Geology of the country around Chesterfield, Matlock and Mansfield. Explanation of one-inch geological sheet 112, New Series

By E. G. Smith, G. H. Rhys and R. A. Eden

Natural Environment Research Council. Institute of Geological Sciences incorporating the Geological Survey of Great Britain, the Museum of Practical Geology and Overseas Geological Surveys

Memoirs of the Geological Survey of Great Britain England and Wales

Geology of the Country around Chesterfield, Matlock and Mansfield. Explanation of one-inch geological sheet 112, New Series

By E. G. Smith, B.Sc., G. H. Rhys, B.Sc. and R. A. Eden, B.Sc., F.R.S.E. with contributions by M. A. Calver, M.A., P. McL. D. Duff, B.Sc., R. K. Harrison, M.Sc. and W. H. C. Ramsbottom, M.A., Ph.D.

London:Her Majesty's Stationery Office, 1967

(Front cover)

(Rear cover)

Preface

The area covered by the Chesterfield (112) Sheet of the One-Inch Geological Map of England and Wales was originally surveyed on the one inch to one mile scale, mainly by W. W. Smyth, J. Phillips, W. T. Aveline and T. R. Polwhele, and the results published between 1852 and 1858 on the Old Series One-Inch Maps 71 NW, 71 NE, 72 NE, 81 SE, 82 SW, 82 SE, most of which were revised between 1866 and 1879. The first six-inch survey, by J. B. Hill, W. Gibson, C. B. Wedd, R. L. Sherlock and G. W. Lamplugh, was carried out between 1904 and 1908, and the first edition of New Series Map 112 was published in 1913. In the same year appeared. 'The Geology of the Northern Part of the Derbyshire Coalfield and Bordering Tracts' by W. Gibson and C. B. Wedd. That memoir described the geology of the Chesterfield (112) Sheet together with the portion of the Sheffield (100) Sheet which lies south of the Yorkshire border.

Apart from small areas in the north-east and north-west mapped by Mr. W. N. Edwards in 1940–41, the six-inch resurvey was carried out between 1947 and 1956 by Messrs. G. H. Rhys, E. G. Smith, R. A. Eden and P. McL. D. Duff, under the supervision of Mr. W. N. Edwards as District Geologist. The revised six-inch maps, published between 1958 and 1962, and the new one-inch map, published in 1963, reflect the great advance in the detailed knowledge of the area, particularly of the exposed coalfield.

The memoir has been written by Messrs. Smith, Rhys and Eden and edited by Mr. D. R. A. Ponsford and Dr. A. W. Woodland. Except for Chapter 2, largely written by Mr. Eden, the memoir has been compiled by Messrs. Smith and Rhys; Mr. Duff has contributed to the details of several chapters. The fossils have been identified by Mr. M. A. Calver and Dr. W. H. C. Ramsbottom, assisted by Messrs. M. J. Reynolds and J. Pattison; Mr. M. Mitchell named some of the corals. Mr. Calver has contributed the palaeontological accounts in chapters IV and V, and Dr. Ramsbottom that in Chapter II. Mr. R. K. Harrison has written Appendix 1 on the petrography of certain of the Carboniferous rocks and also supplied mineralogical data for some Permo-Triassic rock samples. Dr. J. Phemister also examined some of the Carboniferous rocks.

The Chesterfield district has a long mining history based on exploitation of its lead, ironstone and coal deposits, the last named being still a major source of mineral wealth. The sandstones, limestones and clay rocks of both the Carboniferous and Permo-Triassic formations are still widely used by the constructional, chemical and metallurgical industries. In addition the great modern civil engineering techniques of heavy building and motorway construction demand a detailed knowledge of the distribution of the rocks, not only near the surface but at depth. The new geological maps of the Chesterfield district, as well as this accompanying memoir, will form a valuable source of basic information for all these industries for many years to come.

Throughout the resurvey much assistance has been given by officials of the National Coal Board, especially the Area Surveyors and their staffs of the East Midlands Division, the officers of the Coal Survey Laboratory, Nottingham, and the Prospecting Officers of the Opencast Executive. This generous help, together with that provided by private mining firms, quarry owners, water undertakings, drilling contractors and others, is gratefully acknowledged.

C. J. Stubblefield, Geological Survey Office, Director, Institute of Geological Sciences, Exhibition Road, South Kensington, London, S.W.7 16 May 1966

List of six-inch maps

Published geological maps included, wholly or in part, in one-inch map Sheet 112 are listed below with initials of the surveyors and dates of survey. The surveyors were: P. McL. D. Duff, R. A. Eden, Wilfrid Edwards, G. H. Rhys and E. G. Smith. The maps are published uncoloured or, to suit individual requirements, hand-coloured. Small parts of one-inch map Sheet 112 are included in six-inch maps SK25SE, SK35SW, SK35SE, SK45SW, SK45SE and SK55SW; these are not yet published, the resurvey of them not having been completed.

Chapter 1 Introduction

Geographical setting

This memoir describes the Chesterfield (112) Sheet of the One-inch Geological Map of England and Wales. The districtThroughout this memoir the word 'district' refers to the area covered by the Chesterfield (112) Sheet. lies chiefly in Derbyshire, but extends in the east into Nottinghamshire and the greater part falls within the East Midlands Coalfield (Figure 1).

The highest ground, rising to 1203 ft O.D. on Beeley Moor, is in the west where Carboniferous Limestone, Millstone Grit and basal Coal Measures rocks form part of the eastern flank of the southern Pennines. This area is essentially one of moorland and hill-pasture with scattered habitations, and the only town is the old spa of Matlock. To the east lies the broad outcrop of the Lower and Middle Coal Measures where alternations of mudstone and sandstone give rise to a varied and undulating topography, generally between 300 and 600 ft O.D. Here coal mining and other industries share the landscape with mixed farming and, in addition to the large town of Chesterfield, there are numerous minor centres of population, among which Clay Cross and Alfreton are noteworthy. In the east of the district, and bounded by the escarpment of the Lower Magnesian Limestone, 500 to 600 ft above O.D., is the outcrop of the Permo-Triassic rocks—most of it a plateau-like area formed by the limestone dip-slope. The northern part of this region has several small colliery towns, but it retains a rural aspect with arable farms, woods and parkland; the southern part, excluding the small area of farmed and forested Bunter Pebble Beds, is largely urban, containing the sprawling towns of Mansfield, Sutton in Ashfield and Kirkby in Ashfield.

The only major river in the district is the south-flowing Derwent in the west. It drains the Carboniferous Limestone, through whose outcrop it runs in a series of narrow gorges, and much of the Millstone Grit. The Coal Measures are drained to the north by the Rother and its tributaries, notably the Hipper, Calow Brook and the Doe Lea, and to the south by the Amber, itself a tributary of the Derwent, and its tributaries, the Alfreton and Normanton brooks. On the Permo-Triassic outcrop the only rivers of note are the Poulter and Meden which flow north-eastwards, in steep-sided valleys cut into the Lower Magnesian Limestone, to join the Idle beyond the district boundary. G.H.R., E.G.S.

Historical

The industrial importance of the district is based on its mineral wealth. Lead mining in the Carboniferous Limestone dates back probably to Roman times, but it was the ironstones, coals and fireclays of the Coal Measures that were largely responsible for the industrial development of the district in the nineteenth century. Lead continues to be found in small quantities, generally as a by-product of the search for fluorspar, and fireclays are still worked on a small scale, but coal is the only major mineral product today.

The first record of mining for coal in Derbyshire dates from 1315 when Thomas de Chaworth, the lord of Alfreton, granted a charter to the monks of Beauchief to supply themselves with coal from his properties at Alfreton and Norton (Glover 1831, p. 48). At first coal was used mainly by the smiths and lime-burners though in some of the coalfield and surrounding areas it was being used domestically during the fifteenth century (Galloway 1898, p. 63). It did not, however, come into general favour as a domestic fuel until the sixteenth century, when in the reign of Elizabeth I, the building of proper chimney-flues made it an acceptable alternative to wood, which was by then in failing supply (ibid., pp. 79–81). During the latter part of the eighteenth century the industrial applications of coal were widened to include its use (as coke) in the smelting of iron. That century also saw the introduction of many notable improvements in coal mining, including the substitution of steam-engines for horses in raising water from the mines, the adoption of gunpowder for blasting, artificial ventilation by means of fire and the circulation of air throughout the mine to prevent accumulations of gas, and the use of horses for underground haulage. The end of the century was marked by the introduction of steam-engines to raise coal from the pits (Galloway 1898, pp. 361–2).

The local importance of the coal industry in the early part of the nineteenth century can be seen from the list of 245 Derbyshire collieries quoted by Farey (1811, pp. 188–215). Furthermore, Glover (1833, p. 294) stated that of the three thousand families living in Chesterfield in 1831 nearly half were 'employed in the extensive collieries, ironstone pits, etc.', while in Alfreton 'the extension of the collieries and iron works in the eastern part of the parish, accounts for the rapid increase of the population in that district' (ibid., p. 7). it was in the late 1830's, however, with the coming of the railways, that the local coal industry received its greatest stimulus. The North Midland Railway from Leeds to London, via Chesterfield and Derby, was routed through a tunnel to be excavated at Clay Cross. The driving of this tunnel, commenced in 1837, revealed some of the more important coals in the Lower Coal Measures, and George Stephenson, realizing the potential mineral wealth of the area, formed the Clay Cross Company to exploit these resources. By 1840 its first colliery was in production and, when the line to London was completed in 1844, the Company supplied the first coal to reach the capital direct by rail. The opening up of the coalfields by the railways created a greater market for coal, and in the years that followed numerous shafts were sunk in the district, the later ones, sunk in the latter part of the nineteenth century and the early years of the twentieth, being in the concealed coalfield.

During and since the last war, production has been supplemented by opencast mining, by which means millions of tons of coal, much of which would otherwise have been unworkable, have been produced within the district. Opencast mining is, however, now on the decline and at the same time the older collieries in the west are being worked out. As these collieries are abandoned mining activity is concentrated on the east of the district where the deeper collieries, with some seams as yet untouched, offer prospects of obtaining coal for many years to come.

Geological sequence

The formations represented on the map and sections are summarized below:

Superficial Formations (Drift)

Solid Formations

Geological history

Pre-Carboniferous rocks have been proved at only one place in Derbyshire, in the Woo Dale Borehole, 14 miles north-west of Matlock in the area of the Buxton (111) one-inch Sheet; they are supposedly of pre-Cambrian age (Cope 1949). The oldest rocks seen in the district, cropping out in the west and known beneath younger deposits from deep boreholes, belong to the Carboniferous Limestone Series. This consists chiefly of massive limestones and igneous rocks, which were deposited in the marine environment of the limestone massif where contemporaneous volcanic activity resulted in extrusions of lavas and ash. Towards the end of the Lower Carboniferous period argillaceous material was deposited along with the calcareous sediments to form interbanded limestones and shales. With the increased influx of argillaceous detritus into the subsiding area of deposition, fewer limestone bands were formed, and eventually only shales were deposited. Deposition of shales, largely marine in origin, continued well into Millstone Grit times and, apart from a possible representative of the Kinderscout Grit, it was not until late in Middle Grit times that sands were deposited over wide areas of the district. These sands formed the Ashover Grit which, like the later Chatsworth Grit, 'Brown Edge Flags', Redmires Flags and Rough Rock, was deposited in a cyclic sequence presumably as a result of periodic subsidence. A complete cycle includes, from the base upwards, marine shale, non-marine shale, sandstone, seatearth and coal. This pattern of sedimentation continued throughout known Coal Measures times, during the early part of which the cycles, containing coarse sands overlain by marine shales, were similar to those of the Millstone Grit. In later Coal Measures times deposition of sands, though locally considerable, was less widespread, and marine transgressions were less frequent.

Carboniferous sedimentation was brought to a close by the Armorican orogeny which uplifted the whole of the Pennine area and produced the major anticlines and synclines which are well seen in the various Carboniferous rocks of the district. A long period of denudation followed during which vast thicknesses of rock were removed.

The Permo-Triassic sediments were deposited on the eroded surface of the Carboniferous rocks, the mudstones and limestones being laid down towards the western limits of the Zechstein Sea, while the sandstones were accumulated under continental conditions.

Any Jurassic, Cretaceous or Tertiary rocks formerly present in the district were removed, together with some of the Permo-Triassic and Carboniferous rocks, by prolonged erosion in Tertiary times. At some time, probably during Miocene times, there was slight tilting towards the east accompanied by minor faulting mainly along pre-existing Armorican fractures.

The small patches of glacial drift found mainly on the higher ground of the Carboniferous Limestone and Millstone Grit in the west, and on the Permo-Triassic strata in the east are thought to be dissected relics of more widespread deposits left after the retreat of an early ice-sheet. Since then landslips and sheets of head have formed, alluvial deposits have been laid down in the river valleys, and peat has grown on some of the higher ground.

Summary of previous research

Probably the earliest work dealing with the geology of the district is that by Whitehurst (1778) which includes an appendix 'Containing some general observations on the strata in Derbyshire' based on the science of 'subterraneous geography'. Whitehurst, anticipating the law of superposition, drew attention to the coal-bearing rocks being everywhere underlain by grit resting upon shale which in turn rested upon limestone, and illustrated his account with horizontal sections across the Millstone Grit and Carboniferous Limestone in the south-west of the present district. He recognized the marine origin of the limestone and the igneous nature of the Derbyshire toadstones, and drew up a succession in which he assigned thicknesses to the Millstone Grit, the underlying shale and the various limestones and toadstones. He regarded coals as being formed from vegetable matter, and the argillaceous strata with which they were associated as being non-marine in origin, pointing out that the shells contained in ironstone 'are not marine productions, but of freshwater lakes, rivers, etc., being actually the remains of mussels'. It is of interest that the particular ironstone to which he referred, and which he traced across the northern half of the district from Tupton to Staveley, is today recognized as a prominent marker-band in the measures overlying the Tupton Coal.

Further observations on Derbyshire geology were made by Pilkington (1789), Farey (1811) and Watson (1811). Farey included a geological map outlining the surface areas occupied by what are now called the Carboniferous Limestone, Millstone Grit and Coal Measures, and also showing the extent of the Permo-Triassic limestones and sandstones. Watson compiled a section showing the strata between Bolsover and Buxton.

A general description of the Carboniferous Limestone was given in the memoir by Green and others (1869), and additional details of many of the lead mines were given in the 2nd edition of this work (1887). Allport (1874) described several specimens of toadstone from Matlock Bath and Bonsall, but Arnold-Bemrose (1894)This and subsequent references in Chapter I are listed at the ends of the appropriate ensuing chapters. gave the first comprehensive descriptions of the microscopic structure of these rocks. In 1897 Sir Archibald Geikie commented on the varied igneous history of the Derbyshire limestone area, and in 1907 Arnold-Bemrose showed that contemporaneous igneous activity had given rise to volcanic necks, tuffs and lava flows and was followed by later intrusions of dolerite. In 1908 Sibly, in dealing with the faunal succession in the Carboniferous Limestone of North Derbyshire and Staffordshire, touched upon the succession in the Matlock and Wirksworth areas. This was followed, in 1913, by Gibson and Wedd's Memoir which included a comprehensive account of the Carboniferous Limestone of the present district. Further detailed aspects of the Carboniferous Limestone succession of the district were covered by Traill (1939; 1940) who dealt with the geology of Millclose Mine, and Shirley (1950; 1959) who described both Millclose Mine and the neighbouring outcrop. Sweeting (1946) and Sweeting and Himus (1946) discussed the limestone at Ashover and gave lists of fossils. Ramsbottom and others (1962) have given details of the limestone proved in boreholes near Ashover.

The first detailed account of the Millstone Grit outcrop was given by Green and others (1869), and a revised account by Green (1887). Additional information was given by Wedd in the Memoir of 1913. Apart from Sweeting and Himus (1946), who added details to the known succession in the Ashover area, no attempt was made to use the goniatites for classification and correlation until the present resurvey was undertaken. A description of the detailed succession encountered in boreholes put down in the Ashover area during this resurvey has been given by Ramsbottom and others (1962).

A stratigraphical account of the Coal Measures was first given by Gibson and others (1913), and details of the portion of the Concealed Coalfield falling within the district have been given in the various editions of the Concealed Coalfield Memoir, the latest of which (Edwards 1951) made use of work by Edwards and Stubblefield (1948) on the marine bands and other faunal markers of the East Midlands Coalfield, and also of information on non-marine lamellibranchs, particularly that given by Clift and Trueman (1929) and Trueman and Weir (1946). The succession in the lower part of the Lower Coal Measures of the East Midlands was described by Eden (1954), who also contributed to a paper (1963) on the tonsteins of this coalfield.

The major investigations of the Permo-Triassic rocks of the district were carried out by Sherlock whose views on the lateral passage between Permian and Triassic are included in various publications between 1904 and 1947. Descriptions of the rocks are also given in the Geological Survey Memoirs of 1879 and 1913, while the Concealed Coalfield Memoir (Edwards 1951) deals with the regional picture as proved at outcrop and in boreholes and colliery shafts. GHR.

References

ALLPORT, S. 1874. On the microscopic structure and composition of British Carboniferous dolerites. Quart. J. Geol. Soc., 30, 529–67.

COPE, F. W. 1949. Woo Dale Borehole near Buxton, Derbyshire. Proc. Geol. Soc., Session 1948–9, iv.

EDWARDS, W. 1951Dated 1951, published January 1952.. The concealed coalfield of Yorkshire and Nottinghamshire. 3rd edit. Mem. Geol. Surv.

FAREY, J. 1811. A general view of the agriculture and minerals of Derbyshire, Vol. 1. London.

GALLOWAY, R. L. 1898. Annals of coal mining and the coal trade. First Series. Colliery Guardian Co., Ltd., London.

GLOVER, S. 1831; 1833. The history and gazetteer of the county of Derby, Vol. 1, Pt. 1; Vol. 2, Pt. 1. Derby.

GREEN, A. H., FOSTER, C. LE NEVE and DAKYNS, J. R. 1869. The Carboniferous Limestone, Yoredale rocks and Millstone Grit of North Derbyshire. 2nd edit. (1887) with additions by A. H. Green and A. Strahan. Mem. Geol. Surv.

PILKINGTON, J. 1789. A view of the present state of Derbyshire, Vol. 1, Derby.

WATSON, W. 1811. A delineation of the strata of Derbyshire. Sheffield.

WHITEHURST, J. 1778. An inquiry into the original state and formation of the Earth. London.

Chapter 2 Carboniferous Limestone Series

Introduction

The Carboniferous Limestone Series underlies all the district, but nowhere has its full thickness been proved and the basement rocks below are unknown. The beds crop out in the Matlock-Wirksworth area in the south-west, where they comprise a segment of the main outcrop of the Derbyshire Dome; they have been proved north of Matlock in the extensive workings of Millclose Mine; there are small inliers at Ashover and Crich, formed by plunge-culminations along a sinuous anticlinal axis approximately 3.5 miles east of the main outcrop; and they have been proved in a number of deep boreholes in the Coal Measures country to the east. There are some difficulties of correlation between these areas, which are therefore treated separately in the account which follows.

The sediments (Figure 5)." data-name="images/P990892.jpg">(Figure 2) are divided stratigraphically into local groups (Eden and others 1959, p. 33):

Interbedded with the limestones are lavasThe Derbyshire term 'toadstone' is normally applied to lavas, but it has also been used for igneous rocks generally, including tuffs and sills (Geikie 1897, pp. 8–22)., tuffs and clay bands (wayboards). The wayboards are, in many cases, believed to be lateral equivalents of lavas and tuffs; such lateral passage may be observed in several places in Derbyshire. In the vicinity of Matlock two thick flows, here termed the Matlock Upper and Lower lavas, may be traced over considerable areas. The Matlock Upper Lava is intercalated with the limestones of the Matlock Group, and at outcrop the Matlock Lower Lava lies between the limestones of the Matlock and Hoptonwood groups. In Millclose Mine a number of lavas are present and their correlation with those at outcrop presents some problems (pp. 27, 32). At Ashover a great tuff and lava pile was proved in boreholes (Ramsbottom and others 1962), but details of its relationship to the flows of Matlock and Millelose are uncertain. Comparable thick lavas and tuffs have, however, been found in boreholes in anticlinal areas in the Coal Measures country to the east.

There is little evidence concerning the two lower groups at Ashover and Crich, and here the Matlock and Cawdor groups are not as easily differentiated as in the main outcrop. There is insufficient information to attempt to apply the classification to the deep boreholes to the east.

The Carboniferous Limestone of Derbyshire may be regarded as belonging to three main facies (Edwards and Trotter 1954): massif—beds deposited over an ancient rigid block; basin—beds deposited in more rapidly subsiding areas around the block; and apron-reef—beds deposited with steep original dips in the marginal zone between block and basin.

The Griffe Grange Bed and Hoptonwood and Matlock groups comprise largely grey massive 'standard' limestones typical of the massif facies, but towards the south in the Wirksworth area the top of the sequence thins and passes in part into irregularly bedded and dark-coloured limestones associated with non-sequences and breccias. It is inferred that these latter beds form part of an apron-reef complex, the main part of which is hidden beneath Cawdor Group and Millstone Grit shales farther south and east. The facies changes may be compared with those which occur in the vicinity of the reef-belt near Castleton about 15 miles to the north-north-west (Eden and others 1964).

Although the apron-reef belt separating massif and basin facies is well defined all round the northern, western and southern margins of the Derbyshire block, from Castleton through Buxton to Brassington, it is unknown in the east and may not be present. The inferred apron-reef of the Wirksworth area, however, possibly strikes in a general east-north-easterly direction.

The Cawdor Group, with its variable lithology, including reef-knolls and dark goniatite-bearing limestones and shales, is of a facies comparable to that found in basin areas, and it appears that the distinction between massif and basin facies had almost broken down by Cawdor times, although the apron-reef near Wirksworth persisted.

Shirley (1959), working in a wider area, has suggested that unconformities exist between D₁ (Hoptonwood Group) and D₂ (Matlock Group), within D₂, and between D₂ and P₂ (Cawdor Group). In the present district there is little evidence for widespread breaks at any of these horizons, although abrupt changes of lithology occur at the tops of both the Hoptonwood and Matlock groups, and an erosional break below the Cawdor Group is well seen in the Middleton–Wirksworth area (pp. 22, 25). There is evidence also for an important erosional break within the Cawdor Group (pp. 23, 25).

Several igneous sills and volcanic vents have been recognized and there is extensive dolomitization, silicification and ore-mineralization.

Matlock-Wirksworth area

Griffe Grange Bed

The Griffe Grange Bed, assigned to the S₂ Zone, comprises the lowest rocks exposed in the district; it has long been recognized as lithologically distinct (Strahan in Green and others 1887, p. 151; Wedd in Gibson and Wedd 1913, p. 14; Shirley 1959, p. 413), but has not been given a stratigraphical name until recently (Eden and others 1959, p. 33). Its full thickness is unknown, but about 100 ft are exposed in crags in the area of Griffe Grange Valley (that part of the Via Gellia Valley west of Nimblejack).

The rock is mainly a pale porcellanous limestone, but oolitic and pisolitic bands occur, as for instance in the crag [SK 2570 5637] south of the main road, 525 yd W. of the road junction at the foot of Nimblejack. There are a few somewhat coarser bands and thin clay partings; the latter are in part red-coloured and may in certain instances mark non-sequences. The bed was penetrated to 119 ft in the Snake Mine [SK 2618 5549], 1000 yd almost due S. of the road junction above mentioned, and was called 'Holystone' by the old miners (Green and others 1887, p. 151)The section given by Green cannot relate specifically to the shaft shown on the six-inch map (Eden and Rhys 1961) as Snake Mine, since the top 120 ft of his section can be correlated with rocks seen in Hoptonwood Quarries, lying for the most part above the strati-graphical level of the top of the shaft.. The top of the bed is well seen in a crag [SK 2617 5644] at this road junction, where it passes up by alternation into the Hoptonwood limestones. Porcellanous limestones west of the crag are succeeded by the lowest bed of the crag, which comprises 12 ft of pale medium-grained partly oolitic limestone, containing fragments of a finer-grained limestone and some crinoid debris. This is overlain by 6 ft of porcellanous limestone which is taken as the top of the Griffe Grange Bed.

Macrofossils are rare in the Griffe Grange Bed, but the 12-ft limestone mentioned above contains a layer of scattered Daviesiella sp. about six feet from its base (p. 47). The presence of this fossil suggests a correlation with beds recorded by Jackson (1922, pp. 461–8) and Cope (1936, p. 129) in the Wye Valley.

Hoptonwood Group

The 250 ft or more of rocks assigned to the Hoptonwood Group consist. normally of pale grey, rather coarse- to medium-grained, massive limestone; they contain a D₁ Zone faunal assemblage, but macrofossils (p. 47) are in general not common in this area except in a few thin bands. The Group is not synonymous with the Via Gellia Limestones of Shirley (1959, p. 413), which include the beds here called the Griffe Grange Bed.

The Group crops out in the Via Gellia Valley, occupying most of the slopes west of its junction with Bonsall Dale; west of the Gulf Fault the outcrop broadens considerably, and it is only here that the base of the group is seen. In the extreme south-west the beds are extensively dolomitized. Limestones of the upper part of the Group are exposed as inliers in quarries on the west, or upthrow, side of the Gulf Fault between Middleton and Wirksworth, and the Group also forms the core of the anticline running from High Tor to Bonsall Moor, north of the Bonsall Fault, where, however, it is but poorly exposed.

Included in the Group are a number of variable clay wayboards, which locally form mappable features. In the vicinity of Wirksworth, just south of the district, the topmost beds pass into disturbed and brecciated strata associated with the inferred concealed apron-reef.

Matlock Lower Lava

The Matlock Lower Lava is a bed of olivine-basalt, usually amygdaloidal (p. 17). The central part is normally hard, but several feet at the top and bottom margins are everywhere altered to a soft green clay. The outcrop is marked by a 'slack' in which the harder central part commonly forms a minor scarp. Overlying limestone is liable to slip or camber over the soft clay top of the lava, the cambering locally being so pronounced that the lava thicknesses in quarry faces are substantially reduced. Red clay soil with fragments of vesicular lava is developed over the outcrop.

The thickness of the lava increases from about 150 ft in the north-west to a calculated 380 ft on Masson Hill, thence thinning and dying out southwards. Tuff is associated with the lava at several places, and in the west the Shothouse Spring Tuff is believed to occupy the same horizon.

The Matlock Lower Lava at outcrop lies at the marked lithological change which occurs between the limestones of the Hoptonwood and Matlock groups. Its precise relationship to the D₁/D₂ zonal boundary is, however, doubtful. In Millclose Mine (p. 27), where a succession of relatively thin lavas is found, it has been established (Figure 5) that the zonal boundary is at the junction of the Two-Foot Limestone and the 129 Limestone. The correlation of the lavas from outcrop to Millclose Mine is, however, not certain, and depending on the correlation adopted the Matlock Lower Lava may belong to either the Hoptonwood or the Matlock Group, or to both.

Matlock Group

In the Matlock area up to about 250 ft of limestone are included in the Matlock Group, but the total thickness is increased by the presence of the Matlock Upper Lava (p. 19). Although its field and thickness are more restricted than those of the Matlock Lower Lava, the Upper Lava behaves in a comparable manner, being at a maximum in the north and thinning southwards and westwards. It was found to be some 120 ft in boreholes in Cawdor Quarry, and it dies away in the vicinity of the Bonsall Fault in the south and near the district boundary in the west. Like the Lower Lava it has a soft clay base and top, and a harder central part.

In the north the Upper Lava divides the limestones of the Matlock Group into two roughly equal parts, both of which, where seen, comprise mainly grey massive beds. In Smart's Quarry Borehole in Cawdor Quarry, however, a considerable proportion of dark limestone was present in the lower part of the Group, not far above the Matlock Lower Lava, of which only the top was proved. These darker beds may be overlapped at outcrop, perhaps due to a thickening of the Lower Lava in that direction (p. 17). Shirley (1959) referred to the beds of the Matlock Group seen in Matlock Dale and to the south as the Upper Lathkill Limestones, and the dark lower beds which are not seen at surface in this area as the Lower Lathkill Limestones.

South of the Bonsall Fault, the Matlock Group thins and changes facies to predominantly dark limestone; non-sequences and breccias are evident as the beds approach the apron-reef inferred to lie below Wirksworth (Figure 3). Just south of the district the Group is believed to be cut out by an unconformity below the Cawdor Group. Because of these southward changes and comparable changes in the Cawdor Group, it is inferred that in later Carboniferous Limestone times the area immediately north of Wirksworth was undergoing less subsidence than the ground farther north, and it seems reasonable to regard it as a relatively positive area associated with the margin of the apron-reef belt bounding the southern side of the Derbyshire block. Over large areas there has been secondary dolomitization in the Matlock Group (p. 18), and both limestones and dolomites locally contain much bedded chert, notably in the north of the area near Wensley and in the south in the vicinity of Middleton Moor. Coral- and shell-beds are not uncommon; clay wayboards and a porcellanous limestone provide useful marker bands.

Cawdor Group

Although lithologically variable the Cawdor Group has well-defined upper and lower limits throughout the Matlock area (Eden and others 1959). Its base is everywhere marked by a sharp lithological change, and the top passes up into Millstone Grit shales with Cravenoceras leion. The name Cawdor Limestone was used for these beds by Shirley (1959). Wedd (in Gibson and Wedd 1913), following Sibly (1908), included most of them in the Cyathaxonia 'Subzone', although he indicated that the Cyathaxonia fauna was in part a facies assemblage.

In much of the ground, the Group comprises three distinct facies: a layer of reef-knolls or closely associated crinoidal beds at the base followed by mainly dark-coloured limestones, which are in turn overlain by dark shales with thin limestone beds (Figure 4). There is evidence of marked stratigraphical breaks at the base of the Group and at the base of the dark shales, but there is no indication that the overlying Millstone Grit Series does not follow conformably. An angular break at the bottom of the Group is demonstrable only in the extreme south of the area, where it could be due to proximity to an apron-reef belt, but Shirley (1959) has reasoned that the beds are separated by a widespread unconformity from the limestones below. The main evidence for this break is the absence of the top part of the D₂ succession seen in Lathkill Dale, some 7 miles west-north-west of Matlock; notably the Orionastraea placenta band is missing and is inferred by Shirley to have been cut out.

Vents and sills

The vents and sills of the Matlock area have been studied by Geikie (1897), Arnold-Bemrose (1894, 1907) and Wedd (in Gibson and Wedd 1913); previously it was not fully appreciated that the Derbyshire toadstones included rocks of diverse origins. Exposures of the sills and vents are in general poor and little can be added to these earlier accounts, although the Bonsall Sill has since been proved in a number of boreholes. Vents on Bonsall Moor and near Pounder Lane were not previously recognized as such. The four vents mapped in the district are inferred to be associated with the local bedded lavas and tuffs; the two sills resemble the lavas petrographically, and the Bonsall Sill is in part in contact with the Matlock Lower Lava. The petrography of the vents and sills is considered on pp. 263–264.

Details

Hoptonwood Group

North of the Bonsall Fault

Beds of the Hoptonwood Group crop out on the hillside north-east of Bonsall and on Bonsall Moor to the west, the two areas being separated by the Bonsall Sill. Near Bonsall, where the Griffe Grange Bed may occur on the lower part of the hillside, the total thickness is calculated to reach about 350 ft. Exposures are poor, and the interpretation of the sequence is complicated by volcanic vents, some mineralization and much silicification. Where unaltered the limestone for the most part resembles that of the Hoptonwood Quarries (see below), although rather finer-grained beds occur in some exposures. A few Lithostrotion have been noted and brachiopods are not uncommon in some exposures close below the Matlock Lower Lava, for example in a 12-ft section [SK 2547 5916] by the Beans and Bacon Mine, 620 yd N. 28° W. of Blake Mere, and again [SK 2827 5870], 300 yd S. 16° E. of Low Farm.

Hoptonwood Quarries

The most complete and accessible exposures are the extensive quarries south of Nimblejack, known collectively as Hoptonwood Quarries. The general succession is:

The base of the section is at the road junction below Nimblejack (p. 11). The two algal beds are indicated as shell-beds on the six-inch map (Eden and Rhys 1961); the upper may be traced throughout the quarries, but the lower is seen only at the extreme north. Except in the algal beds the limestone is coarse to medium in train; small crinoid debris is commonly abundant although less so towards the base; the limestone is uniformly pale in colour and massively bedded. The clay beds are grey, weathering to brown, soft and structureless; they are possibly of volcanic origin. The names in quotes are those given by Strahan (in Green and others 1887, p. 151) as the miners' names for these clays. The 'Black Beds' recorded near the base by Strahan have not been recognized at surface but the bottom part of the Group is not well exposed and darker limestones may be present in the slack above the crags of the Grille Grange Bed.

Via Gellia Valley

The lower of the algal beds in Hoptonwood Quarries may be followed eastwards along the Via Gellia Valley. It is well seen in an exposure [SK 2692 5663] just north of the road, 800 yd N. 74° E. of the junction below Nimblejack, where the succession is:

The algal bed occurs on the main ledge at this exposure. The petrography of a specimen from a nearby exposure is considered on p. 258. The same bed, overlain and underlain by clay bands, is to be seen in a quarry [SK 275 572] north of the road, 1000 yd S. 75° W. of the junction of Bonsall Dale with the Via Gellia Valley, where it is 10 ft thick and known as a 'blue bed'. The 'blue bed' differs lithologically from the pale massive limestones above and below chiefly in containing large patches of grey limestone, but also includes a 2-in clay band in the middle and thin bands of breccia. The clay bed above the algal limestone is up to 6 ft thick in this quarry, but it is absent a mile to the south-west in Hoptonwood Quarries, where it is represented only by a well-marked bedding plane.

Quarries between Middleton and Wirksworth

West of the main road at Middleton, and about a mile east of the Hoptonwood Quarries, is Hoptonwoodstone Quarry, exposing the top 103 ft of the Hoptonwood Group and showing no distinctive litho-logical or faunal horizons. There is some variation in the coarseness of the crinoid debris and fine shell debris is common in some bands; the petrography is detailed on p. 258. Rare shells occur towards the top and base. There are five well-marked bedding planes, possibly in part representing some of the clay bands of the Hoptonwood Quarries, but no clay was observed.

Farther south, in the quarries west of the Gulf Fault, the limestones seem to be similar to those in Hoptonwoodstone Quarry, but they are for the most part inaccessible. Bedding planes are level and persistent. Macrofossils are rare, but Shirley (1959, p.418) has recorded D.septosa and Product us cf. maximus.

In the disused Baileycroft Quarry [SK 287 542], 0.33 mile S. of the district boundary, the topmost beds of the Group undergo an abrupt facies change as they approach the apron-reef belt inferred to lie beneath the southern part of Wirksworth (Figure 3). On the western side of the quarry the top 10 ft of the Hoptonwood Group is in part grey, fine-grained limestone and includes a shaly band with many shells. On the eastern side, bordering the main road now running through the quarry, there is a confused section of limestone, in part fine-grained and shelly, with bands of breccia and an impersistent rubbly shell-bed. The equivalence of this limestone to the topmost beds of the Hoptonwood Group is inferred on geometrical grounds but cannot be proved because critical parts of the old quarry face are now concealed. The limestone has yielded the D₁ corals Carcinophyllum vaughani Salee, Dibunophyllum bourtonense Garwood and Goodyear and Palaeosmilia murchisoni Edwards and Haime and other fossils (loc. 3). In the access tunnel to Dale Quarry, about 100 yd nearer the inferred apron-reef than this quarry face and some 80 ft vertically lower, normal pale massive limestone of the Hoptonwood Group may be examined. Evidently hereabouts the facies change affects only the topmost beds of the Group, which are above the level of the tunnel.

Matlock Lower Lava

The main features of the outcrop of the Matlock Lower Lava have been described in detail by earlier workers (Arnold-Bemrose 1907, pp. 257–9; Wedd in Gibson and Wedd 1913, pp. 29–30), and the intricacies of its crop may be followed on the six-inch map (Eden and Rhys 1961). The thickness is variable but it is clearly at its maximum on Masson Hill. If, as seems likely, the observed dips of the limestone above and below persist through the lava crop in this area, it is calculated that the thickness is approximately 380 ft. A substantial thickness hereabouts was also indicated by Green and others (1887, p. 23), who stated that the bed was proved to be 240 ft at 'a mine called Porter, two miles south of Snitterton'. These thicknesses are greatly in excess of the estimated 150 ft in the vicinity of Tearsall Farm [SK 261 599], 2 miles W.N.W. of Masson Hill, and a maximum of 83 ft a mile to the south in Bonsall Wood Basalt Quarry [SK 2825 5745], 250 yd W. of the junction of the Via Gellia Valley and Bonsall Dale. The lava is mapped as dying out southwards along a sinuous line running west from Middletoncross. It is absent in the quarries west of the Gulf Fault south of Middleton-cross; it also thins away along the crop about a 0.25 mile S.S.E. and S.W. of Hoptonwood Quarries.

The lava floors three inliers in the Derwent Valley at Matlock Dale and southwards from Matlock Bath. At two small old roadside quarries 250 to 350 yd N.N.W. of High Tor may be seen small crags of greenish black basalt with scattered amygdales. The best exposures of the lava are, however, in the Via Gellia Valley. In a small quarry [SK 2880 5728] below Allsop's Quarry, by the roadside 500 yd S.E. of the junction with Bonsall Dale, is a section showing 20 ft of rather fine-grained dark greenish basalt with a few amygdales in the top 6 ft. Some 150 yd W. of the same junction lies Bonsall Wood Basalt Quarry where 8 ft of soft green and brown clay are seen between limestone above and 30 ft of basalt below.

In Hoptonwood Quarries [SK 263 558] only 6 ft of clay is to be seen, pinched between limestone, but it is reputed that the clay behind the face is at least 15 ft thick, and in Bradhouse Mine, 800 yd to the S.E., the 'toadstone' is said to be 78 ft (Gibson and Wedd 1913, p. 30). A mile east of Hoptonwood Quarries at Hoptonwoodstone Quarry [SK 277 557] the bed is largely concealed by cambering, but what is probably nearly the full thickness may be seen downfaulted south-west of the junction of the Gulf and Gang faults:

The brecciated limestone passes laterally into clay with amygdales; this and the presence of limestone lenses in the lower part of the section suggests that limestone was being formed penecontemporaneously with the lava at this edge of the flow.

Bedded tuff occurs close above the top of the Matlock Lower Lava in the vicinity of Tearsall Farm, and was formerly to be seen in place [SK 2633 5984], 200 yd S. 78° E. of the farm. In the debris now visible rare rounded pebbles of limestone are enclosed in a fissile tuff. Some 900 yd N.W. of the road junction below Nimblejack the lava is mapped as passing laterally into the Shothouse Spring Tuff. The latter is not now exposed within the district. Near Grangemill in the Buxton (111) district two well-known agglomerate-filled vents are associated with this tuff (Geikie 1897, pp. 13–5). Wedd (in Gibson and Wedd 1913, p. 29) recorded the presence of agglomerate in a tip heap [SK 2745 5817] south-east of Upper Town, Bonsall. He believed this to have come from a deep shaft, penetrating either to a contemporaneous vent, or more probably to a bedded tuff. The material is perhaps from the horizon of the Shothouse Spring Tuff.

Matlock Group

The lower limestones north of the Bonsall Fault

The lower limestones are well seen in cliffs in Matlock Dale. From here northwestwards along the strike to the district margin, and southwards to beyond Matlock Bath they maintain a thickness of some 100 to 120 ft. Throughout this area the beds at outcrop are mainly massive rather pale grey imestones with a number of clay-wayboards and fossiliferous bands, but the only bed traceable for any distance is one of the clay-wayboards in the Derwent Valley. There are two areas of intensive dolomitization—one extending north-westwards from near Tearsall Farm, and the other southwards of Masson Hill, through the Heights of Abraham and round the crop to the area south of Bonsall. In the second area the eastward limit of dolomitization is roughly a north–south line following the Derwent Valley.

North and north-west of Tearsall Farm these limestones appear to have been completely altered to dolomite, but exposures in old workings [SK 2629 6002], 220 yd N.E. of the farm, where lenses and bands of limestone are present, indicate that the dolomite is fingering out eastwards, and a 1-ft clay parting is seen to be overlain by 2 ft of limestone crowded with small colonial corals (loc. 16, p. 51). Extending north-eastwards from 200 yd E. of Tearsall Farm is a dry valley leading down to Northern Dale, in which are seen 105 ft of unaltered limestone. For the most part medium-grained and pale grey, it is markedly Shelly in its central parts, and bears corals near the base. For one mile eastwards from the dry valley the basal beds of the limestone are coral-bearing and form a line of crags (locs. 12 and 13). In Jughole Wood, 2000 yd S. 80° E. of Tearsall Farm, there is a 60-ft crag of massive limestone with a clay parting up to 6 in thick some 15 ft below the top. Chaetetes sp. and some bands of small silicified shells occur above the clay, but access to the lower part is difficult. Some signs of wedge-bedding may be observed.

On the northern side of Masson Hill, at the north end of Masson Quarry, only a few feet of limestone occur above a flat of fluorspar overlying the Matlock Lower Lava, and these are in turn overlain by dolomite. Dolomite has evidently fingered in eastwards again, because the debris on the hill slope as much as a quarter of a mile to the north-west includes dolomite as well as limestone blocks. Fossils in the limestone of Masson Quarry are listed on p. 49 (loc. 9). The limestone thins away very irregularly south-eastwards so that the crest of Masson Hill consists almost entirely of dolomite with some silicification. The dolomite persists along the western part of the outcrop as far south as the Bonsall Fault; dolomite is well seen in workings in the Great Rake and the Coalpit Rake, and also in massive crags in the Pavilion Gardens, some 350 yd W. of Holy Trinity Church, Matlock Bath.

Eastwards the dolomite gives way laterally to massive limestones, seen in crags on both sides of the River Derwent at Matlock Dale, but on the east side only at and south of Matlock Bath.

The section proved in Cawdor Quarry by Smart's Quarry Borehole is abnormal in its thickness (177 ft when corrected for dip) and in the presence of substantial beds of dark coloured limestone in the lower part (see Appendix 2, p. 379).

An easily accessible exposure [SK 296 591] showing a more normal section of these beds is that on the east bank of the river at the foot of the slope west and north-west of High Tor; it is continued upwards in the cutting at the south end of the High Tor Tunnel. In the following section beds above the 17-ft gap were measured in the cutting; all limestones are grey to pale grey:

In the railway tunnel through High Tor, De la Beche (1853, p. 560) recorded the presence of an impure coal resting on an underclay; this possibly lies in one of the unexposed parts of the above section.

In another almost complete section just over a mile farther south [SK 296 574], 550 yd S. 15° E. of Holy Trinity Church, Matlock Bath, the beds are similar but have thinned to about 100 ft. As at High Tor there is a ledge on the cliff face possibly formed by a clay band. A similar ledge, at about the same horizon, is present on the west side of the valley at Matlock Dale.

The Matlock Upper Lava

The outcrop of the Matlock Upper Lava was described in detail by Wedd (in Gibson and Wedd 1913, pp. 32–3) and is depicted on the six-inch maps (Eden and Rhys 1961; Smith and others 1962).

On the district margin [SK 253 603], 1000 yd N. 65° W. of Tearsall Farm, the flow appears to die away to the west. Eastwards it forms a widening slack and there are a few small exposures; toadstone debris is found around old shafts. When Oxclose Shaft [SK 2753 5994], 1550 yd almost due E. of Tearsall Farm, was reopened in 1949, the lava was found to be 95 ft thick. On the north flank of Masson Hill vesicular lava is to be seen in Salter Lane [SK 285 596]. In the area of Masson Hill the crop widens and small scarps are formed by the harder central parts of the flow. East of the hill the harder parts have slipped with the overlying limestone over the clay base of the flow and in the landslip scar [SK 2897 5898] up to 10 ft of massive basalt may be seen, vesicular in part; similar basalt may also be seen in old open workings [SK 2959 5934], 450 yd N.N.W. of High Tor, where it is cut by the High Tor Rake.

Five inclined boreholes in the vicinity of Cawdor Quarry have been sunk to the Seven Rakes; all penetrated the Matlock Upper Lava, proving a thickness of some 120 ft. The lava is also well known in the area of High Tor, Riber Mine and Matlock Bath Station Quarry where it averages some 60 ft. It is seen in the railway cutting [SK 2967 5875] south of High Tor.

Debris of the lava may be seen in crags [SK 296 574] below Cat Tor, 570 yd S. 18° E. of Holy Trinity Church, Matlock Bath. In two areas of old workings on a branch of the Bonsall Fault the lava is weathered to clay. The more northerly [SK 2839 5776], 650 yd S.48° E. of St. James's Church, Bonsall, shows grey and yellow limonitic clay in which fragments of fine-grained basalt occur; the more southerly [SK 2901 5739], an adit worked by Messrs. Banks and Barton, 1380 yd S. 53° E. of the same church, shows green toadstone clay both at surface and in workings 50 ft deep. Arnold-Bemrose (1907, p. 259) recorded exposures in the vicinity of this adit indicating the lava here to be unusual in that it contained phenocrysts of feldspar.

The upper limestones north of the Bonsall Fault

The upper beds of the Matlock Group are magnificently exposed in crags, quarries and cuttings along the sides of the Derwent. In general they comprise a series of grey to rather pale grey, medium- to fine-grained, massive limestones with shelly bands and several thin clay partings. Chert is associated with a few feet of porcellanous limestone near the middle; in both the northwest and the south-west of the area, however, chert extends its vertical range and is abundant through almost the full thickness of the beds. The band of porcellanous limestone is a useful marker and provides one of the few relatively persistent features of the succession, being traceable from Cawdor Quarry in the north to near the district boundary in the south. The petrography of a specimen from this band in Johannesburg No. 10 Borehole is detailed on p. 259. Most of the upper beds of the Matlock Group contain shells and crinoid debris, in some places abundantly.

In the north the lower half of these beds conforms to the general description given above. Pseudobrecciation in the massive limestones is a common feature in a number of sections (p. 259). South of High Tor a progressive change sets in. Limestones immediately below the porcellanous bed become thin-bedded, darker in colour and contain carbonaceous partings; non-sequences and wedge-bedding are to be observed. At Scarthin Rock [SK 297 570], lying between two branches of the Bonsall Fault, the Upper Lava is probably represented by a thin clay, and the beds close above are crinoidal and shelly.

Dolomitization affects these beds in much the same way as the beds below the Matlock Upper Lava. The margin of the area of dolomite shown on the western boundary of the sheet is notional. In Big Dungeon [SK 260 608] and Little Dungeon [SK 258 607], which are landslip scars 0.5 mile W.S.W. of Wensley, it may be observed that the dolomitization fingers laterally westwards into the limestone. A lens-shaped patch of dolomite has been mapped in the area centred about 0.75 mile E. of Tearsall Farm, where the Upper Lava provides a lower limit to the alteration. Dolomitization is also present farther east in the area of Shining Cliff [SK 293 593], 0.33 mile E. of Masson Lees Farm; in this case it was not found practicable to delimit the dolomite on the map. South of Shining Cliff the beds are commonly dolomitized to the west of the River Derwent, but not much affected to the east, and here again the boundary is notional.

In Big Dungeon 40 ft of limestone near the base of these beds are seen. The lower 6 ft and the top 15 ft contain many chert bands, and shells are common in the lower 25 ft. Eastwards along the hillside exposures are poor, but material in walls shows the presence of rolled-shell limestone and the persistence of chert almost as far east as Cawdor Quarry. In Cawdor Quarry and in Harveydale Quarry [SK 296 597], 0.25 mile farther south, chert is only present, somewhat below the middle, in a bed a few feet thick and is associated with fine-grained, almost porcellanous limestone. The basal beds are pseudobrecciated, and shells tend to be concentrated in the middle, in and above the fine-grained limestone. In an easily accessible section in the railway cutting [SK 297 587] south of High Tor the chert is present in beds 7 ft 8 in thick, the top 4 ft being porcellanous. The section here may be regarded as characteristic:

Some of the shells are partially silicified and there is some dolomitization.

Johannesburg No. 1 Borehole (p. 338) proved a 20-ft limestone with carbonaceous partings just below the middle of the group of beds; this limestone may be examined in crags below Cat Tor.

At Scarthin Rock the porcellanous limestone is 13 ft thick and free from chert, although farther west a little is present close below. In the adjacent road cutting lower limestones with signs of non-sequence or wedge-bedding rest upon shelly crinoidal limestone which, in turn, overlies the 8-in clay believed to represent the Matlock Upper Lava. It is to be noted that the total thickness of the beds here is some 110 ft, appreciably thicker than the 70 to 80 ft recorded farther north where the Upper Lava is present.

South of the Bonsall Fault

Close to the south side of the Bonsall Fault the whole of the Matlock Group is exposed in the eastern part of the Via Gellia Valley, the total thickness being some 150 to 200 ft; the Matlock Upper Lava is either absent or very poorly developed. The basal beds are well seen in Bonsall Wood Basalt Quarry [SK 2827 5747], just west of the southern entrance to Bonsall Dale (p. 258), and some 500 yd farther south-east in Allsop's Quarry [SK 288 572]. In each place the basal 8 ft of beds resemble those which in the overlying Cawdor Group are associated with reef-knolls. They consist of coarse-grained, rather pale-coloured limestone containing abundant shells; crinoid debris, including large ossicles, is common, and in Allsop's Quarry brecciated limestone fragments are present. In this vicinity the overlying beds of the Matlock Group comprise mainly grey medium-grained limestone with fewer shells and less prominent crinoidal debris than in the basal beds. The top 55 ft are well seen in Slinter Tor [SK 2885 5710], on the south side of the Via Gellia Valley opposite to Allsop's Quarry. These include some fine-grained limestones, one of which is inferred to represent the porcellanous limestone seen from Scarthin Rock northwards and also in the area south of Middleton. Chert is absent although some silicification of shells occurs. A band of colonial corals was noted 41 ft below the top (loc. 27).

South of the Bonsall Fault the Matlock Upper Lava dies out abruptly. It may, however, be represented by a thin clay seen near the top of the face in Allsop's Quarry, and Wedd (in Gibson and Wedd 1913, p. 32) recorded toadstone fragments weathering out at a similar horizon [SK 2830 5764], 225 yd N. 33° W. of the junction of Bonsall Dale and the Via Gellia Valley.

Westwards the limestones of the Matlock Group form the plateau surfaces flanking the Via Gellia Valley as well as the topmost crags of this deeply incised valley. The limestones are grey and maintain a generally massive, medium-grained lithology. A number of clay partings have been mapped, and brachiopods and corals occur sporadically. Shelly beds are to be seen in Cotterhole Quarry [SK 2650 5680] on the north side of the valley about 1 mile W.S.W. of the junction with Bonsall Dale, and again on Nimblejack [SK 2665 5645], where there appears to be room for little more than some 120 ft of strata in the Matlock Group. The beds are here only partly exposed but the top 14 ft include a considerable amount of irregular chert.

The cherty beds on Nimblejack are the most northerly expression of a chert-bearing facies of the top beds of the Matlock Group in the area of Middleton Moor, comparable with the similar facies seen in the upper part of the Group in the north. They are well seen in Redhill Quarry [SK 275 552], 0.25  mile W. of Middletoncross, although neither their top nor their base is exposed; partially silicified brachiopods and three coral bands have been found (loc. 23).

Beneath the cherty beds in the Middleton Moor area, and in part passing laterally into them, are limestones, some massive and others rubbly, varying in colour from grey to fairly dark grey. Shell beds are common. As in the Via Gellia Valley the bottom part includes limestone comparable to that associated with reef-knolls. This 'reefy' bed is 25 ft thick in Hoptonwood Quarries (loc. 10), where it includes breccia. A similar bed of about the same thickness occurs in Hoptonwoodstone Quarry [SK 277 557].

The limestones of the Matlock Group, together with overlying and underlying beds, have been worked in a series of large quarries disposed along the limestone escarpment on the west side of the Gulf Fault, and a southwards change of facies across the district border may here be studied in detail (Figure 3). The Matlock Lower Lava, seen to have a thickness of at least 35 ft at Hoptonwoodstone Quarry, dies out southwards around Middleton. The limestones o f the Matlock Group become progressively darker in colour, less cherty and more thinly bedded in the same direction. Around Dale [SK 284 541], Baileycroft [SK 287 542] and Stoneycroft [SK 285 544] quarries a prominent non-sequence is developed within the Group, lenticular bedding is in evidence and beds of breccia appear. As these southward changes occur the overlying Cawdor Beds progressively cut down into the limestones of the Matlock Group. On the district boundary at Monkey Hole [SK 281 549] the plane of unconformity lies at the level of the porcellanous limestone in the Matlock Group and fragments of this material are seen to be incorporated in the basal breccia of the Cawdor Beds. The unconformity cuts down to even lower levels southwards and in part of Baileycro ft Quarry it appears probable that the Matlock Group is entirely missing.

Cawdor Group

Main outcrop west of Cawdor Quarry

On the district margin west of Wensley, feature mapping suggests that limestones of the Cawdor Group are cut out, the overlying shales overstepping them to rest directly on Matlock Group dolomite. In and around Wensley the limestones appear from beneath this inferred sub-shale unconformity, forming lines of crags up to 40 ft high along the sides of Wensley Dale. The bulk of the limestone hereabouts is dark, cherty, and of medium-grain, and contains beds of crinoid debris and large Productid shells. There is a lens of pale reef-knoll limestone some 18 ft or more thick in a crag [SK 2678 6090], 630 yd S. of St. Mary's Church, Darleybridge. This knoll is unusual in that it appears to be within the dark cherty limestone rather than at its base.

In Northern Dale are exposed 35 ft or more of dark cherty limestone resting on pale crinoidal limestone of which about 30 ft are seen but which is possibly some 0[sic]ft thick. The dark limestone is similar to that of Wensley Dale; the pale limestone is of the type commonly associated with reef-knolls—bedding varies from poor to good, there are layers of small brachiopod shells, and in parts an abundance of large crinoid ossicles. In this area the pale limestone is dolomitized in patches, and contains ramifying old workings. Although isolated dark shale exposures seen in the area west of Cawdor Quarry are inferred to belong to this group, no fossil evidence of their age has been found.

Darleybridge

An inlier a short distance west of Darleybridge shows a 100-yd wide knoll of crinoid- and shell-rich limestone in dark cherty limestone with large Productids. At a locality [SK 2665 6175], 300 yd N. 24° W. of St. Mary's Church, the knoll limestone, here lying some 10 ft above the base of the dark limestones, is seen to swell eastwards from 0 to over 35 ft in a distance of 60 yd. On the sides of the knoll the overlying limestone is represented in part by bedded cherty limestone rich in shells and crinoids, dipping off the knoll at up to 50°. At a position [SK 2671 6177], 300 yd N. 12° W. of St. Mary's Church, dark shale rests on this bedded limestone with an angular discontinuity which suggests that it lapped up the sides of a limestone mound. Wedd (in Gibson and Wedd 1913, p. 35) drew attention to this local unconformity.

Cawdor Quarry

The succession at the west end of Cawdor Quarry is:

All the dark limestones are fine- or fairly fine-grained and, like the shales, are fossiliferous. Hudson (1943) drew attention to the rich Zaphrentid fauna which occurs in a bed believed to be the 5 to 7-ft limestone listed above, and Robinson (1959) described an ostracod fauna from the shales. Shirley (1959, p. 417) recorded the P_2a goniatite Goniatites (Mesoglyphioceras) granosus Portlock 15 ft above the base of the Group, but, because of thickness variations, it is not clear whether this came from above or below the unconformity at the base of the predominantly shaly beds. In the present collections Sudeticeras sp. has been recorded 3.5 ft below the unconformity, Sudeticeras stolbergi Patteisky in shale 2 to 4 ft above the 2.5-ft limestone bed, and Lyrogoniatites aff. georgiensis Miller and Furnish of P_2c age at 14 to 15 ft above the same limestone. The unconformity therefore lies within P₂ at this point.

The thin, fine-grained limestone seen at the west end of Cawdor Quarry does not persist far along the crop, for at the other end of the same quarry, 0.5 mile to the E., the limestone of the Cawdor Group comprises over 47 ft of grey and dark grey, mainly medium-grained limestone with abundant dark chert. There are thin shaly limestone partings, and shells include abundant large Productids near the top of the exposed section.

Matlock to High Tor

At Harveydale Quarry [SK 296 597], west of the road at Matlock Bridge, the general section is:

A fauna collected from the 'marble bed' at Shining Cliff is of 'reefy' aspect, containing a remarkable variety of Productids, but, notably, no Gigantoproductus (loc. 37). East of the Derwent this bed swells into a series of impressive knolls up to nearly 100 ft high in the riverside crags. The tops of three such knolls are readily accessible in the south bank of the River Derwent north of St. Giles's Church, Matlock. They comprise pale, mainly fine-grained, poorly bedded limestone with abundant small shells and some large crinoid ossicles. Draped over their crests lies predominantly dark, medium-grained, cherty limestone with large Productids. The well-known knoll in the face of High Tor is just under 100 ft high and its main mass about 140 ft wide (Plate 3A). It is inaccessible but shows poor internal bedding dipping outwards at apparent angles of up to 30° on the north side and up to 45° on the south. Black (1954, pp. 271–5) has discussed the bedding in this knoll, concluding that during its growth it protruded from the sea floor as an asymmetrical and increasingly steep-sided mound. It was eventually buried by thinly bedded limestones lapping up its flanks and over its crest.

Riber Mine to the Bonsall Fault

Between the Great Rake and the Bonsall Fault, the Cawdor Group is well displayed in an almost continuous line of sections along the River Derwent. It is also seen in the railway cuttings north [SK 2970 5865] and south [SK 2987 5806] of Matlock Bath Station, in the Matlock Bath Station Quarry adjoining the cutting south of the station, and in the adit [SK 2999 5885] of the Riber Mine, 700 yd N. 15° E. of the station. It was penetrated by boreholes put down in the course of mineral prospecting half a mile east of the Derwent on the Great Rake (Johannesburg Nos. 6, 9 and 10) and in Station Quarry (Johannesburg Nos. 1, 2 and 3). These sections may be summarized:

Basal knolls and crinoid beds are absent.

The mass of the limestone in the vicinity of the two cuttings, like that in Harveydale Quarry, is cherty, medium-grained, and contains grey bands and abundant large Productids; whereas the limestone of Riber Mine and Boreholes 6, 9 and 10 is predominantly fine-grained, dark-coloured, and relatively thin, resembling the facies at the west end of Cawdor Quarry. No evidence of unconformity at the base of the shale has been recorded in Riber Mine, but in the cutting south of Matlock Bath Station shale rests unconformably upon wedge-bedded limestone of the Cawdor Group, 9 ft of which is cut out in a distance of about 30 yd.

Riber Mine and Johannesburg boreholes 6, 9 and 10 near the Great Rake are the only sections in the Matlock vicinity in which the full thickness of the shale in the Cawdor Group has been proved. Both 9 and 10 have yielded P₂ faunas, including Lyrogoniatites and Sudeticeras. The unconformable shale in the cutting south of Matlock Bath Station is difficult of access and, although it is inferred to be of P₂ age, no diagnostic fossils have been found. The shale 800 yd farther south, in the cutting near Cromford Station [SK 3025 5745], contains a fauna assigned to high P₂ (loc. 43).

Cawdor Limestone of a facies generally similar to that seen in the Matlock Bath cuttings persists down the Derwent to near Cromford and across the Bonsall Fault into the eastern ends of the Via Gellia Valley and Bonsall Dale.

Bonsall to Cromford

In both Via Gellia Valley and Bonsall Dale pale very crinoidal limestone, similar to the 'marble bed' of Harveydale Quarry and containing small brachiopods, wedges in between the Matlock Group and the overlying dark limestones; it is up to about 50 ft thick. This pale limestone has been shown on the maps as knoll limestone, to which it is related, but for the most part it occurs not as knolls but as a continuous sheet. It is to be seen wedging-in on Slinter Tor [SK 2886 5712] and is well exposed east of the main road in the southern part of Bonsall, where it has in part a knoll-like form; in each vicinity it forms lines of crags overlain by dark limestone.

At Dene Quarry [SK 289 563], 900 yd S. W. of Cromford, the pale crinoidal limestone is well displayed. It is here 53 ft thick with many well-preserved shells and large crinoid stems. Polished blocks from this quarry have been widely used as an ornamental marble (p. 241). A large brachiopod fauna has been collected (loc. 44); it is of 'reefy' aspect but differs considerably in composition from that found in the knoll at Shaw's Quarries (see ((Table 1), p. 56). In particular it contains Gigantoproductus giganteus (J. Sowerby), which is not typical of reef limestone, and an abundance of Brachythyris planicostata McCoy. The pale crinoidal limestone is overlain by 35 ft of dark, bedded limestone which is also commonly crinoidal both here and in the area to the south; it yields a fauna which has elements in common with the pale beds below but which is much less varied.

Vicinity of Shaw's Quarries

In the area 0.33 mile E.S.E. of Middletoncross the Cawdor Group is well exposed in a series of small quarry faces and cuttings comprising Coal Hills Quarry [SK 285 553], Steeplehouse Station Quarry [SK 287 554] and Shaw's Quarries farther south. The generalized succession in Shaw's Quarries is:

The knoll limestone has been worked in a small quarry [SK 2875 5528], 1150 yd S. 60° E. of Holy Trinity Church, Middleton, from which a reef fauna including many lamellibranchs has been collected (loc. 45). In an adjoining quarry [SK 288 551], 1250 yd S. 55° E. of Holy Trinity Church, an abrupt southward change occurs in these beds. The 75-ft knoll limestone passes into a 6-ft breccia which cuts down into the bedded reef limestone below. There appears to be a further non-sequence below the latter, and another above the knoll limestone. While it is possible that these changes are characters which simply denote the margin of the knoll, it is considered likely that they indicate an approach to the apron-reef belt, here buried beneath shale, as at Wirksworth.

Vicinity of Gulf Fault

South-west of the Gulf Fault the Cawdor Beds are represented by cherty limestones, mainly thin-bedded. They include dark, fine-grained limestone and pale grey, coarse crinoidal beds; small brachiopods are not uncommon, particularly in the crinoidal beds, which resemble those associated with the knolls farther north-east. The beds are exposed, although not readily accessible, in Intake Quarry [SK 271 550], Dale Quarry [SK 285 540], and in the series of quarries on the west side of the Gulf Fault. The basal unconformity is well seen in Intake Quarry, where 28 ft of Matlock Group beds are cut out south-eastwards in a distance of 200 yd. The basal breccia above the unconformity is seen to include limestone fragments up to a foot long in a crag [SK 2791 5503], 760 yd S. 5° E. of Holy Trinity Church, Middleton. A fauna collected from the topmost beds of Middlepeak Quarry resembles that found in the pale crinoidal beds of Dene Quarry, except that it is more restricted (loc. 47); another fauna from Intake Quarry (loc. 48) consists almost entirely of Gigantoproductids, present in great variety.

In the south-east corner of Baileycroft Quarry [SK 2868 5416], south of the district boundary, the unconformity is inferred to cut out the Matlock Group (loc. 46), for about 8 ft of breccia-bearing limestone and shale believed to belong to the Cawdor Group lie directly on limestones of the Hoptonwood Group. The beds believed to belong to the Cawdor Group contain a fauna comparable to that of this Group in Cawdor Quarry, including Rotiphyllum costatum (McCoy) and species of 'Zaphrentis' and Cyathaxonia. The limestone and shale bed is overlain by 9 ft of dark shale which contain abundant Caneyella membranacea (McCoy), characteristic of the highest beds of P2, and which therefore certainly belong to the Cawdor Group. In the south-east corner of Dale Quarry dark shale of the same or later age rests unconformably upon Matlock Group limestones, having apparently cut out 25 ft of Cawdor Group limestone within the width of the quarry.

In the Wirksworth area there would therefore seem to be two unconformities associated with the Cawdor Group—one beneath the limestones and one beneath the succeeding shales. The latter unconformity is possibly at the same horizon as that seen within the Group in Cawdor Quarry. A diagrammatic reconstruction of the Wirksworth–Middleton area prior to the erosion preceding shale deposition (Figure 3) suggests the presence of the margin of a buried apron-reef near Wirksworth. It has been mentioned above that the postulated apron-reef may continue northwards beneath shale in the vicinity of Shaw's Quarries. The higher beds of the Hoptonwood Group (p. 17), and the Matlock (p. 22) and. Cawdor (p. 25) groups are all affected by proximity to the supposed apron-reef, but lower beds of the Hoptonwood Group are not so affected where it is possible to study them.

Vents and sills

Bonsall Sill

The sill is delineated on the six-inch map (Eden and Rhys 1961). As recognized by earlier authors it is bounded to the north by the Matlock Lower Lava, with which its relationship is unknown; to the south by the Bonsall Fault, seen in surface workings [SK 2750 5830], 550 yd N. 70° W. of St. James's Church, Bonsall; and to the east by limestones of the Hoptonwood Group. There seems little doubt that it transgresses these limestones through some 350 ft vertically in about half a mile northwards from Bonsall. To the west it passes under limestones of the Hoptonwood Group, and here again considerable transgression is inferred.

Two small quarries [SK 2754 5927], [SK 2752 5896] have been worked north-east of Bonsall and the sill has been proved in the vicinity of Becks Mere in four boreholes, none of which, however, penetrated to the base of the sill, although the deepest proved it to a depth of 182 ft. A notable feature was the presence within the generally compact crystalline rock of amygdaloidal bands (p. 264). For example, Becks Mere No. 1 Borehole [SK 2754 5927], sunk in the quarry 1330 yd N. 20° W. of St. James's Church, Bonsall, in which a 9-ft face of fresh, hard, greenish black olivine-dolerite is exposed, proved 165 ft of dolerite, amygdaloidal between 110 ft and 131 ft.

In most of the other small exposures the sill is badly weathered, although material from it has been widely used for walling over the area of its outcrop. Following Wedd (in Gibson and Wedd 1913, p. 25), a very fine-grained hard basalt [SK 2812 5884] seen 100 yd S.S.W. of Low Farm has been mapped as a marginal phase of the Bonsall Sill, although its true relationships are obscure; it may form part of the Pounder Lane Vent complex. The petrography of the sill is considered on pp. 263–264.

Ible Sill

The Ible Sill, on the margin of the district nearly two miles west-south-west of Bonsall, is mapped as separated from the Shothouse Spring Tuff (p. 18) by a fault, but exposures near the margins are poor and the position of this fault uncertain. The sill is emplaced in limestones of the Hoptonwood Group. It is well exposed in an old quarry [SK 253 568], 1100 yd N. 67° W. of the road junction below Nimblejack, some 200 yd west of the district boundary, where may be seen about 100 ft of rather coarse-grained dark dolerite (p. 263) with numerous irregular, weathered joints and thin veins. The dolerite shows a tendency to spheroidal weathering. No amygdaloidal material is seen, but the quarry face is difficult of access. A tuff [SK 2513 5702] seen by the roadside 180 yd E. of Ible chapel has been mapped as incorporated in the sill. Arnold-Bemrose (1907, p. 275) referred to marmorization of the limestone south of the sill, but most of the southern margin is now covered by tipped material.

