is no clear separation of the foraminifera and Lingula phases. The Dunbarella and goniatite-rich horizons near or at the base of the sequence occur in dark mudstone tougher and more fissile than the overlying Lingula-rich horizons. As noted by Gibson and Wedd (1913, p. 71) and Edwards and Stubblefield (1948, p. 216) the upper Lingula-bearing horizons alternate with mudstones containing stunted mussels. Paraparchites and abundant foraminifera including Glomospira and Glomospirella associated with stunted Anthracosia spp. were present at this level in the Eastwood Hall Borehole.

The 5 ft 11.5-in sequence of the Clay Cross Marine Band in Seagrave Borehole is shown on (Figure 72). Here some 2 ft 1.5 in of non-marine mudstone underlie the marine band. This is unusually thick for this district; normally there are only a few inches of such mudstone above the Joan Coal horizon. The mussels from this mudstone include Anthracosia regularis and Naiadites aff. quadrates. Anthracoceratites vanderbeckei and Dunbarella papyracea mut δ are common near the base of the marine band and are indicative of maximum marine influence. The mussels which are interbedded with the Lingula horizons in the retreat phase of the marine incursion include Anthracosia spp. of the nitida and ovum/aquilina groups.

There is no permanent section of the Clay Cross Marine Band in this district, except at the bottom of a shallow ditch [SK 4975 4267] 450 yd SW of Strelley Park Farm, where dark mudstones containing Dunbarella sp. can be found. The marine band has been recorded in the following temporary and underground sections; where known the thicknesses over which marine fossils have been found are indicated:

Agnes Site [SK 4250 5030], 2 ft 9 in and [SK 4300 4949], 1 ft 3 in (Appendix 2): Beechdale Road Borehole, 8 ft 7 in: Carrington Coppice Site [SK 413 455], 3 ft 8 in: Catstone Hill Site [SK 4974 4151], 2 ft (Appendix 2): Denby Hall Colliery Drift [SK 3992 4859], 2 ft: Digby Clay Pit c. [SK 485 450]: Eastwood Hall Borehole, 4 ft 7 in: Ford's Borehole, 6 ft 7 in: Godber's Lum Site [SK 4053 4787]: Grammer Street Borehole, 2 ft 11 in: Heanor Gate Borehole, 6 ft 5 in: Hucknall No. 1 Colliery; No. 2 Shaft, 4 ft 3 in; Drift, 6 ft 3 in; Boring from Top Hard to Deep Soft Drift, 7 ft 10 in: Hucknall No. 2 Colliery; No. 3 Shaft, 3 ft; No. 5 Shaft: Linby Pit Bottom Underground Borehole, 7 ft 5 in: Linby Engine House Underground Borehole, 6 ft 11 in: Manchester Wood Borehole, 4 ft: Model Farm No. 1 Borehole, 5 ft 1 in; No. 3 Borehole, 5 ft 1 in: Moorgreen Waterloo 3's Borehole: Motorway Cutting [SK 4959 4112]: Park Meadows Site [SK 3977 4718], 1 ft 3 in: Seagrave Borehole, 5 ft 11.5 in: Shipley Park Borehole, 1 ft 8 in: Stoneyford Borehole, 4 in: Swanwick Colliery, Dyson's Heading c.[SK 404 532], 2 ft 6 in: Tavern Houses Site [SK 4115 4683], 3 ft 3 in.

The measures between the Clay Cross Marine Band and Second Ell Coal

The Measures between the Clay Cross Marine Band and Second Ell Coal form part of a single cycle and range in thickness from 48 ft in Linby Pit Bottom Underground Borehole to 94.5 ft in Grammer Street Borehole, The thicker sequences are mainly in the western and south-eastern parts of the district. Sandstones occur in the uppermost third of these measures; the most persistent is found to the west of Beanor. The mudstones are rich in mussels, which may be pyritized with. 40 ft of the marine band, but may also be preserved in calcareous and ferruginous material. Many of the mudstones display worm tracks and burrows, and there are plants at the higher levels. Ironstones are common and frequently exhibit cone-in-cone structure.

In Eastwood Hall Borehole the mussels are present in mudstones throughout the cycle and are commonly pyritized and of small size. Anthracosia aff. ovum, A. phrygiana, A. aquiline and variants, Anthracosphaerium exiguum, Naiadites fragments and indeterminate ostracods were present in the lowest 37 ft of the cycle underlying to 10-ft thick sandstone. In the 14 ft of mudstone overlying this sandstone were Spirorbis sp. Anthracosia sp., nov. aff. phrygiana and Naiadites quadratus.

The Second Ell Coal

The Second Ell Coal is extremely variable both in thickness and composition. Near outcrop in the north-west and as far south as Upper Hartshay Colliery it is a split seam similar to that described by Smith and others (1967. p. 158) in the Alfreton area to the north. The upper leaf (Tanyard Coal) is of medium quality and ranges in thickness from 18 in at Broad Oak Site to 28 in at Upper Hartshay Colliery; it is separated from the 1 to 8-in lower leaf of dirty coal by up to 26 in of seatearth.

Within a wide area in the north and west of the district the seam is composed wholly or largely of cannel. Two leaves are frequently present and the sequence reaches exceptional thicknesses at Ormonde Colliery (9 ft 4 in, see p. 172a) and the adjacent Bailey Brook Colliery (20 ft 1 in, see p. 165b). The 14-ft separation of the leaves at Bailey Brook Colliery is exceptional; normally it is 1 to 4 in. The individual cannel beds are normally 15 to 20 in thick in sections near Ilkeston, but are locally as much as 31 in, as at Coppice Colliery No. 2 Shaft.

The sequence at Shipley Park Borehole dirty cannel 9.5 in, ironstone 3 in, coal 5.5., seatearth 4.5 in on dirty coal 1.5 in — appears to represent the passage from cannel to the 18 in of coal proved in Mapperley Colliery shafts. Cannel is present in the upper part of the seam in two further, but restricted, areas. Firstly in part of Catstone Hill and Macfez sites, Turkey Field Colliery and Seagrave Borehole (p.172e) the two leaves include up to 16 in of cannel at the top. Secondly, in the shaft sections of Hucknall No. 1 and 2 collieries there are 7 to 9 in of cannel at the top of the seam. Elsewhere within the district the Second Ell is a single or split coal in which the lower leaf or the lower part of the single seam is commonly composed of dirty coal. The thickest known section is 19 in of coal underlying 48 in of dirty coal in Strelley Borehole, and the maximum proved separation of the two leaves is 6 ft at Moor Farm Borehole.

The measures between the Second Ell Coal and First Ell Coal

The Measures between the Second and First Ell Coals average about 50 ft over much of the district, with a minimum of 31 ft at Hempshill Colliery Heading and a maximum of 65 ft at Turkey Field Colliery. They are composed of a single cycle which includes, over most of the district, only a small amount of arenaceous material; the 36 ft of sandstone underlying the First Ell seatearth at Turkey Field is exceptional. The mudstones are very fossiliferous, and the mussels may have a pyritous, calcareous or ferruginous mode of preservation. Ironstones are fairly common. The fauna in Eastwood Hall Borehole included Spirorbis sp. Anthracosia spp., Anthracosphaerium bellum, fragmentary Naiadites and fish remains, including Rhizodopis sp.

The First Ell Coal

The First Ell Coal shows great variations both in quality and thickness. It is thickest to the south-west of Heanor and in the Erewash Valley, east of Ilkeston. South-west of Heanor it is mainly 30 to 42 in thick, although only 23 in were recorded in Coppice Colliery No. 2 Upcast Shaft.

Analyses from opencast sites show that it is rather poor to very poor in quality in this area.

North and north-west of Heanor the First Ell is of medium to very poor quality. It is 18 to 27 in thick at the northern boundary of the district, thickening to 36 in at Bailey Brook Colliery Shaft. Dirt partings, 5 in or leas in thickness, are recorded from several localities.

East of Ilkeston, analyses from opencast sites in the Erewash Valley show sequences of up to 48 in, as at Coventry Lane Site, but up to 17 in of the sequence may be dirt partings and cannel. The over-all quality of the team is very poor to very inferior.

In the eastern part of the district the First Ell is absent in Hucknall No. 2 Colliery No. 2 Drift and Underground Borehole. Elsewhere it is a divided inferior seam.

The measures between the First Ell Coal and Fourth Waterloo Coal

The measures between the First Ell and Fourth Waterloo Coals are about 40 ft thick over most of the district. They are thickeat near Heanor, where they total 56 ft in Coppice Colliery No. 2 Shaft, and thinnest in the south-east of the district, where they are only 10.5 ft at High Ley. Borehole, Hucknall, 12 ft thick at Broxtowe Colliery Shaft and 16 ft at Wollaton Colliery No. 1 Shaft. In most sections they comprise only one cycle, but at Bailey Brook, Ormonde and Mapperley collieries, Shipley Park Borehole and in the Woodlinkin Drift a thin coal or seatearth is recorded 6 to 17 ft below the Fourth Waterloo. This coal is probably a split from the Fourth Waterloo (see below) although direct evidence is lacking.

In the immediate roof of the First Ell a lenticular ironstone, usually up to about 2 in thick with kaolinite ooliths and pyrite, forms a useful lithological marker. It is exposed in a stream [SK 4001 4852] near Marehay. Its discontinuous nature, observed in the nearby Godber's Lam Site (Appendix 2 ), accounts for its absence in many borehole sections, although it is very widely distributed. In this site the nodules were up to 8 in thick and protruded into the underlying coal, In Eastwood Hall Borehole the ironstone was 1 in thick and infilled Stigmaria.

The Fourth Waterloo Coal

The Fourth Waterloo Coal is variable both in thickness and in quality and may comprise up to three leaves of coal of which the middle leaf is the most persistent and important. Only Linby Pit Bottom Underground Borehole (p.170b) and Hucknall No. 1 Colliery No. 2 Shaft Deepening (p.168d) encountered all three leaves and detailed correlation throughout the district is therefore subjective. The seam has been worked locally by opencast means.

A thin floor coal, up to 7 in thick and lying up to 15 in below the middle leaf of the seam, has been proved in New Selston Colliery Shaft, Linby Pit Bottom Underground Borehole, shafts at Hucknall No. 1 and No. 2 collieries, and in Codnor Common, Catstone Hill, Coventry Lane and Kim sites. This floor coal is probably the correlative of the thin coal in the meaeures underlying the seam elsewhere (see above).

The main or middle leaf of the seam is 15 to 29 in thick in the north-west of the district, where it is medium to rather poor in quality; at Agnes Site it is 21 to 22 in thick with quality ranging from good to poor; it was 6 hi thick at Coppice Colliery No. 2 Shaft, 10 in in Mapperley Colliery Shaft and 17 in in Manners Colliery Shaft. The leaf is thickest, 34 in, in a water bore at Wollaton and is 29 to 30 in thick in Wollaton Colliery; northwards it thins to 18 in or less in provings at Hucknall and Linby collieries. The quality of the 31-in leaf in Beechdale Road Borehole was good to medium, but in Coventry Lane and Catstone Hill sites, where the thickness varied from 24 to 32 in, the quality varied from good to poor. It consists of 11 to 15 in of cannel In some records from Shilo Site and Pye Hill Colliery Trial Borehole, and of 7 to 8 in of cannel in Moorgreen Colliery shafts; a few inches of cannel are also sporadically recorded at the top of the leaf elsewhere.

A thin roof coal or seatearth is present in Brookhill Colliery Shaft (Smith and others 1967, p. 308), Pye Hill Colliery Trial Bore, Selston Colliery (Underwood) Shaft, Eastwood Hall Borehole, Linby Pit Bottom Underground Borehole. Linby Engine House Underground Borehole, Hucknall No. 1 Colliery No. 2 Shaft and No. 2 Colliery No. 2 Drift, Kimberley Colliery Shaft, Hempshill Colliery Heading and Broxtowe Colliery Shaft. This roof coal is usually very thin and dirty and is as much as 18 ft above the middle leaf of the seam in Linby Engine House Underground Borehole.

The measures between the Fourth Waterloo Coal and Third Waterloo Coal

The measures between the Fourth and Third Waterloo Coals are usually 30 to 45 ft thick, but vary from 27 ft in Butterley Park Engine Shaft to 76 ft in Ormonde Colliery Shaft. Thicknesses are related to the proportion of sandstone present. The two component cycles cannot be separately distinguished, though 19 widely distributed provings in the district record a this coal or seatearth 12 to 20 ft (exceptionally 38 ft in Woodside Colliery Shaft) below the Third Waterloo Coal. It is 1 in thick 16 ft 3 in below the Third Waterloo Coal in Brookhill Colliery Shaft, where Smith and others (1967, pp. 308 and 161) suggest that it may be a leaf of the Third Waterloo Coal. In Linby Engine House Underground Borehole and Kimberley Colliery Shaft (Plate 5) this coal lies some 20 ft above the roof coal or seatearth of the Fourth Waterloo, which has a more restricted distribution. Woodside Colliery Shaft encountered an anomalous 24-in coal at this horizon instead of the more usual 1 to 3 in.

The argillaceous roof measures of the Fourth Waterloo Coal contain fish debris, ostracods, burrows and plants. Anthracosia cf. beaniana occurred in Eastwood Hall Borehole in mudstones within a 16-ft sequence of interbedded sandstone, siltstone and mudstone near the top of these measures. A. disjuncta was present in these measures in Annesley Park Borehole.

The Third Waterloo Coal

The Third Waterloo Coal ranges from 12 in in Ripley Colliery Shaft to a multiple sequence of coal and dirt, 48 in thick at Catstone Hill Site. In the north and north-east the seam is about 2 ft thick over wide areas, and dirt partings are recorded only in Wansley Hall Site, where an overall thickness of 21.5 in includes0.5 in of dirt 2 in from the top, and in Dobbs Site, where a total thickness of 17.5 in includes in of dirt 5 in from the top of the seam. A hard coal parting is present in the bright coal of the seam. Usually in this part of the district the leaf is of medium quality, but one analysis from William IV Site showed poor quality.

Near Heanor, in Agnes, Corfield and Plastic sites, detailed sections show a dirt or hard coal parting near the base of the seam. The dirt is thickest in Plastic Site, where the section is coal 29 in, dirt 4 in, on coal 6 in; the leaf is medium in quality. A section in Agnes Site showed that the lower 7 in of the seam was cannel with 21 in of overlying coal. It is possible that the cannel is the equivalent of the thin coal or seatearth which occurs 12 ft or more below the Third Waterloo in Shipley Park and Eastwood Hall boreholes, Selston Colliery Underwood Shaft, New Selston Colliery and Swanwick Colliery New Pit.

Well south of Heanor, at an outcrop near Mapperley Colliery, there is a dirt parting near the top of the seam; at Mapperley Colliery No. 2 Shaft the sequence is coal 2 in, batt 4 in, on coal 24 in. The seam is at a local maximum thickness in the adjacent Jople Site, where the sequence is coal 2.5 in, dirt 3.5 in, on coal 31 in; there is a hard coal band in the middle of the lower coal in this sequence. In Heanor Gate Borehole a 2-in dirt parting separates 3 in of dirty coal at the top of the seam from the underlying 25 in of coal, and in Shipley Park Borehole the upper 5 in of the 22-in sequence comprises dirty coal. The quality in this part of the district varies from good to poor with moderate to high sulphur content. At Shilo Site the seam ranges from 17 to 31 in with only one of 15 recordings showing the upper dirt parting; the quality varies from good to poor and the sulphur content from low to high. In the south-east of the district, although the overall thickness of the seam tends to be greater than elsewhere there are more dirt partings. The dirt parting near the top of the seam is present in most of the detailed records and shows a rapid and local expansion as indicated by the representative sections in (Table 12).

In Beechdale Road Borehole the seam was 7 in thick. Its quality in opencast sites in the south-east of the district is medium to poor.

The measures between the Third Waterloo Coal and Second Waterloo Coal

The measures between the Third and Second Waterloo Coals vary in thickness from 46 ft at Swanwick New Pit to 16 ft at Wollaton Colliery No. 1 Shaft. They locally contain a this coal which is usually up to 3 in thick, but may be thicker when in close proximity to the Second Waterloo Coal.

The measures include a variable amount of sandy strata and the mudstones contain many mussels, some of which may be pyritic, together with fish debris, Spirorbis sp. Planolites montanus, worm tracks and borings.

The Second Waterloo Coal

The Second Waterloo Coal consists of two principal elements which, vinere they constitute separate seams, are named the Bottom Second Waterloo and Top Second Waterloo coals (Figure 35). This split is irregular and is illustrated by borehole sections from Babbington and Macfez Sites (Figure 73). The two leaves are re-united in the south-west of the district only within a restricted area of Jople Site. The Top Second Waterloo Coal itself divides in the south-east of the district. Graphic sections of the seam are shown on (Figure 74). The interpretation of the Second Waterloo Coal sequence is based upon a report by the former Nottingham Coal Survey Laboratory (Turner 1961b).

Away from the line of split the Second Waterloo Coal is 49 to 57 in thick with two dirt partings totalling up to 10 in. The lower parting divides the Bottom and Top Second Waterloo elements, but the upper parting is also conspicuous and can be widely traced in sections of both the Second Waterloo and the Top Second Waterloo. The Second Waterloo Coal has been extensively worked from Moorgreen Colliery and is generally of medium quality with a moderately low sulphur content.

The Bottom Second Waterloo, up to 31 ft below the Top Second Waterloo in the west of the district, is generally between 12 and 18 in thick (Figure 35), though in Shipley Park Borehole it is 21 in and in Shilo Site it ranges from 10 to 25 in. The few analyses show it to be of medium quality, but to the north-west of Ripley Colliery it is composed wholly of cannel up to 18 in thick.

Deep mine provings at the eastern margin and in the north-east of the district show the seam to be not more than 17 ft below the Top Second Waterloo and under 13 in thick, but it varies from 8 to 27.5 in in opencast sites on the eastern side of the Erewash Valley to the east of Ilkeston.

The measures between the Bottom and Top Second Waterloo coals are largely argillaceous, but include appreciable amounts of sandy strata near Heanor. Mussels occur at the base of the cycle.