Bonsall Moor Vent

The Bonsall Moor Vent lies in the core of the main east–west anticline north of the Bonsall Fault, and has been mapped on the evidence of weathered tuffaceous material in the soil. Its eastern margin is exposed in a large subsidence hollow [SK 2575 5936], 700 yd S. 36° W. of Tearsall Farm. Weathered clay, red near the limestone contact, but normally yellow and green, contains small rounded to angular fragments of limestone and chert and large angular blocks of red-stained silicified limestone. The clay abuts against mottled grey limestone to the east. The junction is extremely irregular, tongues of clay extending into the limestone, which is slightly marmorized (p. 30). It is possible that the silicified limestone blocks were incorporated into the clay during weathering.

Fresh tuffaceous agglomerate from the Bonsall Moor Vent may be found in an old mine tip [SK 2563 5968] by the roadside, 550 yd S. 69° W. of Tearsall Farm. It contains rounded fragments of limestone and amygdaloidal basalt in a pale grey ash matrix and resembles the agglomerate in the well-known Grangemill Vents (p. 264) (Geikie 1897, pp. 13–5; Arnold-Bemrose 1907, pp. 262–3), which is exposed in a quarry [SK 244 578] some 1100 yd W. of the district boundary.

Moor Lane Vent

Poor exposures [SK 2674 5856] of weathered agglomerate in Moor Lane, 1430 yd N19° W. of St. James's Church, Bonsall, led Arnold-Bemrose (1907, p. 264) and Wedd to map a small elongated vent along the line of the Bonsall Fault. The evidence is poor, but in this vicinity much igneous material of a variety of types is to be seen in tips from old lead workings.

Pounder Lane Vent

Field walls west of Pounder Lane, about a quarter of a mile north of Bonsall, contain many blocks of coarse agglomerate. Small angular ash fragments are set in a matrix of limestone, commonly tuffaceous. The general poverty of bedding in this material and its concentration in an oval area which is in part bounded by a feature, point to the possibility that the material lies in a vent, although Arnold-Bemrose (1907, p. 265), who saw the rock in situ and Wedd (in Gibson and Wedd 1913, p. 29) regarded it as an interbedded tuff.

Ember Lane Vent

First recorded by Geikie (1897, pp. 17–8) and also discussed by Arnold-Bemrose (1907, pp. 263–4) and Wedd (in Gibson and Wedd 1913, pp. 27–8), the agglomerate of Ember Lane contains a high proportion of limestone in both matrix and included fragments. Several exposures are to be found immediately east of Bonsall, notably 220 yd N.E. of St. James's Church [SK 2816 5827], but the material is better displayed in the local walls. It comprises a wide variety of types, ranging from tuff with small rounded limestone fragments to finer-grained limestone up to 3 in diameter. A wood fragment was recorded by Arnold-Bemrose. The agglomerate appears to transgress the bedding of the Hoptonwood Group in which it lies. R.A.E.

Millclose Mine

Workings of Millclose Mine extend some 2.5 miles northwards from Wensley Dale, penetrating the lower beds of the Millstone Grit, the Cawdor Group, the Matlock Group and over 200 ft of the Hoptonwood Group (Figure 5). The deeper, more recent workings are in the north; little is known about the old shallow workings near outcrop in the south. The mine is now flooded and the present account is based mainly on studies by Trail (1939, 1940) and Shirley (1950), together with a re-examination of a large fossil-collection presented to the Geological Survey by the latter.

There is a clear distinction between the D₁ (Hoptonwood Group) and D₂ (Matlock Group) beds in the mine, but there is doubt as to the correlation of the lavas between the mine and outcrop. Traill and Shirley believed that the Matlock Lower Lava was not present in the mine and that its horizon lay at or near the Passby Wayboard, but it is more probably the equivalent of some or all of the lavas proved in the mine below this wayboard.

Hoptonwood Group

Only the upper part of the Group has been seen, chiefly in the north of the mine. The succession of limestones and toadstones can be summarized (after Traill 1939, 1940, except for lowest division):

The limestones are described as pure, very coarse-grained, crinoidal and light coloured. Traill noted two thin wayboards in the upper part of the 129 Limestone. The fossils recorded by Shirley (1950) indicate that the limestones belong to the D₁ Zone (loc. 17).

The toadstones are lava flows, with the possible exception of a 4 to 5-ft bed at the top of the Lower 129 Toadstone in the Pithough area which Traill described as a dark palagonite tuff full of small Rhynchonellids and fragments of foraminifera, and containing rounded limestone nodules. Traill's 'tuff' at the base of the Upper 129 Toadstone, which he described as being soft and green, is almost certainly toadstone clay formed by the alteration of the margin of the lava flow.

Matlock Group

The limestones that succeed the Upper 129 Toadstone are markedly different lithologically from those below, but there are difficulties of correlation between the northern and southern ends of the mine (Figure 5). The following composite section is based on that given by Traill:

The two uppermost divisions have been explored in the southern part of the mine, and the lower ones in the northern part. In addition to the divisions listed above, another toadstone, 90 ft thick, was proved 33 ft above the 103 Toadstone in the Pilhough Rise at the north-western extremity of the workings. From its position Traill correlated it with the 'Intermediate Tuff' but it may be the equivalent of the Upper Toadstone of the southern part of the mine. The collection of fossils made by Shirley (1950) is listed on p. 49–51 (loc. 17).

Cawdor Group

The succession in Millclose Mine comprises a wayboard, 0 to 3 ft thick, overlain by thinly bedded dark cherty limestones, with knolls at or near the base, in turn overlain by an unknown thickness of dark shale. Excluding the large knolls, the limestones reach 32 ft in thickness. The wayboard, according to Parsons (1897), consists of grey clay which becomes darker near the 1-in coal locally present at its top.

The limestones are known as 'black beds', and they may be missing in places. They are exposed in the older parts of the workings which were mostly inaccessible when Shirley (1950) visited the mine. The exposures he examined were not very fossiliferous, and the only fossils he mentioned are Cyathaxonid corals found in a fallen block of black limestone at Ventilation Shaft [SK 2554 6333].

A large knoll about 0.25 mile N. of Lees Shaft [SK 2593 6264] projects up into the overlying shales; it has an irregular upper surface and a considerable fauna (loc. 49a). Another knoll, or possibly an extension of the same one, penetrates the shale to the surface east of Lees Shaft, where 4.5 ft of knoll limestone are seen in the river bank [SK 2620 6270]; the following fossils have been collected: Eomarginifera?, Gigantoproductus sp., Krotovia cf. aculeata (J. Sowerby), Punctospirifer ?, Schizophoria sp.

Little is known about the shales of the Cawdor Group in Millclose Mine; they have been seen only in the shafts and at one place where an off-shoot of ore extended up from the limestone for a short distance into them. Parsons (1897) stated that they were very bituminous and emitted large quantities of fire-damp into the workings.

Details

Hoptonwood Group

The full thickness of the 144 Pump Station Toadstone has not been recorded. When Trail wrote his account it had been penetrated to a depth of 49 ft but not bottomed. He described it as a hard fine-grained basalt, vesicular at the top, which thins south-westwards. The nose of the flow was seen near No. 2 Winze [SK 2549 6461] where it contained flattened pillows up to 3 ft in length.

The Lower 129 Toadstone is 14 to 26 ft thick over most of the proved area at the north end of the mine but only 10 ft in the Pilhough area. It is, according to Traill, a hard dark grey-green to nearly black dolerite becoming amygdaloidal in the top 4 ft or so. Pillows have been seen in it. A toadstone has been proved near the same horizon farther south near No. 1 Winze [SK 2545 6359] but there are indications that this thins to the north.

The Upper 129 Toadstone consists of hard light-grey to black dolerite with few vesicles, and a thin layer of soft green 'tuff' at the base. A specimen has been examined by Dr. I. Phemister who reported that it is a pale grey, amorphous-looking rock composed of brown fibrous material forming a matrix to rolled fragments of the same composition; sharply angular quartz grains are scattered throughout the rock, and there is no sign of any tuffaceous material nor of any fresh pyrogenetic material. The hard toadstone dies away north-westwards leaving only a bed of tuff' which is probably the attenuated representative of the lava altered to toad-stone clay.

An unusual feature of the limestone–lava relationship in the mine is the marmorization of limestone under lava at two horizons. Traill stated that the top 2 to 3 ft of the Ten-Foot Limestone and the 129 Limestone are marmorized at several localities. Two specimens of the contact surface of the 129 Limestone with the Upper 129 Lava have been examined by Dr. Phemister; one shows no signs of marmorization, but the other is a compact white marble consisting of clear shapeless equidimensional grains of calcite forming a mosaic, with a few small prisms of an unidentified biaxial negative mineral. Limestone below the Matlock Upper Lava is also marmorized in Millclose Mine (p. 31). Marmorization of limestone by toadstone is rare, and only four instances are known in Derbyshire outside this mine, viz: the Ible Sill (Arnold-Bemrose 1907), the Peak Forest Sill (Geikie 1897; Barnes 1902a and b), the Tideswell Dale Sill (Arnold-Bemrose 1899a) and the Bonsall Moor Vent (p. 26). In all these the igneous rocks concerned are considered to be intrusive.

Matlock Group

The Two-Foot Limestone is nodular or conglomeratic in the bottom 6 in. Above this bed, or above the 144 Pilhough Toadstone where it is present, are 30 to 40 ft of dark brown to black thinly bedded limestones, cherty in the upper part. There follow over 20 ft of coarse-grained, massive, light grey limestone with crinoids in the upper part, and then a further 20 ft or more of dark, thinly bedded shelly limestones with coral bands. The rest of the limestone below the 103 Toadstone is massive, changes in colour from brown to light grey upwards, and has sporadic coral bands.

This section of the limestone between the Upper 129 Toadstone and the 103 Toadstone contains, according to Traill, eight wayboards in addition to the wayboard of the 144 Pilhough Toadstone where the lava is absent. One of these, 78 to 98 ft below the 103 Toadstone, is the so-called Passby Wayboard which Traill suggested is the lateral equivalent of the Matlock Lower Lava. Shirley has pointed out that it is a shaly wayboard with a thin coal in places, and is therefore unlikely to be the representative of a lava.

The 84 Limestone is a pure, coarse-grained, light grey limestone with a few shells at the bottom, and contains two wayboards. The 'Intermediate Tuff' was described by Traill as a pale green, very fine-grained, homogeneous bed, 12 to 18 in thick; it is probably a clay wayboard rather than a tuff. It is important in that it is thick enough, and sufficiently impervious, to form a cap rock for ore-bodies. The 'Intermediate Beds' are brown shelly limestones with two wayboards.

The limestones above the Upper Toadstone are, at the base, shelly and thinly bedded with numerous dark bands, and pass upwards into massive, light grey, coarse-grained limestone. At about 20 to 25 ft above the lava there is a bed of cherty limestone crowded with Productids. There are few corals in the limestones except in two bands of largely similar fossil-content described by Shirley from about 80 to 110 ft above the lava (loc. 25). At one locality, which he calculated to be 108 ft above the lava, Shirley found Orionastraea placenta (McCoy) associated with other corals.

The 144 Pilhough Toadstone, seen only in the extreme north of the mine, is a hard, dark green, coarsely crystalline, very vesicular dolerite. Shirley correlated it with the Upper 129 Toadstone found farther south, but Train evidence shows it to be a higher lava flow, for the Two-Foot Limestone, nodular at the bottom and shelly above, lies above the Upper 129 Toadstone and below the 144 Pilhough Toadstone. Moreover, in an intermediate area where both lavas are absent, there are two way-boards which Traill stated to be the horizons of the two flows, and they are separated by the same Two-Foot Limestone. The upper of these wayboards has been followed southwards into the field of the Upper 129 Toadstone, maintaining its position two feet above that lava.

The 103 Toadstone is very amygdaloidal in the bottom 1 to 4 ft, and Traill described this part as consisting of 'a mass of nut-like amygdaloids of various sizes up to 0.5 in, with a relatively small amount of matrix. The latter has been altered to a pale green or even white colour, while the vesicles are lined with a bright green chloritic mineral and filled with calcite and iron pyrites.' Little is known of the rest of the flow but it would appear to consist of compact dark green crystalline basalt. In only two places has the thickness been determined. It thins south-westwards and its place is taken by a clayey wayboard 2 or 3 in thick.

The Upper Toadstone consists of hard, dark grey-green to black, coarsely crystalline and highly vesicular basalt, except for the lowest 13 to 14 ft which are soft, light green and much decomposed. Where the 'main vein' cuts through the lava, the top is similarly bleached and softened. The lava has marmorized the underlying limestone to a depth of 2 ft in places. The Upper Toadstone, which is assumed to be identical with the Matlock Upper Lava, is present everywhere in the southern part of the mine, and is consistently 60 to 70 ft thick south of Munition Winze (SK 2553 6306]. It thins rapidly northwards from Munition Winze, being 33 ft thick in Taylor's Winze, less than 250 yd to the north, and absent in Blackpool Winze [SK 2542 6348] a further 250 yd away. In the latter wine it is represented by a wayboard less than 1 ft thick. E.G.S.

Correlation with outcrop

The position of the Matlock Lower Lava in Millelose Mine is doubtful. Three possibilities have been considered:

1. Shirley (1950, p. 356) and Traill (1940, p. 203) believed the Lower Lava to die out northwards and its position to lie near or at the horizon of the Passby Wayboard in the mine. If this is so the lava horizon is entirely within the Matlock Group and the lava is of D₂ age. Some of the evidence for this correlation lies outside the present area, in the vicinity of Gratton Dale, 5.5 miles west of Matlock. Here Shirley recorded dark D₂ limestones (Lower Lathkill Limestones) which he believed to be below the horizon of the Matlock Lower Lava, and at the same level as the comparable limestones below the Passby Wayboard. He suggested that coral-bearing beds above the Passby Wayboard were to be correlated with similar beds above the Lower Lava at outcrop (p. 18) and implied that the dark limestones of the lower part of D₂ were cut out at outcrop by an unconformity below the Lower Lava.

2. On grounds of thickness all four lavas in Millelose Mine from the 144 Pilhough Toadstone downwards might be expected to pass laterally into the Matlock Lower Lava. In this case the D_1/D₂ zonal boundary would lie at or near the top of the latter. The dark limestones in the lower part of D₂ in Millelose Mine are not seen at outcrop, but their absence could be explained by facies change or by their being overlapped as the Lower Lava thickens southwards.Such an overlapping of dark limestone on the margin of a thickening lava flow has a parallel in the Wye Valley, where similar limestones are overlapped above the Upper Lava of Miller's Dale as it thickens in Litton Railway Cutting (Cope 1937, fig. 2). It should be noted, however, that Smart's Quarry Borehole shows predominantly dark D₂ limestones resting on the Matlock Lower Lava (Appendix 2, p. 379).

3. Because there is no evidence at outcrop that the Matlock Lower Lava, despite its thickness, is a composite flow, it is possible that it is the equivalent of the Upper 129 Toadstone in the mine, lying at the D₁/D₂ zonal boundary. The underlying lavas may then be represented by the clay wayboards found at outcrop (p. 16).

The information at present available is inadequate to settle this question, but Smith and others (1962) have considered the second correlation most likely to be correct. E.G.S., R.A.E.

Ashover

At Ashover the River Amber flows along the axis of a periclinal dome in which the lowest exposed bed is the Ashover Tuff. The tuff is succeeded by limestones of the Matlock and Cawdor groups, and is underlain by a succession of basalts and limestones of uncertain age (Ramsbottom and others 1962).

The tuff is well bedded and of variable grain size and colour. It contains fragments of chert, limestone and igneous material set in a matrix of lapilli, volcanic dust and calcite (Arnold-Bemrose 1894, pp. 639–40; 1907, p. 266).

The overlying limestones are seen in numerous small exposures on either side of the Amber Valley, and in the major quarries within the inlier. They are of two main types: generally massive grey or light brownish grey limestones containing few fossils and rare chert; and thin-bedded, dark grey, cherty limestones containing abundant fossils among which Gigantoproductids are particularly prominent. Comparison with the Matlock area of the main outcrop suggests that these limestones belong to the Matlock and Cawdor groups respectively. Fossils are listed on pp. 49–54 (locs. 31–2, 50–3).

The full thickness of limestone overlying the tuff has been penetrated only in the Hogsland Shaft [SK 3558 6227], on the south-east side of the anticline, where it is about 185 ft (corrected for dip). A thickness of about 190 ft is calculated between Milltown Quarry and the southern boundary of the outcrop. In the north the calculated thickness in the vicinity of Butts Quarry is about 165 ft.

Details

The tuff is best seen 450 yd S. 18° E. of All Saints' Church in the cutting [SK 3508 6272] leading to Hockley Quarry limekiln, where the top 10 ft or so are visible beneath the limestone cover. Here the colour varies from purple to green, and lapilli of limestone and igneous material up to an inch or two in diameter occur in ill-defined bands. Calcite veining is prominent. Some 20 ft of tuff are visible in another exposure [SK 3525 6255], 275 yd to the south-east; fragments of dolerite up to 6 in. in diameter have been noted here (Arnold-Bemrose 1894, p. 640). On the west side of the river the tuff is visible at various points along the private road running south-east down the valley and in the sides [SK 3478 6266] of Salter Lane which runs between Ashover village and Overton Hall. In the north-west of the inlier 2 ft of tuff were formerly exposed in Butts Quarry (Sweeting 1946, p. 128), though at the present time only a small tip of weathered toadstone clay is visible. Near the southern boundary of the inlier the tuff is exposed in Milltown Quarry where, in the north-west corner, massive grey limestone rests on 3 ft 10 in of inter-banded green toadstone clay and grey-green tuffaceous limestone, indicating that the tuff was deposited in water in which limestone was being formed. The maximum proved thickness of the tuff is nearly 320 ft in Fallgate Borehole (see below and Appendix 2). Only 228.5 ft, including beds of basalt and limestone, were proved at Milltown Quarry Borehole (see below and Appendix 2), and the old shaft [SK 3527 6256] near the limekiln at Fall Hill was sunk 210 ft in tuff without reaching the base (Green and others 1887, p. 154).

The limestone succession is best seen at Butts Quarry [SK 3407 6305] (locs. 34 and 51), near the north-western limits of the outcrop:

It is calculated that a further 30 ft of limestone once present above the beds exposed in the quarry have been eroded away. These upper beds, mainly dark grey limestone with chert, are visible in small exposures on the other side of the River Amber, north and north-east of the quarry. The topmost beds are seen in a small quarry [SK 3425 6333], 680 yd N. 71° W. of Ashover church: 5 ft of dark grey cherty limestone with a mudstone parting near its top, and containing Zaphrentid corals, are overlain by dark grey shale assumed to belong to the Cawdor Group.

At Hockley Quarry, on the eastern side of the River Amber, 10 ft of limestone are seen resting on the tuff in the cutting [SK 3507 6272] leading to the old limekiln. In the main face of the quarry [SK 3513 6284], 30 yd to the north-east, 23 ft of massive fine- to medium-grained, grey to light brownish grey limestone of the Matlock Group are overlain by 55 ft (including about 15 ft of inaccessible beds at top) of rather thin-bedded dark grey and grey cherty limestone with many Gigantoproductids, regarded as belonging to the tawdor Group (loc. 52). Between the limekiln and the main face an estimated 35 ft of beds are unexposed so that the total thickness of Matlock Group limestones at this locality is about 68 ft.

In the south about 65 ft of limestone are exposed in Milltown Quarry [SK 3527 6213] (locs. 31 and 53). This area has been intensely mineralized, and the only clear section is in the north face:

320 yd S.S.E. of the quarry the topmost Cawdor limestones are exposed in a shallow excavation [SK 3540 6183]: 4 ft of grey shale rest upon the undulating surface of 1.5 ft of grey fine-grained cherty limestone overlying 3 ft of grey coarse-grained crinoidal limestone. The shale is badly weathered and no fossils were found in it.

Other sizeable limestone quarries include two at Fall Hill: one [SK 3539 6250] shows up to 30 ft of much-mineralized grey massive limestone–reefy limestone recorded here by Sweeting and Himus (1946, pp. 141–2) was not visible at the time of the resurvey; at the other [SK 3550 6250] up to 30 ft of mainly dark grey cherty limestone are exposed. In Cockerspring Wood [SK 3485 6230] there are many exposures in dark grey cherty limestone.

On the west side of the inlier pale fossiliferous knoll limestone is exposed in the crags above the River Amber (loc. 50). It is overlain by dark cherty limestone of the Cawdor Group and rests upon Matlock Group limestone. By analogy with the Matlock area it is assumed that the knoll belongs to the Cawdor Group.

The subsurface geology has been explored in two boreholes drilled near the southern margin of the inlier (Figure 5)." data-name="images/P990892.jpg">(Figure 2). Fallgate BoreholeFor a more complete account see Ramsbottom and others 1962. [SK 3542 6219] commenced at the top of the tuff and proved it to be nearly 320 ft thick. Beneath the tuff were 43.5 ft of grey limestone with some dark bands at the top; 321 ft of basalt, the greater part brecciated; 18 ft of limestone; and 259 ft of basalt and brecciated basalt, the base of which was not reached. In Milltown Quarry BoreholeFor a more complete account see Ramsbottom and others 1962. [SK 3527 6209], 200 yd to the south-west, the tuff was encountered over a vertical range of only 228.5 ft of which nearly 54 ft were taken up by a bed of basalt and contained much limestone and tuffaceous limestone. Beneath the tuff were 9 ft of limestone resting on the upper basalt and brecciated basalt as proved in the Fallgate Borehole.

The great thickness of basalt at Ashover is considered (Ramsbottom and others 1962) to have been extruded on the flanks of a volcano which ended its activity with the ejection of the tuff now visible at the surface. The precise ages of the various volcanic episodes are not known, but the fauna of the limestone between the upper basalt and the tuff in Fallgate Borehole is suggestive of a high D₁ or low D₂ age, and thus the basalts are likely to be in the Hoptonwood Group, and the Ashover Tuff to be in, or at the base of, the Matlock Group.

Further boreholes proving the Carboniferous Limestone Series in the Ashover area have been drilled at Highoredish, Tansley and Uppertown (Ramsbottom and others 1962). Highoredish Borehole [SK 3541 6032], 1.75 miles S. of Ashover, and Tansley Borehole [SK 3313 5960], 2.5 miles S.S.W. of Ashover, ended in amygdaloidal olivine-basalt of the Matlock Upper Lava, which is overlain by just over 100 ft of grey to light grey limestones of the Matlock Group. Chert is abundant in the upper part of these limestones at Highoredish, but occurs only sporadically at Tansley. The overlying Cawdor Group at Highoredish comprises just over 100 ft of dark grey cherty limestones similar to those at Ashover, followed by 10 ft of mudstone with limestone bands. At Tansley the beds of the Cawdor Group comprise some 17 ft of dark grey limestone overlain by about 46 ft of mudstone with bands of limestone. Uppertown Borehole [SK 3237 6425], 1.67 miles N.W. of Ashover, finished in beds of the Cawdor Group which consisted of nearly 16 ft of mudstone with limestone bands resting on some 37 ft of dark grey cherty limestone.

Crich

A plunge-culmination brings the limestone to the surface in a long narrow periclinal dome with an axis trending generally to the north-north-west. Only the northern half of the structure lies within the district, where it forms a pronounced hill whose maximum elevation of about 950 ft O.D. coincides roughly with the crest of the dome. The dips are generally between 10° and 15° except on the western limb, where dips of 35° to 40° are common in surface exposures. About 160 ft of limestone are exposed in the one big quarry within the district, and from this and the records of shafts the following general succession is built up:

The toadstone, together with the overlying 100 ft and underlying 550 ft of limestone, has been encountered only in shafts which are now abandoned.

Details

The lower limestones were reached in the Glory Shaft [SK 3427 5589] and Oldend Mine [SK 3458 5576]. Their thickness of 550 ft compares with the 350 ft of limestones proved 4.5 miles to the west, where, in the Via Gellia area, the upper 250 ft belong to the Hoptonwood Group and the lower 100 ft to an unbottomed Griffe Grange Bed (pp. 10–11).

The toadstone appears to be at the same horizon as the Matlock Lower Lava. It was seen in the Wakebridge Mine [SK 3392 5568] by Arnold-Bemrose (1899b, p. 177) who recorded decomposed amygdaloidal olivinedolerite interbedded with the limestones. The following thicknesses are recorded (Green and others 1887, pp. 154–5): Glory Shaft 57 ft, Pearson's Venture 66 ft, Bacchus Pipe 120 ft. Both the latter are on the west side of the anticline where high dips greatly exaggerate the true thickness. Workings along the Glory Vein (Great Rake) passed through the toadstone in 40 yards (op. cit. p. 155); allowing for a dip of about 45° the toadstone here would be about 85 ft thick.

Matlock Group limestones have a total thickness of about 260 ft, calculated from the depths to the toadstone in the Glory Shaft and Oldend Mine. The lowest 100 ft are not exposed. The remainder is visible in Cliff Quarry where the general succession is:

Fossils from this quarry are listed on pp. 49–51 (locs. 18, 33).

The clay bands seen in Cliff Quarry are of variable thickness and rest on hummocky or pot-holed surfaces of the underlying limestone (Green and others 1887, pp. 82–3). Such clays are generally regarded as being the lateral extensions of beds of toadstone, a view supported by the evidence of Alsop (1845) who stated that during mining operations at Crich a 1-ft bed of clay was seen to pass within a short distance into a bed 14 ft thick containing large nodules of compact toadstone. There is no indication as to which of the clay bands this observation referred but it may well have been the thickest clay, lying about 70 ft from the top of the sequence. This is in the approximate position of the Matlock Upper Lava and is taken to be its lateral equivalent. Arnold-Bemrose (1899b, p. 77) described this clay as a black shale containing a few fossils, with upper and lower margins decomposed to a clay, but Sargent (1912, pp. 408–11) stated that this lithology is found only in one small exposure. During the resurvey the clay was found to be grey and purple in its upper part and light grey-green in the lower; it yielded specimens of Rugosochonetes sp.

The Cawdor Group limestones are dark grey and chesty and are best seen in quarries to the south of the district boundary, where they are about 60 ft thick (Gibson and others 1908, p. 17). Within the present district there are small exposures [SK 341 561] approximately 900 yd N.N.W. of Crich Stand Monument. Some of the lower beds were formerly visible in the south-eastern face of Cliff Quarry, and were described by Sargent (1912, p. 407) as thin-bedded blue limestone with chert about 12 ft thick, underlain by 1 ft of clay. The 20 to 30 ft of Cawdor Group shales overlying the limestones are not exposed, their presence being inferred from the boreholes at Highoredish and Tansley. G.H.R.

Provings in deep boreholes

Carboniferous Limestone has been reached in five deep oil or gas wells, Brimington, Heath, Hardstoft, Ironville No. 2 and Calow No. 1 (see (Figure 5)." data-name="images/P990892.jpg">(Figure 2)), sunk into anticlines in the exposed coalfield. The first four were sunk in the years immediately after the first World War, though Hardstoft was cleaned and deepened in 1938, and Calow No. 1 was put down in 1957–58. Ironville No. 3 [SK 4325 5232], 1.5 miles south of the district boundary, was drilled in 1956. All these boreholes were chipped for the most part, but the chippings were geologically examined. The earlier series of bores was described by Giffard (1923) and the later by Falcon and Kent (1960).

In nearly all the deeper provings, as in the Ashover area, thick and variable beds of extrusive igneous rocks make up a large part of the sequence. Since these provings are on anticlines it is not certain how typical they are of the district as a whole. As at outcrop, darker limestones are commoner towards the top, and grey or brown crystalline limestones towards the base, but no worth-while correlation with outcrop can be made.

Details

Brimington

(p. 306). Much igneous rock was recorded, together with a substantial thickness of anhydrite, a mineral unknown in the Carboniferous Limestone at outcrop, although found in Hathern Borehole, 10 miles S. of Nottingham (Falcon and Kent 1960, p. 20). Chippings indicated the following succession: limestone 175 ft; toadstone, with anhydrite towards base 603 ft; limestone 62 ft; toadstone 190 ft; limestone 5 ft.

Calow No. 1

(p. 309). Although only some 1.25 miles farther south, the igneous horizons (Figure 5)." data-name="images/P990892.jpg">(Figure 2) cannot be equated with those at Brimington: limestone, mudstone and siltstone 34 ft; limestone 283 ft; toadstone 84 ft; tuff, limestone and agglomerate 310 ft; limestone 141 ft; tuff 80 ft; limestone 61 ft.

Two sections of the beds above the topmost toadstone were cored (p. 310). A length of core from 2750 to 2775 ft (base 267 ft above top of toadstone) yielded a typical P₂ fauna including: Antiquatonia cf. sulcata (J. Sowerby), Chonetes sp., Echinoconchus sp., Leiorhynchus carboniferus Girty, Lingula sp., Martinia sp., Orbiculoidea nitida (Phillips), Productus sp., Spirifer cf. bisulcatus J. de C. Sowerby, Tornquistia sp. and indeterminate Orthotetids. The Leiorhynchus, found in the topmost 5 ft, is a form known only in high P₂.

A length of core from 2892 to 2984 ft (base 57 ft above top of toadstone) yielded a poor fauna of D age, possibly D₂, including: Antiquatonia sp., Buxtonia sp., Eomarginifera sp., Gigantoproductus sp., Productus sp. and Orthotetid fragments. A further core from 3704 to 3709 ft (base 8 ft above bottom of borehole) yielded another fauna probably of D age: Syringopora sp., Megachonetes cf. siblyi (Thomas) and indeterminate Productid and smooth Spiriferid fragments.

Heath

(p. 334). 87 ft of limestone were proved. In chippings the limestone was seen to include grey, brown, very dark brown, greenish and pyritous varieties.

Hardstoft

(p. 334). 125 ft of limestone rest on 75 ft of tuff with limestone bands. The limestone includes black, brown, grey and pale grey varieties, and dolomite, pyritous shale and vein material were also recorded.

Ironville Nos. 2 and 3

Only one comparatively thin igneous bed was recorded in Ironville No. 2: mainly limestone 296 ft; toadstone, limestone and bed of shale 99 ft; mainly limestone 582 ft. The topmost limestone is grey and brown, and the chip-pings include some chert and dark shale; that at the bottom is mostly grey and brown crystalline limestone, but about 25 ft of darker, muddy limestone occurs in the middle. Two miles farther south at Ironville No. 3 Borehole the topmost limestone is some 167 ft thick, resting on about 300 ft of tuff and this on 42 ft of pale brown crystalline limestone.

Minerals associated with limestone

Much of the Carboniferous Limestone exposed in the district has been subject to intense mineralization. Large areas have been dolomitized; there are substantial patches of silicification; and the ore-bodies, principally of fluorspar, calcite, barytes, galena and sphalerite, are of considerable economic importance (pp. 242–247).

Dolomite

Intense dolomitization affects almost every stratigraphical division in the Carboniferous Limestone. It is clearly secondary (p. 264) and preceded the ore-mineralization (Dunham 1952a, p. 402) and much of the faulting. The areas affected are indicated on the published six-inch and one-inch maps and are considered in the stratigraphical account above. Since dolomite, locally known as dunstone, is markedly different in physical properties from limestone its weathering has produced distinctive scenery. In place of the smooth pale-coloured crags and field-walls of the limestone country there are jagged crags and walls of a dark grey rock with a porous texture.

The contact between dolomite and limestone is commonly sharp, and may be observed cutting abruptly across the bedding at many localities. The field relationships were discussed in detail by Parsons (1922). Chemical analyses are reproduced on pp. 241, 265.

In the Hoptonwood Group dolomite occurs only in a small area in the extreme south-west of the district where it constitutes the north-eastern part of a much larger tract. Both laterally to the north-east and vertically downwards the dolomite has a sharp undulating margin, which appears to be entirely independent of the original bedding. This margin may be studied in Golconda Mine, of which the main shaft [SK 2490 2515] is situated 1 mile W.S.W. of Hoptonwood Quarry and some 600 yd beyond the southern boundary of the district. The base of the dolomite is seen in the main part of this mine to have the form of an irregular dome, although the bedding of the underlying limestone where seen is near-horizontal. The dolomite cuts across the limestone in irregular steps, the slope of the junction varying from horizontal to 45° or more. Commonly the junction is occupied by an ore-body (Carruthers and Strahan 1923, pp. 81–2: Dunham and Dines 1945, pp. 91–2), but where this is absent a thin film of dark clay may be seen between dolomite and limestone. It has been inferred (Dunham 1952a, p. 415) that the solutions which produced the dolomitization in this area were derived from a Zechstein sea, although no marine deposits of this age have been found locally.

The lateral margins of the areas of dolomitization recorded in the beds of the Matlock and Cawdor groups south of Wensley and around Bonsall commonly show an interfingering of dolomite and limestone, with well-defined interfaces. A good example may be seen in the landslip scars at Big Dungeon and Little Dungeon, 0.25 mile W.S.W. of Wensley, where flat lenses of dolomite up to 3 ft thick are developed within massive limestone. The margins do not lend themselves to precise plotting, and the lines shown on the maps are therefore generalized.

Chert and silica-rock

Bedded chert is found chiefly in the upper beds of the Carboniferous Limestone, where it occurs either as tabular sheets up to 10 in thick or in layers of nodules of diverse shapes and sizes. The colour generally approximates to that of the enclosing sediments. Sargent (1921) detailed occurrences, petrology and likely sources, concluding that the cherts are mainly of direct inorganic origin and are contemporary with the associated limestones and clays.

Silica-rock and silicified limestone, first described by Arnold-Bemrose (1898) and discussed by Gibson and Wedd (1913, p. 20), are easily distinguished from chert in the field in that they form masses which have ill-defined margins, commonly show a rough gritty texture, and are generally found as large irregular bodies many feet across. They are seen in places to be associated with ore-mineralization, and Arnold-Bemrose established that they were formed as a result of partial or complete replacement of limestone by the progressive growth and unification of quartz crystals. There is a passage from limestone, through limestone with well-formed quartz crystals, to rock composed almost wholly of quartz. Selective alteration has not been observed in the present district.

Dunham (1952b, p. 12) has stated that silica also occurs widely as a minor constituent of ore-bodies, but silicification is most marked in a 2.5-mile long east–west belt along the crest of the anticline north of the Bonsall Fault (Figure 34). The Hoptonwood Group in the core of the anticline is the stratigraphical unit most affected, and in the ground 0.25 mile N.E. of Bonsall partial silicification extending through several hundreds of feet is in evidence in a series of crags. The walls of the Great Rake are here locally converted to a hard completely silicified rock (p. 265). There is also much silicification about 1 mile W.N.W. of Bonsall, and farther north-west the limestone on the east side of the volcanic neck on Bonsall Moor is partly silicified and haematitized. In the ground northwards from the Great Rake, silicification in the Matlock Group is associated with the Masson Hill fluorspar flat (p. 43), and in some specimens it can be seen that silicification post-dated fluoritization.

Ore-bodies

Aerial photographs show in a striking fashion that the Carboniferous Limestone country is deeply marked by a pattern of old excavations and spoil-heaps. Most were made by lead miners, but some are due to mining for fluorspar, barytes, zinc, ochre and wad; locally tips have been turned over again, particularly for their barytesIn this account the name baryte is used for the pure mineral, and the name barytes for the commercial product from the mines, which is not, of course, pure baryte. Fluorite and fluorspar are respectively used in a similar way. and fluorsparIn this account the name baryte is used for the pure mineral, and the name barytes for the commercial product from the mines, which is not, of course, pure baryte. Fluorite and fluorspar are respectively used in a similar way. content. The workings are disposed as narrow belts of intensive mining and open excavation along veins, as irregular pock-marked areas on mineralized flats, and as criss-cross patterns where minor crossing veins (scrins) have been exploited. Although most of the spoil heaps are grassed over and the land used as pasture, little effort has been made at restoration, and there are many hundreds of old cairn-covered shafts. This is largely because one provision of the ancient mining laws forbade the filling-in of workings.

The surface positions of many of the veins can readily be deduced from the old workings and are shown on the six-inch maps. In the case of mineralized flats and ore-bodies of uncertain shape most of the known shafts are shown, but it has proved practicable to indicate only the major shafts on the veins.

The principal gangue minerals are calcite, baryte and fluorite; the principal primary metallic ores are galena (lead sulphide) and sphalerite (zinc sulphide or blende); secondary ores are cerussite (lead carbonate), smithsonite (zinc carbonate) and hemimorphite (zinc silicate). Other minerals which have been recorded, some only in small quantity, include the lead-bearing minerals anglesite, dundasite, matlockite (first described from Level Mine, Cromford, by Greg 1851, p. 120), mimetite, phosgenite or cromfordite (first described from Bage Mine, Bolehill) and pyromorphite, and the zinc-bearing minerals aurichalcite, rosasite (Braithwaite and Ryback 1963) and hydrozincite; other minerals include bravoite, bornite, chalcopyrite, cinnabar (Braithwaite, Greenland and Ryback 1963), native copper, greenockite, gypsum, malachite, manganese oxide (black wad), marcasite, millerite, pyrite, pyrrhotine, quartz and siderite. Yellow and red ochre have been worked. Hydrocarbons are present in small quantities in pockets and fossil cavities and have been discussed by Mueller (1954).

Calcite is yellow, white or colourless and is found in massive, columnar and saccharoidal forms; dog-tooth spar is common in cavities. Fluorite ranges from mauve to colourless; yellow forms are also found, and at Ashover a red variety has been recorded. The colour of pale yellow Derbyshire fluorite has been attributed to europium (Przibram 1938, p. 970). Harvey (in Dunham 1952b, pp. 10–12) detailed trace elements in fluorite, and Ford (1955) summarized work on Blue John. Fluorite occurs in massive, granular and well-developed crystal forms; Derbyshire localities were listed by Sweet (1930, p. 264). Its mineralogy and chemistry were discussed by Dunham (1952b, pp. 8–12). Mueller (1953) described inclusions in fluorite, and also in quartz and calcite. Barytes is found in pink and white varieties, both crystalline (boulder) and earthy (caulk). Descriptions of the principal baryte localities were given by Wilson and others (1922, pp. 64–9), and Sweet (1930, pp. 263–4) listed localities in Derbyshire. Dunham and Dines (1945) gave a comprehensive account of the mineralogy and sources of baryte.

Form of ore-bodies

The ore-bodies include (a) veins, ranging from major ore-bodies of considerable lateral extent to minor mineralization on joint-planes, (2) replacement deposits and (3) cavity infillings. Some of the ore-bodies are combinations of two or three types producing a considerable variety of form and in many cases an irregular shape. Most of them fall into one of the following categories, as was recognized by Wedd and Drabble (1908), and discussed also by Varvill (1937), Jones (1941), Dunham (1952b) and other writers.

Veins are numerous throughout the limestone area. Major veins, which commonly have an easterly trend, are locally known as rakes. Many are intruded along steeply dipping faults; others, although they may exhibit slickensides, are not associated with any measurable displacement. Minerals are arranged roughly in zones parallel to the walls and in some cases envelop large lenses of limestone or dolomite (e.g. Coalpit Rake). Minor veins, or scrins, often follow joint planes, which in some cases form intersecting series (Bonsall Moor and Bonsall Leys). Limestone walls of veins are locally replaced by ore material (Slit Mine). Veins are seen in many places to cut through lava flows, but mineralization within the lava is commonly greatly reduced; also the hade decreases, so that a downward continuation of a vein in a lower limestone is squinted ' sideways in relation to its position above.

Flats are irregular replacement bodies roughly following the dip of the rocks. Most appear to have been initiated around intersecting scrins or small veins (Masson Hill). Their disposition is controlled by the bases of impervious layers of lava, clay or shale (Millclose Mine), or by the bases of secondary dolomite masses (Golconda Mine).

The term 'pipe' is an imprecise one which has been used for various forms of ore-bodies displaying a rough linear arrangement. It includes veins developed in a ribbon-like form between closely spaced impervious beds, and scrins or irregular veins within flats. The old mines on Masson Hill were of the latter type. Varvill (1937) has described pipes formed at the junction of joints and bedding planes in Millclose Mine.

Pockets of ore occur in pre-mineralization cavities, not always completely filled, in flats (Oxclose Mine) and along fault planes (Riber Mine). They also occur in post-mineralization solution cavities where ore-bodies are in some cases reduced to a clayey rubble which may contain natural concentrates (Millclose Mine). In Intake Quarry a number of scrins are seen reduced to this condition. Miners refer to the rubble as throstle-breasted

Controls of ore deposition

Traill (1939) and Shirley (1950) discussed the principles underlying the deposition of Derbyshire ore-bodies, with particular reference to Millclose Mine. They concluded that mineralizing solutions had a strong tendency to ascend, travelling laterally in successive steps, and filling open joints and replacing favourable limestones (massive, light-coloured, more or less coarse-grained beds). Each ore-body has an impervious cap-rock, the main one being the shale cover (Dunham 1947, p. 22). Shirley drew attention to the concentration of ore-bodies in anticlines, but the resurvey has shown that, in much of the present district, this is not easily demonstrated.

Varvill (1959) laid stress on the fact that ore-bodies are interconnected, ascribing the successful development of Millclose Mine to the policy of following ore-shoots, or water which tends to run along the mineralized zones, rather than attempting to calculate the position of the ore.

It was established by Wedd and Drabble (1908) that there is a noticeable zoning in the occurrence of the principal gangue minerals, fluorite being concentrated in the eastern part of the main limestone crop, and in the Crich and Ashover anticlines. Dunham formalized this in a map upon which he showed the surface extent of the fluorite-bearing zone. He indicated, however (1952b, p. 83), that the mineral zoning is not clear-cut; there is almost everywhere a considerable mixture of gangue materials. Apart from the general westward replacement of fluorite by baryte and calcite, fluorite has been observed to give way to calcite downwards, for example at Crich, on the Gang Vein, and in Millclose Mine, and also towards the centre of the syncline between Matlock and Ashover. It is said (Varvill 1959) that the richest lead mines have in most cases had calcite as their dominant gangue mineral, but because some calcite veins are barren, old miners regarded fluorite as a better lead indicator.

Lead and zinc ores also show lateral and vertical variation; in Millclose Mine galena gave way northwards and downwards to sphalerite, and in Riber Mine the proportion of sphalerite to galena increased eastwards. The secondary minerals cerussite and hemimorphite are most common near outcrop.

Schnellmann and Willson (1947) suggested that the relatively poor mineral zoning might be due to mineralization having occurred in several separate episodes. They also suggested that the mineralization proceeded from a conjectured north–south fault bounding the limestone massif on the east (1947, p. 11). There is, however, no evidence for the existence of such a boundary fault.

In many mines a downward impoverishment has been recorded (Green and others 1887, p. 122); in some cases this was perhaps due to increasing distance below the cap-rock. In Millclose Mine, where cap-rocks also occur at depth, considerable mineralization was followed down to many hundreds of feet below the shale cover, and this has led to the suggestion (p. 245) that comparable ore-bodies might exist elsewhere at depth below suitable cap-rocks.

Age of mineralization

Moorbath (1962, p. 335) has calculated a mean modal age of 180 ± 30 millon years for the galena of North Derbyshire, based on samples from Millclose, Riber and Moletrap mines and Wheels' Rake. This falls within Moorbath's Period 5 of British mineralization. Period 5 is regarded as being Mesozoic in age; on geological evidence elsewhere some mineralization of this period, although not necessarily all, is considered to be certainly post-Keuper but probably not later than Lower Jurassic. The local geological evidence is that the ore-mineralization is post-dolomitization, which Dunham (1952a, p. 415) has suggested to be associated with a Zechstein sea. R.A.E.

Details of ore-bodies

Because the ores are widely distributed the division for descriptive purposes into the localities indicated below is largely artificial.

Millclose Mine

The mine workings are situated on the north-eastern flank of a minor syncline complementary to the small anticline whose axis lies west of Churchtown and Darleybridge (see (Plate 9)). The mineralizing fluid rose up dip along joints and faults, particularly along the north–south 'Main Joint', spreading out to form a flat under each lava, and stepping up southwards from lava to lava until it reached the shales—the final cap-rock. These flats, found at six horizons, tend to occur in the gentle arches of secondary folds (Shirley 1950, p. 358), the easterly plunge of which explains why the flats are, as a rule, situated on the western side of the 'Main Joint' (Traill 1939, p. 873). The disposition of the ore-bodies and the fact that they are largely replacement deposits has led Traill (1939, pp. 868–71) to compare them with the lead–silver deposits of Northern Mexico described by Prescott (1926), and to apply the term 'manto' to them.

The principal primary minerals at Millclose are galena, sphalerite, pyrite, calcite, fluorite and baryte, and the commoner secondary minerals hemimorphite and cerussite. Greenockite also occurs, and small quantities of bravoite were found at the lowest level in the mine. For the history and production of the mine see p. 244. E.G.S.

Area west of Wensley

South of Millclose Mine there is a complex of surface workings in the area west of Wensley. These are along north-trending veins and in a broad irregular belt apparently associated with a flat at the junction of dolomite and limestone of the Matlock Group. A confusion of shafts and spoil-heaps on the shale outcrop west of Wensley gives little indication of the form of the ore-body there, but the oldest workings thereabouts were, at least in part, in a flat below the base of the shale.

Northern Dale

Ramifying old workings in dolomitized knoll limestone may be seen in Northern Dale. North of the dale there is a well-developed set of north–east trending veins in one of which old open workings 30 ft wide were noted. Several soughs are believed to drain this area to Wensley Dale (Kirkham 1962).

Slack Mine and Bonsall Moor

The Bonsall Moor Vent, situated on the crest of the anticline north of the Bonsall Fault, is surrounded by old lead workings which extend to a considerable depth below the Matlock Lower Lava. To the north, Slack Mine [SK 257 597] yielded much lead (Farey 1811, p. 267) from an ore-body of uncertain form. The tips include fragments of vent agglomerate and basalt. To the west a swarm of subparallel north-westerly veins and scrins is marked by open workings, in one place 35 ft wide; some of the shafts are several hundred feet deep. To the south there is an east–west vein with subsidiary veins approximately at right angles; reworking for fluorspar at the eastern end has revealed that it comprises an anastomosing series of veinlets.

In the Bonsall Moor area the dominant gangue mineral is calcite, with subsidiary fluorite and baryte.

Oxclose and Jughole mines

Oxclose Mine [SK 2753 5994], which is drained to the River Derwent by Oxclose Sough, was re-opened in 1949 and worked on a small scale for fluorspar. The main ore-body is a flat at the 300-ft  level close above the Matlock Lower Lava; it is similar to that at Masson Hill but less well developed. Fluorite is associated with calcite, baryte, galena, blende and veins of pyrite up to 1 in thick. In general the deposit ends sharply against a flat limestone roof, but some irregular veinlets ramify up into this. There is a similar flat at the 200-ft' level close below the Matlock Upper Lava, where some of the mineralization occurred in natural cavities. Lumps of decomposed amygdaloidal basalt are found in fluorite a dozen feet below the base of the lava, having apparently dropped into pre-mineralization caverns. Green and others (1887, p. 148) reported that a level was said to have been taken through the Matlock Lower Lava to seek lead in the limestone below, without success.

Jughole Mine [SK 2793 5971] (Dunham 1952b, p. 101) worked what appears to be essentially a fluorspar flat at the same horizon as that at Masson Hill and the lower one at Oxclose Mine. Belts of old workings indicate the probable presence of flats above both the Lower and Upper Matlock lavas mile S.W. of Oxclose Mine.

Masson Hill

A fluorspar-bearing flat, up to 50 ft thick, is developed on Masson Hill in limestone between the Matlock Lower Lava below and dolomite above. It has a proved extent of nearly 800 ft down dip and 1600 ft along the strike. Ramifying old workings connect the deposit to the Great Rake and it has been exploited at outcrop in a large quarry. The earliest mining in the flat was for lead, but galena was only a minor by-product from the quarry. Dunham (1952b, pp. 97–101) indicated that the ore-body is a replacement deposit in which mineralization appears to have developed from two sets of joints—one trending W. 30° N. and the other nearly at right angles. In deeper workings the ore is seen to consist of pale yellowish, greenish or faintly mauve fluorite mixed with some fine-grained quartz, dolomite, calcite and minor amounts of baryte. Near surface the deposit commonly breaks up into a sand consisting largely of limonite-coated fluorite cubes. For notes on workings see p. 246.

Seven Rakes

Old workings in the Seven Rakes are well seen in Cawdor Quarry; it is recorded that the vein was first worked above, then below, and finally within, the Matlock Upper Lava (Green and others 1887, p. 124). The vein was investigated in Cawdor Quarry by inclined drilling in 1950–51 (Johannesburg Boreholes Nos. 4, 5 and 7) and in 1957 (Smart's Quarry Borehole p. 379). Johannesburg Borehole No. 7 proved that cavities exist at a depth of at least 225 ft. Southwards the vein splits into the Slit Rake on the east and High Tor Rake on the west, both joining the Great Rake. Old workings to a depth of 70 ft are still open on High Tor Rake, where they are known as Fern Cave. Old workings 6 ft wide in basalt are also open where this vein crosses the crop of the Matlock Upper Lava south of the Derwent. For an analysis of fluorspar from Slit Rake see p. 247.

The Seven Rakes is crossed by the Dimple Vein in the Dimple area of Matlock, and Dimple Mine was situated at the junction of the two veins.

Great Rake and Coalpit Rake

The Great Rake is one of the strongest veins in the district, and, as it is likely to have been easily accessible in High Tor, the Roman Cave' there may well have been excavated in the earliest days of lead mining.

At the western end the vein runs mainly in silicified limestone of the Hoptonwood Group, and old open workings are 20 to 60 ft wide. These and underground workings at Low Mine [SK 2837 5857] were mainly for fluorspar, of which a high quality grade was produced [Dunham 1952b, p. 103) and which included a pure white granular variety. Low Mine worked two parallel veins, one reaching a maximum width of 10 ft and the other 9 ft. Stratigraphically these are amongst the lowest fluorspar workings in the district, extending some hundreds of feet below the Matlock Lower Lava. Recent surface re-working for fluorspar has revealed a 60-ft wide belt of mineralization in dolomite close above the Matlock Lower Lava [SK 2880 5867]; farther east Masson Cavern (SK 2916 5870], 20 ft wide on the line of the vein, connects with workings into the Masson Hill flat to the north.

On the east of the Derwent, the Great Rake has been worked in recent years from Riber Mine [SK 2999 5885] (p. 244) and workings were also carried into the Coalpit Rake. A maximum width of vein material (21 ft) was found at the junction of the two rakes; there was a general downwards and eastwards deterioration and no flats were recorded below either the Matlock Upper Lava or the overlying shale. Gangue minerals are mainly calcite, dominant in the east, and fluorite. Galena and sphalerite occur, the former commonly in the shattered variety known as 'steel ore', providing evidence of post-mineralization movement along the line of the Great Rake. Bornite and native copper associated with dog-tooth spar were recorded by Varvill (1959, p. 197).

The western end of the Coalpit Rake has recently been worked on a small scale for fluorspar in several places. One such working showed a 70-ft wide mineralized belt 1000 yd west of where the rake crosses the Derwent, comprising veins of fluorite, calcite and galena in dolomite.

Whitelow mines

A set of intersecting north-north-east and north-north-west veins is centred on a mile-long easterly-trending vein south of Blake Mere. This vein, which lies on the line of the Great Rake of Matlock, has old workings up to 30 ft wide. Gangue debris is calcite and fluorite, and there has been some re-working for the latter.

Bonsall Leys

An extensive series of closely spaced north-east and north-west veins is traversed by two east-trending rakes—Parson's Rake and Great Rake. Old open workings in Matlock Group limestones are up to 10 ft wide; gangue is principally calcite and baryte, although fluorite also occurs. Barytes was produced here in 1915–16. Several adits have been driven into the measures below the Matlock Lower Lava from the Via Gellia Valley.

Bonsall Fault, parallel veins and associated flats

There is little evidence of mineralization on the main branch of the Bonsall Fault except that 400 yd west of Bonsall recent workings have revealed a 10-ft wide belt of mineralization in limestone abutting against the Bonsall Sill [SK 2750 5831]. Fluorite occurs as veinlets and replacements, calcite as large transparent crystals; galena stringers and white baryte were also recorded. Open workings were up to 30 ft wide, suggesting a local swelling of the vein.

There are four subparallel mineralized faults north of the Bonsall Fault in the Derwent Valley; three have been worked in the last fifteen years. The southernmost is a branch of the Bonsall Fault on which an adit [SK 2901 5739] was driven in 1955 on an 18-ft fluorite-bearing vein. Baryte and fluorite are seen in the tips of another vein some 100 yd to the north, and farther north again the Moletrap Vein (Dunham 1952b, p. 104) has recently been worked on a small scale for fluorspar at Wapping Mine [SK 2946 5752]. This vein has a range which probably exceeds a mile, and old workings include New Bullestree Mine [SK 3029 5747], at least 420 ft deep. Wedd and Drabble (1908, p. 576) reported that the vein was about 10 ft wide to the east.

Speedwell Cavern [SK 2915 5785] and Cumberland Cavern [SK 2924 5773] are both associated with old workings in a 50-ft mineralized north-west fault. The fault throws dolomite down on the south against the Matlock Lower Lava. In limestone above the lava on the north of the fault an irregular replacement flat of fluorite and calcite is developed at a similar horizon to that of Masson Hill. The deposit varies in thickness up to a few yards, and the calcite commonly occurs above the fluorite. Messrs. Derbyshire Stone commenced workings for fluorspar from Speedwell Cavern in 1951; Dunham (1952b, p. 104) gave an account of earlier workings here and in the adjoining Hopping Mine.

In the Via Gellia Valley south of the Bonsall Fault a number of old workings were observed but the exact location of the well-known Ball Eye Mine was not proved. Short (1734, pp. 73–74) stated that this mine yielded 20 oz of silver from a fudder (22.5 cwt) of ore. The silver-bearing ore was notably sulphurous. The shaft was 300 ft deep, penetrating the Matlock Lower Lava to the underlying Hoptonwood limestones. It was recorded that the ore-body was in one place 42 to 48 ft high and 120 ft wide, but its form is not clear.

Cromford to Middleton

The area bounded by the Via Gellia, the Gulf Fault, the Gang Vein and the shale outcrop has been intensively worked, particularly the closely spaced north-easterly veins in the north and east, and the north-westerly veins in the south and west. The complex of workings extending for about a mile from the south end of Cromford to the north end of Middleton are known as the Dragoneye or Dunrake Vein and appear to involve several branching veins. Some of the shafts are very deep. The latest workings were for barytes (Dunham and Dines 1945, p. 91). Workings on the Dunrake, Tinder and other veins have been taken some hundreds of yards eastwards below the shale cover, and drained by a series of soughs of which the latest was the Cromford Sough, issuing at about 300 ft O.D. near the centre of Cromford [SK 2952 5687]; it drained an area as far south as, and including, the Gang Vein.

Most of the visible workings are in the limestones of the Matlock and Cawdor groups, but workings extending under the area from the south side of the Via Gellia enter a set of east-north-easterly veins in the Hoptonwood Group. Baryte is the main gangue mineral, but calcite is also common; fluorite is rather rare.

The Gulf area

The Gulf is a shale-covered graben between the Gulf Fault and the Rantor Vein. A series of north-northwesterly veins run parallel to these, both in The Gulf and in the ground to the east; several of them are along faults. The east–west Gang Vein cuts across all these veins and in Hoptonwoodstone Quarry may be seen traversing the Gulf Fault.

This is an area in which occurred one of the last major concentrations of lead mining in Derbyshire, and some barytes mining has also been undertaken (Dunham and Dines 1945, pp. 90–91). The final lowering of the water table was accomplished by the Meerbrook Sough, started in 1772 (p. 251): one branch leads along the Gang Vein and others de-water The Gulf area and the veins to the east; the outlet is at 250 ft O.D. Workings were detailed by Farey (1811), Lecornu (1879), Green and others (1887) and Carruthers and Strahan (1923); the most recent, in the 1920's, were at Shore [SK 2890 5566] and Cromfordmoor [SK 2912 5570] mines, near the east end of the Gang Vein. The Gang Mine was situated in the same vicinity, although the exact site is uncertain. The best production was from the limestone close below the shale, but the mine also yielded lead from the shale and the Matlock Lower Lava (Green and others 1887, p. 150).

Minerals recorded include galena, cerussite, pyrite, sphalerite, fluorite, calcite, baryte, 'plumose white gypsum', petroleum and ochre. Baryte is generally the main mineral in the tips, followed closely by calcite; fluorite is less common. The Gulf Fault where seen is commonly mineralized by anastomosing calcite veinlets, but there are indications that it may have been worked for lead at depth.

West of Gulf Fault

The Gang Vein continues into the ground west of the Gulf Fault, where its western range was last worked for barytes at Partridge [SK 2670 5513] and Bradhouse [SK 2700 5530] shafts in the 1920's; at 405 ft below surface in the latter mine the vein had pinched down to 18–36 in of calcite (Carruthers and Strahan 1923, p. 79), but there is a complex of associated subparallel veins. Traversing the line of the Gang Vein, and lying roughly parallel to the Gulf Fault, is a series of north-northwesterly veins which continue, with cross veins, northwards to the Via Gellia. Mineralization extends down into the Griffe Grange Bed. The Snake Mine (Green and others 1887, p. 151), 330 yd S.E. of Pearson's Farm [SK 2618 5549], penetrated 119 ft into this bed. R.A.E.

Ashover

The numerous workings for galena, and more recent re-workings for fluorspar, are confined to the limestone above the Ashover Tuff, and are largely concentrated in the southern half of the inlier. The dominant trends of the veins are to the west and to the north-west or north-north-west (parallel to the anticlinal axis), with a subordinate trend to the north-north-east. Most of the veins are a few feet in width, but in some instances metasomatic replacement of the limestone walls has resulted in much wider deposits, as at Fall Vein which is said to have had a total width of 30 to 40 ft, although much of this was silicified limestone with strings of fluorite (Carruthers and Strahan 1923, p. 85). Apart from their richness in fluorite and galena, the veins have yielded calcite and small quantities of sphalerite, the latter being recorded particularly in Fall Vein where it was found close under the shale cover (Carruthers and Strahan 1923, p. 85). Antimony, in the form of antimonial galena, has also been recorded (Pilkington 1789, p. 184), as have small amounts of pyrite, baryte and silica.

The more persistent veins have been worked for some distance below the shale cover where they die out down dip. The mineralization appears therefore to be related to the structure. The centre of the mineralization, however, does not coincide with the area of maximum uplift, but lies on the flank that has suffered the maximum flexure and, as a result is likely to have been most heavily fissured.

Cores of the Ashover Tuff in Fallgate Borehole, and of tuff and associated basalt in Milltown Quarry Borehole, contain numerous thin veins of calcite but no traces of fluorite or galena (Ramsbottom and others 1962, p. 141). Farey (1811, p. 269) noted that ore occurred in the toadstone at Westedge, but it is likely that this was no more than the tailing off of the vein into the underlying toadstone, a feature observed more recently by miners working the lower reaches of the veins in the vicinity of Milltown Quarry. Beneath the tuff, 9 ft of limestone were encountered in Milltown Quarry Borehole and over 40 ft in Fallgate Borehole. The cores of this lower limestone contain traces of galena, sphalerite and fluorite, in addition to calcite, but there is insufficient evidence to estimate the extent of the mineralization.

Crich

The ore-bodies are concentrated in the area of maximum folding, in the north of the inlier, where the veins trend roughly north-west and north-east. In addition to the veins there are, on the steeply-dipping west side, rich pipes in which mineralization is limited vertically to one or two beds, although extending laterally for some hundreds of yards (Green and others 1887, p. 122; Wedd and Drabble 1908, pp. 508–9).

The limestones above and below the toadstone (the equivalent of the Matlock Lower Lava) are affected by the mineralization which persists to great depths, the deepest workings, at Oldend Mine on the east side of the inlier, being over 900 ft below the surface, and those at Glory Mine, in the centre of the mineralized area, 810 ft. Below these depths the veins are thin. Fluorite is said to have been practically confined to the limestone above the toadstone, while calcite was the chief gangue mineral in the limestone below (Wedd and Drabble 1908, pp. 516, 519). Galena, although obtained both above and below the toadstone, was most abundant about 70 ft below its base (op cit., p. 519). G.H.R.

Palaeontology

Griffe Grange Bed

The only brachiopods collected (p. 11) are very thick-shelled Daviesiella and these are difficult to extract from the matrix. It seems most probable, from the thickness of the shell, that these are D. liangollensis (Davidson), but the details of the divaricator muscle impressions have not been seen. Foraminifera, small gastropods seen only in section, and Lithostrotion cf. martini complete the collected fauna. The Lithostrotion is of the S₂ form in which the major septa are slightly withdrawn from the columella. From the evidence of the coral and of the Daviesiella these beds are assigned to the S₂ Zone.

Hoptonwood Group

The rocks of the Hoptonwood Group contain an assemblage typical of the D₁ Zone. The principal corals are Carcinophyllum vaughani, Dibunophyllum bourtonense and Palaeosmilia murchisoni, and the brachiopods include Davidsonina septosa and Linoproductus hemisphaericus. There is great variety in the species of Lithostrotion, but the most notable feature is the rare Lonsdaleia, a fossil normally typical of D₂, for both L. duplicata and L. floriformis are represented by single occurrences in the upper beds of the Group.

The principal fossils collected, and their localities, are:

Matlock Group

The lowest beds just above the Matlock Lower Lava and the equivalent Shothouse Spring Tuff form escarpments affording good opportunities for collecting (Nos. 10–13 below). The rich D₂ coral fauna enters the succession at this horizon. It includes Clisiophyllids in abundance, especially Dibunophyllum, several species of Lithostrotion and Diphyphyllum, Lonsdaleia (common), Palaeosmilia regia, and Caninia of the juddi group. Palaeosmilia murchisoni and Carcinophyllum may be regarded as relicts of the D₁ fauna and only occur in the lowest beds of the Matlock Group.

Some of the lower beds show a tendency towards a `reef '-type fauna with common brachiopods including Productus s.s., Antiquatonia, Echinoconchus, and Brachythyris planicostata, and also trilobites and gastropods (loc. 10), though these are associated with colonial corals such as are not found when the reef ' fauna is fully developed elsewhere. In the south of the district, at Crich (loc. 18), the lower beds contain many large Gigantoproductids which are not so common further north.

The Matlock Group divides conveniently into an upper and lower part at the horizon of the Matlock Upper Lava or its clay-band correlatives, and although this is not a palaeontological division, it is convenient to distinguish in the lists the fossils from these two divisions of the Group. The fauna of the upper beds is not as rich as that of the lower beds. Though many species are common to the two divisions, Lithostrotion martini and L. maccoyanum are not found in the collections from the upper beds. New entrants here include Corwenia rugosa, and at one locality Orionastraea placenta has been found (see p. 31). The principal forms collected are:

Cawdor Group

Several distinctive facies may be distinguished in the Cawdor Group, each with characteristic lithology and fauna. (Table 1) shows the typical fauna of five of the principal facies. It may seem from the list of Cawdor Group fossils below that there is sometimes a mixing of the facies, but this is because fossils have been collected from several lithologies at some localities. Briefly the shales and dark limestones (as at Cawdor Quarry) contain goniatites, lamellibranchs, a few distinctive brachiopods, and also ostracods (described by Robinson 1959) and holothurians. Pulfrey (1932, p. 198) recorded radiolaria in nodules from these beds at Cawdor Quarry, and Hudson (1943) has described some elements of the coral fauna. Dark limestones of lithology and fauna similar to those in Cawdor Quarry are in places brecciated, as at Baileycroft Quarry, Wirksworth (loc. 46a). The fine-grained dark limestones contain principally a varied Gigantoproductid fauna, but also locally Productus concinnus in abundance. These beds are probably on the type horizon of Gigantoproductus giganteus s.s. which fossil is locally common here. G. giganteus also extends into the bedded very crinoidal beds as at Dene Quarry, Cromford (loc. 44) where many elements of a true 'reef' fauna occur in association with it. The pale massive knoll-type limestones have an abundant fauna, but Gigantoproductus has not been found in them. Their fauna typically includes many of the smaller Productids, Spiriferids, Rhynchonellids, uncommon gastropods and lamellibranchs, and trilobites (locs. 37, 45, 49a, 50). Rather rarely colonial corals occur in these beds (locs. 37, 41, 45).

The age of the Cawdor Group may be determined as P_2a-e on the evidence of Goniatites (Mesoglyphioceras) granosus Portlock and Lyrogoniatites aff. georgiensis Miller & Furnish at Cawdor Quarry (see p. 23). A high P₂ age for the upper beds is also indicated by the presence of Leiorhynchus and Caneyella membranacea (McCoy). There is, however, no direct evidence of the zonal position of the knoll limestones which generally occur at the base of the group (see also Ramsbottom and others 1962, pp. 135–7). The principal forms collected are:

Type and figured specimens. Among the type and figured specimens from the Carboniferous Limestone of the district are the following:

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SHIRLEY, J. 1950. The stratigraphical distribution of the lead-zinc ores of Millelose Mine, Derbyshire and the future prospects in this area. 18th Int. Geol. Cong., 7,353–61.

SHIRLEY, J.  1959. The Carboniferous Limestone of the Monyash-Wirksworth area, Derbyshire. Quart. J. Geol. Soc., 114, 411–29.

SHORT, T. 1734. The natural experimental and medicinal history of the mineral waters of Derbyshire, Lincolnshire and Yorkshire. London.

SIBLY, T. F. 1908. The faunal succession in the Carboniferous Limestone of the Midland area. Quart. J. Geol. Soc., 64, 34–82.

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WILSON, G. V., EASTWOOD, T., POCOCK, R. W., WRAY, D. A. and ROBERTSON, T. 1922. Barytes and witherite. 3rd edit. Mem. Geol. Surv., Min. Resources, 2.

Chapter 3 Millstone Grit Series

Introduction

The Millstone Grit outcrop extends southwards and south-eastwards from the north-west corner of the district, and is widest in the centre where it swings round both sides of the Ashover Anticline. In the north only the upper part of the series falls within the district, but around Ashover and east of Matlock the full sequence is present. The following table, showing the major subdivisions, is based on evidence available at outcrop and in boreholes to the east:

Variations in thickness and lithology are shown diagrammatically in (Figure 6).

Sweeting (1946, p. 123) used the name Butts Shales for all the argillaceous rocks below the Ashover Grit, but as these include beds ranging from the uppermost Carboniferous Limestone Series to the lower part of the Middle Grit Group, the name is not used here.