The Top Second Waterloo Coal is thickest in the extreme north-west of the district where it may include a basal cannel up to 42 in thick, as Swanwick Colliery, Common Pit. The thickest proved sequence is 64 in at Swanwick Colliery, Old Pit; elsewhere to the west the thickness ranges from a doubtful 24 to at Shipley Park Borehole to 57 in at Codnor Common Site. The detailed sequence of the seam is variable, including many dull coal bands and, as at Brake House Site, one and sometimes two dirt partings some 8 to 12 in above the base. Its quality is medium with a moderately low sulphur content. It has been worked underground from Coppice and Woodside collieries and has extensive opencast workings.

At the eastern margin of the district, at Hucimall and Linby collieries, the Top Second Waterloo Coal is 22 to 33 in thick; and over an area in the south-east it divides into two leaves along a line slightly north and west of the split between the Top and Bottom Second Waterloo coals. The line of split on (Figure 35) is drawn approximately at the 18-in isopach of the separating measures and, as emphasized by Turner (1961b), it occurs at a higher horizon in the seam than the prominent dirt parting which can be widely traced to the district (Figure 74). The maximum proved separation of the two leaves is 15 ft to an outline record of Cederhill Colliery No. 2 Shaft. Very localized splits up to about 3 ft at the same horizon are apparent in some records from Shilo Site and Macfez Site (Figure 73), but are not shown on (Figure 35). A typical section of the split seam is provided by Cinderhill Colliery No. 4 Shaft Deepening: coal 22 in, measures 14 ft 8 in, on coal 11 in (Turner 1961, fig. 1). Similar sequences were present in Seagrave and Chilwell Dam boreholes and Broxtowe and Wollaton No. 3 Colliery shafts (Figure 74).

The Measures between the Second and First Waterloo Coals

The Measures between the Second and First Waterloo Coals are thickest—65 ft—in Swanwick Colliery New Pit in the north of the district and thinnest in Beechdale Road Borehole where they total only 23 ft. This southward attenuation continues a trend mentioned by Smith and others (1967, p. 164), but is irregular for the measures are only 31 ft thick at Ripley Colliery, 29 ft in Seagrave Borehole and 36 ft in Hucknall No. 2 Colliery No. 5 Shaft. Temporary sections near Ripley, Smalley, Heanor, llkeston, Brinsley and Strelley are described in Append. 2. They comprise two main cycles divided by the Waterloo Marker Coal, plus, locally, a third thin cycle caused by splitting of that coal. The thicknesses of the main cycles are variable, for instance the lower, which averages about 20 ft for the district, ranges from less than 1 ft at Gutter Slang and New Covert sites in the south-east to 30 ft in Swanwick Colliery New Pit (see also (Figure 73)). Both cycles contain sandy measures, but these are absent from the lower where it is thin. There are mussels at the base of both the main cycles, and 'aineoids' have been frequently recorded, mainly, however, from the lower cycle. Anthracosia phrygiana occurs in the roof of the Second Waterloo in Eastwood Hall Borehole with S A. aquiline, A. beaniana, A. phrygiana, Naiadites quadrates and Carbonita humilis in the mudstones overlying the Waterloo Marker Coal.

The Waterloo Marker Coal is a persistent this coal or cannel which serves as an indicator horizon between the First and Second Waterloo coals. It rarely exceeds 12 in in thickness and is of no economic importance. Seatearth alone marks its horizon at Greenhill Lane Colliery, Riddings, and Wollaton Colliery No. 3 Shaft; it is represented by 15 in of carmel in Brinsley Colliery Shaft and by two 6-in leaves of cannel, 18 in apart, in Annesley Colliery Shaft. Where split, the two thin leaves are usually a few inch.; apart, but are as much as 8 ft 2 in apart in Selston Colliery Underwood Shaft, where the leaves are each 1 in thick. Exceptional thicknesses have been noted in Swanwick Colliery, New Pit, 48 in of 'coal and clench'; Nutbrook Air Shaft, 48 in of coal; Moorgreen Colliery No. 1 Shaft, cannel 46 in, underlain and overlain by 9 in and by 5 in of 'batt' respectively; Kimberley Colliery Shaft, coal 16 in, 'batt' 5 in, on coal 13 in. The coal is exposed in the Loscoe Brick Pit [SK 426 471], Heanor (Appendix 2),

The First Waterloo Coal

The First Waterloo Coal forms a single seam over two large areas in the east of the district (Figure 36). As described by Turner (1961a), these two areas are separated by a narrow corridor within which the seam is split into the Bottom and Top Waterloo coals and which extends north-eastwards from Greasley Castle Borehole to Linby Colliery. The corridor opens at both ends into wide areas covering the northern and western parts of the district where the seam is similarly split.

In the northern area of undivided coal the minimum thickness of the First Waterloo is 34 in, in Annesley Colliery Shaft. It contains a prominent dirt parting, normally 1.5 to 6 in thick, but reaching a maximum of 12 in, in Linby Colliery Shaft. The lower leaf of coal varies from 16 in at Anneeley Colliery Shaft to 25 in at Moorgreen 1's Underground workings and the upper leaf from 14 in a drift [SK 4851 4816] at Moorgreen Colliery to 27 in in Moorgreen 23/10. Underground Borehole.

In the southern area of undivided coal the First Waterloo reaches a maximum of 59 in in Moorgreen 10's RH Underground Borehole; it thins eastwards to 21 in in Cinderhill l's Main Gate Underground Borehole and 29 in in Beechdale Road Borehole. The dirt parting, 5 to 11 in thick near the line of split, is only 0.5 to 0.75 in thick in the sections of opencast sites on the east site of the Eyewash Valley and is not recorded in many of the deep mine provings in this part of the district. Below the prominent central dirt parting, the seam (Figure 36) consists largely of bright coal of medium ash and moderately high to high sulphur content; there is frequently a dirty coal or dirt parting 2 to 4 in above the floor of the seam, which is traceable into the areas of divided coal in the west and north of the district. Above the prominent dirt parting the seam is more variable with bands of hard and dirty coal; its quality is variable, again a thin dirt parting is present near the base in some sections. There are small isolated underground workings in the combined seam.

The corridor of split coal which divides the field of the First Waterloo was encountered in Moorgreen 2's Drift, Moorgreen Wathall Drift (for locations see (Figure 36)) and in Linby Engine House and Pit Bottom Underground boreholes; its extension between Moorgreen Wathall Drift and Linby Colliery is not proven, but the interpretation shown in (Figure 36) follow. Thence (1961a). Turner emphasised that the split in the corridor which takes place at the prominent dirt parting, is accompanied by partial or complete washout of the bottom leaf of the seam. The two leaves of the First Waterloo are 31 ft apart in Moorgreen 2's Drift with 6 in of cannel representing the lower leaf or Bottom First Waterloo. The dividing measures are largely siltstone, and the Top First Waterloo consists of dirty coal 8 in, coal 9 in, dirt 2.5 in, on coal 2.5 in; in a drift [SK 5060 4795] near Watnall Colliery, the Bottom First Waterloo is 2.5 in of cannel lying 37 ft below the Top First Waterloo, here coal, 20 in, capped by 2 in of dirty coal. In Linby Pit Bottom Underground Borehole only the Top First Waterloo, 16 in thick, was proved, the Bottom First Waterloo Coal being washed out; in the Engine House Underground Borehole, only 270 yd to the south, the Bottom First Waterloo is 11.5 in thick separated by 33 ft of mainly silty measures from the 14-in Top First Waterloo. In workings 1200 yd NW of Linby Colliery Shaft the First Waterloo consisted of hard coal 12 in, bright coal 3 in, dirt 4 in, on bright coal 24 in.

Over the remainder of the district, that is, in the north and west, the seam is divided into Bottom and Top First Waterloo coals; the line of splitting shown on (Figure 36) is drawn at the 12-in isopach of the dirt parting at which the split occurs. The maximum division of the leaves is in the north-west of the district and amounts to 39 ft in Swanwick Colliery, Common Pit. The dividing measures are composed of a single cycle.

The Bottom First Waterloo Coal is recorded as comprising 30 in of cannel in Swanwick Colliery, Common Pit, although this maximum thickness must be regarded as doubtful because only 12 to 15 in of coal were recorded in nearby shafts of the same colliery. The seam is mainly 18 to 24 in thick, but reaches 27 in at Brineley Wharf and Nutbrook sites and 28 in in Dovecote Road Borehole. The seam was not recorded in Nutbrook Air Pit, where presumably it was washed out amongst the 18 ft of sandy measures below the Top First Waterloo Coal.

Apart from cannel, recorded as being 24 in thick in Woodside Colliery Shafts, some 20 to 22 in at Shilo Site, 60 in at Whiteley'. Plantation. Site and 18 in at Codnor Common Site, the Bottom First Waterloo consists largely of bright coal of variable quality. An impersistent dirt parting near the base divides off a thin floor coal of poor quality. Some sections, however, show a band of hard coal within the brights and others, like Dovecote Road and Lower Beauvale boreholes, may have up to 11 in of dirty coal at or near the top of the seam. The sulphur content is variable, many records showing it to be moderately high. At Broad Lane, Wansley Hall and Hobsic sites, in the north-central part of the district, the seam improves to good or medium quality, but still has a variable but generally moderate sulphur content. There are sporadic opencast workings in the seam. It is exposed in the Loscoe Brick Pit.

The Top First Waterloo Coal is thickest adjacent to the lines of split in the First Waterloo Coal. It is 30 in thick in Moorgreen Colliery 10's workings of which 15 in is dirty coal or dirt; 22 in in a drift [SK 5060 4795] near Watnall Colliery, of which 2 in is dirty coal; and 19 in in Bentinck W.1 Underground Borehole, of which 5.5 in is dirty coal.

Away from the lines of split the seam is frequently recorded as cannel, usually about 12 in thick, but reaching 23 in in Brinsley Colliery shafts. Some 22 in of coal occur in Portland Colliery No. 7 Shaft immediately north of the district and 24 in at Headhouse Farm Site in the south-west. The coal is economically unimportant.

The measures between the First Waterloo Coal and Dunsil Coal

The measures between the First Waterloo and Dunsil Coals form a single cycle normally about 30 ft in thickness, but ranging up to 57 ft as in Bentinck W. 1 Underground Borehole. The measures are variable in lithology and many sections show an unusually thick seatearth below the Dunsil Coal amounting to, for instance, 12 ft in Selston Colliery Underwood Shaft and Wollaton Colliery No. 2 Shaft and 16 ft in Coppice Colliery shafts. Small Anthracosia cf. phrygiana were recorded from the roof measures of the First Waterloo Coal in Eastwood Hall Borehole and A, ditjuncta and Naiadites sp. in Annesley Park Borehole. Plant debris is present throughout the measures; sineoids and worm tracks have also been noted.

The Dunsil Coal

The Dunsil Coal usually consists of a main leaf 18 to 34 in thick and a thin floor coal a few inches below. Over large parts of the district (Figure 37) the floor coal is not recorded separately and it appears from detailed sections that it is locally united with the main leaf. Elsewhere, particularly at Cromford Canal Site and over most of the eastern part of the district, less reliable evidence suggests that it has died out. The isopachs of the seam are shown in (Figure 37).

The thickest overall sequence at Damstead Lily Site is 50 in, of which the floor coal is 10 in and the dirt parting 7 in; the remaining 33 in of coal represents the second thickest record of the main leaf in the district. Other records from the same site show a 7-in floor coal, a dirt parting varying from 5 to 9 in and a 29-m main leaf. The seam also exceeds 42 in in the adjacent Broad Oak Site (floor coal 7.5 in, dirt 11 in, main leaf 25.5 in) and in Beauvale Borehole (floor coal 1 in, dirt 10 in, main leaf 32 in). The thickest record of the main leaf was in Moorgreen Colliery No. 1 Shaft, adjacent to Beauvale Borehole, and totalled 34 in of which the basal 4 in was composed of dirt and 'batt'; the floor coal was 1 in of 'batt' 4 in below the main leaf. The record of the Dunsil Coal in No. 2 Shaft at Moorgreen Colliery is;- floor coal, 1 in; 'clunch' 26 in; 'batt' 4 in; coal ('contains stone and smut') 32 in. The dirt parting does not exceed 11 in elsewhere in the district. Throughout the remaining areas of split seam the total thickness is not less than 24 in and the main leaf not less than 18 in.

In those parts of the district where the floor coal has not been separately recorded, the seam is thickest, 40 in, in Swanwick Colliery New and Deep pits. A record of 38 in in Wollaton Colliery No. 3 Shaft is doubtful, for only 23 in were noted in No. 1 Shaft. More detailed records from opencast sites nearby suggest that the floor coal is united with the main leaf. The seam is 36 in thick at Birdswood Site and Shipley Colliery, Deepfields Shaft, 35 in at Dobbs Site, 34 in at Ellerslie Site, 35 in in Bentinck 31's Underground Borehole and 31 in at St. Helen's Site and Woodside Colliery Shaft. The minimum thicknesses are 18 in in Brinsley Colliery Shaft and 16 in, of which the top 3 in are cannel, at Linby (Engine House) Underground Borehole. In Deepfields Shaft and Woodside Colliery the floor coal appears to be united with the main leaf.

The floor coal normally comprises bright coal which, in some analyses, is dirty; the main leaf has variable thicknesses of bright coal at the balm and top with dull or banded bright and dull coal in the middle. Cannel, up to 11 in thick, is present at the top of the seam near Hucknall No. 2 and Linby collieries and at Katie and Kim sites to the south-east of Eastwood. An analysis from Station Site and another from High Leys Borehole showed a thin dirt parting near the top of the seam. The quality of the Dunsil is good to medium, with low to medium ash content and low to moderately low sulphur content. The seam has been mined locally, but it has mostly been worked by opencast means.

The measures between the Dunsil Coal and Top Hard (or Top Hard Floor) Coal

The measures between the Dunsil and Top Hard (or Top Hard Floor) Coals form a single cycle about 40 ft in thickness, but as much as 54 ft in Shipley Colliery Deepfields Shaft and as little as 24 ft in Selston Colliery Underwood Shaft. Anthracosphaerium exiguum, fragmentary Anthracosia sp. and Carbonita humilis were present in the roof of the Dunsil Coal in Eastwood Hall Borehole and A. disjuncta, A. aff. phrygiana, C. humilis, and C. cf. scalpellus in Annesley Park Borehole and sineoids and worm tracks are also known. Ironstones are prominent in the mudstones, though in places, as at Deepfields Shaft, the cycle is mainly composed of sandstone.

Top Hard Coal to Mansfield Marine Band

The general thickness and lithological characteristics of this group of strata are shown on (Figure 46). Thicknesses range from a maximum of about 590 ft in the High Park Colliery area to a minimum of 520 ft at Hempshill Colliery. The chief coals mined underground are the Top Hard–Comb at the base, and the Cinderhill, High Hazles, Lowbright and Mainbright higher in the sequence. Coals of lesser importance are the Mainsmut, Brinsley Thin and Two-Foot. Sandstones are common and are locally prominent above the Cinderhill coals and between the Lowbright Coal and Haughton Marine Band. Washouts occur in the Top Hard and Clown seams. The Two-Foot Marine Band is found throughout the area but the Manton 'Estheria' Band and Haughton Marine Band are impersistent. The Top Hard is a convenient boundary to take between the A. modiolaris and Lower similis-pulchra zones for it separates the characteristic A. phrygiana fauna below, from the equally distinctive Anthraconaia pulchella Broadhurst fauna above.

The lowest distinctive fauna of the Lower similis-pulchra Zone occurs above the ?Second St Johns Coal and includes Anthraconaia pulchella, Anthracosia cf. planitumida and A. simulans.

Slightly higher in the sequence, above the Cinderhill Coal, representatives of the Anthracosia caledonica fauna were proved. In addition to this species the assemblages included A. sp. cf. fulva.

The mussel-bands between the High Hazles and Two-Foot coals are notable for the first appearance of the Anthracosia atra group. The associated species include Anthracosia simulans and Naiadites cf. obliquus. The A. atra group attains its acme in the beds overlying the Clown Coal. In the higher beds up to the Mansfield Marine Band museels are not common but include Naiadites aff. angustus.

The Top Hard–Comb Coal

The Top Hard–Comb Coal consists of four elements, namely, the Top Hard Floor Coal, the main part of the Top Hard Coal and the Lower and Upper Comb coals, which occur in a variety of combinations in strata ranging in thickness from 12 ft at Shipley Colliery Deepfields Shaft to 87 ft at Dobbs Site (Figure 39), (Figure 40), (Figure 41).

Over most of the outlier at Heanor all four seams are united and the dirt partings in the sequence may total as little of 10 in, as at Shipley Colliery. The various lines of split in the composite seam are shown on (Figure 39)a.

The Top Hard Floor Coal is separately identified north-east of Eastwood ((Figure 39)a). It is derived from the Top Hard seam by a split off the Bottom Brights (see below) and is of variable quality. It is separated from the Top Hard by up to 48 ft of measures in Newstead Colliery No. 1 Shaft. It is thickest near the line of split, e.g. 20 in at Moorgreen Colliery shafts, 5 to 9 ft below the Top Hard, and a maximum of 28 in in Kimberley Colliery Shaft, 2 ft below the Top Hard. It averages 16 in in the Selston area and at the nearby Hobsic Site 17 in of bright coal are underlain by 4 in of cannel. In Annesley Park Borehole in the north-east, 3 in of cannel overlie 1.5 in of coal. A cannel is well known at this horizon in the south-west of the Chesterfield district (Smith and others 1967, p. 169). At Hucknall No. 2 Colliery the Floor Coal is 9 in thick some 14 ft below the Top Hard and at Broxtowe Colliery 17 in thick, 20 ft below. It is thinner elsewhere in the south-east of the district and in Beechdale Road Borehole is absent. Sporadic records, e.g. at Parkfield Farm and Catstone Hill sites (Figure 40) show a thin (up to 3 in) parting near the base of the Floor Coal, separating off the lowest 1 to 2 in of coal.

The Top Hard Coal itself consists of bright coal at the base and top of the seam, the Bottom Heights and Top Brights, separated by a variable thickness of hard coal, the Hard. (Figure 40). The hard coal provided an excellent locomotive and steam fuel and the 'bright.' a house coal. The overall high quality made it one of the principal economic seams in the coalfield and it was the first to be exhausted in the present district. In many early workings only the 'hard.' were removed leaving the 'heights' as a roof and floor; these remnants have been exploited by opencast means in recent years and are still eagerly sought. Variations in thickness of the Top Hard are shown in (Figure 41). In Hucknall Nos.1 and 2 collieries there is cannel at the base of the seam, 27 in thick in No. 2 Colliery No. 5 Shaft. According to Elliott (1965, pp.133–141) the cannel was formed in a pool flanking a 'swilley' which is present to the east of this district. At Madan Site one record shows an anomalous 63 in of cannel at the base of the 130-in seam section.

The Comb Coal in the Heanor outlier is usually less than 9 in above the Top Hard, but locally as much as 15 in. The following section of the Comb from Office Site (2 in above the Top Hard) may be taken as typical: Lower Comb Coal, 18 in; dirt, 8.5 in; Upper Comb Coal, 27 in. The dirt parting within the Comb expands gradually southwards and is 3 ft thick at the line of split shown on (Figure 41). In Shipley Lake Site the dirt has passed into argillaceous measures about 40 ft thick. The Upper Comb Coal, normally 24 to 30 in thick in this site, is 60 in in one proving, and the Lower Comb, 12 to 27 in thick, lies 4 in to 3 ft above the Top Hard. This split in the Comb Coal occurs sub-parallel to, and appears to be related to, a linear 'washout' of the Lower Comb and Top Hard coals which occurs in the southern part of the site.

At Codnor Common Site, in the outlier at Ripley, the Comb Coal totals 52 in, including the 4-in dirt parting, and is 5 ft above the Top Hard. The separation from the Top Hard is up to 87 ft in Dobbs Site, in the north of the district, where the overall thickness of the seam is 25 in, of which only 0.25 in is dirt. Nearby, at Damstead Lily Site, the upward sequence was coal 19.25 in, dirt 2 in, coal 1 in, dirt 2 in, coal 13.25 in. Cromford Canal Site [SK 460 481] exposed a 40-ft trunk of Lepidodendron in position of growth, with its base in the Top Hard Coal and its top close to the base of the Comb seam. (Plate 6). In the remainder of the district the Comb Coal varies from 21 in at Linby Colliery to a maximum of 46 in, including 6 in of dirt, in the Kimberley Colliery area. Over a wide area it lies less than 18 in above the Top Hard Coal.

The measures between the Comb Coal and Mainsmut Coal

The measures between the Comb and Mainsmut Coals range in thickness from 21 ft at Moorgreen Colliery No. 1 Shaft to 71 ft at Anneeley Park Borehole (Figure 75). The Comb Coal is closely succeeded over wide areas by sandstone or interbedded sandstone, siltstone and mudstone, which is locally referred to as the 'Top Hard Rock'. This is thickest (over 50 ft) in the Hucknall area, and over much of the exposed coalfield forms a pronounced feature or is part of a composite feature upon which Swanwick, Ripley and Heanor are sited.

The following is a composite section of these measures built up from measurements along a face [SK 4568 4823] at Cromford Canal Site, near Eastwood.

The Mainsmut Coal

The Mainsmut Coal has been traced from Pittston in the north of the district to Wollaton in the south, but its crop is concealed beneath Permo-Triassic rocks for about 1 mile in the Strelley–Kimberley area. It also occurs to the west of the main crop in several faulted synclines near Swanwick, Ripley, Eastwood and Shipley. In the type area around Shipley, Kimberley and Watnall, the seam is generally 24 to 36 in thick (Figure 75). A maximum of 39 in was recorded at Shipley Park Borehole, where the seam was composed of two 17-in bands of bright coal separated by 5 in of 'hards'. North-eastwards the seam splits into two leaves, up to 27 ft apart, and deteriorates both in quality and thickness. The ash content of the seam in the south and west is usaully moderately high (7 to 10 per cent) but in the north and east it is very high (29.8 per cent at Delves Site near Swanwick). The sulphur content is typically low.

The Mainsmut Coal is unusual because of the presence of inclusions within the upper part of the seam. They vary from sandy laminae to lenses of quartz itic sandstone. In City Site, the Coal Survey Laboratory recorded that sandstone replaced large parts of a tree stump. 'Stone' inclusions have also been recorded from Hobsic, Cromford Canal and Poplar Farm sites. Earthquake activity following deposition may be a contributory factor to the formation of the inclusions but the coal is typically overlain by silty mudstone, and only rarely by sandstone.

The measures between the Mainsmut Coal and Cinderhill Coal

The measures between the Mainsmut and Cinderhill Coals range in thickness from 106 ft in Moorgreen No. 1 Colliery Shaft to 42 ft at Hucknall No. 2 Colliery No. 5 Shaft. They contain, in the areas of thickest sedimentation, several cycles and two thin coals (up to 9 in thick) or seatearths. These coals may equate with the Second St John's Coal of the Chesterfield district to the north.

Sandstone, up to 50 ft thick, is common and forms good features in the Pinxton–Brinsley area. Bivalves are recorded at various horizons, notably some 30 and 60 ft above the Mainsmut Coal (Appendix 1, p. 165a). They are usually found either in black shale as at Beechdale Road Borehole (at 153 ft), or preserved in ironstone nodules or bands. Fish scales were recorded above a 1-in coal at Seagrave Borehole, some 45 ft above the Main nut.

The Cinderhill Coal

The Cinderhill Coal sometimes referred to as the Cinderhill Main, is 44 in thick in Cinderhill Colliery No. 4 Shaft and consistently a little under 4 ft in the surrounding area. It was mined in the 1920's on both sides of the Cinderhill Fault. This belt of thick coal trends west-north-westwards through Nuthall and Kimberley and has been worked opencast in synclinal outliers south of Heanor, at Poplar Farm and Johnson Farm sites (Figure 76). In these thick sections the coal is composed essentially of 'heights' with banded dull and bright coal forming a thin parting in the middle of the seam. Ash content is low to moderate and sulphur percentages are moderate to moderately high.

At Hempshill, less than a mile to the north of the Cinderhill area. the upper half of the coal contains many dirt partings. North-east of a line through Strelley, Kimberley and Eastwood the Cinderhill splits and may be represented to the north and east by up to three coals (Figure76)b i.e. an upwards sequence of a Cinderhill Coal, an Upper Leaf and a split from the Upper Leaf. The interval between the Cinderhill and the Upper Leaf seam ranges from 9 in at Watnall Colliery No. 7 Shaft to 30 ft at Cromford Canal Site. The Upper Leaf is 18 in thick in Watnall Colliery No. 6 Shaft and varies between 10 in and 24 in at Cromford Canal Site. It thins to the north to less than 6 in. The Upper Leaf is split over a large area by a parting up to 22 ft thick at Hill Top Colliery. The highest leaf, however, is commonly absent and represented only by a seatearth. Smith and others (1967, p. 174) state that the Cinderhill Coal cannot be recognised with certainty in the shaft sections east of Alfreton, but infer from its position relative to the High Hazles that it may be the correlative of the First St John's Coal of districts to the north.

The measures between the Cinderhill Coal and High Hazles Coal

The measures between the Cinderhill and High Hazles Coals vary between 105 ft at Hempshill Colliery in the south and 48 ft at Newstead Colliery in the north, although leaves of the two coals are only 27 ft apart at Moorgreen Colliery. The succession in the areas of maximum deposition is dominated by sandstone, which is over 80 ft thick at Hempshill Colliery. At Newstead this sandstone was recorded as 'exuding grease'.

The High Hazles Coal

The High Hazles Coal is an economically important seam which has been worked in the past from Linby, Bulwell and Cthderhill (Babbington) collieries. It has promising reserves in the north-east of the district, where it is well documented from over 50 provings. The main seam is a maximum thickness of 36 in in Linby 52's Underground Borehole in the north-east, but it splits and thine to the south and west beyond Hucknall and Annesley (Figure 42). There are three this But coals, all 12 in or less in thickness, with. 27 ft of strata below the main seam in Cinderhill Colliery No. 4 Shaft. They are represented by seatearths in Garfit House Borehole and farther south are missing, eg at Annesley Lodge Borehole.

West of the main split of dirty coal from the bottom of the High Hazles the main seam is this in a sinuous belt extending from Portland Colliery through Annesley Lodge to Kimberley (Figure 42). This belt corresponds closely in position to underlying sandstones and siltstones and is attributed by Elliott (1969, p. 120, fig. 3) to a swamp drainage feature subsequently filled with distributory deposits. West of this belt the main seam is 42 in thick at Rap Site and 45 in thick in an isolated area at Allens Green Site. Farther west in the Swanwick Syncline, opencast sites such as Tramway and Sleet Moor/Alfred Sleet show up to four divisions in the main seam with dirt totalling up to 15 ft. The top part of the main seam commonly contains 'stone' inclusions over much of Sleet Moor Site.

The High Hazles Coal consists largely of bright coal, but both the top and bottom of the seam are dirty. A sinuous belt of inferior coal developed in the top of the seam has been traced by Elliott (1969, fig. 3) north-east of Hucknall, and is comparable in trend with the belt of this coal referred to above.

Patches of cannel are developed locally at the top of the seam, as at Newstead. The ash content varies considerably; it is lowest in the areas of thickest coal at Linby (3.7 per cent) and Aliens Green Site (2.9 per cent) and high to very high in the Swanwick Syncline. Sulphur content is moderately low.

The Brinsley Thin Coal

The Brinsley Thin Coal is separated from the High Hazles Coal by largely argillaceous measures ranging in thickness from 20 ft at Hempshill Colliery to 45 ft at Portland Colliery No. 2 Shaft. In the type area near Brinsley village, two miles north of Eastwood, the Brinsley Thin consists of up to 48 in of coal and dirt, but its average thickness is 2 ft at outcrop between Selston and Watnall and it decreases to under 6 in in the north-east of the district. In the Swanwick Syncline the coal is characterised by numerous splits and dirt partings. A belt of thin coal is present between Annesley Lodge Borehole and Cinderhill, a similar position to that in the underlying High Hazles seam (p.164b).

North and east of this belt a this coal, the Brinsley This (Upper Leaf), is proved above the Brinsley Thin. It is represented by a seatearth 9 ft 3 in above the Brinsley Thin in Kennel Wood Borehole and is a 4-in coal at Annesley Park Borehole. It thickens eastwards to a 13-in seam, 12 ft 2 in above the Brinsley Thin, in Linby 52's Underground Borehole.

The Brinsley This Coal is variable in quality with ash content ranging from good to very inferior (3.6 to 27.0 per cent). Sulphur content varies from low to moderately high (0.5 to 2.4 per cent). The best coal was obtained from Pepper Hill Site, but wide variations occur even within one site (e.g. at Aliens Green Site; ash content 5.3 to 27.3 per cent). As a result of such variability, coupled with As limited area of coal over 2 ft thick, the Brinsley This has never been an economic proposition for deep mining.

The measures between the Brinsley Thin (Upper Leaf) Coal and Lowbright Floor Coal

The measures between the Brinsley Thin (upper Leaf) and Lowbright Floor Coals range in thickness from 50 ft at Selston Colliery in As north-west to 25 ft at Hempshill Colliery in the south-east. They comprise largely argillaceous strata containing sporadic 'mussels' including Naiadites cf. obliquus, particularly common in the roof of the Brinsley Thin, together with plant fragments and Planolites. The mudstones contain ironstone bands up to 8 in thick.

The Lowbright (Furnace or Abdy) Coal

The Lowbright (Furnace or Abdy) Coal is over 30 in thick in much of the district, reaching a maximum of 46 in in the south-west at Lambclose House Site (Figure 43). It has been worked underground to a limited extent at Newstead, Watnall and Cinderhill (Babbington) collieries, but has been extensively exploited by opencast workings between Pinxton and Kimberley. The seam thins to below 30 in around Kennel Wood Borehole (21 in) and Watnall Colliery No. 3 Shaft (12 in). These areas of thinning appear to be related to the belts of this coal in the underlying Brinsley Th. and High Hazles seams (pp. 00 and 00). The Lowbright Coal shows a deterioration in quality, with several thick dirt partings, in the north-west of the district. The Sleet Moor Site in the Swanwick Syncline typifies this split inferior coal sequence (Figure 43). The Lowbright is composed largely of 'brights', with a persistent band of 'hards' about the middle of the seam, at which level the splits tend to occur. In the areas of thinner coal (see above) only that part of the seam below the 'hards' is present. In the Annesley–Linby area the bottom of the seam includes inferior pyritic coal. The ash content varies from very low (2.5 per cent) in the Hucknall–Watnall area to high (over 15 per cent) in the Portland area. Sulphur percentages range from his to moderate.

The Lowbright Coal was exposed in bridge foundation holes [SK 5246 4302] near Broxtowe Colliery, where the following section was measured:

The Floor Coal usually occurs less than 10 ft beneath the Lowbright. In the north-east of the district it closely approaches the main seam and in Newstead N1 Underground Borehole a separation of only 5 in is recorded. The Floor Coal, which is commonly split by a dirt parting in the area around Hucknall and Newstead, is composed largely of 'brights' averaging some 10 in, but increases in thickness north-westwards to 16 in at Oaktree Farm Site and between 22 in and 32 in at Sleet Moor Site in the Swanwick Syncline.

The measures between the Lowbright Coal and Two-Foot Coal

The measures between the Lowbright and Two-Foot Coals consist predominantly of interlaminated and interbedded sandstone and siltstone and are thickest, up to 44 ft, in Kennel Wood Borehole. The sandstone occurring at this locality is unusual. It contains two this breccia horizons made up of siltstone fragments and ferruginous nodules, and shows many sedimentary structures such as current ripples, disturbed laminae, crumpled bedding and rib and furrow development. The sequence is thinnest (26 ft) in the vicinity of Selston Colliery, where the roof measures of the Lowbright Coal contain bivalves.

The Two-Foot (Sough or Middlebright) Coal

The Two-Foot (Sough or Middlebright) Coal exceed. 18 in over much of the district, but varies from 29 in at Rap Site in the south-west to about 6 in in the extreme north-east (Figure 78). In the Swanwick Syncline it average. 24 in. Sporadic sections such as Cinderhill Colliery No. 4 Shaft show a minor dirt parting within the middle of the Two-Foot Seam. The seam is of little economic value for deep mining, but its close proximity to the Mainbright Coal along most of the outcrop has led to the extraction of both seams from the same opencast workings. The seam consists largely of 'bright.), but many analyses show the upper half to be rather dirty. The ash content therefore varies widely, from low (4,3 per cent, Garfit House) to very high (21.7 per cent, Whyburn House) in under two miles. Sulphur percentages range from low (0.8 per cent. Wansley Hall) to very high (4.4 per cent, Aliens Green).

A thin floor coal, 2 to 9 in thick, is present some 2 ft to 10 ft below the Two-Foot between Cinderhill and Selston. In Cinderhill Colliery No. 2 Shaft a 7-in coal some 10 ft above the Two-Foot may be an upper leaf of the seam.

The measures between the Two-Foot Coal and Mainbright Coal

The measures between the Two-Foot and Mainbright Coals range between 19 ft in Linby 52's Underground Borehole in the east and 10 ft at Willey Wood Colliery in the west. The Two-Foot Coal is invariably overlain by dark grey mudstone—'black bind' in the old shaft records. It is slightly silty, rather fissile and contains ferruginous laminae, some with a speckled appearance, possible due to kaolinisation, whilst others are oolitic. The mudstone is richly fossiliferous, containing fish debris, 'Estheria' sp., bivalves and microfossils, together with pyritized and carbonised plant fragments (Appendix 1., p. 164d).

The Two-Foot Marine Band forms a reliable marker horizon and has been proved to be of wide lateral extent throughout the district. It comprises that part of the above-mentioned fossiliferous mudstones which contains Lingula and foraminifera, commencing immediately or close above the Two-Foot Coal and extending up to 5 ft 2 in above. The Two-Foot Marine Band is some 2 ft 6 in thick in Whyburn House Borehole with the lowest part represented by Lingula mytilloides only. The upper part contains both Lingula and and Parapachites together with fish remains.

In Felley Lane Borehole the fauna contains Myalina sp. in addition to the above species an assemblage which is typical of the Halina facies present at this horizon in the Notts–Derby Coalfield. Lingula has been recorded by Mr W.N. Edwards in the roof of the Two-Foot [SK 4710 5140] in Bagthorpe Site and in poorly exposed mudstone [SK 4784 5200] together with fish scales in Middle Brook near Seleton. Dr J. Shirley found Lingula 2 to 3 in above the coal in Willeywood Farm Site [SK 4707 4899]. Lingula was also recorded in Cinderhill Mainbright Drift, Cinderhill Return Drift and Bulwell Steps Drift. The marine band has been detected in shallow proving holes at Sleet Moor Site near Swanwick, and on the line of the M1 Motorway near Pinxton, just beyond the northern margin of the district. The following recent borehole. drilled by the N. C. B. passed through the Two-Foot Marine Band, the thickness of which is indicated in brackets: Annesley Lodge (4 in), Annesley Park (13 in), Felley Lane (3 in), Garfit House (9 in), Hucknall High Main 27's (4 in), Mapplewells (38 in), Newstead N3 Underground (47 in) and Whyburn House (30 in). The dark grey mudstones in the lower half of this cycle pass up into silty mudstones with sporadic siltstone laminae containing a few mussels including Anthraconaia cymbula and scattered plant fragments.

The Mainbright Coal

The Mainbright Coal is an economically important seam, which has been worked from Hucknall, Watnall, Bulwell, Hempshill and Cinderhill collieries, but its best reserves lie beyond the eastern limits of the present district. The type section of the seam is at Hucknall No. 2 Colliery, No. 5 Shaft, where it consists of 3 in of bright coal containing a 5.5-in parting of banded 'dull' and 'brights'.

In the main area of outcrop, the Mainbright Coal is thickest in the south and west with a maximum of 49 in recorded in a temporary section [SK 5276 4307] near Broxtowe Wood (Figure 44). It thins northwards to 36 in in the Hucknall–Selston area and to 24 in near Annesley Park and Mexborough. The coal deteriorates in the north-east corner of the district, where it splits into thin seams with dirt partings, or is represented by cannel and inferior coal as at Newstead. A washout was encountered in Garfit House Borehole and the top of the seam is partially eroded beneath sandstone at Linby 52's Underground Borehole. In Annesley Colliery Shaft 'grey and brown rock mixed with fossils and coal' was recorded 8 ft above a 6-in coal at the Mainbright horizon and a partial washout is indicated in Mapplewells Borehole by thin coal, cannel and batt at a similar horizon.