Beneath the cover of Coal Measures to the east, the Millstone Grit Series has been explored in boreholes for oil. Two of these, Calow No. 1 and No. 2, were cored in part and provided valuable information, including details of some of the fossil horizons. The remainder were not cored and their evidence is incomplete and perhaps less reliable. (Figure 7) shows the lithology and suggested correlation of four of these boreholes, all of which penetrated the full thickness of the series. It will be seen that the Kinderscout Grit, thought to be present in Calow No. 1 and Ironville No. 2, is absent in the intervening ground, though it may be represented by beds recorded as 'sandy shale' in Hardstoft No. 1. The thickest development of the Kinderscout Grit is found in Ironville No. 2, where the Millstone Grit succession is thinnest; a thin development of beds above the base of the Ashover Grit in this borehole compensates for the thick Kinderscout Grit. The diagram brings out the southward thinning of the Series—from 1840 ft in Calow No. 1 to 1175 ft in Ironville No. 2—which persists from the Sheffield district where the oil boreholes at Ridgeway, Renishaw and Whittington proved thicknesses of 2030 ft, 2380 ft and 2190 ft respectively (Eden and others 1957, pp. 11, 14). The Series also thins to both east and west of the oil boreholes. To the east the only evidence lies beyond the district boundary, in the Mansfield No. 1 Borehole (Edwards 1951, p. 270) where the detailed succession in the 1513 ft assigned to the Series is not known, and in the boreholes drilled at Eakring where a thickness of about 550 ftBased on thickness quoted by Lees and Taitt (1946, p. 284) and amended as a result of work by Howitt (Brunstrom 1964, pp. 15–6). has been proved. At outcrop in the west the average thickness is about 1350 ft and, as in the oil bores, an apparent southward thinning is probable, though the evidence is incomplete because the lower parts of the sequence are as yet unproved in the north. The attenuation towards the outcrop is largely due to a thinner development of the beds below the Ashover Grit, including the complete absence of the Kinderscout Grit.

The upward succession in the Millstone Grit of the Chesterfield district, as elsewhere in Britain, reflects the more or less complete transition in conditions of deposition from the wholly marine environment of the Carboniferous Limestone to the mainly non-marine conditions of the Coal Measures. In the lower part of the sequence the shales of E₁ to R₁ ages contain fossils indicative of marine or near-marine conditions almost throughout, but in the Middle Grit and Rough Rock groups marine fossils are confined to comparatively thin bands within a cyclic pattern of sedimentation in which thick beds of sandstone are prominent. In these upper groups 'barren' strata make up the bulk of the sequence; positive evidence of non-marine conditions, in the form of plant-beds or  'mussel'-bands, while rare, is more noteworthy towards the top of the Series.

Throughout the largely marine sequence several distinct faunal phases have been recognized (Ramsbottom and others 1962, pp. 114–33); these are repeated again and again in the same general order and reflect the cyclic nature of sedimentation even in these superficially monotonous shales. In the ideal complete cycle these phases are arranged as follows:

• (k) Fish phase
• (j) Planolites ophthalmoides phase
• (i) Lingula phase
• (h) Mollusc spat phase
• (g) Anthracoceras or Dimorphoceras phase
• (f) Thicker-shelled goniatite phase
• (e) Anthracoceras or Dimorphoceras phase
• (d) Mollusc spat phase
• (c) Lingula phase
• (b) Planolites ophthahnoides phase
• (a) Fish phase

Seldom, if ever, is the complete sequence of phases developed, but among those phases that are present the same order can nearly always be discerned. The sequence (a) to (f) is thought to represent the incursive stage of increasing salinity associated perhaps with increasing depth, and the sequence (f) to (k) the corresponding regressive stage of lessening salinity associated with shallowing. There are a few occurrences where the goniatites are accompanied or replaced by a more varied 'calcareous' fauna including brachiopods and trilobites. Although this fauna can be considered as representing a separate phase, it is unlikely to reflect any further increase in salinity, and it cannot be said to form part of the typical cycle in the present district. A phase marking the end of a faunal cycle may be followed by strata which are apparently barren, and in certain instances at least this may mark the establishment of truly non-marine conditions.

Petrographic examination of the named sandstones has been made by Mr. R. K. Harrison, and his results are setout in Appendix 1, pp. 267–276. His work tends to confirm that there are no essential differences between the sandstones of the present district and those of Yorkshire described by Gilligan (1920) and Dunham Wayboardin Stephens and others 1953). The coarser particles in these rocks are generally rounded, and in consequence the term 'sandstone' is used for general descriptive purposes in preference to 'grit', a term retained only in the naming of individual beds where the usage is deeply entrenched.

Kinderscout Grit Group and underlying shales

At outcrop these beds are between about 200 and 300 ft thick and consist of shale with sporadic thin bands of 'cank' and, at the base, limestone. They form the lower slopes of the Derwent Valley from Matlock northwards to the north-westerly trending fault above Darley Dale, and the lower parts of the concave slopes between the Ashover Grit and the Carboniferous Limestone from Matlock southwards and around the inliers at Ashover and Crich. There are few exposures.

The beds have been explored in the Uppertown, Highoredish and Tansley boreholes in the Ashover area, near the centre of the Millstone Grit outcrop. The boreholes have been described in detail elsewhere (Ramsbottom and others 1962) and (Table 2) summarizes the proved faunal succession. There is no break between the Lower and Upper Carboniferous: the limestone of the Carboniferous Limestone Series passes upwards into transitional beds of shale with bands of limestone, up to 70 ft thick, near the top of which a band with Cravenoceras cf. leion Bisat is taken as marking the base of the Millstone Grit Series. The measures up to and including the Reticuloceras reticulatum horizon consist almost entirely of marine shale in which there is a profusion of fossils including great numbers of goniatites. G.H.R.

Details

Beds below the Kinderscout Grit Group

The lowest beds were seen during the resurvey in the top part of the Riber Mine drift [SK 2998 5885], where 12.5 ft of dark grey shale, with a 26-in band of dark grey limestone near the top, yielded Martinia sp., Caneyella membranacea (McCoy), Posidonia corrugata (R. Etheridge jun.); ?orthocone nautiloid, Eumorphoceras sp. In the absence of Cravenoceras leion the base of the Millstone Grit Series is suggested by the occurrence of Caneyella membranacea in association with Eumorphoceras sp. This lamellibranch is also recorded from the tip of the old shaft [SK 2805 6061], 25 yd E. of the road between Snitterton and Oaker Side. Cravenoceras cf. leion has, however, been found in the Matlock area: it is recorded at 424 ft in the inclined Johannesburg No. 10 Borehole [SK 3033 5909], situated 340 yd N. 83° W. of Riber Castle. G.H.R., R.A.E.

In Calow No. 1 Borehole, cores between 2600 ft and 2663 ft show a virtually complete section through the E₁ shales. A band 4 ft 10 in thick at the base contains Posidonia corrugata, Cravenoceras cf. leion, Dimorphoceras sp. s.l., Eumorphoceras sp. and fish fragments. The overlying 8 ft 2 in, containing Lingula mytilloides J. Sowerby, P. corrugata, indeterminate Dimorphoceratids and fish debris, is itself overlain by the Eumorphoceras pseudobilingue Band. This is 6 ft thick, including a 16-in limestone, and is a composite band with a thin layer containing E. pseudobilingue C Bisat at the top separated from the E. pseudobilingue s.s. fauna. The band contains Orthotetid juv. indet., P. corrugata, Dimorphoceras sp. s.l., E. pseudobilingue (Bisat) and E. pseudobilingue C. The succeeding 32 ft 7 in of dark shale contain fish debris, mainly Acanthodian and Palaeoniscid scales, and, near the base, ?sponge spicules, P. corrugata, a Nautiloid [Nautilus quadratus group] and Coleolus?. The top 11 ft 5 in of E₁ shales carry much collophane; they contain the Cravenoceras malhamense Band, with the following fauna: Actinopteria persulcata (McCoy), Caneyella membranacea, P. corrugata, Cravenoceras malhamense (Bisat), Dimorphoceras sp. s.l., Kazakhoceras scaliger (H. Schmidt) and fish debris. The association of the E. pseudobilingue and C. malhamense bands with beds containing much fish debris confirms the earlier view expressed by Ramsbottom and others (1962, p. 133) that the beds containing abundant fish debris above the C. leion Zone in the Ashover area represent the zones of E. pseudobilingue and C. malhamense. G.H.R.

E₂ shales of the Nuculoceras nuculum Zone have been seen at two localities. In the bank of the River Derwent [SK 2607 6304], 660 yd N. 84° W. of St. Helen's Church, Churchtown, Darley Dale, 2 ft of calcareous mudstone contain P. corrugata and Nuculoceras nuculum Bisat. The same species, together with Eumorphoceras bisulcatum Girty, occurs in the banks [SK 3034 5744] of a stream flowing south through the small wood adjoining Cromford Station on its eastern side. Some 10 ft of shale are exposed and the goniatites are in a band about 6 ft above the stream. In a tributary about 30 yd to the east, a small exposure of grey shale with P. corrugata is thought to belong to the same zone. In the Ashover boreholes N. nuculum is found in three bands (Ramsbottom and others 1962, pp. 129–30). Two of these bands have been recorded in the inclined Johannesburg No. 10 Borehole [SK 3033 5909]. G.H.R., E.G.S.

In the Bridgetown Brook dark marine shales of E₂ age are well exposed for some 230 yd eastwards of a place [SK 2607 6182] 810 yd N. 65° W. of St. Mary's Church, Darleybridge. Fossils collected include P. corrugata and P. corrugata cf. gigantea Yates. It is inferred that shales resting unconformably on limestone of the Cawdor Group farther downstream (p. 22) are of P₂ age, but fossil evidence is not conclusive and these shales might also be referred to the Millstone Grit Series. R.A.E.

The only exposure of note in the shales of H age occurs in the bank of the River Derwent [SK 2603 6401], 750 yd N. 89° W. of Stancliffe Hall. Here the Hudsonoceras proteus Band has yielded Caneyella sp., Dimorphoceras?, Homoceras? [juv.] and Hudsonoceras proteus (Brown). The fossils are preserved in a band of dark limestone, and it is of interest that this horizon in the Ashover boreholes (Ramsbottom and others 1962, p. 127) is marked by a similar hard band, described as being 'canky'. E.G.S.

Homoceratoides prereticulatus Bisat, found near the top of H, has been identified at 68 ft 7 inches in the Johannesburg No. 6 Borehole, and Homoceras cf. eostriolatum Bisat is recorded between 68 ft 10 in and 70 ft 7 in. In the No. 9 Borehole Homoceratoides? has been identified at 241 ft.

In the Uppertown, Highoredish and Tansley boreholes the beds below the Kinderscout Grit Group have an average thickness of about 125 ft, and consist largely of mudstones or shales which are rarely silty and are predominantly dark grey in colour, though distinct bands of a lighter colour also occur. Pyrite is common and is abundant at certain horizons. Hard bands, described as 'tank' (Ramsbottom and others 1962, p. 77) and consisting largely of minerals of the ankerite–dolomite group, are fairly common; thin limestones are also present. The bands of lighter-coloured mudstone, many of the pyrite-rich horizons and most of the hard bands persist from borehole to borehole; as already noted, the hard band at the Hudsonoceras proteus horizon has been found at outcrop and some of the other bands have been recorded farther afield (Ramsbottom and others 1962, pp. 129, 131).

The beds of E₁ age in these boreholes are 20 to 30 ft thick and contain only one determinable goniatite fauna—that of Cravenoceras leion at the base. The zones of Eumorphoceras pseudobilingue and C. malhamense are represented by a condensed deposit, with abundant fish debris but no goniatites (see p. 65), which gives rise to a prominent radioactivity peak in the gamma-ray logs of all three boreholes (Cosgrove in Ramsbottom and others 1962, p. 164). The beds of E₂ age are 40 to 60 ft thick and contain a well-developed sequence of goniatite and other phases, with 'barren' beds at two horizons and fish phases at intervals throughout the sequence. There is comparatively little variation in the thickness of H₁, the range being between 45 ft and 52 ft. The lower and upper parts of these beds bear numerous goniatite phases, but towards the middle are some 16 ft to 21 ft of mudstone carrying spat phases alternating with bands usually containing only pyrite.

Kinderscout Grit Group

The lowest beds are seen in the banks of Marsh Brook at the northern end of the Ashover inlier where dark grey marine shales dip to the north at about 30°. Fossils collected by W. N. Edwards, J. V. Stephens and C. B. Wedd from the stream banks 40 yd upstream from a point [SK 3432 6340] 110 yd N.N.W.of the road bridge at Marsh Brook, include Caneyella sp., Dunbarella sp., Reticuloceras cf. todmordenense Bisat and Hudson, R. aff.umbilicatum Bisat and Hudson and R. sp. (circumplicatile group). During the resurvey the most northerly exposure yielded C. squamula (Brown), Dunbarella rhythmica (Jackson) and R. cf. dubium Bisat and Hudson. West of the Crich inlier dark grey shales dipping west at 60° are exposed in the banks of the stream at Wakebridge. Over a distance of 100 yd south of the bridge [SK 3394 5555], the following fossils, indicating an horizon slightly higher than that seen at Marsh Brook, have been found: C. squamula, Dunbarella sp., Anthracoceras or Dimorphoceras sp., Homoceras sp., Hudsonoceras ornatum (Foord and Crick), Reticuloceras sp.(of nodosum group).

In the Uppertown, Highoredish and Tansley boreholes the Kinderscout Grit Group ranges in thickness between about 110 ft and 130 ft and has a similar lithology to that of the underlying beds. The lowest zone, that of Reticuloceras circumplicatile, is completely marine, though fossils are rare in the top few inches. The R. eoreticulatum Zone is largely marine but includes two fish phases and some barren beds. The R. reticulatum Zone is marine at the base, but the goniatite phases give way to a succession of spat phases, Planolites phases and 'barren' beds in the middle part of the zone. These are followed by the goniatite phase of the R. aff. reticulatum horizon which in turn gives way to 'barren' beds at the top of the zone. G.H.R

Middle Grit Group

The beds of the lower part of the group, from the Reticuloceras gracile early mut. horizon to the R. bilingue late mut. horizon, are approximately 100 to 150 ft thick and consist of mudstone with a few bands of ironstone and tank '. R. gracile early mut., R. gracile and R. gracile late mut. have been found in boreholes or at the surface, and occur in beds with a total thickness of up to about 30 ft. R. bilingue early mut. is separated from R. bilingue by up to 101 ft of mudstones which are silty in parts. R. bilingue late mut. has been found in situ in only one locality, where it occurs about 6 ft above R. bilingue. Mainly argillaceous rocks persist for up to 150 ft above this latter horizon, but they include a high proportion of silty beds and merge imperceptibly with the interbedded siltstones and sandstones which mark the lower part of the Ashover Grit.

The Ashover Grit lies between R. bilingue late mut. below and R. superbilingue above, and is, therefore, the equivalent of the Roaches Grit west of the Pennines. It consists of a massive development of sandstone, up to about 200 ft thick, overlying some 200 ft of beds comprised of siltstones and silty mudstones with irregular bands of sandstone. In the south the massive sandstone is medium- to coarse-grained with bands of pebbles, but it thins northwards, passing into a generally finer-grained sandstone with interbedded siltstone and mudstone. It is most prominent in the southern half of the district where it gives rise to the bold escarpment around the Ashover inlier and forms the marked features of Matlock Bank and Riber Hill to the north-east and south-east of Matlock. South of the Derwent it is seen in the spectacular crags of Black Rocks (Plate 4A), and it also forms the gently inclined Cromford Moor. Northwards from Matlock argillaceous bands are developed within the massive sandstone, which passes into a complex of sandstone with siltstone and mudstone bands. North of Beeley this complex, some 200 ft thick, comprises the entire thickness of the Ashover Grit, the underlying sandstone bands having died out to the south. At the margin of the district, to the north-west of Chatsworth House, the Ashover Grit is about 100 ft thick, and 2.5 miles farther north it dies out in the eastern outskirts of the village of Curbar in the south-east corner of the Chapel-en-le-Frith (99) Sheet.

The beds between the Ashover and Chatsworth grits are between 50 and 200 ft thick and average about 125 ft. They consist mainly of mudstones, silty mudstones and siltstones which are grey to dark grey in colour. Ironstone bands and lenses occur sporadically. Two coals are developed locally in the south: the lower lies on, or close above, the Ashover Grit and is up to 2 ft thick; the upper is known only at Longway Bank where it is calculated to be about 40 ft above the Ashover Grit. The Reticuloceras superbilingue Marine Band is found in the upper part of these beds in the north. In the central part of the Millstone Grit outcrop it occurs in the lower half of the sequence and in the south it lies close above the Ashover Grit. The Pygmaeoceras sigma Band lies at a variable distance above R. superbilingue and has been found at several localities. Lingula mytilloides has been recorded a few feet below the R. superbilingue Marine Band and has also been found above the upper coal.

The Chatsworth Grit includes all sandstones between the R. superbilingue Band below and the Baslow Coal above. In the type area around Chatsworth House in the north-west of the district there are two main sandstones separated by up to 200 ft of shale with local beds of sandstone, the whole complex averaging about 500 ft in thickness. The lower of the main sandstones dies out southwards near Chatsworth House, though thin sandstone bands occurring locally as far south at Matlock, may be its lateral equivalent. The upper of the main sandstones persists southwards and varies in thickness between 70 and 125 ft. In the north it is the dominant geological control moulding the form of the high moorland country between the Derwent Valley and the coalfield. In the centre of the Millstone Grit outcrop it forms the nearly flat expanse of moorland along the axis of the shallow syncline between the Derwent Valley and the Ashover Anticline. In the south it forms a prominent escarpment at Lea and is seen in outliers at Longway Bank and Coddington, along the district boundary.

The Chatsworth Grit and Redmires Flags are separated by up to 85 ft of beds, predominantly shale, which include two seatearths with associated coals known only in the northern half of the district. At the base the Baslow Coal lies on, or close above, the Chatsworth Grit. Overlying it a sandstone up to 40 ft thick, the 'Brown Edge Flags' (Pulfrey 1934, p. 259), is present in places. The higher coal, or more commonly only its associated seatearth, lies midway between the Chatsworth Grit and the Redmires Flags, and above the 'Brown Edge Flags' where these are present. In the shales above the sandstone non-marine lamellibranchs and Lingula have been found. The general succession is similar to that encountered in the Rod Moor boreholes (Eden and others 1957, pp. 18, 20; Pulfrey 1934, pp. 255–9) and suggests the correlation of the Saslow Coal with the Ringinglow Coal.

The Redmires Flags are not persistent along the outcrop. They are best developed in the north where they are up to 45 ft thick. North of Chatsworth they include some 'coarse grit', but elsewhere they consist of fine-and medium-grained sandstones which are flaggy in places and massive in others. From the vicinity of Ashover southwards they occur only locally and have a proved maximum thickness of only 12 ft.

Details

Beds between Reticuloceras gracile early mut. and the Ashover Grit

The R. gracile early mut. and the R. gracile horizons are not exposed though they are recorded in Tansley, Uppertown and Highoredish boreholes (Ramsbottom and others 1962, p. 121). R. gracile late mut. was not found in the boreholes but it occurs at outcrop south of Ashover in the bank of the stream [SK 3557 6027], 1033 yd S. 20° E. of Raven House. The dark grey shale dipping W.N.W. at 70° contains Caneyella sp., Dunbarella aff. speciosa (Jackson) and R. gracile late mut. Bisat. G.H.R.

The R. bilingue early mut. horizon is not exposed but the R. bilingue Band can be seen at several localities. In Beeley Brook [SK 2698 6745], 570 yd S. 66° E. of St. Anne's Church, Beeley, 2 ft of dark grey shale yielding Reticuloceras bilingue (Salter) are overlain by 2 ft of grey silty shale. On the edge of Lindup Wood [SK 2579 6700], 1050 yd S. 48° W. of St. Anne's Church, Beeley, 2 ft of soft dark grey shale with Caneyella rugata (Jackson), Dunbarella sp., Anthracoceras or Dimorphoceras sp. and R. bilingue rest on 12 ft of barren dark grey shale with ironstone nodules in the lower part. About 6 ft above this exposure, 6 ft of hard dark grey silty shale belonging to the R. bilingue late mut. horizon contains C. rugata, Anthracoceras or Dimorphoceras sp. and R. bilingue late mut. Bisat. The fact that these two marine bands occur near together at this locality has already been noted by Dr. W. S. Bisat (Hester 1932, p. 41 footnote). In the bank of the River Derwent [SK 2592 6644], 630 yd N. 8° E. of Rowsley Station, weathered shale has yielded R. bilingue. E.G.S.

Further exposures of the R. bilingue horizon occur south of Ashover. In the stream [SK 3453 6127] in Ravensnest Wood, 770 yd N. 82° W. of Raven House, dark shale contains Anthracoceras sp., R. bilingue and mollusc spat. In the steep bank [SK 3516 6067] on the south-west side of Hole Wood, 530 yd S. 9° W. of Raven House, weathered black shale has yielded Caneyella sp., Dunbarella sp. and R. bilingue. A similar fauna, but including Posidonia sp. nov., has been obtained from a steep bank of shale [SK 3511 6078] in the western prolongation of Hole Wood, 435 yd S. 18° W. of Raven House. This exposure is in a landslip and the shales lie approximately 50 ft below their correct position. Farther south R. bilingue late mut. and Caneyella sp. occur in landslip [SK 3065 5728], 370 yd S. 75° E. of Cromford Station.

The Uppertown and Tansley boreholes show the R₂ beds below the Ashover Grit to be between 220 ft and 250 ft thick, comprised largely of mudstones which are commonly silty and in places laminated, the laminations consisting of alternations of silty and less-silty material (Ramsbottom and others 1962, p. 119). There are sporadic ironstone bands, and 'cank' is present at some of the marine horizons. At Tansley 27.5 ft of siltstone with sandstone bands are recorded in the upper part of these beds. The R. gracile Zone, approximately 25 ft thick, is marine in its lower part where the R. gracile early mut. and R. gracile horizons are separated by, at most, 15 in of sediments. The rest of the zone, apart from a spat phase near the top, is non-marine and specimens of Naiadites sp. nov. cf. subtruncatus were found at Uppertown. The remaining 200 to 225 ft of mudstones proved in Uppertown and Tansley boreholes belong to the R. bilingue Zone. The bottom 9 ft 5.5 in at Uppertown and 8 ft 1.5 in at Tansley are marine and contain the R. bilingue early mut. horizon. Above it 101 ft of beds at Uppertown and 67 ft at Tansley contain only rare fish fragments and, at Uppertown only, rare Cochlichnus kochi (Ludwig) and Planolites?. They are succeeded by beds, from 5 ft to 8.5 ft thick, that are largely marine and include several faunal phases of which the chief is the goniatite phase constituting the R. bilingue horizon. This is the highest goniatite horizon proved in the boreholes and, apart from a 1.5-in Lingula band found about a foot above it, the overlying mudstones contain only rare Palaeoniscid scales, scattered plant fragments and C. kochi. G.H.R.

Ashover Grit

This is exposed in the banks of the River Derwent [SK 2566 7019], west of Chatsworth House, where it is medium grained and includes much interbedded siltstone and silty mudstone. A micaceous slab [SK 2560 7041] weathering out 460 yd N. 64° W. of the north-west corner of Chatsworth House yielded several large specimens of C. kochi. R.A.E.

The beds below the main part of the Ashover Grit are exposed in Beeley Brook [SK 275 677], east of Beeley, where they consist of mudstone and siltstone, and in Hall Dale [SK 284 639], north of Two Dales, where bands of sandstone occur together with mudstones and siltstones. The sandstones give rise to features between Beeley and Rowsley on the east side of the River Derwent, and as far south as Oaker Side on the west. The main part of the Ashover Grit in this area includes subordinate bands of mudstone and siltstone and, as a result, the escarpment consists of two or three benches rather than a single feature. The sandstone is flaggy in parts, especially in the numerous exposures to be seen in the gardens of Chatsworth House. In other places it is coarse grained and pebbly, but it is for the most part a massive fine- or medium-grained rock that has been extensively quarried for building stone. The most noteworthy quarries are at Stancliffe [SK 267 638] where the famous 6 Darley Dale Stone, is wrought from a down-faulted mass of Ashover Grit (see pp. 239 and 271). E.G.S.

South of Two Dales the Ashover Grit forms a single prominent escarpment as far as Matlock Bank. It is coarse-grained and massive with bands of pebbles at Bank Quarry [SK 2962 6115] and Jackson Tor [SK 2986 6101] immediately north of Matlock. South of Matlock Bank there is an additional, lower, bed of sandstone, well exposed in Lumsdale, which joins the main bed further south, at Tansley. The full thickness of the Ashover Grit has been proved in Tansley Borehole (Ramsbottom and others 1962, pp. 78–9, 117–8) where the main bed is 204 ft including, 23 ft below the top, 8 ft of mudstone and seat-earth with, possibly, a thin coal (see below); below the main bed a further 190 ft of silty mudstone and siltstone with sandstone bands are recorded. The thick sandstone forms the impressive Riber Hill, which dominates the landscape on the eastern side of the Derwent, and Cromford Moor, which reaches a height of over 1000 ft above O.D. On the flanks of Riber Hill the sandstone bands below the main bed form discontinuous benches below the main escarpment. One such sandstone is 25 ft thick in the old quarry [SK 3027 5882], 465 yd S. 60° W. Of Riber Castle. South of High Leas Farm a feature formed by a sandstone band below the main bed extends southwards as a narrow neck of high ground from which extensive landslips stretch to both east and west. An outlier of the main bed of sandstone forms a small plateau, above 500 ft O.D., south of Lea Bridge, and an old quarry [SK 3194 5604] on its northwestern margin shows 30 ft of pinkish brown coarse-grained sandstone. A thin sandstone lower in the sequence forms an irregular feature to the east of the outlier.

The Ashover Grit crops out around the inlier of Carboniferous Limestone at Ashover though it is masked in places in the north by boulder clay. For the most part it occurs as a single bed about 200 ft thick and forms conspicuous craggy escarpments. It consists of medium- to coarse-grained sandstone with bands of pebbles and is visible in numerous quarries. The most notable of these is Robin Quarry [SK 3425 6165] situated at Cocking Tor, 1730 yd S. 22° W. of All Saints' Church, Ashover. Of the 30 to 35 ft of sandstone exposed here the top 5 to 10 ft are flaggy; the remaining 20 to 25 ft are massive and show increasing coarseness downwards. According to Sweeting (1946, p. 126) an 80-ft face was exposed prior to 1940, the lower portion consisting of fine-grained, compact, thickly bedded sandstone. Until recently millstones and pulpstones up to 5 ft in diameter were made from the stone. At Slack on the western limb of the anticline, the Ashover Grit divides into two beds each forming a distinct feature. The two sandstones were penetrated in the Cuckoostone Borehole [SK 3175 6220] about 1.5 miles N.E. of Matlock: the upper is 93 ft thick and the lower (with interbedded shale) 54.5-ft thick, and they are separated by 136.5 ft of beds, mainly shale. In the northern part of the anticline the lower bed of sandstone occupies the ground flanking the River Amber and its tributaries, and is seen in numerous exposures showing up to 20 ft of sandstone, commonly flaggy. The upper bed, which consists of yellow to buff medium-grained sandstone, occupies fairly high ground and forms a scarp which, though prominent over much of the outcrop, is broken by faulting and, in places, is hidden by boulder clay. It is of variable thickness, being up to 150 ft around Shooterslea [SK 3150 6470] and Peasunhurst [SK 3185 6613] and only 70 to 80 ft in the neighbourhood of Spring House [SK 3300 6530]. It is exposed in the disused Roach Quarry [SK 3149 6624], and in the nearby Peasunhurst Quarry [SK 3150 6650] is worked for building stone.

Around the Crich inlier the dips are fairly steep and the few available exposures of the Ashover Grit show brown, buff or purple, medium- to coarse-grained, in places pebbly, sandstone. Consisting essentially of a single sandstone, the Grit here is about 200 ft thick on the north side and rather less on the south; at least 200 ft has been proved in Lea Hall Borehole. A few hundred yards south of the district boundary two boreholes, Hanson Farm [SK 3232 5458] and Wigwell [SK 3169 5464], have proved about 175 ft of 'grit' resting on mudstone with bands of sandstone. Between the latter boreholes and Crich 90 ft of brown or purple, massive, false-bedded, medium- to coarse-grained sandstone are exposed at Birchwood Quarry [SK 3263 5514] on the western bank of the Derwent. On the eastern bank up to 50 ft are seen in the old quarries [SK 3336 5488] south-east of Leashaw Farm.

At Matlock Bank, north of Matlock, a coal between 8 and 24 in thick is recorded by C. B. Wedd (in Gibson and Wedd 1913, p. 43) near the top of the Ashover Grit. The section, measured in a water tunnel [SK 3068 6101], shows up to 6 ft of shale above the coal with 8 to 10 ft of coarse, pebbly sandstone overlying the shale. The seam probably lies at the same horizon as the seatearth encountered 27 ft 7 in below the top of the Ashover Grit in the Tansley Borehole. G.H.R.

Beds between the Ashover Grit and the Chatsworth Grit

The beds below the Reticuloceras superbilingue Marine Band are best seen in Bar Brook [SK 261 725], west and south-west of Far End, Saslow, where they comprise dark grey mudstones and shales containing ironstone bands and lenses. Grey mudstones are also exposed in the beck at the head of Hall Dale [SK 283 653] where the interval between the Ashover and Chatsworth grits is only 50 ft. In Bassetbarn Farm Borehole [SK 3554 6416] they are 58 ft thick, and consist of dark grey silty mudstone with a few ironstone bands and plant debris, and with fish debris in the top 25 ft; a 1-in band containing Lingula mytilloides is recorded 4 ft 7 in below the R. superbilingue Marine Band, foraminifera and indeterminate lamellibranchs 251- ft below, and further indeterminate lamellibranchs 38 ft below. G.H.R., E.G.S., R.A.E.

From Butterley Reservoir [SK 345 600] southwards a thin coal is developed locally above the Ashover Grit. It has been mapped from the reservoir, where it is said to be 18 in thick, to near Doehole on the southern tip of the Ashover Anticline where [SK 3556 5890], 385 yd due E. of the road junction at Doehole, a smut is seen resting on Banister. On the eastern flank of the Crich Anticline coal debris is present in the soil immediately east of the Ashover Grit escarpment, and the coal has been mapped between Plaistow and Edge Farm [SK 3542 5534]. At the farm it is recorded as being 4 in thick, while 340 yd to the north-north-west [SK 3527 5565], it is said to be as much as 24 in. G.H.R., P.M.D.D.

In the north the R. superbilingue Marine Band has been found in the following localities (distances and bearings relate to the north-west corner of Chatsworth House): (1) 2730 yd N. 3.5° W. A roadside exposure [SK 2579 7273] on the east side of Baslow where marine shale weathers out. (2) 3050 yd N. 5° E. A section in a small watercourse [SK 2615 7303] shows the R. superbilingue Band to be 42 in thick including a 6-in bed in the upper part which is cemented and weathers to 'gingerbread rock '. The following fossils are found: Caneyella sp., Gastrioceras sp., Homoceratoides aff. divaricatus (Hind), R. superbilingue Bisat. Above this exposure another small watercourse about 15 ft below the Chatsworth Grit contains a 3-in band of shale with Pygmaeoceras sigma (Wright). (3) 2230 yd N. 25° E. A section [SK 2683 7209] in the south bank of Heathy Lea Brook shows the R. superbilingue Band to be 77 in thick, with the following fossils: Caneyella sp., Dunbarella speciosa (Jackson), D. sp. [4 costae on anterior ear], Gastrioceras spp., Homoceratoides fortelirifer Ramsbottom and R. superbilingue. The exposure is near the foot of a face of shale about 30 ft high. Eighteen feet above the marine band 3 in of weathered papery shale contain the P. sigma Band with C. rugata, Dunbarella sp., Gastrioceras sp. and P. sigma. (4) 1100 yd N. 14.5° E. A small section [SK 2621 7121] near a spring shows 12 in of shale with R. superbilingue. R.A.E.

The marine band was formerly exposed in Hall Dale [SK 2829 6551] in the upper part of the beds between the two grits, and was described by C. B. Wedd during the earlier survey as 'dark blue and black carbonaceous shale with Glyphioceras bilingue, fish scales and 'Posidonia'. None of the specimens recorded from this exposure survive. E.G.S.

On the north-east side of the Ashover Anticline the R. superbilingue Band was found 58 ft above the Ashover Grit in Bassetbarn Farm Borehole [SK 3554 6416]. It is 8.5 ft thick and consists of dark grey mudstone, silty mudstone and siltstone, with pyritic bands; fossils include foraminifera, Caneyella sp., an orthocone nautiloid, Anthracoceras sp. and R. superbilingue. The P. sigma Band in this borehole occurs only 2 ft above and, in addition to P. sigma, contains Caneyella?, Anthracoceras sp., Gastrioceras sp. and R. superbilingue.

In the bank of Carr Brook [SK 3593 6014], 1510 yd N. 83° E. of the eastern corner of Butterley Reservoir, an exposure of marine shale shown on six-inch map SK 36 SE as the G. cancellatum Marine Band is now considered to be the R. superbilingue horizon. Numerous R. superbilingue are associated with specimens of Gastrioceras which are not typical of the G. cancellatum Band.

R. superbilingue has not been found farther south within the district, but 400 yd beyond the southern boundary it occurs in shales in an exposure [SK 3214 5448] only a few yards up-stream from the exposed flaggy top of the Ashover Grit.

The beds above the R. superbilingue horizon are best recorded in the Bassetbarn Farm Borehole which commenced a few feet below the Chatsworth Grit and proved 141 ft of mudstone, silty mudstone and siltstone with thin ironstone bands. The siltstone occurs in the upper part of the sequence and contains thin layers of sandstone which may well be lateral extensions of some of the sandstones included in the bottom part of the Chatsworth Grit in the north of the district.

In the extreme south a local development of coal is present about 90 ft below the Chatsworth Grit in the outlier at Longway Bank, about 1 mile south of Lea Bridge. It was not visible at the time of the present survey but is recorded by C. B. Wedd at the disused Wigwell Brick and Tile Works [SK 3237 5501], 750 yd W. 27° S. of Leashaw Farm, where it was formerly worked from shafts and an adit. The recorded section is coal 18 in, yellow and purple clay 9 to 12 in, on hard clay. In the wall of the adit 25 ft of the overlying shale are visible, including a band about 5 ft thick containing Lingula mytilloides. G.H.R.

Chatsworth Grit

In Chatsworth Park and the area around Baslow the Chatsworth Grit is a complex of interbedded sandstones and shales. There are two main sandstone beds, each of which is split in places by beds of shale, while further sandstones are developed locally within the 200 ft of shale between the main beds.

The lower main sandstone attains a maximum thickness of a little over 100 ft to the north-east of Baslow, where it forms the prominent steep-sided spur of Baslow Bar. Except on this spur most of its outcrop is over-ridden by a mantle of head, which has crept down the slopes from the higher horizons of the Grit. Where exposed the rock is massive and medium-grained. Only in the banks of Heathy Lea Brook, skirting the northern end of Chatsworth Park, does it form crags, here some 20 ft high; elsewhere its outcrop is marked by a rounded feature, or a series of features between which slacks, inferred to be due to shale bands, exist. Not far south of Heathy Lea Brook the lower sandstone splits into two beds, both of which die out a few hundred yards north-east of Chatsworth House.

The upper of the main sandstones has an average thickness of about 125 ft and forms a series of spectacular west-facing crags and scarps topped by undulating heather-clad moors. In the extreme north Baslow Edge forms a craggy skyline towering above Curbar, and is conttuued southwards by the cliffs of Blackstone Edge, Gardom's Edge and finally Dobb Edge, giving way in turn to the steep tree-clad escarpment overlooking Chatsworth House. The upper beds, exposed in the cliff sections, and on the roadside near Robin Hood [SK 2756 7216] (see p. 272), are coarse grained and markedly false bedded with scattered pebbles. The pebbles, up to 0.5 in across, are more abundant towards the top, where they tend to be concentrated in seams. At the southern extremity of Baslow Edge the lower beds of the upper sandstone are exposed in a series of small quarries [SK 262 736], 300 yd W.S.W. of Wellington's Monument; 25 ft of medium-grained level-bedded sandstone with soft partings are seen, and individual posts vary from 6 in to 2 ft thick.

East of the outcrop the Chatsworth Grit comprises 158 ft of 'gritstone', sandstone and shaly sandstone in Linacre Borehole (p. 346). In Ca]ow No. 1 Borehole, approximately 8 miles east of the outcrop, it is only 53 ft thick. R.A.E.

South of Chatsworth House, as far as Sydnope Hall [SK 2938 6405], elements of the Grit range over nearly 200 ft of beds comprised of lower sandy shales with impersistent sandstone bands and an upper main sandstone between 70 and 125 ft thick. The latter forms a prominent scarp above the less well-developed bench or benches of the Ashover Grit on the east side of the Derwent Valley. Below the scarp the outcrops are obscured by a sheet of head extending down over the sandy shale and shales below, and in places over-riding the outcrop of the Ashover Grit. The numerous crags and abandoned quarries along the edge overlooking Beeley and Rowsley show the sandstone to be medium-grained and massive, with well-developed false bedding in some localities. E.G.S.

A thin bed of sandstone forms a feature in the hillside below the main Chatsworth Grit escarpment at Farley, north of Matlock, and on either side of Bentley Bridge, north-east of Matlock. Apart from this local development which lies about 50 ft below the main escarpment, the Chatsworth Grit around the Ashover and Crich anticlines, and along the Derwent Valley from Sydnope Hall to the south, consists of a single development of sandstone with a thickness of about 100 ft. It has been proved at Lea Hall Borehole [SK 3354 5753], 1000 yd S. 58° E. of St. John the Baptist's Church, Dethick, where it is recorded as 99 ft of red and grey sandstone with red shale near the top. It is best seen in the old quarries which are found both on the escarpments and on the broad plateau extending from Beeley Moor in the north to Tansley Moor and Scotland Nursery in the south. It is generally medium grained though coarse in some localities; at an old quarry [SK 3011 6184], 800 yd E.S.E. of Farley, bands of pebbles have been noted. The colour varies between cream, yellow, buff and brown, and in some localities weathering has produced shades of pink, red and purple. At the time of the resurvey the grit was being worked at Lumshill Quarry [SK 316 9124], 500 yd E.S.E. of Bentley Bridge, Matlock, and Derbyshire Oaks Quarry [SK 3342 6052], 900 yd W. 25° S. of Red House (p. 239). G.H.R.

Beds between the Chatsworth Grit and the Redmires Flags

The Baslow Coal at the base of these beds has been extensively worked near its outcrop from the vicinity of Robin Hood to Emperor Lake in Chatsworth Park, but no detailed information is available. There are a number of shafts, but most of the older workings were from bell-pits on both sides of the Baslow–Chesterfield road at Robin Hood. It is said that the coal was last worked during the 1914–18 war and that it was of poor quality. Fragments in the soil along the line of outcrop north-west of Wellington's Monument suggest that the coal here [SK 268 741] is underlain by ganister. In Linacre Borehole (p. 346) 40 in of coal and dirt are recorded; in Calow No. 1 Borehole there are 11 in of coal. R.A.E.

The coal was formerly worked from a number of shallow shafts and bell-pits near its outcrop north of Hell Bank Plantation [SK 284 684]. A report dated 1835 states that the seam was 18 to 21 in thick at outcrop and of variable thickness in the workings. It is exposed at Hunger Hill in Messrs. Hinckleys' sandpits [SK 3261 6741] and [SK 3267 6732] where 11 to 14 in of coal lie 4.5 to 8 ft above the Chatsworth Grit. It is floored at all these exposures by mudstone-seatearth or silty mudstone-seatearth. It is not recorded in Whispering Well Borehole [SK 3323 6947] but its associated seatearth lies at 447.5 ft, some 10 ft above the Chatsworth Grit. At Hunger Hill Borehole 12 in of coal and sandy shale are separated from the Chatsworth Grit by 3 ft of clay and sandy shale. The coal is not recorded south of Hunger Hill. E.G.S.

Above the Baslow Coal or, where that is absent, the top of the Chatsworth Grit, the beds up to the Redmires Flags consist largely of shales. Exposures are poor but where they are seen in Cat Hole [SK 314 680], immediately east of Harewood Grange, they contain sporadic layers of ironstone nodules. The fireclay locally present towards the middle of the shales, and above the 'Brown Edge Flags', where these are developed (see below), is exposed in two places [SK 3137 6797] and [SK 3147 6795], respectively 220 yd and 330 yd S. 80° E. of Harewood Grange. At the former locality there is a 1-in smut above the clay. The fireclay is recorded in Whispering Well and Hunger Hill boreholes, the log of the former also mentioning coal of unspecified thickness. The shales up to about 14 ft above the coal have been seen in the stream bank [SK 3132 6801], 150 yd E. of Harewood Grange, where they contain ironstone nodules with fish scales. In the south of the district Lingula is recorded from shale lying above a local development of the 'Brown Edge Flags' in an exposure [SK 3542 5577], 440 yd N. of Edge Farm. L. mytilloides, together with sponge spicules and fish scales, has been recorded between 67 ft and 73.5 ft in Walnut Opencast Site Borehole 67/40 (p. 387), above sandstone and siltstone that are possible local representatives of the 'Brown Edge Flags'. About twenty feet above the marine fossils there are poorly preserved mussels ', identified as Carbonicola ornata ? Trueman, C. deansi ? Eagar and Naiadites? E.G.S., G.H.R.

In Calow No. 1 Borehole (p. 309) the shales below the Redmires Flags are 45 ft thick. Near their base a non-marine lamellibranch band 5.5 ft thick (at 1018 ft 10 in) contains: Carbonicola ornata, C. pseudacuta Trueman, Naiadites sp. cf. productus (Brown). Scattered fish debris and Lingula mytilloides occur both above and below the band. The fauna is similar to that in the Victoria Mills Borehole, Huddersfield (Trueman 1929) from which the types of C. ornata and C. pseudacuta were obtained. At Huddersfield the fossils were 70 ft below the G. cancellatum Band, compared with 50 ft here, and Lingula occurred immediately above the non-marine lamellibranchs. A few poorly preserved non-marine lamellibranchs were found about 30 ft higher in the sequence in Calow No. 1 Borehole. G.H.R.

Sandstone, the equivalent of the 'Brown Edge Flags', is best developed between Harewood Grange and Stone Edge, where it attains a maximum thickness of about 40 ft and is well exposed in Cat Hole and in the banks of the Hipper's north-flowing tributaries. It is variable in character—from massive sandstone to flags with beds of siltstone and sandy mudstone. Over most of the area it rests either immediately on the Baslow Coal or is separated from it by only a few feet of mudstone. At the sandpits at Hunger Hill (p. 235) the sandstone is poorly cemented and has been excavated as loose sand. It is believed that the uneven nature of the topography around and including Hunger Hill is due to differential cementation of this sandstone. In Calow No. 1 Borehole the flags are about 24 ft thick and have rootlets in the top 3.5 ft. E.G.S.

Redmires Flags

These beds form a well-marked feature extending from the northern margin of the district to near Swiss Cottage in Chatsworth Park. On the moors east of Gardom's Edge many blocks of coarse 'grit' weather out from this feature, and where it crosses Heathy Lea Brook on the north side of Chatsworth Park debris of ganister is seen [SK 2788 7201] above 6 ft of ill-sorted 'grit', which in turn rests on 7 ft of dark micaceous mudstone. The Red-mires Flags would appear to be abnormally thin in this section. They are not exposed elsewhere to the north of Swiss Cottage, but it is inferred that they thicken locally to some 30 ft. In Linacre Borehole they are 12 ft thick, the top 6 ft being coarse-grained. In Calow No. 1 Borehole (p. 309) they comprise less than 10 ft of fine-grained sandstone. R.A.E.

The feature seen in Chatsworth Park continues south of Swiss Cottage and is well developed over most of the ground as far as Harewood Grange [SK 3115 6800]. Farther east, between Stonehay Farm [SK 3319 6749] and the Chesterfield–Matlock road it is again prominent. The few exposures show the Flags to consist largely of massive sandstone north and west of Harewood Grange, and flaggy sandstone to the south and east (p. 274). In the former area, on Beeley Moor, they have been worked, presumably for walling stone, in shallow quarries now completely overgrown. Their maximum thickness appears to be about 45 ft. At Whispering Well Borehole they are represented by 19 ft of sandstone, shaly sandstone and shale. E.G.S.

East of the Chesterfield–Matlock road the Redmires Flags persist for only half a mile, forming a narrow ill-defined bench in the area of steep dip east of Spitewinter [SK 3413 6656]. North-east of Ashover a small feature above the Chatsworth Grit probably marks a local development of the Flags. Approximately equidistant between these two localities the Flags have been proved in Northedge and Press No. 3 boreholes where they are respectively 21 ft and 24 ft thick (see pp. 359 and 367). In the south, small exposures of up to 10 ft of buff and pink, fine-grained massive sandstone on Dethick Common are near the northern limits of an area of Redmires Flags, half of which is covered by boulder clay, lying in the shallow syncline to the west of the Ashover–Crich Anticline. The sandstone proved to be 12 ft thick in Lea Hall Borehole (p. 345) where the top 12 in is recorded as ganister. The ganister is visible in the stream bed [SK 3366 5775], 500 yd N.E. of Lea Hall, and a few yards from the Hall on its north-east side 6 ft of the underlying sandstone are seen in another stream [SK 3340 5750]. About 75 yd south-west of the Hall the Flags die out. On the east side of the Crich Anticline features at the horizon of the Redmires Flags have been mapped at two localities. The northern one is southwest of Lindwaylane Farm and the southern north-east of Edge Farm; there are no exposures.

Rough Rock Group

Shales, between 85 and 130 ft in thickness, make up the bulk of this group, and they are overlain in places by a thin Rough Rock. Although the underlying Redmires Flags are topped in places by ganister, no associated coal has been recorded, and the lowest horizon of note is the Gastrioceras cancellatum Marine Band. The true G. cancellatum fauna has not been found and the band is represented here by the G. crencellatum fauna of the upper part of the band (Bisat 1940, p. 331), as in the Sheffield District to the north (Eden and others 1957, p. 21). Between 25 and 60 ft above it lies the G. cumbriense Marine Band, underlain locally by a thin flaggy sandstone. Near the top of the shales non-marine lamellibranchs occur in a similar position to those recorded south of Sheffield (Eden and others 1957, p. 21) and in a corresponding position to those of the Sand Rock Mine to the west of the Pennines (Eagar 1952). The Rough Rock is impersistent and nowhere exceeds 40 ft in thickness. It varies in composition from a siltstone with sandy bands to a hard flaggy sandstone.

The Pot Clay is a refractory bed about 2.5 ft thick, consisting, generally, of fireclay in the north and ganister in the south. The Clay was mined at the time of resurvey at Cat Hole, between Harewood Grange and Holymoorside; the ganister has been worked at Alton, south of which the full thickness is rarely seen. The Pot Clay Coal has been found only in the north where the maximum recorded thickness is 6 inches in the Linacre Borehole. G.H.R.

Details

Between the northern boundary and Swiss Cottage the shales in the Rough Rock Group are 100 to 130 ft thick. The marine shale weathering out above the Redmires Flags in Heathy Lea Brook [SK 2788 7201] is on the horizon of the G. cancellatum Marine Band, but no diagnostic fossils have been found. R.A.E.

Up to 85 ft of shale are present in this group between Swiss Cottage and the Chesterfield–Matlock road. The G. cancellatum Marine Band is exposed in the stream-bed [SK 3128 6808] on the north side of the bridge over the River Hipper at Harewood Grange, where dark shale overlying the Redmires Flags contains Posidonia aff. insignis (Jackson), Agastrioceras carinatum (Fresh) and G. crencellatum Bisat. Marine shale from this horizon was also seen in a small heap of debris [SK 2775 6919], evidently excavated from immediately above the Red-mires Flags, about 440 yd E. of Park Farm. During the earlier survey C. B. Wedd recorded dark marine shale at the same horizon east-north-east of Hell Bank Plantation in an exposure [SK 2899 6833], 2080 yd S. 63° E. of Park Farm. The G. cumbriense Marine Band, estimated to lie some 25 to 35 ft above the G. cancellatum Marine Band, is exposed at two places in the banks of the River Hipper. Sixty yards up-stream [SK 3125 6811] from the bridge at Harewood Grange the following fauna was collected: Ariculopecten aff. losseni (von Koenen), Caneyella multirugata (Jackson), G. cumbriense Bisat and Palaeoniscid scales. The other exposure [SK 3309 6826], in Cat Hole, 850 yd N. 6° W. of Stonehay Farm, yielded similar fossils.

The shales in the upper part of the group, where seen in scattered small sections, are generally grey in colour and commonly contain ironstone bands and nodules. Non-marine lamellibranchs, in a similar position to those recorded in Smeekley No. 3 Borehole (Eden and others 1957, pp. 23, 218), have been found in the banks of the River Hipper at two localities. North of Harewood Grange, 5 ft of grey shale with numerous ironstone bands immediately below the Rough Rock [SK 3113 6831] have yielded: Spirorbis sp., Anthraconaia angulosa Pastiels, Carbonicola exporrecta Eagar, C. cf. protea Wright, C. sp. cf. rhomboidalis Hind, Naiadites sp., Geisina arcuata (Bean). Spores from this and nearby localities are listed by Neves (1961, pp. 249, 269). The 3 ft of dark shale with ironstone nodules, lying close below the Pot Clay at a locality [SK 3324 6844] 1010 yd N. 3° E. of Stonehay Farm, yielded: Spirorbis sp., Carbonicola exporrecta, C. cf. protea; G. arcuata. Sixty yards east of this exposure W. Gibson saw 'mussels' in the shale beneath the Pot Clay, but the exposure is now overgrown. The fauna from these exposures was identified by Mr. M. A. Calver, who compares it with that described from above the Sand Rock Mine of Lancashire (Eagar 1952); several of the shells can be matched withthose figured by Eagar (figs. 3 and 4). The A. angulosa is an interesting occurrence since Anthraconaia is rare in the Millstone Grit. E.G.S.

South of Ashover the upper part of the G. cancellatum Marine Band was proved in Walnut Opencast Site C11 Borehole [SK 3636 6013], drilled on the north bank of Carr Brook, 1970 yd N. 86° E. of the eastern corner of the Butterley Reservoir. The fossils, encountered between 24 and 28 ft from the surface, include Dunbarella elegans (Jackson), C. multirugata, Agastrioceras carinatum, G. cf. crencellatum, G. cf. rurae Schmidt, G. sp. [fragments with cancellate ornament], and conodonts including Hindeodella sp.

North-north-west of the Crich Anticline the shales are visible in streams to the north-east and east of Lea Hall. The G. cancellatum Marine Band is not exposed, but shale containing Lingula mytilloides is seen [SK 3358 5770] close above the ganister topping the Redmires Flags, 350 yd N.W. of the Hall. The G. cumbriense horizon occurs in the stream bank [SK 3353 5737], 220 yd S.E. of the Hall, and the following fauna was obtained: Caneyella sp. [juv.]; Anthracoceras sp., G. crenulatum Bisat, G. cumbriense, Homoceratoides aff. divaricatus; and a Palaeoniscid scale. The fossils occur in dark grey silty shale above a thin fine-grained sandstone, of which 5 ft are exposed a few yards downstream. Lea Hall Borehole (p. 345), sited just below the feature formed by this sandstone, proved the top of the Redmires Flags at 52 ft, making the G. cumbriense Marine Band here about 60 ft above the flags.

In Calow No. 1 Borehole the shales between the Redmires Flags and the Rough Rock are a little over 100 ft thick (p. 309). The G. cancellatum Marine Band at the base contains the upper or G. crencellatum fauna: Crurithyris sp., Caneyella multirugata, Dunbarella elegans; Agastrioceras carinatum, G. crencellatum; and Acanthodian scales. The 42 ft of beds between the Gcancellatum and G. cumbriense bands contain Naiadites sp. (subtruncatus/productus group) and fragments of Carbonicola? in their upper part. The G. cumbriense Band yielded Dunbarella sp., an indeterminate Nautiloid, Anthracoceras?, G. cf. crenulatum, G. cumbriense and, in a 4-in band of dark grey silty mudstone at the base, Lingula naytilloides. G.H.R.

Rough Rock

A feature which is rarely well marked can be traced at this horizon from the northern boundary of the district to a point in Chatsworth Park about 0.75 mile S. of the Chesterfield-Baslow road. There are no exposures, but the size of the feature suggests a thickness of up to 25 ft for the Rough Rock. R.A.E.

Between Beeley Moor and Harewood Grange the presence of sandy beds is indicated by a feature on the slope above the Redmires Flags. Recent trial pits to the Pot Clay have proved the feature to be formed by the Rough Rock. It is exposed in the bed of the River Hipper [SK 3113 6831], 350 yd N. of Harewood Grange, where 9 ft of soft micaceous siltstone and silty sandstone may be seen. East of the river a poor feature indicating the horizon of the Rough Rock may be traced for 550 yd. No Rough Rock is recorded in Whispering Well Borehole where there are 76 ft of shale between the Redmires Flags and the Pot Clay. E.G.S.

North-east of Ashover the Rough Rock forms a small but marked feature, extending for over a mile to the west and south of Alton. The only exposure is on the southwest side of the village where, in the small opencast working [SK 3607 6420] the Pot Clay ganister (see p. 236) can be seen to pass down into fairly massive sandstone. North of the village, Northedge Borehole, Northedge New Bore and Press No. 3 Borehole have proved 13 to 38 ft of probable Rough Rock. G.H.R.

A feature formed by the Rough Rock extends southwards from near Mather's Grave [SK 360 590] to the district boundary, a distance of over 2.5 miles. The only exposures are in the stream [SK 3547 5593], about 100 yd S. of Hollins Farm, where hard brown flaggy sandstone lies near the base of the feature, and in the stream [SK 3514 5693], about 500 yd N.E. of Plaistow, where a similar rock is seen dipping at 50° to the south-west. G.H.R., P.M.D.D.

To the east, the Rough Rock has been proved in several boreholes drilled through the Coal Measures cover, though it is absent in Linacre Borehole. In Calow No. 1 Borehole (p. 309), in the north, it is 40 ft thick though much of the sandstone contains partings of grey micaceous silty mudstone. In the Clay Cross Borehole (p. 311) it is nearly 70 ft thick, including bands of shale and silty shale. In Morton Colliery Borehole (p. 351) siltstone bands occur in the 39 ft of sandstone proved beneath the Pot Clay Marine Band. Alfreton Colliery (1952) and Wingfield Manor underground boreholes proved respectively 33.5 ft and 59.5 ft of mainly sandy beds at what is probably the Rough Rock horizon. These thicknesses include a seatearth or ganister in a similar position to the Sand Rock Mine of Lancashire. At Alfreton a 2-ft seatearth is recorded 10.25 ft below the top of the sandstone, and at Wingfield Manor there are 15 in of ganister 12.5 ft below the top. No non-marine lamellibranchs are recorded at this horizon from these boreholes. G.H.R.

The Pot Clay and Pot Clay Coal have generally been seen in sections which include the overlying Pot Clay Marine Band marking the base of the Coal Measures. Details of these sections are given with the descriptions of the marine band on p. 100. In addition, the Pot Clay fireclay has been recorded at Old Cathole Clay Mine [SK 3316 6841] (abandoned 1930), 1000 yd N. of Stonehay Farm, where a general section from the workings is: shale on 30 in of clay and cank '. The Pot Clay ganister has been worked at Stubben Edge Ganister Mine [SK 3642 6370] (abandoned 1937) where one section gives ganister 4 ft on fireclay 6 in, and another, soft bind 15 in, ganister 4.5 ft, on fireclay. G.H.R., E.G.S.

References

BISAT, W. S. 1940. An early Gastrioceras (G. branneroides sp. nov.) from North. Wales. Trans. Leeds Geol. Assoc., 5, 330–5.

BRUNSTROM, R. G. W. 1964. Recently discovered oilfields in Britain. Proc. 6th World Petroleum Congress, 1, 11–20.

EAGAR, R. M. C. 1952. Growth and variation in the non-marine lamellibranch fauna above the Sand Rock Mine of the Lancashire Millstone Grit. Quart. J. Geol. Soc., 107, 339–73.

EDEN, R. A., STEVENSON, I. P. and EDWARDS, W. 1957. Geology of the country around Sheffield. Mem. Geol. Surv.

GIBSON, W. and WEDD, C. B. 1913. The geology of the northern part of the Derbyshire Coalfield and bordering tracts. Mem. Geol. Surv.

GILLIGAN, A. 1920. The petrography of the Millstone Grit of Yorkshire. Quart. J. Geol. Soc., 75, 251–94.

HESTER, S. W. 1932. The Millstone Grit succession in North Staffordshire. Sum. Prog. Geol. Surv. for 1931, Part II, 34–48.

LEES, G. M. and TALTT, A. H. 1946. The geological results of the search for oilfields in Great Britain. Quart. J. Geol. Soc., 101 for 1945, 255–317.

NEVES, R. 1961. Namurian plant spores from the southern Pennines, England. Palaeontology, 4, 247–79.

PULFREY, W. 1934. A boring in the Millstone Grits, Rod Moor, Sheffield. Proc. Yorks. Geol. Soc., 22, 254–64.

RAMSBOTTOM, W. H. C., RHYS, G. H. and SMITH, E. G. 1962. Boreholes in the Carboniferous rocks of the Ashover District, Derbyshire. Bull. Geol. Surv., No. 19, 75–168.

STEPHENS, J. V., MITCHELL, G. H. and EDWARDS, W. 1953. Geology of the country between Bradford and Skipton. Mem. Geol. Surv.

SWEETING, G. S. 1946. An outline of the geology of Ashover, Derbyshire. Proc. Geol. Assoc., 57, 117–36.

TRUEMAN, A. E. 1929. Some new Carboniferous lamellibranchs. Ann. Mag. Nat. Hist. (10), 4, 82–95.

Chapter 4 Coal Measures: general account

Introduction

In the Chesterfield district the Coal Measures crop out in a belt some twelve and a half miles wide in the north and about eight miles in the south. They conformably succeed the rocks of the Millstone Grit Series which crop out to the west, and are unconformably overlain by Permian rocks over an area of some fifty-five square miles in the east. The latter area forms part of the Yorkshire–Nottinghamshire Concealed Coalfield. The maximum thickness of the Coal Measures is estimated to be between 4000 and 4500 ft in the northeast of the district. In the Lower and Middle Coal Measures there is evidence of attenuation towards the east and south. The measures consist chiefly of mudstones with beds of siltstone and sandstone and numerous coal seams, and throughout show a monotonously repetitive sequence of sedimentary cycles. Deposition of the elastic rocks is considered to have taken place in water which was for the most part shallow, usually fresh or brackish and only occasionally in direct contact with the sea.

Lithology

The rocks constituting the Coal Measures can be conveniently described in terms of the sedimentary cycle, or cyclothem (see for instance. Wanless and Weller 1932, p. 1003; Edwards and Stubblefield 1948, p. 212). A fully developed cycle may be considered as comprising in upward succession: dark mudstone, marine at or near the base; grey mudstone, becoming silty; siltstone or sandstone; seatearth; coal. One or more of the phases may be absent, but the seatearth and grey mudstone are usually present. Cycles may be of any thickness up to 200 ft or more, but the average is 30 to 40 ft: most are widespread, especially the ones containing marine beds, but wedging out is not uncommon.

The mudstones, generally dark grey or even black at the base of a cycle, become progressively paler and more silty upwards until they pass into, or are overlain by, sandstones. Most of the animal fossils are contained in the lower mudstones and they tend to occur in an ordered sequence (Robertson 1932, p. 163; Pastiels 1956), The most important animal fossils, apart from marine forms, are non-marine lamellibranchs or 'mussels' (see pp. 87–89). Plant remains may be found anywhere in the mudstone phase, but they are most abundant and best preserved in the grey mudstones, silty mudstones and siltstones.

In some cycles sandstones are rarely or never present, but in others they are persistent, as, for example, is the case with the Crawshaw Sandstone and Wingfield Flags. Generally speaking, however, the development of sandstone is extremely variable and most of the beds are flattened lenses. Sandstones may die out by lateral passage through silty beds into mudstone, or they may wedge out. Wedging out may be sudden with a thick sandstone disappearing in a few yards, a phenomenon seen to advantage in opencast coal excavations in progress at the time of the resurvey. There may be upward passage between the mudstone and sandstone phases of a cycle, or the sandstone base may be abrupt. In the latter case downward transgression is common, and may extend far enough to 'wash out' the coal seam at the top of the cycle below. Most of the Coal Measures sandstones are fine grained and contain argillaceous bands and partings and carbonaceous micaceous laminae which weather rapidly on exposure, giving rise to flags. Some sandstones contain coarse and, in a few instances, conglomeratic bands, but only the Crawshaw Sandstone is typically coarse grained. Fossils in the sandstone phase consist chiefly of plants, which are represented by Calamites and other stems, and comminuted debris.

Seatearths consist of unbedded fireclays, mudstones, silty mudstones, siltstones and sandstones, which normally contain abundant Stigmarian and other roots. Clayey types are by far the commonest and these usually show the effects of leaching from the top and iron-enrichment in the lower parts. Only a few clayey seatearths are refractory fireclays, and only a few of the sandy seatearths in the lowest few hundred feet of the succession are ganisters.

About eighty coal seams have been proved in the Chesterfield district. Many of these are thin and of no economic importance, but about thirty seams, half of them more than a yard thick over wide areas, have been worked in one part or another of the district. Physically and chemically the coals are typical bituminous coals. Dirt partings are common, and bands of cannel are developed in places. Thicknesses of coal seams tend to be fairly constant over considerable areas, but are subject to regional variation as the isopachs in (Figure 13)." data-name="images/P990902.jpg">(Figure 12), (Figure 15)." data-name="images/P990904.jpg">(Figure 14), (Figure 18). For sections at lettered localities see (Figure 17)." data-name="images/P990906.jpg">(Figure 16), (Figure 20)." data-name="images/P990909.jpg">(Figure 19), (Figure 25). Dotted lines outside outcrop are conjectural indications of links between isolated areas." data-name="images/P990914.jpg">(Figure 24), (Figure 27), (Figure 29). Dotted lines outside outcrop are conjectural indications of links between isolated areas." data-name="images/P990918.jpg">(Figure 28), (Figure 31)." data-name="images/P990920.jpg">(Figure 30), (Figure 31) showThe isopachs in these figures are based on the coal content of the seams, and do not include dirt layers.. Similarly the physical characters of individual seams, such as the pattern of bright and dull bands and the number and thickness of dirt partings, are recognizable over wide areas—see (Figure 13), (Figure 15), (Figure 17), (Figure 18), (Figure 20), (Figure 22), (Figure 25), (Figure 26), (Figure 29). Dirt partings may swell out and become many feet of measures, splitting the seam into two or more beds which may continue as seams in their own rights (the Low Tupton and Cockleshell are produced from the Tupton in this way, see pp. 131–134). Coals may deteriorate laterally becoming thin and dirty, or they may even disappear—see for instance the First Ell Coal (p. 159).

'Washouts' are areas where the coal has been removed and its place taken by downward transgressing roof measures, commonly sandstone, though in places siltstone or silty mudstone may be involved. They are common in two seams, the Deep Hard (pp. 141–145, (Figure 20)." data-name="images/P990909.jpg">(Figure 19)), and the Top Hard (pp. 169–172, (Figure 29). Dotted lines outside outcrop are conjectural indications of links between isolated areas." data-name="images/P990918.jpg">(Figure 28)), both of which have persistent sandstone horizons close above. The washouts tend to be large, and, in plan, show elongation in a north-easterly direction.

Ironstone is found in all phases of the cycle. In the mudstones it occurs as nodules, lenses and bands which are normally sideritic (clay-ironstones), but the 'Mansfield Cank' (see p. 185) is ankeritic. Most is found in the non-marine mudstones, and the bands and nodules therefore commonly contain non-marine lamellibranchs. Oolitic ironstone is found locally in the argillaceous measures overlying coals and seatearths. Sporadic sideritic concretions occur in the sandstones, and almost invariably nodules occur in the lower parts of seatearths, some of which contain abundant sphaerosiderite. Pyrite occurs in many coals, especially those with marine roofs.

The Coal Measures immediately below the Permian unconformity show secondary reddeningThe term 'reddening' is used in a loose sense to connote a red, pink, purple or brown colouration. Reddening in places affects the whole of a bed but more commonly occurs as mottling and banding. Green mottling and banding also occur in association with the reddening.. In places this may extend down as far as 60 ft, but on average to only 25 ft, and is thus similar to the occurrence of reddening described by Anderson and Dunham (1953) in Durham and Northumberland. The phenomenon is considered to be due largely to partial oxidation by weathering of the sub-Permian surface rather than to staining by iron-bearing solutions percolating downwards from the Permo-Triassic rocks, for the argillaceous rocks are more affected than are the arenaceous (see Trotter 1953, pp. 10–12). The oldest measures affected are at the 2nd Waterloo horizon below the Permian outlier at Whiteborough, near Tibshelf.

Classification

The Coal Measures have been divided into zones on the basis of their non-marine lamellibranch content (Figure 8) and their flora (Dix 1933; Crookall 1955). Recent interest in plants for classification purposes has been concentrated on microspores, and six microspore zones have been erected for the British Coal Measures (Butterworth and Millott 1960).

It has long been Geological Survey practice to separate the Coal Measures of England and Wales into upper, middle and lower divisions. In the previous memoir covering the Chesterfield district, Gibson and Wedd (1913, p. 46) followed Green, Russell and others (1878, pp. 75–6) in using the term 'Upper Coal Measures' to denote red beds, and dividing the underlying grey beds at the Silkstone Coal. The latter boundary between Middle and Lower Coal Measures was in use until recently (Eden and others 1957, pp. 27–9), but this classification has now been abandoned in favour of one applicable to other British coalfields (Stubblefield and Trotter 1957). This uses the top of the Top (Anthracoceras cambriense) Marine Band and the base of the Clay Cross (A. vanderbeckei) Marine Band to divide the Coal Measures into Upper, Middle and Lower divisions. The base of the Pot Clay (Gastrioceras subcrenatum) Marine Band is in general use as the basal boundary of the Lower Coal Measures. E.G.S.

Stratigraphy

The following brief account, which should be read in conjunction with (Figure 8), deals with the main features of the stratigraphy of the Coal Measures. For a more detailed description see Chapter V, pp. 100–193.

Lower Coal Measures

Measures between Pot Clay Marine Band and Kilburn Coal

This group varies in thickness from about 650 to 740 ft, the thinner sections occurring in the south and east. The lower half of the group includes several coals of which only the Alton, between 3 and 4 ft thick in certain localities in the west, is of appreciable thickness. Associated with the majority of the coals are the ganisters and fireclays below and the marine fossils commonly found in the shales above. Goniatites are present in the Pot Clay (Gastrioceras subcrenatum) Marine Band and in the Alton (G. listeri) Marine Band; the other marine bands commonly contain only Lingula. Non-marine lamellibranchs are not numerous, the best-known horizons being above the Belperlawn and Norton coals (see p. 115). There are several prominent sandstones in these lower measures, the most notable being the Crawshaw Sandstone and the sandstone immediately below the Forty-Yards Coal—the local equivalent of the Loxley Edge Rock of the Sheffield district. The upper half of this group—above the horizon of the Upper Band Coal—comprises argillaceous beds below, and mainly sandy beds, including the Wingfield Flags, above.