The seam generally is of good quality with low ash and sulphur contents. It is composed largely of 'brights', with subsidiary partings of dull or banded bright and dull coal throughout (Figure 44). In the Swanwick Syncline the Mainbright Coal is exceptionally thick (up to 50 in) but contains several dirt partings and the upper half of the seam is dirty coal with an ash content as high as 21.3 per cent.

The measures between the Mainbright Coal and the Mansfield Marine Band

The measures between the Mainbright Coal and the Mansfield Marine Band vary from 246 ft at Anneeley in the north to 185 ft at Cinderhill in the south. They include several that coals of no economic value such as the Clown and ?Swinton Pottery. Marine bands and marker horizons proved in these measures in the Chesterfield and Ollerton districts to the north tend to be leas persistent and only the Haughton Marine Band has been proved with certainty in the present district. The measures are rich in ironstone nodules and ferruginous patches; sphaerosiderite is common locally, as in the seatearth of the Clown Coal. Worm burrows are much in evidence and are often lined by ferruginous residues; root structures in the seatearths are replaced by ironstone.

'Estheria' is found in the roof of the Mainbright Coal in many recent boreholes, e.g. Annesley Lodge, Annesley Park. Felley Lane, Kennel Wood and Mapplewells. The fossil is preserved mostly as irridescent films in a grey mudstone, and is associated with ostracode, small mussels and fish remains.

Distorted roof measures have been observed on the Mainbright Coal. Shirley (1955, p. 274) recorded near-vertical 'dykes' of hard sandstone 2 to 5 ft thick, in roof measures at Bagthorpe Site. He attributed this phenomenon to earthquake tremors, the effects of which he has traced in other parts of the coalfield at this horizon (Shirley in Eden and others 1957, p.112). Shirley (1955, p. 275) noted that the roof of the Mainbright in Hucknall No. 1 Colliery, in a small area south-west of the shafts, is composed of a mixture of sandstone, mudstone and coal, which may be due to either washouts or to earthquakes. The lowest cycle lying between the Mainbright Coal and the Manton 'Estheria' Band. contains beds of sandstone up to 50 ft thick which make a strong feature and have been mapped in the Mexborough–New Portland area [SK 47 54]. A this coal at the Manton Estheria Band horizon has been proved in Mapplewells, Kennel Wood, Whyburn House, Anneeley Park and Annesley Lodge boreholes and in Hucknall No. 2 Colliery No. 5, Linby Colliery No. 1, Newstead Colliery No. 1 and Willey Wood Colliery shafts. It is thickest (18 in) at Annesley Park Borehole, but contains many sandy inclusions and lenses. It is represented by a seatearth at Wiley Wood Colliery Shaft and is probably washed out in the Cinderhill area to the south.

The Manton 'Estheria' Band horizon occurs in Annesley Park Borehole. where 'Estheria' associated with fish scales is present hi 8 in of black mudstone. Nearby boreholes which showed mussels and fish debris in dark grey to black mudstones, commonly silty and carbonaceous, at this horizon are: Kennel Wood, 6 in with mussels; Mapplewells, 17 in, with fish debris and mussel. 9 in above a 4-in coal; Whyburn House, 6 in with fish debris and muesels.

Some 7 ft above the ?Manton 'Estheria' Band in Grives Quarry Borehole [SK 5015 5492], just beyond the northern edge of the district, a kaolin oolith bed was recorded. Kaolin also cements a sandstone 24 ft above the Band in Felley Lane Borehole.

The strata between the ?Manton 'Estheria' Band and the Clown Coal range from 78 ft in the west at High Park Colliery to 12 ft in the east at Annesley Park Borehole. South of Hucknall the absence of the Manton 'Estheria' Band and presence of washout sandstones at the Clown horizon make correlation uncertain.

The Clown Coal is thickest in the west, amounting to 78 in in Wansley Hall Site, but thinning rapidly eastwards. Beyond Watnall and Newstead it is either washed out, thin or represented by a seatearth (Figure 45).

The coal commonly contains many dirt partings which render the seam economically worthless. The Coal Survey Section at Dixie Site [SK 4765 5020], near Selston, was coal 12 in at top, dirt 165 in, coal 3 in, dirt 14 in, sandstone 2 in, coal 8 in, dirt 1 in, coal 33 in, dirt 2 in, with coal 17 in at bottom.

In the High Park area, the Clown Coal is split into two leaves by some 12 ft of measures. This split increases northwards to 35 ft at Wiley Wood Colliery, where the looser leaf thins out and is represented only by seatearth. At Linby Colliery No. 1 Shaft, two coals of 10 and 9 in, split by a 15-in dirt parting, are separated by 21 ft of measures from an underlying 17-in cannel. Leaves of the Clown Coal were exposed in the M1 Motorway cuttings [SK 4735 5390] near Selston where the following section was recorded:

Temporary sections in pipe trenches [SK 4765 5237] on Selston Common proved the Clown crop, with the following partial section:

Some 80 yd farther south the following section was recorded [SK 4739 5381]:

The oolitic ironstone is very variable in thicknese over a 50-yd length of cutting. The upper coal is probably the same seam as the 2-ft coal in the adjacent section.

In Selston Colliery yard [SK 4687 5040] a temporary section showed 12 in of coal immediately overlain by a sandstone which has washed out the Clown Coal to the north in Wansley Hall Site. Further washout phenomena were proved in Felley Lane and Annesley Lodge boreholes, Hucknall High Main 27.e Underground Borehole and Hucknall No. 2 Colliery No. 5 Shaft, which lie in a clearly defined belt trending west-north-west to east-south-east (Figure 45).

The strata overlying the Clown Coal are either dark grey mudstones or thick sandstones, the latter in places filling washouts in the seam. The sandstones produce a marked feature in the Underwood area, upon which part of the silage is sited. Boreholes through the concealed measures to the east proved up to 80 ft of sandstone (Watnall Colliery No. 1 Shaft), but thicknesses vary irregularly; for instance, from 45 ft at Annesley Park Borehole, where the rock is a pale grey-green colour to only 10 ft at the nearby Linby Colliery Shaft.

The dark grey to black mudstone intermittently forming the roof of the Clown Coal contains variable amounts of fish and carbonaceous plant debris in the lowest few inches. In Mapplewells Borehole, fish scales are common, but they are rare in Annesley Park Borehole. In Whyburn House Borehole the fish scales were preserved in a 'canky' siltstone. In the Chesterfield district to the north the mudstone also contains large specimens of Lingula and forms the Clown Marine Band.

The mudstones above the horizon of the Clown Marine Band contain numerous 'mussels' typical of the Anthracosia atra fauna, together with pyritic plant fragments and ferruginous bands showing evidence of boring organisms. Some 20 ft above the Clown Coal, in Mapplewells Borehole, such mudstones and slltstones are of a distinctive pale greenish grey colour. This colouring may be penecontemporaneous, for the Permo-Triassic unconformity is some 440 ft above.

There are a number of coals or seatearths between the Clown Coal and the Haughton Marine Band. The thickest seam is 29 in at Cinderhill Colliery No. 4 Shaft. At Hucknall Colliery No. 1 Shaft a group of coals and dirts has an over-all thickness of 139 in. It is not clear whether the first coal or seatearth below the Haughton Marine Band is the Swinton Pottery of districts to the north, or whether several or all of the coal horizons between the Marine Band and the Clown represent a split Swinton Pottery.

The topmost coal lies either immediately below the Haughton Marine Band or is separated from it by up to 5 ft of variable measures including mudstones, siltstone and sandstones. The mudetones are grey to black with ironstone bands and plant fragments. At Annesley Park Borehole an oolitic ironstone,0.5 in thick. immediately underlies the marine band and in Hucknall High Main 27's Borehole a 1-in kaolin oolith band was recorded in a 2-in ironstone immediately above the coal.

The Houghton Marine Band consists of dark grey mudstone with marine fossils. It is characterized by gastropods and Tomaculum sp. which occur together with Lingula and fish debris. The marine band is not seen at outcrop, but has been proved in Cinderhill Colliery No. 4 Shaft and the following boreholes; Annesley Park, Felley Lane, Hucknall High Main 27's, Kennel Wood and Mapplewella. It is only 1 in thick in Drives Quarry Borehole just north of the district boundary, and is probably washed out in Hucknall Colliery No. 5 Shaft. In Felley Lane Borehole the assemblage included Euphemites anthracinus. Bellerophontoid gastropods were also recorded in Kennel Wood Borehole. where Lingula mytilloides, Serpuloidea stubblefieldi and fish debris were found near the base of the marine band. The mudstones are particularly rich in ironstone and pyrite, and listric surfaces, some of which are associated with the zone of compression around ironstone nodules, are common.

The measures between the Haughton Marine Band and the Mansfield Marine Band

The measures between the Haughton Marine Band and the Mansfield Marine Band comprise two main cycles totalling 57 to 78 ft in thickness. They are largely mudstones with mthordinate arenaceous strata; aphaerosiderite is common. The top of the first cycle is marked by a thin, but persistent coal which has a maximum thickness of 15 in at Cinderhill Colliery No. 4 Shaft. In the north-east of the district this coal splits into several leaves, as in Annesley Park Borehole: coal 6 in at the top, dirt 64 in, coal 12 in, dirt 20 in, coal 2 in. The coal is generally of poor quality (inferior 'brights') and is interdigitated with ironstone at Kennel Wood Borehole. Just beyond the northern limit of the district, in Grives Quarry Borehole,0.5 in of irregular ironstone occurs with a 7-in coal at this horizon, and in Newstead NI Underground Borehole a 9-in ironstone with incipient cone-incone structure immediately overlies the coal.

This coal is overlain by the 'Sutton Marine Band in Mapplewells Borehole. The marine band may also be present in Grives Quarry Borehole and Hucknall Colliery High Main 27's Underground Borehole, but it is apparently missing over the greater part of the Derby district. At Mapplewells Borehole the possible marine band consists of 9 in of dark mudstone with pyrite and phosphatic nodules, its fauna consisting largely of fish debris.

The top of the cycle containing the Sutton Marine Band is invariably marked by a coal and/or seatearth. The coal is thickest (7 in) in Cinderhill Colliery No. 2 Shaft. This horizon is in places separated from the overlying Mansfield Marine Band by a few inches of mudstone or siltstone with pyritised and coaly plant fragments and non-marine bivalves.

Westphalian C

Mansfield Marine Band to Top Marine Band

These strata, some 350 ft thick, contain only one economically important coal, the High Main. They are concealed by Permo-Triassic rocks except for a narrow strip cropping out between Greasley and Pinxton. The general characters of the strata are shown in (Figure 47).

Above the Mansfield Marine Band, the mussel fauna is less varied than in the lower beds, with Naiadites as the dominant genus. Between the Mansfield Marine Band and the Edmondia Band the species include Naiadites melvillei and N. cf. productus. Above the Edmondia Band N. cf. hindi is common. The lowest occurrence of Lioestheria vinti in this part of the sequence is in the roof measures of the first coal above the Edmondia Band, and this fossil recurs in several bands up to the Top Marine Band. Ostracods in these measures include Geisina subarcuata and Carbonita pungens.

The Mansfield Marine Band

The Mansfield Marine Band consists of up to 15 ft of dark grey mudstone with an abundant and varied fauna, A bed of fossiliferous 'cank' (hard ankeritic siltstone) occurs in the lower part and provides a reliable and persistent lithological marker horizon which is recognisable even in the records of old shafts and ethkings. The 'cank', which is 6 in to 32 in thick, has a distinctive conchoidal fracture and is irregularly veined by calcite. Its petrography was described by Dunham (in Edwards and Stubblefield 1948, pp.249–252).Chonetoid brachiopods and small Lingula are commonly present.

The 'cank' has been seen at outcrop in two localities near Felley. At one [SK 4829 5217] in Middle Brook. Millington Springs, it is 6 in thick, and at the other, in a small stream [SK 4852 4993] 100 yd S of Felley Mill, it is 2 ft thick and contains Lingula.

The Mansfield Marine Band has been recorded in the boreholes and shafts noted in (Table 13).

The presence of cank has been established in the following shaft records: Annesley Colliery No. 1, 1 ft 6 in; Cinderhill Colliery No. 2, 1 ft 9 in; Cinderhill Colliery No. 6, 1 ft 9 in; Hempshill Colliery, 10 in; Hucknall Colliery No. 1, 1 ft 4 in; Hucknall Colliery No. 2 Pit No. 3, 1 ft 8 in; Rudman No. 2 Pit No. 5, 1 ft 2 in: Linby Colliery No. 1, 2 ft 7 in; Newstead Colliery, 2 ft 4 in; Wathall Colliery No. 1, 1 ft 9 in.

The Mansfield Marine Band in Annesley Lodge Borehole is some 6 ft 9 in thick and shows three distinct phases. The basal 5 in contains a benthonic fauna of Lingula, Euphemites and Hollinella. The acme of the marine incursion is represented by the central part, which contains Coleolus and 'Anthracoceras' hindi. A regression phase in the top 4 ft has an assemblage of foraminifera and Lingula.

Annesley Park Borehole proved only a this marine band with an impoverished fauna at this horizon. Anthracoceras is common in the lower part of the band but poorly preserved. The top part of the band contains foraminifera including Ammodiscus, together with Lingula mytilloides, Orbiculoidea cf. nitida, cf. Geisina, fish debris and fucoide.

The measures between the Mansfield Marine Band and High Main Coal

The measures between the Mansfield Marine Band and High Main Coal vary from 158 ft in the north-west, in Mapplewells Borehole, to 115 ft in the south-east, at Hucknall Colliery No. 2 Pit, and contain up to four coals. The measures crop out just to the west of the Permo-Triassic escarpment in the Annesley–Woodhouse–Selston Underwood areas, but are concealed by the younger rocks south of Wathall.

The variations of thickness in the measures are related to the presence of sandstones, particular) in the lowest and highest cycles. The sandstone beneath the High Main Coal is partially exposed in Beauvale Brook between Felley Priory and Felley Mill, where up to 10 ft of brown flaggy sandstone are visible [SK 4857 5016].

Eden and others (1963, p. 54) record the sporadic occurrence of a kaolinite-rich band below the High Main Coal in boreholes to the south-east of the present district. The following boreholes indicate that this bed is widespread, but because of the difficulty of differentiating such tonstein-like bands from normal ironstones and ferruginous mudstones it may have been missed in many of the records. The figures in brackets indicate the depth below the High Main Coal:

The measures between the Mansfield Marine Band and the High Math Coal are rich in ferruginous concretions, and sphaerosiderite is particularly common in the seatearths. Ironstone bands are locally oolitic and often have kaolin-filled centres. Kaolin patches and spots have been recorded in Hucknall High Main 27's and High Math 52's underground boreholes below all the minor coal seams within these measures. The lowest of these minor coals is considered to be the probable equivalent of the Wales Coal of the East Retford area (Smith and others 1973, p. 88). It is not known whether the overlying coals are splits from the Wales or represent higher seams including the Sharlston Low of Yorkshire.

The ?Wales Coal is about 12 in thick in the north-west of the district, where it lies some 85 ft above the Mansfield Marine Band. Traced south-eastwards this interval is halved and the seam deteriorates until, in the Cinderhill area, it is represented solely by eeatearth. Analysis of this coal obtained from Newstead NI Underground Borehole just north of the district boundary, shows a medium ash content and low sulphur percentage.

The thickest single seam recorded in the measures up to the High Main Coal is 23 in at Hucknall Colliery No. 2 Pit No. 3 Shaft in the second cycle above the Mansfield Marine Band. Analysis of this seam from Babbington Pit Yard Boring showed poor quality (13 per cent ash) and high sulphur content (3.6 per cent).

The highest coal in these measures occupies a fairly persistent position some 40 ft below the High Main. An analysis from Linby 36's Slant Underground Borehole showed it to consist of bright coal which becomes inferior towards the middle and base of the seam. Overall quality is poor. with an ash content of 7.7 per cent and 0.93 per cent of sulphur.

Fish scales and associated debris have been recorded above this coal at Linby 36's Slant and Linby 52's Underground boreholes. At Hucknall High Math 27's Underground Borehole a fish jaw with teeth was noted at this horizon.

Sporadic mussels occur in the measures between the Mansfield Marine Band and the High Main (Appendix 1, p. 000).

The seatearth below the High Main Coal and most of the seatearths above this horizon have a distinctive grey-green. creamy grey or pale brown coloration. Similar colours commonly occur in the stained measures below the Permo-Triassic; those found in the High Main seatearth are some 300 ft below the stained zone in this district and are considered to be a reflection of the changing conditions of deposition in the upper part of the Westphalian.

The High Main Coal

The High Main Coal is commonly 4 ft thick, but ranges from 43 to 62 in (Figure48). It is mined in Newstead and Linby collieries at depths ranging from the 150 ft cover line in the west to 500 ft in the south and east. The seam consists of two major divisions (Figure 48)—a thin upper brights and a thick lower brights separated by a variable but generally this dull coal or 'bluestone'

Between Annesley Woodhouse and Greasley the seam is split above the 'bluestone' over a zone some 600 to 1200 yd wide, comparable in plan with a meandering north-south channel (Figure 48). A detailed section across the split zone is afforded by Brookshill Farm Site, where some 200 trial bores were drilled. (Figure 79) shows isopachs of the measures, largely seatearth and mudstone, separating the two leaves. A longitudinal section A–B illustrates the present configuration of the coals. The lower heights have been partially washed out in only one borehole (Whyburn South) and the upper heights are fairly uniform in thickness.

If it is assumed that the configuration of the coals in section A–B is largely of penecontemporaneous origin, then at the end of the formation of the High Math Coal, when the upper leaf should have been nearly horizontal, the lower bright.. seam would have the profile a–b. Such a profile suggests a NE–SW belt of rapid subsidence.

There is evidence of disturbed sandy laminae 1 ft 7 in below the seam in Kennel Wood Borehole; disturbed micaceous coaly planes 1 ft 3 in below the seam in Whyburn South Borehole; overfolded laminae 4 ft 9 in below the seam in Weavers Lane Borehole and a 12-in breccio-conglomerate in a sandstone in Allotment Garden. Borehole. These disturbances may have been caused partly by the collapse of river levees (Elliott 1969, p. 117), but the presence of presumed earthquake structures in the roof measures of the High Main seam near Calverton Colliery, south-east of the present district, strengthen the idea that the cause of the split was a short lived subsidence along a pre-existing channel and/or tectonic line.

The quality of the coal varies from good to rather poor with ash content, less dirt, ranging between 4.6 and 9.6 per cent. Sulphur content is low.

The seam crops out for some 3 miles close to the foot of the Permian escarpment between Felley and Greasley. In places, westerly projecting spurs of Permian rocks, e.g. near Garfit House Farm [SK 490 520] and Beauvale Manor Farm [SK 490 480], conceal parts of the crop. The northernmost exposure was seen in a pipe trench [SK 4937 5284] near Davis Bottom, where disturbed bright coal, some 4 ft thick, was recorded in the bottom of a steep-sided valley.

The High Main Seam was worked opencast only at William Wood Site where the extent of the take was limited by the close proximity of the Permian scarp. A section totalling 56 in at the north end of the site [SK 4865 5163] was recorded as follows: heights 13.5 in; seatearth 2.5 in; 'bluestone' (dirty hard coal) 2.5 in on hards and brights 37.5 in. Dr J. Shirley recorded the following section from the middle of the same site [SK 4881 5115]: mudstone with fish scales 5 ft 1 in; mudstone with ironstone bands and mussels including Naiadites daviesi 6 ft 7.5 in; seatearth 4 ft; mudstone 24 ft on the High Main Coal.

Eden and others (1963) recorded a tonstein with. the High Math Coal at several widely spaced localities in the East Midlands Coalfield. In the present district no definite occurrences are known, but the following records may be related to tonsteins or fragmental clayrocks: ironstone streaks in a dark grey mudstone 6 in above the High Math Upper Leaf in Mapplewells Borehole, an 'ironstone' lens in the roof of the High Math Upper Leaf in Washdyke Lane Borehole; several small clay-ironstone pockets 1 in above the top of the Upper Leaf in Cavendish Crescent Borehole; kaolinite vesicles (possibly former ooliths) in the roof of the Upper Leaf in Allotment Gardens Borehole and 1 in of ferruginous kaolinite rock 4 in above the High Main Upper Leaf in Annesley Lodge Borehole.

In Newstead Colliery Workings [SK 5050 5289] an oolite bed about i in thick surrounded by thinly laminated argillaceous material was collected from within the coal. Mr Siddiqui reports that: 'The ooliths (average diameter 0.35 mm) are mostly elongated and subrounded, but a few are well-rounded. They are altered to fine-grained granular well-crystalised kaolthite. The ooliths are firmly bedded in a dense matrix of micro-granular siderite. Pyritic aggregates occur in small localized patches. Carbonaceous staining is common, but is mostly restricted to the thinly bedded argillaceous horizons. The graditional contacts between oolites and shaly bands locally show ripple structures'.

The measures between the High Main Coal and Edmondia Band

The measures between the High Main Coal and Edmondia Band are some 30 to 40 ft thick and consist largely of mudstone though a washout siltstone, some 23 ft thick, overlies the High Math Coal in the Whyburn South Borehole and a 10-ft sandstone overlies the same seam at crop in the Beauvale Abbey area [SK 490 490]. They contain up to two thin coals. The lower coal, present only in the south-east of the district, where the two cycles are clearly defined in the Linby, Hucknall and Watnall areas, is possibly a split from the High Main Coal. This coal lies 10 to 20 ft below the higher coal, which is up to 11 in thick. Mussels occur locally above both coals, and they lie generally 5 ft but up to 17 ft below the Edmondia Band.

The Edmondia Band

The Edmondia Band has been found in 33 boreholes and shafts in the present district. It ranges in thickness from 24 ft in Annesley Lodge Borehole to 1 ft 11 in in William Wood Borehole. It is thickest in a restricted belt of country which corresponds closely to the zone of split in the High Math Coal (Figure 48). This belt seems to have been liable to increased subsidence intermittently throughout this short period of geological time. Edwards (1967, p. 110) noted that the band included a distinctive pale grey mudstone in the Ollerton area. Whilst pale rnudstones are present within the band in this district they are variable in both thickness and position. Foraminifers are found in both pale and dark grey mudstones and were particularly well preserved in the Whyburn House Borehole. In Annesley Lodge Borehole the Edmondia Band contained abundant foraminifers including Glomospira, Glomospirella and Tolypammina. In the middle of the band, Myalina and Hollinella occur, an assemblage typical of the Myalina facies which is the usual development shown by this band throughout the Yorkshire and East Midlands Coalfield. In Kennel Wood Borehole Curvirimula was found in association with Myalina cf. compressa. Curvirimula does not occur above the top of the C. communis Zone except in the retreat phases of some of the Westphalian B marine bands (Calver 1968a, p. 151). The basal part of the band contains cf. Planolites ophthalmoides and pyritized strap-like markings (fucoids). Thin bands and small nodules of ironstone occur throughout and pyrite is common as grains, clusters, concretions, coatings and infillings and replaces many of the plant fragments, worm burrows and fossils. The Edmondia Band contains galena in Misk Farm, Whyburn South and Kitty's Wood boreholes.

The measures between the Edmondia Band and Shafton Marine Band

The measures between the Edmondia Band and Shafton Marine Band are normally about 100 ft thick, though a maximum of 156 ft was recorded at Cavendish Crescent Borehole. They include up to six variable coals. The measures are particularly sandy and are broadly equivalent to the Mexborough Rock of South Yorkshire. They are nowhere exposed, being almost wholly concealed beneath the Permo-Triassic rocks.

The lowest cycle, commonly arenaceous and averaging 50 ft in thickness, is normally topped by a thin coal. The two succeeding thin cycles contain thin coals which are overlain by rnudstones with Lioestheria.

The lower of these bands which may be the "Main 'Estheria' Band" of Edwards and Stubblefield (1948, p. 231), consists of 1 in to several feet of grey mudstone. It is rich in Lioestheria sp. together with fish debris and ostracods. Pyrite is common, often replacing plant and shell fragments and infilling worm burrows. The carapaces are distinctive, appearing as abundant iridescent blotches in the mudstone. The size of the carapaces both within the band and throughout the district is variable but averages 3.0 mm. The coal underlying this 'Estheria' band has been appropriately called the 'Bug Coal' by miners in the Ollerton area (Edwards 1951, p. 110).

The higher of the Lioestheria-bearing bands, up to 23 ft 5 in above the lower, is from 3 in to a few feet thick, and is restricted in its distribution to the areas where the High Main Coal is split and the Edmondia Band is thick, Whatever the cause of this localized increase in thickness of sediment (p. 69) it affects over 100 ft of strata.

The first cycle above the higher Lioestheria band is usually between 20 and 30 ft thick with a seatearth and/or coal up to 25 in thick, at the top. The coal, of poor quality, is composed of brights or banded brights and hards with cannel in the highest parts. It is thickest west of Linby Colliery (Figure 80) but thins northwards, becomes cannelly and is represented by a seatearth in the northern part of the district near Annesley Woodhouse. The coal, unnamed in the Nottingham area, may be the Shafton of south Yorkshire, though Edwards (1967, p. 111) correlates the coal close below the Shafton Marine Band in the Ollerton district with the Shafton Coal. In this memoir the seam is referred to as the ?Shafton Coal.

The cycle succeeding the ?Shafton ranges from 5 ft 8 in in Annesley Hall Borehole to 25 ft 10 in in Kitty's Wood Borehole. The measures overlying the ?Shafton contain kaolin ooliths in Weavers Lane, Whyburn East and Whyburn West boreholes, and fish scales were recorded in the measures at Annesley Park Borehole, The cycle is topped by a coal which underlies the Shafton Marine Band and is apparently the equivalent of the seam in a comparable position in south Yorkshire, though evidence from the Ollerton district (see above) raises the possibility that it is the Shafton or a leaf of that seam. This coal is thickest in the Annelsey Park area (Figure 80) and thins northwards, passing into batt and cannel in Mapplewells Borehole. The over-all quality is poor with high ash and sulphur contents.

The Shafton Marine Band

The Shafton Marine Band recorded at fifteen localities within the district ranges in thickness from 8 in to 11 ft 7 in. The fauna includes Anthraconaia spathulata, ostracods such as Paraparchites, fish fragments, fucoids and worm burrows. Lingula is common in Washdyke Lane Borehole and has been recorded in two other bores. In Cavendish Crescent Borehole 9 ft 8 in of silty mudstones separate two bands of strata containing Lioestheria which is a common fossil at all localities.

The band usually closely overlies a coal or seatearth (see above), but may be separated by up to 14 ft 8 in of measures, as at Misk Farm Borehole.

The measures between the Shafton Marine Band and Top Marine Band

The measures between the Shafton Marine Band and Top Marine Band vary from 46 ft at Washdyke South Borehole to 64 ft in Hucknall Colliery No. 2 Pit No. 5 Shaft. They contain up to three cycles with locally associated coals, The lowest cycle supports a dirty coal 6 to 13 in thick in the Annesley Park area. To the south and east around Hucknall, Linby and Bulwell the horizon is represented by a seatearth. To the north, both the coal and the seatearth are absent.

A dark grey rnudstone at the base of the second cycle contains Lioestheria in Annesley Hall and Washdyke boreholes, and fish debris in Heather-dale Pond, Annesley Park and Thurland Hall borehole, This band is only recorded in the Annesley–Whyburn zone of thick measures (p. 69). Elsewhere the second cycle comprises some 20 ft of measures. At the top, in the southern part of the district, is a coal which has a maximum thickness of 37 in in Whyburn South Borehole. The coal splits northwards into two leaves in the Annesley Park area, the lower leaf ranging in thickness from 18 to 31 in, separated by up to 21 in of dirt and dirty coal from an upper leaf, 3 in to 5.5 in thick. At Thurland Hall Borehole the seam is further split as follows: basal coal 31 in; dirt 18 in; batt 3 in; dirt 9 in; coal 3 in; dirt 6 in; overlain by batt 5 in. Analysis shows the seam to be composed throughout the district of dirty coal of poor to very poor quality with ash ranging from 8 to 17 per cent. Sulphur is variable, ranging from moderately low to moderately high (1.4 to 2.8 per cent).

The coal is overlain by mudstones containing fish scales in Annesley Park and Kennel Wood boreholes. In Whyburn East Borehole a 7-in septarian nodule with kaolinite-filled cracks was recorded 7 ft above the coal. Just beyond the eastern margin of the district Springfield Hosiery Borehole [SK 5551 4620] at Bulwell, yielded Lioestheria sp. some 18 ft below the Top Marine Band.

The third cycle comprises some 15 ft of measures with a coal at the top, under the Top Marine Band. This coal, never more than 12 in thick, varies irregularly over the district. Mussels occur sporadically in all of the three cycles between the Shafton Marine Band and the Top Marine Band, but are most common in the lowest (Appendix 1, p. 164c)

The Top Marine Band

The Top Marine Band is a valuable and persistent marker horizon which has been proved throughout the district from Annesley Woodhouse in the north to Bulwell in the south. It usually comprises 2 to 7 ft of grey to dark grey mudstone containing a varied fauna of foraminifera, goniatites, brachiopods including Lingula, bivalves including Dunbarella, gastropods, ostracods, fish, fucoids, Planolites and Lioestheria, Pyrite is common, replacing and coating plant and organic debris.

In Annesley Park Borehole the marine band is some 6 ft 9 in thick and although poorly preserved shows the varied fauna typical of this horizon. A. Planolites phase occurs at the top with fucoids and fish debris and the fully marine fauna is confined to the basal 1 ft 4 and includes Orbiculoidea sp. Aviculopecten?, Dunbarella sp. Polidevcia sp. faecal pellets including cf. Tomaculum sp.

Measures above the Top Marine Band (Upper Coal Measures)

Some 500 ft of measures above the Top Marine Band are calculated to have been preserved in the extreme north-eastern part of the district, but westwards they are overstepped by the Permo-Triassic rocks. The maximum thickness proved is 350 ft at Linby Colliery. In the pact 10 years many boreholes have been drilled by the National Coal Board in the east of the district, but these measures are rarely cored because they lack workable coals.

The measures comprise two thick and persistent cycles near the base overlain by many thinner and variable cycles. One of the highest cycles some 220 ft above the Top Marine Band, contains a coal about 2 ft thick known as the Manor Coal (Edwards 1951, p. 75).

The measures are commonly arenaceotta and mussels occur only sporadically in the argillaceous beds. A change in the non-marine bivalve fauna takes place near the base of the Upper Coal Measures with the loss of Naiadites and the incoming of Anthraconauta The dominant form is A. phillipsii.

The Top Marine Band Cycle

The Top Marine Band Cycle reaches a maximum thickness of 78 ft in Washdyke North Borehole and is the thickest single cycle in Westphalian C. Sandstone and gallstone, containing scattered plant fragments. form a large proportion of the total, but a 15-in seatearth was recorded in Washdyke North Borehole some 19 ft below the top of the cycle. A coal, here named the Annesley Coal, is commonly present at the top of the cycle. It thickens from 9 in at Heatherdale Pond Borehole to 16 in at Annesley Park Borehole, but outside this localized east-west belt between Annesley and Watnall, variations are considerable. It is represented by a ganister at Linby and a cannel at Hucknall. The Annesley Coal is overlain by dark grey mudstones containing 'Estheria' in Springfield Hosiery Borehole and fish debris in Hucknall No. 2 Colliery No. 5 Shaft and in Washdyke Lane, Thurland Hall, Heatherdale Pond and Annesley Park boreholes. In addition, ostracods were recorded at Heatherdale Pond Borehole and phosphatic fragments at Whyburn East Borehole. Mussels, including Anthraconauta phillipsii are also present in the lower part of this cycle. It may well be that the Annesley Coal is the correlative of the Scofton Coal of the East Retford district, which is similarly overlain by mudstones with 'Estheria', mussels and ostracods (Smith and others 1973, p. 94).

The Second Cycle above the Top Marine Band

The Second Cycle above the Top Marine Band ranges in thickness from 42 ft at Springfield Hosiery Borehole to 56 ft at Annesley Park Borehole. Above it there is a complex series of seatearths, coals, batts and carbonaceous shales spread over up to an additional 40 ft of measures. One of these coals is 30 in thick in Hucknall No. 2 Colliery No. 5 Shaft.

Fish fragments were recorded at two horizons between these coals at Annesley Park Borehole and at one horizon in Washdyke North Borehole. Ostracods are also present in both boreholes but at slightly different levels. Sphaerosiderite is a common constituent of the seatearths in Springfield Hosiery, Washdyke North and Whyburn East boreholes.

Above these coals are siltstones and sandstones 30 ft thick at Newatead Colliery No. 1 Shaft to 90 ft at Hucknall Colliery No. 2 Pit. They are succeeded by a group of eight minor impersistent cycles, which in Linby Colliery No. 1 Shaft comprise 120 ft of measures.

The Manor Coal

The Manor Coal at the base of this group, reaches a maximum of 27 in in Hucknall No. 2 Colliery No. 5 Shaft, where it is overlain by 36 in of cannel. In the Hucknall–Linby area the coal is generally over 2 ft thick but thins northwards to 21 in at Newstead.

At Linby Colliery the Manor Coal is overlain by 110 ft of largely argillaceous strata, extending up to the unconformable Permo-Triasaic cover. Sandstones are common in the Newstead and Hunknall areas. Primary red measures have not been recorded in the district.

Stained measures

The Westphalian strata underlying the Permo-Triassic rocks (Figure 49) are normally stained to about 50 ft below the unconformity, but range from 10 ft at Annesley and Hucknall collieries to 115 ft at Whyburn East Borehole. Red, brown, pink, purple and green coloration is common in the mudstones and sandstones.

Seatearths show purple mottling, although in the measures above the Mansfield Marine Band they are commonly a pale grey or cream colour. contrasting with the darker seatearths of lower horizons (p.24). Ironstone nodules, normally pale brown or buff, are markedly reddened. Sandstones often show staining to greater depths than do other lithologies. Staining is considered to be due to sub-aerial weathering and oxidation of the Westphalian land surface in late Carboniferous and possibly Lower Permian times (Anderson and Dunham 1953; Trotter 1953; Smith and others 1967). Because argillaceous rocks are as highly coloured as other lithologies, percolating solutions are probably less important than weathering, though the increased depths of staining in areas of porous strata would suggest that the former process took place penecontemporaneously with the denudation. Where the Permo-Triassic rocks are present, staining affects measures above the Mansfield Marine Band, but evidence from the west of the present district 26) shows that the lowest sandstone in the Westphalian, i.e. the Crawshaw Sandstone, is similarly stained although the Permo-Triassic strata have long since been eroded.

The measures immediately below the unconformity are often leached to a depth of a few inches.

Chapter 5 Permo-Triassic. Details

Permian Basal Breccia

At the time of the resurvey the breccia was exposed in numerous temporary excavations throughout the district, but the only permanent sections were in the Kimberley railway cuttings [SK 4510 4520], where it averaged 24 in with a maximum recorded thickness of 56 in (Sherlock 1907, p. 106). Rail closures since the resurvey have endangered the permanence of even these sections. The breccia, which rests on pink, purple and pale green stained Westphalian mudstones, consists of a grey-brown sandy calcareous matrix containing fragments of red ironstone, purplish and pale-grey quartz and Upper Carboniferous sandstones and siltstones. Some 24 in of breccia at the eastern side of Kimberley station exhibit cross-lamination with foreset beds at angles of 20° and indicate current directions from the south-south-west.

Mr K. S. Siddiqui has described a thin section (E44773) of the 5 ft 9 in thick breccia in the Mapplewells Borehole. He found a wide range of lithoclasts averaging 0.5 mm in size including feldspathic sandstone with closely packed quartz grains, fine-grained compact sandstone with preferentially orientated sericite flakes. fine-grained dolomitic limestone showing abundant well crystallized rhombs, of dolomite, hematite grains and cherty fragments. The finer clastics showed a predominance of angular to subangular fragments of quartz accompanied by orthoclase, plagioclase, a few grains of microcline and well crystallized grains of kaolinite. The cement comprised a mixture of submicroscopic carbonates (calcite-dolomite), clays (illite and kaolinite) and hematite.

Blocks of breccia, up to 16 in thick, were exposed in a temporary gas pipe trench [SK 4890 5278] about 1 mile south-west of Annesley Woodhouse. During the war-time reconnaissance survey, Dr J. Shirley recorded a red-brown and yellow conglomerate and sandstone with pebbles and fragments up to 12 in in diameter at the northern end of the William Wood Opencast Site [SK 4859 5175]. Large boulders of breccia are still present in the hedgerows of this area.