Measures between Kilburn and Blackshale coals

These vary in thickness from about 450 to 550 ft with the thicker sections occurring in the northwest. The group includes many coals, most of which are thin, and an alternation of flaggy sandstones (most prominent in the north) and shales. Of the named coals the Kilburn, over 3 ft in the south-west where it has been worked, and the ?Mickley Thin, locally nearly 3 ft thick though generally less than 2 ft, are the most important. Marine fossils have been found at only one locality, where Lingula has been recorded in the roof-measures of the Kilburn Coal. Non-marine lamellibranchs are numerous above the Mickley Thin Coal and are found sparingly at other horizons.

Measures between Blackshale Coal and Clay Cross Marine Band

These are about 460 to 490 ft thick. The variation in thickness is irregular but in general the measures thin to the east. The named coals include, in upward succession, the Blackshale, Yard, Threequarters, Tupton, Piper, Deep Hard, Deep Soft, Sitwell and Chavery, and it was upon the more important of these-the Blackshale, Tupton and Deep Hard coals-that the mining industry around Chesterfield was originally based. The Blackshale is 3.5 to 4 ft thick in the west where it has been worked extensively; it thins to the east and is little more than 2 ft thick in the south-east. In the extreme north-west the Blackshale and Yard are united to form the Silkstone Coal. The Yard, generally a dirty coal up to 3 ft thick, has been mined on a small scale in several areas, mainly in the south. The Threequarters, over 3 ft thick in the north, and between 2 and 3 ft elsewhere, has been worked extensively in the west. The Tupton, which has a maximum local thickness of nearly 7 ft in the north of its field and thins to a little over 3 ft in the south-east, splits northwards into the Low Tupton and the Cockleshell coals. The Low Tupton is up to 4 ft thick near the line of union with the Cockleshell but thins northwards to less than 1 ft; the Cockleshell has a maximum thickness of 2 ft and varies irregularly down to a few inches. The Piper, which has been worked underground on a limited scale, is present as a single seam only to the west of the Brimington Anticline where, in isolated sections, it comprises up to 18 ft of coal and dirt; elsewhere it divides into Second and First Piper coals. The Second Piper is developed chiefly in the north where it has been worked at outcrop around the Brimington Anticline and locally underground. The First Piper has been widely worked at outcrop, but underground workings are mainly in the south. The Deep Hard has been worked extensively, particularly in the west where it is up to 7 ft thick and includes a Roof Coal; in the east the Roof Coal is widely separated from the rest of the seam which thins to about 2 ft in the extreme south-east. The Deep Soft, absent or represented by two thin seams in the north, is over 4 ft thick in the south where it has been worked. The Sitwell contains up to 5 ft of coal in the northwest but less than 2 ft in the south and east. In the north the Sitwell unites with the Chavery to form the Clay Cross Soft, comprising up to 11 ft of coal and dirt, the lower part of which has been worked in the west. The Chavery is of significant thickness only in the north-west where it includes 3 to 4 ft of coal and a variable thickness of dirt.

Sandstones are common in this group though they are normally thin and local in development; thick sandstones of wide extent are found only above the Tupton and Deep Hard coals. Ironstones occur widely in the argillaceous rocks and their concentration at certain horizons gives rise to the 'rakes', the most prominent of which are: the Blackshale Rake above the Yard Coal; the Dogtooth Rake in the measures between the Cockleshell (or Tupton) and the Piper group of coals; and the Pinder Park Rake in the measures between the Chavery Coal and the Clay Cross Marine Band. Non-marine lamellibranchs are present in great numbers above the Cockleshell (or Tupton) and Chavery coals and are also found, though less abundantly, at many other horizons.

Middle Coal Measures

Measures between Clay Cross Marine Band and Top Hard Coal

This group varies in thickness between about 425 and about 525 ft, being thickest in the north. The named coals in upward succession are the Second and First Ells, the Fourth, Third and Second Waterloos, the Waterloo Marker, the First Waterloo and the Dunsil. The Second Ell Coal is up to 4 ft thick in the north, where it has been worked underground; but to the south it is less than 2 ft over a wide area. The First Ell is up to 2.5 ft thick in the north-west, but elsewhere is thin or, in a few instances, absent. It has been worked only at outcrop in opencast sites. The Fourth and Third Waterloo coals are of local importance in the south-west where they are very variable in thickness; in the north they cannot be recognized with any certainty. The Second Waterloo has been worked extensively both underground and at outcrop; it is divisible into two parts which in several areas diverge widely and can be considered as separate seams—the Bottom and Top Second Waterloos. The former varies in thickness up to about 2.5 ft, and the latter up to about 5 ft. The Waterloo Marker Coal is a thin seam of no significance except, as its name indicates, as a marker horizon. The First Waterloo Coal is up to 5.5 ft thick, and like the Second Waterloo consists essentially of two parts; these may be up to 40 ft apart in the east and south where they are separately named the Bottom and Top First Waterloo. The seam has been extensively worked opencast, but underground workings are confined to the north-west where the combined seam and, over a limited area, the Bottom First Waterloo have been mined from a number of collieries. The Dunsil Coal has been worked extensively in the south where it is up to 4 ft in thickness, but in the north, where it is split, it is of little value.

The measures between the coals are largely argillaceous. Impersistent bands of sandstone occur throughout the succession but none is of any great importance. Ironstones occur abundantly at a number of horizons and have been worked locally. There is only one marine band in the group—the Clay Cross, at the base—but there are numerous non-marine lamellibranch bands.

Measures between Top Hard Coal and Mansfield Marine Band

This group varies in thickness between about 650 and 1050 ft, the thicker sections being in the north. The named horizons are, in ascending order: Top Hard Coal, Comb Coal, Second and First St. John's coals, High Hazles Coal, Furnace Coal, Two-Foot Coal, Two-Foot Marine Band, Mainbright Coal, Manton 'Estheria' Band, Clown Coal, Clown Marine Band, Swinton Pottery Coal with overlying Haughton Marine Band, Sutton Marine Band.

The Top Hard Coal, averaging 5 to 6 ft in thickness, was formerly the most important seam in the district, but is now largely worked out. In the south the Comb Coal, between 1 and 3 ft thick, lies from a few inches to about 50 ft above the Top Hard and is sometimes worked in association with it. The St. John's coals are thin except in the extreme north where they are worked locally. The First St. John's is a split seam over most of its field. The High Hazles Coal is worked in the north-east and at outcrop; it is, in general, 2 to 4 ft thick in the north and 1.5 to 2 ft thick in the south. The Furnace Coal, called the Lowbright in the south, is in most sections between 2 and 3.5 ft in thickness, but is often of inferior quality and has been worked only by opencast methods. The Two-Foot Coal, which is everywhere overlain by the Two-Foot Marine Band, is thin in the south, and in the north is spoiled by the presence of a thick dirt band in the middle. The Mainbright Coal is worthless except in the north-east where it is up to 5 ft thick and contains less dirt than elsewhere. 'Estheria' is found above the Mainbright Coal at a number of localities, but the chief occurrence of this fossil in this group of measures is in the Manton 'Estheria' Band, a thin band of dark shale above a seatearth between the Mainbright and Clown coals. The Clown Coal, with the intermittently developed Clown Marine Band immediately above it, is of little importance in the south, but in the north, where it is up to 5 ft thick in recorded sections, there are likely to be large workable reserves. The Swinton Pottery Coal is thin and locally dirty, and has nowhere been worked. A few feet above it lies the Haughton Marine Band, 16 to 34.5 ft thick but with a sparse fauna. The Sutton Marine Band, which lies roughly one third of the distance up from the Haughton to the Mansfield Marine Band, has been found at only five localities, all in the north of the area.

Sandstone occurs at a number of horizons in these measures, the most notable and persistent bands being those above the Top Hard, High Hazles and Clown coals.

Measures between Mansfield Marine Band and Top Marine Band

This group is estimated to be 550 to 600 ft in thickness, the precise position of the Top Marine Band not being known.

The Mansfield Marine Band consists of 11 to 16.5 ft of dark mudstone with a rich marine fauna, and commonly contains the well-known 'Mansfield Cank' near its base. Towards the top of the known part of these measures lie the Edmondia Band and the Shafton Marine Band; between them 'Estheria' occurs at several horizons. The only coals of note in these measures are the Wales and the Highmain which lie between the Mansfield Marine Band and the Edmondia Band. The Wales is over 3 ft thick in the north-east where it is worked, but elsewhere is a thin, or split, seam. The Highmain is worked in the south, where it is 3 to 4 ft thick; in the north it is generally under 2 ft.

Sandstones are not prominent in these measures, and are notable only between the Wales and Highmain coals.

Upper Coal Measures

These measures lie entirely beneath a cover of Permo-Triassic rocks, and have not been provedNote. Since going to press the Top Marine Band and 323 ft of Upper Coal Measures have been proved in Cauldwell Borehole [SK 5249 5855] south-west of Mansfield and on the north side of the fault through Sutton in Ashfield and Stonehills (see p. 191). The cores were examined by Messrs. J. G. O. Smart, N. Aitkenhead and S. Brunskill, who report that the main part of the Top Marine Band is 10 ft 5 in thick and lies 632 ft 10 in from the surface and 346 ft above the Highmain Coal. It consists of dark mudstone from which Mr. M. A. Calver has identified the following fauna: foraminifera; Planolites ophthalmoides; Crurithyris sp., Lingula sp., Orbiculoidea sp., Dunbarella sp., Hollinella cf. bassleri; cf. Tomaculum sp. H. cf. bassleri is also recorded 23.25 ft higher, where it is associated with Curvirimula sp. The intervening measures, in which no marine fossils were observed, consist of grey silty mudstone and contain slump structures in parts. The Upper Coal Measures are largely argillaceous and are composed of about ten cycles, the majority of which have a few inches of coal; Anthraconauta phillipsii (Williamson) occurs at several levels. E.G.S.. It is calculated, however, that as much as 700 ft may be present in the south. E.G.S.

Palaeontology

The earliest detailed account of the distribution of the Coal Measures fossils in the district was given by Moysey (in Gibson and Wedd 1913, pp. 143–67). Moysey's list (ibid., p. 145) of the publications providing the source of many of his records, also gives the history of the earlier palaeontological investigations. Subsequently, the various editions of the memoir on the Concealed Coalfield, particularly the 3rd Edition (Edwards 1951), have all contained observations on the occurrence of the more important fossils. Moysey (ibid., p. 165) and Wilson (1926, p. 12) had advocated detailed study of the non-marine lamellibranchs as an aid to correlation of the local Coal Measures, and the value of this was borne out by the investigations of Clift and Trueman (1929). These authors demonstrated the application of the basis of the current zonal classification to the rocks of the Nottinghamshire–Derbyshire coalfield, and in so doing made several references to faunal horizons in the district. Details of the faunas of the Coal Measures marine bands at certain localities were discussed by Edwards and Stubblefield (1948); other faunal records from the lower part of the Lower Coal Measures were referred to by Eden (1954). In addition, several specimens of local non-marine lamellibranchs have been figured by Trueman and Weir (1946–56).

The present account is concerned with the characteristics and distribution of the main groups of fossils found in the Coal Measures of the Chesterfield district. The animal fossils are considered under the general headings of 'non-marine' and 'marine': a brief reference is also made to the fossil plants.

The classification of the Coal Measures and the zonal sequence based on the non-marine lamellibranchs is shown in (Figure 8). The main features of the faunal succession are summarized on pp. 95–97; details of individual bands, marine and non-marine, and discussion of their zonal significance are included in Chapter 5, pp. 100–191.

Non-marine fossils

Lamellibranchs

The non-marine lamellibranchs or 'mussels' are the typical animal fossils of the Coal Measures and when concentrated in relatively thin layers form the familiar 'mussel'-bands. The species are allocated to seven genera which have the following stratigraphical distribution (see also Calver 1955, fig. 3). Carbonicola is dominant in the main  'mussel'-bands of the Lower Coal Measures but is replaced a short distance below the horizon of the Clay Cross Marine Band by Anthracosia. This genus is characteristic of the lower part of the Middle Coal Measures but in turn disappears from the sequence just below the Haughton Marine Band. Anthracosphaerium first appears in the beds above the Blackshale Coal and occurs spasmodically at several horizons up to and including the  'mussel'-band overlying the Clown Coal. Anthraconaia is rare in the Lower Coal Measures except in the uppermost beds; the genus is fairly common in the lower and middle parts of the Middle Coal Measures, but restricted to a few distinct bands in the measures above the Mansfield Marine Band. Naiadites occurs throughout the Lower and Middle Coal Measures and is the dominant lamellibranch in the beds above the Mansfield Marine Band. Curvirimula is characteristic of the measures up to the Tupton Coal, but then disappears from the sequence to re-appear in the strata just below the Haughton Marine Band and in the upper part of the Edmondia Band. Anthraconauta has not been recognized, but this is explained by the fact that the proved succession does not include the Upper Coal Measures to which the genus is virtually confinedNote. Since going to press the Top Marine Band and 323 ft of Upper Coal Measures have been proved in Cauldwell Borehole [SK 5249 5855] south-west of Mansfield and on the north side of the fault through Sutton in Ashfield and Stonehills (see p. 191). The cores were examined by Messrs. J. G. O. Smart, N. Aitkenhead and S. Brunskill, who report that the main part of the Top Marine Band is 10 ft 5 in thick and lies 632 ft 10 in from the surface and 346 ft above the Highmain Coal. It consists of dark mudstone from which Mr. M. A. Calver has identified the following fauna: foraminifera; Planolites ophthalmoides; Crurithyris sp., Lingula sp., Orbiculoidea sp., Dunbarella sp., Hollinella cf. bassleri; cf. Tomaculum sp. H. cf. bassleri is also recorded 23.25 ft higher, where it is associated with Curvirimula sp. The intervening measures, in which no marine fossils were observed, consist of grey silty mudstone and contain slump structures in parts. The Upper Coal Measures are largely argillaceous and are composed of about ten cycles, the majority of which have a few inches of coal; Anthraconauta phillipsii (Williamson) occurs at several levels. E.G.S.. However, shells which are homoeomorphs of small Anthraconauta phillipsii (Williamson) are found in assemblages of juvenile Naiadites just below the Haughton Marine Band and below the Edmondia Band.

The 'mussels' inhabited the relatively shallow tracts of water which spread over extensive areas consequent upon the drowning of the Coal Measures forests. Although much information has been assembled in recent years on the palaeoecology of the 'mussel'-bands there is still doubt as to the precise nature of the conditions under which the various genera lived. The mutual exclusion of the 'mussels' and typical marine fossils is generally accepted as evidence that the habitat of the 'mussels' was not marine (Trueman 1946, p. lxii). But whether they favoured a fresh-water or brackish environment is not yet established, although it is evident that the salinity ranges of the different genera varied (Weir 1945). This is borne out by the relative position of the different genera in the sequence of faunal phases corresponding to the progress of the sedimentary cycle, particularly their relationship to the marine incursions. The evidence suggests that the habitat of Curvirimula, and Naiadites to a lesser degree, approached closest to marine conditions. Also, although the majority of Anthraconaia spp.are typical of the non-marine sediments, the more elongate forms are commonly found in the closing stages of a marine incursion at the transition to the non-marine environment, e.g. cf. Anthraconaia pruvosti (Weir and Leitch) of the Shafton Marine Band. Carbonicola, from ifs frequent association with Curvirimula and the ostracod Geisina arcuata (Bean), seems to have favoured slightly more saline conditions than Anthracosia and Anthracosphaerium. Thus the non-marine phases of the Middle Coal Measures may have been less subject to marine influence than those of the Lower Coal Measures; this accords with the progress of the gradually changing environment in the transition from the predominantly marine Millstone Grit to that of the Upper Coal Measures in which no marine bands are known and in which the lamellibranch fauna is restricted to Anthraconauta and rare Anthraconaia. In addition to variations in tolerance of salinity, other factors such as food supply, bottom conditions and sedimentation affected the distribution and abundance of the various genera; these and other factors have recently been reviewed by Eagar (1960).

Anthropods

The commonest arthropods are the ostracod crustaceans represented in the 'mussel'-bands by Geisina and Carbonita. These genera may occur intimately associated with the lamellibranchs or in distinct layers within the detailed faunal profile of individual 'mussel'-bands. In addition, Geisina is commonly found in beds adjacent to the marine bands. The species G. arcuata is virtually confined to the Lower Coal Measures although stunted or immature forms appear in the upper part of the Clay Cross Marine Band and in the basal layers of the overlying 'mussel'-band (p. 157). The genus is then absent from the sequence up to the horizon of the Two-Foot Marine Band where specimens closely related to G. arcuata are found associated with the marine fossils. The next appearance of the genus is represented by G. subarcuata (Jones) which occurs in the beds above the Highmain Coal and the overlying faunal bands, including the highest part of the Edmondia Band. This close association of Geisina with certain of the Middle Coal Measures marine bands, and its absence from much of the intervening measures suggests a preference for a more saline habitat than that of the Middle Coal Measures 'mussel'-bands. On the other hand Carbonita is known throughout the Coal Measures and, although recorded at some horizons in close association with G. arcuata, it is seldom found in beds near to marine strata. The general inference to be drawn from its associations and occurrence is that Carbonita favours a less saline environment than Geisina. The common Carbonita species is C. humilis (Jones and Kirkby), although forms recalling C. salteriana (Jones) occur at several horizons.

Of the other crustacea only 'Estheria' assumes any importance. These fossils have not been found in the Lower Coal Measures of the district except at the extreme top where they occur at some localities immediately below the Clay Cross Marine Band. In the Middle Coal Measures 'Estheria' is known rarely between the Top Hard and Second St. John's coals, but is more common between the Two-Foot and Clown coals, particularly in the Manton 'Estheria' Band, a valuable marker horizon in the East Pennine Coalfield. Apart from a few records between the Sutton and Mansfield marine bands, the next appearance in any numbers is in the beds between the Edmondia Band and Shafton Marine Band. The mode of occurrence of these fossils is usually as iridescent films; although this preservation is characteristic in itself, the generic and specific identity can rarely be established and in these circumstances the non-committal designation 'Estheria' is employed. At some horizons they are sufficiently well preserved to suggest comparison with Lioestheria vinti (Kirkby), originally described from the top of the Upper similis-pulchra Zone of the Durham Coalfield (Kirkby 1864). The tendency for 'Estheria' to occur in bands at discrete horizons is analogous to the behaviour of the marine bands. This similarity is emphasized by the common occurrence of 'Estheria' in beds immediately preceding a marine incursion or associated with marine strata. The presence of 'Estheria' in the sequence seems to have been dependent on the existence of special conditions for comparatively short periods, and suggest that 'Estheria' was not part of the endemic fauna of the Coal Measures swamps (Defrise-Gussenhoven and Pastiels 1957, p. 65).

Its most likely habitat was in the brackish regions between the marine areas and the non-marine lamellibranch environment. At times of excessive subsidence or comparable eustatic change the 'Estheria' facies moved into the swamps, replacing temporarily the normal non-marine fauna, and, on the occasions when subsidence continued, to be replaced in turn by the marine incursion.

Specimens originally described as Estheria striata binneyana by T. R. Jones (1862) are stated to have been obtained from an horizon between the Whin-moor and Blackshale coals in an ironstone pit at Lowndsley Green, Chesterfield. As noted by Weir (1960, p. 304) these specimens are more likely to be the lamellibranch Curvirimula, although the horizon cannot be far below the position of the Low 'Estheria' Band of adjacent areas.

The crustacean Anthrapalaemon is known from a 'mussel'-band just below the Clay Cross Marine Band, and is recorded together with Arthropleura armata Jordan and Cyclus sp. from the measures between the Deep Hard and Silkstone coals of Bond's Main Colliery, which measures are also the source of an example of Belinurus and the arachnids Anthracosiro fritschi Pocock and Trigonotarbus? (Moysey in Gibson and Wedd 1913, pp. 147–67). Moysey gave further records of arthropoda from the district, the many clay-pits then being worked providing a fruitful source of the ironstone nodules upon which intense collecting activities were concentrated.

Worms

The only definite worm known from the Coal Measures is the serpulid Spirorbis, but certain trace-fossils are attributed to the activity of worms and interpreted as burrows or trails.

The coiled tubes of Spirorbis occur commonly attached to Naiadites and have also been noted on Anthracosia and Carbonicola; they are rarely found on the shells of Anthraconaia, Anthracosphaerium and Curvirimula. They may also occur isolated or adhering to plant debris. Although the above instances are typical of the non-marine environment, Spirorbis has also been found at several localities in the Clay Cross Marine Band attached to Dunbarella ((Plate 5), fig. 19). The trace-fossils, which are usually found in smooth mudstone or slightly silty mudstone, are only rarely associated with other fossils. The sinuous markings referred to Cochlichnus [Belorhaphe] kochi (Ludwig) and interpreted as locomotion trails are notably found in the C. communis Zone, in the measures above the High Hazles Coal and also in the beds overlying the Mansfield Marine Band. A similar preservation and facies is shown by the vague strap-like markings with, a central longitudinal depression which are referred to Gyrochorte carbonaria Schleicher; they lie on the bedding plane and may be collapsed horizontal burrows. The structures named as Planolites montanus Richter are the so-called 'wormy beds' and represent the fillings of burrows of irregular course and direction; they are preserved in ironstone and confined to non-marine strata. On the other hand, the inclined tube-like burrows of Planolites ophthalmoides Jessen are usually associated with marine incursions (see below), but they have also been noted rarely in apparently non-marine strata in the C. communis Zone. More common in these beds are similar but smaller markings [1.0 to 2.0 mm], with a sharply defined outer margin, which are thought to be distinct from P. ophthalmoides and are referred to in the memoir as cf. Planolites (see also Woodland and others 1957, p. 55).

Fish

Fish remains, mainly isolated scales but including teeth and spines, are found most commonly in the roofs of the coals, particularly where the beds are cannelly. Scattered scales also occur throughout the argillaceous part of the cycle, the common genera such as Elonichthys, Megalichthys, Rhabdoderma, Rhadinichthys, Rhizodopsis and undetermined Acanthodians and Platysomids being found in both marine and non-marine strata. The only fish remains found exclusively in non-marine sediments, either in isolation or with plants or 'mussels', are the Elasmobranch egg-capsules Fayolia, Palaeoxyris and Vetacapsula. Palaeoxyris helicteroides (Morris) is known from several localities in the measures between the 'Waterloo' and Top Hard coals; V. johnsoni (Kidston) and V. cooperi Mackie and Crocker are recorded from above the Dunsil Coal and from an horizon between the Deep Hard and Silkstone coals respectively (Crookall 1928, p. 92). Further records of the distribution of individual species are given by Moysey (in Gibson and Wedd 1913, pp. 155, 165). The beds above the Kilburn are notable for the abundance of well-preserved fish remains; other prominent fish horizons are the Manton 'Estheria' Band and the roof measures of the Clown Coal.

Marine fossils

Apart from the Top Marine BandNote. Since going to press the Top Marine Band and 323 ft of Upper Coal Measures have been proved in Cauldwell Borehole [SK 5249 5855] south-west of Mansfield and on the north side of the fault through Sutton in Ashfield and Stonehills (see p. 191). The cores were examined by Messrs. J. G. O. Smart, N. Aitkenhead and S. Brunskill, who report that the main part of the Top Marine Band is 10 ft 5 in thick and lies 632 ft 10 in from the surface and 346 ft above the Highmain Coal. It consists of dark mudstone from which Mr. M. A. Calver has identified the following fauna: foraminifera; Planolites ophthalmoides; Crurithyris sp., Lingula sp., Orbiculoidea sp., Dunbarella sp., Hollinella cf. bassleri; cf. Tomaculum sp. H. cf. bassleri is also recorded 23.25 ft higher, where it is associated with Curvirimula sp. The intervening measures, in which no marine fossils were observed, consist of grey silty mudstone and contain slump structures in parts. The Upper Coal Measures are largely argillaceous and are composed of about ten cycles, the majority of which have a few inches of coal; Anthraconauta phillipsii (Williamson) occurs at several levels. E.G.S. the full number of marine horizons known from the East Pennine Coalfield has been proved in the district (see Figs. 8, 9). In addition there is the record of Lingula from a short distance above the Kilburn horizon at one locality (p. 121). The Low 'Estheria' Band has not been recorded, but in the neighbourhood of Nottingham this horizon has been found exceptionally to contain Lingula and foraminifera (Edwards 1953, p. 30). The following comments summarize the main features shown by the marine faunas in the district.

The faunas vary from the rich goniatiteflamellibranch assemblages of such horizons as the Pot Clay, Alton and Mansfield marine bands to the Lingula/ microfaunal associations typical of the minor marine bands at the base of the Coal Measures, e.g. Upper and Lower Parkhouse marine bands and the Forty-Yards Marine Band. In the Middle Coal Measures the Clay Cross and Two-Foot marine bands and the Edmondia Band contain, in addition to other fossils, a characteristic assemblage of Myalina, Hollinella and Paraparchites; these fossils are closely associated at some levels within individual bands with stunted non-marine lamellibranchs suggesting a less-saline environment at this period of deposition of the marine band. In thickness the bands vary from the few inches of the minor marine bands near the base of the Coal Measures to the order of 15 to 25 ft of the Mansfield and Haughton horizons.

The marine bands occur in the lower parts of the cycle, generally in the roof measures of the coal, or overlying the seatearth where coal is not developed. In some cases the marine fossils follow upon the coal seam but more usually the immediate roof of the coal contains only fish remains. In addition in several instances a brief non-marine phase with lamellibranchs and ostracods precedes the marine incursion, and exceptionally a layer with 'Estheria' intervenes between the lamellibranchs and the marine fossils. The distribution of the individual fossils within a marine band can be related to an ideal sequence of faunal phases, corresponding to stages in the development of the marine band and the regression to non-marine conditions. The successive stages are considered to reflect changes in salinity, but other factors such as depth of water and temperature may also be involved. There is usually some degree of overlap in the various faunal phases, and in certain marine bands some phases may not be developed, particularly at the base of the cycle. This absence and the fact that the richest fauna usually occurs in the lower part of the marine band suggest that the advance was more rapid than the retreat. It follows that the faunal phases are best illustrated by the regression sequence which occupy the middle and upper parts of the band. The faunal profile of each band, although conforming to the same general pattern, differs in detail and therefore tends to be distinctive. These individual differences persist over much of the district and examples of the detailed faunal sequence of many of the marine horizons are given in Chapter V. Typical marine fossils from the Coal Measures are illustrated on (Plate 5).

Excluding the preliminary stages referred to above, the ideal sequence of faunal phases in the development of a marine band and the return to non-marine conditions can be summarized as follows; the phases are indicated by their characteristic fossil or fauna, and are listed with the earliest at the base.

• 1 Planolites ophthalmoides—retreat
• 2 Foraminifera—retreat
• 3 Lingula—retreat
• 4 Cephalopod/lamellibranch acme
• 3 Lingula—advance
• 2 Foraminifera—advance
• 1 Planolites ophthalmoides—advance

A brief description of the characteristics of the individual phases is given below.

1. Planolites ophthalmoides phase

The burrows of this supposed worm typically occur in strata transitional from non-marine to marine conditions. This means that, although they may be found rarely associated with non-marine lamellibranchs, their appearance in any abundance is usually associated with the beginning and end of a marine incursion. The typical lithology is a smooth grey mudstone and the fossil is absent from carbonaceous or highly arenaceous beds. In the present district P. ophthalmoides is not common, the records being largely confined to the regression stage of the incursions, e.g. Haughton and Mansfield marine bands.

2. Foraminifera phase

Arenaceous foraminifera are abundant in most of the marine bands above the Alton horizon; they are represented by such genera as Ammodiscus, Ammonema, Agathammina, Glomospira, Glomospirella, Hyperammina and Tolypammina. The marine bands of the Middle Coal Measures contain more varied assemblages than those of the Lower Coal Measures. Foraminifera have not been noted from the Pot Clay Marine Band or the minor marine bands associated with the Holbrook and Smalley coals. These basal bands are a continuation of the Millstone Grit pattern of faunal phases in which a `foraminifera phase is also absent (p. 63). Foraminifera are found most abundantly in a smooth grey mudstone and, as in the case of P. ophthalmoides, do not occur in carbonaceous mudstones.

3. Lingula phase

This, the most common of the faunal phases, is known from all marine bands in the district with the exception of the Edmondia Band. Lingula may occur in isolation, e.g. Clown Marine Band and the marine bands above the Holbrook and Smalley coals, but from its tolerance of wide-ranging conditions is commonly found as a member of varied associations representing other phases. Several of the marine incursions proceed no further than the Lingula phase before the retreat commences. In those bands where a richer fauna occurs (see below) a basal layer with Lingula usually precedes the main incursion even though the earlier phases may be absent. Lingula may persist alongside the fossils of the richer development but becomes dominant again when the regression reaches the appropriate stage. The most usual lithology is a dark slightly silty mudstone, but Lingula has been found in beds ranging from carbonaceous mudstone to siltstone.

4. Cephalopod/lamellibranch phase

This phase, corresponding to the acme of the marine incursion, is divisible into three sub-phases, each representative of a different facies and characterized by a distinctive faunal association.

(a) Gastrioceras/Dunbarella/Posidonia sub-phase. The assemblage is characteristic of the Pot Clay and Alton marine bands, and to a certain degree of the Norton Marine Band, and represents a continuation of the Millstone Grit facies. Conodonts and mollusc spat are abundant but there is a notable absence of typical benthonic fossils. The lithology is commonly a pyritous mudstone and the beds seem to have been laid down in deeper water and under a slower rate of deposition than the other sub-phases.

(b) Anthracoceras/Dunbarella/Myalina sub-phase. This association is typically found in the Clay Cross Marine Band, but is seen to a lesser extent in the Two-Foot Marine Band and Edmondia Band. Ostracods including Hollinella and Paraparchites are common, and benthonic organisms in general are more in evidence than in the Pot Clay and Alton faunas; there is also a close association at some levels between representatives of this fauna and elements from the non-marine facies. The lithology is typically a dark, slightly silty mudstone and the assemblage suggests a relatively shallow water, in-shore environment.

(c) Cephalopod/calcareous brachiopod/gastropod sub-phase. The richest Coal Measures marine faunas are found in such bands as the Mansfield Marine Band, and are distinguished by the presence of calcareous brachiopods associated with numerous lamellibranchs such as Nuculids and Pectinids, Bellerophontid and other gastropods, and cephalopods in variety. The occurrence of a typical benthonic fauna plus numerous examples of free-swimming cephalopods suggest that this fauna represents a more open-sea environment. An approach to the conditions exhibited by the Mansfield is shown by the Haughton and Sutton marine bands, although in these cases the fauna is more restricted.

The cephalopod/lamellibranch phase represents the maximum advance of the incursion and the establishment of fully marine conditions. On the commencement of the retreat stage this fauna is gradually lost from the sequence and replaced in turn by the Lingula, Foraminifera and Planolites phases, leading to the return to a non-marine environment.

Plants

Plants have been collected from several horizons in recent boreholes, notably in the measures above the High Hazles Coal, but no systematic study has been carried out in connexion with the resurvey. Fragmentary plant remains are found in most phases of the cyclothems, but the more complete specimens usually occur in the silty measures in the upper part of the cycle. A list of plants obtained from the district was given by Horwood (1912) and Moysey (in Gibson and Wedd 1913), and further records appear in the memoir on the Concealed Coalfield (Edwards 1951, pp. 91–2).

Non-marine faunal succession

The zonal classification shown in (Figure 8) is that now generally applied to the British Coal Measures, and taken in conjunction with the marine bands provides a sound basis for correlation between the different coalfields. A more detailed subdivision of the non-marine lamellibranch succession was applied by Wright (1939) to the Lancashire and Yorkshire coalfields and discussed by Trueman and Weir (1946, p. xxxii; 1956, pp. xxxiii–iv). In the following account the succession had been divided into convenient sections corresponding in general to changes in the non-marine faunas (see also Calver 1955). The main faunal characteristics of each section are outlined below in ascending stratigraphical order.

Lower Coal Measures

Lower Coal Measures (comprising the A. lenisulcata Zone, the C. communis Zone and the lower part of the A. modiolaris Zone). The representatives of the Carbonicola fallax Wright and C. protea Wright groups are found in the beds between the Holbrook and First Smalley coals. The characteristic species include C. artifex Eagar, C. declinata Eagar, C. rectilinearis Trueman and Weir, C. haberghamensis Wright and C. pilleolum Eagar, associated with Curvirimula sp. nov. [fine ornament, narrow form], Naiadites sp. nov. [oblique] and rare Anthraconaia lenisulcata (Trueman). These beds correspond in part to the sequence above the Soft Bed Coal of Yorkshire and the Bassy Mine of Lancashire. Between these 'mussel'-bands and the Norton  'mussel'-band few lamellibranchs have been recorded, but they include rare Carbonicola from above the Alton Marine Band and scanty Curvirimula.

The Norton mussel'-band, which is well developed in the district, is the highest fauna referred to the A. lenisculata Zone. The fauna comprises Carbonicola proxima Eagar, C. extenuata Eagar, C. crispa Eagar and Curvirimula sp. nov. [broad form]. Representatives of this assemblage have been recorded from South Wales (Woodland and others 1957) and southern Ireland (Eagar 1962).

The earliest C. communis Zone fauna is found just below the Wingfield Flags, and is represented by C. bipennis (Brown) with rare Anthraconaia sp. nov.of A. modiolaris group, Naiadites flexuosus Dix and Trueman and Curvirimula sp. Variants of C. bipennis such as C. subconstricta Wright (non J. Sowerby) persist into the measures occurring a short distance above the Kilburn Coal.

The entry of the C. pseudorobusta Trueman group about 100 ft above the Kilburn can be taken as the base of the middle C. communis Zone. The associated lamellibranchs are C. acuta (J. Sowerby), C. communis Davies and Trueman, and C. polmontensis (Brown). This group of 'mussel'-bands extends up to just below the Blackshale Coal. Curvirimula is common in these beds with the species C. trapeziforma (Dewar) and C. subovata (Dewar); Naiadites is again represented by N. flexuosus, but Anthraconaia has not been noted.

The measures from the Blackshale to the Tupton can be referred to the upper C. communis Zone. Carbonicola is not common but includes C. pseudorobusta. The characteristic Curvirimula is C. candela (Dewar), but C. subovata is also identified. The earliest Anthracosphaerium found in the district occurs above the Blackshale as A. boltoni (Wright). Naiadites flexuosus persists from the lower beds, but again Anthraconaia has not been recorded.

The beds occurring between the Tupton Coal and the Clay Cross Marine Band, and representing the lower A. modiolaris Zone, can be divided on faunal grounds approximately at the Deep Soft Coal. The lower beds contain the C. cristagalli Wright fauna with C. rhomboidalis Hind, C. robusta (J. de C. Sowerby), C. oslancis Wright and Anthraconaia sp. nov., all strongly represented in the well-developed 'mussel'-band above the Tupton Coal. In contrast with the faunas below, that of the band above the Tupton is distinguished by the presence of Anthraconaia and the absence of Curvirimula and typical Carbonicola pseudorobusta. These facts make this a suitable fauna to take as the base of the A. modiolaris Zone. The upper beds, those between the Deep Soft and the Clay Cross Marine Band, are marked by the entry of Anthracosia and the virtual disappearance of Carbonicola. A. regularis (Trueman) and variants dominate the 'mussel'-bands, but rare Anthraconaia modiolaris (J. de C. Sowerby) and Anthracosphaerium sp. have been collected. The common Naiadites is a form intermediate between N. productus (Brown) and N. quadratus (J. de C. Sowerby). The last survivors of Carbonicola are represented by C. oslancis and C. venusta Davies and Trueman. The ostracod Geisina arcuata is abundant at several levels in these measures.

Middle Coal Measures

Middle Coal Measures (embracing the upper A. modiolaris Zone, and the Lower and Upper similis-pulchra zones). In the beds between the Clay Cross Marine Band and the First Ell Coal the Anthracosia aquilina (J. de C. Sowerby)/A. ovum Trueman and Weir group is dominant with A. subrecta Trueman and Weir and subsidiary A. phrygiana (Wright). Anthraconaia of the A. modiolaris group is common, particularly above the Second Ell Coal where A. cf. curtata (Brown), A. modiolaris (J. de C. Sowerby) and A. williamsoni (Brown) have been recorded. N. triangularis (J. de C. Sowerby) and N. quadratus are the characteristic Naiadites in these beds. Anthracosphaerium exiguum (Davies and Trueman) has been found rarely in the 'mussel'-band above the Clay Cross Marine Band.

From the First Ell to the Top Hard Coal the A. phrygiana group including A. beaniana King and A. disjuncta Trueman and Weir becomes increasingly important, gradually replacing A. ovum and its variants as the dominant forms. Anthracosphaerium is common only in the  'mussel'-band above the First Ell where it occurs in variety. The typical Naiadites is N. quadratus continuing from the lower beds, but Anthraconaia is rare. The acme of the A. phrygiana group occurs in the beds above the Dunsil.

The Top Hard is a convenient boundary to take between the A. modiolaris and the Lower similis-pulchra zones for it separates the characteristic A. phrygiana fauna below from the equally distinctive Anthraconaia pulchella Broadhurst fauna above. Included in the latter fauna in addition to the eponymous species are variants of Anthracosia caledonica Trueman and Weir, A. planitumida (Trueman), Anthracosphaerium turgidum (Brown) and Naiadites productus (Brown).

The 'mussel'-bands between the High Hazles and Two-Foot coals are notable for the first appearance of the Anthracosia atra (Trueman) group which is typically found in the middle and upper parts of the Lower similis-pulchra zone. The associated species include A. planitumida, A. caledonica, A. lateralis (Brown) and A. simulans Trueman and Weir with Anthracosphaerium propinquum (Melville), N. productus and N. obliquus Dix and Trueman. Variants of these species also occur in the  'mussel'-band above the Two-Foot Coal, in which the Anthracosia acutella (Wright)/A. concinna (Wright) group is distinctive and is accompanied by Anthraconaia librata (Wright), Anthracosphaerium radiatum (Wright) and N. alatus Trueman and Weir.

The A. atra group is also common above the Mainbright Coal, but attains its acme in the beds overlying the Clown with a characteristic fauna of A. atra, A. fulva (Davies and Trueman), A. barkeri Leitch and A. elliptica (Chernyshev). A distinctive variety of Anthraconaia librata is found in the lower part of this mussel '-band in which Carbonita humilis (Jones and Kirkby) is abundant. Other fossils include Naiadites angustus Trueman and Weir and Anthracosphaerium cf. exiguum.

In the higher beds, up to the Mansfield Marine Band, 'mussels' are not common. Anthracosia and Anthracosphaerium have disappeared and the only common fossils are species of Naiadites such as N. productus and N. angustus.

From the Mansfield Marine Band to the top of the proved sequence (i.e. just below the horizon of the Top Marine BandNote. Since going to press the Top Marine Band and 323 ft of Upper Coal Measures have been proved in Cauldwell Borehole [SK 5249 5855] south-west of Mansfield and on the north side of the fault through Sutton in Ashfield and Stonehills (see p. 191). The cores were examined by Messrs. J. G. O. Smart, N. Aitkenhead and S. Brunskill, who report that the main part of the Top Marine Band is 10 ft 5 in thick and lies 632 ft 10 in from the surface and 346 ft above the Highmain Coal. It consists of dark mudstone from which Mr. M. A. Calver has identified the following fauna: foraminifera; Planolites ophthalmoides; Crurithyris sp., Lingula sp., Orbiculoidea sp., Dunbarella sp., Hollinella cf. bassleri; cf. Tomaculum sp. H. cf. bassleri is also recorded 23.25 ft higher, where it is associated with Curvirimula sp. The intervening measures, in which no marine fossils were observed, consist of grey silty mudstone and contain slump structures in parts. The Upper Coal Measures are largely argillaceous and are composed of about ten cycles, the majority of which have a few inches of coal; Anthraconauta phillipsii (Williamson) occurs at several levels. E.G.S.) the fauna is less varied than in the lower beds, the genera represented being Naiadites and Anthraconaia, the latter occurring only rarely. In the lower beds up to the Edmondia Band, the species include N. hindi Trueman and Weir and N. melvillei Trueman and Weir, with A. cf. adarnsi (Salter) recorded from one horizon just below the Highmain Coal. The lowest appearance of Geisina subarcuata (Jones) is also just below the Highmain and the species continues up to the Shafton Marine Band. A short distance below the Edmondia Band are bands with numerous juvenile Naiadites, many of which are homoeomorphs of Anthraconauta phillipsii (Williamson) from the Upper Coal Measures. Above the Edmondia Band the fauna is similar to that just below, with the addition of Lioestheria vinti (Kirkby). M.A.C.

References

ANDERSON, W. and DUNHAM, K. C. 1953. Reddened beds in the Coal Measures beneath the Permian of Durham and South Northumberland. Proc. Yorks. Geol. Soc., 29, 21–32.

BUTTERWORTH, MAVIS A. and MILLOTT, J. O'N. 1960. Microspore distribution in the coalfields of Britain. Proc. Int. Committee for Coal Petrol., 3, 157–63.

CALVER, M. A. 1955. Die stratigraphische Verbreitung der nicht-marinen Muscheln in den penninischen Kohlenfeldern Englands. Z. deutsch. Geol. Ges., 107, 26–39.

CLIFT, S. G. and TRUEMAN, A. E. 1929. The sequence of non-marine lamellibranchs in the Coal Measures of Nottinghamshire and Derbyshire. Quart. J. Geol. Soc., 85, 77–108.

CROOKALL, R. 1928. Palaeozoic species of Vetacapsula and Palaeoxyris. Sum. Prog. Geol. Surv. for 1927, pt. 2, 87–107.

CROOKALL, R. 1955. Fossil plants of the Carboniferous rocks of Great Britain (2nd Section), pt. 1. Mem. Geol. Surv. Pal., 4.

DIX, EMILY. 1933. The sequence of floras in the Upper Carboniferous, with special reference to South Wales. Trans. Roy. Soc. Edin., 57, pt. 3 (No. 33), 789–838.

DEFRISE-GUSSENHOVEN, E. and PASTIELS, A. 1957. Contribution a l'étude biométrique des Lioestheriidae du Westphalien supérieur. Publ. Assoc. Étud. Paléont. Strat. Houill., No. 31, 1–71.

EAGAR, R. M. C. 1960. A summary of the results of recent work on the palaeoecology of Carboniferous non-marine lamellibranchs. C. R. 4me Cong. Strat. Carb. Heerlen, 1958, 1, 137–48.

EAGAR, R. M. C. 1962. New Upper Carboniferous non-marine lamellibranchs. Palaeontology, 5, 307–39.

EDEN, R. A. 1954. The Coal Measures of the Anthraconaia lenisulcata Zone in the East Midlands Coalfield. Bull. Geol. Surv. Gt. Brit., No. 5, 81–106.

EDEN, R. A., STEVENSON, I. P. and EDWARDS, W. 1957. Geology of the country around Sheffield. Mem. Geol. Surv.

EDWARDS, W. 1951Dated 1951, published January 1952.. The concealed coalfield of Yorkshire and Nottinghamshire. 3rd edit. Mem. Geol. Surv. 1953. In Sum. Prog. Geol. Surv. for 1951, 30.

EDWARDS, W.  and STUBBLEFIELD, C.J. 1948. Marine bands and other faunal marker- horizons in relation to the sedimentary cycles of the Middle Coal Measures of Nottinghamshire and Derbyshire. Quart. J. Geol. Soc., 103 for 1947, 209–60.

GIBSON, W. and WEDD, C. B. 1913. The geology of the northern part of the Derbyshire Coalfield and bordering tracts. Mem. Geol. Surv.

GREEN, A. H., RUSSELL, R. and others. 1878. The geology of the Yorkshire Coalfield. Mem. Geol. Sum

HORWOOD, A. R. 1912. Investigation of the fossil flora and fauna of the Midland coalfields. Rep. Brit. Assoc. for 1911, 105–11.

JONES, T. R. 1862. Fossil Estheriae. Palaeont. Soc., 1–1 34.

KIRKBY, J. W. 1864. On the occurrence of fossils in the highest beds of the Durham Coal Measures. Trans. Tyneside Nat. Field Club., 6, 220–5.

PASTIELS, A. 1956. Contribution a l'étude des foraminifères du Namurien et du Westphalien de la Belgique. Publ. Assoc. Etud. Paleont. Strat. Houill., No. 27.

ROBERTSON, T. 1932. The geology of the South Wales Coalfield. Part V: The country around Merthyr Tydfil. 2nd edit. Mem. Geol. Surv.

STUBBLEFIELD, C. J. and TROTTER, F. M. 1957. Divisions of the Coal Measures on Geological Survey maps of England and Wales. Bull. Geol. Surv. Gt. Brit., No. 13, 1–5.

TROTTER, F. M. 1953. Reddened beds of Carboniferous age in north-west England and their origin. Proc. Yorks. Geol. Soc., 29, 1–20.

TRUEMAN, A. E. 1946. Stratigraphical problems in the Coal Measures of Europe and North America. Quart. J. Geol. Soc., 102, xlix-xciii.

TRUEMAN, A. E. and WEIR, J. 1946–56. A monograph of British Carboniferous non-marine Lamellibranchia. Pts. 1–9. Palaeont. Soc.

WANLESS, H. R. and WELLER, J. M. 1932. Correlation and extent of Pennsylvanian cyclothems. Bull. Geol. Soc. Amer., 43, 1003–16.

WEIR, J. 1945. A review of recent work on Permian non-marine lamellibranchs and Palaeozoic. Trans. Geol. Soc. Glasgow, 20, 291–340.

WEIR, J. 1960. A monograph of British Carboniferous non-marine Lamellibranchia Pt. 10. Palaeont. Soc.

WILSON, G. V. 1926. The concealed coalfield of Yorkshire and Nottinghamshire. 2nd edit. Mem. Geol. Surv.

WOODLAND, A. W., ARCHER, A. A. and EVANS, W. B. 1957. Recent boreholes into the Lower Coal Measures below the Gellideg–Lower Pumpquart horizon in South Wales. Palaeontology by M. A. Calver. Bull. Geol. Surv. Gt. Brit., No. 13, 39–60.

WRIGHT, W. B. 1939. Subzones of the productive Coal Measures of Yorkshire. Bull. Geol. Surv. Gt. Brit., No. 1, 37–46.

Chapter 5 Coal Measures: details of stratigraphy

Introduction

During the resurvey of the Coal Measures a vast amount of information was collected, not only by direct observation in the field, but also from plans and sections of mines and opencast workings, and from the detailed examination of boreholes. The preparation of the present chapter has therefore involved drastic selection and condensation, and, wherever practicable, seam-maps have been used to summarize the details of the coals. Abbreviated sections of all shafts and boreholes mentioned in the text are given in Appendix 2 (p. 283 et seq.), where also will be found full details concerning their sites. Exposures and other sections are generally related in the text to localities shown on the One-inch Geological Map and are supported by National Grid References. Appendix 3 (p. 392) gives the locations of opencast sites referred to. E.G.S.

Lower Coal Measures

Base of Coal Measures to Kilburn Coal

Variations in thickness and lithology, as well as the proved faunal bands are shown in (Figure 9). The measures are thickest in the north where as much as 840 ft are calculated to be present; they thin to the south and east to a recorded minimum of about 650 ft in Hardstoft No. 1 Borehole. The lower half of the sequence includes a number of coals of which the Alton is the chief; ganister or fireclay is developed beneath most of the coal horizons.

Pot Clay Marine Band

The Pot Clay Marine Band, which marks the base of the Coal Measures, is characterized by Gastrioceras subcrenatum (Frech); it consists of up to 23 in of black shale containing, in addition to the goniatites, a few Lingula and lamellibranchs. In some localities it is separated from the Pot Clay Coal or seatearth by up to several feet of mudstone, generally dark and containing plant and fish remains, which rightly belong to the Millstone Grit Series. Recorded sections of the marine band and associated beds are as follows:

1. [SK 3111 6835]. In the bed of the River Hipper, 360 yd upstream from the bridge at Harewood Grange; dark shale has yielded the following fossils: Caneyella multirugata (Jackson), Dunbarella papyracea (J. So werby), Posidonia cf. gibsoni Salter, P. insignis (Jackson), P. sp. [juv., ? sp. nov.]; Anthracoceras sp., Gastrioceras subcrenatum, G. sp. nov. [widely spaced lirae], G. sp. [crenulate, especially on nodes], Homoceratoides sp.; mollusc spat; Hindeodella sp., platformed conodont; Elonichthys sp.
2. [SK 3127 6822]. Trial pit, 250 yd N. 22° E. of Harewood Grange; dark mudstone 3 ft, grey mudstone with plants 3 ft 5 in, dark grey mudstone with marine fossils 23 in, dark grey mudstone 6 in, brown mudstone with a few rootlets 3 in, coaly shale 2 in, on fireclay 31 in.
3. [SK 3267 6833]. Rippings in underground workings near Cathole Farm, 1080 yd N. 32° W. of Stonehay Farm; dark grey mudstone 6 in, black silty mudstone with marine fossils 22 in, black silty mudstone with fish debris 14 in, coaly shale with coal bands 4 in, on fireclay (dark in top 4 in) 34 in. Fossils recorded are: C. multirugata, D. papyracea, P. cf. gibsoni; Anthracoceras sp., G. subcrenatum, G. sp. nov. [widely spaced lirae], Reticuloceras superbilingue Bisat; mollusc spat; Ozarkodina sp.
4. [SK 3280 6808]. 760 yd N. 33° W. of Stone-hay Farm (this section has been obscured since its examination in 1949); grey mudstone 9 ft, dark marine shale (1 ft seen) containing D. cf. papyracea, P. cf. gibsoni, Anthracoceras sp., G. subcrenatum, not seen 5 ft, siltstone 5 ft.
5. [SK 3308 6835]. Steep bank between the road and river 950 yd N. 6° W. of Stonehay Farm; dark shale with marine fossils 9 in, dark shale 39 in, coal 2.5 in, fireclay 36 in, on ganister-like sandstone.
6. [SK 3338 6848]. Bed of the River Hipper, 1100 yd N. 12° E. of Stonehay Farm; dark shale contains D. sp., P. cf. insignis, G. subcrenatum and Homoceratoides? at the base. During the earlier survey a section near here, now obscured, was described as follows: coarse gravel 3 ft, black shale with lamellibranchs and goniatites 1 in, sandy fireclay 5 ft, shale with 'mussels'.
7. [SK 3607 6420]. Abandoned opencast workings south-west of Alton; weathered dark grey shale with D. sp., G. subcrenatum and Hindeodella sp. 2 ft, ganister 2 ft 6 in, on sandstone 1 ft.
8. [SK 3612 6014]. Stream in Clattercotes Wood, 400 yd N. 15° E. of Whitecarr; silty mudstone with C. multirugata, D. papyracea, Posidonia sp., Anthracoceras sp., G. subcrenatum, G. sp. nov. [widely spaced lirae] and Homoceratoides sp., on ganister 3 in, on sandstone.
9. [SK 3619 6013]. Another section in the same stream, 420 yd N. 21° E. of Whitecarr; marine shale containing C. multirugata, D. cf. papyracea, P. cf. gibsoni, G. subcrenatum and Homoceratoides sp., on ganister 1 ft.

The marine horizon has also been identified in the following boreholes:

1. 1. Calow No. 1: dark grey mudstone with marine fossils 1 ft 4 in, resting on ganister 2 ft 7 in and ganister-like sandstone 9 in.
2. 2. Napoleon Opencast Site: shale with a few marine shells 7 in, on ganister 1 ft 10 in.
3. 3. Morton Colliery Underground: black carbonaceous mudstone with marine shells 1 ft 2 in, on ganister 1 ft 3 in and greenish grey sandstone with rootlets 2 ft.
4. 4. Wingfield Manor Underground: black shale with marine fossils 1 ft, dark shale with pyrite 4 in, on ganister and sandstone 1 ft 10 in. E.G.S.

The marine band contains the characteristic goniatite–Pectinid assemblage known at this horizon throughout the main Pennine coalfields. The complete list of fossils collected from the district is as follows: Lingula mytilloides J. Sowerby; Caneyella multirugata, Dunbarella papyracea, Posidonia cf. gibsoni, P. insignis; orthocone nautiloid, Metacoceras sp. nov.aff. pulchrum (Crick), Anthracoceras sp., Gastrioceras subcrenatum, G. sp. nov. [widely spaced lirae], G. sp. nov. [crenulate lirae, especially on the nodes], Homoceratoides sp., Reticuloceras superbilingue [one locality]; mollusc spat; abundant conodonts including Hindeodella sp., Lonchodina sp., Ozarkodina sp., platformed conodonts undetermined; Acanthodian scales and Elonichthys spp.

The record of R. superbilingue from this band in the fireclay mine, east of Cathole Farm (see above), is of interest; this form is now known as a rarity from the G. subcrenatum horizon in several British coalfields (Shanklin 1956, p. 540; Earp and others 1961, p. 196; Kellaway, in preparation). The G. spp. nov., which also occur at the fireclay mine and at other localities, including the River Hipper, are characteristic of the G. subcrenatum assemblage (Calver in Woodland and others 1957, p. 55; Ramsbottom and Calver 1962, p. 572). Foraminifera have not been noted either in washings or in thin sections prepared from this band. M.A.C.

Measures between the Pot Clay Marine Band and the Crawshaw Sandstone

The measures between the Pot Clay Marine Band and the Crawshaw Sandstone vary between about 20 ft and 120 ft. The latter thickness is reached only in the Whispering Well–Cat Hole area where up to 50 ft of sandy measures occur towards the middle of the sequence; elsewhere the thickness rarely exceeds 70 ft, though exact measurements are difficult to determine since, in many localities, there is gradual upward passage into the Crawshaw Sandstone.

The mudstones and silty mudstones are best seen in the stream between Slagmill Plantation and Harewood Grange. The sandy measures, which have their base roughly 25 ft above the Pot Clay Marine Band, are well exposed in the roadside quarry [SK 330 683] at Cat Hole where the sandy shale and siltstone with bands of sandstone are used for making rustic bricks. South of Stone Edge Plantation [SK 342 672] the interval between the Pot Clay Marine Band and the Crawshaw Sandstone decreases, and from Alton southwards it is nowhere more than 45 ft. The only exposure is in Clattercotes Wood [SK 3633 6011] where about 20 ft of shales are seen.

Of the boreholes which penetrate these measures, that at Whispering Well records a thickness of 122 ft, including sandy measures in the middle of the sequence; and Alfreton Colliery Underground (1952), Calow No. 1, Clay Cross, Morton Colliery Underground, Napoleon Opencast Site and Wingfield Manor Underground boreholes all record thicknesses of less than 50 ft. At Calow No. 1 Cochlichnus kochi (Ludwig) is recorded about 25 ft above the Pot Clay Marine Band and Carbonicola cf. limax Wright and cf. Anthraconaia bellula (Bolton) were found close below the Crawshaw Sandstone. The 'mussels' are in a similar position to those found in coarse siltstone just above the G. subcrenatum horizon at Goyt's Moss (Eagar 1956, p. 332). G.H.R., E.G.S.

Crawshaw Sandstone

The Crawshaw Sandstone, 50 to 180 ft thick, forms a well-marked escarpment along the greater part of its outcrop, particularly between the northern boundary of the district and Stone Edge where it is, in places, weathered into crags. Sloping eastwards from the highest ground the heatherclad, block-encumbered dip-slope forms the higher part of Brampton East Moor (north of Robin Hood) and Gibbet Moor. Here the sandstone averages 115 ft excluding the thin sandstone leaves which occur both below (see p. 102) and above. This main bed is predominantly a gritstone ', although generally less coarse grained than the Chatsworth Grit. Like the Chatsworth Grit it is commonly false-bedded, but unlike that Grit it becomes, in places, coarser grained downwards. A 50-ft quarry [SK 2817 7196], 300 yd S.E. of the Inn at Robin Hood, shows flaggy medium-grained sandstone passing down into coarse-grained 'grit' with a few small pebbles at the base. A similar downwards coarsening was also seen in Smeekley No. 3 Borehole, 2 miles north of the sheet-boundary (Eden and others 1957, p. 217); but in the Linacre Borehole the coarsest part of the bed is in the middle. The presence of scattered pebbles up to 0.25-in diameter has been noted in several places. A number of sections mostly in and near the northern end of Umberley Brook show Crawshaw Sandstone of a red, purple or yellow colour instead of the normal grey. R.A.E.

The sandstone is about 180 ft thick in the Bunker's Hill–Harland Edge area, where it is split by a thin shale into two leaves, the upper forming a long dip-slope. It thins south-eastwards to about 90 ft in the Stone Edge area, its average thickness in the intervening ground being about 100 ft. There are numerous exposures and it has been quarried in the past for building and roadstone and, at Stone Edge, for millstones. It is in most places a coarse- to medium-grained sandstone, usually massive or false-bedded, but a shallow quarry [SK 3354 6753] on the edge of Matherbank Plantation, 250 yd N.W. of Stone Edge Plantation, shows fine-grained sandstone with sandy shale partings. E.G.S.

From Stone Edge to Highashes Farm [SK 3474 6597] the sandstone dips steeply to the east and forms a narrow north-northwesterly ridge in which the only exposure is in the floor of the lane [SK 3462 6630] leading to Haslehurst Farm; the dip at this point is about 45°. Between Highashes Farm and Alton the Crawshaw Sandstone dips northeast at not more than 10° and forms a long dip-slope down to Press reservoirs; several old quarries provide sections, the best one [SK 3612 6455] being immediately north of Alton where 35 ft of rather coarse, brown sandstone are exposed. The boreholes in this area, Press No. 3, Northedge and Northedge New Bore, record a thickness of between 90 and about 100 ft. Southwards from Alton the dip again steepens considerably along the eastern side of the Ashover Anticline and exposures are poor. East of Ashover Hay the sandstone is repeated by a strike fault, and the easterly outcrop forms a gentle dip-slope down to the River Amber. Moorwood Quarry [SK 368 607] is situated on this dip-slope and up to 30 ft of fairly coarse-grained false-bedded sandstone are visible. A borehole at Napoleon Opencast Site on the north side of the river showed red and purple sandstone with partings of micaceous mudstone. Further boreholes, at Clay Cross and Morton Colliery, show that the sandstone maintains its thickness of about 100 ft at least two miles east of the outcrop. At Calow No. 1 Oil Borehole, 1.5 miles east of Chesterfield, the thickness is less than 70 ft. G.H.R.

The outcrop of the Crawshaw Sandstone is repeated by strike-faulting north of Brackenfield, and between Brackenfield and Wessington it forms a wide dip-slope, much obscured by boulder clay. Between Mathersgrave and Lindwaylane Farm the sandstone forms a marked feature, but south of the latter locality it dips at 30° or more on the east limb of the Crich Anticline and has a narrow outcrop. It is exposed in Clattercotes Wood where it is difficult to estimate the thickness with any accuracy for the exposures are complicated by faulting and show variable dips up to 70°; about 70 ft seems probable. A borehole at Lindway Springs records over 100 ft, but this is exceptional for the area. South of Lindway Springs the estimated thickness is 50 ft or less. South of Clattercotes Wood exposures are not numerous and the rock has been quarried only on a small scale. Such exposures and records as exist show fine to fairly coarse-grained sandstone, massive and well-jointed, and in many cases of a pink or reddish colour. E.G.S.

Belperlawn Coal

The Crawshaw Sandstone was encountered in underground boreholes at Wingfield Manor and Alfreton collieries where 72 ft and 50 ft respectively were proved.

The Belperlawn Coal has a maximum proved thickness of 24 in, though it is on average between 12 and 18 in. It is absent at surface between Alton and Clattercotes Wood, and underground as far as Morton. Elsewhere, it occurs close above the Crawshaw Sandstone and is underlain in most localities by a fireclay though silty or sandy seatearth has also been recorded. G.H.R.

A number of bell-pits have been sunk to an outlier of the seam in the central part of Gibbet Moor, the debris from the pits including both coal and coaly ganister; it is inferred that the seam was of little value. R.A.E.

Between Loads and Stone Edge the Belperlawn Coal has been recorded at number of points underground. These are: (i) Grove Farm, Nether Loads where the Opencast Executive proved 12 to 23 in of coal in boreholes; (ii) Whispering Well Borehole where it is recorded as being 12 in thick at 54 ft; (iii) Workings near Holymoorside [SK 3286 6837] about 1000 yd N. 19° W. of Stonehay Farm; the section given on the abandonment plan (dated 1919) is: coal 19 in on clay 14 in; (iv) Slatepitdale Mine where workings in the eastern part of Stone Edge Plantation were abandoned about 1895; the section is: rock roof, coal 15 in, fireclay 30 in. In this area the coal may rest directly on the Crawshaw Sandstone, as at Whispering Well, or may be separated from it by several feet of shale. Neither the Belperlawn nor its fireclay is seen in Nab Quarry [SK 3339 6864], near Holymoorside, 1380 yd N. 10° E. of Stonehay Farm, where 12 ft of dark grey silty shale can be seen resting on the Crawshaw Sandstone. E.G.S.

Some 400 yd S.E. of Highashes Farm the Belperlawn Coal is present in an outlier [SK 351 656] on the dip-slope of the Crawshaw Sandstone, where it is said to be 18 in thick. To the east the coal is thought to crop out beneath a sandstone feature along the northern banks of Press reservoirs, and in the Northedge New Bore a 9-in coal has been proved beneath the same sandstone. Coldwell Farm Borehole, drilled 1125 yd S.E. of Northedge New Bore and approximately 690 yd E. of the outcrop, encountered 19 in of coal separated from the underlying Crawshaw Sandstone by 3 ft of seatearth. A further 1.5 miles to the east the 6-in coal at 1460.25 ft in the Clay Cross Borehole is thought to be the Belperlawn. The southernmost proving of the coal in the Alton area is at Press Mill Opencast Site where a cored borehole [SK 3687 6407] found 16 in of coal at 201 ft 4 in. Between this borehole and Clattercotes Wood, 2.5 miles to the south, the Belperlawn is absent. To the east its absence has been proved as far as Morton Colliery Underground Borehole, though at Tibshelf No. 1 Borehole, a further 1.75 miles to the east, it is 7 in thick. G.H.R.

The Belperlawn is believed to be present close above the Crawshaw Sandstone over most of the ground south of Clattercotes Wood. A smut has been observed above the Crawshaw Sandstone in the Clattercotes Wood stream [SK 3666 5985], and further south the thin coal that has been worked across Brackenfield Green and Wessington Green is also believed to be the Belperlawn. The 9-in coal exposed in the stream [SK 3525 5806] 200 yd S. of Lindwaylane Farm may be the Belperlawn, but high dips and probable faulting make its identity uncertain. At Ilett Opencast Site near South Wingfield a borehole [SK 3656 5521] proved the seam to be 17 in thick with a 3-in dirt parting 2 inches from the base. E.G.S., P.M.D.D.

Within the southern part of its field the Belperlawn Coal has been proved in Alfreton Colliery Underground Borehole (1952) where it is only 1 in thick. At Wingfield Manor Colliery Underground Borehole (p. 390) it is probably the 3-in coal at 591 ft.

Measures between the Belperlawn and Alton coals

The measures between the Belperlawn and Alton coals are extremely variable in both thickness and lithology. At outcrop between Stubben Edge Ganister Mine [SK 364 637] and Clattercotes Wood [SK 361 602], and underground as far east as Morton, the measures are virtually absent or are represented by the uppermost part of the local Crawshaw Sandstone, which is succeeded close above by the Alton Coal. To the north of this area, the measures vary in thickness between 50 and 100 ft, and include, locally, a thin coal. To the south the variation in thickness is between 27 and 88 ft and up to three coals are present in a succession similar to that recognized by Eden (1954) in Nottinghamshire and Derbyshire, and regarded as being comparable with that of Eagar (1947) in Yorkshire. G.H.R.

From the northern boundary of the district as far south as Brampton East Moor the measures consist of sandstone with shale bands resting upon shale; they are poorly exposed. The shale has yielded no fauna in situ, but debris from the bell-pits to the Belperlawn coal on Gibbet Moor includes shale with abundant ostracods and many fragmentary 'mussels'. These fossils can only have come from the roof-measures of the Belperlawn Coal, and indicate the presence of the well-known 'mussel'-band found above this coal in Yorkshire and elsewhere (Eagar 1952). This is the only locality in the district from which fossils are recorded at this horizon. The sandstone beneath the Alton Coal was referred to by Gibson and Wedd (1913, p. 54) as 'the sill of the Alton Coal', and in other records it is referred to as the 'Alton Sill'; in Appendix 1 it is called the Sub-Alton Sandstone. Although persistent the sandstone is variable in character: in places it is thick and forms a prominent scarp and dip-slope, as on Brampton East Moor; elsewhere it is thin and includes an interbedded shale, as where it crosses Blackleach and Wadshelf brooks near Stone Low. R.A.E.

The measures are 80 ft thick in one of the trial borings [SK 3309 6974] for the Chanderhill Reservoir project, about 0.5 mile N.W. of Holymoorside. They crop out between Eastmoor and Holymoorside, but are faulted out to the east. They contain two sandstones, the upper of which is the thicker and better exposed. These sandstones form features to the west and south of Holymoorside, but to the north and west of Longside Moor and to the north of Whispering Well they appear to come together. The slack representing the shale between them dies out on Longside Moor, and the above-mentioned Chanderhill borehole shows them to be separated by only 5 ft of fireclay. The horizon of the Clay Coal of the Sheffield area is assumed to lie between these sandstones and to be washed out where they come together—this is evidently the case at Smeekley No. 3 Borehole (Eden and others 1957, pp. 41 and 217) to the north of the district boundary. Borings at Grove Farm [SK 3232 6938], Nether Loads, have proved 10 to 18 in of coal at this horizon; two of the sections show a 1.5 to 2-in dirt near the top of the seam. There is no evidence of coal at outcrop but ganister and fireclay have been worked from adits at two localities near Holymoorside. At one of these [SK 3284 6844], 1100 yd N. 19° W. of Stonehay Farm, the section given on the abandonment plan is: ganister 4 in on clay 36 in; and at the other, Nab Wood Ganister Mine [SK 3345 6875], 1400 yd N. 12° E. of Stonehay Farm, ganister 3.5 ft, divided into tops 1.5 ft and bottoms 2 ft. It is not certain that these workings are in the same seat-earth; they are only 700 yd apart and yet one section is entirely of ganister and the other predominantly of fireclay. In the Sheffield country there appear to be as many as three refractory beds near the Clay Coal horizon (Eden and others 1957, p. 40).

The sandstone below the Alton Coal is about 40 ft thick, but when combined with the thinner sandstone below the Clay Coal horizon, may reach nearly 70 ft. It has a wide outcrop between Eastmoor and Holymoorside, being responsible for the long dip-slope of Holy Moor. It is well exposed in the stream flowing through Nether Loads where it is seen to be fine-or medium-grained, in parts false-bedded and micaceous with, in places, bands of sandy shale. E.G.S.

From Highashes Farm to Stubben Edge Ganister Mine the Belperlawn Coal is overlain by a fairly coarse-grained sandstone which forms a prominent feature above the outlier of the coal south-east of Highashes Farm (see p. 104); an exposure [SK 3508 6573] on the north side of the outlier shows at least 15 ft of shale between the probable horizon of the Belperlawn Coal and the base of the sandstone. About 1100 yd north-east of the outlier, in Wingerworth No. 3 Borehole, the sandstone contains many shale bands and lies 30 ft above the coal. South of the Northedge–Press road the feature is again well developed, and a borehole here, the Northedge New Bore, has proved 26 ft of sandstone with its base 7 ft above the coal. Between the sandstone and the Alton Coal 20 to 30 ft of siltstone with thin bands of sandstone and mudstone have been proved, but they are not exposed.

At Coldwell Farm Borehole (p. 314) a 14-in coal was found 22 ft below the Alton Coal, its seatearth resting on 11.5 ft of sandstone thought to be the upper leaf of the sandstone overlying the Belperlawn Coal. The lower leaf, with a thin sandy seatearth at its top, is separated from the upper by about 4 ft of mudstone and shale with Lingula mytilloides at the base and 'mussel' above. The latter include Carbonicola declinata Eagar and C. pilleolum ? Eagar, and suggest a correlation with the Upper Division of the Soft Bed succession at Honley in Yorkshire (Eager 1947), and therefore with the cycle above the Second Smalley Coal in the south of the district (see below). It follows therefore that the overlying 14-in coal is the Clay Coal (Middle Band) of Yorkshire. This coal has also been proved locally in a borehole at Press Mill Opencast Site where it is 21 in thick and lies 23 ft 7 in below the Alton. Some 200 to 300 yards to the south-west of this borehole, evidence from opencast exploration and working suggests that this coal merges with the overlying Alton Coal (see p. 108). A further 300 to 400 yd to the south-west the Alton seatearth lies very close above the local Crawshaw Sandstone, and the Belperlawn Coal and its associated overlying argillaceous measures are not developed. A similar sequence was proved in Morton Colliery Underground Borehole, 3 miles east of the outcrop, though further north, in the Clay Cross Borehole, a coal thought to be the Belperlawn is separated from the Alton by 40 ft of measures, mainly shale. G.H.R.

In the south of the district the measures between the Belperlawn and Alton coals generally contain four cycles, namely those above the Belperlawn, Holbrook and Second and First Smalley coals (Eden 1954, pp. 87–90). These cycles are the equivalents of those in the Yorkshire Coalfields containing the richly fossiliferous beds of the Lower, Middle and Upper divisions of the Soft Bed sequence of Eagar (1947), plus that overlying the Middle Band (Clay Coal) horizon. At outcrop the measures are estimated to have an average thickness of about 70 ft. Where proved underground, in Alfreton Colliery Underground (1952), Ilett Opencast Site, Tibshelf No. 1 and Wingfield Nos. 1 and 2 boreholes, they are up to 88 ft thick. In Wingfield Manor Underground Borehole the ?Belperlawn is separated from the Alton by only 28 ft of siltstone and sandstone in a succession regarded as being abnormal for the area.

As proved in the boreholes, each cycle consists largely of mudstone and siltstone with an impersistent sandstone phase. In the lowest cycle, that above the Belperlawn Coal, no fossils have been found in this southern area. At the Holbrook horizon a 3-in coal is recorded in Tibshelf No. 1 Borehole, but no coal has been proved near the outcrop. Lingula was found above the seatearth in Alfreton Colliery Underground Borehole (1952), and is the only record of marine fossils at this horizon in the district. However, the 'mussel'-band above the Holbrook Coal was found in Tibshelf No. 1 Borehole and in Ilett Opencast Site Borehole (Eden 1954, p. 87). The specimens are not well preserved but include Carbonicola aff. fallax Wright, C. cf. haberghamensis Wright, Curvirimula sp. nov. [cf. Price and others 1963, pl. iv, figs. 3–5], and Geisina arcuata (Bean), and are consistent with the correlation with the Middle Division of the Soft Bed succession (Eagar 1952, p. 52). The Second Smalley Coal is 5.5 in thick in an exposure [SK 3719 5646] in Birches Brook, 1250 yd S. 6° W. of Christ Church, Wessington. It is 4 in thick in Tibshelf No. 1 Borehole, 12 in thick in Wingfield No. 1 Borehole, 8 inches in Wingfield No. 2 Borehole, and in Ilett Opencast Site Borehole it is represented by 8 in of cannel. The seatearth beneath this seam is a ganister at Wingfield No. 2 Borehole; at other localities near the outcrop there is a ganister-like seatearth immediately, or a short distance below. Ganister is recorded well to the east of the outcrop in Tibshelf No. 1 and Alfreton Colliery Underground (1952) boreholes. Lingula was found in the roof measures of the coal in Wingfield No. 2 Borehole, but normally in this area the cycle contains only non-marine fossils. The 'mussel' may be seen towards the top of the 12 in of mudstone exposed above the coal in Birches Brook (see above) where the following were collected: Anthraconaia lenisulcata (True-man), Carbonicola declinata?, C. fallax and C. limax ? Wright. The same 'mussel'- band has been proved in Ilett Opencast Site, Tibshelf No. 1 and Wingfield No. 1 boreholes, and the composite fauna from the three localities includes Spirorbis sp., Carbonicola artifex Eagar, C. aff. C. aff. limax, C. aff. rectilinearis Trueman and Weir, Curvirimula sp. nov.(see above) and Naiadites sp. nov. [oblique]. There is a general agreement between this assemblage and that from the Upper Division of Eagar (ibid., p. 52). The First Smalley Coal has been mapped in the area between Brackenfield and Birches Brook. It is exposed in two places, one [SK 3711 5643] in Birches Brook, 1300 yd S. 9° W. of Christ Church, Wessington, where 14 in of coal can be seen above 16 in of ganister, and the other, 85 yards farther downstream, where the section is coal 12 in on ganister 20 in. The coal has also been seen in a number of temporary exposures, the most notable of which was a trial pit [SK 3705 5698] 730 yd S. 21° W. of Christ Church, Wessington, where the section was coal 12 in, ganister 15 in, coal 1 in, ganister 12 to 14 in on fireclay. The First Smalley ganister was formerly worked on a small scale at a number of places in the Wessington area, but is reputed to be open-grained and impure, and therefore of little value. It is often seen to be in two leaves separated by a thin band of fireclay or shale, in places with a thin coal, this fact being used by the prospectors to recognize the bed. The two leaves of ganister-like sandstone with mudstone containing Lingula between them, which are exposed in the stream [SK 3523 5694] 420 yd S. 28° E. of the United Methodist Church, Wheatcroft, are thought to be at the First Smalley horizon. In Ilett Opencast Site, Tibshelf No. 1 and Wingfield Nos. 1 and 2 boreholes, the First Smalley Coal was respectively 7 in, 8 in, 6 in and 8 in thick and was underlain by ganister. In Alfreton Colliery Underground (1952) Borehole there was ganister but no coal. In all these boreholes Lingula was found above the coal horizon, generally associated with fish remains. At Wingfield No. 1 Borehole Hindeodella sp. was also found. The Lingula at this horizon is generally proportionately broader than typical Lingula mytilloides. Indeterminate Carbonicola are recorded above the marine band in Tibshelf No. 1 and Wingfield No. 1 boreholes. It is significant that no foraminifera were observed in the marine bands above the Holbrook, Second Smalley and First Smalley coals. This is in contrast to their widespread abundance in the succeeding Coal Measures marine bands (see below). E.G.S., G.H.R., M.A.C., P.M.D.D.

Alton (Ganister, Hard Bed) Coal

The Alton (Ganister, Hard Bed) Coal and its seatearth are both of economic value. The seatearth is an important source of ganister which, though not as well developed here as in the country around Sheffield (Eden and others 1957, pp. 42–4), has been exploited at many localities in the south of the district. In the north the ganister passes locally into fireclay. The coal varies greatly in thickness: in the north it is generally less than 2 ft, but south of Alton village it is over 4 ft thick in many localities and has been worked underground and at the surface. It consists of bright coal with variable amounts of fusain and has a low ash but high sulphur content. G.H.R.

Many years ago the Alton Coal was worked [SK 291 721] north of New Bridge, where the road from Robin Hood to Bleak House crosses Blackleach Brook, and there are extensive tips of marine shale, together with ganister and coal. Much coal debris is also to be seen 300 yd S.E. of Stone Low [SK 2922 7136]. Farther south a complex of faults on Brampton East Moor shifts the coal to the eastern edge of the moor, where 15 in of dirty coal were seen in a stream [SK 2995 7001] 1600 yd S. 29° W. of New Inn, Eastmoor. The coal was 12 in thick in Linacre Borehole. R.A.E.

The coal has been worked at outcrop on a limited scale in the vicinity of Syda Farm [SK 3112 6932], Upper Loads, where it is said to be 10 to 18 in thick. Borings at Grove Farm [SK 3232 6938], Nether Loads, showed the coal to be between 9 and 17 in thick, and to average 12 to 15 in over the area drilled. A trial pit [SK 3243 6946], 100 yd N. of Nether Loads Farm, showed 13 in of bright coal with streaks of fusain. Two of the Chanderhill Reservoir boreholes [SK 3316 6986], [SK 3309 6974] passed through the Alton; one recorded 2 ft of coal and fireclay, and the other 2 ft of fireclay with a show of coal. E.G.S.

Between Press Mill Opencast Site (600 yd S.E. of Alton) and Carr Brook (a further 2.5 miles to the south) the Alton Coal is generally 3 to 4 ft thick and the seatearth consists largely of fireclay. The coal has been worked at and near the outcrop but the general high dips have precluded large-scale workings. The most northerly workings are those at Press Mill Opencast Site where the Alton was found to be in two leaves (see below). Adjoining this site on the south are the old workings of Alton Colliery and Stubben Edge Mine whose abandonment plans give the following sections: (1) black shale, coal 52 in, black soft dirt 8 in on fireclay; (2) dark shale, coal 42 in on fireclay; a dip of 27° is recorded on one plan and the workings are of limited extent. Less than 300 yd to the east the shafts of Alton New Colliery encountered the Alton Coal at 595 ft, dipping eastwards at about 30°. Some 600 yd S. of Littlemoor a small area of coal has been worked from two shafts [SK 3635 6236] where the dip was recorded as 42°. South of Stubben Edge Hall the Little Stubbin Opencast Site proved 54 to 71 in of coal dipping at up to 60°. At Napoleon Opencast Site the coal was generally over 48 in thick. In the ground to the north-east and east of the opencast site the following boreholes all proved over 36 in of coal: Handley Lodge, Handley School, Horsecar House, Meadow Farm, Morton Colliery Underground, Parkhouse Colliery Underground, Woolley Moor No. 1. A fault along the line of the River Amber in the Woolley Moor area throws the Alton Coal up on the south side of the river and the outcrop has been traced from Alders Wood [SK 372 606] in the east to Carr Brook [SK 3680 5987]. In this area the coal is generally between 30 and 45 in thick, though it thins to about 12 in west of Walnut Farm where the overlying sandstone is within 3.5 ft of the coal.

Press Mill Opencast Site lies at the northern extremity of the area of thick coal south-east of Alton village. Sections here and in the adjoining Alton Colliery show the northward deterioration of the seam to be the result of splitting into two leaves, accompanied by a deterioration in the lower part of the upper leaf (see (Figure 10)). In the worked area the two leaves are separated by up to 18 in of dirt. In Press Mill and Coldwell Farm boreholes, however, over 20 ft of measures separate the two seams, the upper of which contains a similar proportion of dirty coal to that recorded in the upper leaf of the combined seam. There is no evidence as to the persistence of the lower seam, but the upper one has been mapped northwards as the Alton. It is not seen again south of the Nether Loads area except in Wingerworth No. 3 Borehole where it is taken to be the 24-in coal at 59 ft. G.H.R.

At outcrop in the area south of Carr Brook the Alton seatearth is of greater economic importance than the coal, most of the workings being primarily for ganister.

On the eastern flank of the Wessington Anticline ganister has been worked [SK 3722 5814] 150 yd E. of Roadnook Farm, Wessington: here the coal is 14 to 18 in thick and the ganister 32 to 36 in. A southward extension of this site, approximately 300 yd S.E. of the farm, gives average thicknesses of 12 in of coal and 30 in of ganister. Farther south, near Dell Farm, 250 yd S. of Christ Church there are old workings [SK 3727 5734] said to have been in number of places on the western flank of the Wessington Anticline, where the coal is between 14 and 16 in thick and the ganister between 18 and 34 in. The ganister exposed in Tomlinson Wood [SK 3670 5742], 610 yd S. 74° W. of Christ Church, Wessington, and associated with coal debris, is believed to be the Alton ganister.

Ganister has been worked [SK 360 581] on the north side of the Moorwood Moor basin, the workings being abandoned because of coal: 14 in of coal have been seen resting on ganister, and the tips have yielded marine fossils. In opencast workings and trial pits between Dell Farm [SK 3741 5728] and Birches Brook [SK 3777 5657], the Aton Coal is between 20 and 25 in thick and the ganister, said to be of inferior quality in parts, up to 33 in. The ganister and coal have been worked both opencast and underground at a the high pyrite-content of the bed. Debris of marine shale can be seen at one point [SK 3559 5789] near the stream west of Lindway Springs [SK 3550 5791], and coal debris at another, but high dips and probable faulting make the position of the Alton outcrop, obscure.

On the south-west side of the Moorwood Moor basin ganister has been worked at Moorwoodmoor Mine [SK 3596 5573] and coal and ganister at Barratt's Pit [SK 365 552]. In this area, which includes Ilett Opencast Site, the Alton Coal is from 12 to 19 in thick, and the ganister 13 to 32 in. P.M.D.D., E.G.S.

Though the Alton Coal at outcrop in the southern part of the district is generally less than 24 in thick, boreholes show it to be considerably thicker to the east. The maximum recorded thickness is 50 in at Wingfield Manor Underground Borehole; other thicknesses are: Uftonfields Borehole 35 in, Carnfield Wood Borehole 37 in, Normanton Brook Borehole 40.5 in. The thickness of the Alton here is comparable with that in the vicinity of Woolley Moor but the two areas of thick coal are separated by one of thin coal which extends from the outcrop north-eastwards to Tibshelf and includes Alfreton. At Alfreton Colliery Underground Borehole no coal was recovered from the Alton horizon and at Tibshelf No. 1 Borehole the seam is only 21 in thick. G.H.R.

Alton Marine Band

The Alton Marine Band rests directly on, or only a few inches above, the Alton Coal, the fossils being preserved in dark grey pyritous shale which in its lower part commonly contains bullions (rounded masses of ironstone) with solid' goniatites (in places preserved in pyrite) including Gastrioceras listed (J. Sowerby). This horizon was first described by Gibson and others (1908, pp. 64–7, 100, 185), although a brief reference to the occurrence of goniatites above the Alton Coal had been made previously by Wedd (1903, p. 12). In both cases the localities referred to were just to the south of the district and in neither account was the name Alton Marine Band used. G.H.R., M.A.C.

At outcrop in the north the marine band is not seen in situ and the only evidence of its presence is the marine shale in the extensive tips [SK 2912 7210], [SK 2891 7247] north of New Bridge, where the road from Robin Hood to Bleak House crosses Blackleach Brook. R.A.E.

In the Holymoorside area the Alton Marine Band has been seen at only one locality—in a shallow hole [SK 3302 6961], 1400 yd S. 78° W. of Riversdale, where a few inches of weathered dark grey shale forming the top of the band yielded: Caneyella multirugata, Anthracoceras sp., mollusc spat and Elonichthys sp. E.G.S.

In the vicinity of Alton village the following marine fossils were obtained from shale and bullions found in the tips (now removed) at Alton Colliery and Stubben Edge Mine [SK 3650 6365] by W. Gibson in 1904 and later by Mr. J. V. Stephens: Caneyella multirugata, Dunbarella papyracea, Posidonia sp. nov. [cf. Price and others 1963, pl. iv, figs. 9 and 10]; Metacoceras?; Orthocone nautiloid; Gastrioceras coronatum Foord and Crick, G. circumnodosum Foord. G. listed; conodonts including Hindeodella sp., Lonchodina sp. and platformed examples.

The marine band was seen 0.75 mile S. of Alton at Little Stubbin Opencast Site by Dr. J. Shirley who collected several species of goniatites from the shales and bullions above the Alton Coal. The fauna includes: Dunbarella sp., Posidonia sp. nov.; Anthracoceras arcuatilobum (Ludwig), G. coronatum, G. circumnodosum and G. listed.

On the south bank of the River Amber [SK 3618 6132], 360 yd S.E. of Dalebank, marine fossils were collected from a shale tip by Mr. J. V. Stephens. The fauna includes: C. multirugata, Posidonia sp., Anthracoceras sp., G. listen and Palaeoniscid scales. G.H.R.

The band is exposed at two places in the Clattercotes Wood section: 480 yd N. 53° E. [SK 3638 6005] and 850 yd N. 83° E. [SK 3681 5988] of Whitecarr. Shale from the former locality yielded: Anthracoceras sp., G. listeri and platformed conodonts. At the latter locality the upper part of the Alton Coal can be seen, succeeded by 10 ft of shale, the top 5 ft of which yielded D. papyracea, G. cf. coronatum and G. listeri. In the opencast ganister workings [SK 3722 5814], 150 yd E. of Roadnook Farm, Wessington, marine fossils have been recorded from the tips of overburden though the marine band was not seen in situ.

The Alton Marine Band was seen on the eastern flank of the Wessington Anticline in an opencast trial pit [SK 3743 5674] between Dell Farm and Birches Brook, and consisted of 21 in of black shale with Dunbarella resting directly on coal. Dunbarella bearing shale lying immediately above the coal has also been seen on the western flank of the anticline [SK 3691 5663], where the coal and ganister have been worked both opencast and underground.

On the south-west side of the Moorwood Moor basin, tips near the old shaft at Moorwoodmoor Mine [SK 3596 5573] have yielded shale with Lingula mytilloides and Palaeoniscid scales. Specimens of Carbonicola cf. prisca (Trueman), also found in this tip, suggest that the Lingula is from the Alton Marine Band (Eden, 1954, p. 94). The marine band was seen further south at Barratt's Pit where marine lamellibranchs were seen in dark pyritous shale above the coal at one place [SK 3653 5510] in the workings. E.G.S., P.M.D.D.

In the north the Alton Marine Band has been proved at depth in Calow No. 1 Oil Borehole, on the crest of the Brimington Anticline, where Dunbarella was found in 12 in of ironstone and shale. In the south of the district it has been proved in the following boreholes: Alders, Cornfield Wood, Coldwell Farm, Golf Links, Handley Lodge, Handley School, Horsecar House, Meadow Farm, Morton Colliery Underground, Normanton Brook, Parkhouse Colliery Underground, Tibshelf No. 1, Uftonfields, Walnut Opencast 91/64, Wingfield Manor Underground and Woolley Moor No. 1. G.H.R.

The fauna obtained from these boreholes is as follows: foraminifera [rare]; sponge spicules; L. mytilloides, L. sp. [broad form]; C. multirugata, D. papyracea, Posidonia gibsoni, P. sp. nov. [right valve with prominent anterior ear]; Anthracoceras sp., Gastrioceras circumnodosum, G. listeri; mollusc spat, including gastropods; conodonts including Hindeodella sp., Lonchodina sp., Ozarkodina sp. and plat-formed examples; fish remains including Acanthodian scales, Elonichthys sp. and Rhadinichthys sp. The fossils extend over some 8 ft with the Gastrioceras; Dunbarella phase developed at the base of the band, and overlain by layers with Anthracoceras and Caneyella. The upper part of the band is a Lingula/fish association which at many localities is separated from the richest part of the band by shale with Geisina arcuata, an occurrence which has been noted previously (Eden 1954, p. 92; Taylor in Magraw 1957, p. 30). Foraminifera are present at the top of the band in Meadow Farm Borehole, and this horizon appears to mark their entry into the local sequence. Non-marine lamellibranchs occur immediately overlying the marine fossils at some localities but are limited to poorly preserved Carbonicola spp. including C. cf. prisca, and Curvirimula sp. nov. [broad form; cf. Price and others 1963, pl. iv, figs. 1, 27]. M.A.C.

Measures between the Alton Marine Band and Forty-Yards Coal

The measures between the Alton Marine Band and Forty-Yards Coal vary in thickness between about 80 ft and 145 ft, and are thickest in the Woolley Moor area, south-west of Clay Cross. They consist normally of two cycles, the lower of which includes the Alton Marine Band at the base; the upper contains Lingula and microfossils, generally in two distinct bands here named the Lower and Upper Parkhouse marine bands. Sandstone is present in the upper part of each cycle, that in the higher one being the local equivalent of the Loxley Edge Rock of the Sheffield country (Eden and others 1957, p. 45). At outcrop the division into two cycles is locally obscured by the merging of the two sandstones. G.H.R., E.G.S., R.A.E.

From the northern boundary of the district to Upper Loads the measures average 120 ft and consist of a lower shaly part and an upper sandy part. Locally shale divides the sandstone into two distinct beds. These are seen at outcrop and also in the Linacre Borehole, and, in some localities, as on the moors north-east of Clod Hall, they are rather coarse-grained. In the northern part of Brampton East Moor the upper sandstone forms low crags of rather coarse siliceous sandstone. R.A.E.

The measures crop out between Rodknoll, 1 mile W. of Loads Head, and Nether Loads, though they are poorly exposed. They are 80 to 100 ft thick and comprise two cycles. The 6 in of fireclay exposed in the stream [SK 3165 6946], 600 yd S. 52° E. of Loads Head, is taken as marking the top of the lower cycle, which consists largely of shale; the upper unit contains variable beds of sandstone, up to 35 ft thick. To the north-west of Upper Loads these sandstones appear to 'wash out' the fireclay horizon below it, and combine with a thin sandstone of the lower cycle, giving a total thickness of sandstone of about 50 ft. E.G.S.

Between Press reservoirs and Woolley, and beneath the surface as far east as Clay Cross and Morton, the measures are between 95 and 142 ft thick. The two cycles are of approximately the same thickness and both contain sandstone in the upper part. The upper sandstone occupies high ground between Sleigh Wood and the Press Reservoirs, and also forms an inlier in Sleigh Wood. The sandstones unite in the vicinity of the River Amber to form one thick bed which has been quarried [SK 3712 6043] at Woolley, where up to 30 ft of coarse buff sandstone with marked false bedding may be seen. G.H.R.

South of Woolley, the measures vary between about 85 and 120 ft. The sandstones are each up to 30 ft thick and are commonly flaggy with bands of siltstone and sandy shale. Apart from the sandstones, the measures are poorly exposed, but one of the Parkhouse marine bands is present in Wingfield No. 1 Borehole. This borehole also shows the presence of ironstone in the mudstones of both cycles; fish debris and rare 'mussels' were collected from above the Alton Marine Band. E.G.S., P.M.D.D.

The most complete sections through these measures are provided by the following boreholes drilled to the Alton Coal in the area south of Clay Cross and west of Tibshelf: Alders, Alfreton Colliery Underground (1952), Carnfield Wood, Coldwell Farm, Golf Links, Handley Lodge, Handley School, Horsecar House, Meadow Farm, Morton Colliery Underground, Normanton Brook, Parkhouse Colliery Underground, Tibshelf No. 1, Uftonfields, Walnut Opencast 91/64, Wingfield Manor Colliery Underground and Woolley Moor No. 1. They all show the development of two cycles though seatearth at the top of the lower one was found only at Morton. The majority of the boreholes show the two Parkhouse marine bands, about 10 ft apart, at the base of the upper cycle. In Alders Borehole and Walnut Opencast Site Borehole, however, the sandstones are almost united; only the lower marine band was present in the former borehole, while in the latter no marine fossils were found. The Lower Parkhouse Marine Band has yielded the following: abundant foraminifera including Agathammina sp., Ammodiscus sp., Ammonema sp.; Planolites ophthalmoides Jessen; Lingula mytilloides [7.0 mm]; conodonts (commonly found in faecal assemblages) including Hindeodella sp. and platformed examples; fish scales including Elonichthys aitkeni Traquair and Rhadinichthys sp. A similar fauna has been collected from the Upper Parkhouse Marine Band, but the foraminifera are smaller and not as numerous. Pyrite is common in both bands. G.H.R., M.A.C.

Forty-Yards Coal

The Forty-Yards Coal, with a maximum thickness of 15 in, is of no economic significance but the seatearth, consisting of ganister and fireclay, has been worked along much of its outcrop. G.H.R.

The seam has been mapped continuously from the northern margin of the district to 800 yd W. of Loads Head. Small scale opencast workings, presumably for refractories, occur at about this horizon near Blackleach Brook [SK 2940 7228], 400 yd S.W. of Clod Hall. The workings were on two levels a few feet apart. Fragments of ganister are to be seen in the stream bank. The floor of the coal is exposed in Wadshelf Brook [SK 2974 7125], 1000 yd W. of New Inn, Eastmoor; it consists of contorted whitish grey sandy fireclay with ganister lenses up to 6 in thick. Coal fragments weather out above. Coal and ganister fragments in the soil are also seen some 800 yd S.S.W. of New Inn. An extensive area of old excavations for fireclay occurs about 1500 yd south of the inn; the clay was worked both opencast and by means of shallow shafts and adits. Rod Knoll Mine [SK 3047 7000], 1450 yd S. 8° W. of the inn, showed the following section: bind, smut 3 to 6 in, ganister 3 to 6 in on fireclay 30 in. Another nearby working showed 36 in of clay under 4 in of ganister and it was noted that the clay only was extracted. In the Linacre Borehole 7 ft of ganister and fireclay were listed at this horizon. R.A.E.

The Forty-Yards Coal crops out between Rodknoll and Nether Loads and the seat-earth has been worked along almost the whole of this tract in both opencast and underground workings; numerous sections have been recorded, showing that 6 to 18 in of ganister overlie 18 to 48 in of fireclay. The only mine working at the time of the resurvey was Siddons Mine [SK 3119 6974], 60 yd S. of Loads Head. The section visible at the adit entrance is: dark shale with ironstone nodules and a 2 to 6-in band of 'tank' 10 ft, coal 6 in on ganister; in the workings the ganister varies between 6 and 16 in, and the fireclay beneath is 3 ft thick. In the entrance to an abandoned adit [SK 3151 6958], 400 yd to the S.E. of Siddons Mine, a 6-in coal, overlain by 10 ft of shale and underlain by 18 in of ganister on fireclay, can be seen.

The outcrop of the Forty-Yards is broken by the north-westerly fault through Nether Loads, but appears again in Stone Edge Plantation, and the ganister apparently occupies the long dip-slope extending down to Sleigh Wood. There are several overgrown ganister workings on this dip-slope, but no records have been preserved. E.G.S.

Both the coal and its seatearth are exposed in the southern extremity of Sleigh Wood [SK 3549 6614]: 3 in of coal overlie 30 in of ganister which, in turn, rest on fireclay. The soil in the neighbouring fields and on the long dip-slope east of Birkin Lane, abounds with fragments of ganister. In Ivyspring Wood [SK 3616 6642] 3 in of coal on 4 ft of ganister were formerly seen. South of Ivyspring Wood the outcrop of the coal follows the top of the underlying sandstone into the vicinity of Stubben Edge Mine where the cored borehole at Press Mill Opencast Site records 1 in of coal at 37 ft resting on a seatearth of brown and green mudstone. In boreholes drilled between the outcrop and Clay Cross and Morton to the east the coal varies in thickness between 1 and 10 in and is underlain in the majority of cases by about 2 to 2.5 ft of ganister or ganister-like sandstone resting on a foot or two of grey-brown fireclay. In some of the boreholes two seatearths, separated by about 2 ft of mudstone or sandstone, are present at the Forty-Yards horizon. The lower seatearth is topped in the Handley Lodge Borehole by a 5-in coal and in the Parkhouse Colliery Underground Borehole by 4 in of cannel. G.H.R.

In the area south of Brackenfield the Forty-Yards seatearth has been dug for fireclay in both opencast and underground workings and has been proved in trial pits and boreholes. The associated coal is from 3 to 15 in thick, including, in places, a dirt parting, and it overlies 3 to 9 in of ganister on up to 6 ft of fireclay. On the western flank of the Wessington Anticline the coal has been proved on the south side of Birches Brook and is seen in Brow Wood [SK 3642 5776], 950 yd N. 78° W. of Christ Church, Wessington, where dark grey silty mudstone 4 ft, brown mudstone 1 ft, coal 6 to 9 in and ganister about 15 in, rest on fireclay. Some 1380 yd N. 88° W. of the same church, the coal exposed in Lindwaysprings Brook [SK 3602 5764] is thought to be the Forty-Yards; coaly shale with fish debris 1 ft, coal 15 in and fireclay 2.5 ft overlie dark grey silty mudstone. The same seam has been proved in a borehole 70 yd to the south-east where it was 18 in thick. South of Lindway Springs it has not been found possible to trace the outcrop of the Forty-Yards except over a limited distance west of South Wingfield where the coal has been seen at two places on the roadside between South Wingfield and Plaistow. At one of these [SK 3700 5559], 650 yd N. 70° W. of South Wingfield Methodist Church, dark iron-stained mudstone 4 ft, soft dark shale with fish debris, including Acanthodian and Palaeoniscid scales, 6 to 7 in, coal 12 in, bastard ganister 2 to 3 in, ganister 3 to 6 in, rested on hard sandy fireclay 12 in. In Wingfield No. 1 Borehole the coal is 8 in thick resting on 2 ft of inferior ganister, fireclay being absent. E.G.S.

In the south of the district, Carnfield Wood, Golf Links, Normanton Brook, Tibshelf, Uftonfields and Wingfield Manor Colliery Underground boreholes all proved coal between 3 and 9 in thick resting on ganister or ganister-like sandstone. At Alfreton Colliery Underground Borehole where the coal was not found, the seatearth includes 20 in of ganister. G.H.R.

Measures between the Forty-Yards and Norton coals

The measures between the Forty-Yards and Norton coals, comprising a single cycle, are thickest in the north where up to 70 ft of mudstone and sandstones occur, and thinnest in the south where as little as 30 ft of argillaceous sediments are found.

Near the northern margin of the district the measures consist predominantly of shale, although some sandstones are present. At Loads Head, the upper half of the cycle is sandy, and 530 yd W.N.W. of the farm thin off-white flags have been quarried [SK 3075 7005] on a small scale. Flaggy beds with bands of sandy shale or siltstone are also visible in small exposures as far south as Press Brook, beyond which sandstone has not been traced. Between Press Brook and the southern margin of the district the measures are almost everywhere argillaceous and the absence of sandstones is reflected in the thinning of the strata to 40 or 50 ft between Press Brook and Carr Brook and to 30 or 35 ft south of Carr Brook. G.H.R., R.A.E., E.G.S.

Boreholes confirm that this general southerly thinning is associated with a decrease in the amount of sandstone. They also show that the mudstones in the lower part of the cycle are predominantly dark grey and contain ironstone bands; fish debris occurs throughout and Curvirimula sp. has been recorded from Normanton Brook Borehole. The sediments immediately above the Forty-Yards Coal commonly contain pyrite, and marine fossils have been found at this horizon in some localities. Lingula is recorded in Wingfield Manor Underground and Wingfield No. 1 boreholes, and foraminifera and fish remains have been found in Handley Lodge, Meadow Farm and Normanton Brook boreholes. It is here proposed to name this horizon The Forty-Yards Marine Band and to regard Meadow Farm Borehole as the type locality (see also Eden 1954, pp. 101, 105). The complete faunal list is: foraminifera including Ammodiscus sp.; sponge spicules [pyritized]; L. mytilloides; platformed conodonts; fish remains including Elonichthys aitkeni, Megalichthys sp. and Rhadinichthys sp. G.H.R., M.A.C.

Norton Coal

The Norton Coal is only a few inches thick in the southern part of the Sheffield (100) district (Eden and others, 1957, p. 47) and it is therefore inferred that an extensive area of old workings [SK 292 728] at this horizon, some 500 yd N.W. of Clod Hall, was for the refractory seatearth flooring the seam. Ganister fragments are to be found in the soil in this area, and much ganister was also turned out from a pipe-trench 300 yd W. of Clod Hall. A well at Stonelow Flat Farm [SK 2962 7203] is said to have penetrated coal 6 in, on ganister 8 in, on fireclay. In a small quarry [SK 3008 7142], 700 yd S.S.E. of this farm the coal is 10.5 in thick and rests on 2 in of ganister overlying 32 in of fireclay. In the stream [SK 3307 6992], 300 yd S.W. of Chanderhill Farm, the section is: coal 4 in, ganister 12 in, on fireclay 9 in. The seam was recorded as 10 inches in Linacre Borehole, the refractory floor being very thin. R.A.E.

Several of the Chanderhill Reservoir borings proved the Norton Coal at shallow depth; in only one [SK 3311 6979] is its thickness recorded-6 in. The thin coal seen in the stream section in Moorlawn Coppice [SK 3404 6836], 1420 yd N. 45° E. of Stonehay Farm, and [SK 3519 6736] 640 yd N. 64° W. of Stubbing Court, is believed to be the Norton. The section visible at the first place was: siltstone 2 ft, coal 4 in, ganister 3 in, on fireclay; and at the second: dark shale 2 ft, yellow clay 1.5 in, coal 2 in, ganister 4.5 in, fireclay 2.5 ft, on flaggy sandstone 4 ft. There are signs of shallow workings on the Norton seatearth along the crop between Stone Edge Plantation and Stubbing Court, but the only known section of the seatearth is that given above. E.G.S.

South of Stubbing Court there are no workings in the coal or its seatearth, and the outcrop cannot be determined with any accuracy except in the South Wingfield–Moorwood Moor area. The coal was formerly seen in the road cutting [SK 3730 5556], 370 yd N. 53° W. of South Wingfield church, and the coal debris visible in the stream 400 yd to the south is assumed to be from the same horizon. In Moorwoodmoor Colliery shaft [SK 3551 5684] the 24-in coal at 240 ft is taken to be the Norton, and nearby trial borings show the seam to be of variable thickness. In Wingfield No. 1 Borehole the Norton is 12 in thick, and in Wingfield No. 2 Borehole a seam recorded as being 18 in thick at 229 ft, but from which no core was recovered, is tentatively correlated with it.

The seatearth is 11.5 ft thick at Wingfield No. 1 Borehole where it was described as grey to dark grey clunch with ironstone. E.G.S., P.M.D.D.

Norton Marine Band

The Norton Marine Band (see Eden 1954, p. 96) has been seen at outcrop only at Moorwood Moor in the stream [SK 3633 5575], 1060 yd N. 65° E. of Edge Farm, where dark mudstone yielded Caneyella sp. nov.aff. multirugata, Dunbarella aff. papyracea, Posidonia cf. gibsoni and conodonts. In Wingfield No. 1 Borehole, a few yards east of the outcrop, it consists of 1 in of dark grey silty mudstone with Dunbarella sp.

The marine band has also been recorded in the following boreholes: Carnfield Wood, Coldwell Farm, Handley Lodge, Horsecar House, Meadow Farm, Normanton Brook, Tibshelf No. 1, Uftonfields, Wingfield Manor Colliery Underground, Woolley Moor Nos. 1, 2 and 3. The coal, where present, is overlain by a variable thickness—. up to 4 ft 3 in is recorded—of sediments containing a high proportion of silty and sandy material, and from which, at Woolley Moor No. 1 Borehole, poorly preserved Carbonicola is recorded. The marine fossils occur in an overlying bed of dark grey shale or mudstone, commonly silty and pyritous, and generally not more than 2 to 3 inches in thickness. G.H.R., E.G.S.

The distinctive nature of the band is typically illustrated by the development in Normanton Brook Borehole, where a 1-in layer with Dunbarella and abundant conodonts overlies an equally thin layer with Lingula and foraminifera. In some localities, e.g. Wingfield Manor Underground Borehole, the Lingula/foraminifera phase also reappears above the Dunbarella. This characteristic faunal pattern and lithology is maintained over a large part of the coalfield. In the present district the complete fauna is: foraminifera (abundant) including Agathammina sp., Ammodiscus sp., Ammonema sp.; C. sp. nov.aff. multirugata, D. aff. papyracea, P. cf. gibsoni; abundant conodonts including Hindeodella sp., Lonchodina sp., Ozarkodina sp., platformed conodonts undetermined; and fish remains. In the Lancashire Coalfield the equivalent horizon, Tonge's Marine Band, shows a -closely comparable development (Earp and Magraw 1955).

The marine band is overlain by 30 to 50 ft of mainly argillaceous sediments with a variable amount of ironstone, but up to 20 ft of siltstone and sandstone are developed locally immediately below the Upper Band seatearth. Towards the middle of the cycle the Norton 'mussel'-band (Eden 1954, p. 97; Eagar 1956, p. 350; 1962, p. 325–6) is up to 12 ft thick and contains a distinctive Carbonicola fauna preserved in dark grey silty mudstone. The fossils found in the Morton Colliery Underground Borehole are typical and include: Spirorbis sp.; Carbonicola crispa Eagar, C. extenuata Eagar, C. proxima Eagar, Curvirimula sp. nov. [broad form, cf. Price and others, 1963, pl. iv, figs. 1 and 2]; Geisina arcuata; Elonichthys sp., Rhabdoderma sp. and Rhadinichthys sp. This is the highest faunal band in the A. lenisulcata Zone, the base of the overlying C. communis Zone being taken at the horizon of the Upper Band Coal (Eagar 1956, p. 355). G.H.R., M.A.C.

Upper Band Coal

The Upper Band Coal is generally thin or absent over much of North Derbyshire (Eden 1954, p. 97) but a coal investigated for opencast working on Leash Fen appears, from its position, to be at this horizon. In a trial pit [SK 2933 7323], 800 yd N. 19° W. of Clod Hall, a roof of micaceous mudstone rested on soft 'brights' 6 in, strong 'brights' 23 in and light grey clunch 18 in. Borings suggest that the seam maintains its thickness for about 500 yd along the strike, beyond which point it suddenly thins. R.A.E.

South of Leash Fen the coal appears to be absent. At Slatepitdale two small mines have worked fireclay at this horizon. One of these, Stone Edge Clay Pit [SK 3432 6795] (abandoned 1927), 1350 yd N. 68° E. of Stonehay Farm, worked 3.5 ft of fireclay below 1 ft of rock; the other, Sitwell Clay Mine [SK 3437 6776] (abandoned 1926), 1320 yd N. 78° E. of Stonehay Farm, worked ganister 3 in on fireclay 4 ft 10 in. The records of the boreholes drilled in the southern half of the district show that the Upper Band seatearth is present everywhere and consists of up to 7 ft of grey, brown or green mudstone.

Measures between the Upper Band and the Wingfield Flags

The measures between the Upper Band and the Wingfield Flags are predominantly argillaceous, though siltstones are common in the upper part; they are about 100 to 220 ft thick. At outcrop they tend to form hollows between the Wingfield Flags and the underlying sandstone-bearing basal Coal Measures, one such hollow being occupied by Leash Fen on the northern margin of the district. Exposures are poor except in the banks of the stream [SK 363 670] issuing from Great Pond, Stubbing Court, where the lowest 60 to 70 ft of mudstones may be seen. They vary from grey to almost black, are silty in parts, and contain scattered ironstone nodules. G.H.R., E.G.S., R.A.E.

The argillaceous nature of the measures is confirmed by the boreholes that have explored below the Wingfield Flags in the Chesterfield district. In the Linacre Borehole in the north, they were recorded as being 104 ft thick. The thickest developments, 200 to 220 ft, are in the Coldwell Farm and Meadow Farm boreholes, near Clay Cross, though the upper limit is ill-defined because the siltstones at the top grade upwards into the Wingfield Flags. Pyrite is present in up to 35 ft of dark grey mudstones that succeed the Upper Band seatearth. In three boreholes marine fossils have been found in a band less than one inch thick some 25 ft above the seat-earth. It is here proposed to call this band the Burton Joyce Marine Band from its occurrence in the borehole of that name near Nottingham, where it was first recorded in the East Midlands Coalfield (Eden, 1954, p. 101). G.H.R.

In Meadow Farm Borehole the only fossils found were foraminifera, including Ammodiscus sp., associated with rare Geisina arcuata and fish debris. Conodonts were obtained from Handley Lodge Borehole, together with fragmentary lamellibranchs identified as Caneyella cf. multirugata and Posidonia sp. nov. [prominent anterior lobe]. Similar lamellibranchs occur two miles to the south-east in Morton Colliery Underground Borehole. Careful examination of these beds in other boreholes within the district has yielded only Geisina arcuata, fish scales including Rhadinichthys sp., and ? Planolites ophthalmoides. This is the highest of the more persistent marine bands in the Lower Coal Measures (but see p. 121). On the west of the Pennines the equivalent marine horizon, the Ditton Marine Band, contains only foraminifera and conodonts (Magraw, 1957, p. 37). Twelve feet above the marine band in Morton Colliery Underground Borehole the telson of a crustacean has been recorded (Eden 1954, p. 98) and is determined as Gen. et sp. nov. cf. Palaeocaris.

The mudstones above the pyrite-rich beds contain few fossils; those noted include the non-marine lamellibranchs Anthraconaia sp. nov. cf. modiolaris (J. de C. Sowerby), Carbonicola bipennis (Brown), C. subconstricta ? Wright (non J. Sowerby), Curvirimula sp. and Naiadites flexuosus Dix and Trueman, and represent the earliest C. communis Zone fauna. Various indeterminate fish remains and one ostracod, Carbonita sp. from Tibshelf No. 1 Borehole, have also been found. M.A.C.

Wingfield Flags

The Wingfield Flags, a group of sandstones with shale and siltstone bands, are the equivalent of the combined Brincliffe Edge (or Greenmoor) Rock and Grenoside Sandstone of the country to the north. These two sandstones come together in the vicinity of Leash Fen, where the resulting sandstone, with impersistent shale and siltstone bands, is 250 ft thick. At outcrop south of Free-birch the interbanded shales and siltstones give rise to ' slacks ' within the main feature with the result that the Wingfield Flags, here varying between 100 and 200 ft, form a series of marked features running through Holymoorside, Moorlawn Coppice, Slatepitdale and Harper Hill. From Bole Hill to Carr Brook the Flags are between 160 and 220 ft thick and sandstone is largely confined to one main bed forming a conspicuous feature. South of Carr Brook the thickness averages about 200 ft and the sandstone is again split by argillaceous bands as far as South Wingfield where the single feature reappears. G.H.R., E.G.S., R.A.E.

In the north the Wingfield Flags are exposed in the Linacre Valley where three sandstone bands with intervening shales and siltstones are to be seen. A generalized section of the strata in the Upper and Middle

The 6-ft sandstone at the top is equivalent to part of the Grenoside Sandstone; a micaceous laminated appearance is characteristic of this sandstone over a wide area (Eden and others 1957, p. 51). R.A.E.

The sandstones, generally micaceous and flaggy though in parts massive, are well exposed in roadside exposures and old quarries. Freebirch Quarries [SK 311 727], at the head of the Linacre Valley, have been worked intermittently over a long period, quarrying fine-grained massive sandstone and flags, with thin beds of shaly sandstone. A small quarry operating here in 1947 showed the following section:

The stone in this quarry is bluish grey when fresh, weathering to a buff colour. At Bole Hill Quarry [SK 368 661] the Wingfield Flags are still being worked and up to 40 ft of grey and buff sandstone with a variable amount of mica are visible. The quarry is situated in an area where the Wingfield Flags are largely composed of one main sandstone bed, and the working face of the quarry shows the sandstone here to be fairly massive and false-bedded, the flags being confined to the top, weathered part of the face. G.H.R., R.A.E.

The siltstone with 'rootlets' recorded in the Linacre reservoirs section given above is possibly at the same horizon as the seatearth noted in the Sheffield district (Eden and others 1957, p. 51) in the measures between the Brincliffe Edge Rock and the Grenoside Sandstone. It is recorded in the majority of the boreholes drilled through these measures to the west and south of Clay Cross. The position of the seatearth relative to the main development of sandstone suggests that in the Clay Cross area and as far south as Morton and Tibshelf the Wingfield Flags consist of a thick development of sandstone (equivalent to the Grenoside Sandstone) above the seatearth, and a variable succession of sandstones, siltstones and mudstones (equivalent to the Brincliffe Edge Rock) below. In the south of the district, however, the principal sandstones are found below the seatearth, the overlying measures up to the Kilburn Coal being largely mudstones up to 70 ft thick. These are well developed in the following boreholes: Alfreton Colliery Underground (1952), Carnfield Wood, Golf Links and Uftonfields, and contain Spirorbis sp., Carbonicola cf. bipennis, Geisina arcuata and fish remains.

In Carnfield Wood, Golf Links, Normanton Brook and Uftonfields boreholes an extra seatearth is developed below the Kilburn. It is regarded as being a split off the Kilburn seatearth, though at Uftonfields the intervening measures are some 16 ft thick and contain non-marine lamellibranchs including Carbonicola sp., Curvirimula trapeziforma (Dewar) and Naiadites sp. G.H.R.

Kilburn Coal to Blackshale Coal

The variation in this group of measures is depicted on (Figure 11). They vary in thickness from about 550 ft in the north-west to about 450 ft to the south of Walton Wood. The thinning is due almost entirely to the smaller proportion of sandstone present in the measures below the Lower Brampton Coal. Borehole sections through this group are few and unsatisfactory in the north, but from Clay Cross southwards numerous comprehensive sections are available, and they show the Kilburn to be the only seam to attain workable thickness. G.H.R.

Kilburn or Grenoside Sandstone Coal

The Kilburn is best developed in the southern part of the district. It deteriorates both in quality and thickness to the north where its position at outcrop is not precisely known. Its equation with the Grenoside Sandstone Coal, which has been mapped in the extreme north, cannot be proved on the ground though both coals lie at a similar stratigraphical position above the Wingfield Flags. G.H.R., R.A.E., E.G.S.

The Grenoside Sandstone Coal is seen in several sections in the Linacre Valley. In a stream [SK 3251 7301] 450 yd N.W. of the north end of the Upper Linacre Dam, for example, the section is coal (fragmentary) 6 in, silty seatearth 30 in, on coal 5 in. In consisting of two leaves split by a dirt parting, the seam is continuing the development characteristic of the southern part of the Sheffield district (Eden and others 1957, p. 53). The seam is not recorded in the vicinity of Freebirch Quarries and it is possibly washed out. It cannot be traced southwards from Linacre Valley and indeed its horizon must be faulted out in the ground immediately north of Chanderhill. About 150 yd S. of Chanderhill, however, a 4-in coal proved in a trench [SK 3321 7003] is believed to be on the same horizon and is believed also to be the northern limit to which the Kilburn Coal can be traced. R.A.E.

Between Chanderhill and Hollins Green, 5 miles to the south-south-east, the position of the Kilburn Coal above the Wingfield Flags is conjectural. East of the outcrop in this area the coal has been proved in two underground boreholes—at Grassmoor Colliery, where it is represented by 8 in of inferior coal, and at Bolsover Colliery, where it is 18 in thick.

Southwards from Hollins Green the outcrop has been located with a view to opencast mining. North of the Stretton–Fletcherhill road the seam is up to 46 in thick but contains a high proportion of dirt. South of the road the coal, though thinner, contains proportionally less dirt and has been worked in a series of long narrow opencast sites in which the eastward dip varies between about 14° and 30°. G.H.R., E.G.S.

The coal has been worked underground from Wingfield Manor Colliery, where the thickness was generally found to be between 24 in and 36 in, although isolated thicknesses of up to 39 in were recorded.

Numerous boreholes have proved the Kilburn in the southern half of the district. Those between Clay Cross and Morton (Clay Cross, Horsecar House, Meadow Farm, Morton Colliery Underground and Parkhouse Colliery Underground) confirm that the northward deterioration persists east of the outcrop. Those south of Morton (underground boreholes: Alfreton Colliery (1952), Alfreton Colliery Nos. 1 and 2, Blackwell 'A' Winning Nos. 1, 2 and 3, Cotespark Colliery No. 1, Kirkby Colliery K1 and K5, Swanwick Colliery No. 2; surface boreholes: Carnfield Wood, Normanton Brook, Tibshelf No. 1 and Uftonfields) prove up to 30 in of coal in the west, a central area where the coal is absent, and a thickness of 15 to 17 in. in the east.

An unusual development of the Kilburn horizon was encountered in Carnfield Wood Borehole where there were 87 in of cannelly shale and shale; the 55 in of cannely shale containing Curvirimula sp., Geisina arcuata and fish debris were divided into two bands by 32 in of dark shale.

The Kilburn Seam is composed largely of bright coal with subordinate bands of dull coal, particularly in the lower part of the seam. Where worked, the coal is of good quality with only a moderate ash content. G.H.R.

Measures between the Kilburn and Lower Brampton coals

The measures between the Kilburn and Lower Brampton coals exhibit, to the west of Chesterfield, the same alternation of flags, shales and thin coals as do the Penistone Flags in the Sheffield district. The generalized section in this ground (section 1 of (Figure 11)) is presented with some reserve, since it is built up mainly from natural exposures in ground which, though well featured, contains few marker-horizons. The interpretation of the surface geology is moreover complicated by the presence of northwesterly trending faults which may well be more numerous than shown on the map. The calculated thickness of about 330 ft is confirmed by the section provided by Nuttack Lane Borehole.

The coal of Chanderhill Farm was said locally to have been 24 in thick where grubbed out at crop [SK 3354 6997] some 450 yd S.E. of the farm, but this record is of a doubtful nature. It is recorded in Nuttack Lane Borehole 25 ft above the seam believed to be the Kilburn. The coal of the Lower Linacre Reservoir is exposed at several places in and around the Linacre Valley. Just below high water level in the southeast corner [SK 3380 7244] of the reservoir a complete section was seen: coal 7.5  in, clay 1.5 in, on coal 5 in. Flagstone bands above and below this coal form well-defined features on the northern side of the Linacre Valley, and the horizon of the coal can be followed northwards to shallow workings [SK 3200 7350], 700 yd E.S.E. of Grange Hill. Here the coal was said to be only 8 in thick. The coal of Barlow Grange was 6 in thick in a ditch [SK 3165 7397], 100 yd N.W. of the farm buildings. Its roof shales contain Spirorbis sp. and large mussels ', and thus closely resemble those of the coal of Crow-hole Reservoir, which lies above the next sandstone up in the succession. The latter seam is well exposed around the reservoir a few hundred yards north of the sheet boundary (Eden and others 1957, p. 55), where it is 3 to 7 in thick, but is not visible in the Chesterfield district. The coal east of Nether Chanderhill was at least 6 in thick in foundations [SK 3357 7047] north of the road, 700 yd W. of Fairfield, but a coal in a similar stratigraphical position, noted in stream sections [SK 3331 7124] 1300 yd N.W. of Fairfield, has a full thickness of only 3 in. The mudstones between this thin coal and the Lower Brampton Coal contain abundant mussels '. The fauna found near Barlow Common half a mile north of the sheet-boundary was detailed by Eden and others (1957, p. 132). The 'mussel'-bearing beds are exposed north-west of Chesterfield in the stream sections a few hundred yards east of Oxton Rakes [SK 330 738] and again in stream sections [SK 334 711] and [SK 3352 7093] 0.25 mile E. of Frith Hall. The following species have been identified: Spirorbis sp.; Carbonicola acuta (J. Sowerby), C. cf. browni Trueman and Weir, C. aff. pseudorobusta Trueman and Naiadites flexuosus. Some sections of the mudstone show many ironstone lenses; this led Gibson and Wedd (1913, p. 60) to suggest that the name Oxton Rakes may indicate former workings of the horizon for ironstone. R.A.E.

The measures are 205 ft thick in Bolsover Colliery Underground Borehole, and appear to be about the same thickness at outcrop between Riversdale and Hill Houses where they consist of mudstones with several thin, impersistent coals and numerous beds of flaggy sandstone which are very variable in both thickness and lateral extent. Exposures in these measures are poor and scattered, the best being in Birdholme Brook [SK 360 688] at Walton where mudstone and sandstone are seen at intervals. Only one coal has been mapped and that for only a short distance in the vicinity of Holymoorside. It is probably the equivalent of the coal of Lower Linacre Reservoir, and was proved in foundations [SK 3404 6973] at the junction of Doghole Lane and Pocknedge Lane, and in excavations for the footbridge [SK 3436 6959] over the River Hipper, respectively 280 yd S. 57° W. and 330 yd S. 20° E. of Riversdale. There is also evidence that it has been worked in the fields [SK 345 689] south-east of Walton Hilltop, 1100 yd S. 16° E. of Riversdale. No sandstone was recorded in the Bolsover Colliery and Grassmoor Colliery underground boreholes, and only one thin seam, 103 ft above the Kilburn is noted in the section of the former. E.G.s.

Southwards from Walton Wood, sandstones, though present at several horizons, are thinner than to the north, and over much of the country occupied by this group at outcrop only two relatively narrow sandstone features occur. Exposures are few and consist of isolated sections in mudstone and flaggy sandstone; no coal exposures have been recorded. The main source of information on the measures in this area lies in the records of the following boreholes: surface boreholes—Carnfield Wood, Clay Cross, Golf Links, Horsecar House, Meadow Farm, Normanton Brook, Tibshelf No. 1, Uftonfields; underground boreholes—Alfreton Colliery (1952), Alfreton Colliery Nos. 1 and 2 (Kilburn), Blackwell 'A' Winning Nos. 1, 2 and 3, Cotespark Colliery No. 1, Kirkby Colliery Nos. K1 and K5, Morton Colliery, Parkhouse Colliery, Swanwick Colliery Nos. 2 and 3. The boreholes show the average thickness of the group to be about 200 ft, consisting, in general, of five cycles, though in some localities only four are recognisable. Coal is not consistently developed at any level and, where it does occur, is rarely more than a few inches in thickness. The fauna is discussed below. G.H.R.

The roof measures of the Kilburn Coal are distinguished by the abundance and good preservation of fish remains, mainly scales, belonging to the genera Elonichthys, Rhabdoderma, Rhadinichthys and Rhizodopsis with associated Acanthodian spines and undetermined Platysomid scales. These occur in dark mudstones which may immediately overlie the coal or be separated from it by several feet. The fish beds are commonly associated above and below with grey mudstones containing cf. Planolites sp. and Cochlichnus kochi. In Carnfield Wood Borehole Lingula was found in association with fish remains in dark mudstone 3 ft above the Kilburn horizon, and is a unique record in the south Pennine area. The Lingula, which measure up to 5.5 mm in length, range through 8 in of core. It is remarkable that no trace of this marine incursion has been noted from the surrounding district or further afield. It is of interest that the underlying Kilburn Coal is here developed as cannelly mudstone (see p. 118). M.A.C., G.H.R.

C. kochi, cf. Planolites sp. and fish debris have also been found in the mudstones of the succeeding cycles. The lowest 'mussel' fauna occurs about 100 ft above the Kilburn Coal in Meadow Farm Borehole and includes Carbonicola aff. bipennis, Curvirimula sp. and Naiadites sp. The earliest appearance of Carbonicola pseudorobusta is some 20 ft higher where it is associated with Spirorbis sp., Carbonicola aff. communis Davies and Trueman, Curvirimula subovata (Dewar), Geisina arcuata, Diplodus sp., Rhabdoderma sp. and Rhadinichthys sp. In some boreholes Carbonitahumilis (Jones and Kirkby) also occurs at this horizon. These shell-bands mark the transition from the C. bipennis faunas of the lower part of the C. communis Zone to the middle C. communis Zone faunas with the C. communis/pseudorobusta group dominant (Calver 1955, p. 33).

The measures between the basal C. pseudorobusta fauna and the well-developed 'mussel '-band between the Lower Brampton and Upper Brampton or ? Mickley Thin seams (see below) include several impersistent faunal bands. The composite fauna comprises: Carbonicola cf. declivis Trueman and Weir, C. pseudorobusta, Curvirimula subovata, C. trapeziforma, Naiadites flexuosus, Geisina arcuata, fish remains and cf. Planolites sp. [2.0 mm diam.] (see Woodland and others 1957, p. 55). In addition, an unusual ostracod, which appears to belong to an undescribed genus, occurs 135 ft above the Kilburn Coal in Normanton Brook Borehole. The specimens resemble Geisina, but differ in the presence of elongate tubercles or horns each side of the median sulcus. The same species was collected from an horizon 240 ft above the Grenoside Sandstone Coal near Moorhall (Eden and others 1957, p. 136), to the north of the present district. M.A.C.

Lower Brampton Coal

The Lower Brampton Coal is the equivalent of the ? Walkers Coal of the southern part of the Sheffield district and is of significance only in the north-west. It was 19 to 22 in thick in trial pits [SK 325 741] north of the Linacre Valley, and similar thicknesses were recorded in shallow workings [SK 336 710] up to 1100 yd south of Old Brampton. Partial exposures of the seam are seen in streams east of Thorpe House [SK 3347 7344] and Frith Hall [SK 3366 7107]. The seam also crops out on the east side of Chesterfield, near the centre of the Brimington Anticline between Brimington Common and Tapton Grove, where its thickness has been proved in shallow boreholes to be between 13 and 23 in. South of Belmont Park the seam has not been seen at outcrop, and in boreholes through these measures elsewhere in the district it is usually represented either by its seatearth or by an inch or two of coal; there is a single record of 13 inches in Swanwick Colliery No. 3 Underground Borehole. R.A.E., G.H.R.

Measures between the Lower Brampton and Upper Brampton or ? Mickley Thin coals

The measures between the Lower Brampton and Upper Brampton or ? Mickley Thin coals are poorly exposed, but the evidence from boreholes, mainly in the central and southern parts of the district, indicates a thickness of 55 to 60 ft. Apart from a sandy horizon immediately beneath the Upper Brampton Coal the strata consists of mudstones, commonly dark grey in colour and containing an abundant 'mussel' fauna associated with ostracods and scattered fish debris. The fauna includes: Spirorbis sp., Carbonicola acuta, C. cf. browni, C. aff. communis, C. pseudorobusta, Curvirimula subovata, C. trapeziforma, Geisina arcuata and fish debris. R.A.E., G.H.R., M.A.C.

Upper Brampton or ? Mickley Thin Coal

The Upper Brampton or ? Mickley Thin Coal. The correlation of the Mickley Thin of the Chesterfield district with that in the type area at Mickley near Sheffield (Eden and others 1957, p. 56) is not definite. The uncertainty arises in the south of the Sheffield district where the seam has been called the ? Mickley Thin. Locally, to the west of Chesterfield it is called the Upper Brampton or Brampton High Coal. G.H.R.

Near the northern boundary of the district the seam has a low ash content, varying from about 1 to 3.5 per cent in trial pits on Abbey Opencast Site, and in this respect it is similar to the Mickley Thin of the Mickley area. Although the pits at Abbey Opencast Site show a variation only from 20 to 22 in, preliminary results in the prospecting of the adjoining Overholme Opencast Site suggest that the variation there is from 15 to 33 in; in old workings within the area of Abbey Opencast Site, immediately north-east of Thorpe House, 33 inches were recorded.

On the east side of Chesterfield, at Fish Opencast Site between Brimington Common and Tapton Grove, the seam consisted of 4 in of dirty cannel on 19 in of strong bright coal with pyrite lenses. In this area the coal has been traced as far south as Cock Alley Opencast Site where it has been proved in shallow boreholes. R.A.E.

South-west of Chesterfield, along the main outcrop, the position of the coal is indicated by old workings in Walton Wood, at . Swathwick and in Bradbury Wood, west of Hill Houses. It was not recorded in Grassmoor Colliery Underground Borehole, but at Bolsover Colliery Underground Borehole it appears to be represented by 48 in of inferior cannel. E.G.S.

Between Newmarket and Smithymoor, about 1 mile S.W. of Clay Cross, the ? Mickley Thin is taken to be the lowest seam proved during the prospecting of Newmarket Opencast Site; it varies in thickness between 16 in and 19 in and is composed of bright coal with fusain partings. G.H.R.

The seam has not been seen at outcrop between Smithymoor and South Wingfield, and for much of this distance it must lie beneath alluvium. During the earlier survey a coal was seen in the river bank [SK 3807 5535], 650 yd S. 30° W. of All Saints' Church, South Wingfield, and recent trial borings have proved it over a distance of 200 yd south of this point, where it averages 20 in. in thickness. E.G.S.

The boreholes drilled in the area south of Clay Cross show a variation in thickness of between 2 in at Kirkby K5 Underground Borehole in the east, and 19 in at Swanwick Colliery No. 3 Underground Borehole in the west.

Measures between the Upper Brampton or ? Mickley Thin and Blackshale coals

The measures between the Upper Brampton or ? Mickley Thin and Blackshale coals are poorly exposed. Information from boreholes shows the thickness to be of the order of 170 to 185 ft, though isolated thicknesses outside this range have been recorded. The Ashgate, identifiable with certainty only in the north, is the only seam of note in these measures. West of Chesterfield it lies 30 to 40 ft below the Blackshale Coal, but locally, to the south and east of the town it is less than 3 ft below.

West of Chesterfield the group exhibits the same general lithology as the underlying measures—a similar alternation of mudstones and sandstones resulting in a diversified topography. At Abbey and Overholme opencast sites near the northern margin of the district two thin coals have been encountered between the ? Mickley Thin and Ashgate coals. The lower, about 100 ft below the Ashgate, consists of 4.5 in of cannel and 4.5 in of coal in trial pits [SK 344 731] between Cutthorpe and Cutthorpe Green; the upper, 60 ft higher, has the following section in a trial pit [SK 3418 7380], 600 yd N.W. of the inn at Cutthorpe: coal 13 in, dirt 2 in, on coal 4 in. East of Chesterfield the succession is less well known, but is evidently comparable with that of the main outcrop west of the town. In the western approach cutting [SK 415 703] of Duckmanton Tunnel the following section is exposed:

South-west of Chesterfield, in the tract of country between Somersall Hall and the west-north-westerly fault through Belfit Hill, two coals have been proved in trial boreholes at Horse Wood Opencast Site, southeast of Somersall Hall, and at Lydgate Farm Opencast Site, between Hill Houses and Walton Wood. The lower seam is thought to be at the same horizon as the lower coal in the Duckmanton Cutting and the correlative of the seam 117 ft below the Blackshale at Morton Colliery Underground Borehole (see (Figure 11)). It is between 6 and 17 in thick at Lydgate Farm Opencast Site and is exposed in a stream [SK 3712 6711] southwest of Hill Houses, 1340 yd S. 75° W. of All Saints' Church, Wingerworth, where at least 18 in of coal may be seen. The 10 in of coal exposed in Birdholme Brook [SK 3682 6879], 190 yd S. 38° W. of Yewtree House, is believed to be the same seam. The upper seam has also been proved on Lydgate Farm Opencast Site where it is 3 to 9 in thick. In Birdholme Brook [SK 3723 6869], 400 yd S. 52° E. of Yewtree House, the following section may be seen: dark shale 2 ft, coal 13 in, pale grey seatearth with ironstone nodules 3 ft, grey silty mudstone 3 ft on sandstone 1 ft. In a temporary section [SK 3760 6678], 0.33 mile S. of Lydgate Farm, the seam was 12 in thick. The associated measures are well exposed in Birdholme Brook where they consist largely of grey mudstone, but contain a number of thin sandstones which are, in most cases, impersistent, though the highest one has been traced southwards to Belfit Hill and forms the high ground on which Lodge Farm, Walton and Hill Houses stand. E.G.S.

South-west of Clay Cross two coals have been proved above the ? Mickley Thin Coal at Newmarket Opencast Site. They are thought to be the equivalents of the coals mapped north of the fault through Belfit Hill. The outcrop of the upper seam is marked by a series of shallow depressions suggesting small-scale surface workings; in trial pits the coal proved to be between 13 and 15 in thick, composed of 'brights' with fusain partings. An exposure in Press Brook [SK 3832 6363] at Henmoor shows 9 in of coal, the top of the seam not being visible. The lower seam is not marked on the map in the Newmarket area but trial pits on the opencast site revealed 10 to 12 in of bright coal with fusain partings. The 10-in coal exposed in Tricket Brook [SK 3790 6639], 350 yd S.E. of Belfit Hill, is thought to be the same seam.

The detailed sections afforded by the many boreholes drilled through these measures in the area south of Clay Cross show that, though only two coals have been proved at outcrop, four seatearths are normally present between the ? Mickley Thin and Blackshale coals, each of which may have a thin coal developed above it. The uppermost of these seatearths, which is split in some sections in the extreme south, may well be at the horizon of the Ashgate Coal. Sandstones are commonly found in the upper portion of each cycle but they are generally thin and impersistent. The measures contain relatively little ironstone, and of the little that is present a large proportion is concentrated in the mudstones above the ? Mickley Thin Coal. G.H.R.

Fossils are not common, but several boreholes have proved a band with small Carbonicola lying up to 25 ft above the ? Mickley Thin. The shells are probably either juveniles or stunted, but are comparable with C. bipennis. Rare 'mussels ' are found above the band and include C. communis and Curvirimula subovata from 120 ft below the Blackshale in Meadow Farm Borehole. Fish occur sporadically and are commonly found in some abundance within a few feet of the top of the ? Mickley Thin. Those identified include an Acanthodian spine, a Platysomid scale, Pleuroplax attheyi (Barkas), Rhabdoderma sp. and Rhizodopsis sp. Planolites has been recorded in each of the cycles; of the specimens examined only one proved to be Planolites ophthalmoides (at 43 ft 7 in below the Blackshale Coal in Blackwell 'A' No. 3 Underground Borehole), the others being identified as cf. Planolites sp. [small var.] (see p. 90). M.A.C.

The Ashgate Coal takes its name from the village two miles west of Chesterfield, near which it has been extensively mined. In this vicinity it was recorded at Tag Opencast Site 33 ft below the Blackshale Coal, with the section: coal and dirt 9.5 in, bright coal 3.5 in, coal and dirt 5.5 in, on bright coal 24.5 in. The seam has been worked at Boythorpe Colliery where a similar section is recorded: coal 5 in, dirt 3 in, on coal 25 in. It has also been worked in the area between Boythorpe Colliery and the outcrop, where it was called the Brampton Thin Coal. The above sections are typical of the seam in the vicinity of Chesterfield, where the thin upper leaf, sometimes called Hand Coal, is normally present. Farther north-west, around Cutthorpe, either the Hand Coal is thicker or the dirt parting is lower in the seam. Sections at Newgate Opencast Site, half a mile north-west of Cutthorpe, showed: bright coal 13 to 20 in, dirt 2.5 to 8 in, on bright coal 12 to 15 in. To the south of Chesterfield the dirt parting is only 0.5 in thick at Barley Mow Opencast Site and separates a top 9 in of bright coal from a bottom 29.5 in (see (Figure 13)). At the neighbouring Hockley Opencast Site the dirt is not recorded and the seam consists of 40 in of bright coal.