The basal breccia, 6 to 18 in thick, was exposed in a new road cutting at Watnall Chaworth [SK 4973 4639].

South-east of Nuthall excavations for the M1 motorway access road provided exposures of the Permian strata faulted against Westphalian. The Permian basal breccia here is only 2 in thick; it contains a preponderance of small quartzite pebbles and ironstone nodules in a well-cemented matrix; the basal unconformity is emphasized by the truncation of a Westphalian ironstone band.

Near Broxtowe Wood [SK 5228 4273], south-west of Cinderhill, a sewer trench encountered a hard well-cemented bed of breccio-conglomerate, variable in thickness up to a maximum of 48 in. Rounded purplish stained quartzites up to 6 inches in diameter are common. Temporary sections on the eastern side of a new road cutting 400 to 600 yd NW of Watnall Hall [SK 4977 4634] exposed the basal breccia which was between 2 in and 18 in thick.

The Catstone Hill Opencast site [SK 5070 4171] provided a continuous exposure of the Permian Basal Breccia for some 400 yd. Over most of the site it cmprises a massive resistant bed up to 3 ft thick, but thins south-west of Catstone Hill Farm to less than 1 ft. The 20 ft of overlying Lower Magnesian Limestone contains many conglomeratic horizons (see p.151d). Locally a distinct basal Permian breccia is absent but the lowest 3 ft of the Lower Magnesian Limestone remain relatively coarse in texture.

An examination of a thin section (E44835) by Mr K. S. Siddiqui from this site revealed a wide variety of lithoclasts in the breccia including slightly metamorphosed sandstone (in places stained with hematite), dolomitic limestone, hematite grains, cherty fragments, well crystallized kaolinite grains, quartzite, siltstone, mudstone and probably a few grains of rhyolite. The carbonate fraction of the rock has largely been recrystallized to dolomite which shows a concentration of rhombic crystals in places; numerous grains of quartz are interspersed with dolomite and feldspars. Specks of muscovite are preferentially orientated along the bedding. The silicate minerals show marked etching at the crystal boundaries and in many cases partial replacement by carbonates. The clasts are well cemented by microcrystalline carbonates slightly stained with ferric oxide.

In excavations, up to 20 ft deep, for sewers in the Beechdale Road area, near the edge of the district, a distinct basal breccia is again absent. Red-brown sandy Lower Magnesian Limestone containing interbanded purplish silty mudstones rests on red-stained Westphalian sandstones and mudstones so that the unconformity is not obvious. However, the basal 2 in of the limestone contains sporadic fragments of red and green marl together with a concentration of coarse quartz grains.

The Permian Basal Breccia has been recorded in the following boreholes:

Allotment Garden (1 ft 10 in), Annesley Hall (5 ft 2 in), Annesley Park (1 in), Audrey Wood (2 ft 7 in), Balaklava Wood (2 ft 6 in), Cavendish Crescent (1 ft 9 in), Chalfont Drive No. 1 (3 in), Charlie's Wood Cottages (3 in) Chilwell Dam Farm (2 ft 9 in), Forest Lodge (2 ft 9 in), Garfit House (4 ft 3 in), Heatherdale Pond (2 ft 4 in), Home Farm (1 ft 4 in), Kennel Wood (1 ft 1 in), Kitty's Wood (1 ft), Mapplewells (5 ft 9 in), Misk Farm (1 ft 6 in), Misk North (1 ft), Pamela's Larches (2 ft), Seagrove (3 ft), Thurland Hall Farm (4 in), Washdyke Lane (North) (5 in), Weavers Lane (4 ft 3 in), Whyburn East (pebbles), Whyburn House (fragments), Whyburn West (5 in), William Wood (2 ft 10 in). It has been recorded or can be recognised from sinkers' records in many of the shafts and bores of the present district (see Appendix 2).

Lower Marl

During the resurvey of the sheet, the Lower Marl was exposed in many temporary excavations, but the only permanent and complete section is in the railway cuttings between Kimberley and Nuthall.

The most northerly exposures examined were in a gas pipe trench near Davis's Bottom [SK 4963 5287] 0.5 mile S of Annesley Woodhouse, where 8 ft of grey-brown dolomitic siltstone with subordinate mudstone partings were preserved in the crest of a small anticline.

East of Felley Mill, a stream [SK 4876 5100] and its small tributary [SK 4982 5032] flowing through The Durables have incised deeply into the Permian scarp to give sporadic exposures of grey dolomitic silty mudstone with plant fragments; at one locality farther downstream [SK 4976 5034] these are underlain by red and purple-stained silty mudstones of Westphalian C age. Excavations [SK 4975 5106] along the line of the M1 motorway in this vicinity exposed 10 ft of flaggy dolomitic siltstones directly underlying the Lower Magnesian Limestone.

A spring [SK 5030 4784] some 50 yd W of Watnall Colliery and Brickworks issues from the base of the Lower Magnesian Limestone. Beneath the spring, 3 ft of buff micaceous calcareous siltstone with carbonaceous plant fragments overlying 1 ft of grey silty mudstone are exposed.

The railway cuttings near Kimberley are now overgrown and parts are concealed by masonry. Wilson (1876) examined them during their excavation and noted a uniform thickness of about 17 ft of 'thin-bedded slate-coloured sandstones and shales' comprising no less than 75 beds from 0.25 in to 8 in thick, some with annelid markings, others with abundant plant remains; sporadic casts of Schixodus were also recorded,

The junction between the Lower Marl and the Lower Magnesian Limestone is marked in the cutting by the presence of numerous springs which renders the lower part of the cutting unstable in wet seasons. After it particularly net period in 1966 a small slip in the now disused northern cutting exposed most of the Lower Marl sequence, as follows:

In the cuttings [SK 5200 4490] made for the M1 motorway and access roads near Nuthall the Lower Marl was well exposed, though affected by faults and folds associated with the Cinderhill Fault system. A few feet of brown silty dolostones at the top of the Lower Marl were exposed in the core of an anticline [SK 5219 4391] on the roundabout excavations 0.5 mile SE of Nuthall. Two hundred yards to the east the top and bottom beds of the Lower Marl are brought into juxtaposition by faulting. The highest beds consist of steely blue-grey laminated siltstones in beds up to 6 in with shaly partings, irregular brown staining and carbonaceous plant fragments. The basal Lower Marl comprises 3 ft of soft dark grey-blue silty mudstone overlain by 6 ft of siltstone with individual beds normally not exceeding 2 in in thickness.

Mapping of the Lower Marl at the base of the escarpment between Felley and Kimberley revealed a variable thickness up to about 30 ft. Gibson and others (1908, p. 107) and Waring (1966, pp. 204–208) suggest that the Lower Marl is absent near Beauvale Priory.

In Annesley Lodge Borehole [SK 4957 4992], where the Permian rocks were not cored, 30 ft of strata have been assigned to the Lower Marl on the evidence of the gamma-ray log. At the old quarry south of Shortwood Cottages [SK 4894 4771] Waring (1966) noted cross-bedded siltstones with rolled mudstone pellets and also thin hard calcareous bands within a 10-ft sandy mudstone which passes up into Lower Magnesian Limestone. Be also recorded the Permian Basal Breccia and 15 ft of marl at Bogend (Sledden Wood Spring) [SK 499 468]. Some 4 ft of banded brown siltstone with many plant fragments were noted at the entrance to the northern rail cutting at Kimberley [SK 4972 4499].

In the Broxtow inlier, a sewer trench [SK 5228 4513], exposed the entire 20 ft or so of the Lower Marl succession. The highest beds, which were grey-brown, showed a marked colour contrast with the reds and buffs of the overlying limestone. The predominant lithology was a buff or pale grey dolostone/siltstone with subordinate shale partings which were stained red and purple near the top and contained many carbonaceous plant fragments, including Ullmania frumentaria. Approximately 10 ft from the base, oolites are associated with calcite-lined vugs.

The basal succession was as follows;

A small exposure [SK 4994 4836] at a spring 480 yd east of Beauvale Farm showed 3 ft of grey mudstone containing buff silty bands with plant fragments including U. frumentaria and indeterminate conifer leaves and cone scales. A 2-in buff dolomite band near the top contained shells of Bakevellia sp. and Schizodus obscurus.

The Lower Marl has been seen in the following modern boreholes (thickness to the nearest foot in brackets) (see also (Figure 70)):

Allotment Gardens (57), Annesley Hall (63), Annesley Park (62), Audrey Wood (56), Balaklava Wood (59), Bulwell Finishing Co. (66), Cavendish Crescent (69), Chalfont Drive No. 1 (6), Charlie's Wood Cottages (57), Forest Lodge (65), Garfit House (57), Heatherdale Pond (55), Home Farm (63), Kennel Wood (60), Kitty's Wood (52), Mapplewells (66), M1 proving hole (20), Misk Farm (52), Misk North (42), Pamela's Larches (about 53), Seagrave (9), Thurland Hall Farm (58), Washdyke Lane (North) (54), Washdyke Lane South (60), Watnall Coppice (50), Weavers Lane (69), Whyburn East (64), Whyburn House (45), Whyburn West (52), William Wood (54). It has been recorded in, or can be recognised from, details of sinkings of many of the shafts through the Permo-Trias (see Append. 1), although exact determination of the Lower Magnesian Limestone–Lower Marl junction is difficult. The Lower Marl was variously described as 'stone-bind', 'blue-bind', 'limestone shale with bands of stone or ironstone girdles'. Mudstones and siltstones in the Permo-Trias, whether calcitic or dolomitic, were invariably called 'marl' in older literature and in the logs of sinkings and borings.

Lower Magnesian Limestone

Northern area between Annesley and Hucknall

In many old quarries in this part of the district, yellow and buff flaggy dolomitic limestone is exposed. Half a mile north of Linby, at Quarry Banks [SK 536 521], the Lower Magnesian Limestone is said to have been quarried by monks from Newstead Abbey in the 12th Century. The abandoned quarries were opened up again after the 2nd World War and the following section was recorded at the present working face:

Railway cuttings to the north and south of Linby provide excellent exposures of up to 10 ft of buff flaggy dolomites dipping to the south-east and east at angles of 1.5–3°. The dip-slope is interrupted by gentle anticlinal 'rolls' which can be traced as features beyond the limits of the cutting (see p. 0001. They appear to be a common feature of the limestone dip-slope and have been detected in gas-pipe trenches south of Newstead Abbey. An anticlinal ridge over four miles long trending north 20° west extends from Newstead through Hucknall to Bulwell and provides sporadic exposures of the Lower Magnesian Limestone (see p.161a).

Two miles west of Hucknall, sandy dolomites on the escarpment edge include breccias up to 2 ft thick about 20 ft above the base of the Limestone. They indicate an approach to the shore. Waring (1966, pp. 207–210 and pl. 11 and 12) described the breccia and figured the section in an old quarry (Abbey Wood) north-north-west of Beauvale Priory [SK 4420 4933]. He also noted that the breccia was interbedded with the dolomite for 3.5 ft in a quarry east-south-east of the Priory [SK 4965 4882]. Nine feet of the lowest beds of the limestone are seen in the abandoned railway cutting 200 yd N of this quarry.

The rocks exposed in quarries on the escarpment edge near Watnall Chaworth comprise flaggy sandy dolomites with harder nodular patches and cross-bedded units up to 1 ft thick. The large quarry near Bogend [SK 4971 4655] exposes 12 ft of extensively fissured, cross-bedded flaggy dolomites. The fissures are up to 5 ft wide and are filled with mud, loam, dolomitic limestone nodules and calcite fragments.

The top of the Lower Magnesian Limestone, exposed in the M1 Motorway cutting near Misk Hill [SK 5025 4925], comprised reddish-brown friable dolomite containing Liebea squamosa and Schizodus obscurus. Other excavations for the Motorway, 600 yd NE of Annesley Lodge, showed the lowest 16 ft of the formation to consist of buff and red-brown friable dolomite; a shell band, some 2 ft from the base, contained Bakevellia binneyi and S. obscurus.

A temporary excavation [SK 5198 4866] on the south-west periphery of Hucknall showed the Lower Magnesian Limestone–Middle Marl junction. The top 4 ft of limestone were soft buff dolomite containing thin red 'marl' bands. Almost the entire thickness of the Lower Magnesian Limestone is exposed in the cuttings adjacent to Hucknall Station [SK 5305 4877], where dolomitic limestone, some 30 ft thick is generally flaggy and cross-bedded from the south-west. Bedding planes up to 13 in apart show undulations up to 2 in in amplitude and 6 in wavelength. Shell bands 4 ft to 6 ft from the base contain B. binneyi and S. obscurus.

Southern area: Kimberley–Strelley–north and west Nottingham:

In the railway cuttings between Kimberley and Nuthall the Lower Magnesian Limestone is continuously exposed for over half a mile, though the northern cuttings are now disused and the branch-line to Watnall Brickworks is being 'allied. Thirty feet of flaggyred-brown dolomitic limestone is recorded [SK 5150 4500] near the road bridge to Nuthall Cemetery. The underlying Lower Marl is exposed beneath the bridge and the overlying Middle Marl occurs in an adjacent field to the north-east. The limestone is in beds up to 6 in thick and commonly displays large-scale cross-laminated units in the top 6 ft. The foreset beds dip at 12° to 20°. The limestone contains ahelly lenses and one of these, about 8 ft from the base, yielded B. cf. Binneyi, L. squamosa and S. obscurus.

Numerous old quarries in the Lower Magnesian Limestone scar the western side of Bulwell. One of the few still worked for 'Bulwell Stone' has a 15- to 20-ft face [SK 5320 4560] of buff fine-grained dolomite stained dark red and pale green along the bedding planes. Fossils include cf. Bakevellia sp., and Schizodus obscurus. Some 300 yd S of the working quarry [SK 5336 4528] the following section was recorded using Smith's (1968) classification:

The top of the Lower Magnesian Limestone is exposed some 500 yd SW of the above section where the Sankey Company have dug the overlying Middle Marl for clay. The upper surface of the Limestone is hard and well cemented with secondary silica, Scattered throughout the top few inches are irregular concentrations of galena.

The formation was well exposed in cuttings for access roads to the M1 Motorway south-east of Nuthall [SK 517 445], where the dolomitic limestone contained Bakevellia sp., cf. Permophorus costatus and S. obscurus, In a sewer trench north of Bilborough [SK 5249 4286] 23 ft of purplish-red and red-brown flaggy dolomitic limestone were recorded overlying the Lower Marl.

There are many small quarries and sections in the Cinderhill area which expose some part of the Limestone and show its typical buff red-brown flaggy cross-bedded dolomitic nature. At Cinderhill Junction [SK 5379 4382] the juxtaposition of limestone and the Lower Mottled Sandstone at the Cinderhill Fault can be seen.

North-west of Strelley [SK 5038 4252] the M1 Motorway was excavated to a depth of some 30 ft, exposing a pinkish limestone with sandy conglomeratic bands in the top part.

An old quarry [SK 5133 4215] in Stonepit Plantation, east of Strelley Hall shows the following section;

The best section. of the Lower Magnesian Limestone were provided by the Catstone Hill Opencast site, which exposed Permian strata for some 700 yd. In the west, 16 ft of buff to red-brown dolomitic limestone underlay the Middle Marl. The top 12 in were well cemented and 7 ft from the base was a 2-ft pale brown sandy micaceous laminated mudstone. A basal breccia varied from 0 to 6 in (see p. 000) and rested unconformably on Westphalian rocks (Plate 9). At the south-eastern corner of the site [SK 5070 4171] the limestone, 20 to 22 ft thick, contained five conglomeratic bands up to 4 in thick in the upper 8 ft. The underlying Permian Basal Breccia, up to 2 ft thick, rested on Westphalian B strata. The conglomeratic bands were mainly of quartz together with red and green mudstone fragments.

Eight hundred yards SE of the Catstone Hill site the following section was exposed in excavations for extensions to Bilborough School [SK 5143 4139]:

The basal Permian beds are very variable along the southern margin of their outcrop, but they form a feature that can be followed south-eastwards for a mile or so from Catstone Hill and Bilborough to Broomhill Wood [SK 5261 4083], where, in factory foundations, a 6-in well-cemented, massive dolomitic limestone band containing quartz grains and red and green sandstone fragments was underlain by the Lower Mottled Sandstone. Some 200 yd to the south-east [SK 5280 4073] six feet of Lower Mottled Sandstone rest directly on Westphalian B rocks showing the locality to lie beyond the southern limit of Lower Magnesian Limestone deposition.

A sewer trench [SK 5447 4079] 1200 yd and more to the east of the above locality, near Radford Woodhouse, showed thin representatives of the Permian basal beds. They are composed essentially of medium-grained buff to red-brown dolomitic limestone containing numerous quartz grains, mudstone and rock fragments. Fossils included Bakevellia sp., L. squamosa and Schizodus sp. The 10 ft of limestone recorded in this area are considered to represent nearly the total thickness of the formation. The Chalfont Drive Borehole [SK 539 410], some 700 yd NW of the sewer excavations, proved 7 ft of buff and red dolomitic limestone with red and green silty mudstone bands, up to 14 in thick, overlying Westphalian mudstones. Wilson (1876) noted that at Bobbers Mill [SK 552 415], south of Basford, the Lower Magnesian Limestone passes from a granular dolomite through a tine to a coarse brecciated rock over a distance of 200 yds. A recent water bore just beyond the eastern margin of the sheet in Nottingham [SK 5575 4209] provided a good section in the Permian basal beds comparable with that recorded at Bilborough School (see p. 151d).

The Lower Magnesian Limestone has been proved in over fifty boreholes, and summaries and details are contained in Appendix 1. Detailed sections of the limestone are provided by the following recent boreholes (thickness to the nearest foot in brackets):

Annesley Hall (28), Annesley Park (36), Audrey Wood (25), Cavendish Crescent (31), Chalfont Drive (7), Charlie's Wood Cottages (30), Chilwell Dam Farm (36), Forest Lodge (34), Home Farm (33), Kitty's Wood (25), Mapplewells (34), Misk North (20), Seagrave (25+). Thurland Hall Farm (36), Whyburn West (31).

Middle Marl

The few exposures of Middle Marl in the Annesley, Linby–Hucknall area show only a few feet of weathered red clay. A gas pipe trench [SK 5446 5250], however, was excavated through the entire thickness of the Marl south of Newstead Abbey, just beyond the eastern limit of the present district. The eastern bank of the River Leen nearby is composed of 20 ft of weathered red clay with pale grey-green streaks. It becomes sandy towards the top and passes up into red sand of the Lower Mottled Sandstone at the top of the bank.