Despite the thickness of 40 in at Hockley and the 24 in maintained in most of the sections around the Brimington Anticline, the seam cannot be traced more than a short distance to the east and south. The area of known Ashgate Coal is shown in (Figure 13)." data-name="images/P990902.jpg">(Figure 12) which also shows the line of split, north of which the Ashgate and Blackshale coals are up to 40 ft apart. South and east of this line the Ashgate, where known, is generally less than 3 ft below the Blackshale (see sections of Hadyhill railway cutting and Barley Mow Opencast Site, (Figure 13)). Elsewhere there is insufficient evidence to say whether the Ashgate dies out or joins the bottom leaf of the Blackshale, or whether in fact, the interval between the two seams widens again and the Ashgate is represented at Seymour Colliery and in the area south of Clay Cross by the first seam below the Blackshale (see sections 4–7, (Figure 11)).

Of the 30 to 40 ft of measures between the Ashgate and Blackshale coals west of Chesterfield little is known. They are thought to consist largely of mudstones, exposures of which are to be seen in the brook [SK 3512 7272] and [SK 3532 7266], 250 to 400 yd N.N.E. of Holme Hall. G.H.R., R.A.E., E.G.S.

Blackshale Coal to Clay Cross Marine Band

Correlation of the coals and variations of lithology within this group are shown on (Plate 6). In thickness, the measures range from 490 to 690 ft, the figures in general decreasing eastwards. The chief workable coals are the Blackshale, Tupton, Deep Hard and Deep Soft; of lesser importance are the Yard, Three quarters, Piper and Clay Cross Soft.

Blackshale Coal

The Blackshale Coal is one of the major seams of the Derbyshire Coalfield, and has been wrought extensively in the west in both opencast and underground workings. The seam, including dirt, is between 2 and 8 ft thick, the average coal thickness in the worked area being between 42 and 48 in. The seam thins to the east (see (Figure 13)." data-name="images/P990902.jpg">(Figure 12)) in which direction the ash and sulphur contents rise, the latter reaching 2.3 to 3. 8 per cent in boreholes at Kirkby, Silverhill and Pleasley.

The seam is divisible into three combinations ponents: the Bottom Softs, the Middle Dirt and the Top Softs—a similar three-fold division to that of the Silkstone (Eden 1957, pp. 62–7). The Top Softs of the Silkstone, however, comprise the Top Softs of the Blackshale plus the Yard Coal, the two being separated by a few inches of dirt.

The Bottom Softs thin from north to south within the worked area of the seam. In the north they range from 20 to 30 in and part of the variation in thickness is due no doubt to the inclusion in some sections of the Tinkers coals of the Middle Dirt, and, in the east, to the possible inclusion of the Ashgate in the lower part of the seam. In the central area, from the southern margin of the Brimington Anticline to Clay Cross, the thickness varies between 18 and 24 in (with an exceptional record of 48 in at Hockley Opencast Site), and from Clay Cross to the southern margin of the district between 12 and 18 in are recorded. The Bottom Softs consist of bright coal—in some northern and eastern sections, of dirty 'brights' with rare dirt bands. A few thin bands of dull coal are recorded in some northern sections. In Glapwell Colliery shafts the Blackshale is composed largely of cannel which comprises all but the bottom 2 in of the Bottom Softs.

The Middle Dirt consists of dirt with a band or bands of bright coal known as 'Tinkers'.In some cases this term is also applied to a mixture of coal and dirt. Where the bands of coal thicken, they do so at the expense of the dirt, and where the latter dies away completely the Tinkers ' may be combined with the Top Softs above or the Bottom Softs below. In some old records of such sections, however, the 'Tinkers' were identified by the old miners and the three-fold division of the seam is recognizable. Up to 12 in of 'Tinkers' coal are recorded. The Middle Dirt, including 'Tinkers', has a maximum thickness of 4.5 ft, though two miles west of Markham Colliery sections in workings suggest that it is locally absent. At Alfreton Colliery, in the workings to the east of the shafts, the ' Tinkers ' and Top Softs are represented by cannel. That portion of the cannel representing the 'Tinkers' passes laterally into inferior coal and bat up to 32.5 in thick, and is separated from the Bottom Softs by a further 15 in of dirt.

The Top Softs are best developed in the area between the Brimington Anticline and Clay Cross, where they are about 24 in thick. North and south of this area they are between 12 and 24 in. Like the Bottom Softs and the' Tinkers ', the Top Softs consist usually of bright coal, though thin bands of dirt and dull coal have been recorded; cannel has been found at isolated localities. At Glapwell Colliery shaft the Top Softs consist entirely of cannel. In the south cannel has been recorded in the upper part of the Top Softs at outcrop near Shirland and in underground workings at Alfreton. In the east cannel has been recorded in sections in the underground boreholes at Langwith Colliery and Sherwood Colliery No. 1 Loader Gate. Cannel has also been recorded in the shaft deepening at New Hucknall Colliery, where it is 13.5 in thick and appears to be an addition to the normal seam, for it is separated from 12 in of top coal by 4 in of dirt.

In the vicinity of Chesterfield, the Blackshale lies close to the Ashgate below and the Yard above. Near the outcrop in the Calow Green area on the Brimington Anticline the three seams again lie close together and it is not uncommon for sections here to include some ten feet of coal with about the same thickness of dirt separating the main beds of coal. Such a section is exposed in Lower Hady railway cutting [SK 4012 7031], 0.5 mile S.S.E. of Hadyhill, and is expressed diagrammatically in (Figure 13) (section 2). From Chesterfield northwards the Blackshale is completely separated from the Ashgate (see (Figure 13)." data-name="images/P990902.jpg">(Figure 12) and (Figure 13)). The separation of the Blackshale from the Yard occurs south of a line of split having a general east-west trend to the north of Chesterfield, but deflected southwards over the Brimington Anticline (see (Figure 13)." data-name="images/P990902.jpg">(Figure 12) and (Figure 13)); the combined seam to the north of this line is the Silkstone Coal of Yorkshire (Eden and others 1957, pp. 62–7). East of the line of split a local development of the Silkstone is probable in the vicinity of Seymour Colliery where the shaft section records: coal 7 in, dirt 23 in, coal 54 in, bat 2 in, coal 3 in, dirt 3 in, on coal 22 in. In this section the Yard is thought to include the upper part of the 54-in coal and the overlying dirt and coal.

Measures between the Blackshale and Yard coals

North of Chesterfield and around the Brimington Anticline, where the Blackshale and Yard are united to form the Silkstone Coal, these measures are represented by dirt which has a minimum thickness of one-inch at Foxley Oaks Pit on the northern margin of the district. South and east of the line of split (see (Figure 13)." data-name="images/P990902.jpg">(Figure 12)) the dirt between the two seams increases abruptly in thickness and passes into measures which are, over the greater part of the district, between 40 and 60 ft thick. The maximum thickness is 83 ft at Langton Colliery in the south of the district; other above-average thicknesses are found in the Shirebrook–Sherwood area, and around Clay Cross. Sandstone is present in most of the underground sections, generally in the upper half of the cycle, though at Alma Colliery over 43 ft of 'rock' are recorded with the base only 10 in above the Blackshale Coal, and at Langton 75 ft of 'rock' and stone-bind have their base 3 ft above the coal. More normally the sandstone is separated from the coal by mudstone or silty mudstone containing a variable amount of ironstone. The top of the sandstone is, in places, immediately below the seatearth of the Yard; in others there is a further development of mudstone between the sandstone and the Yard. G.H.R., E.G.S., R.A.E.

Between the Blackshale and the sandstone, fish remains and Cochlichnus kochi have been recorded in several boreholes. In Cross Hills Borehole Anthracosphaerium boltoni (Wright) and Curvirimula subovata are found about 20 ft above the coal; the former shell is known from an approximately similar horizon in the Lancashire Coalfield (Wright in Tonks and others 1931, p. 136). A higher band, above the sandstone, in Kirkby Colliery K1 Underground Borehole contains Gyrochorte carbonaria Schleicher, Curvirimula candela (Dewar), Carbonita humilis and Palaeoniscid scales. M.A.C.

West of Chesterfield the measures, which include a bed of sandstone, crop out in the banks of the River Hipper [SK 3611 7034] southeast of Upper Moor. The sandstone is not exposed elsewhere within the district but it has been observed in opencast sites. At High Stair Opencast Site, for example, it is recorded on the abandonment plan as having a thickness of 40 ft, of which the lower 20 ft is hard; farther north, at Royal Oak Opencast Site, 33 ft of soft sandstone and bind are recorded. G.H.R., R.A.E.

Yard Coal

The Yard Coal over most of the district comprises three main elements of which the middle one is the most important. Typical sections have been recorded at Berresford Moor Plantation Opencast Site and in Grassmoor Colliery Shaft (see (Figure 13)). The lower coal has a maximum thickness of 40 in (at Blackwell 'A' Winning) though more usually it is about 12 in. Bright and dirty bright coal are present, and cannel is recorded in the majority of sections (see (Figure 13)), being particularly prominent in the vicinity of Clay Cross where a section at Holmgate Opencast Site revealed 21 in of cannel overlain by 12 in of 'brights' with fusain partings. South of this site an old pit [SK 3880 6332], 350 yd W. of St. Bartholomew's Church, Clay Cross, worked a small area of cannel, the recorded section being: inferior coal 5 in, dirt 1 in, on cannel 16 in. The lower coal appears to be absent east of a line through Creswell, Bolsover, Glapwell, Silverhill and Blackwell 'B' collieries; in the west it has not been recorded near the outcrop north of Hockley Opencast Site or south of Clay Cross. It is not certain that it has not combined with the middle coal in these areas.

At Creswell Colliery in the north-east, the cannel of the lower coal is developed immediately below the main coal of the Yard, with no separating dirt. Elsewhere the lower and middle coals are separated by dirt, consisting in the main of seatearth, which is only an inch or two in thickness at outcrop on the eastern side of the Brimington Anticline (e.g. Nether House Opencast Site). The maximum separation is found at Holmgate Opencast Site where there are 20 ft of beds consisting of mudstone with ironstone nodules overlain by seatearth. Excluding these extremes the average thickness of the dirt is about 48 in.

The middle coal is the thickest and most persistent, and in areas where it is widely separated from the lower and upper elements has itself been named the Yard. Over the greater part of their field the middle and upper coals, separated by only a few inches of dirt, comprise the Yard Coal as named in many of the collieries. The thickness of the middle coal ranges between 24 and 36 in, except along the eastern flank of the Brimington Anticline and in the Langwith area, where it is thinner. The coal consists mainly of 'brights' and dirty 'brights' with, in the areas around Kirkby, Pleasley and Silverhill, thin bands of dull coal; bands of dirt up to 6 inches in thickness also occur. The coal has a high ash content and workings are largely confined to the south—at Alfreton, Cotespark and Pinxton collieries—where the proportion of dirt is least. Small areas have also been worked at Pilsley and Silverhill collieries and in the Duckmanton area.

The upper dirt and the top coal are best developed in the north and the succession here is similar to that in the Sheffield country where the coal is sufficiently separated from the main part of the Yard to be recognized as a separate seam and named the Silkstone Rider (Eden and others 1957, p. 67). At Foxley Oaks Shaft, on the northern margin, the dirt is represented by about 30 ft of measures and the coal above is 27 in thick. Similar thicknesses of measures are found in the vicinity of Cutthorpe, where a substantial bed of sandstone is included, and at the western end of Duckmanton Tunnel where a 30-ft sandstone may be seen with a washout at its base cutting down into the Silkstone Coal. Though other sections in this northern area show up to about 12 ft of dirt (Figure 13) the average over the entire field is between 12 and 24 in, and in some southern sections the dirt is absent. The top coal is less than 12 in thick over most of its field and consists of 'brights' or, more commonly, dirty 'brights', divided in some localities by a central dirt band.

Measures between the Yard and Three-quarters coals

The measures between the Yard and Three-quarters coals are between 64 and 153 ft, with the thickest sections in the north, around Chesterfield, and the thinnest in the south-east, around Kirkby. Within this general pattern of south-easterly thinning the local thickness variations are erratic and commonly fail to follow the regional trend.

In the north the measures comprise shaly beds with ironstone, overlain by sandy beds which form the main part of the Silkstone Rock. Traced southwards the amount of ironstone decreases and the Silkstone Rock loses its identity as it splits into several impersistent bands of sandstone.

The term Blackshale Rake is applied to the dark shales with numerous bands and lenses of ironstone generally not more than 4 in thick, which succeed the Yard Coal; it has also been used loosely to include any ironstone worth working in the measures between the Yard and Threequarters coals. At Avenue Colliery, for instance, the Blackshale Rake sensu stricto is 9.25 ft thick but ironstone occurs up to 72 ft above the Yard. In the area east of Chesterfield the ironstone-bearing shales are divided by barren measures into a 'Top Rake' and a 'Bottom Rake', the complete sequence being up to some 50 ft in thickness. The Rake was formerly an important source of iron-ore and was much worked both opencast and underground along the northern part of its outcrop as is testified by the numerous bell-pits, shafts and old tips in the vicinity of Chesterfield and Clay Cross. There are few recorded sections, but an old plan of workings (abandoned in 1875) at Walton, between Riggott's Plantation and the golf course, shows that 14 bands of ironstone were worked in 34 ft of strata. The measures are well exposed in Lower Hady railway cutting [SK 4006 7032], 750 yd S.S.E. of the road junction at Hadyhill. The Rake is poorly developed in the east and along the outcrop south of Clay Cross. Sections in these areas show that the measures above the Yard contain a variable amount of ironstone which nowhere approaches the concentration found around Chesterfield; many sections, particularly in the extreme east, fail to record any ironstone.

The Silkstone Rock around Chesterfield is markedly thinner than in the southern part of the Sheffield country where, at Campbell and Hartington collieries, it is represented by over 100 ft of sandy measures. This thickness persists as far as Seymour Colliery just within the northern boundary of the Chesterfield district, but from here southwards the sandstone thins and also divides into two or three leaves. The Rock normally consists of fine-grained, flaggy sandstone, but in places this passes laterally into sandy siltstone, siltstone or sandy shale. At outcrop there is rarely more than one sandstone and that generally not more than 20 to 30 ft thick. It nevertheless forms a marked feature which may be traced as far south as Hockley where, to the north of the hamlet, it is particularly prominent. In underground sections the sandstone is commonly found in two or, rarely, three leaves separated by mudstone or silty mudstone.

In certain sections throughout the district a seatearth is recorded about half way be-between the Yard and Threequarters, and above it, in rare instances, a thin coal is developed. The coal is recorded as 14 in of bassy coal at Morton Colliery but elsewhere it is not above 2 in. The seatearth is developed above the lower leaf of sandstone which is present in nearly all the sections through these measures in the southern half of the district, and is commonly overlain by mudstone containing ironstone bands. This ironstone horizon may be the one recorded at Brightside and Rotherham Main collieries to the north of Sheffield (Eden and others 1957, p. 68). G.H.R., E.G.S., R.A.E.

Fossils are not abundant in these measures. Large specimens of Curvirimulacandela, together with fish remains, occur in a stream exposure [SK 3554 7282], 440 yd N. 14° E. of Holme Hall. Elsewhere non-marine lamellibranchs have been found in the ironstone-bearing mudstones overlying the Yard only at Bolsover Colliery Nos. 4 and 5 Underground, Norwood Farm and Silverhill Colliery No. 1 Underground boreholes. Fish debris is more widespread and has been noted in many boreholes. The following fauna has been obtained: Cochlichnus kochi, cf. Planolites sp. [2.0 mm]; Carbonicola sp., Curvirimula cf. subovata; Carbonita humilis, Geisina arcuata; Rhabdoderma sp., Palaeoniscid scales indet. Fish debris also occurs, though to a lesser degree, above the locally developed seatearth or coal above the Yard. At this horizon in Uftonfields Borehole a small specimen of Carbonicola pseudorobusta was found and, some 2.5 ft higher, G. arcuata. M.A.C., G.H.R.

Threequarters Coal

The Threequarters Coal has in the past been called the Tupton Threequarters and, in the Grassmoor area, the Lees Coal. It is of fairly consistent thickness, the variation over the major part of its field being between 24 and 36 in, with the thicker sections in the northern and central areas. It exceeds 36 inches in an area bounded on the south by a line which swings southwards from Creswell Colliery almost as far as Bolsover Colliery, whence it swings northwards to Oxcroft before turning southwards again and passing west of the Markham pits to intersect the outcrop on the south of the Brimington Anticline. In the south-east the Three-quarters has been proved to be less than 24 inches in underground boreholes K1, K3 and K5 at Kirkby Colliery. The seam has been worked from many collieries in the west of its field, the most important workings being at Alfreton, Blackwell 'A', Bond's Main, Clay Cross No. 4, Grassmoor, Morton, Parkhouse, Pilsley and Williamthorpe collieries. It has been worked extensively along the crop by opencast methods. In central and eastern areas the seam is virtually unworked and is known mainly from shaft and borehole records.

The seam consists essentially of 'brights' with a few streaks and bands of dull coal and fusain. In some sections, particularly in the west, a few inches of dirty coal occur in the bottom part of the seam; at Williamthorpe Colliery these are called 'jacks'. In and around Chesterfield, the Three-quarters consists of the normal seam of bright coal, commonly overlain by inter-banded coal, dirty coal and dirt. In some of the old shaft sections near the northern margin, the seam is recorded as a coal several feet thick (50 in at Foxley Oaks Pit, 47 in at Highfield Colliery, 43 in at Tapton Colliery) and it seems probable that in some cases, at least, these thicknesses include the upper dirty part of the seam recorded in other old sections as bat '. Except in the vicinity of the Brimington Anticline there are many sections showing a thin floor coal separated from the main part of the seam by a variable thickness of dirt or measures. Between Clay Cross and Grassmoor the separation consists of over 14 ft of clunch, stone-bind, bind and shale. This thickness, however, is exceptional, the average figure being of the order of 5 to 6 ft. The minimum interval between the coals is found in the south, at Kirkby K5 Borehole, where it is 6 in; at Brookhill and Langton collieries it is 30 in and 18 in respectively. The floor coal itself is dirty and generally not more than 6 in thick, the maximum thickness being 16 in at Pleasley Colliery. It is not recorded in the majority of sections in the east, and it is not clear whether the coal dies out in this direction or whether it is joined to the main seam. In the north it is recorded in Duckmanton Tunnel and Arkwright Drift in a position similar to that of the 16-in coal in Nesfield Pit in the Sheffield district (Eden and others 1957, p. 74). G.H.R., E.G.S., R.A.E.

Measures between the Threequarters and Tupton coals

The measures between the Threequarters and Tupton coals are thickest in the north-west where about 46 ft are recorded in Duckmanton Tunnel and where shaft sections show 30 to 40 ft. They maintain a thickness of over 20 ft as far south as Alma, Holmewood and Glapwell collieries and similar thicknesses also occur at Shirebrook and Sherwood in the east. South of these localities the measures are less than 20 ft thick and are thinnest in the south-east, in the area including Bentinck, Brookhill and Kirkby collieries, where they are generally less than 12 ft and where the minimum value for the district of 8 ft 8 in has been recorded at Bentinck Colliery No. 2 Shaft. Sandstone or stone-bind is present where the measures are thickest; it is recorded in the section of Duckmanton Tunnel and has been mapped around Calow Green and Boythorpe. Elsewhere the measures consist largely of mudstone and seatearth, both of which contain ironstone, and in the thinnest sections little more than seatearth is developed. G.H.R., E.G.S.

The ironstone has been worked locally at outcrop. A general section of the Winger-worth Estate mines and workings, dated 1862, is as follows:

The seatearth at the top of the measures has been worked as a fireclay over a wide area around Chesterfield. It was generally worked in conjunction with the overlying Low Tupton Coal, as it still is at Newbold Colliery where a section seen in 1948 showed 0 to 9 in of ganister-like sandstone on 28 in of silty grey fireclay. Walton Clay Pit (abandoned 1904) and Langer Lane Clay Pit (abandoned 1919) worked the upper 27 in and 24 in of the seatearth respectively in conjunction with the Low Tupton Coal.

Non-marine lamellibranchs have been recorded from the mudstones overlying the Threequarters in boreholes in the northeast of the district; Carbonicola spp.,including small C. pseudorobusta, and Naiadites flexuosus have been identified. E.G.S., R.A.E.

Tupton Coal

The Tupton Coal consists of two elements which, where separated, are known as the Low Tupton and Cockleshell coals. The seam diagram (Figure 15)." data-name="images/P990904.jpg">(Figure 14) shows where the separate coals are found. The main area is in the north where the separation reaches as much as 60 to 70 ft. There is also a small area in the south, around Kirkby, Bentinck and Brookhill collieries, where the two coals are up to 5 ft apart.

The Tupton Coal was formerly one of the most important seams in the exposed coalfield and it has been worked extensively both underground and opencast. In the east the seam is largely unworked and is known only from borehole sections. (Figure 15)." data-name="images/P990904.jpg">(Figure 14) shows that it increases in thickness from south-east to north-west with the area of maximum thickness centred on Parkhouse and Pilsley collieries. The isopachs are based on the main variations in seam thickness, and ignore isolated sections which distort the general picture. The maximum recorded thickness of the seam, excluding dirt, is 83 inches in workings half a mile north-west of Williamthorpe Colliery, where, however, most sections show less than 70 in of coal. A similar instance of local thickening is seen about two-thirds of a mile south-east of Glapwell Colliery shafts, where 82 in of coal have been measured among other sections showing between 60 and 70 in. The minimum thickness of 37 in has been recorded in boreholes at Kirkby Colliery (K1, K5 boreholes). The seam consists of bright coal though rare thin bands of dull coal have also been recorded, particularly in the lower part. Fusain partings and dirt bands are also present, the most prominent dirt being that separating the Low Tupton portion of the seam from the Cockleshell. At outcrop this dirt parting is only 0.5 in thick at Holmgate, High Stair and Skeggerleg opencast sites; and at intervening localities it is absent, though the junction of the two elements is commonly marked by a fusain parting. It is also absent from many of the sections obtained from shafts and underground workings, while in others it is up to 13 in thick (shaft sections at Bond's Main and Morton collieries). In the extreme east dirt bands have been encountered in boreholes drilled from underground workings at Shirebrook and Sherwood collieries. At Shirebrook No. 1 Underground Borehole the section was coal 2 in, dirt 1 in, coal 8 in, dirt 5 in, cannel 14 in, dirt 30 in, on coal 22 in. It is uncertain which dirt separates the Cockleshell from the Low Tupton here, but it is likely to be the 5-in band, and if this is the case the 30-in dirt reflects a deterioration of the Low Tupton element on the eastern margin of the district. Similar sections were recorded farther south in boreholes at Sherwood Colliery: at 4's Loader Gate Borehole the section was cannel 5 in., cannelly shale 5 in, cannel 9.5 in, shale 18.5 in, cannel 6 in, on coal 19 in: at 1's Loader Gate Borehole the section was inferior cannel 6 in, mudstone 18 in, cannel 10 in, mudstone 4 in, inferior cannel 7 in, on coal 23 in. Though the cores from these two holes were poor it is suggested that the 30-in dirt recorded in the Shirebrook hole thins southwards, and this would be in accord with the results obtained from the Kirkby Colliery underground boreholes K1, K3 and K5 in the south-east of the district, where the presumed Low Tupton part of the seam contains no dirt. The cannel recorded in the boreholes at Shirebrook and Sherwood appears to be a local development extending westwards to Pleasley, where the top 1 in of the seam in Pleasley B1 Borehole was found to be cannel, and southwards to Kirkby, where in K6 Borehole cannel is found in the upper parts of the separated Low Tupton and Cockleshell coals (see (Figure 15)). G.H.R., E.G.S.

The Low Tupton Coal is thickest in the neighbourhood of Grassmoor (see (Figure 15)." data-name="images/P990904.jpg">(Figure 14)); it thins northwards and develops bands of dirt or dirty coal in its upper part (see (Figure 15)). The seam thins markedly to the east of Tom Lane Borehole and is less than 12 in at Elmton Green Borehole and Bolsover Underground Borehole No. 7. Still farther east the thickness increases again and is over 30 in at Langwith Underground Borehole, though the top 6 in is dirty coal. The seam has been worked extensively in the area between Grassmoor and Chesterfield, where it consists of bright coal with fusain partings, and has a varying proportion of dirt in the upper part of the seam. In the area of thin coal between Bolsover and Elmton Green Borehole cannel has been recorded, but farther east, at Norwood Farm and Langwith Underground boreholes, the Low Tupton is composed of bright and dirty bright coal with subsidiary dirt.

The Low Tupton and Cockleshell coals are separated by measures which attain a maximum thickness of some 60 to 70 ft in the north. The beds are commonly silty with sandstone and mudstone beds; ironstone has been noted in some sections. The proportion of sandstone tends to be greater in the thicker sections, and at Norwood Farm Borehole 40.5 ft out of a total thickness of 53.25 ft are sandstone: at Ireland Colliery No. 4 Underground Borehole 43 ft of sandstone are overlain by a seatearth lying 15 ft below the Cockleshell Coal.

Non-marine lamellibranchs have been found in the roof shales of the Low Tupton in Bolsover Colliery underground boreholes; they include Carbonicola sp. and Naladites flexuosus, found in association with Geisina arcuata.

The Cockleshell Coal varies irregularly in thickness up to a maximum of 24 in. To the west of the Brimington Anticline the minimum recorded thickness is 12 in at Tapton Colliery, less than half a mile from Highfield Colliery where the maximum value was recorded. East of the Brimington Anticline the minimum thickness is 4 in at Elmton Green Borehole. West of the anticline the seam consists of clean bright coal, but on the east side dirt and dirty coal bands have been found in it.

Measures between the Tupton (or Cockleshell) Coal and the Piper group of coals

The measures between the Tupton (or Cockleshell) Coal and the Piper group of coals. The Tupton (or Cockleshell, where that is separate from the Low Tupton) is succeeded almost everywhere by mudstones, most of which are dark grey and contain ironstones. They are generally 20 to 70 ft thick, though they are less than 10 ft thick at Golf Links and Kirkby K6 boreholes, and in Cotespark and Kirkby shafts, and they are not developed at Glapwell Colliery. Within the mudstones at a variable distance above the Tupton or Cockleshell, lies a seatearth or thin coal not above 10 in thick. Though apparently absent in the north and east this horizon is thought to be the equivalent of the upper leaf of the Cockleshell of the Sheffield country (Eden and others 1957, p. 77). It is above this coal that ironstones are generally most abundant and constitute the much-worked Dogtooth Rake. At Arkwright Drift ironstone is present throughout 54 ft but it is probable that the thickness of measures worked at the surface rarely exceeded 10 ft. Detailed sections of the rake are uncommon. There is evidence of extensive opencast workings for ironstone at this horizon along the western outcrop between Boythorpe and Wingerworth, and also in the vicinity of Tupton. G.H.R., E.G.S., R.A.E.

Non-marine lamellibranchs are abundant in the mudstones and in some of the ironstones above the Tupton and Cockleshell seams—hence the name of the latter—and they are also present in the roof of the thin coal referred to above. These ' 'mussel'bands provide a valuable marker horizon which is well known throughout the Pennine coalfields, and is taken as marking the base of the A. modiolaris Zone. The assemblage is dominated by the Carbonicola cristagalli Wright-C. rhomboidalis Hind group, and lacks the typical C. pseudorobusta and Curvirimula spp. of the underlying zone. Moreover, forms of Anthraconaia which are characteristic of the A. modiolaris Zone make their first appearance. Certain of the larger Carbonicola shells approach C. pseudorobusta (cf. Trueman and Weir 1948, pl. ix, fig. 3) but they have less subumbonal depth and a higher anterior end than that species; they are probably extreme variants of C. cristagalli. The combined fauna from this closely associated series of 'mussel' bands includes: Spirorbis sp.; Anthraconaia sp. nov. [cf. Wright 1938, fig. 4b], Carboni-cola cristagalli, C. rhomboidalis, C. cf. robusta (J. de C. Sowerby), C. sp. intermediate between cristagalli and pseudorobusta, Naiadites flexuosus; Carbonita humilis, Geisina arcuata; and fish remains. M.A.C.

In the extreme north the mudstones with ironstones constitute most of the strata between the Tupton and Piper horizons, sandstones being of minor significance and occurring mainly in thin beds in the upper part of the sequence. Sandstone is also relatively unimportant in much of the ground extending southwards from Clay Cross No. 4 and Williamthorpe collieries. Certain sections, however, (e.g. Tibshelf Old, Blackwell 'A' and 'B' and Cotespark collieries) show the presence of up to 20 ft of sandstone or stone-bind at one or more horizons. These sandstones thicken both eastwards and westwards, finally merging with one another and with the rock and stonebind between the Second and First Piper coals. The resulting sandstone, known locally as the 'Tupton Rock' is over 100 ft thick on the west and between 125 and 160 ft in places on the east. Its field roughly corresponds with the stippled area on (Figure 18). For sections at lettered localities see (Figure 17)." data-name="images/P990906.jpg">(Figure 16). The top of the sandstone is close below, or within 25 ft of, the First Piper Coal, the Second Piper being absent; at Langwith Colliery Underground Borehole both the Piper coals are absent. The sharp base of the sandstone is generally 25 to 50 ft above the Tupton, and fragments of siltstone, mudstone and coal commonly occur in the basal few feet. At Kirkby Colliery, the base of the sandstone is only 6 ft 8 in above the Cockleshell Coal in the North Shaft and only 1 ft 4 in above it in the K6 Underground Borehole. At Glapwell Colliery, where the sandstone is thickest, nearly 160 ft of rock and stone-bind rest directly on the Tupton Coal. G.H.R., E.G.S.

The 'Tupton Rock' forms an impressive north–south feature in the southern part of the district, the escarpment rising 120 ft above the adjoining countryside between Clay Cross and Higham, where the main Derby–Chesterfield road runs along the crest of the feature. Small exposures of the sandstone are visible at various places along this road, the best being in an old quarry [SK 3895 5937] 100 yd W.N.W. of the Greyhound Inn, Higham where 30 ft of fine-grained massive sandstone can be seen. Further small exposures lie along the minor road to Hollybank in the south, and the sandstone is well seen in an old quarry [SK 3873 5576], 250 yd E. of Wingfield railway station, and in the escarpment [SK 3849 5505] to the west of Hollybank itself.

Piper group of coals

The Piper group of coals consists basically of the First and Second Piper coals with middle dirt, but a more complex subdivision by variable dirt bands is apparent on close inspection, and is shown in tabular form below (the divisions of the First Piper are those recognized in the Sheffield district by Eden and others 1957, pp. 79–80). The detailed account which follows is necessarily lengthy and involved; it will more readily be understood by reference to (Figure 18). For sections at lettered localities see (Figure 17)." data-name="images/P990906.jpg">(Figure 16), (Figure 17) and (Figure 18)).

Only in a small area in the north-west are the First and Second Piper coals sufficiently close together to be considered a single seam (see (Figure 18). For sections at lettered localities see (Figure 17)." data-name="images/P990906.jpg">(Figure 16), (Figure 17) and (Figure 18)). Elsewhere they are separate, though over much of the district the Second Piper is absent and the sole representative of the Piper is the upper coal of the 1st Piper (see (Figure 18). For sections at lettered localities see (Figure 17)." data-name="images/P990906.jpg">(Figure 16)).

The Piper CoalSometimes called the Townend Thin or Pancake Coal: in the present account the name ' Pancake ' is restricted to a thin coal at the bottom of the Piper. consists essentially of bottom coal, middle dirt and top coal. The bottom coal (equivalent to the Second Piper) is commonly the best part of the seam in the neighbourhood of Chesterfield, where the southward thickening noted in the Sheffield country (Eden and others 1957, p. 80) continues as far as Boythorpe Colliery at which 39 in of coal are recorded in the shaft. Sections in the workings hereabouts indicate the presence of up to three thin dirt bands, and a nearby section at Grangewood Farm Opencast Site shows three dirt bands totalling 4 inches in a section of 40 in (see (Figure 17)). Southwards from Boythorpe the Second Piper element deteriorates as a middle dirt (possibly represented by the median 1.5 in of dirt at Grangewood Farm) increases in thickness and divides the coal into two parts, the upper of which is commonly dirty. At Victoria Opencast Site (see (Figure 18)) this upper portion appears to be absent and the lower part, composed of dirty coal, is all that remains. In the north of the district a thin dirt band, usually found near the base of the Piper swells locally to several feet, separating the few inches of Pancake Coal at the base from the remainder of the seam. Such is the case at Newbold Colliery where the Pancake is 9 in thick and 6 ft 9 in below the main part of the seam.

The middle dirt of the Piper Coal, often recorded as containing coal bands, normally varies from an inch or two to 18 inches, though at Highfield Colliery it is apparently absent. Eastwards it swells to separate the First and Second Piper coals.

The First Piper element of the Piper Seam is divided into two coals separated by dirt. The lower coal is commonly of inferior quality and is recorded as: coal and dirt; coal, dirt and 'duns'; dirty coal; or even locally included as dirt not separately detailed from the dirt above and below. Thicknesses of between 11 and 35 in have been recorded, the thicker sections being at and to the south of Avenue Colliery. The dirt (equivalent to the middle dirt of the First Piper) includes some thin bands of dirty coal. It is less than 12 in thick in the opencast sites of Victoria and Belfit Hill but increases northwards and westwards to 3 ft or more in the north-west of the district. The upper coal is itself divided into two beds equivalent to the top and middle coals of the First Piper, separated by a dirt band (the First Piper top dirt). The lower of these beds consists of 13 to 22 in of bright coal with rare thin dirts. The dirt is over 5 ft thick north-west of Newbold Colliery and thins southwards; it is not recorded at and south of Boythorpe Colliery, though at Grangewood Farm Opencast Site, its position is taken as the 0.75 in. dirt 16 in from the top of the section (Figure 17). The upper bed of coal (the top coal of the First Piper) is variable and locally absent; north-west of Newbold Colliery it is represented by 60 in or more of cannel; it is absent at Highfield and Newbold collieries. Where the dirt is absent the upper coal of the First Piper element consists of up to 41 in of mainly bright coal.

At the time of the resurvey the Piper was exposed in the roadside [SK 3800 6745], 360 yd W. of All Saints' Church, Wingerworth, where 54 in of coal could be seen overlain by 1 ft of grey mudstone. The seam has been worked at outcrop in the west and on a limited scale in deep workings from Walton, Boythorpe, Avenue and Tupton collieries.

The Second Piper Coal, lying east of the line of split shown in (Figure 18). For sections at lettered localities see (Figure 17)." data-name="images/P990906.jpg">(Figure 16), is largely confined to an area north and north-east of Clay Cross No. 4, Alma and Williamthorpe collieries. Here the median dirt band already noted in the bottom coal of the Piper is generally present as far east as Bolsover Colliery, producing the same threefold division of the seam into an upper and generally dirty coal, a central dirt and a lower coal. The lower coal of the Second Piper, normally 11 to 15 in thick, has a maximum thickness of 23.5 in at Williamthorpe Colliery (where it is, divided into two nearly equal parts by 13 in of dirt) and a minimum thickness of 3 in at Bolsover Colliery No. 10 Underground Borehole. It consists of bright coal with, at some localities at outcrop around the Brimington Anticline, bands of dull coal; and dirt partings have been recorded at Calow Brook Opencast Site. The middle dirt has a maximum thickness of 18 in in Bolsover Colliery Shaft but is normally less than a few inches; at Brim and Parker's Wood opencast sites it is represented by 1 to 5 in of dirty coal. The upper coal of the Second Piper is up to 21 in thick and consists normally of dirty coal or of dirt with coal bands; dull bands have also been noted, and at Bolsover Colliery, where the maximum thickness is developed, it consists entirely of cannel. In Seymour Colliery Shaft on the northern margin, the Second Piper is recorded as coal 4 in, dirt 21 in, on coal 7 in, but apart from this occurrence the seam north and east of Bolsover consists of one leaf of coal 12 to 22 in thick. Most sections show it to be bright coal or 'brights' with fusain, containing in places dull bands in the top few inches. It is not clear, however, whether this single leaf of coal represents the whole of the Second Piper or is equivalent only to the lower coal. Be that as it may, to the north-west of the Brimington Anticline, a single leaf of coal represents the whole of the Second Piper (section 1, (Figure 18)) and it is likely that this is the case north and east of Bolsover. The Second Piper has been worked at outcrop around the Brimington Anticline and underground, on a small scale, at Grassmoor Colliery.

Within a tract of country extending from Clay Cross No. 4 and Williamthorpe collieries to the southern margin (see (Figure 18). For sections at lettered localities see (Figure 17)." data-name="images/P990906.jpg">(Figure 16)) only a thin coal or, more commonly, a band of smut, bat or clunch is present at the Second Piper horizon. At Brookhill and Langton collieries the coal is 17 in and 14 in respectively; at Clay Cross No. 2 Colliery it comprises coal 2 in, dirt 10 in, on coal 12 in; other sections show, at most, an inch or two of coal.

The middle dirt of the Piper Coal expands east and south of the line of split (see (Figure 18). For sections at lettered localities see (Figure 17)." data-name="images/P990906.jpg">(Figure 16)) and passes laterally into measures separating the First and Second Piper coals. The measures are thickest at Pilsley where they are 105 ft; in other sections in the west they are, except in the immediate vicinity of the line of split, 30 to 60 ft thick. In the north-east they are 16 ft at Elmton Green Borehole (Section H, (Figure 17)), 6.5 ft at Creswell Colliery and 5.5 ft at Norwood Farm Borehole. They are largely argillaceous in the north, but stone-bind and rock are commonly found in sections at Clay Cross and farther south. Non-marine lamellibranchs were recorded in the roof shales of the Second Piper at Bolsover Colliery No. 6 Underground Borehole and Elmton Green Borehole. They are poorly preserved and only Carbonicola cf. cristagalli [juv.] has been identified.

The First Piper is also a variable seam. Its field is divisible into areas in which both the upper and lower coals are present and areas in which only the upper coal is found. (Figure 18). For sections at lettered localities see (Figure 17)." data-name="images/P990906.jpg">(Figure 16) shows the main area containing both coals to be in the north. A further narrow area (almost identical to that in which a thin Second Piper is present) extends southwards from Clay Cross No. 4 and Williamthorpe collieries to the southern margin; and on either side of this area the upper coal of the First Piper is—except at Clay Cross No. 2 Colliery—the sole representative of the Piper group of coals, and is underlain by thick sandstone.

The lower coal of the First Piper is variable in both thickness and quality. In the northern area the thinnest section is 6 in of dirty coal at Norwood Farm Borehole; a rather similar section is recorded at Bond's Main Colliery to the south of the Brimington Anticline—coal 2 in, dirt 6 in on coal 2 in. The thickest section is at Bolsover Colliery—coal 4 in, dirt 6 in, coal 5 in, coal and dirt 19 in, on coal 24 in; at Tupton Hall Opencast Site there are 37.5 in of bright coal with bands of hard coal and dirt ((Figure 18)), and at Alma Colliery 51.5 in of coal and dirt are thought to be at this horizon. Other thick sections are found in the extreme north—32 in at Seymour Colliery—, and near the southern end of the Brimington Anticline-26 inches in Calow Drift. The northern records are of clean bright coal, but elsewhere bands of dull coal and dirty coal occur, and in general the seam shows a westward deterioration in quality so that to the west of the Brimington. Anticline sections are described as coal and dirt, or dirty coal, and those at Clay Cross No. 4 and Williamthorpe collieries as smut, bad coal and bat. A section visible in Hadyhill Railway Cutting [SK 3964 7032], 700 yd S.S.W. of Hadyhill, shows the lower coal to consist of coal 18 in, cannel 2 in, on bad coal 6 in.

Southwards from Clay Cross No. 4 and Williamthorpe collieries the lower coal of the First Piper is represented by coal and dirt or, more commonly, by bat. As far south as Tibshelf only bat is present, but at Blackwell 'A' and Cotespark collieries, for instance, coal and dirt are recorded. At Brookhill and Langton the lower coal may be represented by the bat recorded immediately below the coal at the First Piper horizon.

The middle dirt of the First Piper is, in most north-westerly sections, 5 to 15 in thick and normally consists of dirt with bands of coal; in some sections it consists of dirty coal, e.g. Moor Farm Opencast Site and Tom Lane Borehole. It is absent in Clay Cross No. 4 Colliery Shaft. In Bolsover Colliery Shaft it is represented by 8.5 ft of measures and in the north-east of the district by between 10 and 17 ft. These measures are thickest at Norwood Farm Borehole where the lower part consists of mudstones with 'mussels', and the upper part of sandstone. In the south, between Williamthorpe and Brookhill collieries, the beds are between 10 and 39 ft thick, the thickest section—at Alfreton Colliery—including 35 ft of stone-bind and rock.

The upper coal of the First Piper is, in the extreme north, divided by the top dirt into the middle and top coals (Figs. 16 and 17). The top dirt is up to 8 in thick in the northeast, but rarely exceeds two or three inches in the west. North-east of Bolsover the separated coals vary widely in thickness, the middle coal between 1 in (at Elmton Green Borehole) and 17 in, and the top coal between 7 and 13 in. In the north-west the middle coal is 13 to 23 in thick and the top coal 12 to 18 in. South of Bolsover the top dirt is not generally present, though certain sections along the southern part of the outcrop (e.g. Goose Green Opencast Site) show up to 3.5 in of dirt which may well be its equivalent. Similarly, in the extreme east in the Shirebrook-Sherwood area, the top dirt may be represented by a dirt band of up to 14 in near the middle of the coal.

The upper coal of the First Piper consists almost exclusively of bright coal and dirty bright coal, this being true both where it is divided by the top dirt and where it occurs as a single leaf of coal; exceptions are found at Cross Hills Borehole, where the top coal includes dull coal, and at Tupton Hall Opencast Site where dull coal is found in the lower part of the seam. The thickness of the upper coal of the First Piper varies between 11 in at Pilsley Colliery and 40 in at Brim Opencast Site. An attempt to show the local variations within these limits has been made by means of isopachs in (Figure 18). For sections at lettered localities see (Figure 17)." data-name="images/P990906.jpg">(Figure 16).

The First Piper has been worked opencast along both the main outcrop and around the Brimington Anticline. It has been mined extensively from Grassmoor Colliery, the northern part of the workings being in the upper coal and the workings south of the shaft in the whole seam; it has also been worked at Alma Colliery on a small scale. In the south the upper coal of the First Piper has been worked from Brookhill, New Hucknall and Sutton collieries, where the thickness is generally between 30 and 36 in, though at Brookhill up to 40 in have been recorded; up to 12 in of coal at the bottom of the seam at these localities are classed as 'inferior'. G.H.R., E.G.S., R.A.E.

Measures between the Piper or First Piper and Deep Hard coals

In the extreme east, in an area including Shirebrook and Sherwood collieries and extending southwards towards Kirkby (see (Figure 18). For sections at lettered localities see (Figure 17)." data-name="images/P990906.jpg">(Figure 16)), the First Piper and Deep Hard coals are separated by a seatearth less than 3 ft thick. Elsewhere the coals are separated by measures which are thickest in the west, attaining 93 ft at Avenue Colliery; between 50 and 60 ft persist in the area of the Brimington Anticline and around Clay Cross; 55 to 65 ft occur at Alfreton, Blackwell 'A' and Cotespark collieries in the south; and at Creswell Colliery and Silverhill No. 2 Underground Borehole over 51 ft of measures are recorded.

The measures normally comprise one cycle, but at Creswell and Grassmoor collieries there are two, with a 10-in coal at the top of the lower cycle. Indications of the extra coal at this horizon are also found in the south at Blackwell 'A' Colliery where 12 in of black bass is recorded, and in Cotespark Colliery No. 1 Shaft, where there is a streak of coal. These records are all in areas where the measures are fairly thick—between 50 and 65 ft—the coal being found between two beds of sandstone or stone-bind. Sandstone and stone-bind are recorded in most sections where the measures are 20 ft or more in thickness and, except for the occurrences listed above, are generally in one bed which is 69 ft thick at its maximum development at Avenue Colliery. Though in isolated sections (e.g. Golf Links Borehole) sandstone rests directly on the Piper, or First Piper, the coal is normally overlain by 10 to 20 ft of mudstones with ironstone bands and nodules; where the overlying sandstone is thin, the mudstones may reach over 30 ft. At Grangewood Farm Opencast Site, fish debris and non-marine lamellibranchs have been recorded from these mudstones.

The sandstone and siltstone are prominent at the surface and form a feature over much of the outcrop between Chesterfield and Clay Cross. The base of the sandstone is visible in the railway cutting [SK 3975 6429] alongside the Clay Cross Works, where 4 ft of sandstone rest on mudstone with ironstone bands. A complete section of the measures was measured at the Cottage Opencast Site:

Deep Hard Coal

The Deep Hard Coal to the east of a north–south line of split (see (Figure 20)." data-name="images/P990909.jpg">(Figure 19)) is widely separated from an overlying Roof Coal; to the west the Roof Coal, though separated from the major part of the seam by dirt in many northern sections, is included under the name 'Deep Hard'. The seam has been widely worked both at outcrop and from deep mines, and is one of the major seams of the exposed coalfield of North Derbyshire. G.H.R.

The seam is thickest in the north-west of its field around the Brimington Anticline and Grassmoor. In this area it is also known as the Potters, Pot House or Townend Coal, and includes several prominent dirt bands. The full section is similar to that described by Eden and others (1957, p. 84 and fig. 18) in the south-west of the Sheffield district, and comprises Roof Coal, dirt, Smithies Coal, dirt, Top Hards, Middle Dirt, Bottom Bed, coal and dirt. Thicknesses of coal range from 57.5 in at Newbold Opencast Site to 83 in at Calow Green Opencast Site, but no regional trend of variation is discernible.

The coal and dirt at the base of the seam is variable in thickness and character and its upper part probably passes laterally into the lower part of the overlying Bottom Bed. In the extreme north-west, at Four Lane Ends Opencast Site (Figure 20) and Newbold Opencast Site, it is 6 to 11 in thick and is variously described as soft brights (with a high ash content), dirty coal, and coal and dirt; elsewhere in the north-west it passes into the bat, branch, jacks, black shale or cannelly shale which is recorded below the main part of the seam. In the workings south of Grassmoor Colliery it is up to 17 in thick and is recorded as jacks; at Balm Oak Opencast Site it consists of 18 in of dark grey shale separated from the main part of the seam by 3 in of dark clunch.

The Bottom Bed comprises the Bottom Softs and Bottom Hards of the Sheffield country (Eden and others 1957, p. 85) and is generally between 20 and 30 in thick. It consists mainly of 'brights' though the more detailed sections show bands and streaks of dull coal; the bed is sometimes recorded as manufacturing coal' and was regarded as being of less value than the Top Hards. The Middle Dirt, not everywhere present, consists of clunch, or coal and dirt, or dirty coal, and is up to 10 in thick. Some of the records of variations in thickness are spurious, being due to differing methods of classification, but there are genuine variations due to lateral passage into the coals above and below. The Top Hards, consisting mainly of 'brights' with dull bands and streaks, are sometimes called the Best Hards' and commonly contain a higher proportion of dull coal than the Bottom Bed. They vary between 12 and 31 in, partly due to lateral passage into the Middle Dirt. The dirt above the Top Hards has a maximum recorded thickness of 4 inches in workings south of Foxley Oaks Pit, and it is commonly absent or represented by no more than a bat parting. The Smithies or Smithies Bottom Bed, generally 7 to 18 in thick, consists of 'brights', in some localities described as strong, and, in places, containing fusain. The dirt between the Smithies and the Roof Coal swells eastwards into measures separating the Roof Coal from the rest of the Deep Hard. In the north-west its thickness varies between 0 and 44 in, though only rarely is it absent altogether. The Roof Coal or Smithies Top Bed consists of 6 to 20 in of bright coal with, locally, a considerable proportion of dirt. On both flanks of the Brimington Anticline a thin dirt band or parting is found near the middle of the coal. R.A.E., E.G.S.

South of Grassmoor the dirt below the Roof Coal is prominent in the recorded sections as far south as Parkhouse Colliery and Gentshill Opencast Site. Its thickness varies between 0.25 in and 48 in and it separates a Roof Coal of between 9 and 20 in from the main part of the seam which is not here divisible into the separate components noted above, but consists mainly of 'brights' with a varying proportion of dull coal and little or no dirt. South of Parkhouse Colliery the Roof Coal merges with the lower part of the seam to form a single bed of bright coal in which subsidiary dull bands are found, the total thickness varying between about 36 and 60 in. G.H.R.

Over most of the area east of the line of split, the Deep Hard is a single bed of coal varying between 25 inches in the south-east (at Kirkby KS Underground Borehole) and about 52 inches in the north-west (see (Figure 20)." data-name="images/P990909.jpg">(Figure 19)). The make-up of the seam is variable, though 'brights' are the main constituent and dull coal occurs in varying minor proportions and is generally more prominent in the upper part. In the workings of Bolsover and Pleasley collieries a band of dirt or dirty coal, thought to be the equivalent of the Middle Dirt, occurs near the middle of the seam. This dirt thickens eastwards and divides the seam into two thin beds of coal as in Shirebrook No. 1 Drift (see (Figure 20)). The lower coal (the probable equivalent of the Bottom Bed) is between 9 and 27 in thick, and in the area between Bolsover and Creswell includes up to 23 in of cannel, though it is possible that part of this is the lateral equivalent of the Middle Dirt. In the workings north-east of Pleasley the lower coal is composed largely of bright coal; at Shirebrook No. 2 Underground Borehole it is recorded as coal 5.5 in, dirt 9.25 in, on coal 5 in. The Middle Dirt has a maximum proved thickness of 32 in at Shirebrook No. 1 Drift, where it consists of grey siltstone and dark grey mudstone with black cannely shale at the base. The upper coal, consisting of 'brights' with a little dull coal and, in the vicinity of Pleasley, a top inch or two of cannel, is between 12 and 27 in thick.

The Deep Hard is affected by two lines of washouts in the south-west (see (Figure 20)." data-name="images/P990909.jpg">(Figure 19)). The smaller of these commences south-west of Tibshelf Old Pit and extends for about a mile to the west-south-west; the larger commences south-east of Tibshelf Old Pit and continues south-westwards to the east of Blackwell 'A' Winning and west of Cotespark Colliery to the boundary of the district. G.H.R., E.G.S.

The Deep Hard is exposed in old workings [SK 383 671], 300 yd S. of Wingerworth church, where several sections show up to 42 in of coal immediately below flaggy sandstone, and in the old railway cutting [SK 4158 6911], 470 yd S. 13° W. of Calow Green, where the following section was measured:

Measures between the Deep Hard and Deep Soft coals

The measures between the Deep Hard and Deep Soft coals. At outcrop in the north the Deep Hard Coal is overlain by sandstone which in many localities rests directly upon the coal, though in others a few feet of mudstone intervene. Down dip the sandstone, which may pass laterally into silty sandstone and siltstone, is generally found above the Deep Hard Roof Coal where that coal is separated from the Deep Hard. At Oxcroft Colliery, however, the Roof Coal is absent and is possibly washed out by the sandstone. Over much of this northern area this sandstone, known as the 'Deep Hard Rock', is nearly 100 ft thick, and at Avenue Colliery in the west and Creswell Colliery in the north-east it is over 150 ft. It is made up of the sandstone phases from a number of cycles which have joined together, thereby obliterating the cyclic succession. One of the cycles locally so obliterated is that containing the Deep Soft Coal, and in much of the area in and around Chesterfield the Deep Hard Rock ' may extend up to the seatearth of the Sitwell Coal. G.H.R., E.G.S., R.A.E.

The 'Deep Hard Rock' is one of the major feature-forming sandstones of the area around Chesterfield, and its outcrop is responsible for the flat ground upon which the northern part of the town is built. It is well exposed in the railway cutting [SK 3889 7225], 800 yd N. of Chesterfield Midland Station, where it is wedge-bedded and contains small ferruginous pellets. R.A.E.

The sandstone is exposed at the southern end of the Brimington Anticline in the following places: (a) Hassochy Lane [SK 4180 6875], Sutton Springs, 1050 yd N. 70° E. of Herne House, where flaggy sandstone may be seen; an N.C.B. Opencast Executive Borehole 100 yd to the east of this exposure was drilled 83 ft into the ' Deep Hard Rock' without reaching the base; (b) in the cutting [SK 4161 6906] of the dismantled railway, 1050 yd N. 48° E. of Herne House, where massive sandstone is visible. E.G.S.

Southwards from Chesterfield the outcrop of the 'Deep Hard Rock' continues along the western margin of the Williamthorpe Syncline where it forms a prominent feature and is exposed at the following localities: (a) in the disused quarry [SK 3826 6895] at Birdholme Bridge, 550 yd N. 23° W. of Birdholme Farm, where up to 14 ft of massive and false-bedded sandstones occur; (b) in old crop workings [SK 383 671] of the Deep Hard Coal at Wingerworth (see p. 144), where the sandstone rests directly on the coal; (c) in the railway cutting [SK 3997 6471] 400 yd N.N.E. of the Clay Cross Works, where there are 30 ft of sandstone with ironstone balls. The sandstone dies out 700 yd S.S.E. of this last exposure. E.G.S., G.H.R.

East of the Brimington Anticline, where representatives of the Deep Soft Coal (see below) are developed in an area extending almost as far as Markham Colliery, the 'Deep Hard Rock' is thin or absent. A section at Tom Lane Borehole shows 49 ft 5 in of sandstone with its base less than 10 ft above the Roof Coal which is 16 in thick and separated from the main part of the Deep Hard by 42 in of seatearth and mudstone. Between the sandstone and the ?Deep Soft (bottom coal) are found mudstone with ironstone and thin sandstone bands and a 4-in coal. In the Arkwright–Calow Drifts the 'Deep Hard Rock' rests on the Deep Hard Coal and is less than 20 ft thick. Above it stone-bind occurs below 26 in of coal and dirt which may possibly be the Deep Soft (bottom coal), though the total interval between the two coals is less than 25 ft. G.H.R., E.G.S., R.A.E.

South of the area with the thick development of sandstone (see (Figure 22)." data-name="images/P990911.jpg">(Figure 21)) the measures between the Deep Hard and Deep Soft coals normally comprise one or two cycles, depending on whether the Roof Coal is joined to or separated from the Deep Hard. In the west where the Roof Coal is an integral part of the Deep Hard, the measures are 40 to 50 ft thick, though in abnormal developments at Blackwell 'A' Winning and Parkhouse collieries they are 71 and 62 ft thick respectively. In most localities mudstone with ironstone bands passes up into silty beds which give way to further mudstones; sandstone is prominent only at Parkhouse Colliery where the thick development referred to above includes 27.75 ft of Deep Hard Rock '. Where the Roof Coal and Deep Hard are separate seams the measures between the Deep Hard and Deep Soft vary in thickness between 45 ft and 110 ft. In the Shirebrook–Sherwood area, however, where the measures are thickest, several cycles are developed in the upper part of the sequence and probably represent splits from the Deep Soft. The coals associated with these extra cycles are only a few inches thick, the thickest being the 9-in coal recorded 15 ft below the Deep Soft at Shirebrook No. 1 Drift.

The Roof Coal in the area south of the thick 'Deep Hard Rock' has a maximum thickness of 14 in at Sherwood Colliery No. 2 Drift Borehole, where it consists of cannel and coal; cannel is present elsewhere, but its thickness does not exceed 12 in. The measures separating the Roof Coal from the Deep Hard attain a thickness of 48.5 ft at Shirebrook Colliery No. 1 Drift, where they consist of mudstone with ironstone and a few mussels' passing upwards into siltstone and sandstone. A similar succession is recorded in most other localities, exceptions being New Hucknall Colliery where only 2 in of bind separate 37 ft of rock from the Deep Hard Coal, and Pilsley Colliery where sandstone rests directly on the coal. The measures above the Roof Coal are more variable than those below; they vary in thickness between 18 and 57 ft, and, though stone-bind is common, the thickest sandstone is the 13 ft recorded in Cross Hills Borehole near the area of thick Deep Hard Rock' to the north. G.H.R.

Carbonicola cristagalli was collected from the roof of the Deep Hard in Shirebrook Colliery No. 1 Borehole. About midway between the Deep Hard and Deep Soft coals (above the possible horizon of the Roof Coal) in Kirkby Colliery K1 Underground Borehole were thin bands with Naiadites sp. intermediate between productus (Brown) and quadratus (J. de C. Sowerby). The paucity of fossils in these beds is in marked contrast to their abundance above the Tupton and in the beds above the Deep Soft Coal. M.A.C.

Deep Soft Coal

The Deep Soft Coal is of economic importance only in the south and south-east of the district (see (Figure 22)." data-name="images/P990911.jpg">(Figure 21)). In the Williamthorpe Syncline and the area to the north-east the seam has been cut out by the upward extension of the ' Deep Hard Rock '. Between the southern limit of this sandstone and the area of thick coal to the south, the Deep Soft is represented by coal and dirt, or by two thin coals separated by a variable thickness of measures. A similar development of two thin coals is thought to represent the Deep Soft in the area beyond the north-western limits of the 'Deep Hard Rock'.

In the south the Deep Soft has been worked extensively underground from Alfreton, Brookhill, Cotespark, Kirkby and Shirland collieries. Sections in the workings show that up to 50 in of mainly bright coal are present. In the majority dirt is recorded near the middle of the seam and, in the western sections, an inch or two of dirt is also present near the base. As the line of deterioration (see (Figure 22)." data-name="images/P990911.jpg">(Figure 21)) is approached the thickness of the median dirt increases and this renders working of the seam uneconomic.

In the east the Deep Soft, with a thickness of about 4.5 ft, has been worked at Sherwood Colliery, where it constitutes the lowest member of a compound seam of which the other coals are the Roof Soft and Sitwell (see p. 151). It is not known how far north these three coals remain closely linked, but at Shirebrook No. 1 Underground Borehole, a little over two miles to the north, the 38-in Deep Soft is over 40 ft below the Roof Soft. Farther  north again, at Shirebrook No. 1 Drift, the Roof Soft is only 64 in above the Deep Soft, but nearly 40 ft below the Sitwell. At Shirebrook No. 2 Underground Borehole the three coals are again found close together, but here the proportion of dirt in the combined seam far exceeds that of coal, and the Deep Soft itself consists of only 29 in of coal.

Beyond the line of deterioration the Deep Soft is recorded in many of the shaft sections as a single seam in which a central dirt varying between 3 in (at Blackwell 'A' Winning) and 60 in (at New Hucknall) separates coals which are commonly only a few inches thick—though the lower one swells to 29.5 in at Morton and to 24 in at Blackwell 'A' Winning, and the upper one is 21 in thick at Sutton. Farther north the top and bottom coals of the Deep Soft are widely separated and in places are represented only by seatearths. Where coals are developed they are generally thin, though at Pleasley the top coal comprises coal 17 in, dirt 2 in, on coal 19 in. At outcrop north of Parkhouse Colliery a coal thought to be the Deep Soft (bottom coal) has been worked at Bluebell Opencast Site; a section of the seam here is: 'brights' 2.5 in, dull coal 7.5 in, dirt 1.5 in, on'brights' 4 in. The two coals, or their seatearths, are recorded in Holmewood, Glapwell, Pilsley, Pleasley and Silverhill collieries and in Cross Hills Borehole where they are separated by 18 to 35 ft of mudstone and seatearth. When traced in a southerly direction through Pilsley, Parkhouse and Morton, the two coals appear to have their equivalents in the two beds of coal of the Deep Soft as worked in the southern area. In the east, however, the sections in Shirebrook Drift, Shirebrook No. 1 Underground Borehole and Sherwood No. 2 Drift Borehole show a thin coal beneath the Deep Soft, and it is likely that the Deep Soft (bottom coal) when traced eastwards through Glapwell and Pleasley passes in part into this thin coal.

North-west of the area of thick ' Deep Hard Rock' representatives of the Deep Soft group of coals have been seen in Tom Lane Borehole and the Arkwright-Calow Drift. In the borehole 8 in of coal and dirt at 1097 ft 8 in and the 29 in of dirt and coal at 1092 ft 5 in are thought to be the respective equivalents of the bottom and top coals. In the drift the bottom coal would appear to be represented by 26 in of coal and dirt and the top coal by a seatearth. It was formerly thought that in and around Chesterfield a thick coal lying higher in the succession was the Deep Soft; but this coal is now seen to be the Sitwell (p. 149).

Measures between the Deep Soft and Sitwell coals

The measures between the Deep Soft and Sitwell coals vary between about 6 and 140 ft. They are thinnest in the workings of Sherwood Colliery and thickest in the south-west, around Alfreton Colliery, but elsewhere are generally between 40 and 80 ft. The measures include the Roof Soft Coal and, in certain sections in the south, an additional coal between the Roof Soft and Sitwell coals. G.H.R.

Where the Deep Soft is absent in the north (see (Figure 22)." data-name="images/P990911.jpg">(Figure 21)) the top of the 'Deep Hard Rock' extends to within 3.5 ft of the Sitwell Coal at Creswell Colliery and 4.75 ft of the Clay Cross Soft (combined Sitwell and Chavery) at Markham Colliery. At other localities within the area of thick sandstone the Sitwell, or Clay Cross Soft, is up to 60 ft above the main mass of silty and sandy beds, and the intervening measures contain a locally developed Roof Soft Coal which attains its maximum thickness (44 in of coal and dirt) at Bolsover Colliery. To the east of the Brimington Anticline, where the ' Deep Hard Rock ' is relatively thin (see p. 145), the measures between the Deep Soft (top coal) and the Sitwell were found to be 39.5 ft thick in Tom Lane Borehole, and contain a 15-in Roof Soft Coal. The 23 ft 4 in of measures between this latter coal and the Sitwell consist largely of mudstones in which a few specimens of Naiadites sp. [juv.] were found in the lower part. E.G.S., R.A.E., G.H.R.

South of the thick 'Deep Hard Rock' the measures between the Deep Soft and Sitwell coals comprise—though not in the area of maximum thickness in the southwest—two cycles, with the Roof Soft Coal at the top of the lower.

In the east, where the measures are thinnest, the Deep Soft and Sitwell are separated by only 6 to 7 ft of coal and dirt, including the Roof Soft. A typical section recorded near the foot of Sherwood Colliery No. 2 Drift is: coal (Sitwell) 31 in, clunch 18 in, coal (Roof Soft) 30 in, clunch (with 3-in coal) 32 in, coal (Deep Soft) 56 in. A similar section has been recorded at Shirebrook No. 2 Borehole where 10.75 ft of dirt and coal separate the Deep Soft and Sitwell. Whether these two localities are parts of a single larger area of closely related Deep Soft and Sitwell coals is, however, not clear as Shirebrook No. 1 Borehole, situated between them, proved the Roof Soft, 20 in thick, 64 in below the Sitwell, with the Deep Soft a further 44.5 ft down (Edwards 1951, p. 241). Westwards the condensed succession at Sherwood persists almost to Sutton Colliery, where only 19.5 ft of measures, consisting of coal, coaly bat, black shale and clunch, separate the Deep Soft and Sitwell coals; the Roof Soft here is taken to be the 36-in of coaly bat and bind 2 ft 11 in above the Deep Soft. Elsewhere the measures are generally 40 to 80 ft thick and comprise mudstones, siltstones and sandstones, the siltstones being particularly prominent in the shaft sections along the southern margin.

Apart from the local thickening at Bolsover Colliery referred to above, the Roof Soft Coal is thickest in the area of Shirebrook and Sherwood collieries in the east, where it is over 40 inches in Shirebrook No. 1 Drift. Elsewhere it is identifiable only in the south where, as the first seam above the Deep Soft, it contains up to 24 in of coal (coal 20 in, dirt 4 in, on coal 4 in at Brook-hill Colliery). North of Blackwell 'A' and 'B' Winnings and Sutton Colliery, the thin coal above the Deep Soft or, in some places, above the Deep Soft (top coal), is probably the Roof Soft, though there is a possibility that it is an extra coal developed as a split from the Sitwell. At Sutton Colliery No. 1 Shaft a 5-in coal is recorded 4 ft 11 in below the Sitwell. This coal, recorded also in the shafts of New Hucknall Colliery and Blackwell 'A' and 'B' Winnings, is thought to be a local split off the Sitwell Coal. It is thickest at New Hucknall where 24 in of coal and dirt lie 49 in below the Sitwell, and thinnest at Blackwell 'A' Winning where it is 3 in thick and 28 ft 7 in below the Sitwell.

In the south-west of its field the Deep Soft is overlain, in many places directly, by sandstone and siltstone which comprise the greater part of the measures up to the Sitwell, and the Roof Soft Coal is absent. In this area, extending eastwards to Alfreton Colliery and northwards to Higham, the measures are over 100 ft thick and reach a maximum of about 140 ft at Alfreton Golf Course RM1 Borehole, where the sandstone has washed out the Deep Soft. Thicknesses of over 100 ft can be traced into the Tibshelf area and here also the Roof Soft is missing; the amount of sandstone present, however, is extremely variable, as is shown by the sections at Tibshelf Old Pit, where less than 5 ft of rock is recorded, and Tibshelf No. 4, where there is over 80 ft of stone-bind and rock in a total thickness of 108 ft 7 in.

The sandstone above the Deep Soft forms a strong feature from Higham southwards. North of Tibshelf a similar feature is produced on the north-eastern flank of the Hardstoft–Mansfield Anticline, and a borehole at Biggin Opencast Site proved 72 ft of sandstone and siltstone beneath the Sitwell Coal. An old quarry [SK 4514 6187] in this sandstone, 200 yd N. of The Hurst, shows 20 ft of false-bedded sandstone with ironstone concretions. G.H.R.

Sitwell, Chavery and Clay Cross Soft coals

The Chavery and Sitwell coals unite in a central area in the north to form the Clay Cross Soft Coal (see (Figure 22)." data-name="images/P990911.jpg">(Figure 21)).

The Sitwell Coal, known also as the Dunston, has in the past been confused with the Deep Soft. Its development to the northwest and west of the field of the Clay Cross Soft is similar to that in the Sheepbridge–Hartington area of the Sheffield district (Eden and others 1957, p. 89), where it consists of a main bed of coal separated by dirt from a thinner upper bed of coal known as the Tops. The seam deteriorates eastwards and southwards (see (Figure 22)) as the main bed of coal is split by dirt bands in the lower part, and over much of the southern part of its field it consists of two thin coals separated by a variable thickness of dirt. In the extreme south the seam is variable and in some instances correlation is doubtful. It is represented in many sections (e.g. at Bentinck and Langton collieries) by only a few inches of coal; at Alfreton Golf Course RM1 and Golf Links boreholes it is thought to be absent, while in a neighbouring borehole, Alfreton Golf Course RM5, the seam consists of 33 in of coal.

West of the line of deterioration most Sitwell sections show the main bed of coal to be between 45 and 60 in, consisting mainly of 'brights', though several bands of dull coal up to 3 in thick are recorded, especially in the top part. Impersistent dirt bands up to about an inch are recorded at several levels in the main bed but only one section, that in the railway cutting [SK 3887 7290], 1600 yd N. of Chesterfield Midland Station, shows a thick dirt. The section of the full seam here is: coal 8 in (Tops), dirt 28 in, coal 27 in, dirt 12 in, on coal 12 in.

The deterioration of the main bed of coal is revealed in sections near Clay Cross. At Hepthorn Opencast Site the top 16 in consists of bright coal with two 1-in dull bands, and the lower 35 in are bright coal with fusain partings and a 6-in dirt. At North Wingfield Borehole, less than a mile to the east, the top 20 in are bright coal and the underlying 38 in comprises 29.5 in of carbonaceous dirt resting on a bottom 8.5 in of dirty bright coal (see section 9, (Figure 22)). Further sections along the outcrop at Parliament, Gentshill, Straw Lane and Aintree opencast sites show the main bed to be represented by up to 29 in of coal with dirt bands resting on dirt and coal; farther south it passes into clunch with coal and, finally, into clunch. Over the greater part of the southern half of the district the main bed of coal consists of less than 12 in of bright coal, and at Blackwell 'A' Winning and Tibshelf Old Pit, it is only 4 in thick, In the north-east, east of the field of the Clay Cross Soft, there is a progressive deterioration southwards from Creswell Colliery through Elmton Green, Norwood Farm and Langwith Colliery Underground boreholes (see Appendix 2 for details). The main bed thins from 35 in of coal, including a 3.5-in dirt band, at Creswell to 23 in of dirt, dirty coal and coal at Langwith. South of Langwith it is not possible to identify the main bed in the underground boreholes and No. 1 Main Drift at Shirebrook Colliery. In the No. 2 Borehole at Shirebrook the position is further complicated by the proximity of the Sitwell (20.75 in of coal and dirt) to the Roof Soft, only 40.25 in below, and the Deep Soft, only 60 in below the Roof Soft. A similar sequence is found farther south in Sherwood Colliery, where sections in the workings show the Sitwell to be about 18 in above the Roof Soft and Deep Soft, which are only 30 in apart. G.H.R., E.G.S., R.A.E.

The dirt above the main bed of coal averages about a foot in the north, varying from a few inches to over 36 in. South of the field of the Clay Cross Soft the average thickness is about 6 in; the dirt is absent in certain isolated sections (e.g. Alfreton Golf Course RM5 Borehole and Sutton Colliery Shaft) and has a maximum recorded thickness of 24 in at Blackwell 'A' Winning.

The Tops consist of 6 to 22 in of bright coal. In the north-west where the main bed of coal is thick, the Tops are insignificant, but east of the line of deterioration of the main bed they commonly form the thicker member of the seam, though the total thickness of coal does not, except at outcrop in the vicinity of Clay Cross, exceed 33 in.

An exposure of the Sitwell Coal is visible in the east face of the Midland Railway cutting [SK 4012 6575], 550 yd N. of Clay Cross Station. The section is: coal (Tops) 20 in, dirt 16 in, coal 48 in. Another section, in the railway cutting north of Chesterfield Midland Station, has been referred to above (p. 149). G.H.R.

The measures between the Sitwell and Chavery coals are of maximum thickness (43 ft 8 in) at Seymour Colliery in the extreme north, where they include a 2-in coal. This coal is possibly a split off the Chavery from which it is separated by 16 ft 4 in of stone-clunch and bind; the underlying measures down to the Sitwell have been described as stone-bind and 'cank'. The Sitwell and Chavery coals, where not combined to form the Clay Cross Soft (see p. 152) are commonly 15 to 30 ft apart. Siltstones and sandstones occur where the greater thicknesses are found, but elsewhere mudstones predominate. Non-marine lamellibranchs occur sparingly in the mudstones; Anthracosia aff.regularis (Trueman) and Naiadites sp. have been identified. Surface exposures of the measures are poor, the best sections being in opencast sites. At Hillhouse Farm Opencast Site the coals were separated by 26.5 ft of measures consisting mainly of siltstone. Northwards the siltstone passes into sandstone which forms a marked feature northwards from Cottagehill Farm to Birdholme Farm Opencast Site where the following section of the overburden was measured by Dr. J. Shirley:

The Chavery Coal (known locally as the Black Rake Coal) attains its maximum development in the north-west where it shows a similar section to that described in the south of the Sheffield district (Eden and others 1957, p. 90); it consists of two beds of coal separated by dirt. The lower coal is only 3 or 5 in thick in the area of Dunston Hall Opencast Site on the district boundary north of Newbold, but sections on the flanks of the Brimington Anticline show 5 to 21 in of bright coal underlain locally by a few inches of coal and dirt. At Seymour Colliery no lower coal is recorded. The middle dirt is 68 in at Ireland Colliery but it decreases to 2 or 3 in at Dunston Hall Opencast Site and Duckmanton Cutting. The upper coal was found to be 34 to 40 in thick at Dunston Hall Opencast Site, but up to 15 in at the top were dirty; two main bands of dull coal are recorded in some sections. On the east side of the Brimington Anticline the thickness is generally between 9 and 24 in and includes, in some sections, a thin dirt band. The thickness increases northwards and at Seymour Colliery it is 39 in, comprising a lower 32 in of coal, 5 in of bat, and a further 2 in of coal. On the southwest side of the Brimington Anticline the few available sections show the upper coal to be between 9 and 13 in, including 1 in of dirt. R.A.E., E.G.S.

East of the presumed limit of the Clay Cross Soft the Chavery is absent in the boreholes at Elmton Green, Norwood Farm and Langwith Colliery, but its seatearth, overlain by shelly measures, is present. The coal comes in again at Shirebrook Colliery where, in No. 1 Main Drift, it is 11 in thick. In the No. 2 Underground Borehole at this colliery it is thought to be split, 11 in of coal being overlain by a seatearth.

South of the Brimington Anticline the seam thins abruptly, and at Avenue and Old Avenue collieries it would appear to be represented respectively by 6 in and 3 in of coal approximately 28 ft above the Sitwell. At Hillhouse Farm Opencast Site, approximately 1.25 miles S.S.E. of Old Avenue Colliery, a 6-in coal lies 26.5 ft above the Sitwell. The Seanor Farm, North Wingfield, Borehole proved a similar succession, the 4-in Chavery being 32 ft above the Sitwell. Throughout the southern part of the district the Chavery is thought to be represented by a few inches of coal, or merely by seatearth, generally present at a variable interval above the Sitwell, though at Tibshelf and in the south-east it has not been traced.

The Clay Cross Soft Coal, formed by the combined Sitwell and Chavery coals, occupies a northern area, the eastern and south-eastern boundaries of which are ill-defined because of lack of information. Within this field the Sitwell and Chavery elements can normally be recognized. The main bed of the former deteriorates along the line shown on (Figure 22)." data-name="images/P990911.jpg">(Figure 21). West of this line the Clay Cross Soft has been worked extensively underground from Alma, Grassmoor, Ireland and Williamthorpe collieries. It has also also been worked opencast at the southern end of the Brimington Anticline.

West of the line of deterioration the main bed of the Sitwell element of the seam varies in thickness between 44 and 58 in and contains only minor dirt bands; east of the line, dirty coal and dirt appear near the middle and increase in thickness eastwards, dividing the bed into an upper coal, a central dirt which includes bands of coal in some sections, and a lower coal which is commonly dirty. Sections illustrating this deterioration are largely confined to the Williamthorpe–Holmewood area in the south-west of the field, but a comparable section is also recorded at Oxcroft Colliery in the north, where the main bed of coal comprises a lower 19 in of coal separated by 33 in of dirt from an upper 12 in of coal.

The Tops of the Sitwell element of the Clay Cross Soft vary from 6 to 30 in, though they are generally between 16 and 30 in. They consist mainly of bright coal, though bands of dull coal and dirt also occur, and are separated from the underlying main bed by up to 16 in of dirt. At Cross Hills Borehole the bottom 17 in of coal and dirt are considered to be the Sitwell, but it is not possible to say which part of this represents the Tops.

The Chavery element of the Clay Cross Soft is separated from the Sitwell element by 2 to 74 in of dirt or, as at Grassmoor Colliery, of dirt and coal. In the extreme west of the field, in opencast sections around the southern margin of the Brimington Anticline and at Grassmoor Colliery, it consists of two leaves of coal, a development similar to that of the separate seam in the north-west (see (Figure 22)). The lower coal is 5 to 9 in thick at these localities, and is separated from the upper bed of coal by up to 21 in of dirt (at Calow Brook Opencast Site.) In the remainder of the field the Chavery element consists generally of a single bed of coal, between 10 and 22 in thick, thought to be the equivalent of the upper bed of the west. Some western sections show a dirt band in the upper coal; this dirt has not been recorded in the east and it is not clear whether the coal here is the equivalent of the whole of the upper coal or of that part of it above the dirt.

Apart from the main area of development of the Clay Cross Soft, the Sitwell and Chavery coals are found close together in two other isolated areas. At Silverhill Colliery the Sitwell consists of coal 14 in, dirt 2 in, on coal 7 in; it is separated by 62 in of dirt from an overlying 8 in of cannel which is thought to be the Chavery. In the south-west of the district a coal 19 to 29 in thick and consisting of brights with fusain partings has been proved at Johno Opencast Site. This is thought to be the Sitwell element of the Clay Cross Soft, the Chavery being represented by a 2-in coal proved 18 in above in one section. Alfreton Golf Course RM5 Borehole, sited in this area just east of the outcrop, proved the Chavery to be 3 in thick and separated by only 15 in of dirt from a 33-in Sitwell. G.H.R., E.G.S.

Measures between the Chavery Coal and the Clay Cross Marine Band

The measures between the Chavery Coal and the Clay Cross Marine Band are thickest in the north-west where 128 ft have been recorded at Arkwright Drift; the thick measures extend southwards to Bond's Main, Grassmoor, Williamthorpe and Holmewood collieries where thicknesses of over 100 ft are recorded. Another area of thick development is found in the east where, at Sherwood Colliery No. 2 Drift, nearly 115 ft of measures were encountered. The measures are thinnest along the southern margin of the district where they are 50 to 60 ft thick, and in the north-east where 52 ft have been proved in the Elmton Green Borehole. G.H.R., E.G.S., R.A.E.

The measures contain up to five seatearths, each overlain locally by a thin coal rarely more than 6 in thick. The only named coals in this sequence are the Brown Rake, lying at the top of the cycle immediately overlying the Chavery, and the Joan Coal, found immediately below the Clay Cross Marine Band or separated from it, as in Shirebrook No. 3 Borehole, by up to 18.5 in of dark mudstone containing mussels ' and ostracods.

The Brown Rake Coal is represented at Cotespark Colliery, in the south-west, by two thin coals separated by 5 ft 4 in of seatearth. Here and in sections to the south of the district, there are no seatearths or coals between the Brown Rake and the Clay Cross Marine Band. Where coals are developed in these measures within the Chesterfield district they are, except for the Joan Coal, likely to be further splits off the Brown Rake Coal.

The Joan Coal is normally present in the north, where it is up to 6 in thick, but has not been recorded south of North Wingfield Borehole, where it is 1 in thick. In the southern area the seatearth is present in some sections but in many others the horizon is marked by only a few feet of silty or sandy beds and even these are absent in the Shirebrook area. G.H.R.

Sandstones are not common in this group. The most prominent is that lying beneath the Clay Cross Marine Band and forming a feature round the southern flanks of the Brimington Anticline at Sutton Springs. It is in a similar position to, but is probably thicker than, the 10 to 15 ft of sandstone developed 15 to 30 ft below the Clay Cross Marine Band in the Williamthorpe area, and extending into the Shirebrook–Sherwood–Sutton area as stone-bind and bind with rock bands. At Holmewood Colliery the top 2 ft of this sandstone are said to be stone-clunch. At Storforth Lane Brick-pit [SK 3884 6968] 10.75 ft of siltstone and sandstone were recorded at this horizon in the following section:

Mudstones comprise a large part of the measures and they generally contain much clay ironstone, which occurs in each of the locally developed cycles. In the north the ironstones are particularly well developed in the immediate roof measures of the Chavery and of the two overlying thin coals, and are collectively known as the Pinder Park Rake. The beds are partially exposed in Duckmanton Cutting where the lower of the three main ironstone-bearing horizons includes a 12-in bed showing cone-in-cone structure as well as shelly ironstones up to 4 in thick, while the middle horizon includes a 9-in shelly ironstone.

To the south of the district the ironstone above the Chavery Coal is known as the Black Rake (Gibson and others 1908, pp. 72, 170). At this horizon in Nottinghamshire (Edwards 1951, p. 33) boreholes have proved a banded calcite mudstone, and Edwards (ibid., p. 234) notes the occurrence of a similar rock in Sherwood Colliery No. 2 Drift where it is recorded as 7 in of blue-grey limestone. This 'Black Rake Carbonate Rock', as it has come to be known, has been found 4.5 miles north of the latter locality at a depth of 504.75 ft in Shirebrook No. 2 Underground Borehole. This rock, 3 in thick, has been examined by Mr. R. K. Harrison, who reports that it is composed mainly of massive grey cryptocrystalline calcite-mudstone with an average grain size of less than 2μ, riddled with fine carbonaceous specks and containing a few fine siderite bands '. The characteristic light grey band through the middle of the calcite-mudstone is due to the presence of sand-grade clastic quartz and rarer chert, showing rudimentary graded bedding. These grains, which are generally angular, are set in a calcite cement with sporadic chlorite and abundant coal remains '. Contributing to the banded appearance in part of the section is a wedge-shaped mass of fibrous calcite resembling a microscopical cone-incone structure '.

A banded ironstone has been noted at this horizon at outcrop in Hillhouse Farm Opencast Site and is shown in the following section which also records a local development of a similar rock at a higher horizon:

A prominent 'mussel'-band occurs above the Chavery Coal and has been proved in numerous boreholes. The collections show that the fauna is almost entirely composed of Anthracosia regularis but also includes rare Anthraconaia sp. Well-developed 'mussel'-bands also occur in several of the cycles above the Chavery horizon, such as that overlying the Brown Rake Coal of the southern part of the district. This latter horizon was typically represented in Dog Lane Farm Borehole from which the following assemblage was obtained: Anthracosia regularis, A. sp. nov.aff.regularis [cf. Melville 1947, fig. 3c], A. sp. intermediate between regularis and phrygiana (Wright), Anthracosphaerium cycloquadratum (Wright), Carbonicola cf. oslancis Wright, Naiadites sp. intermediate between productus and quadratus; G. arcuata [abundant]; Anthrapalaemon sp. nov.; and Rhizodopsis. In this collection there is much variation in the A. regularis group; the larger shells depart furthest from regularis s.s. but the differences may be partly gerontic features. Additional fossils recorded from between the Chavery Coal and Clay Cross Marine Band include: Anthraconaia modiolaris (J. de C. Sowerby), Anthracosphaerium cf. exiguum (Davies and Trueman), Naiadites cf. triangularis (J. de C. Sowerby), cf. Carbonicola venusta Davies and Trueman; Carbonita humilis. M.A.C.

Middle Coal Measures

Clay Cross Marine Band to Top Hard Coal

Variations in thickness (about 425 to 525 ft, decreasing towards the south) and general lithological characters of the group are shown in (Figure 23). The chief workable coals are the Second Ell, the First and Second Waterloos and the Dunsil.

Clay Cross Marine Band

The Clay Cross Marine Band was named by Clift (1930, p. 267) after the locality first recorded by Gibson (1903, pp. 15–6) in the railway cutting [SK 4073 6160], 1615 yd N. of Holy Cross Church, Morton, and about 1.5 miles S.E. of Clay Cross. The section described by Gibson (in Gibson and Wedd 1913, p. 71) as consisting of 4 ft of dark blue shales with Lingula, Pterinopecten, and goniatites' is no longer exposed.

The Geological Survey Collection contains the following fossils from this locality, submitted by Gibson: sponge spicules [cited Edwards and Stubblefield 1948, pp. 238–9]; Lingula sp., Strobeus sp., Dunbarella papyracea mut. δ(H. Schmidt), Myalina compressa Hind; Anthracoceras cf. vanderbeckei (Ludwig); Streptognathodus sp. At the time of the resurvey the marine band was visible at only two surface localities—in Duckmanton Cutting [SK 4238 7039], 550 yd W. of Arkwright Town Station, where marine fossils are recorded from the lower part of 11 ft of dark decomposed mudstone with thin ironstones, which overlies a 2.5-in coal, and in Storforth Lane Brick-pit [SK 3884 6968], where 6 ft 4 in of dark grey mudstone with ironstone lenses yielded marine fossils. W. Gibson collected the following fossils from the Duckmanton locality: Ammodiscus sp. [seen on weathered surface of clay-ironstone], Ammonema sp., Spirorbis sp., L. mytilloides; Dunbarella sp., Myalina sp. At Storforth Lane recent collecting yielded the following fauna: Ammodiscus sp., Ammonema sp., Spirorbis sp., L. mytilloides; Anthracosia sp. [stunted], D. papyracea mut. δ, Naiadites sp., Geisina arcuata, Hollinella cf. bassleri (Knight), Paraparchites sp. Most of the above collections consist of fossils found in clay-ironstone.

The marine band is thought to be everywhere present at outcrop except in one small area between Inkersall Green and Brimington Common in the north where it appears to be washed out by the thick sandstone in the measures between the Chavery and Second Ell coals.

Underground, the band has been identified at the following localities (thickness, where recorded, is given in brackets): Alfreton Golf Course RM1 Borehole, Alfreton Road, Tibshelf, Borehole (9 ft), Arkwright No. 2 Drift (8 ft 5 in), Biggin Opencast Borehole (2 ft 6 in), Bolsover Colliery No. 3 Shaft, Creswell Colliery Sinking, Cross Hills Borehole (9 ft 8 in), Dog Lane Farm Borehole (11 ft 3 in), Elmton Green Borehole (7 ft 5 in), Golf Links Borehole, Langwith Colliery Underground Borehole (4 ft 4 in +), Mill Lane Borehole (8 ft 7 in), Nethermoor Borehole (5 ft 5 in), Normanton Brook Borehole (5 ft +), Norwood Farm Borehole (6 ft 10.5 in), Rouse Street Borehole (5 ft 6 in), Seanor Farm Borehole (3 ft 7 in), Sherwood Colliery No. 2 Drift (about 7 ft 4 in), Shirebrook Colliery No. 1 Drift (12 ft + ), Shirebrook Colliery No. 1 Underground Borehole (10 ft 6 in), Sutton Lane Borehole (8 ft 1 in), Tom Lane Borehole (7 ft). These sections show the marine band to consist of dark grey mudstone with lenses and thin bands of ironstone, containing an abundant marine fauna. E.G.S., R.A.E.

A composite list of marine fossils based on these sources is as follows: Ammodiscus sp., Ammonema sp., Tolypammina sp.; sponge spicules; Spirorbis sp. [attached to Dunbarella]; Lingula mytilloides, Orbiculoidea cf. nitida (Phillips); Leptoptygma sp., Aviculopecten sp., Dunbarella papyracea mut δ, Edmondia sp., Myalina compressa; Anthracoceras vanderbeckei; Hollinella cf. bassleri, Paraparchites sp., Hindeodella sp., Streptognathodus sp. Typical examples are illustrated in (Plate 5).

Throughout this district the stages in the development of the Clay Cross Marine Band follow the pattern noted by Edwards and Stubblefield (1948, p. 216) for the Nottinghamshire–Derbyshire area as a wholeAt certain localities, e.g. Dog Lane Farm Borehole, a thin non-marine development with macrospores, Anthracosia ovum Trueman and Weir, G. arcuata, 'Estheria' and fish remains intervenes between the underlying coal and the marine band.. A brief basal phase with foraminifera and Lingula is followed by the appearance of the characteristic fauna of the band composed of Myalina, Hollinella and Paraparchites, with or without Lingula; the fossils from this assemblage occur intermittently throughout. The maximum development of the marine incursion, denoted by the presence of Dunbarella, Anthracoceras and conodonts, and locally of Orbiculoidea, occurs in the lower part of the band, suggesting that the advance phase of the incursion was more rapid than the retreat. The disappearance of the Dunbarella fauna marks the beginning of the regression, in which foraminifera reappear and are more abundant than in the basal phase. The end of the incursion is marked by the development of the thick 'mussel'-band lying immediately above the highest marine fossils. The forerunners of the non-marine lamellibranchs appear in the uppermost layers of the marine band, and this close association with the marine fossils, frequently side by side on the same bedding plane, is a well-known feature of the Clay Cross horizon. The lamellibranchs, mainly Anthracosia ((Plate 5), fig. 15), do not appear to have drifted into the marine environment in which they are now found, since the shells show little signs of transport and in many cases both valves are in contact. Their concentration at certain levels has been interpreted as intercalations of the non-marine facies within the marine band (Edwards and Stubblefield 1948, pp. 216–7; Edwards 1951, p. 34); an alternative explanation is to regard this juxtaposition of the non-marine and marine fossils, and the wide extent of the phenomena as indicating coexistence in a common environment at this stage of the regression. The Anthracosia are seldom found at the levels where the typical marine fossils such as Anthracoceras, Dunbarella and Orbiculoidea occur, but more usually in association with the foraminifera/Lingula/Myalina/Hollinella fauna, which appears to be tolerant of less than fully marine conditions.

The Anthracosia, which are smaller than in the overlying 'mussel'-band, are accompanied by small specimens of Geisina, which may represent stunted or immature Geisina arcuata. The implication is that both these genera can tolerate, but not flourish in, an environment which will support marine forms, and that this has a higher salinity than the normal habitat of the 'mussels'. It is likely that such a brackish environment existed in the transitional period of the regressive phase of the marine incursion, prior to the establishment of the conditions under which the overlying ' 'mussel'-band accumulated. M.A.C.

Measures between the Clay Cross Marine Band and the Second Ell Coal

The measures between the Clay Cross Marine Band and the Second Ell Coal are generally between 50 and 75 ft thick, but vary from 32 ft in Elmton Green Borehole in the north-east to between 80 and 90 ft in the shafts of Swanwick and Pinxton collieries a few hundred yards beyond the southern boundary of the district. Typically, they comprise one well-developed cycle of sedimentation. The Clay Cross Marine Band is succeeded by mudstones, dark at the base and grey above, which contain much ironstone in the form of bands and lenses. Abundant 'mussels' occur in both the mudstones and ironstones, some specimens from the latter being preserved in carbonate. The ironstone-bearing measures have been named the 'Cement Rake' in Old Avenue Colliery shaft, and have been divided into the 'Ball Rake' below and the Whetstone Rock Ironstone ' above at Swanwick Deep Pit. There appears to be no clear dividing line between the two named units at Swanwick, and the lower includes the Clay Cross Marine Band at its base. There is nowhere any evidence that ironstone has been worked at this horizon.

The mudstones are succeeded by siltstone and stone-bind ' and they, in turn, give way in many places to sandstone. E.G.S., G.H.R., R.A.E.

The measures are poorly exposed and lie too far above the Clay Cross Soft or Chavery Coal to be included in the overburden of opencast sites. They have been seen in many places, however, in boreholes and colliery sinkings. The only surface exposure of note at the time of the resurvey was at Storforth Lane Brick-pit [SK 3884 6968], where the following section was visible:

'Mussels' are confined to the lower part of the cycle immediately overlying the marine band. In Alfreton Road, Tibshelf, Borehole the ' mussel-band is 24 ft thick and contains the following fauna: Spirorbis sp., Anthraconaia modiolaris, Anthracosia aff. aquilina (J. de C. Sowerby), A. aff. disjuncta Trueman and Weir, A. ovum, A. cf. ovum [large], A. cf. phrygiana [not typical], A. subrecta Trueman and Weir, A. sp. cf. caledonica Trueman and Weir, A. sp. intermediate between ovum and aquilina, A. sp. nov., Anthracosphaerium exiguum, Naiadites quadratus, N. cf. triangularis; Geisina sp. The assemblage is dominated by the A. aquilina/ovum group with the main trend towards A. subrecta. The other Anthracosia spp. are not common and probably represent extreme variants of the dominant forms. The Geisina sp. is present at several levels in the lower half of the band; it is unusual to find this genus in the upper A. modiolaris Zone, in contrast to its abundance below the Clay Cross Marine Band. As noted above (p. 157) Geisina occurs spasmodically in the upper part of the marine band, and the present collection shows that rarely it persists into the overlying 'mussel'-band. A similar fauna, apart from Geisina, is found in Normanton Brook and Elmton Green boreholes with the addition of Anthraconaia williamsoni (Brown) from the former. M.A.C.

Second Ell Coal

The Second Ell Coal has been mined from Markham, Grassmoor, Alma and Holmewood collieries, and worked opencast along practically the whole length of its outcrop. It is of good quality with a low ash content, though the sulphur content is high in sections containing pyrite.

In the north the seam is split into two leaves by a middle dirt which thins southwards from 36 in at Ireland Colliery Borehole; it never exceeds 3 inches in underground workings south of the Duckmanton area or at outcrop, and dies out between Bond's Main and Williamthorpe. The lower leaf of coal consists of 13 to 24 in of 'brights' with dull streaks and bands, mainly in the middle and towards the top. The upper leaf is 12 to 23 in thick, consisting of bright coal with, in some places, partings of fusain, dirt and pyrite.

In the Grassmoor–Holmewood–North Wingfield area the Second Ell is 30 to 52 in thick, divided into a basal 6 to 17 in of bright coal (the Bottom Softs), 6 to 17 in of mainly dull coal (the Hards), and 9 to 24 in of bright coal (the Top Softs). In Williamthorpe Colliery Shaft there is a 0.5-in dirt 2.5 in from the base of the seam; this thickens to 1.5 in at Holmewood and can be recognized in most of the outcrop sections around the Hardstoft Anticline and to the south of Morton. Usually less than 6 in thick, it is 14 to 15 inches in the Tibshelf area, 15 to 16 in at Johno Opencast Site, and probably represents the 13 ft 1 in of measures at 201 ft 11 inches in Alfreton Colliery Shaft. It divides the Second Ell into a thin lower leaf and an upper or main leaf, locally called the Tanyard Coal. The lower leaf consists, in the west, of bright or dirty bright coal, rarely more than 7 in thick; it is absent east of a line through Glapwell, Tibshelf and Swanwick. The main leaf shows rapid variation in thickness between 14 and 31 inches in the west where it consists in many sections of clean bright coal, though other sections show fusain partings and, in the lower part, variable bands of dull coal. East of Blackwell few sections have been recorded; none shows more than 24 in of coal, and the minimum thickness is 15 in at Sutton Colliery. It is absent, probably because of a washout, at Kirkby North Pit. At Pleasley Colliery the Second Ell is represented by 22 in of cannel, and in Sherwood Colliery Drift the top 4 in of the 24-in seam consists of cannel. E.G.S., R.A.E., G.H.R.

In workings at Markham No. 2 Colliery, lenses of eye-coal up to 2.5 in thick are found in 4 ft of slickensided shale immediately overlying the Second Ell. According to Mr. D. Yates, the colliery surveyor, who obtained the specimens now in the Geological Museum collection, the eye-coal occurs in an east-north-easterly trending belt, some 250 yd wide, about 0.33 mile north of Bolsover Colliery shafts. E.G.S.

Measures between the Second Ell and First Ell coals

The measures between the Second Ell and First Ell coals are less than 30 ft thick at Seymour Colliery in the north and at Brookhill Colliery in the south; elsewhere they vary between about 40 and about 65 ft. They consist usually of one cycle, in places of two, and are predominantly argillaceous. The Second Ell Coal is everywhere succeeded by mudstone which, as in the Duckmanton Cutting section, contains much ironstone and fairly abundant 'mussels'. The upper half of the 30 ft or so of these measures in Bond's Main Shaft and Nethermoor Borehole consists of sandstone, but elsewhere sandy and silty beds, if present, are confined to a few feet immediately below the seat-earth of the First Ell Coal. E.G.S., G.H.R., R.A.E.

The fauna from roof mudstones of the Second Ell is well represented in Shirebrook Colliery No. 1 Underground Borehole, from which the following were collected from 2 to 23 ft above the coal: Spirorbis sp., Anthraconaia cf. curtata (Brown), A. modiolaris, A. williamsoni, Anthracosia aquilina, A. ovum, Naiadites aff. quadratus [figured Trueman and Weir 1955, pl. xxix, fig. 13], N. cf. triangularis. The assemblage is distinguished by the abundance of the Anthraconaia and Naiadites. A similar fauna was present in opencast sites in the vicinity of Shirland and Alfreton. In particular, at Stonebroom Lane Opencast Site abundant lamellibranchs, preserved as internal moulds in ironstone, were obtained from 6 ft above the coal. Several of the Naiadites in this collection were figured by Trueman and Weir (1955, pl. xxviii, figs. 7–26) as N. aft productus but are here referred to N. quadratus and N. triangularis. A band of crushed Naiadites cf. triangularis in black shale has been noted at several localities at about 7 ft above the coal. Thin bands with Anthraconaia modiolaris, A. aff. Anthracosia ovum and N. quadratus have been found up to 40 ft above the coal in borings. M.A.C.

First Ell Coal

The First Ell Coal over most of its field is of uneconomic thickness, although it is generally of good quality with a low ash content. It has been worked sporadically along its outcrop in opencast sites, but underground only on a limited scale from Grassmoor Colliery. It is thickest north of the Hardstoft Anticline and west of a line running between Ireland and Seymour collieries southwards to Hardstoft. In this area it consists of 20 to 30.5 in of bright coal with dull bands especially in the lower part. A few inches of cannel are locally present at the base in the north. Some sections show a dirt parting up to 2 in thick 3.5 to 9 in from the top of the seam, and this thickens north-eastwards to 26 in of coal and dirt at Ireland Colliery and 55 in of dirt at Seymour. At Williamthorpe Colliery there is an additional 3.5-in dirt near the base of the seam. This thickens to 14 in at Holmewood and probably represents the 10.5 ft of measures between the 24 in of coal and the lower 1 in of coal at Seanor Farm Borehole. East of the area of relatively thick coal already mentioned, the First Ell is split by thick dirt partings, and is worthless. At Markham No. 1 Colliery and Cross Hills Borehole only one leaf of coal, respectively 8 in and 2 in thick, is present, but elsewhere there is 5 to 16 in of coal in two or more leaves which are spread over up to 10 ft of measures.

South-west of the Hardstoft Anticline the First Ell is a single bed of coal without dirt partings. It was not recorded in Pilsley Colliery No. 2 Shaft and Rouse Street and Alfreton Road boreholes, and is absent in Pinxton No. 3 Shaft a few yards south of the district boundary. Its absence at Pilsley is probably explained by a washout, the beginnings of which are visible in the railway cutting [SK 427 631] on the east side of the colliery where, in one exposure, 12 in of coal are overlain by sandstone, while an adjacent exposure shows coal interleaved with sandstone. Elsewhere it varies erratically in thickness from 9 in at Nethermoor Borehole to 27 in at Wren Opencast Site, but there seems to be a general thickening towards the south-west. In most sections in this area south-west of the Hardstoft Anticline, the seam consists of clean bright coal, but fusain and thin bands of dull coal are noted in some records. It is exposed in the railway cutting [SK 4094 6110], 330 yd S. 15° W. of Padleywood Farm, where it varies in thickness between 14 and 20 in. In Blackwell 'A' Shaft, where the seam is 18 in thick, it has been named the Sedgitt Coal.

South-east of the Hardstoft Anticline the few recorded sections show 10 to 20 in of coal or coal and dirt. The seam is absent at Kirkby Lowmoor Pit and Bentinck Colliery.

Measures between the First Ell and Second Waterloo coals

The measures between the First Ell and Second Waterloo coals are between 120 and 220 ft thick in the north and between 110 and 140 ft in the south. They normally comprise four or five cycles and there are even more in places in the north. They contain several coals which are rarely more than 12 in thick in the north, but which include, in the south, the Third and Fourth Waterloos. Ironstone and 'mussels ' occur at several levels, and are particularly conspicuous in the roof mudstones of the First Ell Coal. In Duckmanton Cutting [SK 4251 7040], 400 yd W. of Arkwright Town Station, the First Ell Coal is overlain by mudstones containing well-preserved solid 'mussels', the state of preservation recalling that seen at the same horizon in Campbell Brickpit (Eden and others 1957, pp. 97 and 190). The ironstone bands above the First Ell are probably those formerly worked in the Duckmanton area under the name Strang Rake. E.G.S., G.H.R., R.A.E.

The combined fauna from the Duckmanton Railway Cutting and from the same horizon in Sutton Rock Opencast Site comprises: Anthraconaia modiolaris [one example only], Anthracosia cf. aquilina, A. beaniana King, A. aff. disjuncta, A. ovum, A. phrygiana, A. aff. retrotracta (Wright), A. sp. intermediate between aquilina and ovum, A. sp. intermediate between aquilina and phrygiana, A. sp. nov. [elongate], A. sp. nov.intermediate between ovum and subrecta, Anthracosphaerium affine (Davies and Trueman), A. bellum (Davies and Trueman), A. exiguum, A. turgidum (Brown), Naiadites quadratus and N. triangularis?.

The assemblage is dominated by the A. ovum and A. phrygiana groups, but is notable for the variety of the Anthracosphaerium spp., recalling the similar abundance above the Bute (Brass) Vein of the South Wales Coalfield (Davies and Trueman 1927, p. 240; Woodland and Evans 1964, p. 25). This same feature distinguishes the First Ell fauna from that above the Second Ell (see p. 159) in which Anthraconaia and Naiadites are comparatively more abundant and the A. phrygiana element less important. In Elmton Green Borehole a slightly higher band, 40 ft above the First Ell, contains a similar but less varied fauna than that in the immediate roof, with the addition of a large species of Anthraconaia probably referable to A. salteri (Leitch). M.A.C.

Sandstones occur locally in each cycle, the most prominent being found in the central part of the district. At Rouse Street Borehole, near Pilsley, 80 ft of sandstone below the seatearth of the Third Waterloo Coal apparently wash out the Fourth Waterloo Coal. This sandstone unites with the one above the Third Waterloo to form a marked feature in the Pilsley area, and is well-exposed in the village itself. The last-mentioned sandstone reaches a maximum thickness of 55 ft in Pleasley Colliery Shaft, where it is recorded as ' rock and stone-bind ', and extends southwards to Sherwood and Silverhill. At outcrop it forms a prominent feature on the eastern flank of the Hardstoft inlier and is particularly well developed west of Stanley. G.H.R.

The Fourth Waterloo Coal is only of significance south-west of a line through Morton, Blackwell 'A' and Langton collieries. To the north and east it is generally less than a foot thick, though locally, as in Holmewood Colliery Shaft, it is as much as 2 ft. It is split in many sections towards the north-east, and cannot be identified with certainty north of a line through Grassmoor and Shirebrook. G.H.R., E.G.S.

In the south-western area defined above, the Fourth Waterloo can be correlated with confidence in all sections, and in places is thick enough for opencast working. The thickness varies erratically between wide limits, i.e. 5 in of dirt and coal at Morton Colliery and 63 in of 'brassy coal' at Blackwell 'A' Shaft; most sections, however, vary between 15 and 25 in of coal. The roof shales commonly contain coal streaks, in places abundantly, and a feature of many seam sections is the presence of a band of bright coal some 2 to 3 in thick lying up to 14 in above the main bed of coal (e.g. Alfreton Road, Tibshelf, Borehole, coal 2 in, bat 1 in, dirt 8 in, bat 3 in, on coal 28 in; Pennytown Opencast Site, bright coal 3 in, dirt 4.5 in, on bright coal 17 in). The main bed of coal consists normally of 'brights', though fusain occurs in places. One or two bands of dull coal up to an inch thick are recorded in some sections (e.g. Starsutal Opencast Site, dirty coal 1.5 in, 'brights' 5 in, dull coal 1 in, 'brights' 2 in, dull coal 1 in, on 'brights' 7.5 in); in others wafer-thin dirt partings are recorded within the bright coal. Ash content is recorded as varying from about 3 to 20 per cent, averaging perhaps 10 per cent. R.A.E.

A thin coal occurs in many sections between the Third and Fourth Waterloo coals. It is usually only a few inches thick and the 13 in recorded at Grassmoor Colliery is exceptional. There is some evidence for attributing its absence in certain sections to its having joined the Third Waterloo; in other sections its horizon is marked by a seatearth.

The field in which the Third Waterloo Coal is recognizable is similar to that of the Fourth Waterloo. The seam is thin in the north, but south of Hardstoft and Sherwood Colliery it averages about 20 in, although varying in thickness up to 28.5 in (at New Hucknall Colliery). It has been worked opencast in places from the Tibshelf area southwards. In its general nature it closely resembles the Fourth Waterloo and, like that seam, usually consists of bright coal with, in some sections, dull streaks or bands up to 1 in. At Starsutal Opencast Site one section showed the bottom 18.5 in as dull coal; others nearby recorded the middle two-thirds of the seam as bright coal with hard streaks. One section at this site showed 6 in of cannel-like black shale at the top of the seam, and at Blackwell 'A' Shaft the seam consists only of 6 in of cannel. The top part of the coal, and in the east of the district, the bottom part also, is usually more dirty than the bulk of the seam. Analysed sections at outcrop show the ash-content of the coal, excluding the dirty top part where present, to vary between 2.5 and 9 per cent. The seam is exposed in the railway cutting [SK 4126 6074], 400 yd N. of Morton Colliery; only the top 4 in is visible at the present time, but 22 in were formerly seen.

Second Waterloo Coal

The Second Waterloo Coal, although a complex seam, is divisible into two prinicpal components which, when separate from each other, are known as the Bottom and Top Second Waterloo coals (see (Figure 25). Dotted lines outside outcrop are conjectural indications of links between isolated areas." data-name="images/P990914.jpg">(Figure 24) and (Figure 25)). In the north the Top Second Waterloo is itself a divided seam. The Second Waterloo, which is more than 4 ft thick over most of the area in which it is a single seam, has been most extensively worked in the south, in the area between New Hucknall, Blackwell, Brookhill and Bentinck collieries. It has also been mined in the Williamthorpe Syncline from Grassmoor, Alma, Wingfield Lane and North Wingfield collieries. The Top Second Waterloo has been worked in the east from Sherwood Colliery. The combined seam, or its component parts, has been worked opencast along the whole of the outcrop.

In the following account the two principal components of the Second Waterloo are considered separately, whether they form separate seams or not.

The Bottom Second Waterloo Coal is absent in the north and on both flanks of the Hardstoft Anticline, its horizon being indicated by a seatearth which in Creswell and Silverhill colliery shafts lies respectively 12 ft and 11.5 ft below the Top Second Waterloo. It is also assumed to be absent eastwards from the Hardstoft area to Pleasley and Sherwood, and to the east of Kirkby. Elsewhere it varies in thickness up to a maximum of 33 in, but over most of its field is between 12 and 24 in. It forms a separate seam in the north and south-west (see (Figure 25). Dotted lines outside outcrop are conjectural indications of links between isolated areas." data-name="images/P990914.jpg">(Figure 24)). The coal is usually recorded as consisting only of 'brights', which may be dirty towards the top or bottom; in a few places bands of dull coal are recorded, as at Wren Opencast Site. At Brim Opencast Site the seam was recorded as a 15-in cannel with 20 per cent ash. In some sections in the south-west bands of coal or dirty coal, which are present in the overlying dirt, join the top of the seam, and the seam may grade up into the dirt through dirty coal with dirt partings. A typical section in this southwestern area is that recorded at Cemetery Lane Opencast Site, some 1000 yd E.N.E. of Alfreton Hall: 'brights' 4.5 in, dirt 0.5 in, dirty 'brights' 3 in, dirt 0.75 in, dirty 'brights' 3 in,on brights' 20.75 in.

The dirt which separates the Bottom and Top Second Waterloo coals varies in thickness from a few inches to a recorded maximum of 21 ft at Shirebrook 127's Underground Borehole. A feature of the dirt where thin is the presence of streaks of coal, usually of poor quality. Where the dirt is thick si milar coal bands tend to occur near its base, and they have therefore been recorded as elements of the Bottom Second Waterloo.

The Top Second Waterloo Coal is divisible, except in the south-west, into two leaves of coal with separating dirt. The lower leaf varies in thickness from a few inches to nearly 2 ft. It consists, in the majority of sections, of 'brights' which may contain dull bands, especially in the north-east. In the north-west cannel occurs at the top of the leaf in some sections, and in places the whole of the leaf consists of cannel, as at Markham No. 1 Colliery. The middle dirt is generally 1 to 16 inches in thickness and is sometimes described as ' bat ', but in the north-west it swells out to become several feet of measures (Seymour Colliery 10 ft, Markham No. 1 Colliery 5 ft, Ireland Colliery and Tom Lane Borehole 3 ft, opencast sites north of Duckmanton Cutting 1.25 to 3.25 ft). In a few sections, such as Silverhill Colliery No. 2 Shaft where the Top Second Waterloo is recorded as 31 in of inferior coal, the middle dirt is not discernible. The upper leaf of the Top Second Waterloo varies in thickness up to 32 in and consists of 'brights', or 'brights' with dull bands. The top part is in places dirty, or contains dirt bands. The most important of these dirt bands is that occurring 4 to 6 in from the top of the coal in the north. It is 2.75 in thick at Bolsover Colliery, 5 inches in Ireland Colliery Borehole and 8 inches in Elmton Green Borehole. This dirt band thickens northwards in the Staveley area to a maximum of 47 in. The resulting tripartite division of the Top Second Waterloo in that area has led to the confusion of the seam with the whole of the Second Waterloo in the Sheffield district (Eden and others 1957, p 98).

In the south-west the Top Second Waterloo rarely contains dirt bands, and the most striking feature of the seam is the presence of a bed of cannel roughly in the middle of the coal. The cannel is commonly about 10 in thick in the vicinity of Alfreton, but some sections farther south show a marked thickening. It is, for example, 20 in thick at Johno Opencast Site; and at Swanwick New Pit just south of the district boundary it has replaced the whole of the lower part of the seam, and here 19 in of coal rest on 42 in of cannel. At Starsutal Opencast Site the bottom part of the seam is cannelly coal rather than pure cannel, the full section being: strong bright coal 10 in, hard coal with a few bright streaks 6 in, cannel 4 in, on cannelly hard coal with irregular bright coal partings 16 in. The cannel thins northwards from the Alfreton area and was observed to pass into dull coal in the Pettifor Terrace opencast sites. Thus at Pettifor Terrace II it was represented by 2.5 in of cannelly dull coal, and at Pettifor Terrace I, 0.5 mile farther north, by 2 in of dull coal. In these sites the middle dirt of the more northerly sections was seen to die out southwards, being 5.5 in thick at Pettifor Terrace I and 0 to 6 in at Pettifor Terrace II. The dull coal that represents the cannel of south-western sections lies 12.5 to 19.5 in above the middle dirt, and the cannel is therefore seen to be an element of the upper leaf of the Top Second Waterloo.

Apart from the cannel the Top Second Waterloo consists, in the south-west, mainly of bright coal with sporadic bands of dull coal up to a few inches thick, which rarely persist from section to section. There are also sporadic partings of fusain.

The ash-content of both the Bottom and Top Second Waterloo coals is variable, ranging in the majority of cases from about 3 to about 10 per cent. Except in the southwest, where the cannel is commonly cleaner than the rest of the seam, cannel bands are normally dirtier than the coals with which they are found.

Measures between the Second and First Waterloo coals

The measures between the Second and First Waterloo coals vary somewhat irregularly in thickness between 40 and 120 ft, but are generally thicker in the north. They consist of two cycles with the Waterloo Marker Coal at the top of the lower one. The two cycles are variable in thickness, but the lower is commonly the thicker. The roof measures of both the Second Waterloo and Waterloo Marker coals are usually mudstone and contain ironstone and 'mussels'. In places sandstone occurs in the upper parts of both cycles, but it is more marked in the lower one. The whole of the interval (30 ft) between the Second Waterloo and Waterloo Marker is occupied by sandstone and siltstone at Tibshelf Old Pit, and there are 43 ft of sandstone in Williamthorpe Colliery Shaft and 51 ft at Alma Colliery.

The Waterloo Marker or Barcelona CoalThe name Waterloo Marker ', adopted by the officers of the Coal Survey Laboratory, is considered preferable to ' Barcelona ', the name given to the seam at Blackwell 'A' Pit (and an alternative name for the Blocking Coal of West Yorkshire).'is a persistent thin seam, the importance of which lies in its value as a marker horizon in correlating the Waterloo coals. It has not been mapped, and has not been worked except incidentally where included in the overburden of the Second Waterloo Coal in opencast sites. It is present everywhere in underground sections except in the shafts of Alma, Blackwell 'B' and South Normanton collieries, where its horizon is indicated by a seatearth. It is thinnest in the east (e.g. Creswell Colliery 3.5 in, Langwith Colliery 1 in, Shirebrook Colliery 4 to 6 in, Sherwood Colliery 8 in) and from Sutton Colliery southwards is commonly represented by cannel (Sutton Colliery 24 in, Kirkby Colliery 12 to 16 in, Bentinck Colliery 25 in). In the west and north-west it is generally between 8 and 24 in thick, a notable exception being the Williamthorpe–Holmewood area where it is 6 in or less. It consists usually of bright coal with rare thin dirt leaves and some fusain. Cannel is recorded from the top of the seam at Ireland Colliery Borehole (4.5 in), and Glapwell Colliery No. 1 Underground Borehole (interbanded cannel and coal 4 in), and the whole seam, 22 in thick, consists of cannel at Hoole Street Opencast Site. The bottom part of the seam is dirty at Elmton Green Borehole, Markham No. 2 Colliery and Pettifor Terrace I and II opencast sites. The seam is split at Arkwright Drift (coal 16 in, dirt 4.5 in, on coal 2.5 in) and at Sawpit Opencast Site (coal 12 in, dirt 1.5 in, on coal with dirt partings 4 in). E.G.S., G.H.R., R.A.E.

The lower of the two 'mussel'-bands in the measures between the Second and First Waterloo coals, that occurring in the roof of the former, is present in Ramcroft Colliery Borehole and contains Spirorbis sp., Anthracosphaerium aff. affine, Naiadites sp. and Carbonita humilis. By comparison the band above the Waterloo Marker Coal is better developed and has a more varied assemblage. The combined fauna of this higher band, based on collections from several boreholes and opencast sites, comprises the following: Spirorbis sp., Anthracosta beaniana, A. aff. disjuncta, A. nitida (Davies and Trueman), A. aff. ovum, A. phrygiana, A. sp. nov. [truncate variety of A. phrygiana group], N. quadratus and fish debris. In Alfreton Road, Tibshelf, Borehole the upper part of the band is developed in grey mudstones with a fauna of small shells belonging to A. beaniana, A. nitida and A cf. ovum. The impression is that these shells are stunted, a condition which is commonly associated with a pale grey mudstone lithology. M.A.C.

First Waterloo Coal

The First Waterloo Coal is a variable seam (Figure 26), but it consists everywhere of two parts, which, when separated by measures, are known as the Bottom and Top First Waterloo coals. The line of split to the east and south is shown on the inset plan on (Figure 26). The unsplit seam has been worked underground from Alma, Glapwell, and Pleasley collieries, and on a small scale from Grassmoor and Holmewood. The Bottom First Waterloo has been worked in the northern part of Glapwell 'take' and from Bolsover Colliery. Except in the extreme south of the district there have been extensive opencast workings at outcrop. Where the coal is of workable thickness it is, excluding the dirt and dirty bands, of medium to good quality with 2 to 10 per cent ash and a variable sulphur content.

In the field of the united seam the thickness, excluding dirt bands, varies from about 3 to 5.5 ft. The Bottom First Waterloo element, varying between 17 and 46 in, usually forms the major part of the seam but, except in the south-east, its basal part is dirty or contains dirt bands. The most persistent of these dirt bands (which occurs lower in the seam in the south) is up to 15 in thick in the north, where it divides the Bottom First Waterloo element into two roughly equal parts. The upper part usually consists of 'brights' with, in some sections, bands of dull coal at the top. The Top First Waterloo element of the seam varies in thickness from 2 to about 26 irt, but is generally about 18 in thick. In the extreme north it consists of dirty coal, but elsewhere of 'brights', commonly with bands of dull coal. At Moor Farm Opencast Site, Arkwright Drift and in parts of the Williamthorpe Syncline it rests directly on the Bottom First Waterloo element, but is usually underlain by up to 15 in of dirt.

The field of the split First Waterloo can be conveniently divided into two areas north and south of Mansfield. In the northern area the Bottom First Waterloo is 30 to 44 in thick in the west, where it is worked, but in the east its thickness varies irregularly from 8 in at Langwith Colliery Underground Borehole to about 30 in at Shirebrook Colliery Drift. It consists largely of bright coal, the basal few inches of which are commonly dirty or contain dirt bands. Bands of dull coal occur in the upper part of the seam in Bolsover Colliery workings and the top 3 in are cannel in Creswell Colliery Shaft. There are few records of the Top First Waterloo in this northern area. It is absent at Langwith Colliery Borehole where its horizon is indicated by a seatearth 20 ft above the Bottom First Waterloo, and has not been recorded in Shirebrook No. 1 Underground Borehole. Elsewhere it varies in thickness from 4.5 in at Bolsover Colliery to 17 in at Creswell Colliery and Sherwood No. 2 Drift, and lies 20 to 40 ft above the Bottom First Waterloo.

In the area to the south of Mansfield both Bottom and Top First Waterloos show rapid lateral variation in thickness, as do the intervening measures, and no regional pattern is discernible. The Bottom First Waterloo varies between 3 and 27 in within the workings at Wren Opencast Site near Alfreton, and most of the sections recorded south of Mansfield fall between these limits. At Pettifor Terrace opencast sites 13 in of cannel were present at the top of the seam. The measures separating the Bottom and Top First Waterloos reach 40 ft at Kirkby Lowmoor Pit and 41 ft at Brookhill Colliery. The Top First Waterloo is 24 in thick at Silverhill Colliery, and 22 in at Sutton and Portland No. 1, but it is commonly less than 18 in and is locally absent.

The measures between the Bottom and Top First Waterloo coals generally consist of mudstone and siltstone in the west, but in the east several sections, notably Cross Hills Borehole and Shirebrook and Sherwood Colliery drifts, show a substantial amount of sandstone in the upper part. Mussels ' occur in the roof measures of the Bottom First Waterloo at Elmton Green, Norwood Farm, Langwith Colliery and Cross Hills boreholes. Anthracosia phrygiana and Naiadites quadratus have been identified at Elmton Green. Fish fragments were found at this horizon in Shirebrook 127's Underground Borehole. E.G.S., G.H.R., R.A.E.

Measures between the First Waterloo and Dunsil coals

The measures between the First Waterloo and Dunsil coals comprise one cycle, 25 to 50 ft thick except in the north-east and east, where the top leaf of the First Waterloo closely approaches the Dunsil and the thickness is generally less than 20 ft. The minimum recorded thickness is 9 ft 1 in at Sherwood Colliery No. 2 Drift.

The First Waterloo Coal is overlain by mudstone which in many places passes up into siltstone and sandstone overlain by the seatearth of the Dunsil Coal. At one of the localities where the measures are thickest Grassmoor Colliery Shaft-35 of the 50 ft consist of 'stone-bind with rock bands'. There are few modern sections of these measures, but in recently drilled boreholes at Elmton Green, Langwith Colliery and Sutton Lane, and at a number of opencast sites working the First Waterloo Coal, the mudstones have yielded non-marine lamellibranchs including Anthracosia phrygiana and Naiadites quadrates. E.G.S., G.H.R.

Dunsil Coal

The field of the Dunsil Coal can be conveniently divided into two parts by an east–west line running roughly through Shirebrook, Glapwell and Grassmoor (Figure 27). South of this line the seam varies between 20 and 48 in, being thickest in the area between Holmewood, Sherwood and Sutton collieries, and around Alfreton, and has been extensively mined in both underground and opencast workings. North of the line the seam is split into a thin and worthless upper leaf and a lower leaf, up to 30 in thick, in which workings are virtually confined to opencast sites round the nose of the Brimington Anticline. The Dunsil is generally a coal of medium to good quality with an ash-content varying between about 2 and 20 per cent.

In the area where it is not split the seam consists typically of three parts: 5 to 17 in of brights' are overlain by 5 to 21 in of dull coal and a further 7 to 12 in of ' brights'. In some sections no dull coal is recorded and in others the middle bed consists of banded dull and bright coal. Dull streaks are also recorded in the 'brights'. To the south of the Hardstoft inlier, the bottom bed of 'brights' is, in many places, split by a dirt band. In general this thickens towards the south-west where it reaches a maximum of 9 in at Damstead Lily Opencast Site, but 9 in is also recorded in part of the workings of Sawpit Opencast Site near Tibshelf. In Sherwood Colliery No. 1 Shaft and No. 1 Drift a 5 to 6.5-in leaf of coal occurs 13 ft below the worked seam. This is possibly a split from the Dunsil, and may also be represented by the 6 in of ' bass' 3.5 ft below the Dunsil at Pleasley Colliery.

North of the line of split shown on (Figure 27) the lower or main part of the Dunsil consists mainly of bright coal, but dull bands are recorded in some sections. The coal is commonly dirty and in places contains dirt bands in its lower part. Over most of its field it is less than 18 in thick; it is absent at Tom Lane Borehole and Arkwright Drifts and is thickest near outcrop in the Bond's Main area-38 in of dirty coal are recorded in Bond's Main Colliery Shaft. The upper leaf is from 8 to 37 ft above the lower, and attains a maximum thickness of 16 in at Glapwell Colliery No. 3 Underground Borehole. It is absent in places, as at Elmton Green Borehole and Langwith Colliery Underground Borehole, where its horizon is indicated by seatearth. In the one section examined in detail—at Sutton Springs Opencast Site—it consists of dull coal 3 in, 'brights' 2 in, dull coal 2.5 in, on 'brights' 5.5 in.

Measures between the Dunsil and Top Hard coals

The measures between the Dunsil and Top Hard coals vary from 40 to nearly 100 ft in thickness, but in most places are between 50 and 70 ft. They consist of two cycles of which the lower is usually the thicker. Ironstone bands occur in the basal parts of both cycles, but more especially of the lower. Many ironstone bands up to 6 in thick occur in the roof measures of the top leaf of the Dunsil at Tom Lane Borehole, and they are believed to have been worked at outcrop in this vicinity. Sandstone occurs chiefly in the lower cycle, usually close above the Dunsil Coal. Nearly 77 ft of sandstone and siltstone are recorded in Holmewood Colliery Shaft, and sandstone is prominent at outcrop between Grassmoor and Stanley, and southwards from South Normanton. Up to 25 ft of sandstone occur in the upper cycle in the north-east. 'Mussels' have been found in both cycles. E.G.S., G.H.R., R.A.E.

A thin coal is everywhere present at the top of the lower cycle. In the north it is 1 to 8 in thick and commonly consists of cannel. In the south-east it is represented by 3 in of cannel at Kirkby Colliery. In the southwest it is 12 to 16 in thick over a substantial area and has been worked opencast on a small scale, for the coal, although thin, is of good quality. Sections at Starsutal Opencast Site, for example, show 14 to 16 in of fragile 'brights' with an ash-content of 2.3 to 3.5 per cent. At Gloves Lane Opencast Site a thickness of 25 in was recorded, the basal 5 in being dirty. At this site the seam is separated from the Top Hard by only 5 ft of measures, and further to the southwest it is probable that it unites with the Bottom Softs of the Top Hard. This would account for the thickening of the bottom section of the Top Hard at Wren Opencast Site and in the Swanwick area (see below and (Figure 29)). R.A.E., E.G.S.

The highest A. modiolaris Zone fauna is represented by the 'mussels' in the roof of the Dunsil Coal including those above the top coal where the seam is split (see above). The acme of the A. phrygiana group occurs at this horizon and the collections obtained from 3 ft above the coal at Pewithall Opencast Site and from Sutton Lane Borehole are typical, although the shells are somewhat small. The assemblage comprises Anthracosia beaniana, A. disjuncta, A. phrygiana and A. sp. intermediate between ovum and phrygiana. In Tom Lane Borehole, A. beaniana and A. phrygiana collected from 450 ft 11 in probably represent the Dunsil fauna, although the seam could not be positively identified. M.A.C.

Top Hard Coal to Mansfield Marine Band

Variations in thickness (about 650 to 1050 ft, decreasing towards the south) and general lithological characters of this group are shown in (Plate 7). The chief workable coals are the Top Hard at the base, the High Hazles and the Clown. Of lesser importance are the Comb, the St. John's seams, the Furnace or Lowbright, the Two-Foot and the Mainbright.

Top Hard Coal

The Top Hard Coal, called the 'Barnsley' in Yorkshire, was formerly one of the most important seams in the district, but it is now almost worked out. It is of good quality with low ash- and sulphur-contentsThe chemical and physical properties of the seam have been investigated by the Fuel Research Board (1942).. It varies in thickness between 36 and 96 in, though over most of the area it is between 60 and 72 in (Figure 29). Dotted lines outside outcrop are conjectural indications of links between isolated areas." data-name="images/P990918.jpg">(Figure 28). It is thickest around Bolsover and Markham collieries (81 in at Tom Lane Borehole), at Harehill Opencast Site (79.5 in) and in the extreme south around Alfreton (96 in at Wren Opencast Site); and thinnest in the south-east (36 to 46 inches in workings south-east of Kirkby Colliery) and at isolated points along the main outcrop south of Grassmoor. A well-marked belt of north-north-easterly elongated washouts affects the seam between the northern edge of the district and Teversal Colliery.

The seam is divisible everywhere on physical characteristics into three parts: the Top Softs (or Top Brights), the Hards, and the Bottom Softs (or Bottom Brights). General variation of these divisions is shown in (Figure 29).

The Bottom Softs, over most of the area, are between 15 and 26 in thick, but are as little as 2 in at Smithy Opencast Site, near Tibshelf, and attain a maximum of 31 in at Wren Opencast Site. At the latter locality, however, and in the Swanwick area generally, it seems probable that the thin seam of bright coal between the Dunsil and the Top Hard has joined the Bottom Softs (see above and (Figure 29)). Cannel, usually of poor quality and referred to as ' jacks ' or ' branch ', occurs in the Bottom Softs in the north. In the north-west, in Ireland Colliery Borehole, Bolsover Colliery and the workings of Ramcroft Colliery, the cannel is 3 to 7 in thick and is roughly in the middle of the Bottom Softs. At Langwith Colliery it is 5 in thick and occurs at the base of the seam; from Langwith southwards to Mansfield it thins from 5 to in and is up to 10 in from the base of the seam. South of Shirebrook there is, in places, a thin dirt parting in that part of the Bottom Softs below the cannel. Many sections of the Bottom Softs around the Hardstoft inlier show them to contain dull bands.

The Hards usually constitute the major part of the seam, though they show great and apparently random, variation in thickness from 7 in at Doehill Lane Opencast Site, near Tibshelf, to 49 inches in Creswell Colliery Shaft and 51 inches in the workings of Swanwick Colliery. The majority of recent sections show them to consist of dull coal with bright streaks or of banded dull and bright coal. In the north-west a band of bright coal, usually only a few inches thick, but 11 in at Tom Lane Borehole, occurs in the upper part of the Hards, and probably represents the 'List' of South Yorkshire (see Eden and others 1957, p. 102). A band of bright coal also occurs in the Hards in the extreme south-west of the district; a section of the Hards in the workings of Swanwick Colliery, about mile south of Alfreton, is as follows: top hards 18 in, best softs 11 in, dicks [sic] 9 in, best hards 12 in.

Cannel occurs in the Hards in the Williamthorpe Syncline and on the east side of the Heath and Hardstoft anticines. In the north-west of this area it forms the upper part of the Hards and overlies the 'List' where that band is present. It is thickest on the south-western side of the Syncline where it attains 37 in and forms over half the total thickness of the Top Hard. In some sections it is of very poor quality, little better than a cannelly shale, and mussels' are recorded from it. Midway between the outcrop and Pleasley Colliery, measured sections in underground workings show between 15 and 17 in of cannel 7 to 8 in from the top of the Hards. Most sections along the eastern flank of the Hardstoft Anticline show the cannel to occupy a similar position in the seam, and the maximum thickness is 27 in at Biggin Opencast Site.

The Top Softs vary in thickness up to 24 in, but in most recorded sections are between 10 and 15 in. There is evidence that they have been partially or totally washed out in some sections where they are overlain by sandstone. In the Williamthorpe Syncline they are inferred to be absent below a mudstone roof, and there the upper part of the Top Hard is composed of cannel which is taken to be the lateral equivalent of the top part of the Hards, but it is possible that the cannel also represents the Top Softs. Cannel occurs at the top of the seam in the Tibshelf and Alfreton-Swanwick areas, but it is not clear whether this overlies the Top Softs or is the lateral equivalent of their upper part. The cannel is respectively 60 and 15 in thick at Doehill Lane and Wren opencast sites; at the latter it was described as canneloid brights In the workings of Swanwick Colliery the top 22 in of the Top Hard, i.e. the part lying above the Hards, is described as 'scuds'. This probably includes the Top Softs and the canneloid 'brights' of Wren Opencast Site. In a few sections, e.g. at Muster, Harehill and Smithy opencast sites, the Top Softs contain streaks and bands of dull coal. E.G.S., R.A.E., G.H.R.

At the time of the resurvey the Top Hard was partly visible at two surface exposures: in the railway cutting below the road bridge [SK 4312 6520], 700 yd S.S.W. of Williamthorpe Colliery, where 30 in of coal could be seen resting on seatearth, and on the south side of the Tibshelf-Fackley road [SK 4692 6102], 290 yd S.S.E. of Silverhill Farm, where sandstone rests on the coal, the top 42 in of the seam being visible. G.H.R.

Measures between the Top Hard and High Hazles coals

The measures between the Top Hard and High Hazles coals are 350 to 400 ft thick in the north, thinning to between 270 and 220 ft in the south. They comprise up to eleven cycles and contain a number of coals which are usually thin, but several, notably the Comb, up to 50 ft above the Top Hard, and the First and Second St. John's, some 200 to 300 ft above the Top Hard, are of local importance. Two thin rider coals, consistently about 50 ft and 100 ft above the Top Hard, can be correlated over much of the northern part of the district. The measures contain numerous 'mussels' (see below) and, especially in the north, ironstone bands; in many places the two are associated, resulting in shelly ironstones. Two ironstone horizons are recorded on old maps as having been widely worked along their outcrops. These ironstones are unnamed but appear to be the beds 123 and 298 ft from the surface in Tom Lane Borehole, that is respectively some 175 and 100 ft above the Top Hard Coal.

The Top Hard Coal is closely succeeded over wide areas by sandstone or interbedded sandstone, siltstone and mudstone which it is convenient to call the 'Top Hard Rock'. This is not generally of any great thickness, 50 ft being unusual, but it is present at outcrop virtually everywhere south of Arkwright Town. It forms a pronounced feature in many areas, and has been seen in numerous opencast sites and small quarries. It commonly fills the washouts in the Top Hard Coal shown on (Figure 29). Dotted lines outside outcrop are conjectural indications of links between isolated areas." data-name="images/P990918.jpg">(Figure 28). E.G.S., R.A.E., G.H.R.

Other sandstones occur locally throughout the measures, the most important perhaps being that between the First St. John's and High Hazles coals. In the north this is 73 ft thick in Cross Hills Borehole and over 60 ft at Markham Colliery, and at outcrop it forms a prominent feature through the town of Staveley, just north of the district boundary, dying out a mile south of the town centre. In the south-east this sandstone is again in evidence, and in Kirkby Lowmoor Shaft, for instance, 73 ft of sandstone are overlain by 26 ft of 'stone-bind, bind and rock' (Edwards 1951, p. 193). R.A.E., E.G.S.

Only limited collections of fossils are available from boreholes through the lower part of the measures between the Top Hard and Second St. John's coals because of the practice of open-holing for some distance above the Top Hard where that seam has been worked. However, Elmton Green, Norwood Farm and Tom Lane boreholes proved an important series of faunal bands lying between the Second St. John's Coal and the upper of the two rider coals recognized above the Top Hard in the northern part of the district (see above). The detailed faunal list below is based on the collections from Elmton Green Borehole, but similar if less varied faunas were obtained from the other boreholes.

• 1019 ft 7 in to 1023 ft 8 in: Spirorbis sp., Anthraconaia aff. pulchella Broadhurst, Naiadites aff. productus, Lioestheria sp. [2.0 mm]
• 1026 ft 11 in to 1031 ft 7 in: Spirorbis sp., A. aff. pulchella, Anthracosia cf. caledonica, A. disjuncta?, Anthracosphaerium cf. turgidum, N. productus, Carbonita cf. humilis
• 1048 ft to 1051 ft 8 in: A. aff. caledonica, A. sp. nov.aff. planitumida (Trueman) [cf. Trueman and Weir, p1. xviii, fig. 19], Anthracosphaerium cf. turgidum, N. productus, N. sp. intermediate between alatus Trueman and Weir and productus (cf. Trueman and Weir, p1. xxx, fig. 11)
• 1160 ft 6 in: Anthracosia sp. cf. fulva (Davies and Trueman)

The faunal assemblage from 1019 ft 7 in to 1031 ft 7 in is significant in terms of inter-coalfield correlation, and can be conveniently referred to as the Anthraconaia pulchella fauna; a similar association occurs near the base of the Lower similis-pulchra Zone in Lancashire (Broadhurst 1959) and in the Northumberland–Durham Coalfield. In both these areas the lamellibranch fauna is closely associated with an 'Estheria' band (Magraw 1960, p. 485; Magraw and others 1963, p. 164), which is probably represented in Elmton Green Borehole by the Lioestheria at 1023 ft 8 in.

The 'mussel'-band overlying the thin coal some 30 ft above the First St. John's Coal was proved in Elmton Green Borehole where it contains abundant but poorly preserved Anthracosia spp.including A. cf. caledonica, A. simulans Trueman and Weir and A. sp. cf. fulva.

In the south-east, in the shafts and workings of Shirebrook, Sherwood and Kirkby collieries, the Comb Coal is between 13.5 and 19.5 in thick and lies between 6 and 49 in above the Top Hard. Where the dirt between the two seams is thin the Comb is worked with the Top Hard. The Comb is generally thicker to the west of Kirkby Colliery and is separated from the Top Hard by an increasing thickness of measures in this direction (Figure 29). At Portland No. 1 Colliery it is 34 in thick (described in the record as 'smut'), 36 in above the Top Hard; at Langton Colliery 30 in thick, 42 in above; at New Hucknall Colliery 12 in thick, 48 in above; at South Normanton Colliery coal 6 in, dirt 27 in, on coal 18 in, 6 ft above; and at Brookhill Colliery coal 6 in, dirt 8 in, on coal 19 in, 4.5 ft above. In the area between Alfreton and the Swanwick pits, the Comb lies about 50 ft above the Top Hard, from which it is separated by measures including a thick bed of sandstone which, in places, occupies almost all the interval between the two seams. A trial pit [SK 4024 5494] at Damstead Lily Opencast Site showed a 43-in section as follows: coal 13.5 in, dirt 2 in, coal 1 in, dirt 2 in, coal 19.5 in, dirt 4 in, on coal 1 in. At Dobbs Opencast Site, 1700 yd S.E. of Alfreton Hall, the coal is thinner (30 in) but less dirty: 'brights' (with 0.25 in of fusain near top) 12 in, clunch and fusain 0.5 in, 'brights' 1 in, clunch 0.25 in, on 'brights' 16.25 in; the ash-content is 5 per cent.

The Comb Coal is recognizable only to the south and east of a line between Shirebrook and Alfreton (see (Figure 29). Dotted lines outside outcrop are conjectural indications of links between isolated areas." data-name="images/P990918.jpg">(Figure 28)). There is insufficient evidence to ascertain its position in the sequence to the north and west of this line. It does not appear to have joined the Top Hard, and it may be represented by the thin coal above the ' Top Hard Rock '. The most likely possibility, however, is that it is absent, its position in the succession being occupied by the 'Top Hard Rock' over wide areas.

The Second St. John's Coal is of importance only in the north-west where it was formerly worked extensively from the old St. John's Colliery just within the northern boundary of the district. It was mined under the name of 'Yard' or 'Low St. John's' Coal and was incorrectly regarded as the correlative of the High Hazles. A small area has been worked as the High Hazles at Markham Colliery, and the seam has been worked at outcrop at Inkersall, Westcroft, Blue Lodge and Bagshaw opencast sites. In the area between St. John's, Seymour and Markham collieries and Bagshaw Opencast Site the seam varies between 30 and 39 in and consists predominantly of bright coal.

Dull bands are recorded in some sections, mainly in the middle of the seam, and a few inches of coal and dirt commonly occur at the base. Analyses of the seam, excluding the basal few inches where they are dirty, show an ash-content ranging from less than 3 to about 8 per cent. Eastwards and southwards from this area of thick coal there is a rapid thinning to 23 in at Oxcroft Colliery, 22 in at Bolsover, 18 in at Muster Opencast Site, 13 in at Palterton Air Shaft, and 12 in at Elmton Green Borehole and Creswell Colliery. Elsewhere the seam is generally less than 12 in thick, and in the south is absent in many places.

The First St. John's Coal has been worked on a small scale in the north, underground at St. John's Colliery under the name ' Two-Foot Coal ', and at outcrop in a number of opencast sites. It is 21 to 27 in thick in the St. John's–Ireland group of pits, 16 to 19 in at Markham Colliery, 21 in at Tom Lane Borehole, and 16 to 21 inches in the opencast sites north of Sutton Scarsdale. Elsewhere in the north, and as far south as Pleasley Colliery, the First St. John's appears to be split into two leaves. In the north, the middle dirt is 19 in at Oxcroft Colliery, 34 in at Elmton Green Borehole and 43 in at Creswell Colliery, and to the south is re-represented by between 8 and 18 ft of measures. The bottom leaf of coal is thick-28 to 34 inches—in the north where the middle dirt is thin, but, apart from 17 in at Langwith Colliery, is from 0 to 10 in where the two leaves are widely separated. The top leaf comprises 28 in of coal and dirt at Langwith Colliery, and 15 in of coaly shale with coal streaks at Cross Hills Borehole; elsewhere it consists of 9 to 22 in of bright coal, which is dirty in part at Norwood Farm Borehole.

The First St. John's is apparently represented by 1 in of bat at 1098 ft in Sherwood Colliery Shaft, and by 10 in and 12 in of coal at Sutton and New Hucknall collieries respectively. It cannot be identified with any confidence farther south, but it may be the 11 in of 'bad coal' at 885 ft in Kirkby South Pit, and at South Normanton, Langton, Portland and Bentinck collieries there are two thin coals, 6 to 12 ft apart, at about this horizon. R.A.E., E.G.S.

A thin coal, lying some 30 to 40 ft above the First St. John's is present in most of the provings in the northern part of the district. It consists of 18.5 in of coal and dirt at Markham No. 1 Colliery, but does not exceed 12 inches in other shafts and boreholes. Trial pits at Blue Lodge Opencast Site, up to 1 mile northwards from Arkwright Town Station, showed 16 in of bright coal with fusain partings. The ash-content was found to be over 10 per cent.

A thin coal, lying up to 60 ft below the High Hazles in the outlier formed by the Swanwick Syncline in the south-west of the district, has been tentatively correlated with the Cinderhill of the Derby (125) Sheet to the south. The seam has been proved in a series of trial bores at Damstead Lily Opencast Site, south of Alfreton, where it consists of an upper leaf of coal, 16 to 18 in thick, separated by 5 to 12 in of dirt from a 3 to 5-in lower leaf of coal. R.A.E.

The ?Cinderhill Coal, as described above, is not recognizable with certainty in the shaft sections east of Alfreton, but it may be the coal lying in a similar position with respect to the High Hazles, and already dealt with above as the possible correlative of the First St. John's. E.G.S.

High Hazles Coal

The High Hazles Coal varies somewhat irregularly in thickness (see (Figure 31)." data-name="images/P990920.jpg">(Figure 30)), but is thickest in the north-east and in general thins to the south and west. The thickest section recorded is in Creswell Colliery Shaft: coal 62 in, dirt 1 in, coal 14 in, dirt 10 in, on coal 5 in; and the thinnest is 6 inches in Dovedale Farm Borehole. The absence of the seam in Kirkby Lowmoor Pit is probably due to washing out, and partial washing out accounts for local wide variations in thickness elsewhere, as at Inkersall and Bagshaw opencast sites. In a large part of its field to the north of the Hardstoft Anticline the seam is between 2 and 4 ft thick, whereas over most of the area to the south it is between 1.5 and 2.5 ft. Three miles west of the main outcrop there is a small faulted area of High Hazles Coal (not shown on (Figure 31)." data-name="images/P990920.jpg">(Figure 30)) on the district margin south of Alfreton. This is part of the outlier that occurs largely on the Derby (125) Sheet to the south and is preserved in the Swanwick Syncline. Here the High Hazles is split into two or three leaves, and thickness variations shown in trial pits on Alfred Street Opencast Site are as follows: coal 10 to 15 in, measures 66 to 82 in, coal 9 to 12 in, dirt 0 to 10 in, on coal 10.5 to 14 in.

The seam consists largely of bright coal which commonly has partings of fusain. The bottom part consists nearly everywhere of dirty 'brights' or 'brights' with dirt bands; a few sections show 'brights' with dull bands. At the top of the seam in some outcrop sections 1 to 4 in of cannel is present, but this has been recorded underground only in the workings of Hazel Ridge Colliery, near Temple Normanton, and South Normanton Colliery Shaft, though the top 3 in at Newstead Colliery N.1 Borehole are described as canneloid 'brights' by the Coal Survey Laboratory.

The High Hazles Coal is generally of good quality with a low ash-content, though in some of the sections analyzed by the Coal Survey Laboratory the sulphur content is moderately high, due to the local occurrence of lenses and thin bands of pyrite in the seam. The only large-scale underground workings are in the north-east from Creswell, Langwith and Warsop collieries, but the seam has been extensively worked opencast along the main outcrop north of Ramcroft Colliery, and in the outlier formed by the Williamthorpe Syncline. There are also a few opencast workings farther south on either side of the Hardstoft inlier. In New Hucknall Colliery No. 2 Shaft, where the seam is 28 in thick, it has been named the 'Hucknall Common Coal'.

Measures between the High Hazles and Two-Foot coals

The measures between the High Hazles and Two-Foot coals are 170 to 220 ft thick in the north, thinning to 120 to 150 ft in the south, and comprise up to six cycles. Each cycle may contain a coal, the Furnace or Low-bright, one cycle below the Two-Foot, being the most important. In the north there is a persistent thin coal consisting of 'brights' with fusain bands, some 70 to 120 ft above the High Hazles. This appears to be a split seam in Ramcroft Colliery Shaft where 21 in of coal (called the Beamshaw ') lie 13 ft 2 in above 18 in of coal and bat. Elsewhere in the north the seam is 12 to 26 in thick, and a small area has been worked at Deep Ring Bell Opencast Site, near Ramcroft. The thin coal (13 to 15 in) that has been mapped in places from Long Duckmanton northwards and worked opencast on a small scale under the name 'Brinsley Thin' , is probably the same seam, as is the 20 to 26-in coal that occurs in the Williamthorpe Syncline and has been worked opencast 800 yd S.E. of Williamthorpe Colliery. The name 'Brinsley Thin' has also been tentatively applied by Edwards (1951, p. 233) to what may be the same seam in Sherwood Colliery No. 1 Shaft—a 34-in coal lying 72 ft above the High Hazles. It is thinner in other sections in the Sherwood area, and absent at Pleasley Colliery, Newboundmill Borehole and to the south-east. In the south-west the ?Brinsley Thin lies 30 to 60 ft above the High Hazles. It has been proved in a small area south of Alfreton, at Alfred Sleet Opencast Site. Here, a series of trial pits showed 22 to 27 in of bright coal, usually clean, but rarely with one or two dirt partings. In this area the seam has hitherto been confused with both the High Hazles and the Lowbright.

Prominent sandstones are found in these measures above both the High Hazles and the ?Brinsley Thin coals. The lower is 80 ft thick at Newboundmill Borehole and the other 40 ft thick in Pleasley Colliery Shaft. At outcrop they form marked features north of Bramley Vale and around New Hucknall Colliery. E.G.S., G.H.R., R.A.E.

The sandstone above the High Hazles is seen to have an erosional base at Inkersall Opencast Site, in the vicinity of the village of the same name. Although no section was examined in which sandstone rested directly on the High Hazles Coal, it is clear that washout conditions exist below the sandstone, and the thin coal sections recorded in this area are probably due to this phenomenon. The roof measures of the High Hazles were examined in a 100-yard cut at Bagshaw Opencast Site, 0.5 mile W. of Long-course Farm, where the following section was recorded:

The nature of the contortions associated with this washing out suggests that they are due to a 'fossil' earthquake (Shirley 1955). R.A.E.

The lowest 'mussel'-band in these measures lies in the immediate roof of the High Hazles Coal. At Highfield Opencast Site the following fossils were obtained from ferruginous mudstones at this horizon: Anthracosiaplaniturnida, Anthracosphaerium sp. cf. propinquum (Melville) [figured Trueman and Weir 1954, pl. xxv, figs. 39–43] and Naiadites cf. carinatus (J. de C. Sowerby) [figured Trueman and Weir 1955, pl. xxix, fig. 27]. The same horizon in Palterton Colliery Borehole yielded Anthracosia simulans. These shells are closely similar to those figured from the opencast site as Anthracosphaerium sp. cf. propinquum. A few feet above the coal the mudstones characteristically contain numerous tracks and burrows including Cochlichnus kochi. The best-developed ' 'mussel'-band is found at a position varying from 30 to 60 ft above the High Hazles and includes the first appearance of the Anthracosia atra group, which becomes more prominent in the measures above the Two-Foot Coal. The composite fauna obtained from this band in Birchhill, Cross Hills, Newboundmill and Palterton Colliery boreholes is as follows: Spirorbis sp., Anthraconaia sp. aff. pulchella, Anthracosia cf. atra (Trueman), A. cf. barkeri Leitch, A. caledonica, A. aff. elliptica (Chernyshev), A. lateralis (Brown), Anthracosphaerium propinquum, N. productus, Carbonita sp. [with shallow sub-central groove]. A similar fauna was found some 40 ft above the last-described, and includes Spirorbis sp., Anthracosia cf. atra, A. aff. elliptica, A. sp. cf. fulva, A. lateralis, Naiadites obliquus Dix and Trueman, N. aff. productus and cf. Planolites montanus Richter. A still higher band was proved in Birchhill and Cross Hills boreholes, about 100 ft above the High Hazles and immediately above the 'Beamshaw' or 'Brinsley Thin' Coal (see above); the fossils at this horizon are Naiadites obliquus, Carbonita humilis and fish remains. The only fossils recorded between the Furnace and the Two-Foot coals were found 25 ft above the former coal in Elmton Green Borehole, from which Spirorbis and pyritized Naiadites were obtained. M.A.C.

The Furnace or Lowbright Coal occurs one cycle, or some 15 to 30 ft, below the Two-Foot Coal. The name 'Furnace' with the alternative of 'Abdy', is in general use for the seam north of a line from Blingsby Gate to Langwith Colliery, and the name 'Lowbright' is applied to the seam in the area south of a line from Teversal to Shirebrook. In the intervening ground it is thin (4 in of dirty coal at Cross Hills Borehole, 9 in at Glapwell Village Borehole, 8 in at Hardwick Lodge Borehole, 12 in, including some dirt, at Newboundmill Borehole) or even absent, as at Pleasley Colliery. E.G.S., G.H.R.

The Furnace Coal shows a steady increase in thickness towards the north-west from 14 in at Norwood Farm and Birchhill boreholes to 42 in at Bagshaw Opencast Site, near Duckmanton Moor. Over much of its field it is more than 2 ft thick. It consists of 'brights', in many sections with layers and streaks of dull coal, especially in the middle part. Dirt bands occur towards the base, and in many places thin leaves of coal occur for several feet below the main seam; the section at Elmton Green Borehole, for instance, is bright coal 15 in, dull coal 2 in, banded dull and bright coal 8 in, dirt 20 in, coal 3 in, dirt 5.5 ft, coal 1.5 in, dirt 1.5 in, coal 1 in, on dirt with coal streaks 7 in. The seam has been worked only at outcrop where, north of Ramcroft Colliery, it has been mined opencast in association with the Two-Foot. E.G.S., R.A.E.

The Lowbright Coal is between 24 and 42 in thick over most of its field, the areas of thickest coal being between Shirebrook, Sherwood and Sutton collieries, and in the south-west around Langton, Portland and Bentinck collieries. The coal is of inferior quality in most places, being usually dirty or interbanded with dirt. For this reason it has not been mined except in what were probably coal-strike workings at outcrop near Whiteborough Station. The seam has recently been investigated in the extreme south by the Opencast Executive and a trial trench [SK 4677 5469], 0.33 mile E. of Brookhill Colliery, has yielded the following section which may be regarded as typical: dirty coal 17 in, dirt 3 in, dirty 'brights' 4.5 in, dirt 2.5 in, dirty 'brights' 9 in, soft brights 9 in, dirt 1 in, on 'brights' 2.5 in. At Portland No. 1 Colliery the Lowbright appears to consist of two main leaves 6 ft apart, the upper 22 in thick and the lower consisting of 34 in of inferior coal. E.G.S., G.H.R.

Two-Foot or Sough Coal

The Two-Foot or Sough Coal consists, everywhere north of Glapwell, of two leaves of coal separated by 12 to 74 in of dirt. The upper leaf is 12 in thick at Cross Hills Borehole, 18 in at Birchhill Borehole and 19 in at Glapwell Village Borehole, but elsewhere it varies between 20 and 32 in. It consists of 'brights' which in some sections have bands of fusain and contain pyrite, but rarely have dirt partings. Thin bands of dull coal occur rarely in the north-west, and one section, at Blue Lodge Opencast Site, shows 2 in of cannel at the top of the seam. The lower leaf varies in thickness between 1 in at Birchhill Borehole and 27 in at Bagshaw Opencast Site. It consists of bright and, especially in the lower few inches, dirty bright coal. Dull bands are recorded at Bagshaw Opencast Site and Elmton Green Borehole.

South of Glapwell the lower leaf of coal is absent except at Teversal Grange Borehole where 3 in of coal are recorded 34 in below the main leaf. The main leaf of coal is 19 in at Glapwell Colliery, 13 in at Shirebrook Colliery and 16 in at Portland No. 1 Colliery; it is absent in Kirkby Colliery shafts and in Kirkby H2 Borehole, and has been washed out in New Hucknall Colliery Shaft; elsewhere in this southern area it varies between 1 and 9 in.

In general the Two-Foot is a good quality coal with low to medium ash, though some sections have a high sulphur content. It has been worked opencast to the north of Glapwell, but there are no underground workings. E.G.S., R.A.E., G.H.R.

Measures between the Two-Foot and Clown coals

The measures between the Two-Foot and Clown coals are variable in thickness. The variation is, to a considerable extent, random, but there is a general thinning from between 120 and 190 ft in the north to between 80 and 120 ft in the south. Typically the measures comprise three cycles, the lowest containing the Two-Foot Marine Band at its base and the Mainbright Coal at its top, and the uppermost the Manton 'Estheria' Band at its base. The lower two cycles are of roughly equal thickness where sandy measures are not developed and the uppermost is some 20 to 30 ft thick. Where the Mainbright Coal is a split seam there may be four or five cycles.

The Two-Foot Marine Band is apparently ubiquitous in the district. North of Pleasley it rests directly on the Two-Foot Coal, but to the south is separated from the coal, or the seatearth where the coal is absent, by 18 to 73 in of mudstone with non-marine fossils and a variable amount of ironstone. The marine band consists of dark grey to black mudstone, silty in parts, and it has been seen at outcrop at Bagshaw, Tom Lane and Woodthorpe Mill opencast sites and recorded in shallow boreholes at Sleetmoor Opencast Site and in the sinking dirt 488 ft from the surface in Bolsover Colliery No. 3 Shaft (Edwards and Stubblefield 1948, p. 221). The only other localities are the following recently drilled boreholes (thickness where known is given in brackets): Bolsover Moor (22 in), Bentinck No. 1 (21 in), Bentinck No. 2 (46 in), Birchhill (24 in), Carr Vale (17 in), Cross Hills (18 in), Elmton Green (7 in), Glapwell Village (about 7 in), Hardwick Lodge (18 in), Kirkby H2 (43 in), Newboundmill (8 ft 8 in), Newstead N.1 (25 in), Norwood Farm (30 in), Palterton Colliery (10 ft 5 in), Rylah (4 ft 2 in), Skegby Sewage Works (4 ft), Sutton No. 1 (10 ft 2 in), Sutton No. 2 (4 ft), Teversal Grange (8 ft 6 in). The thinner sections probably represent only the basal phase of the marine band of the thicker sections. E.G.S., G.H.R.

The marine fauna obtained from the band within the district includes: Ammonema sp., Glomospira sp., Glomospirella sp., Tolypammina sp., Lingula mytilloides, Myalina cf. compressa, Hollinella cf. bassleri and Paraparchites sp. The assemblage is of the same nature as that found in the Clay Cross Marine Band (p. 155) and the Edmondia Band (p. 190), and is characteristic of the special fades where non-marine fossils are closely associated with the marine fauna. The main difference from the Clay Cross fauna is the absence of the Dunbarella/Anthracoceras element and the replacement of Ammodiscus by Glomospira and Glomospirella. Furthermore, the 'mussels' most commonly found in the upper part of the marine band are Naiadites rather than Anthracosia. The ostracod Geisina is again present at several levels within the band. It is significant that Geisina is absent from the sequence between the close of the Clay Cross marine episode and the incursion of the Two-Foot Marine Band; this supports the inference that Geisina is linked to a more saline habitat than that favoured by the Middle Coal Measures mussels ' (see also pp. 89, 157).

The following details of the faunal sequence are taken from Sutton No. 1 Borehole, where the thickness between the highest and lowest marine fossils is 10 ft 2 in.

Throughout the district the marine band shows much the same faunal profile as detailed above. Lingula and foraminifera are largely confined to the base of the band; Myalina occurs in the upper part in which stunted Naiadites, Carbonita and Geisina are also found. The ostracods Hollinella and Paraparchites appear intermittently throughout the band. A non-marine phase, with or without 'Estheria', is present at some southern localities between the coal and the base of the marine band; the fauna includes Anthracosia aff. atra, Naiadites aff. obliques and Carbonita humilis.

The Two-Foot Marine Band is overlain by dark grey mudstone which becomes lighter in colour upwards and contains abundant 'mussels'. This ' 'mussel'-band, which is characterized by the Anthracosia acutellal concinna group, is well developed in Cross Hills and Elmton Green boreholes, although the shells are crushed and not well preserved. Here the fossils are spread over 10 ft and 14 ft respectively and the following have been identified: Spirorbis sp., Anthracosia acutella (Wright), A. cf. aquilina, A. aquilinoides (Chernyshev), A. aff. concinna (Wright), A. elliptica, A. cf. caledonica, A. aff. planitumida, A. cf. full:a, A. cf. lateralis, A. sp. intermediate between atra and elliptica, Anthracosphaerium radiatum (Wright), Naiadites alatus Trueman and Weir, N. aff. productus; Carbonita humilis [not common]. In Palterton Colliery Borehole the collections included Anthraconaia aff. librata (Wright); representatives of this fauna were also obtained from Woodthorpe Mill Opencast Site. The assemblage listed above is widespread in the Pennine province and in association with the underlying marine band provides a valuable faunal marker-horizon. In the Lancashire Coalfield it is known as the Ashclough fauna: in North Staffordshire it occurs above the Moss Cannel Coal, and in Northumberland and Durham the equivalent `mussel'-band overlies the High Main Marine Band. M.A.C.

The shelly mudstone above the Two-Foot passes upwards, in many sections, into siltstone and sandstone. There is a 96-ft sandstone with a conglomeratic base in Birchhill Borehole, 84 ft of sandstone overlain by 40 ft of stone-bind at Oxcroft Colliery, and 48 ft of sandstone overlain by 30 ft of siltstone with thin bands and laminae of sandstone in Bolsover Moor Borehqle. Sandstone, however, is not much in evidence at outcrop in the north except around Pools-brook. Dovedale Farm Borehole proved 69 ft of sandstone overlain by 15 ft of inter-banded sandstone and mudstone, above the Two-Foot Coal. Nearby at outcrop in the vicinity of Dovedale Wood, this sandstone appears to be in two distinct beds which form prominent features. The lower bed is exposed in a quarry [SK 4660 6280], 1040 yd S. 18° E. of Hardwick Hall, and the upper in a quarry [SK 4617 6337] immediately below the Magnesian Limestone escarpment, 390 yd S. 20° W. of Hardwick Hall.

'Estheria' was found in the seatearth of the Mainbright Coal at Bolsover Moor Borehole. E.G.S., G.H.R.

The Mainbright or Foxearth Coal. The name 'Foxearth' is applied to the seam only at outcrop in the extreme north-east of the area where it has been worked in Woodside, Ireland and Blue Lodge opencast sites. Elsewhere the seam is called the 'Mainbright', but it has not been mapped to the north of Brookhill Hall. There are no other opencast workings and nowhere has the seam been mined. The seam is thickest and contains least dirt in the area between Creswell and Sherwood collieries; sections are as follows: Creswell Colliery, coal 65 in; Norwood Farm Borehole, 'brights' 28.75 in, dirty coal 4.75 in, 'brights' and dirty 'brights' 5.25 in, dirty coal 3 in, dirt 1.5 in, on 'brights' 10 in; Langwith Colliery, coal 58 in; Shirebrook Colliery, coal 13 in, dirt 27.5 in, on coal 42 in; Sherwood Colliery, coal 36 in. Westwards from this area the seam thins and the bottom part is split by dirt bands. At Elmton Green Borehole 27.75 in of coal rest on 24.25 in of coal and dirt; at Cross Hills Borehole the section is 'brights' with shale streaks 13 in, dirt 1.5 in, 'dirty brights' 9.5 in, dirt 10.5 in on dirty 'brights' 1 in. The sections west of Shirebrook and Sherwood collieries show a 4 to 41-in band of coal, or coal with dirt, overlying the worthless mass of dirt and coal or an abnormally thick seatearth. At Oxcroft Colliery and in Birchhill Borehole the Mainbright is only 8 in thick, and in Carr Vale, Hardwick Lodge and Dovedale Farm boreholes it is absent. In the last two boreholes its position is occupied by sandstone. Elsewhere to the north and north-west of Glapwell it is divided into two leaves separated by up to 40 ft of measures. The lower leaf is usually a mixture of coal and dirt similar to that underlying the main part of the seam to the south and east. The upper leaf consists of 12 to 22 in of bright coal with fusain. Both leaves were seen in a trial pit [SK 4410 7311] at Ireland Opencast Site where the section was: 'brights' 21 in, measures 10 ft 5 in, coal and dirt 7 in, 'brights' 6 in, dirt and coal 6 in, on 'brights' 4.5 in. South of Sherwood Colliery the Mainbright consists of either interbanded coal and dirt (there being more dirt than coal in most places) or cannel which has a maximum recorded thickness of 34 in at Sutton Colliery. E.G.S., R.A.E., G.H.R.

'Estheria', associated with fish remains, is found above the Mainbright Coal in Birchhill, Sutton Colliery No. 2, Kirkby Colliery H2, Bentinck Colliery Nos. 1 and 2 and Newstead Colliery N.1 boreholes. The 'Estheria' are preserved as iridescent films and measure up to 3 mm. The measures between the Mainbright and the Manton 'Estheria' Band are usually entirely argillaceous, and in many places contain non-marine lamellibranchs. These occur a few feet above the Mainbright, but preservation is generally poor. The shells identified include Anthracosia atra, A. cf. aquilinoides, A. lateralis, Naiadites obliquus, Carbonita humilis and fish remains. There is a 29-ft bed of sandstone at Norwood Farm Borehole and, in the south-west, up to 40 ft of sandstone are present in several sections and have been traced at outcrop from Huthwaite to the southern margin of the district. E.G.S., M.A.C.

In the east the Manton 'Estheria' Band is underlain by a thin coal which attains a maximum recorded thickness of 17 in of ' bat and coal ' in Langwith Colliery Shaft. In Skegby Sewage Works Borehole and Newboundmill Borehole this coal appears to be split into two thin leaves, respectively 10 and 17 feet apart.

The Manton 'Estheria' Band consists of 2 to 57 in of dark grey to black mudstone, which is silty in some localities, cannelly in some of the thinner sections, and in a number of places contains ironstone. It contains rare to abundant 'Estheria' and usually fish debris. Locally it rests directly on the seatearth or thin coal previously described, but may be separated from it by up to 7 ft of grey or dark grey mudstone with plant debris. In Norwood Farm Borehole this intervening mudstone, 23 in thick, contains non-marine lamellibranchs, ostracods and fish debris. Recent boreholes suggest that the Manton 'Estheria' Band is everywhere present north of Sutton Colliery, but to the south it has been seen only in Sutton Colliery No. 2 Borehole and at outcrop in The Dumbles (1.5 miles S.E. of Sutton in Ashfield) where P. McL. D. Duff found 'Estheria' in mudstone or cannelly shale above the thin coal which is exposed at several places. The 'Estheria' are about 2 mm across and are similar in form and preservation to those from the roof of the Mainbright Coal (see above).

The 15 to 30 ft of measures between the Manton 'Estheria' Band and the Clown Coal usually consist of mudstones which locally contain 'mussels', including Anthracosia cf. atra, and fish remains. A thin sandstone in these measures forms a low feature between Long Duckmanton and Sutton Scarsdale.

Clown Coal

The Clown Coal. North of the Hardstoft Anticline this seam varies somewhat irregularly in thickness between 22 and 61 in (see (Figure 31)). The maximum thickness of 61 in is recorded from Woodside Opencast Site in the north-west and, in general, the seam thins towards the south and east. Local thickening occurs in Newboundmill Borehole and in the Shirebrook–Sherwood area, but further exploration is needed here to determine the exact limits of thick coal.

South of Hardstoft the seam deteriorates rapidly and is only 7 to 16 in thick in underground sections. At outcrop it is somewhat thicker; it is at least 18 in thick in the railway cutting [SK 4737 5637], 650 yd S. 34° E. of Crow Trees, and has been proved at Fulwood and Bloomer Wood opencast sites to consist of a 6 to 14-in upper leaf separated by 7 to 10 in of dirt from a 7 to 12-in lower leaf. There is evidence that the seam was formerly worked in the vicinity of Bloomer Wood. In this southern area the coal consists of 'brights' with a variable amount of fusain, and the few sections that have been analysed show a medium to high ash-content.

In the field of thick coal to the north, the Clown is a good quality coal with low sulphur- and ash-contents, and consists of 'brights' with bands and streaks of dull coal and fusain. Cannel commonly occurs at the top of the seam and may be up to 15 in thick, but it is of inferior quality in some sections. Dirt partings are rare and do not exceed 0.5 inch in thickness.

The Clown has been worked from Shirebrook Colliery where it is known as the 'Main Hard', and from surface drifts at Oxcroft and Bramley Vale, near Glapwell. At outcrop it has been worked in an almost continuous series of opencast sites north of Glapwell Colliery. To the south it crops out on the slopes below the Permian escarpment, the crop being hidden in places by the unconformable newer rocks, usually for short distances, but, where the eastern prolongation of the Hardstoft Anticline affects the seam, for about three miles. It reappears at the surface north of New Hucknall Colliery, but from here southwards its position on the maps is largely inferred. E.G.S., G.H.R.

Measures between the Clown Coal and the Haughton Marine Band

The measures between the Clown Coal and the Haughton Marine Band thin from between 90 and 140 ft in the north to 50 or 60 ft in the south. Typically they are composed of three cycles, but in places of two or four. Each cycle may develop a coal, but the seams, with the exception of the Swinton Pottery at the top, are everywhere thin and of no importance.

The Clown Marine Band is intermittently developed but, where present, immediately overlies the Clown Coal; it consists of up to 6 in of dark shale, in places cannelly, especially where the top of the underlying Clown seam is of cannel. At outcrop it has been seen at The Oaks, Tom Lane and Arkwright Arms opencast sites by Dr. J. Shirley (Edwards and Stubblefield 1948, p. 223) and at Longcourse Farm Opencast Site by R. A. Eden. In parts of The Oaks Opencast Site the marine band is absent and Shirley noted that, eastwards across the site, overlying shale with coal streaks appeared to cut it out. It consists at this site of 3.5 in of black cannelly shale with fish and abundant Lingula mytilloides, and overlies 7.5 in of cannel (the top part of the Clown Seam) which also contains fish. The marine band proved to be absent a short distance away in Oxcroft Colliery Drift, and farther south at Deep Ring Bell Opencast Site it was not found.

Underground, the marine band has been recorded by Mr. A. Dawe of the Coal Survey Laboratory, Nottingham, in the shaft pillars of Langwith, Shirebrook and Sherwood collieries (Edwards and Stubblefield 1948, p. 223). Of the numerous recent boreholes that have been drilled through this horizon, only Glapwell Village and Hardwick Lodge encountered the marine band. Two inches of dark shale with L. mytilloides and fish scales were recorded at the former locality, and at the latter Mr. S. Brunskill of the N.C.B. found Lingula 6 in above the Clown Coal. E.G.S.

The fauna of the Clown Marine Band is restricted. It is essentially a Lingula band in which L. mytilloides attains a greater average size (up to 9 mm) than in the other marine bands. The only other fossils are fish debris and Hindeodella sp., a single specimen of which was recorded at Arkwright Arms Opencast Site (ibid., p. 223). The limited fauna, particularly the absence of foraminifera, is thought to be a consequence of the carbonaceous lithology.

Overlying the marine band are up to 4 ft of grey mudstones with a characteristic fauna in which Anthraconaia sp. nov.aff. librata is typically found and C. humilis is abundant. The associated Anthracosia spp.are mainly small forms of A. atra and variants; other fossils include Anthracosphaerium cf. exiguum, Naiadites angustus Trueman and Weir and Pleuroplax affinis Salter. A shell from this band in Tom Lane Opencast Site was figured as Naiadites aff. modiolaris (J. de C. Sowerby) by Trueman and Weir (1955, pl. xxix, fig. 45). A second 'mussel'- band is found up to 15 ft above the Clown Coal in black mudstone which is cannelly in places. The lamellibranchs generally occur as 'solids', either as internal moulds or with the shell preserved, and have a distinctive pale brown coloration; they are also much larger than those in the underlying band. A large collection from this upper band was obtained from Arkwright Arms Opencast Site and the following have been determined: Anthracosia atra, A. cf. elliptica, A. fulva, A. sp. intermediate between atra and barkeri, A. sp. intermediate between atra and lateralis, A. sp. nov.cf. phrygiana. The two main trends from typical A. atra are towards elongation (atrallateralis) and the development of a posterior snout (cf. Barker and Leitch 1947, pl. xxvii, fig. 4). In the upper part of the band a distinctive shell occurs which does not compare closely with any described form; it has oblique posterior truncation and the pronounced tilting of the growth lines shown by the A. phrygiana group occurring lower in the succession.

Fossils occur intermittently in the beds above, and in the main belong to Naiadites and Carbonita; 'Estheria' is present at about 40 ft above the Clown in Elmton Green Borehole. A persistent 'mussel'-band occurs some 70 ft above the coal and has been found in Elmton Green, Birchhill and Cross Hills boreholes and in Bramley Vale No. 1 Drift. The fossils include A. aff. atra, N. angustus, N. productus, C. humilis and fish remains including Elonichthys sp. and Rhizodopsis sp. In the upper part of this band in Bramley Vale Drift and also in Newboundmill Borehole there is an interesting occurrence of Curvirimula. The genus is rare in the measures above the horizon of the Tupton Coal (p. 88), but is known in several coalfields in the upper part of the

Lower similis-pulchra Zone, particularly in the strata associated with the marine horizons (Magraw and Calver 1960, p. 346; Calver in Magraw 1960, p. 482). In the Bramley Vale No. 1 Drift the shells collected from 18 ft below the Haughton Marine Band include juvenile Naiadites bearing a close resemblance to Anthraconautaphillipsii (Williamson) from the Upper Coal Measures. Similar shells were recorded from 1911 ft in Maltby sinking (Dix and Trueman 1931, fig. 6; Edwards 1951, p. 85). M.A.C.

Sandstone occurs from place to place in these measures, but is most marked in the uppermost cycle in the north and in the lower two cycles in the south. At outcrop the most prominent sandstone lies below the estimated horizon of the Swinton Pottery Coal in the area between Shuttlewood and Doe Lea. It forms the scarp on which Far Duckmanton and Long Duckmanton stand and makes a strong feature along the whole of its outcrop. Over much of the area it is estimated to be about 30 ft thick, and is exposed in the railway cutting [SK 4400 7085], 450 yd N. of Longcourse Farm, where it is false-bedded and has an erosional base.

The Swinton Pottery Coal is of no economic value, and there is no record of its having been worked. It is usually thin, dirty, and split into two or three leaves which may be several feet apart. It is best developed in the north-east: e.g. Creswell Colliery Shaft, coal and dirt 36 in; Norwood Farm Borehole, coal 17 in, dirt 10 in, coal 7 in, dirt 33 in, on dirty coal 5 in; Langwith Colliery Shaft, coal 18 in, dirt 58 in, on coal 8 in. In the few sections in the south that include its horizon it is absent except at Bentinck No. 1 Borehole where 5 in of coal were recorded. E.G.S.

The Swinton Pottery is separated from the Haughton Marine Band by 4 to 14.5 ft of measures consisting largely of mudstone, dark at the base, and becoming grey and silty upwards. They usually contain ironstone bands and plants, and have yielded fossils at Cross Hills, Elmton Green, Norwood Farm, Palterton Colliery, Birchhill and Glapwell Village boreholes and in Bramley Vale No. 1 Drift. These include Naiadites sp., Carbonita cf. humilis and fish remains. Sandstone laminae or a band of sandstone commonly occur at the top of the measures.

The Haughton Marine Band consists of 16 to 34.5 ft of dark grey mudstone which may be silty in parts and contain nodules, lenses and thin bands of ironstone which may be locally abundant. Where the band is overlain by seatearth, rootlets commonly occur in the top few feet. The band has not been seen at outcrop, but has been recorded at Bramley Vale No. 1 Drift where it is 12 ft thick and in the following boreholes (thickness in brackets): Bentinck No. 1 (1 ft +), Bentinck No. 2 (5 ft + ), Birchhill (20 ft 6 in), Bolsover Moor (24 ft 9 in), Carr Vale (31 ft 1 in), Cross Hills (29 ft), Dovedale Farm (18 ft 3 in), Elmton Green (29 ft 1 in), Glapwell Village (16 ft 1 in), Hardwick Lodge (17 ft 5 in), Newboundmill (19 ft Sin), Norwood Farm (16 ft + ), Palterton Colliery (34 ft 6 in), Rylah (27 ft 11 in). It has apparently been completely washed out by overlying sandstone at Kirkby Colliery H2 Borehole, and all but the basal 1 ft has been eroded at Bentinck No. 1 Borehole. The upper part of the band may have suffered a similar fate in Bentinck No. 2 Borehole. The band was not found in Newstead Colliery N.1 Borehole. Here there is very little sandstone in the measures between the Clown Coal and the Mansfield Marine Band, but the absence of the Haughton horizon may be due to faulting of which there is evidence in the borehole. At Bolsover Colliery samples of sinking dirt from between 130 and 162 ft from the surface (the expected horizon of the marine band) consist of shale that is apparently marine, but faunal evidence is inconclusive. E.G.S., G.H.R.

Although fossils are sparse in the Haughton Marine Band the assemblage and faunal profile are distinctive and make it a readily recognizable horizon. The collection obtained from Palterton Colliery Borehole and listed below is representative of the nature and distribution of the fauna in the district.

The macrofauna shows marked contrast to that exemplified by the Clay Cross Marine Band and other bands of similar facies (see pp. 179–190). The differences also extend to the foraminifera which in the Haughton Marine Band are represented mainly by Tolypammina, Hyperammina and various rod-like forms referred provisionally to Hyperammina. The latter genus was not seen in the washings from the Clay Cross, Two-Foot or Edmondia marine bands. In its general features the collective assemblage of the Haughton Marine Band shows a closer approach to that of the Mansfield Marine Band and suggests a more saline environment than that of the Clay Cross/Two-Foot type of marine fauna.

In this district the band can be divided into four more or less distinct beds, each characterized by a particular fossil, or group of fossils. At the base is a thin layer with Campylites [Sphenothallus], which occurs at this horizon in most of the Pennine coalfields (Magraw and Calver 1960, p. 348; Calver in Magraw 1960, p. 482; Calver in Taylor 1961, p. 13; Calver in Earp 1961, p. 165). This basal layer is overlain by up to 10 ft of mudstones containing the richest fauna of the band, including Orbiculoidea, gastropods in variety, and cf. Tomaculum. In addition to the fossils listed above from the Palterton Colliery Borehole, this particular bed elsewhere in the district contains Euphemites anthracinus (Weir) and Edmondia?. The upper part of the band, corresponding to the regression of the incursion, is divided into a lower bed some 2 ft in thickness with foraminifera, Lingula and Nuculids, and an upper part consisting of 10 to 15 ft of mudstones with a sparse fauna of P. ophthalmoides, Lingula, Cypridina and various faecal deposits.

A distinctive feature of the band is the universal occurrence of small, elongated, ovoid bodies [about 2.0 mm by 0.5 mm], preserved in ironstone, and referred to in the above list as cf. Tomaculum sp. [(Plate 5), fig. 6]. They are found either isolated or, more usually, in large, compact masses of the order of 10 cm across by 1 cm thick, and are interpreted as faecal accumulations (see Edwards and Stubblefield 1948, p. 224, footnote). The isolated pellets commonly show a full-length longitudinal groove but in the present collection this feature has not been seen in the clusters forming the aggregates, which occur mainly with the richest fauna in the lower part of the band. Their close association with the Pleurotomariid gastropods determined as cf. Shansiella is thought to be significant [(Plate 5), fig. 9], since similar faecal deposits are produced by some recent gastropods (Moore 1931). Another line of evidence that the Pleurotomariids may be the source of the cf. Tomaculum is their mutual occurrence in other Coal Measures marine bands, such as the Top Marine Band (Goossens 1952, p. 194). Other faecal remains are probably represented by curved, rod-like segments, up to 4 mm long.

The Lingula cf. elongata [(Plate 5), fig. 3] of the above list has been seen in several boreholes at this horizon and is distinguished by being proportionately narrower than typical L. mytilloides [(Plate 5), fig. 4]. M.A.C.

Measures between the Haughton and Mansfield Marine bands

The measures between the Haughton and Mansfield Marine bands are of consistent thickness in the northern half of the district, varying only between 116 and 128 ft, but they are markedly thinner in the southern half, being 97 ft at Sherwood Colliery and, while not directly measurable, appear to be between 70 and 85 ft thick farther south. They consist of five, in places of six, cycles including the one containing the Haughton Marine Band at the base. In some section; the measures are entirely argillaceous, bu thin sandstones occur locally in all the cycles At outcrop sandstone is prominent only it the area between Shuttlewood and Deepdale Farm, Sutton-cum-Duckmanton, and underground in Shirebrook Colliery shafts and in the Kirkby and Bentinck Colliery boreholes. The thickest development is 35 ft, at the base of the group, in Kirkby Colliery 112 Borehole, and in this area, as previously mentioned, it tends to wash out the Haughton Marine Band. Coal is developed locally in each of the cycles, but the seams are usually only a few inches thick and are commonly dirty. The thickest coal recorded (18 in) is that below the Sutton Marine Band in Elmton Green Borehole. The coal underlying the Mansfield Marine Band attains a maximum thickness of 10 in at Bolsover Moor and Carr Vale boreholes; elsewhere it varies between 0 and 7 in. E.G.S., G.H.R.

The Sutton Marine Band occurs locally in the north of the area where it has been found in five boreholes: Bolsover Moor, Carr Vale, Elmton Green, Palterton Colliery and Rylah. In these boreholes it lies at the base of the second cycle above the Haughton Marine Band, roughly one third of the distance up from the Haughton Marine Band to the Mansfield Marine Band. It consists of dark grey mudstone with ironstone nodules, lenses and bands. At Elmton Green it was recorded as being 9 ft 2 in thick resting on 18 in of dirty coal, and separated from overlying seatearth by 6 ft 4 in of mudstone with rootlets and fish debris. At Bolsover Moor and Carr Vale it is respectively 5 ft 10 in thick above a 13-in coal and 4 ft 8 in thick above a 14-in coal. At both places the marine band contains rootlets throughout its thickness and is directly overlain by seatearth. At Rylah it is similarly succeeded by seatearth, but rootlets occur only in the upper part of the band; it is here 10 ft 4 in thick and rests on an 8-in coal. At Palterton Colliery Borehole Lingula sp. was recorded at 111 ft 8 in. E.G.S.

The fauna is unusual in that, although the band has a restricted distribution, the characteristic fossils are those that are commonly found in the major marine incursions. Thus in Elmton Green Borehole the following were collected from 7 ft of mudstones: Lingula?, Orbiculoidea cf. nitida [(Plate 5), fig. 2]; Bucanopsis? navicula ((Plate 5), fig. 8]; Aviculopecten delepinei Demanet. In other boreholes the fauna is largely confined to Orbiculoidea (some specimens attaining a size of 12 mm), but Euphemites cf. jacksoni (Weir) (P1. V, fig. 5] is also present in Bolsover Moor Borehole. Foraminifera have only rarely been noted from the band, but washings from the regression stage in Carr Vale Borehole include Ammonema, Tolypammina and Glomospira.

Non-marine fossils have been found in these measures only above the Sutton Marine Band or its horizon and are not common. The lamellibranchs are mainly Naiadites such as N. aff. angustus and N. productus. A juvenile Anthraconaia occurs 53 ft below the base of the Mansfield Marine Band in Elmton Green Borehole, while in Birchhill Borehole Lioestheria vinti (Kirkby) and fish remains are present some 15 ft higher. Carbonita humilis was found at about this level in Cross Hills Borehole. M.A.C.

Mansfield Marine Band to Top Marine Band

This group consists of about 550 to 600 ft of measures in which the only coals of note are the Wales in the north and the Highmain in the south. Most of their outcrop ' south of Glapwell is concealed by Permo-Triassic rocks. The general characters of the group are shown in (Figure 32).

The Mansfield Marine Band consists of 11 to 16.5 ft of dark grey mudstone with an abundant and varied marine fauna. Nodules, lenses and thin bands of ironstone are present in some sections, and in most places a conspicuous bed of ' cank ' (hard ankeritesiltstone) occurs near the base. The marine band has not been seen at outcrop, but has been recorded in the following boreholes (thickness in brackets): Birchhill (13 ft 4 in), Bolsover Moor (15 ft), Carr Vale (11 ft 9 in + up to 3 ft 6 in), Cross Hills (15 ft), Elmton Green (9 ft 10 in + up to 4 ft 3 in), Glapwell Village (15 ft 9 in), Hardwick Lodge (12 ft 9 in), Kirkby Colliery H2 (9 ft 9 in), Newboundmill (14 ft 8 in), Newstead Colliery N.1 (16 ft 6.5 in), Norwood Farm (14 ft 11 in), Rylah (2 ft 8 in +), Top Farm (11 ft 8 in). The cank ' is absent at Cross Hills and Birchhill and was not recorded at Hardwick Lodge; elsewhere it varies in thickness from 6 in at Top Farm to 21 in at Newboundmill, and lies from 6 to 47.5 in above the base of the marine strata. The thickness of the cank ' is roughly proportional to the thickness of marine mudstone below it. This mudstone is usually dark grey in colour and canky ' in parts, especially towards the top, but at Newboundmill a 6.5-in band of light brown mudstone is recorded 37.5 in below the 'cank' and 2 in above the roof of the underlying coal.

Apart from the above boreholes, the Mansfield Marine Band has been recorded only at Creswell Colliery where samples of sinking dirt from 375 ft below the surface yielded a number of marine fossils (see Edwards and Stubblefield 1948, pp. 228–9). In other sinkings that passed through the horizon—Langwith, Shirebrook, Pleasley, Sherwood and Kirkby—its position can be readily inferred, and indeed, except at Shirebrook, is fixed with certainty by the mention of ' cank ' occurring near the base of a fairly thick development of dark bind. At Langwith the recorded thickness of 4.5 ft for the cank ' is the maximum for the district. E.G.S., G.H.R.

The fauna is the most varied of all the Coal Measures marine bands and is notable for the occurrence of cephalopods, calcareous brachiopods and lamellibranchs. In this district the band shows similar features to those described from adjacent areas (Edwards and Stubblefield 1948, pp. 225–9; Edwards 1951, p. 66). The richest fauna is found towards the base of the band and is succeeded by mudstones with Lingula, Nuculids and ostracods; the top of the band is represented by abundant foraminifera and Planolites ophthalmoides. The fauna listed below is based on collections from all localities examined; the assemblage, see (a) below, obtained from the lower part of the band and belonging to the maximum development of the incursion is listed separately from the fossils representing the regression stage, (b) below.

(a) Lower part of band.  Crinoid columnals [circular]; Lingula mytilloides, Orbiculoidea sp., Rugosochonetes skipseyi (Currie), Tornquistia diminuta (Demanet); Euphemizes cf. anthracinus, Platyconcha hindi Longstaff, Straparollus sp.; Anthraconeilo taffiana Girty, Dunbarella macgregori (Currie), D. cf. carbonaria (Hind), cf. 'Nucula' luciniformis Phillips, Palaeoneilo sp. nov., Pernopecten sp., Polidevcia acuta (J. de C. Sowerby), P. attenuata (Fleming), Prothyris cf. carbonaria Wilson, Streblochondria fibrillosa (Salter); Orthocone nautiloids, Huanghoceras costatum (Hind), Metacoceras aff. cornutum Girty, M. cf. perelegans Girty, Anthracoceras hindi Bisat, Politoceras politum (Shumard), Gastrioceras cf. depressum Delepine, goniatite referred to Gen. et sp. nov. [cf. Currie and others 1937, pl. iv, figs. 9, 10]; Hollinella sp.; conodonts including assemblages with Hindeodella and platformed types; Acanthodian scales, Elonichthys sp., Rhabdoderma sp.; cf. Tomaculum sp.

(b) Middle and upper part of band. Agathammina sp., Glomospira sp., Glomospirella sp., Hyperammina sp., Tolypammina sp.; sponge spicules [pyritized]; Planolites ophthalmoides; Lingula mytilloides; Palaeoneilo sp., Polidevcia acuta; Cypridina Corsin, Hollinella cf. bassleri; Rhabdoderma sp.; pyritized strap-like markings ('fucoids').

The occurrence of Gastrioceras [(Plate 5), fig. 1] in the cank ' from the lower part of the band in several of the boreholes is of interest. The genus is rare at this horizon but is recorded from Maltby sinking (Edwards 1951, p. 89; see also Bisat 1930, p. 81). The present material is fragmentary but compares with G. depressum Delepine from the equivalent marine band in Belgium (Delpine 1937). The goniatite referred to in the above list as Gen. et sp. nov.was obtained from Newboundmill Borehole and Kirkby Colliery H2 Underground Borehole; the omparison is made with the examples figured by Currie and others (1937, pl. iv, figs. 9, 10) from Skipsey's Marine Band and with specimens from the Bolton Marine Band of Cumberland (ibid., p. 441). Foraminifera are abundant and well preserved in the upper layers of the band. The assemblage is mainly composed of Glomospirella, Tolypammina and Hyperammina, the presence of the latter genus recalling the Haughton Marine Band fauna (see p. 183). M.A.C.

Measures between the Mansfield Marine Band and the Wales Coal

The measures between the Mansfield Marine Band and the Wales Coal constitute the bulk of the single cycle which includes the Mansfield Marine Band at its base and the Wales Coal at its top and are 50 to 75 ft thick. Some sections, especially in the south, consist entirely of mudstone which is silty in the upper part, but in others the mudstone passes upwards into siltstone, 'stone-bind' and sandstone. There are over 40 ft of sandstone and siltstone below the seatearth of the Wales at Cross Hills Borehole, and sandstone at this horizon is exposed in the ailway cutting [SK 455 709], 0.33 mile W. of Bolsover Colliery, and in the road cutting [SK 4643 7160], 200 yd N.W. of Over Woodhouse. E.G.S., G.H.R.

Fossils are not common in these measures, but those obtained from Newboundmill Borehole are representative of the sequence in the district. In this borehole fish and Naiadites sp. are found immediately above the Mansfield Marine Band; some 20 ft higher the mudstones contain Cochlichnus kochi at two levels. The highest faunal band occurs 8 ft below the Wales Coal, and contains Naiadites sp. and Carbonita humilis; this band was also found in Bolsover Moor Borehole. It is of interest that a band rich in Carbonita humilis is known in the Lancashire Coalfield (Wright in Tonks and others 1931, p. 149) just below the Parker Mine which is the first prominent coal above the Dukinfield ( = Mansfield) Marine Band. M.A.C.

Wales Coal

The Wales Coal crops out between Shuttlewood and Ault Hucknall, but it is nowhere exposed. To the north and south the ' outcrop ' is beneath the Permo-Trias. In the Sheffield country to the north there are two Wales Coals (Eden and others 1957, p. 120) and it is not clear whether the Wales Coal of the present district represents both these seams or only the lower, or Second Wales, seam. The coal is mined only from Langwith Colliery, where it is known, misleadingly, as the 'Highmain', and where the workings extend over about two square miles to the north of the shafts. Over the greater part of this area the coal is dirt-free and varies in thickness between 36.5 and 39 in. In the northern part of the workings, however, a central dirt parting appears; this is 2 in thick at Norwood Farm and 8 in at two other localities nearby. Farther north at Frithwood Farm, the section is: coal 14 in, dirt 18 in, on coal 27 in. In Creswell Colliery shaft the dirt parting is again in evidence, the section being: coal 13 in, dirt 10 in, on coal 22 in. South-eastwards and south from Langwith Colliery the seam appears to maintain its thickness as far as Shirebrook where 36 in, including 3 in of dirt, are recorded. It is 32 in thick in Top Farm Borehole, and 36 inches in Warsop sinking just east of the sheet boundary. Westwards and south-westwards from Langwith attenuation of the seam begins. At Cross Hills Borehole the section is coal 12 in, dirt 1.5 in, coal 9 in, dirt 1 in, on coal 2.5 in; at Birchhill Borehole coal 18 in; at Bolsover Moor Borehole coal 4 in, dirt 1 in, coal 4 in, dirt 4 in, on coal 2 in; and at Carr Vale Borehole coal 5 in, on dirty coal 3 in. Shallow borings by the Opencast Executive in the vicinity of Carr Farm between Bolsover and Palterton showed the seam to be between 11 and 16 in thick, though in one hole 41 in of dark shale and coal were reported from the Wales horizon. E.G.S.

South of Shirebrook the Wales has been seen at only eight localities. In the Glapwell–Sherwood area it is up to 64 inches in overall thickness, but contains a high proportion of dirt in up to four bands. The thickest section is at Pleasley sinking: coal 11 in, dirt 12 in, coal 24 in, dirt 11 in, on coal 6 in. Farther south there are 19 in of coal in Kirkby Colliery H2 Borehole, 15 in of coal in Kirkby Lowmoor Pit, 27 in of bad coal in Kirkby South Pit and 27 in of coal split up by dirt in Newstead Colliery N.1 Borehole. The shafts show a 10-in seam respectively 15 and 29 feet above the Wales, from which it may be a split, and in the boreholes there are several thin seams in the overlying measures whose relationship to the Wales is not known. E.G.S., G.H.R.

Measures between the Wales Coal and the Edmondia Band

The measures between the Wales Coal and the Edmondia Band, typically comprising eight cycles, are about 200 to 250 ft thick in the north thinning to about 170 ft in the south. They contain impersistent sandstones at various levels and a number of coals of which the only economically important one is the Highmain.

The most notable sandstones are the one occurring a short distance above the Wales Coal at outcrop in the Bolsover area, and that underlying the Highmain Coal at a number of localities. The former has been quarried in the New Bolsover area where exposures visible at the time of the resurvey showed up to 15 ft of sandstone which was hard and massive in some sections, but soft and flaggy with hard bands in others. The sandstone below the Highmain is nearly 70 ft thick at Bolsover Moor Borehole, 90 ft at Shirebrook Colliery and about 30 ft in Kirkby Colliery shafts and H2 Borehole. At outcrop it is well seen in the faulted exposure [SK 472 697] in the railway cutting east of Carr Vale; on the eastern side of the fault 30 ft of sandstone, massive in the lower 20 ft, are seen and on the western side 12 ft of sandstone with micaceous shaly partings containing plant debris.

The mudstones in this group of measures are poorly exposed except at New Byron Brickworks near Doe Lea Bridge where 20 ft of silty mudstone with siltstone bands overlying at least 25 ft of mudstone and silty mudstone with ironstone bands and nodules were being worked at the time of the resurvey. E.G.S.

Boreholes show that 'mussels' are common at certain horizons in these measures. In the lower part only Naiadites, including N. hindi Trueman and Weir, and fish remains have been found, e.g. at Cross Hills Borehole. In Birchhill Borehole, some 80 to 100 ft above the Wales Coal, and below the Highmain Coal, there is a prominent faunal horizon, in two bands separated by 20 ft of barren measures. The lower band contains Spirorbis sp., Naiadites aff. melvillei Trueman and Weir, C. humilis, Geisina subarcuata (Jones) and Rhabdoderma sp. and is the lowest horizon at which G. subarcuata has been found in the district. The upper band contains Spirorbis sp., Anthraconaia cf. adamsi (Salter), Naiadites sp. cf. productus, Carbonita humilis and fish remains including Rhizodopsis. Between the unnamed seam lying above the Highmain in the north of the district (see below) and the Edmondia Band are thin bands with fish remains and Naiadites. In Birchhill and Newboundmill boreholes the Naiadites spp. include N. cf. carbonarius Dawson, N. aff. hindi and numerous juvenile forms; these small shells are homoeomorphs of Anthraconauta phillipsii. In Cross Hills Borehole the approximately equivalent horizon contains Spirorbis sp., Anthraconaia sp. [juv.], N. aff. hindi, Carbonita sp., G. subarcuata and fish remains. M.A.C.

The Highmain Coal is mined from Kirkby Colliery where the workings extend for about a mile to the north and east of the shafts, and from Annesley Colliery. It consists of bright coal with dull bands, and is of good quality with a fairly low ash-content. Over most of the worked area it varies between 41 and 47 in, but it thins to 33 inches in the eastern part of Kirkby workings.

To the north of Kirkby the Highmain was recorded in Sherwood Colliery sinking as: coal 6 in, dirt 7 in, on coal 32 in. A similar section was proved at Newboundmill Borehole (coal 4 in, dirt 6 in, on coal 30 in), but at Pleasley Colliery only 24.5 in of coal were recorded. Of the underground sections north of Pleasley only Glapwell Village Borehole (coal 24 in, dirt 39 in, on coal 16 in) shows the seam to be more than 18 in thick, and the minimum thickness recorded is 6 in at Cross Hills Borehole. The seam crops out below the Permian escarpment between Bolsover and Gruff Wood, Ault Hucknall, and was worked during the nineteenth century from an adit at Bathurst Main Colliery near Carr Vale, where it is recorded as being 23 in thick and was known as the Silkstone '. Immediately south of these old workings a number of trial pits dug by the Opencast Executive proved the Highmain to be 23 to 24.5 in thick and to consist of bright coal with a 1.5 to 2.5,-in dull band 12 in from the base.

From Sherwood Colliery northwards there is an unnamed coal 25 to 30 ft above the Highmain. This is, in many places, thicker than the Highmain, but at Bathurst Main Colliery, where it was worked until 1891, it is the same thickness of 23 in and, like the Highmain, was known as the 'Silkstone'. The seam is split in Birchhill, Carr Vale and Glapwell Village boreholes and in Pleasley Colliery Shaft; the upper leaf, varying from 14 to 21 in and containing cannel at Carr Vale Borehole, is separated from a 4 to 7-in lower leaf by 5 to 30 in of dirt. It is only 7 in thick at Bolsover Moor Borehole, and is represented by 7 in of coal and dirt at Sherwood Colliery: other underground sections show between 14 and 21 in of coal.

Tonstein has been recorded from a 0.5 in dirt band in the Highmain Coal at Glapwell Village Borehole (Eden and others 1963, p. 56), and a parting of kaolinite mudstone has been found in a 9-in coal 6 ft below the Highmain at Newboundmill Borehole. As the thin coal at Newboundmill is possibly a leaf of the Highmain, the two occurrences may be at the same horizon.

At the top of these measures and below the Edmondia Band there is a thin coal, up to 14 in thick. Coal is present in all those sections where the Edmondia Band has been identified (see below) and in every case, except at Cross Hills Borehole, the marine band rests immediately upon it. At Cross Hills there are 9 ft 5 in of mudstone between the marine band and the 0.5 in coal, and they have yielded Naiadites cf. daviesi Dix and Trueman, N. aff. hindi, Rhizodopsis sp. and plant debris.

Edmondia Band

The Edmondia Band is nowhere exposed, but is calculated to crop out below the Permian escarpment between Bolsover and Glapwell. It has been seen in the following boreholes (thickness in brackets): Birchhill (2 ft 6 in), Cross Hills (7 ft), Glapwell Village (8 ft 7 in), Newboundmill, Norwood Farm (1 ft 5 in), Top Farm (8 ft 9 in). It consists of grey to rather dark grey mudstone with a poor macrofauna but abundant foraminifera. Thin ironstone bands were found at Top Farm and Birchhill. E.G.S., G.H.R.

The distinguishing features of this marine horizon in the East Pennine Coalfield are the abundance of foraminifera and their association with the macrofaunal assemblage characteristically found in the less-saline marine environments (see comments on the Clay Cross and Two-Foot marine bands, pp. 157, 178). The foraminifera are represented mainly by the genera Ammonema, Glomospira, Glomospirella and Tolypammina, which is a similar assemblage to that recorded from the Two-Foot horizon (p. 178); the other fossils are Edmondia sp., Myalina cf. compressa and Hollinella cf. bassleri. Finely comminuted plant debris is noticeably abundant in the matrix of the band. Associated with the marine fossils at most localities are several examples of Geisina subarcuata, which species is also common in the 'mussel'-bands in this part of the sequence. The close relationship between this ostracod and the Myalinal Hollinella marine fades recalls the analogous situation concerning Geisina in the Clay Cross and Two-Foot marine bands (pp. 157, 178). A further close comparison with the nature and development of these two bands is emphasized by the presence of non-marine lamellibranchs in the upper part of the Edmondia Band. However, in this case the lamellibranchs are Curvirimula which is found only rarely above the top of the C. communis Zone, and then at or near to the horizons of the A. similis–A. pulchra Zone marine bands (Weir 1960, pp. 298–9; see also p. 183 above). The connexion between Curvirimula and the marine incursions implies that Curvirimula tolerated, or possibly favoured, more saline conditions than the other non-marine lamellibranch genera. The presence of Curvirimula and G. subarcuata in the upper part of the Edmondia Band suggests a brackish environment at this period of the regression, and recalls the similar conditions suggested for the closing stages of the Clay Cross and Two-Foot marine bands (pp. 157, 178). M.A.C.

Measures between the Edmondia Band and the Shafton Marine Band

The measures between the Edmondia Band and the Shafton Marine Band, or at least their lower part, crop out between Bolsover and Glapwell, but are not exposed. The only accurately measured sections through the entire group are provided by Birchhill and Glapwell Village boreholes where they are respectively 188 and 196 ft thick. Their inferred thickness in Shirebrook and Pleasley Colliery shafts is about 190 ft and about 174 ft. Other sections—Norwood Farm Borehole, Langwith Colliery Shafts, Top Farm, Cross Hills and Newboundmill boreholes, Sherwood and Kirkby Colliery shafts—are of the lower part only. The measures comprise six cycles at Birchhill and Glapwell Village, and at the latter locality each contains a thin coal. Sandy or silty beds are developed to a small extent in each cycle. E.G.S., G.H.R.

The following faunal information is based largely on the collections obtained from Birchhill and Glapwell Village boreholes. The fauna is similar to that from the lower part of the Upper similis-pukhra Zone, with the addition of Lioestheria vinti (Kirkby), which occurs at several levels, the lowest at 70 ft above the Edmondia Band. L. vinti, which attains a size of 3.5 mm, is particularly abundant in a band 37 ft below the Shafton Marine Band, and this is probably the equivalent of the Main 'Estheria' Band (Edwards and Stubblefield 1948, p. 232). The best-developed faunal bands are found about 100 ft above the Edmondia Band and the following fossils have been identified: Planolhes montanus; Naiadites cf. carbonarius, N. hindi, N. aff. melvillei; Lioestheria vinti, Carbonita sp. cf. salteriana (Jones), G. subarcuata, and fish remains including Elonichthys sp., Rhabdoderma sp., Rhadinichthys sp., Rhizodopsis sp. and Platysomid scales indet. M.A.C.

Shafton Marine Band

The Shafton Marine Band is inferred to be present in Shirebrook and Pleasley Colliery shafts (at 263 ft 10 in and 184 ft 3 in from the surface respectively), but it has been positively identified only at Birchhill and Glapwell Village boreholes. At Birchhill it was found to be 12 in thick, consisting of 9 in of grey mudstone with Lingula sp., Myalina? and fish remains, overlying 3 in of grey clunchy siltstone with Anthraconata pruvosti (Weir and Leitch non Chemyshev). At Glapwell Village well-preserved Ammodiscus sp., cf. Anthraconaia pruvosti and fragments of 'Estheria' sp. were collected from the basal 9 in of 5 ft 3 in of grey slightly silty mudstone containing patches of pyrite. A. pruvosti occurs alone in the top 1 in of the band. E.G.S.

Middle Coal Measures above the Shafton Marine Band

The Middle Coal Measures above the Shafton Marine Band. These measures, of which only the lower part has been seen within the districtNote. Since going to press the Top Marine Band and 323 ft of Upper Coal Measures have been proved in Cauldwell Borehole [SK 5249 5855] south-west of Mansfield and on the north side of the fault through Sutton in Ashfield and Stonehills (see p. 191). The cores were examined by Messrs. J. G. O. Smart, N. Aitkenhead and S. Brunskill, who report that the main part of the Top Marine Band is 10 ft 5 in thick and lies 632 ft 10 in from the surface and 346 ft above the Highmain Coal. It consists of dark mudstone from which Mr. M. A. Calver has identified the following fauna: foraminifera; Planolites ophthalmoides; Crurithyris sp., Lingula sp., Orbiculoidea sp.; Dunbarella sp.; Hollinella cf. bassleri; cf. Tomaculum sp. H. cf. bassleri is also recorded 23.25 ft higher, where it is associated with Curvirimula sp. The intervening measures, in which no marine fossils were observed, consist of grey silty mudstone and contain slump structures in parts. The Upper Coal Measures are largely argillaceous and are composed of about ten cycles, the majority of which have a few inches of coal; Anthraconauta phillipsii (Williamson) occurs at several levels. E.G.S. (in Birchhill and Glapwell Village boreholes), are about 90 ft thick at Manton Colliery four miles to the northeast (Edwards 1951, p. 208), but less than this in other eastern sections (ibid., p. 70). Birchhill Borehole proved 51 ft 8 in of Middle Coal Measures above the Shafton Marine Band (for details see Appendix 2, p. 296). The only fossils recorded are from 20 ft above the Shafton Marine Band at Birchhill. These consist of Naiadites cf. daviesi [juv.], Geisina subarcuata and fish remains including Diplodus sp. and Elonichthys sp. E.G.S.

Upper Coal Measures

The Upper Coal Measures have not been seen in the districtNote. Since going to press the Top Marine Band and 323 ft of Upper Coal Measures have been proved in Cauldwell Borehole [SK 5249 5855] south-west of Mansfield and on the north side of the fault through Sutton in Ashfield and Stonehills (see p. 191). The cores were examined by Messrs. J. G. O. Smart, N. Aitkenhead and S. Brunskill, who report that the main part of the Top Marine Band is 10 ft 5 in thick and lies 632 ft 10 in from the surface and 346 ft above the Highmain Coal. It consists of dark mudstone from which Mr. M. A. Calver has identified the following fauna: foraminifera; Planolites ophthalmoides; Crurithyris sp., Lingula sp., Orbiculoidea sp.; Dunbarella sp.; Hollinella cf. bassleri; cf. Tomaculum sp. H. cf. bassleri is also recorded 23.25 ft higher, where it is associated with Curvirimula sp. The intervening measures, in which no marine fossils were observed, consist of grey silty mudstone and contain slump structures in parts. The Upper Coal Measures are largely argillaceous and are composed of about ten cycles, the majority of which have a few inches of coal; Anthraconauta phillipsii (Williamson) occurs at several levels. E.G.S. and with the possible exception of Shirebrook Colliery sinking, where the supposed horizon of the Shafton Marine Band lies 66 ft below the base of the Permo-Trias, have not been penetrated by any shaft or borehole. Upper Coal Measures are, however, inferred to be present beneath Permo-Triassic rocks east of Langwith and north of Mansfield Woodhouse, and on the downthrow side of the north-westerly trending fault through Sutton in Ashfield and Stonehills. In the last-named area it is estimated that some 700 ft have been preserved. E.G.S.

But see note on page 99.

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