Within the district, at Newstead [SK 5173 5258], the same gas-pipe trench exposed the lowest beds of the Middle Marl in the following section:

Sporadic pockets of red marl on the Lower Magnesian Limestone dip-slope between Newstead and Papplewick were cut through by this trench. Invariably the lowest few inches of 'marl' in contact with the limestone are pale grey to green in colour. Sherlock (in Gibson and others 1908, p. 110) recorded the following section, 9 ft 3 in thick, from a now disused and infilled marl pit [SK 5260 5060] and former brickyard at the side of Wighay Road, Linby:

He noted that the sequence varied considerably in the excavation.

Temporary excavations [SK 5198 4866] on the western periphery of Hucknall showed 4 ft of dark red clay of the Middle Marl overlying the Lower Magnesian Limestone. The basal 1 in of the clay was pale green. South of Hucknall exposures of red and grey sandy marl up to 6 ft thick were seen in open graves [SK 5376 4837] in the cemetery. The graves were floored by a buff dolomitic limestone at least 12 in thick—presumably a band within the Middle Marl.

An outlier of Middle Marl occurs some 300 yd to the east. Red clay was dug out during road work excavations [SK 5405 4870] beneath Portland Road and Hankin Street.

Excavations through Kennel Gorse Wood [SK 4993 5054] and Watnall Coppice [SK 5035 4900] for the M1 Motorway facilitated accurate delineation of the boundaries of the Middle Marl, but provided little in the way of detailed sections. Proving holes [SK 5069 4759] showed that it was 19 ft thick.

Southern area

At Bulwell the complete sequence of Middle Marl exposed in the Sankey Plant Pot Company's excavations for clay [SK 5290 4510] is as follows:

The details are variable as shown by further trial pits and excavations to the west [SK 5243 4522].

The overall clay content of the Middle Marl appears to decrease westwards thus limiting the workable area of marl.

Some 800 yd to the west in New Farm Wood [SK 5166 4512], the M1 Motorway not through 11 ft of beds near the base of the Middle Marl, exposing the following section:

There are many old 'marl' pits in the Bulwell–Cinderhill area, most of which are now infilled.

An old record provided by Mr G. Fowler of the Brickyard at Cinderhill Colliery approx.[SK 535 440] is as follows:

This section does not agree with the following record quoted by Gibson and others (1908, p. 109) for the same Brickworks, illustrating the problems of detailed correlation within even a small area:

The proximity of this Brick Pit to the Cinderhill Fault, usually associated with many minor dislocations, may account for the differing sections. Wilson (1876, p. 533) recorded hard red and yellow mottled and soft grey sandstones, some 40 ft thick in beds from 1 in to 6 ft thick, near Hempshill. He considered that they may be passage beds between the Permian and Bunter.

The railway viaduct [SK 544 459] over the River Leen between Bulwell and Hucknall on the eastern margin of the district is built largely on Middle Marl. A section near the top of the formation measured in the foundations at the southern end showed:

Housing development [SK 5425 4336] east of Basford Hall exposed red clay and sandy clay in the upper part of the Middle Marl. An outcrop of red 'marl' up to 10 ft thick and with thin dolomitic limestone bands was also discovered in a fault 'graben' which was not through by a sewer trench at Broxtowe Wood [SK 5273 4319] (see also p. 150d). At Nuthall Temple, M1 Motorway excavations [SK 5159 4400] exposed small lenses, up to 6 ft thick, of red and green clay of the Middle Marl caught up in the Cinderhill Fault Complex (see also p.161a).

The M1 Motorway excavations provided further sections [SK 5054 4283] of the Middle Marl north of Strelley from which the following sequence was compiled:

The basal yellow-brown sandstone in the Middle Marl is not easily distinguished from the Lower Magnesian Limestone. The clay beds represent some 57 per cent of the section here compared with 75 per cent at Bulwell.

One mile to the south-south-east in the Catstone Hill Opencast Site [SK 5033 4147] the Middle Marl was only some 2 ft to 2 ft 6 in thick. The section measured in the south-west of the site was:

The south-eastern corner of the site [SK 5070 4171] showed up to 10 ft of red sandy clay which overlay and filled hollows in the Lower Magnesian Limestone (see p. 000).

In trenches and excavations at Bilborough, less than one mile to the east, the marl consists of red sandy clay and clayey sand, 5 to 10 ft thick, which passes up into the Lower Mottled Sandstone forming the outlier upon which St. Martin's Church is built.

In the Radford–Bilborough area there are patches and pockets of red clay resting upon the feather-edge of the Lower Magnesian Limestone. Patches up to 10 ft thick have been reported in places. In Chalfont Drive Borehole the driller recorded 8 ft 6 in of red clay with this bands of yellow sandy dolomitic limestone. At Newcastle Colliery [SK 546 422] just beyond the eastern margin of the district, Middle Marl is absent, the Lower Mottled Sandstone resting directly on Lower Magnesian Limestone. There is no evidence of

Middle Marl beyond the limits of the area of Lower Magnesian Limestone deposition.

The Middle Marl has been recorded in the following boreholes and shafts (thicknesses to the nearest foot in brackets):

Annesley Colliery No. 1 Shaft (27), Annesley Hall (26), Cavendish Crescent (28), Charlie's Wood Cottages (19), Cinderhill Colliery No. 6 Shaft (23), Forest Lodge (28), Heatherdale Pond (25), Hempshill Colliery Shaft (21), Home Farm (26), Mapplewells (34), Misk North (25), Motorway Proving Hole (21), Newstead Colliery No. 1 Shaft (21).

Triassic

Moira Breccia

In a landslip on the east side of the Derwent valley in Croft Wood [SK 3663 3932] near Breadsall, 2 ft of ochreous brown and red mottled breccia in a gritty matrix underlie 5 ft of Pebble Bed rocks. In the rail cutting [SK 3798 3945] 1 ft 4 in of coarse sandy breccia with fragments, up to 6 in long, of fine sandstone, red ironstone and green-grey mudstone in a coarse sandy matrix overly and probably occupy a hollow in 'reddened' Namurian mudstones.

For 150 yd of the course of Ferriby Brook, sections [SK 389 398] show up to 3 ft of red and ochreous mottled breccia, locally with a clayey matrix, amid small sections of friable Ashover Grit.

Two localities [SK 3955 4089] and [SK 3960 4074] in the road cuttings south-west and south of Morley church show up to 1 ft of Moira Breccia. At the former locality red-brown soft sandstone is exposed beneath the breccia and is assumed to be interbedded with it.

To the north of Morley church the breccia mantles part of a scarp face formed of Westphalian sandstones which underlie and overlie the Kilburn Coal; on its western side the outcrop is apparently transgressed by sandy micaceous Waterstones. The breccia is also exposed in the brook known as The Gripps [SK 3979 4124], where 4 ft of red-brown and ochreous gritty and clayey sand overlie 2 ft ft + of breccia composed of ironstone, sandstone and siltstone in a red and ochreous sandy matrix. Similar rocks with quartzitic pebbles litter the soil.

Cores of the Moira Breccia have been seen from two boreholes at the Rose and Crown Opencast Site. The sequence proved below Waterstones and resting on stained Westphalian sandstone [SK 3937 4239] was 2 ft of breccia (Plate 8) on 1 ft of red silty clay on 7 ft of purple and brown mottled sand with clayey seams near the base on 3 ft of breccia.

A this section (E37601) of the breccia from this borehole was described by Mr K.S. Siddiqui. This is a reddish brown, well lithified rock with subrounded to well-rounded pebbles, up to 5 cm in diameter of fine-grained dolomitic and arenaceous limestone, mudstone, siltstone, hematitic siltstone, fine-grained sandstone quartzite, kaolinized fragments and semi-translucent rock particles heavily stained with iron oxide. The fines consist, in order of abundance, of quartz, feldspars, micas (sericite) and carbonates. The feldspars include plagioclase, orthoclase and a few grains of microcline. Granules of well-crystallized kaolite and hematite are also dispersed among the detritus. In some places the presence of well formed rhombs of dolomite indicates secondary recrystallisation of the carbonate. Microgranular calcite and some grains of chart are also scattered in the matrix. Goethite and cryptocrystalline ferric oxide constitute the bulk of the intergranular cement.

An X-ray powder photograph of the whole rock showed the presence of quartz, dolomite, kaolinite, illite, calcite, goethite and feldspar.

Lower Mottled Sandstone

South and western areas

At the eastern end of the Morley Tunnel [SK 3995 4009] the total thickness of Lower Mottled Sandstone is approximately 60 ft (Figure 83), of which some 45 ft of cross-bedded pebbly sandstone are poorly exposed. Pebbles are less common than in the overlying Pebble Beds and the sandstone appears to be partly dolomitic.

Near Dunnshill, at the western end of Dale Hills [SK 4261 3837], the Lower Mottled Sandstone is well-exposed in old quarry faces:

Dale Abbey boreholes Nos. 1 and 2 were drilled from the floor of the quarry and proved red marl and yellow sandrock to 48 ft 6 in. A faulted outlier north-west of Dale has been worked for sand near Hagg Farm [SK 4310 3930]. In an old pit [SK 4347 3889] at the foot of Arbour Hill the following section was exposed:

The junction between the Lower Mottled and Bunter Pebble Beds is exposed some 10 yd to the west, where 10 ft 6 in of buff sand and medium-grained sandstone with small pebbles are underlain by 14 ft of fine-grained red and buff mottled sandstone.

At the western extremity of the outcrop around Dale Abbey petrographical examination by Dr Berridge reveals that the clasts of the typical fine-grained sandstones are less rounded than normal for the formation; angular grains are almost as abundant as the standard subangular type. One sample (E36090) contains a very high proportion of partly replacive interstitial baryte. It resembles the Pebble Bed lithology of the Hemlock Stone (p.154d) and it is significant that accessory interstitial baryte is present in the overlying Pebble Beds at Dale Abbey [SK 4334 3897] (E36089). Accessory detrital minerals identified from the Lower Mottled Sandstone in this area include apatite and staurolite in addition to the more usual opaque oxide ores, zircon and tourmaline.

Farther east, near Grove Farm a small pit [SK 4520 3858], shows 12 ft of massive, friable, yellow-brown, fine-to medium-grained, slightly micaceous sandstone; cross-bedding suggests sources to the north-east. On the opposite side of Dale Road in another pit [SK 4522 3852], some 18 ft of similar sandstone, are overlain by 6 ft of laminated slightly silty micaceous mudstone, pale grey-green in colour, sporadically reddened, particularly at the top. Gibson (1908, p. 127. fig. 10) illustrated this region with a section showing the burying and partial re-emergence of the Pre-Triassic landscape. The resurvey shows that although the interpretation is complicated by faulting, the Crawshaw Sandstone formed a feature in the pre-Triassic landscape, for example at Thackers Wood [SK 4570 3850].

West of Stanton are several faulted outcrops of red and buff marly sand which are considered to belong to the Lower Mottled Sandstone. In one old sand pit [SK 4600 3820] bounded on the north by faulted Crawshaw Sandstone are 15 ft of fine-grained sandstone, predominantly red, but weathering to a yellowish colour with mottling and staining. Rare cross-bedded units indicate provenance from the north. Sporadic coarser quartz layers, 1-in bands of silty mudstone, pale grey-green in colour, and dolomitic bands also occur. There are many variations within the pit, but generally the sandstone is more marly towards the top and the southern end of the exposure.

Dr Berridge reports that tourmaline is present in all this sections from this locality but accessory grains of zircon, andalusite, garnet and epidote are less regular in their distribution.

At Stoney Clouds, east of Stanton, the lower part of the scarp may include the topmost beds of the Lower Mottled Sandstone. The following section was measured in an old quarry [SK 4788 3765]:

A small outlier of Lower Mottled Sandstone occurs at New Stapleford [SK 4950 3830]. The rock is generally less than 10 ft thick and composed of soft red fine-grained sand. Over 80 ft of massive red sandstone are seen in a disused quarry on the opposite side of Coventry Lane [SK 4990 3885]. The lower 30 ft contain many red marly partings, and the upper 50 ft sporadic buff patches and bands together with pebbles. Cross-bedding indicates a derivation of sediment from the north-east.

In the Stapleford Hill area, Bramcote sand quarry [SK 5030 3890] shows the following section:

Taylor and Houldsworth (1973, p. 165) recorded some 40 ft of Mottled Sandstones resting unconformably on Westphalian sandstone in Swancar Quarry [SK 491 393], which is west of the outcrop shown on the map.

Excavations for a roundabout [SK 5050 3792] on the Sandiacre–Stapleford By-pass exposed the following section, considered to lie near the top of the Lower Mottled Sandstone;

A small outlier of Lower Mottled Sandstone occurs at Balloon Wood, where an excavation [SK 5087 3978] showed some 10 ft of red fine-grained sandstone with sporadic small pebbles and red marly patches.

Opposite the northern entrance to Nottingham University [SK 5462 3880] on the eastern side of the Nottingham Ring Road an old sand pit contains faces of Lower Mottled Sandstone up to 30 ft high. The sandstone is predominantly red in colour with buff patches, bands and mottling. It is commonly calcareous, partly dolomitic and was extracted for moulding sand in the 1930's.

Lower Mottled Sandstone crops out over about 1.25 square miles in the Wollaton Park area, but apart from a few excavations of red sand in Wollaton village, exposures are poor. The best exposures occur near and on the University Campus. Massive fine-grained sandstone up to 35 ft thick is seen in an old quarry face [SK 5440 3863] south-east of Lenton Firs. It is generally red in colour, with buff to pale brown discontinuous bands, commonest at the top of the face. Cross-bedding indicates derivation from the north-east. Swinnerton (1910) recorded lenses of dolomitic sandstone from this locality. Detailed petrological examination of the Lower Mottled Sandstone on the Nottingham University Campus indicates an absence of a coarse-grained fraction and in part it grades into siltstone. The apparent eastward trend towards an increasing degree of clast-roundness is not maintained throughout the formation. Despite the general fine-grained nature of the sediments and the presence of some comparatively well-sorted and rounded material, the rocks are subarkosic rather than protoquartzitic and, although chert or siltstone cleats probably outnumber those of metamorphic rocks, accessories include garnet, hornblende, andalusite and staurolite, none of which were identified in Catstone Hill thin sections (see p.151d). The compositional affinity is with the Stanton by Dale and Dale Abbey rocks rather than those of Catstone Hill. The Lower Mottled Sandstone at Nottingham University Campus is more consistently affected by dolomitic cementation than at the other localities discussed.

Many boreholes have proved the Lower Mottled Sandstone in the Nottingham–Derby area (plate 10). In the Beeston area, Station Road and Stoney Street boreholes (Nos. 13 and 14, (Plate 10)) proved the basal breccia/conglomerate contains angular to rounded fragments of quartz, quartzite, limestone, dolomite, green igneous rocks and Westphalian mudstones; some fragments are larger than the 2 in diameter of the borehole.

The Lower Mottled Sandstone, as proved in the bores, is a little under 100 ft in the south-east of the district, just west of Nottingham, and thins westwards to about half this thickness around Dale Abbey. Exact figures cannot be established in this latter area, where the majority of the boreholes date from the 19th Century and are inadequately logged.

Eastern area

Much of the outcrop in the north-west of this area is obscured by boulder clay, but 12 ft of brick-red, fine-grained, soft, friable sandstone were excavated [SK 4998 5398] on a building site near Armesley Woodhouse. and 20 ft of pink cross-bedded sandstone were exposed at Nuncargate [SK 5035 5410].

There are many small exposures of Lower Mottled Sandstone, up to 20 ft thick, in the Annesley, Newstead and Hucknall areas, as at [SK 5105 5351], [SK 5399 5412], [SK 5165 5245] and [SK 5050 5178]. Cross-bedding suggests a west and north-west origin for the sand.

The largest exposure in the Hucknall area occurs at Long Hill [SK 5191 4913]:

There are many small outliers of Lower Mottled Sandstone between Wathall and Hucknall, for example at Hucknall Cemetery [SK 5288 4826] and at Butlers Hill.

At Bulwell the Lower Mottled Sandstone forms the eastern bank of the River Leen. West of the town, near the northern cemetery, the Middle Marl has been worked for clay with a cliff-like exposure of Lower Mottled Sandstone forming the back wall of the excavation. Of the 18 ft of pinkish red, fine-grained sandstone still visible, the upper 10 ft are cross-bedded from the south-west; the lower 8 ft are massive and contain red marl pellets (3 in x 0.5 in) in the basal 3 ft. A large outlier of Lower Mottled Sandstone occurs between Bulwell and Nuthall. On the north side of the Cinderhill Fault there are several exposures of red sandstone containing sporadic pebbles. Up to 18 ft can be seen in a railway cutting [SK 5295 4442] and some 39 ft of sandstone were proved in the old Hempshill Colliery Shaft. Some 11 ft of red sandstone with a soft marly base were recorded by Mr Fowler in the old Cinderhill Brickyard [SK 534 441] to the north of the fault. South of the dislocation he recorded:

The above section is now obscured by tipping but 6 ft of fine-grained calcareous red-buff sandstone are still visible in the nearby railway cutting at Cinderhill [SK 5369 4379]. Red sand was dug during a new housing development east of Basford Hall [SK 5422 4344].

A fault slice of Looser Mottled Sandstone was exposed in a sewer trench near Broxtowe Wood [SK 5278 4314], where some 8 ft of red and buff fine-grained sandstone were seen. A similar fault trough between Kimberley and Nuthall Temple, forms a ridge of Lower Mottled Sandstone, with several exposures, e.g. in Knowle Wood [SK 5040 4443]. Nearby, a temporary excavation [SK 5052 4412] for the Nuthall By-pass exposed the southern boundary fault, with Lower Magnesian Limestone thrown against red fine-grained sandstone.

Between Strelley Windmill and Strelley Hall, the M1 Motorway cut through an elevated ridge of the Lower Mottled Sandstone; 15 ft of red marly sand, capped by a few feet of drift. The underlying Middle Marl (p.152b) contains many sandstone bands and the gradual passage between the two formations was well displayed.

The best exposures seen in the southern part of the eastern outcrop were at Catstone Hill Opencast Site [SK 5033 4147] and the adjoining quarry [SK 5076 4151]. At the top of the quarry, a lens, 10 to 12 ft thick, of buff pebbly and conglomeratic sandstone is well cemented by baryte—a lithology comparable with that of the Pebble Beds (cf. Bramcote Stone: p. 154d). The lens is aligned north-north-eastwards and probably represents a washout channel. The following section was recorded in the opencast site:

At Broomhill Wood [SK 5280 4072] temporary excavations exposed 6 ft of red, fine-grained, soft sandstone resting unconformably on stained Westphalian rocks. Nearby (see p. 152a). dolomitic limestone was recorded within the Lower Mottled Sandstone.

The lowest 50 ft or so of the Lower Mottled Sandstone have been proved in some 11 boreholes and shafts in the eastern part of the district, and old water bores [SK 5470 4260] in Basford just beyond the margin of the sheet penetrated 100 ft of red sandstone which are assigned to the formation.

Pebble Beds

Western area

The large sand and gravel quarries of the Mercaston–Muggington area provide representative sections of the Pebble Beds and are described first in the following account. Sections from other areas are omitted except where they show variation from this norm.

The quarries just over 1 mile SW of Turnditch [SK 2800 4540] provide an almost complete succession through the Pebble Beds:

Mr Siddiqui reports that sand samples from the top 20 ft have subangular to subrounded grains, some showing surface pitting. They are stained by pale yellow clay. The sand fraction is mainly of quartz in a matrix of chlorite, illite, fibrous kaolinite and thin flakes of muscovite. Feldspars are mainly plagioclase with traces of orthoclase and microcline, grains of chert, scattered specks of hematite and lithic particles of sandstone and quartzite are common. Heavy minerals include tourmaline, zircon, anatase and possible sphene. Manganese staining is common in bands or near joints.

The gravelly portion is composed mainly of fine-grained quartzite pebbles, which are generally elongated and have conchoidal fractures, and smooth surfaces without cavities or striations. Angular fragments of milky and pink quartz and of quartzite and pebbles of sandstone, limestone, chert, mudstone, and igneous rocks are also present.

The gravelly portion is commonly cross-bedded (see (Plate 11)), but otherwise appears to be homogeneous and massive, except where thin layers of mudstone or siltstone pick out complex minor structures (p.93), Sporadic joints are commonly filled with red clay.

Old disused sand pits at Bullhurst Hill show up to 20 ft of buff massive sandstone with rare pebbly layers. Red marl bands up to 12 in thick are common 20 ft or so above the base of the formation. The marl bands thicken north-eastwards and unite to form 12 ft of red, poorly laminated micaceous mudstone with thin green and yellow silty and sandy bands and laminae—the thickest 'marl' known in the Pebble Beds succession.

At Muggington Quarry [SK 2930 4340], near Bullhurst Hill, the top 50 ft of the Pebble Beds consist of ill-sorted sand and gravel containing wedge-shaped lenses, up to 4 in thick, of yellow-brown sandstone. The lower quarry faces are formed of some 40 ft of massive buff sandstone with sporadic pebbles. The pebbles, aligned in bands, have red marl coatings.

A small old gravel pit north-west of Bullhurst Hill [SK 2855 4390] contains about 20 ft of clayey sand and gravel, well cemented in places to form a conglomerate which was presumably responsible for the abandonment of the workings.

Exposures in a pipe trench east of Weston Underwood showed a feather edge of sand, clay and pebbles, overlying purplish red mudstones of the Widmerpool Formation. One excavation [SK 2972 4245] gave the following sequence:

The sand is assumed to lie at or near the limit of deposition of the Pebble Beds.

Two boreholes [SK 2535 4167] and [SK 2572 4159] at Brailsford proved up to 30 ft of sand and gravel. An old gravel pit [SK 2540 4170] contains up to 10 ft of ferruginous sand and fine gravel, worked in the past on both sides of Luke Lane.

Exposures of Pebble Beds north of the Mercaston–Mugginton area contain a greater than normal proportion of rock fragment., including chert, sandstone, siltstone and silty mudstone, e.g. at Ireton Wood [SK 2783 4874]. Outliers of Pebble Beds occur near Bullhill [SK 2735 4905], at The Mountain [SK 2680 4920] and Blackwell [SK 2560 4950], The last was once extensively quarried for sand and gravel, but is now largely obscured by tipping and afforestation though at one place [SK 2558 4948] 13 ft of buff, fine to medium well-sorted sand with pebbles are visible. The lower part is soft with cross-bedding indicating a source to the east-north-east. A sample obtained from the lowest 5 ft showed a bimodal grain size distribution.

Pebble Beds form a series of irregular outliers capping the escarpment south-west of the Ecclesbourne valley between Weston Underwood and Allestree. The formation, about 90 ft thick at Gun Hills, thins rapidly south-westwards to disappear in the vicinity of Kedleston, where the Waterstones appear to rest directly on Carboniferous rocks.

In a stream section [SK 3016 4437] near The Clouds, 2 ft of near-horizontal red mudstone with green sandy lenses are exposed beneath the main Pebble Beds feature and probably represent a local basal mudstone. Because of their relationship to the overlying Waterstones, red and green mudstones in old clay pits [SK 3050 4158] in Brick Kiln Covert, Kedleston, are similarly assigned to the basal Pebble Beds rather than to the Keuper Marl as proposed by Wedd (in Gibson and others 1908, p. 122).

Pebbly sandstone is exposed in a few small pits near Ireton Farm [SK 3142 4180], Cocks-hut-hill [SK 3220 4280] and Allestree Park [SK 3416 4070], where up to 12 ft of moderately to poorly cemented, buff, cross-bedded sandstone in beds 1.5 to 3 ft thick are visible. The sandstone contains a few rounded quartzite pebbles, up to 3 in diameter, concentrated in thin lenses or along the cross-bedding.

Southern area

The Pebble Beds form faulted outcrops which are well exposed between Nottingham and Derby. Three water boreholes in Slack Lane [SK 336 362], Derby, proved 33.5 ft of sandstone without bottoming the sequence, and the King Howman and Co. Water Borehole [SK 3434 3675] proved a total thickness of 36 ft (Stephens 1929, p. 90), of which the lowest 21.5 ft were without pebbles. This lithology resembles that of the Littleworth Beds of Stevenson and Mitchell (1955, p. 32) and is thus assigned to the Pebble Beds rather than to the Lower Mottled Sandstone.

A few feet of coarse, brown, cross-bedded, soft sandstone contain lenticular pebbly beds up to 1 ft thick near Allestree [SK 5016 3950]. The total thickness of Pebble Beds hereabouts is calculated to be between 25 and 30 ft. They are a similar thickness on the eastern side of the Derwent valley, where they appear to be cambered. In Croft Wood [SK 3663 3932], Breadsall, at the top of the stream cutting there are 6 ft of soft khaki sandstone; 15 to 20 ft below, but within a landslip, there are 5 ft of brown sandstone with 1 to 2-in angular fragments of sandstone and quartzite overlying the Moira Breccia (p.1520). To the east of Breadsall [SK 3761 3940], where the Pebble Beds have been dug for gravel, 6 ft of coarse brown and red-brown mottled sand and sandstone contain many pebbles and two fissures, up to 1 ft wide, filled with red mud.

A section [SK 3836 4105] east of the roadway near Breadsall Lodge comprises 7 ft of coarse brown sand with quartzite and sandstone pebbles and cross-bedding which dips to the north-east. A pit [SK 3837 9090] nearby shows 11 ft of cross-bedded, soft brown, sandstone with scattered quartzite, sandstone pebbles and fragments of sandstone and chert. Most of the gravel here occurs in the lowest 3 ft at the east end of the pit in beds and poorly defined masses.

Sections of a few feet of pebbly sandstone are seen in the railway cuttings west of Morley Tunnel and in a pit [SK 3886 4006] north-east of Broomfield Hall, where they underlie the Woodthorpe Formation (p.154d). Wedd (MS map) recorded 10 ft+ of 'coarse shingle' in a now obscured pit [SK 3902 3986]. The total of 25 to 30 ft of Pebble Beds here is similar to the thickness in the Derwent Valley. The visible section in the cutting [SK 3995 4009] to the east of Morley Tunnel is poor compared to that illustrated by Gibson and others (1908, p. 125). Beneath remanié Woodthorpe Formation on the north of the cutting, and according to Gibson and others (1908, p. 124) below overlapping Waterstonee on the south, are some 45 ft of sands which are densely packed with pebbles of quartzite, light and dark siliceous rocks, limestone and granitic rocks. Beds of soft khaki and red-mottled micaceous sand, up to 1 ft thick on the north side of the cutting and 2.5 ft on the south, occur within the pebbly sands. These Pebble Beds rest on 60 ft or more of Lower Mottled Sandstone.

Exposures of Pebble Beds, up to 20 ft thick, occur west of Dale at Arbour Hill [SK 4340 3855], near The Flourish [SK 4285 3875] and Dunnshill [SK 4210 3845]. At the last locality, bands of red-stained sandstone are common.

A faulted scarp [SK 4540 3815] near Dale Abbey contain. three exposures of up to 20 ft of massive brown medium-to coarse-grained sandstone. Dips of cross-bedded units, some pebbly, indicate derivation from the south-west, south-east and north-east.

South of Dale, a north-facing scarp of sandstones over a mile long provides excellent exposures of massive, pale brown to buff, cross-bedded, pebbly sandstone. Pebbles are up to 4 in in diameter, but average between 1 and 2 in. Cross-bedding dip direction. range from south-east through south-west to north-west. The gradational contact with the underlying Lower Mottled Sandstone is exposed at the western end of the scarp near Dunnshill [SK 4261 3836] where inclusions and lenses of pale grey-green mudstone and rare buff fine-grained sandstone fragments occur in the basal 15 ft. The uppermost beds are exposed in Ockbrook Wood [SK 4360 3833], where the top 9 in are silicified and overlain by mudstones and sandstones of the Waterstones. The measured thickness of Pebble Beds in the Dale area is 70 ft. An old quarry [SK 4680 3785] at Stanton by Dale shows a face of soft, massive, buff, medium-to coarse-grained sandstone. Pebbles are locally common, particularly within cross-bedded units.

At Stoney Clouds the Bunter Pebble Beds form a bold north-facing fault-scarp, some 100 ft high, of buff, pebbly, poorly cemented sandstone. At Burn Hill [SK 5040 3730], south-west of Bramcote Church, 26 ft of red-stained, buff, cross-bedded sandstone are seen in a cliff-like feature; provenance is from the north west. Two hundred yards south of Bramcote Church, along the sides of Chilwell Lane [SK 5070 3730], the junction between the Pebble Beds and the Woodthorpe Formation is exposed, the former comprising up to 35 ft of red-brown and buff, medium to coarse-grained, pebbly, cross-bedded sandstone. The top 2 in of the sandstone are pale grey with a concentration of small pebbles.

West of the River Eyewash there are numerous old sand quarries which show the typical buff, off-white and reddish, massive sandstone, with sporadic pebbles. The red coloration is in the form of banding along the foresets of the cross-bedding.

There are many exposures of Pebble Beds in the Stapleford–Sandiacre area. A 60-ft quarry face [SK 4933 3735] north of the cemetery exposes a mottled red and buff, massive, cross-bedded. medium-to coarse-grained sandstone. The red colour is predominant, probably due to staining from 10 ft or so of overlying Waterstones.

Within the Clifton–Highfields Fault system the highest part of the Pebble Beds is exposed at Tottle Brook [SK 5280 3828]. A conglomerate about 4 ft thick comprises a coarse sand containing pebbles, predominantly quartzites, up to 4 in but averaging 1 in, and ironstone fragments, and is underlain by 3 ft of buff medium-grained cross-bedded sandstone. This is assumed to be the locality where Shipman (1889, p. 126) found pebbles with Orthis, Rhynchonella and Atrypa. The basal 12 ft are a reddish colour and the top 15 ft buff.

South of the Clifton–Highfields Fault system many exposures resulting from building and road construction showed brown Bandy loam with pebbles overlying red-brown, buff, cross-bedded sandstone with sporadic pebbles. This rock, typical of the Nottingham area, weathers very quickly to become friable or running sand.

An old river cliff [SK 5410 3791] at the side of the University Lake exposes 20 ft of buff to light brown, medium-to coarse-grained sandstone. Crose-beddirig is common but variable in direction with origins from the south-west and east-north-east. Layers of pebbles occur, usually quartzites with a maximum pebble diameter of 3 in, together with mudatone and other sedimentary rock fragments.

Wollaton Hall is sited on a prominent feature of Pebble Beds forming the highest ground in Wollaton Park, and two old quarries [SK 5352 3870] and 540 390] show sections of up to 12 ft of buff, brown and reddish fine-to medium-grained sandstone.

Boreholes along the south-eastern margin of the Derby district, between Nottingham and Derby, show that the Lower Mottled Sandstone is everywhere overlain by a coarser, pebbly, red-brown, pale buff to grey sandstone of Pebble Beds lithology, which varies from 170 ft in Highfields Borehole [SK 5439 3751] at Beeston, just beyond the margin of the district, to about 70 ft in the Dale Abbey area east of Derby (Plate 10).

Eastern area

Between Newstead and Wollaton the Pebble Beds are present largely as thin capping. or outliers on hills of Lower Mottled Sandstone; they are readily confused with Pleistocene sands and gravels, composed mainly of re-worked Triassic sandstones which are also present in this area,

The largest outcrop occurs north-east of Newstead Abbey on a spur [SK 543 543] between Swinecotte Dale and Knightcross Dale, but exposures are few.

Another ridge [SK 510 545] of Pebble Beds extends east of the present district to form the Shoulder of Mutton Hill, some of the highest ground in Nottinghamshire at 609 ft. All Saints' Church, New Annesley, is built on an outlier at the southern end of this ridge, where yellowish sand and pebbles have been dug out. Small outliers also occur near Castle Wood between Annesley and Newetead Abbey.

At Catstone Hill [SK 5076 4151] a buff conglomeratic sandstone, up to 12 ft thick, occurs above a quarry in typical Lower Mottled Sandstone, (p. 153d). The presence of haute cement in the conglomerate has been cited by Aveline (1880) as evidence of a Keuper affinity, but the resurvey suggests that the rock probably occupies a washout channel, trending north-north-east, cut into fine-grained Lower Mottled Sandstone at the onset of Pebble Beds deposition.

At Alexandrine Plantation well-cemented conglomerate is again exposed [SK 5190 3852]. It has been argued that this conglomerate also is of basal Keuper age (Aveline 1880; Shipman 1889). If so, the deposit is little more than the reworked top of the Pebble Beds since it has few affinities with the Woodthorpe Formation (p.154d).

A borehole, about [SK 5015 3855], at Bramcote Hill proved 140 ft of sandstone, the lower part of which must be Lower Mottled Sandstone. At the surface 8 ft of massive cross-bedded fine-to medium-grained sandstone is predominantly red in colour with irregular buff bands and patches up to 2 ft across. Here, and to the west, distinction between the Lower Mottled Sandstone and the Pebble Beds becomes difficult. At the top of Bramcote Hill [SK 5030 3860], 3 ft of buff, red-brown, pebbly sandstone are irregularly weathered because of uneven barytes cementation.

In Bramcote Sand Quarry [SK 5035 3880] the formation overlies Lower Mottled Sandstone and is distinguished from it by a red-brown rather than red colour, and being composed of medium-grained sandstone with coarse and pebbly units and a low percentage of clay. Some 200 yd to the south-east an old quarry exposes 35 ft of massive sandstone, the lower part of which is predominantly red with sporadic buff bands and irregular patches. The upper part is red-brown or buff with rare pebbles. A marl band conveniently divides the face into Pebble Beds above and Lower Mottled Sandstone below. On the opposite side of the road the Pebble Beds form the impressive feature of Stapleford Hill, rising to 332 ft and providing exposures of almost the total sequence, here some 100 ft thick. The beds are fine-to medium-grained, with well-developed cross-bedding dipping to the south-west. The sandstone exposed at the top of the hill is pebbly, well-cemented and commonly red-stained. In thin section, baryte is accompanied by a significant proportion of ferric oxide testiest. Feldspar and non-quartzose lithic clasts are not as common as farther west near Dale Abbey.

The Hemlock Stone [SK 4995 3866] is a quarry-remnant of Bunter Pebble Beds left unworked because of a resistant cap of rock with a baryte cement. It is cross-bedded in large units, with current directions from the north-east and north-west. Samples from the Hemlock Stone show that the bands relatively resistant (E36080) and susceptible to weathering (E36081) are respectively richer and poorer in baryte. The baryte-rich rock has a texture very similar to that of heavily calcitized rocks from the top of the Pebble Beds farther west. The partially replacive poikilitic baryte crystals are individually as much as 1.2 mm in diameter and the mineral probably constitutes about 30 per cent of the rock volume. The bands in the Hemlock Stone which are more susceptible to weathering are slightly finer-grained and the baryte cement has probably replaced a lower proportion of the sand content. Other specimens from Stapleford Hill are coarser in sand grain size, but their interstitial baryte cement is more tenuous.

Woodthorpe Formation

An old pit [SK 3886 4006] on the roadside at Broomfield Hall exposes a partly disturbed section of the Woodthorpe Formation below some 4 ft of boulder clay. A basal, coarse, grey-brown, fairly hard sand with quartzite and sandstone pebbles and fragments of black chert is overlain by 8 in of greenish clayey sand with a thin red clay seam and with many pebbles which are more angular than those of the Pebble Beds. The succeeding well-bedded fine khaki sand, 10 in thick, 113 in turn overlain by 1 ft of red clay. This is the most westerly known occurrence of the formation.

The formation is intermittently exposed in the railway cutting and associated watercourses for 600 yd west of the west portal of Morley Tunnel. One exposure [SK 3943 3971] shows the basal 1 ft 3 in resting on a few in of Pebble Beds. In the cutting east of the tunnel an impersistent few in of greenish clay with pebbles is sandwiched between the boulder clay and the top of the Pebble Beds. Gibson and others (1908, p. 124) recorded overlap of the Pebble Beds by the Waterstones in this cutting.

Between Morley and Nottingham numerous exposures and temporary sections of the Woodthorpe Formation have been recorded. An indication of the rapid westerly thinning of the formation was provided by an old quarry [SK 4340 3885] at Dale Abbey:

The most complete section of the formation is located in a cutting [SK 4744 3770] on the M1 Motorway, near Stanton: