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Geology and hematite deposits of South Cumbria. Economic memoir for 1:50 000 geological sheet 58, and southern part of sheet 48

W. C. C. Rose and K. C. Dunham

Bibliographical reference:Rose, W. C. C. and Dunham, K. C. 1977. Geology and hematite deposits of South Cumbria. Econ. Mem. Geol. Surv. G.B., Sheets 58, part 48.

Contributors

• Stratigraphy W. B. Evans
• Palaeontology M. Mitchell, B. Owens and A. W. A. Rushton
• Petrography R. K. Harrison, N. G. Berridge and B. R. Young
• Geochemistry T. J. Shepherd

Geological Survey Of Great Britain England and Wales. Institute of Geological Sciences Natural Environment Research Council. London Her Majesty's Stationery Office 1977. © Crown copyright 1977. Printed in England for Her Majesty's Stationery Office by Ebenezer Baylis and Son Limited, The Trinity Press, Worcester, and London. ISBN 0 11 880780 3*

• Authors
• W. C. C. Rose, CBE, MSc 10 Park View, Hatch End, Middlesex
• Sir Kingsley Dunham, DSc, FRS Charleycroft, Quarryhead Lane, Durham DH1 2DY
• Contributors
• N. G. Berridge, PhD, W. B. Evans, BSc, NI. Mitchell, MA and B. Owens, PhD Institute of Geological Sciences, Ring Road Halton, Leeds LS15 8TQ
• R. K. Harrison, MSc, A. W. A. Rushton, PhD, T. J. Shepherd, PhD and B. R. Young, MSc Institute of Geological Sciences, London

(Front cover)

(Rear cover)

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

Books

• British Regional Geology: Northern England (4th edition)

Maps

• 1:625 000
• Sheet 2 Solid
• Sheet 2 Drift
• 1: 250 000
• Lake District (in press)
• Liverpool Bay (in press)
• 1: 50 000 (and one inch to one mile)
• Sheet 37 (Gosforth)
• Sheet 58 (Barrow-in-Furness)
• Sheet 66 (Blackpool)
• 1:25 000
• Dalton-in-Furness (in press)
• 1:10 560 See p. ix

Preface

This memoir describes the geology of the district covered by the 1:50 000 Sheet 58 and the southern part of Sheet 48; it also forms the explanation for the special 1:25 000 Dalton-in-Furness Sheet. The primary survey of one-inch sheets 48 and 58 was carried out in the years 1865–70 by W. T. Aveline and A. C. G. Cameron. The mining of hematite iron ore in the district was then coming up to its peak. T. Ainsworth, in Chemical News, No. 24, 1871, records an approach made by representatives of the industry to the Lord President asking for the continuation of work on the iron orefield by the geological surveyors. Their request was refused but some of the six-inch maps were subsequently published in 1879; they show the distribution of the solid and drift formations, but do not indicate the location of the ore deposits in relation to these. A short descriptive memoir by Aveline for one-inch Sheet 58 appeared in 1873, but no memoir was issued for one-inch 48. It was not until World War I, when the hematite field was already declining in importance, that the deposits were investigated, Dr Bernard Smith's Special Report appearing in 1919 and a second edition following in 1924.

It was plain from this report and from subsequent scientific controversy that many unsolved geological problems remained in the area, Smith's work having been limited by wartime exigencies. In 1937, output of hematite now having declined and many mines being closed, it was decided that the supply of this high-grade ore could be of critical importance. Mr W. C. C. Rose and Dr K. C. Dunham were therefore assigned to carry out a full resurvey of the iron orefield and the New Red Sandstone, under the direction of Mr Tom Eastwood, District Geologist. The two seasons 1937 and 1938 were devoted to the work in the field and during this time every accessible underground working was also visited. Manuscript maps had been prepared and an accompanying memoir was partly written when, in 1939, the approaching World War II necessitated their assignment to other tasks. Their conclusions on the chances of finding large new orebodies were by this time pessimistic, and the work was suspended, following the issue of a summary of its results in Wartime Pamphlet, No. 16 (1941). Resumption of the writing-up after the war was not practicable.

Sir Kingsley Dunham, when Director, wrote as follows: 'Mining came to an end with the closing of Hodbarrow Mine in 1968. Nevertheless I decided to bring the investigation to fruition for three reasons: that an offshore area still has potential for exploration; that the results of the survey could give other practical aids to this fast-developing area; and that geologically the district is one of high scientific interest for, not only are the ore occurrences unique, but the Lower Palaeozoic, Carboniferous and Permo-Triassic rocks are all of much interest.

The opportunity to have Mr Rose back with the Geological Survey after he had completed his service with the Ministry of Power in 1968 was therefore eagerly welcomed. He has extended our work into the Lower Palaeozoic outcrops and has brought up to date the mapping of the younger rocks. The memoir is largely his work.

'We have benefited from having Mr W. B. Evans, District Geologist, North-West England, as editor; his knowledge of the saliferous formations has contributed significantly to the work. Dr E. H. Francis has also given expert advice on the petrography and field relationships of the Ordovician volcanic rock deposits. The palaeontology of the Carboniferous rocks, a formidable task in this highly fossiliferous area, was begun by Sir James Stubblefield but has been carried out mainly by Mr Murray Mitchell, with some help from Dr W. H. C. Ramsbottom and Dr B. Owens. Work on the Lower Palaeozoic faunas has been largely the responsibility of Dr A. W. A. Rushton, with specialised assistance from Dr P. T. Warren, Dr R. B. Rickards, Professor D. Skevington and Dr C. Downie. Much of the field collecting was done by Mr J. Pattison and Mr M. J. Reynolds, and Mr Pattison also dealt with the Permian faunas. Petrographical descriptions are by Mr R. K. Harrison, Chief Petrographer, and Dr N. G. Berridge. Geochemical data are contributed by Dr T. J. Shepherd, and X-ray data by Mr B. R. Young.'

'I wish to express my gratitude for the manner in which the mining companies at the time of the resurvey made all their data available; particularly I wish to mention Major Barratt and Mr R. B. Davies of the Hodbarrow Mining Company, Colonel Hugh Kennedy and Mr Severs of Kennedy Brothers Ltd, Mr Cornwall of Beardmore's Ltd, the Millom and Askam Haematite Iron & Steel Co. Ltd, the Barrow Haematite Steel Co. Ltd, Broughton Estates Ltd, Holker Estates Ltd, Lowther Estates Ltd and Muncaster Estates Ltd. The Barrow Naturalists Field Club has also helped during the study.'

'Since 1970 four boreholes have been drilled for the Institute within the district. The deepest of these, at Roosecote, was supervised by Dr N. Aitkenhead and Mr R. S. Arthurton, who have published a summary of its log and will shortly be producing a full account of their work. We have drawn heavily on their results.'

'Mr Rose has also received particular help in the field from Mr W. Grieve of Ulverston, Mr Eric Holland of Stainton and Mr H. Kellett of Dalton to whom our thanks are due.'

Austin W. Woodland. Director Institute of Geological Sciences Exhibition Road London SW7 2DE, 1 October 1976

Six-inch maps

The following list shows the six-inch maps included wholly or partly within the area of Sheet 58 (Barrow) of the Geological Map of England and Wales and the resurveyed portion of Sheet 48 (Ulverston). All the maps are on National Grid lines, lying within 100 kilometre square SD. Uncoloured dyeline copies of all the six-inch sheets, except for those indicated by an asterisk, will be available shortly from the Institute's office at Leeds, and will be available for public reference at that office and at the Geological Museum in London. The surveyors were K. C. Dunham and W. C. C. Rose.

Notes

• The Institute has adopted international practice in the spelling of haematite: it is therefore spelled hematite throughout this memoir.
• All grid references refer to National Grid square SD.
• Colour codings given in the Rock Color Chart published by the Geological Society of America are used throughout.
• Letters preceding specimen numbers refer to Institute collections as follows:
• SAL Palynology, Leeds
• E English sliced rock
• X X-ray powder film, London
• DX X-ray diffractometer trace, London
• LZ Leeds presentation series
• MI Mineral, London

Geology and hematite deposits of South Cumbria—summary

Younger Ordovician, Silurian, Carboniferous and Permo-Triassic rocks crop out in rudely parallel belts that sweep around the highland core of Cumbria. The Carboniferous limestones, both in the west around Egremont and on the shores of the Duddon, acted as hosts to massive deposits of hematite that nurtured an iron and steel industry of considerable national importance.

The present work deals with the southern of these two mining districts which, although now abandoned, once extended eastwards from Millom to Ulverston. The stratigraphy and palaeontology of the Carboniferous limestones are dealt with in detail. The underlying Lower Palaeozoic rocks and the overlying Permo-Triassic ones are also fully described.

Particular attention is given to the form and nature of the orebodies, the account up-dating and supplementing earlier ones. Of special interest are the descriptions of the sops east of the Duddon, since nowhere else in Britain are there orebodies of this type. The controls of mineralisation are fully enumerated and discussed, and the authors advance a provocative theory to explain the origin of the hematite.

Geological succession

The formations represented on the 1:25 000 and 1:50 000 maps and sections are summarised below:

Chapter 1 Introduction

Geography

The old iron-ore mining district of South Cumbria lies on either side of the estuary of the River Duddon, which drains the south-western part of the Lake District. This memoir is primarily a description of the geology of the orefield, but the proper understanding of this demands attention not only to the Carboniferous rocks which contain the hematite, but also to the Lower Palaeozoic basement upon which these rest and to the Permo-Triassic and Quaternary cover. It was also considered desirable to include the Cark–Cartmel district east of the estuary of the River Leven, where there were a few iron ore prospects. West of the Duddon, the Millom area includes a short stretch of the coast and the low-lying ground south and south-east of Black Combe. Neither the Skiddaw Slates which form the Combe nor the Borrowdale Volcanic Group of Millom Park are, however, included in this account. East of the Duddon Estuary, the northern boundary is, more or less, the boundary between High Furness, that part of the Lake District formerly lying within Lancashire, and the peninsula of Low Furness. The district thus includes Askam, Ireleth, Greenodd, and the southern part of the high ground of Kirby Moor, High Haume and the hills behind Ulverston, ranging up to about 250m above sea level. An account of the Ordovician and Silurian rocks of these uplands is included, as well as a description of the geology of the whole of the lower part of the peninsula. On the east side of the Leven Estuary a number of masses of Carboniferous Limestone project through the marine alluvium and drift. Silurian rocks forming the high ground to the east of the Haverthwaite–Cark road are succeeded along a NNE line through Cartmel by Carboniferous Limestone. This latter also crops out prominently at Humphrey Head overlooking Morecambe Bay, and the eastern margin of the district is drawn beyond Grange-over-Sands and Lindale, where another outcrop of Silurian rock is faulted against Carboniferous Limestone.

The hills underlain by Lower Palaeozoic rocks, mainly slates and greywackes, have smoothly rounded outlines but in detail, especially above Ulverston and Greenodd, they contain many small craggy outcrops. In part pleasantly wooded, they also provide upland pastures. Between Cartmel and Grange-over-Sands, Carboniferous Limestone outcrops produce extensive pavements of grikes, and this is also true in Furness around Urswick and Birkrigg Common.

Good cliff-sections in these limestones are found along the east shore of the Leven Estuary as well as at Humphrey Head. The lower ground, especially in the Furness peninsula, has been given a definite grain by large numbers of drumlins of boulder clay, which march regularly in a general southward direction, their higher ends facing north.

They produce good agricultural land, as do the extensive areas of marine alluvium along the east sides of the two estuaries.

The old mines lie near Millom, where a sea-wall was built to facilitate working under the sands of the Duddon, and thence swing round from Askam and Roanhead through Dalton in a belt 3 to 4 km wide reaching almost to Ulverston. The remains of the workings are fast disappearing into the landscape. Dumps, chiefly of limestone, are being covered with vegetation, and the subsidences, where great hematite orebodies have been extracted, now contain ponds and small lakes that cover once unsightly waste. Few mining buildings remain. The old country towns of Ulverston, Millom and Dalton have seen the mining and smelting industry come and go; they have grown in response to it, but probably without greatly changing in character. The industry did, however, give rise to one major town. At the southern tip of the peninsula, Barrow-in-Furness in 1850 was a fishing village with only a few houses; thirty years later it had become a thriving port and, growing out of the smelter and steelworks, there is now a major shipbuilding and engineering industry, largely situated on Barrow Island. Walney Island, the long narrow island of boulder clay and other Quaternary deposits which shelters the coast from the Irish Sea, has now been partly developed as a holiday resort. A comparison of the 1:10560 map of 1852 with the recent editions shows how greatly the erection of Barrow with its docks and made-ground has modified the former topography; while for the coast of Walney it reveals that in places at the south end as much as 150m has been lost to coastal erosion in a century.

Almost concealed from the world in the Vale of Nightshade, the great Cistercian Abbey, founded by monks from Savigny in 1147, was the centre of spiritual and temporal power for a wider region than Low Furness until the Dissolution in the 16th century. Conishead Priory, the great house on the east coast south of Ulverston, was originally a religious foundation.

Three kinds of building stone were widely used before the coming of the now ubiquitous brick. The red St Bees Sandstone is seen to best advantage in the ruins of Furness Abbey and in the Town Hall at Barrow. White and pale grey Carboniferous Limestone is often combined with sandstone cornerings, while the quarries in bluish grey slate and green volcanic ash along the Duddon Valley provided the roofs.

History of mining

From the discovery of two hand-axes of presumed Neolithic age beside a face of hematite in an old working near Stainton (Tweddel, 1876), it is supposed that pre-Roman Britons first worked the red ore. Certainly human occupation was well established in the district by Mesolithic times, when flint-implement makers left their flakes behind at the northern end of Walney Island. Of Roman mining we have no evidence and the first records come from late mediaeval times, when the records of Furness Abbey begin. According to J. D. Kendall (1885a, 1893), there is a record of 1235 telling of a dispute between Henry of Orgrave and the Abbot about iron ore from a mine that can still be identified between Dalton and Ireleth. Alinscales (Elliscales) belonged to the Abbey in 1282, and in 1400 the mines at Dalton, Orgrave and Merston (Marton) were taken over. In the reign of King Edward II (1307–27) William de Lancaster granted ore at Plumpton to the Priory of Conishead. By the Dissolution in 1537 a serious scarcity of timber had developed owing to the inroads of the smithies that made iron by smelting with charcoal, and later on there are records that hematite was shipped to West Scotland, where timber was more plentiful. There is no doubt that availability of charcoal held back the development of the field until the 19th century, when smelting with coke was introduced. Nevertheless, Speed's map of 1745 shows a furnace on the Duddon, and in 1750 four furnaces in Furness made 580 tons of pig iron between them. According to Nicholson and Burns (1777) mining had already begun at Millom. Pennant (1790) mentions extensive mining at Whitriggs in 1772 and refers to 'immense beds of ore beneath pintel and limestone'. This is probably the first printed reference to the local name, pinnel, for glacial drift. Whitriggs, 'the Peru of Furness', was followed by developments at Crossgates and Lindal Moor; at the latter the firm of Harrison Ainslie was already established by 1824. The building of the Furness railway in 1846 from Piel to the mines gave a huge impetus to production, and when in 1857 the link to Carnforth was completed, permitting Durham coke to be brought in, Mr Schneider, founder of the Barrow Haematite Steel Cornpany, had sufficient confidence to erect his major blast furnace and steelworks at Hindpool, Barrow. He was fortified in this decision by his discovery in 1849 of the Park orebody [SD 213 754], the largest in the district (in discussion on Shaw, 1880, p. 377). At the time of the opening of the railway, output had reached 180 000 tons of hematite; by 1868 it was four times as much, and the million tons mark was passed in 1880. The particular suitability of the ore for the Bessemer process of steelmaking stimulated demand. Hodbarrow was already a large mine by the middle of the 19th century and, by the same time, the Kennedy family had appeared in the western part of Furness, working the smaller part of the Park deposit. The discovery of two more major deposits, Rita [SD 207 752] and Nigel [SD 203 755], lay ahead of Kennedy Brothers Ltd. Production from Park rose to over 300 000 tons by 1881 but had fallen back to less than 100 000 in 1917, and the deposit was exhausted before the end of World War I, having yielded about 17 million tons. The Nigel deposit, still operating at the time of the resurvey, was finally exhausted in 1950. Hodbarrow then remained the only operating mine, closing as recently as 1968 and probably producing over 25 million tons. In a little over a century of main activity, the orefield had yielded approximately 80 million tons of ore.

The highly irregular nature of the deposits led to a special method of mining which has gone into the mining textbooks under the name of top-slicing. The ore was worked from the top downwards, from shafts sunk in the limestone clear of the orebodies. In the sop orebodies, the top slice, taken 2.75m high under the boulder clay or sound roof, was very heavily timbered. Extracted on the retreat, the removal of the ore caused the collapse of the timber roof, forming an interlocked mat beneath which lower slices were systematically removed, each level subsiding in its turn. The external result was a conical depression but a very high proportion of the orebody, whatever its shape, was recovered. At Hodbarrow, which had special problems owing to the proximity of the estuary, a sand-filling method was eventually adopted in place of top-slicing, while in a few of the veins of the field normal stoping practice proved to be possible.

Mining activity has thus ended, but the several square kilometres under the Duddon Estuary between the Hodbarrow sea-wall and Askam–Roanhead, lying in the main path of the mineralised belt, remain unexplored save for a few boreholes (Shaw, 1903). If the field has any future to match its distinguished past, this is where it most probably lies (p. 115).

Previous research

The principal contributors to geological research in South Cumbria are listed here, but discussion of their work will be found in the appropriate detailed chapters. Sedgwick (1836), on the New Red Sandstone, has pride of place. E. W. Binney (1847, 1855, 1868) follows with the first accounts of the ore deposits, advocating their volcanic origin. Murchison and Harkness (1864) developed the Permian succession. G. C. Greenwell (1865–66) described the Askam deposit. P. Wurzburger (1872) laid much stress on the structural importance of the Haume anticline. J. D. Kendall, who for nearly half a century was to be the most influential geologist in West Cumberland and Furness, published his first paper in 1875; others followed in 1882, 1885, 1886, 1920, and his book in 1893. His outstanding contribution was the proof of the large-scale metasomatic emplacement of the hematite. J. Bolton (1862) and Miss E. Hodgson (1863) record what may be an interglacial peat from Lindal Cote water-level. Bolton's book (1869) preserves interesting details of the hematite deposits then being worked. W. T. Aveline (1873) described the southern part of the peninsula. J. L. Shaw (1880) proposed that the iron for the hematite came from Lower Palaeozoic sources; J. G. Goodchild (1889–90) was the first to connect it with New Red Sandstones, while Hudleston (1889–90) derived it from 'the reddened waters of the Permian Sea'. Schneider (1884–85) and Kendall (1881–82) both published maps showing the distribution of the deposits, which were not indicated on the primary map of the Geological Survey (One-inch sheets 48 and 58). In one of the few early papers on the stratigraphy of the Carboniferous in the district, Kendall (1885b) proposed that the continuous limestone succession of Furness was the equivalent of the Sixth and Seventh limestones of West Cumberland, and that the overlying rocks correlated with the Yoredales of the Pennines. J. E. Marr and H. A. Nicholson (1888) described the Stockdale Shales, and Marr (1892) the Coniston Limestone Series in the district. Marr (1916) and J. F. N. Green (1913) were among those involved in the controversial question of the relationship of the Coniston Series to older strata, the latter publishing the only detailed map of Greenscoe Craggs previous to the present study. Works of fundamental importance on the stratigraphy of the Carboniferous were contributed by E. J. Garwood (1913, 1916). B. Smith (1919, 1924) produced the authoritative report on the hematite ores in their geological setting, and we have summarised the results of our resurvey (1941). E. G. Holland (1962) and Harris (1970) placed data on Hodbarrow Mine on record and we have described the Permo-Triassic rocks (1944). The latest contributions, by Gresswell (1962) and Grieve and Hammersley (1971), deal with the glacial and recent succession; and there is an account of a Yorkshire Geological Society visit in 1970 (Dunham and Rose, 1971).

Outline of geological history

When the Skiddaw Group began to accumulate, what is now Britain formed part of a trough—the Caledonian Geosyncline—that on present-day ideas separated the incipient continental masses which have become Europe and Greenland–North America. The bottom environment was probably stagnant, preserving carbonaceous matter from oxidation, the principal living creatures being floating organisms particularly the graptolites. After the black mud had become consolidated, volcanic rocks, probably connected with the Borrowdale episode of late Llanvirn or Llandeilo times, broke through. This event was followed in still later Ordovician times by folding, uplift and extensive erosion before another inundation beneath the waters of the trough–at first shallower than before—permitted a neritic fauna to develop and, in areas free from mud or sand, limestone to be deposited. Some volcanic activity still continued. Without a break, continued subsidence in Silurian times deepened the trough as it received an immense load of mud, silt and sand from neighbouring mountains undergoing erosion. Turbidity currents moved flows of fine sand and mud; and, particularly in the later Ludlow period, dispersion of the sediment in deep water produced graded bedding, the coarser material having settled out more rapidly than the finer. Conditions were unfavourable for life, no doubt because of the fast-moving sediment; the few organisms preserved are chiefly remains of graptolites that floated near the ocean surface. Well over 7000m of sediment accumulated during the period to 400 million years BP, compressing and consolidating the buried mass until eventually the major earth movements of the Caledonian orogeny produced the broad folds, with many sharp minor folds, that we now see. A slaty cleavage was imposed by these movements. Throughout the succeeding epoch (the Devonian) the Lower Palaeozoic sediments formed part of a mountain chain undergoing erosion.

Sedimentation was resumed in Lower Carboniferous times, roughly 350 million years ago. By this time a depression or valley had been cut along the site of the present Duddon Valley. Torrent-deposits from the nearby mountains formed conglomerates containing pebbles and boulders of Borrowdale lavas and slaty rocks. These deposits interdigitated with mud (now shale) laid down in a shallow sea, while beds of impure limestone began to form offshore. As these Basement Beds built up to over 200m thick, they began to submerge the nose of the Stewnor Anticline, and to spread towards the site of present Ulverston. Subsidence followed and the supply of clastic sediment greatly decreased; shallow warm shelf seas became established and persisted for perhaps 20 million years. At first, algae were prominent, and the finely comminuted calcite mud from their disintegration produced the Martin Limestone. For a while, calcitic pellets drifted about the sea floor while mollusca flourished, and the Red Hill Oolite accumulated.

Calcareous mud, dark with carbon, now began to arrive intermittently but, after a long period during which the Dalton Beds formed, the supply was suddenly cut off and a clear sea with many invertebrate organisms provided the conditions for the Park Limestone, and changed only to the extent that occasional influxes of greenish mud arrived when the Urswick Limestone was forming. Corals and brachiopods were now abundant. Lower Carboniferous times terminated with the approach towards Furness of the outer edge of the great Yoredale delta which lay across what is now north and north-eastern England and parts of Scotland. The rhythmic advances and retreats of this feature had long since begun to produce the cyclothemic sequences that commence low down in the Viséan or even in the Tournaisian in Scotland and Northumberland, and that mark the successive advances of the front of the delta to the Craven country and Yorkshire before later Viséan and early Namurian times. It may well be that in Furness we have the westward continuation of the interfaces between open-sea deposits, pro-delta muds, and the rhythmic alternations of the delta front. In the Namurian pro-delta, mud with a few sand incursions was the dominant sediment. No record of Westphalian–Stephanian (Coal Measures) times remains, but these Series probably extended over the district and were removed after the late-Carboniferous uplift and faulting. Considerable erosion now ensued, laying bare the limestone surface much as we now see it in South Cumbria.

Towards the end of Carboniferous times the coal-forming swamps gave place to conditions favouring a widespread development of red laterite soils. Iron, already concentrated in ferrous form in the Westphalian swamps, now became still further concentrated in the laterites and it is suggested that the lateritic material remained available from adjacent land throughout the long period during which shallow marine, playa, sabkha and fluviatile conditions prevailed in Permian and Triassic times, resulting in the widespread red colouration of these rocks. Like the Carboniferous, the Permian opened with torrent breccias, though these may be terrestrial rather than marine. The Magnesian Limestone episode represents an incursion of the land-locked Zechstein lagoon, the first deposits in which were the Kirksanton Grey Beds in this district. Offshore, anhydrite was being deposited. Muddy flats followed, and then the sandy alluvium of a great river running through desert country formed the St Bees Sandstone. Marine lagoons received the red, and occasionally green, mudstones of the 'Keuper', and there was, as in the Preesall and Cheshire areas, a prolonged period when salt was laid down.

Jurassic rocks may have covered the district, Cretaceous rocks almost certainly did, but neither remains today. At some stage or stages in Mesozoic or Tertiary times, earth movements produced a linked series of NW–SE and W–E faults, some of which displace Triassic rocks. These, in conjunction with solution features that may have developed previously on the pre-Permian erosion surface became the channels through which hypersaline formation-waters moved, bringing in great quantities of iron which were deposited as hydroxide and oxide. The period of mineralisation had a definite term to it, and had been concluded before erosion re-exposed the old Permian land surface, probably in later Tertiary times. In the Quaternary at least two advances of ice occurred, the first probably enclosed englacial streams which deposited well-sorted sands; later on, sand and gravel deltas formed on top of the boulder clay left by the ice, and these were in turn briefly overridden by another advance of the ice. Considerable changes in sea level accompanied the glaciation, in part due to removal of ocean water to augment the polar ice caps, in part due to depressions of the continents by superincumbent ice. There is evidence of a stand at about 25m below present sea level, but lower levels were probably reached. In interglacial stages, and immediately after the final retreat of the ice, intense rainfall probably stimulated cavernisation in the Carboniferous Limestone that post-dates the hematite mineralisation. K CD

References

AVELINE, W. T. 1873. Geology of the southern part of the Furness district in North Lancashire. Mem. Geol. Surv. G.B.

BINNEY, E. W. 1847. A glance at the geology of Low Furness, Lancashire. Mem. Lit. Philos. Soc. Manchester, 2nd Ser., Vol. 8, pp. 423–445.

BINNEY, E. W. 1855. On the origin of ironstones. Mem. Lit. Philos. Soc. Manchester, 2nd Ser., Vol. 12, pp. 31–45.

BINNEY, E. W. 1868. On the age of the haematite iron deposits of Furness. Mem. Lit. Philos. Soc. Manchester, Vol. 7, pp. 55–61.

BOLTON, J. 1862. On a deposit with insects, leaves, etc. near Ulverston. Q. J. Geol. Soc. London, Vol. 18, pp. 274–277.

BOLTON, J. 1869. Geological fragments collected principally from rambles among the rocks of Furness and Cartmel. Ulverston and London. 264 pp.

DUNHAM, K. C. and ROSE, W. C. C. 1941. Geology of the Iron-ore field of south Cumberland and Furness. Wartime Pamphlet Geol. Surv. G.B., No. 16.22 pp.

DUNHAM, K. C. and ROSE, W. C. C. 1949. Permo-Triassic geology of South Cumberland and Furness. Proc. Geol. Assoc., Vol. 60, pp. 11–37.

DUNHAM, K. C. and ROSE, W. C. C. 1971. Field meetings: Ulverston 3rd-6th July 1970. Proc. Yorkshire Geol. Soc., Vol. 38, pp. 429–433.

GARWOOD, E. J. 1913. The Lower Carboniferous succession in the North-West of England. Q. J. Geol. Soc. London, Vol. 68, pp. 449–589.

DUNHAM, K. C. and ROSE, W. C. C. 1916. The faunal succession in the Lower Carboniferous rocks of Westmorland and North Lancashire. Proc. Geol. Assoc., Vol. 27, pp. 1–43.

GOODCHILD, J. D. 1889–1890. Some observations upon the mode of occurrence and the genesis of metalliferous deposits. Proc. Geol. Assoc., Vol. 11, pp. 45–69.

GREEN, J. F. 1913. The older Palaeozoic successions of the Duddon Estuary. London. 23 pp.

GREENWELL, G. C. 1865–66. On the haematite mines of the Ulverston district. Trans. Manchester Geol. Soc., Vol. 5, pp. 248–252.

GRESSWELL, R. K. 1962. The glaciology of the Coniston Basin. Liverpool Manchester Geol. J., Vol. 3, pp. 83–95.

GRIEVE, W. and HAMMERSLEY, A. D. 1971. A re-examination of the Quaternary deposits of the Barrow area. Proc. Barrow Nat. Field Club, (New Series) Vol. 10, pp. 5–25.

HARRIS, A. 1970. Cumberland Iron: the story of Hodbarrow Mine 1855–1968. Truro. 122 pp.

HODGSON, E. 1863. On a deposit containing diatomacea, leaves, etc. in the iron ore mines near Ulverston. Q. J. Geol. Soc. London, Vol. 19, pp. 19–31.

HOLLAND, E. G. 1962. Hodbarrow mines, Cumberland. Min. Quarry Eng., Vol. 28, pp. 220–227.

HUDLESTON, W. H. 1889–90. Geological History of Iron Ores. Proc. Geol. Assoc., Vol. 11, pp. 104–144.

KENDALL, J. D. 1875. The haematite deposits of Whitehaven and Furness. Trans. Manchester Geol. Soc., Vol. 13, pp. 231–283.

KENDALL, J. D. 1876. Haematite in the Silurians. Q. J. Geol. Soc. London, Vol. 32, pp. 180–183.

KENDALL, J. D. 1881–82. The haematite deposits of Furness. Trans. North Engl. Inst. Min. Mech. Eng., Vol. 31, pp. 211–237.

KENDALL, J. D. 1885a. Notes on the history of mining in Cumberland and North Lancashire. Trans. North Engl. Inst. Min. Mech. Eng., Vol. 34, pp. 83–124.

KENDALL, J. D. 1885b. The Carboniferous rocks of Cumberland, N. Lancashire and Furness. Trans. North Engl. Inst. Min. Mech. Eng., Vol. 34, pp. 125–136.

KENDALL, J. D. 1893. Iron ores of Great Britain and Ireland. London. 430 pp.

KENDALL, J. D. 1920. Lateral distribution of metallic minerals. Min. Mag., Vol. 23, pp. 75–80.

MARR, J. E. 1892. The Coniston Limestone Series. Geol. Mag., Dec. III, Vol. 9, pp. 97–110.

MARR, J. E. 1916. The geology of the Lake District and the scenery as influenced by geological structures. Cambridge. xii + 220 pp.

MARR, J. E. and NICHOLSON, H. A. 1888. The Stockdale Shales. Q. J. Geol. Soc. London, Vol. 44, pp. 654–732.

MURCHISON, R. I. and HARKNESS, R. 1864. On the Permian rocks of the North-West of England, and their extension into Scotland. Q. J. Geol. Soc. London, Vol. 20, pp. 144–165.

NICOLSON, J. and BURN, R. 1777. History and antiquities of the counties of Westmorland and Cumberland.

PENNANT, T. 1790. A tour in Scotland. London.

SCHNEIDER, H. W. 1884–85. On the haematite iron mines of Low Furness. Trans. Cumberland Assoc., No. 10, pp. 99–108.

SEDGWICK, A. 1836. On the New Red Sandstone in the basin of the Eden and north-western coasts of Cumberland and Lancashire. Trans. Geol. Soc. London, 2nd Ser., Vol. 4, pp. 383–407.

SHAW, J. L. 1880. The haematite iron mines of the Furness district. Proc. Inst. Mech. Eng., pp. 363–369.

SHAW, J. L. 1903. The probability of iron ore lying below the sands of the Duddon estuary. J. Iron Steel Inst., No. 2, pp. 197–205.

SMITH, B. 1919. Iron ores: Haematites of West Cumberland, Lancashire, and the Lake District. Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B., Vol. 8. iv + 182 pp.

SHAW, J. L. 1924. Iron ores: Haematites of West Cumberland, Lancashire, and the Lake District. Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B., Vol. 8, 2nd edition.

SMYTH, W. W. 1856. The iron ores of Great Britain. Part 1-The iron ores of the north and north-midland counties of England. Mem. Geol. Surv. G.B.

TWEDDEL, G. M. 1876. Furness Past and Present. Ulverston.

WURZBURGER, P. 1872. The haematite iron ore deposits of Furness. J. Iron Steel Inst., No. 1, pp. 135–142.

Chapter 2 Ordovician rocks

Skiddaw Group

During the Primary Survey rocks called 'the Blue Shale' by the hematite miners, and known to underlie much of the drift-covered ground between Askam and Greenscoe, were correctly referred to the Skiddaw Slates (now Skiddaw Group). Most of the provings have been in boreholes and mines. Natural exposures are few, but there are extensive sections in Askham Shale Quarry, Park Farm [SD 218 755], between Dalton and Askam. The mudstones of the Skiddaw Group are a satisfactory raw material for brick-making after crushing, although selective quarrying is necessary to exclude sporadic veins and strings of quartz. In recent years increasing overburden and the presence of intrusive volcanic rocks have hampered quarrying.

The quarry exposes a uniform mass of relatively soft mudstones, containing some clastic mica, but little or no quartz silt and no sandy beds. A full petrographic description of specimens from the faces, together with a chemical analysis are given respectively on p. 11 and in (Table 2). When freshly exposed the mudstones are almost coal-black, but many pyritic inclusions give rise to deep ferruginous stains on weathering. In places a faint lamination is apparent but strong cleavage, intense crushing and minor contortions all combine to make it difficult to determine the general dip, though this appears to be south-easterly at a steep angle. The crushing is accompanied in places by the injection of secondary quartz stringers. Faunas have been recorded from two of the faces, and have been determined by Professor D. Skevington. One quarry [SD 2175 7540] yielded Glyptograptus dentatus (Brongniart), Climacograptus sp. cf. C. tailbertensis Skevington, ?Cryptograptus sp., Didymograptus sp., ?D. euodus Hopkinson & Lapworth, D. sp. cf. D. hirundo Salter, together with a phyllocarid crustacean. The other [SD 2185 7550], produced the following assemblage: Didymograptus acutidens Elles & Wood, D. simulans Elles & Wood, D. sp.ex gr. affinis Elles & Wood, Glyptograptus dentatus, G. sp., ?G. shelvensis Bulman. Professor Skevington comments that, taken collectively, the specimens are most probably indicative of the Didymograptus hirundo Zone, the highest in the Arenig, and that the faunal list agrees closely with those of Jackson (1961, 1962) from the upper part of the Mosser–Kirkstile Slates of the Keswick area.

Much of the outcrop north of Greenscoe Craggs is drift-covered, but the mudstones are exposed in four small stream-sections [SD 2231 7618] to [SD 2234 7617]; [SD 2226 7650] to [SD 2255 7662]; [SD 2242 7704]; and [SD 2230 7762]. A rich microfaunal assemblage (SAL 1334) was obtained from a small exposure [SD 2319 7775] at Hare Slack Hill and has been identified by Dr C. Downie as follows:

Acritarchs

Baltisphaeridium aff. breviciliatum Martin, B. multipilosum (Eisenack), B. hirsutoides (Eisenack), B. suecicum? Eisenack, B. lucidum (Deunff), Micrhystridium radians Martin, M. shinetonense Downie, M. raspa Martin, M. spp., Hystrichosphaeridium' ? aff. longispinosum Eisenack 1951 (pl. 3, fig. 6), Veryhachium lairdi Deflandre, V. trisulcum Deunff, V. trispinosum Eisenack, V. valiente Cramer, V. cf. quietum Martin, V. sartbernardense Martin, Leiofusa sp., ?Deunffia sp., Peteinosphaeridium breviradiatum (Eisenack), P. paucifurcatum (Eisenack), Acanthodiacrodium cf. seratinum (Timofeev) Deflandre & Deflandre-Rigaud, A. cf. augustizonalis Burmann, Leiospheres, Synsphaeridium sp.

Chitinozoa

Conochitina chydea Jenkins, C. oelandica Eisenack, C. cf. lepida Jenkins, C. cf. simplex Eisenack, Cyathochitina calix Eisenack, Rhabdochitina turgida Jenkins. Two shallow trenches [SD 2204 7567]; [SD 2266 7636], dug to assist the mapping, produced poorer, but similar, assemblages. Dr Downie considers the three faunas to be roughly contemporary, to be indicative of a Llanvirn age, and probably to come from the D. bifidus Zone, the lowest in the Llanvirn, or from the D. murchisoni Zone. They are thus probably younger than the mudstones in Askham Shale Quarry.

The Skiddaw Group ('Blue Shale') has been proved in the footwall of the main branch of the Park–Yarlside Fault.

System near Park Sop to a depth of −256m OD, while in the Askam–Park Knott and Ireleth–Dunnerholme areas many old boreholes have recorded 'slate rock' or 'blue slate', interpreted as mudstones of the Skiddaw Group, beneath Lower Carboniferous strata.

Volcanic neck deposits

During the Primary Survey outcrops of cleaved ashes and hard porphyritic rocks were identified, and interpreted as the representatives of the 'Borrowdale Volcanic Series'. Their junctions with the Skiddaw Group were believed to be everywhere faulted, though at that time the only relevant exposure was in Hole Gill, Ireleth, a section which subsequently gave rise to much controversy. The junction was also thought to be faulted by Marr (1900), but Green (1913), relying partly on the then new section in Askham Shale Quarry, believed it to be conformable, maintaining that the 'blue shale' was interbedded with 'mottled shale', and that the latter was the basal tuff of the Borrowdale Group. In more recent years Greenscoe Quarry was opened for road-metal in the volcanic rocks at Greenscoe Craggs, and Askham Shale Quarry has been extended and has proved further volcanic outcrops. These sections show that most of the contacts between volcanic rocks and the Skiddaw Group mudstones are nearly vertical, and the former have been interpreted as 'vent fillings' (Soper, 1970). The results of the resurvey are in broad agreement with this view, though the term 'neck' is preferred, because it does not imply a void at any formational stage or erosional level, but does allow both for fluidisation structures formed during emplacement phases and for collapse structures in post-eruptive phases. Several smaller outcrops are believed to be remnants of smaller necks, also intrusive into Skiddaw Group mudstones.

Agglomerates, fluidised tuffs and andesites are intimately associated within the necks, the incorporated clasts in the pyroclastic rocks being a mixture of andesites, tuffs and Skiddaw Group mudstones (Plate 2.1). Towards the steeply inclined margins of the necks the amount of incorporated mudstone in the tuffs steadily increases; tuffaceous breccias derived from disintegration of the neck-wall result, and pass outwards into Skiddaw Group mudstones. Near the neck-margins highly inclined sheets of andesite are common; they are bleached and contain much carbonate along their contact with the wall-rock. These sheets, the fluxion-banding locally developed in the tuffs, and the general orientation of the larger clasts in the pyroclastic rocks, are all rudely parallel to the steep contacts with the country rock, which are also in places faulted. A few more massive andesites may be extrusive flows, but their relationships to the neck-deposits are obscure.

All these features are typical of volcanic necks (Francis and Hopgood, 1970). The tuffaceous breccias represent the initial effect of a gas-fluxion process on the neck-wall, which fractured and was permeated by a tuffaceous gas stream rising under pressure in advance of an andesite magma column. Mudstone lenses and bands were stopedoff the neck-wall and incorporated in fluidised tuffs. Irregular intrusions of andesite magma into tuffs followed; some of these were along the neck-wall, probably a line of weakness, and so were intrusive partly into country rock and partly into tuffs. The common alignment shown by these sheets, by the fluxion-banding and by the clasts is probably an original feature, though this is unproven because the end-Silurian cleavage has a similar dip and affects all the deposits other than the andesites and andesitic clasts. Some of the larger andesitic bodies may have consolidated within the neck; others may have been extrusive and may have foundered to their present positions through cauldron-type subsidences.

The petrographic characteristics of the andesites make it likely that these necks represent some of the feeders to the lava flows and tuffs of the Borrowdale Volcanic Group. Nevertheless it seems undesirable to classify them with that Group, for they represent levels well below the extrusive surface. The intermixture of lithologies is so intimate that the entire suite has been classed as volcanic neck deposits on the published sheets. WCCR

Details

Greenscoe Craggs

An outcrop of volcanic rocks has been dug into extensively at the Greenscoe Quarry [SD 222 760]. It is roughly elliptical in shape with a long-axis of about 550 m aligned NE–SW; its south-eastern margin is partly truncated by faulting. The main rock types exposed are agglomerates, andesitic and rhyolitic fluidised tuffs, intrusive andesites and volcanic breccias. Their broad distribution is shown in (Figure 1), together with a horizontal section through the neck.

The coarser agglomerates are restricted to a roughly circular area centred about the main quarry, where they are associated with ill-defined masses of fine-grained agglomerates and fluidised tuffs together with some small andesitic intrusions. The pyroclasts of the agglomerates are a mixture of cognate andesites and tuffs and accidental fragments of the bluish grey mudstones of the country rock, set in a matrix of fine-grained andesitic lapilli-tuff which in places includes much comminuted mudstone. The larger clasts of dark green andesites and paler buff-coloured tuffs are mostly subangular or subrounded in shape and vary greatly in size, the largest being 3 m long (see (Plate 2.1)). The andesite clasts probably represent the cognate magma of a late eruptive phase that has been fragmented in the molten state and rapidly chilled in a fluidised gas stream. The mudstone clasts are usually much smaller than the andesites but lengths of over 1 m have been recorded; they are very like the cleaved Skiddaw mudstones of the neck-wall and were evidently derived from it, although probably from levels deeper than those now exposed. They show traces of induration, and include some pale green spots (up to 3 mm) which, under the microscope (E39094), prove to be inclusions of magmatic material. These mudstone clasts carry a strong, post-incorporation cleavage; the andesite clasts do not. In many places the clasts show a marked alignment, dipping steeply south-eastwards; this can be well seen in a rock face near the entrance to the main quarry where the dip of the alignment is 70° south-east. Although this direction is approximately parallel to the regional cleavage the alignment of large uncleaved andesite clasts in the agglomerate seems more likely to be volcanic in origin than to have formed by rotation under the pressures that induced the regional cleavage.

Most of the tuffs on the western side of the complex and in the main quarry consist of unsorted and unbedded clastic material, mainly dark bluish grey mudstones, tuffs, and andesite clasts, in a fine-grained matrix of fluxioned tuffaceous material, comminuted mudstone and chalcedony (E39096). They merge into coarse agglomerates. Between the main quarry and the upper quarry, and in the western face of the latter, medium- and fine-grained crystal-lithic-tuffs and andesitic lapilli-tuffs occur, and commonly are fluxion-banded (E38211) and strongly cleaved. Some pale pinkish grey flinty rocks appear to be crystal lithic-tuffs injected by rhyolitic lava; they contain euhedral pyrite, or goethite pseudo-morphs after pyrite. Other tuffs in the upper quarry contain a high proportion of sand and silt mixed with volcanic material (E38073); they are laminated in places, the dip of the laminations being steeply south-westwards, that is, inwards from the line of the neck-wall in this vicinity. A small patch of dark brown fine-grained rock exposed on the extreme southern edge of the upper quarry also contains a good deal of orthoclastic silt mixed with pyroclastic material (E39539).

The larger andesitic masses tend to be concentrated along, or close to, the neck margin. They are mostly highly inclined irregular intrusive masses with limited lateral extension. The rock is mostly dark green when fresh, with noticeable feldspar phenocrysts, up to 3 mm long, usually altered to chlorite-quartz-carbonate aggregates; in hand specimen it resembles the andesitic Eycott lavas of the Borrowdale Volcanic Group. The andesites can be readily distinguished from andesitic tuffs by their rich brown ferruginous weathered skin, their relatively massive character, and their absence of cleavage. An altered purplish green amygdaloidal andesite occupies the central and eastern parts of the upper quarry (E38077), (E40544). It is probably a late stage intrusion into tuffs, or possibly a small flow which has reached its present position by later subsidence analogous to that of calderas (Francis, 1970). A full description of the rock appears on p. 8, and its chemical analysis is given in (Table 1). A small intrusive andesite to the south-east [SD 2215 5579] is dark green, and markedly porphyritic, much chloritised, carbonated and silicified (E38224).

The contacts of the volcanic rocks with the surrounding mudstones of the Skiddaw Group provide strong evidence in favour of the neck hypothesis. The position of the contact along the north and west sides of the neck can be accurately fixed, even though exposures of mudstone, once visible near the quarry workshop (see (Figure 1)) are now obscured. Within a zone about 20 m wide from the contact there are several exposures of steeply inclined masses of andesite and tuff, with associated bands and lenses of dark blue mudstone, in places fragmented in a tuffaceous matrix. The best are along a quarry road between 100 and 200 m S of the workshop. At one locality (marked by the 60°–70° dip arrow in (Figure 1)), andesite is underlain towards the neck-margin by a 70 cm band of slightly indurated slate, which, in turn, passes outwards gradually into a tuffaceous slate-breccia with occasional small pyroclasts of andesite. Similar associations of highly inclined bands of andesite and thin bands or wedges of slate occur in the old quarry 100 m S of the workshop. The general dip of these marginal intrusions and of the detached slate lenses in tuff seems to be at a high angle to the east or south-east, roughly parallel to the present dip of the neck-wall. At the contacts the andesite is altered to a highly carbonated pale rock and the slate, though unbleached, is indurated, and commonly permeated by tuffaceous and andesitic material. As the neck-wall is approached the tuff contains progressively more slate, merging into tuffaceous breccias derived from disintegration of the wall; so that much of the matrix of both the tuffs and the breccias is comminuted mudstone. At one point [SD 2197 7950] a band of andesite several metres thick with wedges and films of indurated mudstone on both sides of and above it, seems to lie at, or very close to, the neck-wall. WCCR

A specimen (E40544) of macroscopically relatively unaltered andesite collected from the upper quarry [SD 2227 7608] at Greenscoe, has a purplish to medium dark grey (N4) groundmass. Abundant amygdales (up to 14 mm long axis) are irregular to spheroidal, black, and aligned along the direction of flowage. They are variably zoned, with cores of chlorite or dolomite, intermediate zones of dolomite or chlorite and rims of quartz. Dolomite forms rhombs with r.i. ω = 1.684, while the chlorite occurs as radiating microfibrous aggregates with the following optics: α = 1.604 ±0.002, γ = 1.605 ± 0.002; pleochroism Z = green, X = pale yellow, absorption Z > X. Interference figures were unobtainable owing to the minuteness of the fibres, but the chlorite appears to be near jenkinsite, on optical grounds. The groundmass is a fluxioned felt of raggedly terminated plagioclase laths averaging 0.3 x 0.09 mm, with microphenocrysts up to 0.7mm length, set in a fine, partly isotropic base of feldspar needles, chloritised devitrified glassy mesostasis, hematite, epidote and leucoxene dust. Feldspar laths are partly carbonated and chloritised, and elsewhere are mainly oligoclase-andesine. No unaltered primary ferromagnesian minerals remain, but the high proportion of feldspars relative to chlorite and glassy base indicates the rock to approach an acid andesite (cf. Dunham in Eastwood and others, 1968, p. 60) rather than andesite-basalt. A full chemical analysis is given in (Table 1).

Modal, and especially normative, computations have little significance in terms of petrogenesis or classification because of the variable size and distribution of amygdales and the altered state of much of the rock. In (Table 1), therefore, norms have not been quoted, and modal ranges are given for amygdales and ground-mass separately.

Although a strict comparison with less altered andesites cannot be made on the basis of the mineralogy and chemistry, the present sample has gained some Mg²⁺, Fe³⁺, CO₂ and Na⁺ with a loss of Ca²⁺, Fe²⁺, and possibly Si⁴⁺, as a result of the late-stage processes of emplacement and cooling. The importance of gas action in this autopneumatolysis is indicated by the abundant amygdales. It is not certain whether the andesitic intrusions had any profound effect on the trace contents in the adjacent Skiddaw Slate, though the relative importance of Ba, Sr, and F in both (Table 1) and (Table 2) may suggest this. RKH

Ireleth

The volcanic rocks around Ireleth and near Old Park are largely drift-covered, but the junction with the Skiddaw Group is well exposed in Hole Gill, where the section [SD 2235 7762] extends downstream for about 110 m from the road-bridge. Greyish black Skiddaw Group mudstones abut at a waterfall against an intrusion breccia consisting of fragments and small irregular masses of mudstone set in a pale grey tuffaceous matrix. A few metres downstream a complex of much altered pyroclastic and andesitic rocks are in contact with Skiddaw mudstones and include irregular bands and lenses of mudstone, mostly slightly indurated, partly fragmented, and permeated by volcanic material. The contact lies at about the foot of the north bank of the stream below the waterfall and is clearly intrusive in character and comparable with those in Greenscoe Quarry. The pyroclastic rocks in this section are unbedded, and made up largely of unsorted fragmentary and comminuted mudstone, with some andesitic clasts, set in an andesitic or tuffaceous matrix. This rock is the so-called 'mottled shale' of Green (1913), which he regarded as a tuff; the inclusion within it of mudstone bands led him to believe that the section demonstrated a passage from Skiddaw Slates into a normal extrusive Borrowdale succession. The newer interpretation is, however, strengthened by exposures about 30m downstream from the bridge, where subangular or ellipsoidal patches of pale-coloured andesitic material in a darker matrix are aligned with steep eastward dips. Although partly modified by subsequent cleavage, this alignment appears to be a neck-marginal feature associated with gas-fluxion and fluidisation. Some larger masses of much altered andesitic material may represent portions of andesitic magma, mixed with fluidised tuff, that have consolidated within the neck (E38228).

Andesites exposed on the hillside north-east of Ireleth seem to be flows extruded at the surface, but their relationships with the neck-marginal rocks of Hole Gill are not clear. Their present position may be due to later cauldron-type subsidence. The exposures are of somewhat altered greyish green or mottled pink porphyritic andesites with a fluxioned microlitic groundmass (E38421).

Hare Slack Hill

A roughly circular outcrop of andesites and pyroclastic rocks forms Hare Slack Hill. At the top of the hill there are several exposures of a pale green speckled brown amygdaloidal andesite, best seen in an old quarry [SD 2337 7790]. The amygdales are chloritic and frequently contain chalcedony (E38206). At several places on the hill, and especially on its north-western slopes, there are outcrops of a cleaved pyroclastic rock, containing much fragmented mudstone, which compares closely with the neck-marginal tuffs of Greenscoe and Ireleth. Skiddaw Group mudstones crop out [SD 2320 7774] on the southern slopes of the hill, but their contacts with the volcanic rocks are not seen. The hill is interpreted as a volcanic neck by comparison with those of Greenscoe and Ireleth, and a diagrammatic section across it appears in (Figure 2).

Other necks

Several small necks are exposed in the Askham Shale Quarry [SD 218 755] (Plate 2.2). One of these [SD 2192 7663] shows a gradual lateral passage over about 30 cm from normal dark bluish grey mudstone, though an intermediate stage of indurated and fractured mudstone with disseminated spots of tuffaceous or andesitic material, into a tuffaceous breccia consisting of fragmented and comminuted mudstone set in a tuffaceous matrix. The neck-margin is clearly analogous to that at Greenscoe Quarry. Other intrusive contacts between andesite or tuff and mudstone can be seen in these quarries, though some have been disturbed by subsequent faulting and by local slipping due to quarrying. At one point [SD 2184 7555] immediately north-east of Park Farm, a vertical contact between andesite and mudstone is exposed. The andesite is carbonated to a white rock for about 1 m from the contact and is locally injected into brecciated and slightly indurated mudstone to produce an intrusion breccia closely resembling the fluidised tuffs at Greenscoe. W C C R

Two samples of Skiddaw Group mudstone, one from the immediate contact with andesites, the other 30 cm from the contact were examined in detail. The mudstone about 30 cm from the contact with intrusive andesite, is medium dark grey (N4) with a slight purplish tinge, dense, and with a perfect cleavage along the bedding, which is picked out by very fine silt-laminae up to 2 mm thick. Thin sections (E39543A) cut normal to the bedding show a very fine-grained base of clay material, with quartz-silt and fine micas oriented along the bedding, which is also emphasised by opaque films of carbonaceous material. The microstructure of the rock is complex, with distinct angular particles and broken laminae of slightly silty, chloritic mudstone; micro-wedges of fine chloritic silt; intercalations of clear and slightly silty, chloritic mudstone, showing finely layered mica flakes; and abundant porphyroblastic chlorite or chlorite crystals in parallel growth with mica, marking a secondary cleavage. Irregular patches of chlorite (up to 0.6 mm across) are associated with films of opaque ?carbonaceous matter, minute annular growths of carbonate and possible granular kaolinite. The chlorite at least, was almost certainly deposited from hydrothermal solutions stemming from the neck intrusion. Framboidal pyrite forms spherical aggregates attaining 0.12 mm in diameter, and is evidence of early diagenetic crystallisation under anaerobic conditions (cf. Love, 1969). Trace detrital constituents include specks of zircon and TiO₂ polymorphs. X-ray powder photographs and diffractometer traces (X6502); (DX596), taken of the analysed sample by Mr B. R. Young, showed major quartz, chlorite and muscovite, with minor siderite, rutile and possibly sodic plagioclase.

The mudstone in immediate contact with the andesite is fissile, medium dark grey (N4), brecciated shale, with an irregular to flaky cleavage. Fine calcite veins ramify throughout and there are abundant spots of dolomite and siderite, associated with goethite. A thin section (E39542) shows a highly complex association of angular silty mudstone particles of differing lithologies. Finely laminated, subopaque carbonaceous shale fragments with films of more silty shale contain strings of siderite (with goethite), which are restricted to the fragments and therefore predate the brecciation. Less well-defined particles of pale silty mudstone appear to contain little muscovite but much illitic base, while a third type of clast is more carbonaceous, finely bedded, and contains abundant muscovite. Trace constituents include detrital zircon and TiO₂ polymorphs. X-ray powder photograph (X6501) and diffractometer traces (DX 595) taken by Mr Young of the analysed sample showed predominant quartz and 2M₁ type muscovite with subordinate siderite and dolomite, and minor rutile and possibly sodic plagioclase. Minute clusters of replacive siderite-dolomite granules are disseminated throughout the rock and are probably attributable to metasomatism by the intrusive andesitic magma. It is uncertain if the brecciation was due to the phreatic effects of neck emplacement, but there is no clear evidence of magmatic activity except, perhaps, for the carbonate clusters.

There are certain significant differences between the two samples. These are demonstrated by the complete chemical analyses in (Table 2), in which, for comparison, analyses of Skiddaw Group mudstones near an intrusion at Barkbeth (Eastwood and others, 1968, pp. 22–23) are given, though the intrusion was there a hornblende-picrite and not an andesite.

The main differences between the major oxides of the present two samples are the higher CaO, SiO₂, Fe₂O₃, CO₂, and lower A1₂O₃, FeO, MgO, FeS₂ and combined H₂O in the contact shale. The carbonates siderite and calcite here account for their respective oxides, and result from the neck intrusion. A somewhat higher quartz content in the contact shale accounts for the higher SiO₂.

The higher FeO, MgO and Al₂O₃ contents in the shale away from the contact are partly accounted for by the conspicuous (24 per cent) chlorite content. The virtual absence of chlorite at the contact may be a pre-intrusion feature of the shale at this particular site, although the thermal effect of the intrusion may have destroyed any chlorite present. Controlled experiments (e.g. Brindley and Ali, 1950) indicate that at 750°–800°C chlorite breaks down and olivine forms. The apparent absence of olivine establishes that the intrusion temperature is most unlikely to have attained 800°C. Indeed it may well have been considerably lower, since non-carbonate carbon has apparently not been ignited (compare the respective C contents in (Table 2)). RKH

A small isolated outcrop of andesite at Park Cottage [SD 2168 7531], probably faulted between the High Haume Limestone and Skiddaw Group mudstone, is a mottled purplish green rock with pseudomorphs up to 4mm in length of feldspar, quartz, chlorite and illite (E38201). It may lie within another small volcanic neck associated with those in Askham Shale Quarry.

There are two other small outcrops of volcanic rocks nearby, both probably necks, though exposures are too poor for their exact forms and relationships to be determinable. One lies east of Greencoe House [SD 2254 7667], where a highly altered amygdaloidal andesite with phenocrystic pseudomorphs of carbonate is exposed in a small disused quarry (E38205). The other is north-north-west of High Haume [SD 2276 7652], where altered purplish grey andesitic rock is exposed, with some associated tuffaceous material (E38219), (E38220), (E38221).

A small exposure of cleaved pyroclastic rock at Stewnor Park [SD 2390 7858] is apparently surrounded partly by Ashgill Shale and partly by Skiddaw Group mudstones. It is a much altered greyish white lapilli-tuff; the unsorted streaky pyroclasts include andesite. Dr N. G. Berridge reports that one of the exposures (E41014) is a breccia consisting of angular lithic fragments, up to 2 mm in diameter, set in a fine-grained felsic matrix. The groundmass is in granular to felsitic intergrowth, and contains minor amounts of chlorite and opaque accessories. The clasts consist mainly of a very fine-grained (about 0.008 mm diameter) intergrowth of chlorite, felsic minerals and accessory opaque granules, with aggregates of white mica pseudomorphing euhedral prismatic plagioclase megacrysts. The rock could well be an altered porphyritic andesite. Vesicles in the breccia are filled with a coarse-grained carbonate, probably calcite. There seems little doubt that the exposure is of another small neck, and it is suggested that its apparently anomalous structural relationship is explained by its lying within an up-faulted and up-folded extension of unexposed Skiddaw Group rocks lying beneath drift (see (Figure 2)). WCCR

Coniston Limestone Group

Throughout the Lake District the highest Ordovician rocks rest with profound unconformity on those lower in the sequence. Their nomenclature has never been precise. Initially termed the 'Coniston Limestone Series' (Aveline and Hughes, 1872), they have been often termed the 'Coniston Limestone', and the definitions of these two terms have varied from author to author (Mitchell, 1956). In this account they have been called the Coniston Limestone Group following Williams and others (1972).

In this district the Group is divisible into three formations. The lowest consists of calcareous shales with an included limestone member. These are here respectively termed the High Haume Mudstone (Formation), and the High Haume Limestone (Member). The recorded fauna is indicative of Zones 1 to 3 of the Cautleyan Stage of the Ashgill Series: the Caradoc Series and the Pusgillian Stage-the lowest within the Ashgill Series-seem to be absent in Furness. A stratigraphic break probably lies at the top of the formation, and is followed by a volcanic sequence here termed the High Haume Rhyolite (Formation), which is assumed to be Rawtheyan in age. The highest formation comprises a sequence of dull bluish grey shales, and for these the traditional term Ashgill Shale (Formation) has been retained. A coarse sandstone within the Shale is here called the Rebecca Grit (Member). The basal beds have been termed the Phacops mucronatus Beds (Marr, 1913), and are Rawtheyan in age. The rest of the formation falls within the Hirnantian Stage, the highest in the Ashgill Series, and is overlain conformably by Llandovery rocks (see p. 18).

The likely relationship between the nomenclature outlined above and that used in the Coniston area (Marr, 1916b) is set out below in (Table 3). WCCR

The shelly fossils from the Coniston Limestone Group are generally too distorted by tectonism for specific determination to be possible. Nevertheless the genera present are distinct enough for the assemblages from the High Haume Mudstones to be clearly separable from those of the Ashgill Shales.

The High Haume Mudstone (locs. O1 to O4)^‡1   yielded about twenty varieties of brachiopods (including nine or ten Orthacea) and ten of trilobites, all of which are characteristic of the Cautleyan Stage (cf. Ingham, 1966; Ingham and Wright, 1970, p. 237). Further evidence for the Cautleyan Stage is provided at loc. O2 by the occurrence of Sampo ruralis? and Diacalymene cf. marginata, but no determinable specimens of the stratigraphically important genus Tretaspis were collected.

The brachiopods from the High Haume Limestone are too poorly preserved for determination but some of the corals and bryozoans indicate an upper Ordovician age: Dr D. E. White reports that Catenipora tapaensis and Streptelasma primum are both known from the Pirgu Stage (equivalent to part of the Ashgill Series) in Estonia, and Miss M. E. Dutton has determined several genera of trepostome Bryozoa known from the higher Ordovician in North America.

The Ashgill Shales are characterised, as elsewhere in the north of England, by the Hirnantia fauna; poorly preserved Cryptothyrella, Dalmanella?, Kinnella, Eostropheodonta and Plectothyrella have been identified, whilst Hirnantia was found at Banks Gill Beck, just north of the district. With these brachiopods there occur long crinoid stems identical with crinoid stems found with the Hirnantia fauna in the vicinity of Ash Gill.

The main fossiliferous localities are listed in (Table 4) and complete faunal lists, including authors' names, are in (Table 5) (p. 14). The corals were determined by Dr D. E. White, the bryozoans chiefly by Miss M. E. Dutton and the remaining fossils by Dr A. W. A. Rushton. AWAR

High Haume Mudstone

The formation is probably 120 to 150m thick, much of this thickness being made up of calcareous, and locally silty, greenish grey cleaved mudstones. North of Ireleth there are a few mudstone outcrops, both above and below the High Haume Limestone. An exposure of highly cleaved, deeply weathered decalcified mudstone in a stream [SD 2238 7847] south-west of Moor Side Farm has yielded abundant brachiopods accompanied by a few trilobites (loc. O1). The fauna is the lowest yet recorded from the formation in the district, and is probably of Cautleyan age. To the west of the farm, and apparently at a slightly higher horizon, hard bluish grey mudstones with thin limestone bands crop out [SD 2248 7862] in the bank of another small stream and lie within the lower part of the High Haume Limestone as mapped. Brachiopods and trilobites occur, together with corals and bryozoans (loc. O2), again suggestive of the Cautleyan. An old quarry [SD 2267 7628] 200m west of High Haume is in strongly cleaved mudstones that dip at 80° to the north-north-west, though the beds may be overturned. For this reason their relations to the High Haume Limestone are uncertain, but they are probably above it. The mudstones are partly decalcified and have weathered brown; they contain large calcareous concretions. A varied, but poorly preserved fauna of trilobites and brachiopods is again present (loc. O3), and is essentially similar to that noted below the limestone, being similarly probably referable to the Cautleyan. A comparable fauna was collected from a stream section [SD 2264 7833] 300m west of Rebecca Quarry (O4), in strata apparently at the same horizon as loc. O2.

The High Haume Limestone generally forms a strong feature and its outcrop, being comparatively easy to identify and trace, provides much of the evidence for the faulting established north of Ireleth, and indeed for the structural interpretation of the High Haume–Greenscoe area. Where thickest near Greenscoe and Park Cottage it is a hard, thickly bedded or massive, dark bluish grey crystalline limestone at least 30m thick. Secondary dolomitisation along joints and bedding-planes is not uncommon, and makes the rock cavernous and susceptible to differential weathering that produces brown and white mottling. Many exposures are so massive that the bedding is unrecognisable. Cleavage is rare, but commonly there is a crude joint-set aligned parallel to the regional cleavage of the associated mudstones, together with other joint-sets of varying directions. Northwards towards and beyond Ireleth the limestone thins to barely 6m, and is less massive, while beds of calcareous mudstone appear locally within it. The fauna of the limestone is different from that in the rest of the Formation. The commonest forms are species of Bryozoa and small solitary corals, together with indeterminate brachiopods, gastropods, trilobites and ostracods. They are non-diagnostic, pointing merely to a late Ordovician age.

Details

The best exposure of the High Haume Limestone is in a disused cutting [SD 2193 7545] east of Park Farm. About 30 m of beds are exposed, disturbed a little by faulting. The limestone is roughly bedded in posts up to 1 m thick, with some thin intervening mudstone partings towards the top of the section. The dip varies, but averages 60° to the south-east. A nearby quarry [SD 2196 7552] is in about 6m of massive dark bluish grey limestone. At both exposures the limestone is much crushed, with secondary dolomitisation and hematitisation rather like that in the Viséan limestones nearby. In two small outcrops in a faulted inlier at Park Cottage the limestone is overlain unconformably by the Basement Beds of the Carboniferous.

There is another small digging [SD 2213 7573] in vertical limestone along the strike to the north-east. Indeterminate brachiopods, gastropods and trilobites are present (loc. O5). Other exposures are at the top of one of the faces of Greenscoe Quarry [SD 2223 7595] where silicified fossils occur (loc. O6), and in a small digging [SD 2203 7575] where Dr N. G. Berridge reports the presence of subordinate silt-grade quartz grains in fine-grained limestone, partially recrystallised to give coarser plates of calcite, and containing numerous scattered rhombic crystals of ?dolomite. Repetition of the outcrop by strike-faulting is general in this area.

West of High Haume Beacon, the outcrop is also repeated by strike-faulting, and a double feature locally results, broken by dip-faults into knoll-like ridges. The richest recorded fauna (loc. O7) has been collected from an old quarry [SD 2244 7601] in this area, and another fossiliferous locality (loc. 08) lies a little to the north [SD 2245 7618]. East of the Holmes Green–Ireleth road the limestone is poorly exposed for some distance, though there are scattered outcrops [SD 2327 7709] east of Far Old Park. It is presumed to be faulted out on both flanks of the Stewnor Park Anticline.

The outcrop can be readily traced north of Ireleth though exposures are few. A small stream section near Paradise [SD 2248 7862] shows thin calcareous mudstone bands within the limestone. However, an old quarry [SD 2259 7886] nearby is in 5 m of massive bluish grey, jointed and roughly cleaved limestone, while farther north some 6 m are exposed [SD 2275 7942] in Mere Beck (loc. O9), and there are other small exposures between High Mere Beck and The Muirlands.

High Haume Rhyolite

The High Haume Rhyolite forms a conspicuous feature along the crest of High Haume ridge and there are many natural exposures, commonly showing quartz-veining and joints paralleling the regional cleavage. It has not been found east of the Holmes Green–Ireleth road, but debris of a similar rock on Hare Slack Hill [SD 2360 7776] may indicate an extension of its outcrop. The flow seems to be about 25m thick. Superficially it resembles a massive coarse ashy grit, pink and white mottled when fresh, and quite unlike the rocks in the nearby Greenscoe neck. In thin section (E41015) Mr R. K. Harrison describes it as consisting of microphenocrysts of quartz, feldspar and mica up to 3mm in length, set in a microgranular rhyolite groundmass largely composed of quartz and chalcedony. There are no obvious flow-textures, but the broken nature of some of the phenocrysts may indicate flow-brecciation, though it might equally well result from the incorporation of ejected crystals into lava. The rock is clearly allied to the rhyolites. Although its upper and lower contacts are not exposed, it seems to represent local Ashgillian vulcanicity, and lies in the same position relative to the Phacops mucronatus Beds as does an ash recorded by Marr (1916b) at Ashgill. In the absence of confirmatory evidence the base of the overlying Ashgill Shale has been drawn at the top of the Rhyolite.

Ashgill Shale

The base of this formation, taken at the top of the High Haume Rhyolite where it is present, is somewhat arbitrary elsewhere for exposures are poor. In the Coniston area it has been taken at the top of the Phacops mucronatus Beds (Marr, 1913), but these latter have been detected in the present district at only one locality, and if present elsewhere have been included, for practical reasons, within the Ashgill Shale, which term is thus used in a slightly broader sense than was done by Marr.

The bulk of the formation consists of a uniform sequence of dull bluish grey strongly cleaved mudstones that weather dull greenish grey or brownish grey. In some sections thin banding and lamination is detectable, but bedding is not normally obvious. In most natural exposures the mudstones break into 'pencils' due to the cleavage. A sandy member in the upper part of the formation is here called the Rebecca Grit.

The overall thickness of the formation cannot be exactly determined, but seems to be appreciably greater than elsewhere in north-west England. Between High Haume and Holmes Green it appears to be about 400m, but this may be an overestimate if there is appreciable repetition by strike faults. Elsewhere the minimum thickness is probably 200m, and a figure of 300m seems more general. An apparently much thinner sequence near High Mere Beck is almost certainly incomplete due to faulting.

Faunas are not abundant but all except one are referable to the Hirnantian Stage, the highest of the Ashgill Series.

Details

The solitary exposure of the Phacops mucronatus Beds [SD 2284 7635] is in the access road to High Haume Farm, where about 9 m of greyish green, brown-weathering, cleaved mudstones are exposed. The locality lies within a fault-belt, and the mudstones are crushed and stained with hematite. The detailed section at this exposure (loc. O10) reads:

Of this sequence only bed c is unequivocally regarded as belonging to the Phacops mucronatus Beds, though bed b may also be part of that division.

The best section in the lower part of the Ashgill Shale is in Rebecca Quarry [SD 2292 7830], formerly worked for slates and slabs. About 15m of hard dark bluish grey mudstones are exposed. Dark bands and laminations cross the joint-faces and show the dip to be 40° to the north-west, while a strong cleavage dips at 75°–80° to the east-south-east. A specimen (E40993) reported on by Dr Berridge consists of rounded to subangular grains up to 0.12 mm in diameter of chlorite (? after feldspar) and quartz set in a dominant matrix of chlorite, white mica, calcite and felsic minerals. The white mica and chlorite are strongly foliated to give a pronounced slaty texture and are associated with a black opaque mineral, probably graphite. The rock effervesces with cold dilute hydrochloric acid. In the quarry entrance (loc. O11) Eostropheodonta hirnantensis (McCoy) is common, together with crinoid fragments, Plectothyrella sp.and Dalmanitina fragments.

Other exposures are relatively small. The cleaved mudstones crop out on the lower slopes near The Muirlands, and in a small digging [SD 2283 7954] at High Mere Beck. Near Stewnor Park a single valve of Kinnella kielanae (Temple) was obtained (loc. O12) in another old quarry [SD 2381 7858]. There are further exposures of cleaved mudstone around Stewnor Bank, on the bank of Poaka Beck reservoir [SD 2419 7838], and in a small quarry [SD 2326 7688] near Far Old Park. Alongside the Holmes Green–Ireleth road another small exposure [SD 2337 7711] shows dips of about 60° to the southeast, and near the road a short stream section [SD 2314 6735] exposes mudstones close below the Rebecca Grit. All except the latter lie in the lower part of the formation.

The highest fossiliferous exposures are in Mere Beck, where [SD 2286 7936] dull grey mudstones overlying the horizon of the Grit have yielded a Hirnantia brachiopod fauna (loc. O13).

All the many outcrops of coarse gritty sandstone within the Ashgill Shale appear to lie within the highest 100m of the formation, and probably mark the same sandy phase, though the scattered outcrops and the very considerable thickness variations of the member suggest that it may be discontinuous at outcrop. The Grit is best exposed on Rebecca Hill, after which locality it is named, and where it is up to 50 m thick. It consists of gritty sandstone–both coarse- and fine-grained–with thin bands of interbedded greenish grey cleaved mudstone; it weathers down to a friable 'gingerbread' rock. The coarser sandstones are conglomeratic with small pebbles of vein-quartz and pellets of shale. A specimen examined by Dr Berridge (E41005) from this outcrop [SD 2300 7835] is a porous dark grey cleaved micaceous sandstone. Angular to subangular moderately well-sorted grains (about 0.3mm) of quartz, feldspar, opaque ore, chert and siltstone are set in a matrix of fairly well-crystallised orientated aggregates of chlorite and white mica, lithic clasts being almost as common as quartz. The dip near the hilltop is steeply to the north-west, and there is another outcrop on the western flank of the Rebecca Syncline, where the dip is east-south-eastwards at a much lower angle. Fragmentary brachiopods, gastropods and crinoids have been collected in the track to Moorside [SD 2271 7855].

Other exposures of the Rebecca Grit lie in Mere Beck [SD 2283 7937]; on the hillside between High Mere Beck and The Muir-lands; on the west bank of Poaka Beck reservoir [SD 2419 7838]; and in the lower part of a stream section [SD 2315 7634], to the east-northeast of High Haume. The exposure at Poaka Beck reservoir is similar in texture to that described above, but Dr Berridge notes that a fresh specimen (E41006) contains about 15 per cent of clastic carbonate, probably mostly calcite, and numerous partly carbonated grains of quartz. WCCR

References

AVELINE, W. T. and HUGHES, T. McK. 1872. The geology of the country between Kendal, Sedbergh, Bowness and Tebay. Mem. Geol. Surv. G.B. (2nd Edition, revised by A. Strahan, 1888.)

BRINDLEY, G. W. and ALI, S. Z. 1950. Thermal transformation in magnesian chlorides. Acta Crystallogr., Vol. 3, pp. 25–30.

EASTWOOD, T., HOLLINGWORTH, S. E., ROSE, W. C. C. and TROTTER, F. M. 1968. Geology of the country around Cockermouth and Caldbeck. Mem. Geol. Surv. G.B.

FRANCIS, E. H. 1970. Bedding in Scottish (Fifeshire) tuffs and pipes and its relevance to maars and calderas. Bull. Volcanol., Vol. 34, pp. 697–712.

FRANCIS, E. H. and HOPGOOD, A. M. 1970. Volcanism and the Ardrose Fault, Fife. Scott. J. Geol., Vol. 6, pp. 166–167.

GREEN, J. F. N. 1913. The Older Palaeozoic Succession of the Duddon Estuary. London. 23 pp.

GUPPY, E. M. and SABINE, P. A. 1956. Chemical analysis of igneous rocks, metamorphic rocks and minerals 1931 to 1954. Mem. Geol. Surv. G.B.

INGHAM, J. K. 1966. The Ordovician rocks in the Cautby and Dent districts of Westmorland and Yorkshire. Proc. Yorkshire Geol. Soc., Vol. 35, pp. 455–504.

INGHAM, J. K. and WRIGHT, A. O. 1970. A revised classification of the Ashgill Series. Lethaia, Vol. 3, pp. 233–242.

JACKSON, D. E. 1961. The stratigraphy of the Skiddaw Group between Buttermere and Mungrisdale, Cumberland. Geol. Mag., Vol. 98, pp. 515–528.

JACKSON, D. E. 1962. Graptolite zones in the Skiddaw Group, Cumberland, England. J. Palaeontol., Vol. 36, pp. 300–313.

LOVE, L. G. 1969. Sulphides of metals in recent sediments. Sedimentary ores; ancient and modern (revised). Proc. XVth Inter- Univ. Congr. 1967. University of Leicester.

MARR, J. E. 1900. Notes on the Geology of the English Lake District. Proc. Geol. Assoc., Vol. 16, pp. 449–483.

MARR, J. E. 1913. The Lower Palaeozoic rocks of the Cautley district (Yorkshire). Q. J. Geol. Soc. London, Vol. 69, pp. 1–17.

MARR, J. E. 1916a. The Geology of the Lake District and the scenery as influenced by geological structure. Cambridge. 220 pp.

MARR, J. E. 1916b. The Ashgillian succession in the tract to the west of Coniston Lake. Q. J. Geol. Soc. London, Vol. 71, pp. 189–204.

MITCHELL, G. H. 1956. The geological history of the Lake District. Proc. Yorkshire Geol. Soc., Vol. 30, pp. 407–463.

RANKAMA, K. and SAHAMA, Th. G. 1950. Geochemistry. Chicago.

SOPER, N. J. 1970. Three critical localities on the junction of the Borrowdale Volcanic rocks with the Skiddaw Slates in the Lake District. Proc. Yorkshire Geol. Soc., Vol. 37, pp. 461–482.

WILLIAMS, A. and others. 1972. A correlation of Ordovician rocks in the British Isles. Spec. Rep. Geol. Soc. London, No. 3.

Chapter 3 Silurian rocks

Introduction

North and north-east of Ireleth Silurian rocks succeed the Ashgill Shale, their outcrop giving rise to the high ground of the Furness and Cartmel peninsulas. Their junction with the Ordovician rocks is nowhere exposed, but is assumed to be a conformable one, as in the main Silurian outcrop of the Lake District. Apart from the ground around the Stewnor Anticline, where the Silurian rocks are involved in the folding, the general dip is south-eastwards at a steep angle. Progressively younger strata thus crop out to the south-east, so that north-east of Ulverston and in Cartmel only the Bannisdale Slates are present at outcrop.

The succession established between Ireleth and Ulverston is shown in (Figure 3). It compares closely in general terms with that of the main Silurian outcrop around Windermere as first established by Aveline (Old Series Sheet 98 NW), and described by Marr (1916), Furness and others (1967), and Warren (in Taylor, 1971). Most of the mappable units are sufficiently similar to those at Windermere for the traditional names to be applied. Difficulty has, however, arisen in the recognition of the Coldwell Beds, and two new terms–the Harlock Grits and the Horrace Flags–have been introduced to cover this part of the succession. The former may be a thicker equivalent of the Lower Coldwell Beds; the latter may equate with the Upper Coldwell Beds. No mappable unit corresponding to the Middle Coldwell Beds has been recognised, but mottled calcareous mudstones, similar to those characteristic of that formation at Windermere, have been noted both in the upper part of the Harlock Grits and in the lower part of the Horrace Flags. A recent study of the Blawith area, about 10 km N of Ulverston, has been undertaken by Norman (1961), who has proposed a set of local lithostratigraphic terms to cover much of the sequence there. It has, however, been considered more appropriate to make use of the Windermere terminology in the present district.

Chronostratigraphic correlation of the sequence is hampered by the paucity of recorded graptolites. There is, nevertheless, sufficient faunal evidence to establish the Llandovery and Wenlock ages of the Stockdale Shales and Brathay Flags respectively. The position of the Wenlock–Ludlow boundary is less certain. It probably lies within the upper part of the Horrace Flags, for the underlying Harlock Grits fall at least in part within the Cyrtograptus lundgreni Zone of the upper Wenlock while a fauna from the Neodiversograptus nilssoni Zone, the lowermost of the Ludlow, has been identified high in the Horrace Flags. The mappable line nearest this boundary is thus the base of the Coniston Grits.

Stockdale Shales

As in the main outcrop, the Stockdale Shales can be subdivided into the Skelgill Shales below and the Browgill Beds above. They mark a period of quiet-water sedimentation, and formed well offshore beyond the reach of turbidity currents. Exposures are too few, particularly in the Skelgill Shales, to make detailed palaeontological zonation feasible, but the Llandovery age of the formation has been confirmed. It is much thinner than its equivalents in Wales.

Skelgill Shales

The Skelgill Shales, about 15m thick, comprise dark grey to black, strongly cleaved mudstone, some of which is faintly laminated. Immediately north-east of Moorside a small exposure [SD 2279 7862] has yielded ?Climacograptus medius Tornquist, ?C. normalis Lapworth, C. rectangularis? (McCoy), diplograptids [indet.], Glyptograptus?, Monograptus atavus? Jones, M. cyphus? Lapworth, monograptid fragments. The assemblage is indicative of a position low in the Skelgill Shales, probably about the M. cyphus Zone. Sections in the eastern bank of Poaka Beck were noted by W. T. Aveline during the Primary Survey and have been described by Marr and Nicholson (1888). Faunas from black mudstones exposed in the Beck are listed below but the three localities are probably separated by small faults.

Locality a: [SD 2409 7770]. Climacograptus miserabilis? Elles & Wood, C. cf. miserabilis, C. normalis Lapworth, C. sp., Dimorphograptus confertus? (Nicholson), D. cf. confertus, Diplograptus modestus Lapworth s.l., Monograptus sp., ?Rhaphidograptus toernquisti (Elles & Wood). This fauna probably comes from the Monograptus atavus Zone.

Locality b: [SD 2412 7776]. Climacograptus sp., diplograptid indet., Glyptograptus tamariscus (Nicholson) s.l., glyptograptid indet., Monograptus aff. decipiens Tornquist, M. limatulus Tornquist, M. cf. limatulus Tornquist, M. lobiferus (McCoy), M. sedgwickii? (Portlock), M. triangulatus (Harkness) s.l. (or M. dicipiens?), M. crenularis? Lapworth, ?Pristiograptus regularis (Tornquist) , Rastrites sp., triangulate monograptid indet. The assemblage indicates the top of the Monograptus convolutus Zone or the M. sedgwickii Zone.

Locality c: [SD 2417 7781]. ?Monoclimacis galaensis (Lap-worth), Monograptus exiguus (Nicholson), M. marri? Perner, ?M. marri (or M. halli Barrande sp.), M. ex gr. nodifer Tornquist, M. cf. proteus (Barrande), M. cf. runcinatus Lapworth, M. sedgwickii? (Portlock) , M. turriculatus (Barrande), M. sp., Orthograptus sp., Pristiograptus regularis (Tornquist), cf. P. regularis, ?P. regularis or ?P. nudus (Lapworth). This fauna is representative of the M. turriculatus Zone.

A few green stripes or laminae appear towards the top of the section and the mudstones pass up into the Browgill Beds, exposed a few metres upstream.

Browgill Beds

The Browgill Beds are better exposed and appear to be about 50m thick. The most common rock is highly distinctive. It is poorly cleaved, unbedded, pale green, hard slightly silty mudstone, having a hackly fracture. In thin section it is strongly chloritic, and some shale bands have a texture common in tuffs, thus suggesting a possible volcanic origin (see below). Dark grey bands and laminations are common, especially near the base, and dark blue banding occurs in places. These darker bands yield graptolites, though no fossils have been found in the green mudstones. The mudstones become generally darker upwards, fine silty laminations appear, and the beds pass up, over a distance of 5 to 10m, into the Brathay Flags. These passage beds are best seen in Bridge House Gill [SD 233 801] just north of the district, but are also exposed in a small quarry [SD 2420 7899] between Stewnor Park and Standish Cote.

The green mudstones crop out in a small stream [SD 2312 7977] east of High Bridge House, and again near Moorside [SD 2281 7860] where dark bands have yielded Monograptus cf. discus Tornquist, M. cf. exiguus (Nicholson), M. marri Perner, M. cf. proteus (Barrande), ?M. pseudobecki Boucek & Pribyl, M. spiralis? Geinitz, M. sp.nov. 1, Monograptus sp., Petalograptus palmeus (Barrande) s.l., Pristiograptus nudus (Lapworth), Retiolites geinitzianus Barrande. The above probably indicate a high horizon in the M. turriculatus Zone. In a slide (E41002) from this latter exposure, Dr Berridge notes that the greenish grey mudstone is essentially a mottled aggregate of microcrystalline, low birefringent chlorite accompanied by silt-grade grains of felsic and carbonate minerals and small flakes of white mica. Dark bluish grey laminae contain much less silt and some appear to be almost wholly chlorite. Included pellets are composed of chalcedonic silica and some are associated with calcite.

In reflected light, patches and layers of all three lithologies reveal slightly undulose platy fabrics containing discontinuities and small flattened ovoid structures, strongly reminiscent of compressed–possibly welded–tuff texture. The strongly chloritic composition of the rock is also in accordance with a volcanic origin. More extensive sections lie in Poaka Beck [SD 2398 7749]; [SD 2387 7722] north of Marton. The latter yielded Monograptus cf. crispus Lapworth, M. marri? Perner, and M. sp.nov. 2, a fauna indicative of the M. crispus Zone. In another stream section nearby the green mudstones have weathered to a pale buff colour. Downstream a small cliff [SD 2364 7690] exposes silty mudstones close to, and passing upwards into, the Brathay Flags.

Brathay Flags

This formation consists of about 300m of thinly laminated dark bluish grey mudstones, that weather dull greenish brown or khaki and are, in places, pink-tinged. The laminations are made up of silty and micaceous layers, normally less than 0.5mm thick. A petrographic description of a typical specimen appears on p. 20. Some buff-coloured silty bands, about 1 to 2 cm thick, occur throughout the formation, becoming more general towards the top; many show current-bedding and ripple marks. Hard ovoid siliceous concretions are common at particular horizons, and there are also a few soft ferruginous and calcareous ones. The lithology is interpreted as marking the earliest encroachment of extreme distal turbidites into the district.

Cleavage is everywhere strong and, coupled with the fine-grain and comparatively uniform lithology of the rocks, has led to the formation of slates and good-quality flags. These have been worked at many small quarries throughout the area.

The cleavage makes identifiable graptolites hard to find, and most of the localities lie low in the formation, most probably from the Cyrtograptus centrifugus Zone, the basal zone of the Wenlock, though a section in Mere Beck exposes strata probably belonging to the Monograptus riccartonensis, M. antennularius, and the Cyrtograptus rigidus zones.

Details

The Brathay Flags give rise to the high ground between High Mere Beck and Standish Close, and also form the higher part of the south-eastern flanks of the Poaka Beck valley, where they are overlain and faulted against Lower Carboniferous rocks. In Poaka Beck, a section [SD 2364 7690] at the extreme base of the formation yields Cyrtograptus sp.[robust early Wenlock type], Monoclimacis vomerina (Nicholson) basilica (Lapworth), M. vomerina cf. basilica, M. vomerina aff. vomerina, M. sp., Monograptus priodon (Bronn), M. cf. priodon. This fauna is probably from the Cyrtograptus centrifugus Zone, the basal zone of the Wenlock. A small quarry [SD 2302 7864], east-north-east of Moorside, that has yielded cyrtograptid (arm of robust low-Wenlock type), Monoclimacis? and Monograptus aff. priodon, also lies low in the formation. These lowermost beds are exposed in another small quarry [SD 2421 7899] near Standish Cote. The following forms have been identified: a. north-eastern part of quarry, Cyrtograptus?, Monoclimacis aff. linnarssoni (Tullberg), M. vomerina s.l., Retiolites geinitzianus (Barrande); b. centre of quarry face, M. aff. linnarssoni, M. vomerina s.l., M. sp., Monograptus priodon, R. geinitzianus (Barrande) angustidens Elles & Wood; c. top of quarry, cyrtograptid, [robust, e.g. centrifugus group], Monoclimacis vomerina s.l., M. vomerina aff. vomerina, Monograptus priodon. The entire fauna is referable to the C. centrifugus Zone.

Beds low in the formation are well exposed above the 350 ft contour in Mere Beck where the section [SD 2312 7927] to [SD 2303 7929] reads:

There are further exposures nearby in a disused quarry [SD 2377 7947] near Moor Side Intake, and [SD 2421 7942] at Standish Cote.

About 30 m of strata lying near the top of the formation are exposed in Walthwaite Moor Quarry [SD 2470 7818]. Dr Berridge notes that a typical specimen (E41012) from the quarry is a silty slate consisting of an aggregate of chlorite, felsic minerals, carbonate and white mica, with a strong slaty cleavage defined mainly by the distribution of opaque black laminae, probably of graphite. Clasts of quartz up to 0.05 mm in diameter are present. Lamination is defined partly by a varying silt/chlorite ratio, but more obviously by the distribution of opaque particles. It has been degraded by the redistribution of the latter in cleavage planes. A mass of coarse-grained carbonate, probably dolomite, at one end of the slide may mark a thin stripe of dolomite within the slate.

There are other extensive sections in Poaka Beck upstream from Scale Bank [SD 2362 7657] and near Holmes Green [SD 2328 7606]. The Poaka Water-level cuts through Brathay Flags for about 75 m from its outfall [SD 2379 7699], but the section is now difficult of access.

Harlock Grits

There appears to be a rapid upward change from the silty mudstones of the Brathay Flags to a coarser turbidite facies, although the passage is not exposed. The overlying formation has been termed the Harlock Grits, from Harlock Hill [SD 254 798]. It consists of a thinly bedded, in places rhythmic, sequence of grey siltstones and cleaved greenish grey laminated mudstones, containing many bands of greywacke-grit averaging 30 to 50 cm, but ranging up to 2 m, in thickness. These lithologies are similar to those of the Lower Coldwell Beds (Marr, 1878). Faulting and folding make it hard to determine the thickness of the formation, but it is probably some 200 to 300 m.

The best exposures are in a long section in Rathmoss Beck [SD 2550 7929] to [SD 2566 7960]. The section is crossed somewhat obliquely by the axial trace of the Stewnor Anticline and an associated fault belt, and it is not possible to place the beds within the formation, though the greater part of the sequence is probably present. Near the head of Pennington Reservoir [SD 2566 7920] there are bands of greenish grey slightly calcareous mottled mudstone that resemble the Middle Coldwell Beds at Windermere (Marr, 1878), and scattered occurrences of similar calcareous mudstone north of Harlock Hill and in a small quarry [SD 252 804] just north of the district lie high in the formation. Other exposures of the Harlock Grits lie on Dalton Moor north and west of Standish Cote, and close to the east of Walthwaite Moor Quarry where there is a small exposure [SD 2485 7805] of interbedded siltstones, slates and greywackes. Dr Berridge notes that a slide of one of the latter (E41008) shows it to be poorly sorted with a fairly even spread of grain sizes between 0.01 and 0.6 mm in diameter. The grains are mainly subangular, and are composed of quartz, feldspar, and lithic fragments, especially chert and siltstone. Flakes of clastic mica, including a little biotite, are widespread. The rock is cemented by chlorite and white mica, commonly orientated in a foliation plane. Accessories include opaque ore grains, mainly leucoxenised ilmenite, and zircon.

The only fossiliferous horizon noted is in Rathmoss Beck, where [SD 2561 7943] graptolites were found; though poorly preserved they probably come from the Cyrtograptus lundgreni Zone high in the Wenlock, which would confirm the suggested general correlation with the Lower Coldwell Beds.

Horrace Flags

Above the Harlock Grits the turbidite currents appear to have waned and there is a reversion to the lithology typical of the Brathay Flags–finely-laminated and strongly cleaved, dull bluish grey, silty mudstones with some thin bands of siltstone, that yield slates and slabs. The formation has been called the Horrace Flags, after Horrace Hill [SD 264 794]. Its overall thickness is difficult to determine because exposures are poor, and folds and faults are common: it is estimated at about 600 m. The famous 'blue slate' quarries at Kirkby-in-Furness, just north of the district, lie within the formation.

Dr Berridge has examined a typical specimen (E41013) of grey silty slate from the bank of Pennington Reservoir [SD 2581 7885]. He reports that there is an apparent lamination parallel to the cleavage, but that this is a metamorphic phenomenon imposed on the rock, the primary laminations of which are now indistinct in hand specimens. The rock resembles the Brathay Flags in texture and composition, but this particular specimen is rather richer in felsic material and poorer in opaques than some specimens of the Brathay Flags, while carbonate material is absent. The original bedding laminae are distinguishable by the uneven distribution of disseminated oxidised iron ore.

The best exposures are in quarries just north of the district, at Knottallow Quarry [SD 270 803] and Mean Moor [SD 250 805]. At the first mentioned locality J. Bolton (1869, frontispiece) collected a slab bearing numerous Scyphocrinites? pulcher (McCoy), a species of crinoid known from the Cyrtograptus lundgreni to Neodiversograptus nilssoni zones in northern and central Wales. On Mean Moor [SD 2503 8055] beds near the base of the formation have yielded graptolites indicative of the Pristiograptus ludensis Zone, the highest in the Wenlock. Another fossiliferous exposure on the eastern bank of Pennington Reservoir [SD 2579 7882] probably lies about 400 m above the base of the formation. The fauna is from near the boundary between the P. ludensis Zone and the N. nilssoni Zone, and so lies near the Wenlock–Ludlow boundary. It seems likely then that this boundary lies high in the Horrace Flags. Other exposures lie in Pennington Beck [SD 2570 7796], and between Pennington Reservoir and Walthwaite.

Coniston Grits

The Horrace Flags pass upwards over some 5 to 10 m into the Coniston Grits, a unit that represents the main onset of greywacke turbidites in the area and is estimated to be about 1800 m thick. The passage is exposed in Pennington Beck [SD 2572 7794] where regular posts of greywacke-grits and thinly bedded siltstones are interbedded with both greenish grey and laminated bluish grey mudstones. About 30 m of strata are visible in an old quarry [SD 2573 7780] alongside the beck. Similar strata are exposed in Hasty Gill [SD 2710 7974].

The main outcrop forms the high ground north-west of Ulverston. There are many exposures of grey or greenish grey greywacke-grit, in posts averaging 2 m and exceptionally up to 5 m in thickness on Gameswell Hill [SD 274 795], Flan Hill [SD 283 797] and in Old Hall Wood [SD 278 795]. Sole structures and ripple marks are common in these posts, which are separated by thinner bedded siltstones with subordinate thin bands of greenish grey or bluish grey cleaved mudstone, the sequence being 80 to 90 per cent arenaceous. The 'grit' bands give rise to minor, but sharp, ridges well displayed on Flan Hill. The dip of the formation is 60°–70° to the south-east.

Some 500 m above the base there are some 75 m of highly cleaved grey or greenish grey micaceous mudstone, including some laminated mudstone of Brathay Flags type. This unit is called the Rosside Flags and is exposed only in the immediate vicinity of Rosside Beck [SD 2718 7881]. The J. Bolton Collection contains large distorted specimens of Cardiola interrupta J. de C. Sowerby, collected from this vicinity. Similar mudstones occur at Ben Cragg [SD 291 876] north of the district, but the faulting and the cover of drift make it uncertain whether these lie at the same horizon, though this seems unlikely. The Rosside Flags may equate with the Sheerbate Flags to the north.

South-west of Rosside the Coniston Grits are exposed in restricted stream sections near Channel House [SD 2638 7813], and in a small quarry [SD 2521 7695] north of Whinfield Farm. Other exposures higher in the sequence can be seen in Gill Banks Beck on the north-western outskirts of Ulverston, and in a small quarry [SD 2818 7884], where greenish grey greywacke-grit with laminated siltstone and mudstone bands is locally purple-stained. Dr Berridge has examined two slides from this quarry; one (E41007) of a greywacke, the other (E41011) of an intercalated fine-grained band. He reports that the former contains moderately well-sorted angular clasts of quartz and feldspar, averaging 0.05 mm in diameter, with subordinate lithic material, calcite, chlorite and flakes of white mica, set in a matrix composed mainly of chlorite. Abundant fine-grained granules of an opaque ore mineral (possibly mainly hematite) partially replace a number of the elastic minerals. In contrast the second specimen is a compact aggregate of apparently subangular grains of quartz and feldspar ranging between 0.002 and 0.008 mm in diameter, intergrown with a decussate fabric of white mica and chlorite laths up to 0.025 mm long. Dark laminations, some only 0.025 mm thick, coincide with relatively high proportions of chlorite. Accessory grains of iron ore are present throughout. The rock is pierced by cylindrical organic burrows up to 2 mm long and 0.2 mm across, several terminating at bedding laminae.

Thinly bedded siltstones on the western bank of Pennington Beck [SD 2565 7771], towards the base of the Coniston Grits, yield graptolites that indicate proximity to the P. ludensis/N. nilssoni boundary. A fauna from a nearby exposure [SD 2572 7754] appreciably higher in the sequence is from the N. nilssoni Zone, as is another from siltstones at a rather lower horizon on Copse Hill [SD 2608 7875]. It thus seems that the base of the Coniston Grits in this area is at, or close above, the base of the Ludlow Series.

Bannisdale Slates

The formation is essentially a turbidite facies but differs from the Coniston Grits in two respects. Firstly, silty mudstones and siltstones predominate over greywacke-grits, discrete bands of the latter making up about a third of the complete thickness. Secondly, much of the sequence is characterised by a banded facies described by Marr (1916) and later referred to as the 'banded unit facies' (Rickards, 1964). The banding is best seen on wet, weathered surfaces; it results from rapid alternations of dark silty mudstone and pale greenish grey or buff siltstone, individual layers ranging from a millimetre or so to 30 cm in thickness, but commonly 3 to 4 cm. An associated rock is a dark grey, commonly micaceous, siltstone, while the greywacke-grit posts, each 10 cm to 6 m thick, are all fine-grained and also mainly pale grey or greenish grey siltstones; some are slightly calcareous. Petrographic descriptions of these rock types appear below.

There is a gradual upward passage from the Coniston Grits into the Bannisdale Slates, the base of which has been taken at the incoming of the banded facies. Above this, the lithology is broadly similar throughout the formation, though there are minor and local variations in the proportion of mudstone and siltstone to that of greywacke-grit, and some indications that the latter becomes less common in the highest beds preserved.

Cleavage is dependent on lithology. There is a strong cleavage in the micaceous siltstones; in the banded facies it is restricted to the mudstone bands; in the greywacke-grits it is absent. Despite the name of the formation, economic slates do not occur.

It is difficult to estimate the thickness of the Bannisdale Slates. For the most part the dips are steep and consistently to the east and south-east in Furness, though there is a local reversal around Tridley Point [SD 319 787]. East of the Leven, however, there are many belts, following the strike, within which sharp minor folds, commonly with steeply dipping axial planes, are common. Their overall effect, together with that of the faulting, is difficult to determine because of the lithological similarity of the sequence. On the assumption that there is no significant strike-faulting and little repetition by folding, the minimum thickness seems to be some 5000 m, much greater than the 1500 m estimated farther north-east, even though the top of the formation does not appear to have been reached.

Details

Exposures are better than those of any of the other Silurian formations. West of the Leven the best are on Hoad Hill, Ulverston [SD 295 791], where dips are about 70° to the south-east; in quarries at the foot of the hill [SD 2973 7904], in Newland Beck [SD 2991 9779], on Great Oath Hill [SD 316 796] and in numerous roadside cuttings and quarries between Ulverston and Greenodd. A typical specimen of banded and laminated siltstone (E41009) from a crag [SD 2995 8027] near Newland, just north of the district, has been examined by Dr Berridge. It is an impure siltstone containing mainly sub-angular clasts up to 0.05 mm in diameter of quartz, feldspar, carbonate and–less commonly–lithic material, with abundant flakes of white mica and chlorite and interstitial white mica and chlorite. The laminations are due to variation in the proportion of phyllosilicate minerals to the other constituents. A preferred orientation of the phyllosilicates is parallel to the cleavage, which is oblique to the bedding and distorts it. The banding is produced by stripes of fine-grained weakly orientated intergrowths of chlorite and white mica with only accessory amounts of silt-grade clastics. A small amount of carbonate is present, enough to make the rock effervesce with dilute hydrochloric acid.

Exposures are more extensive east of the Leven. There are outcrops at Lady Syke [SD 326 831], at Mearness Point [SD 321 817] in the western half of the Roudsea Wood, and in an extensive road cutting at Backbarrow, just north of the district. Most of the outcrops are, however, on the hills and moors north-west of Cartmel, and also on Newton Fell, north of Lindale. In both areas the topography is distinctive and typical of the formation, greywacke grits forming steep-sided strike-ridges separated by peaty hollows following the banded silty mudstones. Individual ridges commonly show sudden twists, marking the position of steeply-plunging minor folds, or they terminate abruptly, suggesting both rapid variation in the thickness and number of the greywacke grits and the presence of dip-faults. Natural sections, though numerous, tend to be small, and more extensive exposures are in Well Know Quarry [SD 3733 7948], in road-cuttings to the west of Lindale, and in Fish House Quarry [SD 3440 8277] near Haverthwaite. About 20 m of beds displaying a small fold are exposed in Well Know Quarry; they consist of banded siltstone and slate with posts, up to 1 m, of siltstone-greywacke, passing up into thick bedded dark grey silty mudstone that is calcareous in parts. In Fish House Quarry a rhythmic series of fine-grained greywackes and banded mudstones and siltstones, about 30 m thick, is exposed showing minor folding about ENE axes, and the greywackes and siltstones have been worked for road-metal. The greywacke posts are up to 3 m thick and are uncleaved. They pass up into a normal banded facies of 5 to 10 cm layers of pale siltstone and dark mudstone in which cleavage is pronounced. Siltstones generally show current bedding. Specimens from separate lithologies within the turbidite sequence have been examined by Dr Berridge from the quarry. One distinctive rock-type (E41000) is a colour-laminated siltstone containing a very high proportion of chlorite and white mica accompanied by felsic clasts and accessory iron ore. The fabric of the micaceous minerals seems almost random. Darker laminae are marked by slightly higher proportions of chlorite and, locally, by heavy mineral concentrations of opaque ore, apparently mainly leucoxene after ilmenite. Incipient cleavage is shown by undulating folii of orientated aggregates of fine-grained chlorite and white mica. Another common lithology (E40999) is a massive fine-grained compact and well-sorted assemblage of subrounded to angular grains of quartz and feldspar cemented by subordinate interstitial chlorite and calcite. Silt-grade flakes of white mica are moderately abundant, showing a strong orientation in the cleavage plane. A finer-grained variety (E40997) is a compact aggregate of felsic minerals and chlorite transected by orientated flakes of white mica. Bedding laminae, as little as 1 mm in thickness, are defined by slight variations in the relative proportions of felsic to phyllosilicate minerals. A further fine-grained variety (E40998) is a strongly foliated intergrowth of chlorite and white mica with disseminated irregular granules of calcite. Scattered silt-grade clasts of felsic material are present together with smaller granules of opaque ore-mineral.

A small intrusion in the Bannisdale Slates has been recorded on Grassgarth Height [SD 3547 8249], about 600 m S of Bigland Hall. The rock is mostly deeply weathered to a rich brown colour, but when fresh is dark grey to black speckled pink. Its relationships suggest that it is a dyke, about 2 to 3 m wide, trending NE–SW. Cleaved mudstone within 1 m of the igneous exposure is slightly indurated.

Four thin sections were made of the rock (E46386), (E46386A), (E46386B), (E46387). Dr Berridge reports that they reveal a fairly typical lamprophyre texture. Large subhedral biotite crystals are set in a mosaic of even larger anhedral feldspars, and the whole fabric is set with relatively small carbonate and chlorite pseuomorphs after probable former pyroxene and olivine. Accessory euhedral magnetite and apatite crystals are quite abundant.

The feldspar crystals are typically about 1 mm in diameter but some are as much as 2 mm. They tend to be elongate but otherwise anhedral. Their composition is variable, because it appears that an initial phase of plagioclase crystallisation was followed by the formation of alkali feldspar. The dominant form present is andesine An„, fairly fresh but generally somewhat clouded by replacive flakes of chlorite and white mica. The andesine is, however, commonly mantled by, or irregularly replaced in patches either internally or marginally, by orthoclase microperthite; locally whole crystals or groups of crystals are composed of microperthite. Both the microperthite and andesine are lightly tinted reddish brown (pink in hand specimen) by what appear to be almost submicroscopic inclusions of ferric oxide. These are commoner in the microperthite than in the andesine; conversely, the microperthite contains far fewer 'clouding' inclusions of white mica and chlorite. The biotite crystals are typically some 0.25 mm thick and 0.5 mm across the subhedral pseudohexagonal basal sections. They are commonly physically distorted, almost 'boudinaged' in some cases, yet the overall orientation fabric appears to be decussate. They are pale yellowish brown in colour with a darker brown marginal zone in many cases, both types being pleochroic to pale straw yellow. In general they are fresh, but some crystals show partial alteration to a pale olive green chlorite along cleavage planes, and there is more wholesale chloritisation adjacent to joints and former interstitial voids. Numerous pseudomorphs after former crystals of probable pyroxene are occupied by fine-grained aggregates of ferroan calcite, generally accompanied by minor amounts of chlorite and traces of iron oxide. The prevailing stumpy form of the pseudomorphs, which are typically about 0.15 mm in diameter, suggests that they represent pyroxene rather than amphibole. Their subhedral form suggests early crystallisation. Less numerous but similar in habit and form are pseudo-morphs after primary olivine. The replacive material is in this case chlorite, outlined and sometimes barred by opaque reddish brown ferric oxide (?hematite). Euhedral octahedral magnetite is a fairly abundant accessory constituent of the rock. Crystals range from about 0.03 to 0.15 mm in diameter, and some of the larger ones appear to have spheroidal cores of ?hematite. Accessory apatite, almost equally abundant, also occurs in euhedral or subhedral form, the prisms ranging up to 0.3 mm in length and 0.08 mm in diameter. Former interstitial voids and joints are filled by the same type of chlorite that has replaced the biotite, olivine and andesine. It is a variety showing very low but normal birefringence, generally occurring as matted aggregates though sometime spherulitic in habit. Relatively large anhedral plates of a carbonate mineral are locally associated with it; it is probably a non-ferroan calcite.

The rock is a fairly typical lamprophyre but it is nevertheless difficult to classify under the standard Rosenbusch system because it bridges the division between kersantite and minette. Since andesine exceeds orthoclase, however, the rock is best called a kersantite. WCCR, NGB

References

BOLTON, J. 1869. Geological fragments collected principally from rambles among the rocks of Furness and Cartmel. Ulverston and London. 264 pp.

FURNESS, R. R., LLEWELLYN, P. G., NORMAN, T. N. and RICKARDS, R. B. 1967. A review of Wenlock and Ludlow stratigraphy and sedimentation in NW England. Geol. Mag., Vol. 104, pp. 133–147.

MARR, J. E. 1878. On some well-defined life-zones in the lower part of the Silurian (Sedgwick) of the Lake District. Q. J. Geol. Soc. London, Vol. 34, pp. 871–885.

MARR, J. E. 1916. The Geology of the Lake District and the scenery as influenced by geological structure. Cambridge. 220 pp.

MARR, J. E. and NICHOLSON, H. A. 1888. The Stockdale Shales. Q. J. Geol. Soc. London, Vol. 44, pp. 654–730.

NORMAN, T. N. 1961. The geology of the Silurian strata in the Blawith area, Furness. Unpublished Ph.D. thesis.

University of Birmingham.

RICKARDS, R. B. 1964. The graptolitic mudstone and associated facies in the Silurian strata of the Howgill Fells. Geol. Mag., Vol. 101, pp. 435–451.

TAYLOR, B. J., BURGESS, I. C., LAND, D. H., MILLS, D. A. C., SMITH, D. B. and WARREN, P. T. 1971. Northern England. Br. Reg. Geol., Inst. Geol. Sci., Fourth Edition.

Chapter 4 Carboniferous rocks

Classification and history of research

In South Cumbria the earliest Carboniferous rocks are conglomerates, sandstones and shales that mark the accumulation of rock-waste from the dissected land surface of Lower Palaeozoic rocks over which the shallow Carboniferous sea advanced. Around the Duddon Estuary up to 240 m are proved, though elsewhere these deposits are much thinner and appear to be absent in Cartmel. As the sea deepened and cleared a shelf-limestone sequence up to some 600 m thick was laid down. Renewed influxes of terrigenous sediments then led to the deposition of alternations of marine limestones, shales and sandstones generally some 100 to 110 m thick, succeeded by at least 450 m of marine shales and sandstones.

This sequence was recognised by Aveline during the Primary Survey of the district in 1865–70. He referred to the lowest unit as the Basement Beds, and grouped all the strata above the main mass of Carboniferous Limestone as Yoredale rocks. This terminology was used on One-inch Geological Sheets 48 and 58 (Ulverston and Barrow); a short memoir was produced for the Barrow district (Aveline, 1873) but no memoir was published for the sheet to the north, which includes the greater part of the Carboniferous outcrop.

The earliest detailed descriptions of the Carboniferous of Furness were published by Kendall (1885, 1893), a local mining engineer who contributed much to the study of the Lower Carboniferous rocks and their contained hematites in north-western England. He adopted Aveline's major divisions and, like him, separated off a group of shales with thin limestones, which he called the Lower Limestone Shales, between the basal conglomerates and the main limestones, and correlated the variable sequence above the limestones with the Yoredale rocks of the Pennines.

During the resurvey of 1937–38 much new information was gathered from the logs of many hundreds of boreholes and from plans of mining operations. Moreover some of the hematite mines were still active and many excellent underground sections were recorded. As a result a new lithological classification was proposed (Dunham and Rose, 1941). The basal deposits were grouped as the Basement Beds, a unit that includes the 'Basement Beds' of Aveline together with at least the lower part–possibly the whole–of his 'Lower Limestone Shales'. The main mass of the limestone was divided into five formations, each of which is remarkably constant in its general character throughout the district. A higher division, the Gleaston Group, was set up to cover the strata above the main limestones.

In the last few years a limited up-dating of the 1937–38 mapping has been carried out. In addition, two boreholes have been drilled into the higher part of the sequence, one near Roosecote and one near Gleaston Castle. Their results have necessitated minor emendations to the previous nomenclature, for they have established that the greater part of the Gleaston Group as originally defined is of Namurian age. It is accordingly proposed to call the Namurian part of the sequence the Roosecote Mudstones, and to refer to the lower part as the Gleaston Formation. It has also been proved that, at Roosecote, the Gleaston Formation has passed into dark limestones that are not developed at outcrop. This unit is here termed the Roosecote Limestone.

The only previous palaeontological study of the Lower Carboniferous (Dinantian) rocks of Furness and Grange was the classic work of Garwood (1913), the present district forming the south-western part of the area described by him and subsequently termed the North West Province. Garwood subdivided the sequence into what were essentially faunal assemblage zones, but these were defined as rock units, each of which is extremely consistent in lithology. Faunal marker bands were used to delimit the zones and subzones and, though the eponymous fossils commonly range beyond the bands, the concentration of certain species at well-defined levels has proved valuable in correlation.

Prior to Garwood's work, a number of coral-brachiopod zones had been erected for the Lower Carboniferous by Vaughan (1905), using the rock sequence in the Avon Gorge as a standard. Much confusion now exists in the usage of these zones, and the Avon section can now be shown to contain a number of non-sequences (Mitchell, 1972; Ramsbottom, 1973; Austin, Conil and Rhodes, 1973). As a result some of the zonal symbols of Vaughan have come to have different meanings in north-west and southwest England: the zones are used here in their south-west England sense.

In a series of publications, Bisat (1924, 1934) erected a number of zones based on the goniatite faunas that occur widely in the Carboniferous strata of parts of northern England. The Roosecote Mudstones fall readily into his scheme: so do parts of the Gleaston Formation, even though recorded goniatites are few.

More recently Ramsbottom (1973) has put forward a different classification of the Dinantian rocks of Britain, which he has suggested can be divided into six 'cycles' or groups of minor 'cycles', each carrying a distinctive fauna, and representing stages into which the Dinantian rocks of Britain fall. He believes that clear-water bioclastic limestones formed during transgressive phases, and that oolites, calcite mudstone (which may contain stromatolitic algae), primary dolomitic limestones and sandstones formed during regressive phases. He has applied this concept to the present district (Ramsbottom, 1973, fig. 3). George and others (1976) have followed this same concept in erecting six Regional (non-Standard) Stages to cover the Dinantian rocks of the British Isles. The stratotype section for one of these proposed Stages–the Holkerian–is at Barker Scar, Holker, within the present district.

The resurvey has enabled a study to be made of the correlation between the lithological units of Dunham and Rose, the various fossil zones, and the 'cycles' of Ramsbottom. Their relationship is set out in (Table 6). KCD, WCCR

General stratigraphy

Basement Beds

Much of the information about the lithology, distribution and thickness of this formation comes from the logs of bore-holes that were sunk between 60 and 100 years ago and are consequently difficult to translate into modern lithological terms. Excellent sections were, however, accessible in mines during the resurvey and these, together with the few surface exposures, enable a satisfactory synthesis of the borehole information to be made.

The formation is thickest along the Duddon, possibly because the estuary marks a pre-Carboniferous hollow that was submerged earlier than other parts of the district. At Dunnerholme some 240 m is recorded, over 200 m as far south as Askam, and nearly 200 m at Hodbarrow. Southwards around Roanhead and Sandscale at least 100 m are present and some 90 m are probably preserved between Dalton and Marton. North-eastwards from Lindal Moor towards Ulverston there seems to be an appreciable thinning to 50 to 60 m. The thinning continues eastwards, for less than 5 m can be assigned to the formation in a recent borehole 3 km SSE of Ulverston, whilst it appears to be absent in Cartmel. Representative vertical sections are shown in (Figure 4).

Around the Duddon the Basement Beds consist largely of conglomerates, sandstones and shales. Some thin and impure limestones occur, mostly in the upper part of the sequence, and there are also a few thin beds of gypsum. In detail rapid lateral variations are general. Limestones are generally insignificant except near the top where there is a transitional passage into the Martin Limestone, and an arbitrary base for the latter has been taken where the proportion of limestone exceeds that of shale: conglomerates die out upwards at about the same level. As the sequence is followed south-westwards from Dunnerholme to Askam and beyond, conglomerates become less important, and the number of limestones increases. In particular a unit of limestones with grey shale partings develops between the Martin Limestone and the red shales and sandstones typical of the Basement Beds around Hodbarrow. It is up to 75 m thick beneath Sandscale Haws. Similarly alternations of limestones and shales, up to 35 m thick, are recorded in this same stratigraphic position between Lindal and Pennington, but appear to be absent at outcrop. These changes are believed to take place towards the open sea, the conglomerates representing torrent deposits laid down in shallow water near the head of an estuary, the gypsum beds suggesting the ephemeral presence of marginal lagoons or sabkhas, and the limestones marking more marine conditions.

The conglomerates are normally made up of well-rounded pebbles, up to 5 cm in diameter, set in a matrix of sub-rounded smaller rock fragments and coarse sand. Coarser conglomerates, with pebbles up to 15 cm, have been recorded at Hodbarrow. Many of the pebbles are andesites and tuffs which can be matched from the nearby Borrow-dale outcrops. Locally derived Borrowdale rhyolites and Silurian grits and greywackes are also common, while many of the smaller pebbles are of vein-quartz. Pebbles of the Ennerdale Granophyre and Eskdale Granite have also been recorded, and east of the Duddon there are some of slate, resembling those of the Skiddaw Group, and others of green mudstone, like the Stockdale Shales. These coarser strata are mainly reddish brown with pale green layers and mottlings, the rapid colour variation suggesting that, despite local secondary reddening, much of the colour variation is primary. Many of the pebbles have a thin red ferruginous pellicle, though others seem unaffected.

The conglomerates grade into coarse sandstones while other sandstones are thinly bedded, fine-grained and micaceous, and grade in turn through shaly sandstones and siltstones into sandy shales. Most are dull reddish brown; others are pale greenish grey, yellow and buff. The pelites are mostly dull red mudstones and sandy shales, with pale green layers and mottlings. Dark grey and black shales with plant remains are not uncommon. They include nodules and nodular layers of yellow or buff impure limestone and dolomite. Thin bands of grey or black limestone also occur.

The Basement Beds have yielded very few macrofossils but the spore assemblages from mudstones in the Poaka Water-level are of Tournaisian age.

Martin Limestone

The upward passage from Basement Beds to the Martin Limestone has been recorded in many borehole logs. The junction could formerly be examined in several places in the Hodbarrow workings, and can still be seen in the Poaka Water-level and at surface near Green Haume. As explained above, the base of the formation is generally taken where limestone becomes dominant over shale. Above this the number and thickness of the shale bands rapidly diminish and the bulk of the formation comprises a sequence of thinly bedded, hard, compact fine-grained limestones, with thin partings or films of calcareous shale between most of the carbonate posts. These lithologies continue upwards to the base of the Red Hill Oolite, which is taken at the top of a persistent algal band–the Algal Band (Dunham and Rose, 1941). This band is conspicuous in the field, on mine dumps, and in some borehole cores (Plate 3.1). It is composed of rounded algal nodules 1 to 2 cm in diameter, showing a concentric structure, and set in a matrix of grey, fine-grained fragmental limestone and crystalline calcite. The algal nodules commonly weather white in contrast to the darker-coloured matrix. A similar nodular band occurs at Ashes Point on the west shore of the Leven.

The average thickness of the formation in the district is about 45 m but there are appreciable variations from this mean. At Hodbarrow and at Dunnerholme it is about 45 m thick; near Roanhead Crag it increases to about 100 m and in the Roanhead mining area to 135 m. South-eastwards to Dalton and thence to Lindal Moor the thickness is about 60 m and it has been assumed that this is maintained beneath the drift-covered outcrop between Lindal Moor and Ulverston. The maximum thickness is only 25 m in Roudsea Wood, on the eastern shore of the Leven, though here the formation may represent only part of the full succession as developed farther west.

The bulk of the Martin Limestone is grey or greenish grey calcilutite–a hard extremely fine-grained limestone having a porcellanous appearance and a brittle fracture–a lithology referred to as 'lime-rock' by Hodbarrow miners. Algal limestones are also common, and some chert nodules have been recorded in boreholes and from mine dumps, though none has been seen at surface. Other less typical limestones are dark grey calcisiltites, consisting essentially of carbonate oozes. Some are laminated and current-bedded, a feature most easily distinguished where secondary dolomitisation has occurred. The coarser laminae are made up of bioclastic grains similar to those in the calcarenites of the Red Hill Oolite. In places the highest beds are fine-grained bioclastic limestones rather than calcilutites.

Locally, dolomitisation is extensive, as in Hodbarrow, Dunnerholme, in the Askam–Roanhead area, and at Lindal Moor. The alteration, however, is patchy and clearly of secondary origin, being associated with faults and joints especially in the vicinity of hematitisation.

Much of the Martin Limestone—especially the fine-grained parts—is poorly fossiliferous. The richest faunas come from the upper part of the formation which is exposed in Martin Quarry [SD 243 768], the quarry that gives its name to the formation. Silicified specimens of Carcinophyllum simplex, Koninckophyllum sp., Thysanophyllum pseudovermiculare and Composita gregaria are common and this assemblage is indicative of the lowermost Viséan, i.e. the upper part of C₁ Zone and the lower part of the C₂S₁ Zone. The lowest part of the Martin Limestone is relatively unfossiliferous: it may well be of Tournaisian age.

Red Hill Oolite

There appears to be a pause in deposition at the base of the Red Hill Oolite, marked by local penecontemporaneous erosion. A calcareous or dolomitic nodular band lies above this irregular surface and algal structures have been described from within it (Nicholas, 1968).

The formation contains much carbonate sand, and the typical sediment is calcarenite. The relatively quiet current-free conditions typical of the deposition of the Martin Limestone were replaced by increased current activity that produced more sorting of the material. The typical rock type is a pale grey or creamy white biocalcarenite with pseudoooliths which are conspicuous in hand specimens. Banding and lamination, commonly accompanied by false-bedding, are fairly general, particularly near the base and towards the top of the formation. A distinctive feature of the Red Hill Oolite is its massive character, bedding planes being poorly developed; this is in sharp contrast to the Martin Limestone below and the Dalton Beds above. The rock seems to have been particularly susceptible, however, to joint stresses and, in addition to closely-spaced vertical joints, it is broken up by small irregular joints and cracks of varying directions.

At the time of the resurvey over 25 m of the Red Hill Oolite were well exposed in Red Hills Quarry [SD 178 793] and there were other good exposures near Hodbarrow Point, but all these sections are now much obscured. In Furness there are good sections at Dunnerholme, Roanhead Crag, around Housethwaite Hill, and between Green Haume and Marton: excellent exposures also occur along the west shore of Cartmel. Over the whole area the lithology of the formation shows little change. The thickness of the formation also remains reasonably constant at about 60 m.

Secondary dolomitisation is extensive especially where the formation contains, or has been partly replaced by hematite. Where alteration is complete the rock is converted into a dense, finely crystalline aggregate of greyish brown dolomite. This was the usual wall-rock in Roanhead and Hodbarrow mines and it makes up much of the mine dumps around Lindal Moor. The effects of secondary dolomitisation and its obvious connections with faults and joints are clear around Hodbarrow Point, near Elliscales Quarry, near Tytup Farm and Lindal Moor, and at Plumpton, east of Ulverston. The probable association between dolomitisation and hematitisation is discussed later.

Fossils are not common in the Red Hill Oolite but small simple corals such as Koninckophyllum cf. praecursor and Palaeosmilia murchisoni can generally be found, together with specimens of the tabulate coral Michelinia megastoma. Large gastropods and small fragmentary brachiopods also occur. The fauna is typical of the C₂S₁ Zone.

Dalton Beds

The Red Hill Oolite is succeeded by a thick division of dark, well-bedded, medium-grained limestones containing partings of calcareous shale. The formation is well exposed around Dalton-in-Furness, after which town it is named. Its base is difficult to define precisely because in most places there is some interbedding between pale grey fragmental limestones of Red Hill Oolite type and the darker grey limestones typical of the Dalton Beds. It has, however, been taken generally at the first appearance of dark grey limestone; in most cases this coincides with an upward change from massive to well-bedded limestones.

The bulk of the Dalton Beds comprises dark grey medium-grained limestone containing crinoid columnals up to 10 mm in diameter. The limestones are bituminous and emit a foetid odour when hammered. Generally they form posts up to 1 m thick, separated along well-marked undulating bedding-planes by thin shale partings. Thicker-bedded limestones also occur, especially towards the base and at the top of the formation.

The frequency of the shale bands and the relative proportions of shale and limestone show considerable variation across the district, there being a marked tendency for a more shaly division to lie near the middle of the formation. The thickness variations are also appreciable. Near Haverigg only the lowermost 60 m have been proved by drilling. Across the Duddon, at Roanhead and Sandscale, the complete thickness is at least 180 m, and possibly 240 m, and shale partings become particularly common upwards from some 90 m above the base. Exceptionally, around Roanhead, pale cherty limestones appear in the middle of the sequence. At Dalton some 255 m are present and eastwards from here to Ulverston the lower part of the formation shows little change but a definite shaly division in the middle of the sequence becomes more distinct. South and east of Ulverston the formation is believed to thin rapidly. It can be no more than 105 to 110 m in old quarries near Plumpton Hall, east of Ulverston, where again thinly bedded limestones and many shale partings occur in the middle of the formation, and the highest limestones are sandy in part. On the east of the Leven there are good exposures both below and above the shaly unit: the overall thickness appears to be about 120 to 130 m.

A striking palaeontological change takes place at the base of the Dalton Beds and, in comparison with the lower formations, fossils are much more common: they are typical of the C₂S₁ Zone. The lowest limestones contain the large brachiopod Delepinea carinata together with abundant corals including Caninia sp. cylindrica group, C. subibicina and Michelinia megastoma.

Park Limestone

This name has been given to a thick unit of cream or pale grey limestone that overlies the Dalton Beds. It forms the wall rock of the Park Sop (see p. 104), from which the name has been taken, but probably the best section is that along the east shore of the Leven near Old Park Wood. In detail the upward change from dark grey to cream limestone can extend over 1 or 2 m but more generally it is even sharper. The abruptness of the change seems to be due to a sudden cessation in the supply of argillaceous material rather than to a pause in deposition.

Several excellent and extensive exposures of this formation show the lithology to be remarkably uniform throughout the district. The limestone is essentially a biocalcarenite. Some oolitic grains are present in places and small crinoid columnals are common. The lithology is superficially similar to that of the Red Hill Oolite, but rounded grains and pseudo-ooliths are much less common. It also resembles the Red Hill Oolite in being generally massive and highly jointed: closely spaced vertical joints and small cracks of varying direction result in the rock breaking into irregular blocks on quarrying. Bedding planes are either undetectable or can be traced laterally for only a few metres.

Throughout Furness and Cartmel the formation maintains an almost constant thickness of 120 to 130 m in all the many available sections and provings. It is now the chief source of road-metal in Furness, and is quarried at Goldmire and Stainton.

The fauna of the Park Limestone, especially in the lower part is not so clearly diagnostic as is that of the Dalton Beds and fossils are less common. Linoprotonia corrugatohemispherica, L. ashfellensis and Lithostrotion minus are recorded, however, and the fauna is characteristic of the S₂ Zone.

Urswick Limestone

This formation is superficially similar to the underlying Park Limestone, being a pale grey limestone made up of skeletal fragments set in a finer-grained matrix and, like it, is a source of road-metal and formerly of building-stone. The most noticeable differences are that it is well bedded and regularly jointed throughout, and pseudobrecciation is common. Individual posts of limestone vary from 0.5 to 5 m in thickness, and are commonly separated by thin partings of shale, which produce a marked scarp-and-dip topography along the outcrop. The joints are much more widely spaced than in the Park Limestone and, together with the bedding planes, have favoured the widespread production of grike surfaces, a feature characteristic of the Urswick Limestone and of all outcrops of equivalent beds in northern England. These fracture planes also facilitate the production of conveniently sized blocks and so account for its former importance as a building-stone. Exposures are particularly good around Little and Great Urswick, on Birkrigg Common, and in Cartmel. The base of the formation is exposed in many places and the change in lithology takes place by gradation within a metre or so, in places being marked by a thin shale parting.

The limestone is compact and harder than most of the lower ones. In this district it is unique in the presence of pseudobrecciation in almost every bed, consisting of irregular dark patches set in the normal pale limestones. Similar pseudobrecciation at about the same horizon has been noted by many earlier workers (Tiddeman, 1907; Dixon and Vaughan, 1912; Garwood, 1913). More recently Nicholas (1968) has concluded that it results from diagenetic re-crystallisation, perhaps associated with vertical load cornpression, while Grayson (verbal communication, 1975) considers it to be a form of bioturbation (see (Plate 3.2)).

A persistent bed of dark grey pyritous shale, averaging 4.5 m thick, lies about 30 m above the base of the formation at Urswick and at Park Sop. It is named the Woodbine Shale, after Woodbine Pit, Newton. At outcrop it weathers to produce a slack, and the presence of a slack in this same position as far east as Cartmel is taken as evidence for the lateral extent of the member well beyond its provings. Thinner beds of shale lie in places between limestone posts, but seem strictly local.

Near Park Sop the Urswick Limestone has been shown to be 120 m thick, and this is also the case in the mines at Newton and Yarlside, around Great Urswick, Baycliff, and Bardsea Park. On the eastern side of Cartmel it thickens to 150 to 160 m.

The fauna is relatively prolific and shows marked differences from that of the Park Limestone. It is typical of the D₁ Zone, and common fossils include Dibunophyllum bourtonense, Palaeosmilia murchisoni, Lithostrotion spp., Davidsonina septosa (in the higher beds), and Gigantoproductus maximus.

Gleaston Formation and Roosecote Limestone

Over the whole of the outcrop a notable change in character of the sediments and their faunas takes place at the top of the Urswick Limestone. The change coincides more or less exactly with a bed containing abundant algal nodules that we identify as the Girvanella Nodular Bed of Garwood (1913), marking the base of his Upper Dibunophyllum (D₂) Zone. In 1941 Dunham and Rose proposed the name Gleaston Group to include all the beds of Carboniferous age above (and including) the Girvanella Bed, defining the group as follows:

'Gleaston Group (formerly called Yoredales)–Black shale, with thin sandstones and limestones; these latter (dark, cherty or coarse crinoidal) confined to the lower 500 ft.'

The total thickness was estimated at 1400ft (427 m). It was recognised that, though it was poorly exposed, the numerous shafts and boreholes penetrating the group revealed that it was far more variable in lithology and facies than the underlying formations.

Significant new information has been provided in recent years by boreholes specially drilled to investigate this part of the succession. It is now clear from the discovery of the diagnostic Cravenoceras leion Band that the Gleaston Group of 1941 includes both Dinantian and Namurian strata. Consequently in defining the Gleaston Formation the term has been restricted to the uppermost Dinantian, that is to the strata above the Urswick Limestone and below the C. leion Band. The Namurian strata are thus excluded from the Gleaston Formation. From the type-locality at Gleaston, where the unit consists essentially of alternating thin mudstones and limestones with impersistent sandstones, a marked thickening and a complex change of facies set in to the south and west. These were suggested by the records of the Stank shafts, showing passage from shale to limestone, and new boreholes now confirm a passage towards Roosecote into thick dark basinal limestone with Posidonia Zone (P₁ and P₂) faunas. Similarly to the west at Haverigg flaws a borehole had proved a facies in which both light-coloured shelf limestones with D, faunas and sandstones have thickened. The details of the passage of these different facies into one another are far from clear, for there are no modern sections in several critical areas. Generalised sections of the relevant strata are given in (Figure 5).

The whole situation is reminiscent of the relationship between the Craven uplands and the Bowland basin, 50 km to the east: in the uplands the clastic sediments between the shelf limestones of the D₂ Zone locally die out and crinoidal bioclastic limestones thicken, as at Toft Gate, Greenhow (Dunham and Stubblefield, 1945), while the equivalent beds to the south are shales and black limestones of Bollandian age. This same shelf/basin relationship apparently continued westward from Craven to Furness.

The Girvanella Nodular Bed lies near the boundary between the Urswick Limestone and the Gleaston Formation, and in drivages at Newton Mine it was well exposed, resting directly on the Limestone. The fullest section of the Gleaston Formation in its type-area is obtained by combining the records of the recent Gleaston Castle Borehole and an older adjacent hole. The full sequence is about 80 m thick. The basal limestones contain a rich D₂ coral/brachiopod fauna. Upwards these are replaced by goniatite/bivalve faunas characteristic of the P₁ and P₂ zones. Precise details of the succession are largely dependent on borehole information. Individual members seem to be highly variable, though to some extent this may be exaggerated by different standards of logging of the older boreholes. In any event it is not possible to trace individual limestones very far, and the one significant sandstone is equally local.

Apart from the topmost 6 m, which consist of muddy limestones and mudstones, the equivalent strata at the Roosecote Borehole comprise a monotonously uniform sequence of dark cherty limestones with regular thin mudstone partings. Over 180 m of these limestones were drilled through without the Girvanella Nodular Bed being encountered. Fossils are rare, but scattered specimens indicate that the entire succession is referable to the P₁ and P₂ zones. A distinct name—the Roosecote Limestone—is here proposed to distinguish this unit.

At Haverigg Haws there are two closely associated beds with Girvanella nodules, within a 10-m basal band of dark limestone that rests on the Urswick Limestone. The lower is taken to be the main Girvanella Nodular Bed of the Urswick Syncline. Above these basal limestones the succeeding 150 m of strata contain thick pale limestones, some coarsely crinoidal with white chert, and some markedly pseudobrecciated. A 14-m sandstone intercalation has its base 36 m above the Girvanella Nodular Bed. The faunas are comparatively rich and are everywhere of D₂ aspect. The faunas and lithologies have many points in common with the West Cumbrian succession; indeed the faunal sequence is also comparable with that of the various limestone members in the Yoredale facies. The limestone is lithologically and faunally different from the Roosecote Limestone, and is overlain by about 33 m of clastic sediments including a 7-m sandstone member and, though the C. leion Band has not been located, the D, sequence is clearly almost complete.

Between the Roosecote and Haverigg Haws boreholes a much faulted sub-drift outcrop of Gleaston Formation runs eastwards from Sandscales to the Yarlside Fault. The succession is not easy to interpret from old borehole logs for not only is the precise base of the Permo-Triassic difficult to determine in some holes (see p. 44), but neither the Girvanella Nodular Bed nor the C. leion Band has been recorded. It is, however, clear that the upper part of the succession contains a major unit of sandstone and sandy shale resting on the main mass of limestone. Individual borehole records and limited surface exposures show that the upper part of this limestone is lithologically very similar to limestones well above the Girvanella Nodular Bed at Haverigg Haws, and quite unlike the Urswick Limestone. The section in (Figure 5) was obtained by combining two adjacent borehole records, and correlates well both in lithologies and thicknesses with the Haverigg Haws sequence.

The most difficult area to interpret lies between the Yarlside Fault and Newton. There are numerous old bore-holes and shafts around Stank, but unfortunately the records are extremely variable partly because many of the holes appear to have passed through faults. At Stank Mine about 25 m of alternation of limestones and shales–typical of the Gleaston Formation–are said to have separated a thick overlying mudstone sequence above from the main mass of limestone below. It seems probable that the anomalies between this sequence and those to the east and west are best resolved by assuming that the upper part of the limestone at Stank is of D₂ age, and that this thins and is progressively broken up by shales towards Newton and Gleaston.

A further substantial outcrop of these strata lies east of the Leven in Holker Park. The sequence is badly exposed and much faulted and the section in (Figure 5) has been produced by piecing together the various exposures. It falls into two halves. The lower part is basically a limestone sequence, though with substantial terrigenous intercalations near the base. About 130 m are exposed, and the Girvanella Nodular Bed probably lies close beneath the lowest part of this section. The limestones are cherty, and many are crinoidal. Their outcrops are separated by a fault from those of two thick sandstones with associated mudstone partings, which form the highest exposed beds and together amount to some 85 m. A thin coal lies between the two sandstones. The sequence at Holker thus seems to be the thickest in the district. Its closest analogy is with Haverigg Haws, rather than with the much nearer Gleaston section.

Roosecote Mudstones

Upper Carboniferous rocks are preserved only along the axis of the Urswick Syncline and beneath the spread of marine alluvium south of Flookburgh, though in the latter area records are few and fragmentary and their correlation far from certain. In both the recent boreholes at Roosecote and at Gleaston Castle Farm, the base of the Namurian marks an upward change to thick mudstones. In the absence of any other evidence the base of the mudstone sequence has been taken as the base of the Namurian throughout the district, and the strata are here termed the Roosecote Mudstones.

Sedimentation appears everywhere to have taken place in a deep muddy sea. Mudstones and fine-grained siltstones are the dominant sediments, limestones being restricted to thin beds associated with a group of faunal bands near the base of the succession. Sandstones are confined to a limited number of turbiditic influxes, presumably representing the distal equivalent of the more proximal Pendle Grits and the more fluviatile Skipton Moor Grits to the east.

Diagnostic faunas are restricted to the closely associated Cravenoceras leion, Eumorphoceras pseudobilingue and C. malhamense bands. The absence of the C. cowlingense and E. bisulcatum bands suggests that the entire sequence falls within the Pendleian Stage (Hudson, 1945).

Vertical sections of the various provings are shown in (Figure 6). Precise correlation of the older holes is not possible, but some indication of the suggested placing of the sections within the sequence is given by their relative positions in the diagram. WCCR KCD

Stratigraphical palaeontology of the Dinantian strata

The fossil-localities and the fossils collected from them during the resurvey are listed by formations in Appendices 2 and 3. The more important fossil records are given in the details of Lower Carboniferous stratigraphy, and the ranges of some of the more significant fossils are given in (Table 7). The authors of specific names are included in Appendix 3.

Basement Beds

Very few macrofossils have been collected from the Basement Beds and none has proved diagnostic of age. However, two well-preserved miospore assemblages were recovered from a sample of mudstone with plant debris in the Basement Beds of Poaka Water-level (loc. C7). A number of forms from these assemblages–including Retusotriletes incohatus Sullivan, Verrucosisporites nitidus (Naumova) Play-ford, Baculatisporites fusticulus Sullivan, Schopfites claviger Sullivan, Raistrickia corynoges Sullivan, Knoxisporites pristinus Sullivan and Auroraspora macra Sullivan–comprise an association of considerable stratigraphical significance. Neves and others (1972, 1973) have noted that all the forms in the above association are characteristic components of the Schopfites claviger–Auroraspora macra Zone, considered to be of Tournaisian age ( =part of Major Cycle 1 of Rams-bottom and approximately equivalent to Z–lower C, age in terms of the Vaughanian coral-brachiopod zonation). Sullivan (1968) has recorded an identical association from the Cementstone Group of Heads of Ayr, Ayrshire, whilst Johnson and Marshall (1971) recorded all of the above forms with the exception of Schopfites claviger from the Pinskey

Gill Beds of Ravenstonedale, which are also of Tournaisian age. The absence of representatives of the genus Lycospora from these assemblages is considered sufficient evidence to preclude an uppermost Tournaisian or a Viséan age for these samples, for deposits of those ages commonly contain representatives of that genus in great abundance. BO

Martin Limestone

No one section exposes the whole of the Martin Limestone. Its lower part, in particular, is poorly seen. It is, however, well exposed in Meathop Quarry, only 3 km NE of Grange, where algal limestones with associated horizons of desiccation polygons occur 2 to 4 m above the base of the section. This level is correlated with the Algal Layer (Garwood, 1913) at the top of the Coldbeck Limestones in Ravenstonedale and is believed to mark the regressive phase of Major Cycle 1. The top of the Algal Layer is currently taken as marking the Tournaisian–Viséan boundary in northern England (Mitchell, 1972, p. 158; Ramsbottom, 1973, p. 58). The beds below the algal limestones at Meathop are, therefore, of Tournaisian age, and the lower part of the Martin Limestone in the present district is also probably of this age.

Rich faunas are recorded from the upper part of the Martin Limestone at Hodbarrow Quarry (loc. C10), the cliffs at Dunnerholme Point (loc. C12) and Martin Quarry (loc. C16). They include the corals Carcinophyllum simplex, Carruthersella aff. compacta, Koninckophyllum meathopense, K. praecursor, K. vesiculosum, Michelinia megastoma [rare small colonies], Syringopora spp., and Thysanophyllum pseudovermiculare, and the brachiopods Cleiothyridina glabristria, Composita aff. ficoidea [of Garwood, 1913, pl. 51, fig. 6] and C. gregaria. Of these T. pseudovermiculare is the most diagnostic element of the fauna and, together with C. gregaria, has not been recorded above the Martin Limestone. The rich coral fauna seen in Martin Quarry and also at Meathop includes many of the species first described by Garwood as from his Seminula gregaria Subzone. It is one of the richest coral faunas of this age, many of the species being comparatively rare in other parts of Britain.

The top of the Martin Limestone is commonly marked by a band of algal limestone–the Algal Band of Dunham and Rose, 1941 (loc. C9b) which rests on fine-grained unfossiliferous limestone at Red Hills Quarry (loc. C9). This band is considered to represent the regressive phase of Major Cycle 2.

Red Hill Oolite

The Red Hill Oolite fauna contains a number of forms which range up from the Martin Limestone but more importantly contains the first representatives of the rich faunas typical of the succeeding Dalton Beds. The fauna is dominated by the corals Caninia ciliata, Clisiophyllum ingletonense, Koninckophyllum meathopense, K. praecursor, Michelinia megastoma [=M. grandis McCoy; large colonies with relatively tall corallites], Palaeosmilia murchisoni and Syringopora spp.Brachiopods are also common and include Cleiothyridina glabristria, Composita ambi gua, Spirifer cf. furcatus and Spiriferellina sp.The rhynchonelloid Stenoscisma isorhyncha, used by Garwood as the subzonal index for this part of the sequence, is represented by a single specimen from the north end of Plumpton Quarry (loc. C35). The base of the Red Hill Oolite marks the entry of archaediscid foraminifera which are not seen in earlier Dinantian rocks.

Rich faunas are present in the Red Hill Oolite at Elliscales Quarry (loc. C33) and at Skelwith Hill (loc. C18) where brecciated limestone (? =Spirifer furcatus Bed of Garwood) lies at the base of the Red Hill Oolite, indicating a possible break in deposition between this formation and the Martin Limestone. Large gastropods are characteristic of the base of the Red Hill Oolite in Red Hills Quarry (loc. C9). The prominent wall-like reef limestone seen in Elliscales Quarry is a unique occurrence at this horizon in this district.

The formation is considered to represent the early transgressive phase of Major Cycle 3.

Dalton Beds

The lower and middle parts of the Dalton Beds contain one of the richest and most widespread Dinantian faunas of north-west Europe, a fauna referred to as the Arnside Fauna (Garwood, 1916, p. 13) after the classic locality on the shore of the Kent Estuary where Garwood's Chonetes carinata Subzone is well exposed. Many of the elements of this fauna persist, though less commonly, in the sandy and dolomitic limestones that characterise the upper part of the Dalton Beds ( = Gastropod Beds of Garwood). The strata are placed in Major Cycle 3, the Gastropod Beds representing the regressive phase of the Cycle.

Both corals and brachiopods are common in the fauna which includes Amplexizaphrentis enniskilleni, Caninia caninoides, C. subibicina, C. sp. cylindrica group [of Garwood, 1916, pl. 14, fig. 5], Clisiophyllum ingletonense, C. multiseptatum, Koninckophyllum praecursor, Lithostrotion martini, Michelinia megastoma [bun-shaped colonies], Palaeosmilia murchisoni, Syringopora spp., Zaphrentis' kentensis, Athyris cf. expansa, Composita ficoidea, C. aff. ficoidea, Delepinea carinata, Echinoconchus punctatus, Linoprotonia sp.hemisphaerica group, Megachonetes cf. papilionaceus, M. cf. zimmermanni, orthotetoids, Productus cf. garwoodi, Pustula pyxidiformis, Rhipidomella michelini, Schizophoria sp.and Syringothyris cuspidate. The lowest beds, well exposed in Iron Pit Spring Quarry (loc. C67b) near Plumpton and at High Frith (loc. C80), are characterised by the large chonetoid Delepinea carinata, one of the more valuable Dinantian brachiopod species because of its restricted stratigraphical range and its ease of recognition. Michelinia megastoma is common towards the middle of the Dalton Beds, and good faunas from this part of the sequence have been recorded from Gasgow Quarry (loc. C66), Plumpton Quarries (locs. C68–71) and Low Frith (locs. C78a–i). Clisiophyllum multiseptatum has a restricted range in the upper part of the Dalton Beds, and forms a coral bed ( =C. multiseptatum Band of Garwood) at a number of localities (e.g. locs. C71 and C76a). The highest beds within the formation are exposed in Plumpton Quarries (locs. C72b–e) and in the sea cliffs at Barker Scar (locs. C76b–j). Lithostrotion martini and Composita ficoidea are common in certain beds at the latter locality and the fauna is closely allied to that in the rest of the formation.

Park Limestone

The fauna of the Park Limestone is more restricted than that of the Dalton Beds, though some beds are crowded with individuals of a single species. The species Diphyphyllum smithi, Lithostrotion minus, Linoprotonia ashfellensis and L. corrugatohemispherica are restricted to the formation. The following longer ranging species are found also in the assemblage: Carcinophyllum vaughani, Clisiophyllum rigidum, Lithostrotion martini [abundant in some beds], L. portlocki, L. sociale, Athyris expansa, Linoprotonia cf. hemisphaerica and Megachonetes cf. papilionaceus [abundant in some beds]. Palaeosmilia murchisoni is rare and the forms of the species are atypical: specimens from near the base of the formation in a quarry (loc. C89) near Bardsea are very large with a diameter of more than 6 cm and others from Plumpton (loc. C99) have the major septa withdrawn (cf. Reynolds and Vaughan, 1911, pl. 31, fig. 6). Good faunas have been collected from Goldmire Quarry (loc. C86), Crown Quarry (loc. C87) and from the foreshore (loc. C99) south of Plumpton.

The Park Limestone is considered to represent Major Cycle 4. Its junction with the underlying Dalton Beds is exposed in the quarries at Plumpton (loc. C72), but the best section in the lower part of the formation is at Barker Scar (loc. C76), where there is a gradual passage from the Dalton Beds (loc. C76j) up into typical Park Limestone (loc. C76 k). The lowest bed of the Park Limestone contains Carcinophyllum cf. vaughani and Linoprotonia corrugatohemispherica, neither of which has been recorded below this horizon. Elsewhere in Britain Davidsonina carbonaria occurs widely at the base of sequences assigned to Major Cycle 4. It has not been found in the Park Limestone, though there is no sharp break at the base of the formation and the sequence is probably complete.

Urswick Limestone

There is an abrupt change of fauna at the base of the Urswick Limestone, the rich incoming coral fauna including the following species which make their first appearance at the base of the formation: Aulophyllum redesdalense, Caninia benburbensis, C. juddi, Clisiophyllum keyserlingi, Dibunophyllum bourtonense, Koninckophyllum 0, Lithostrotion arachnoideum and L. pauciradiale. This assemblage, together with the longer ranging species Carcinophyllum vaughani, Lithostrotion martini and Palaeosmilia murchisoni, which are also common, is the well-defined and widespread Lower Dibunophyllum (D₁) Zone fauna. Lithostrotion junceum has been recorded only from the upper part of the Urswick Limestone and from the succeeding Gleaston Formation. Brachiopods are also common with Athyris expansa, Gigantoproductus spp., Linoprotonia hemisphaerica and Megachonetes cf. papilionaceus commonly occurring in large numbers, though these species are not diagnostic of age.

There is no detectable change in the fauna throughout the thickness of the Urswick Limestone, except that Davidsonina septosa is restricted to a single level about 20 to 25 m below the top of the formation. In other areas this species has a considerable range through the upper part of the beds of comparable age to the Urswick Limestone, and the reasons for its apparent restriction in the present district are unknown.

One single pebble (LZ8343, see Ramsbottom, 1971, p. 91), collected and presented by Mr P. F. Dagger, from the Permo-Triassic breccias at Roughholme Point west of Humphrey Head is composed almost entirely of the reef goniatite Bollandites castletonensis (Bisat). The source of this pebble is problematical, for there are no known reefs within the Urswick Limestone, the formation from which it is most likely to have come.

Almost the complete sequence of the Urswick Limestone is seen in the Stainton Quarries (Crown Quarry locs. C87 and 109 and Devonshire Quarry loc. C110), which expose its junction with the Park Limestone, the Woodbine Shale (loc. C110a) and the Davidsonina septosa Band (loc. C1101). The base of the Gleaston Formation is just above the exposed quarry section. The junction with the Park Limestone is well seen also on Birkrigg Common (loc. C95), Bardsea Park (loc. C96) and Wart Barrow (loc. C103) near Allithwaite.

The Urswick Limestone belongs to the Fifth Group of Minor Cycles. In the Kirkby Stephen area beds at the base of this Fifth Group contain Daviesiella llangollensis (Davidson). This species has not been recorded in the present district, and there may be a considerable non-sequence at the base of the formation, though no sign of any such break is detectable in the field.

Gleaston Formation and Roosecote Limestone

The Gleaston Formation displays a wide range of lithologies and a corresponding variety of faunas, and is considered to fall into the Sixth Group of Minor Cycles. The following species are restricted to the formation: Aulophyllum pachyendothecum, Dibunophyllum bipartitum, Diphyphyllum lateseptaturn, Lonsdaleia floriformis, Eomarginifera cambriensis, Productus hispidus and Pugilis pugilis. Several of the Urswick Limestone fossils, especially species of Lithostrotion, are also common.

Around Gleaston the formation consists of alternations of shale and limestone, but exposures are few and restricted. A Girvanella band which is correlated with the Girvanella Nodular Bed of Garwood (1913, p. 529) lies at the base of the formation in Newton Mine (loc. C136) where 0.1 m of shale separates it from the top of the Urswick Limestone. At Bean Well Bank (loc. C145) about 4 m of dark grey limestone lies between the Girvanella Nodular Bed and the Urswick Limestone. The limestones exposed at Gleaston Castle (locs. C141 and 142) are thought to be some way above the base of the Gleaston Formation. They carry rich faunas, Lonsdaleia floriformis being common in the more northerly quarry (loc. C142) suggesting a correlation with the Hardraw Limestone of the Askrigg Block. A collection from tipped shales at Stank (loc. C135) contains Euchondria cf. losseni (high B₂ or low P_1a), and presumably comes from a horizon low in the Gleaston Formation. Another tip collection in the same area (loc. C131) has yielded faunas including Posidonia corrugata (P_1a or P₂ in age), probably from the upper part of the formation. The highest beds were proved in the Gleaston Castle Borehole and consist of shales with thin limestones containing a zaphrentoid fauna. Sudeticeras cf. splendens (Bisat) of probable P₂b age has been identified by Dr Ramsbottom at 160.49 m, and the tabulate coral Michelinia [Emmonsia] parasitica, which normally suggests an age low in the P₁ Zone, has been recorded from 160.40 and 161.65 m.

In the Roosecote Borehole practically the whole proved sequence consists of dark argillaceous poorly fossiliferous limestones. Zaphrentoid faunas occur including Cyathaxonia rushiana, Fasciculophyllum sp.and Rotiphyllum costatum. M. parasitica is again present between 720.34 and 722.50 m.

The most complete section is in the Haverigg Haws Borehole, just west of the western margin of the district, but the lithologies present are markedly different from those at Gleaston and Roosecote. About 9.5 m (711.40 to 720.85 m) of dark limestones are present at the base of the formation, and contain abundant Girvanella nodules at their base, a level correlated with the Girvanella Nodular Bed. Saccamminopsis sp.is common at the top of this dark unit which is correlated with the Upper Hawes Limestone of the Askrigg Block. Above this unit, the sequence is composed of pale limestones with subordinate shales and sandstone. Lonsdaleia floriformis has been recorded between 699.21 and 699.82 m, and this level may be comparable with that in the northern quarry (loc. C142) at Gleaston Castle. Between 663.85 and 670.56 m the presence of Lithostrotion maccoyanum and Orionastraea placenta suggests a correlation with the Potholes Limestone of West Cumbria and the Jew Limestone of the Alston Block.

To the east of the Leven Estuary the sequence is again distinctive, with alternations of limestones, shales and sandstones being exposed around Holker. The lowest part of the formation is seen only at Humphrey Head (loc. C127). The basal 7 m are dark grey argillaceous limestones (locs. C127d–g) with a fauna including Diphyphyllum lateseptatum, Lonsdaleia alstonensis, L. duplicata and Productus hispidus (Humphrey Head is the type locality for this stratigraphically valuable species). They are correlated with the Lower Hawes Limestone. Above them lies one of the best exposures of the Girvanella Nodular Bed (Garwood, 1913, p. 529).

Saccamminopsis sp.is common in the highest bed exposed, and the beds between the base of the Girvanella Nodular Bed and the top of the section correlate with the Upper Hawes Limestone. Garwood (1913, p. 530) listed an extensive fauna from Humphrey Head though, of the fossils that he recorded, Lonsdaleia floriformis and Palaeosmilia regia have not been found during the present survey.

The exposures in the Holker area cannot be accurately localised in the succession and the faunas are poor. The limestone at Godderside Gate (loc. C148), however, contains a rich brachiopod fauna which is possibly indicative of a back-reef environment. A comparable fauna is recorded from a small roadside quarry at Bolton Chapel (loc. C138) north of Gleaston at a horizon which is probably in the lower part of the Gleaston Formation.

These changes in facies appear to reflect the position of the district in relation to the contemporary basin margin, the Holker and Haverigg sequences representing comparatively shallow-water conditions, the Roosecote Limestone forming a basinal sequence with relatively restricted circulation, and the outcrops around Gleaston lying in a transitional belt between these two extremes. However, while it is usual to find that basinal sequences are thicker and more argillaceous than those of blocks, this is not the case in the present instance. The Holker and Haverigg sequences are extremely thick—certainly comparable with that at Roosecote even though that sequence was not completely penetrated. Moreover the Roosecote sequence is essentially a carbonate one, the main argillaceous successions lying in the transitional area where the sequence is apparently thinner than in either the block or basin areas. Exposures and recent provings are too scattered to enable an explanation of these anomalies to be put forward. Anw

Petrography of the limestones

The Viséan limestones cropping out in the district are of varied lithologies, and include pseudo-oolites, pseudobreccias, fine-grained porcellanous limestones, and bioclastic limestones. There is local dolomitisation, hematitisation and silicification. Each of the stratigraphical formations, however, is lithologically distinctive, and representative examples from each have been examined in the following study though no attempt has been made at an exhaustive examination of all lithologies within each formation.

In the main, the granularity terminology used is based on that of Grabau (1904), Pettijohn (1957) and Carozzi (1960) , though the term 'micrite' (Folk, 1959) has been adopted rather than 'calcilutite' for the finest carbonate grades present, because in most cases it is difficult or impossible to determine their genesis. The difficulties in adopting a genetically-based classification are shown, for example, by Bathurst's observations (1971, p. 289) on bioturbation and (secondary) micritisation in contemporary carbonate oozes in the Bahamas. Owing to varying degrees of crystallisation in the present samples, only a general classification has been attempted, based on Pettijohn, 1957 and Folk, 1959.

Martin Limestone

This is distinguished by the prominence of micritic lithologies. Both porcellanous and non-porcellanous types occur, but thin sections commonly show a coarser texture (calcisiltite to fine calcarenite), with fine pellety aggregates, calcispheres, and abundant bioclastic particles. Electron micrographs of the micrite show common crystal forms, but these cannot be used as evidence of the depositional environment. The overall fineness of grain suggests, however, a low-energy environment with negligible current action, though evidence of sporadic wave-action has been illustrated by Nicholas (1968, pl. 8).

Well-bedded, sub-porcellanous, fine-grained, pale grey limestone (E40023), (E40539) near the top of the formation at Martin Quarry [SD 243 768] is a calcisiltite, though the macroscopic appearance suggests a more micritic rock. In thin section ((Plate 4).2, p. 43) closely packed grains of subspherical micrite average 0.06 mm across and are too fine to show internal structures. Microbioclasts–shell particles, foraminifera and unidentifiable scraps–are common and, together with the micrite grains, are set in a micritic matrix with patchy sparry calcite containing crystals of dolomite. Electron micrographs (Plate 4).1 taken by Mrs A. E. Tresham of a broken surface of micrite (E40955), show a crystalline texture, the crystals averaging about one micron. The micrite grains have clearly re-crystallised and show no evidence of pre-existing aragonite. The origin of the micropellets is unknown. Duedall and Buckley (1971) have described the delayed precipitation of spheroids of CaCO₃.H₂O in sea water, but a biochemical origin is not ruled out.

A more typical pale grey porcellanous limestone with conchoidal fracture (E40955) from Hazelhurst Point [SD 334 800], taken from near the top of the formation, resembles in section the previous specimen, except that the subspherical grains of micrite are less easily distinguishable.

This is the rock referred to as 'calcite mudstone' in the general account. Fine-grained bioclasts (averaging 0.06 mm) are plentiful (shells, spines, bivalves, gastropods, ?algae, crinoid stems) and are intimately associated with the micritic material. The latter is partially resolved as aggregates of spheroids which are more distinct where some recrystallisation of the matrix has occurred. The origin of the micrite grains remains, however, in doubt. There are scattered silt-grade quartz grains, mainly showing marginal replacement by calcite, and these are probably detrital. Nicholas (1968, p. 119) has noted up to 5 per cent by volume of exogenetic quartz in the Martin Limestone.

Red Hill Oolite

The formation contains well-sorted and rounded pseudoooliths, readily visible in hand specimen, and cemented by sparry calcite. In section true ooliths are scarce, the majority being rounded litho-micritic and bioclastic pellets, probably indicating, like ooliths, a relatively high-energy environment with vigorous current action. Again, however, caution in interpreting the textures is necessary, because some at least of the rounding of the pellets may have been due to secondary crystallisation in the matrix. Dolomitisation has, in places, obscured the primary textures, particularly the matrix, of certain specimens.

A specimen (E40024) of sparry pseudo-oolitic biocalcarenite from Red Hills Quarry [SD 179 792], was collected some 10 m above the base of the formation. It is pale grey, stained pink, markedly 'oolitic', and exhibits a grading of the constituents in the range of 0.5 to 3.0 mm mean diameter. The average grain size is about 0.8 mm, and the 'ooliths' are well-rounded, mainly spheroidal to ellipsoidal (or broken) pellets of structureless micrite with bioclastic inclusions ((Plate 4).3, p. 43). Only rarely are growths visible indicating a true oolith structure. Other skeletal components include rolled bioclasts–foraminifera, corals and crinoid stems–set in a clear sparry calcite cement. Any primary micritic matrix has apparently been washed from the skeletal components during accumulation, indicating a high-energy environment; the structureless nature of the micritic pellets remains, however, unexplained by normal oolith-forming processes. One explanation may be that the rounding is partly due to replacement of more homogeneous micritic rock by secondary calcite. The micro-pelletal Martin Limestone described above, however, shows embryonic pellets, which probably resulted from chemical precipitation. It may thus be that the present pseudo-oolite represents an extension of unimpeded precipitation, followed by an unspecified degree of attrition, with partial replacement by secondary, sparry calcite. A further specimen (E40543) from Elliscales Quarry [SD 224 748], however, shows pronounced grading of the pellets and bioclasts, clearly demonstrating current action. Dolomitisation has formed porphyroblastic rhombs which have replaced the micritic matrix. Authigenic euhedral quartz crystals occur mainly in the matrix, but their relation to the dolomite is not clear.

Pale purple specimens (E38212A) of dolomitised calcarenite from Elliscales include subspherical micropellets (0.07 mm) in a matrix similar to those described above from the Martin Limestone. Microstylolites contain bituminous material, and the overall colour of the rock is due to dispersed specks of hematite. Two generations of dolomite appear to be present: an earlier fine-grained matricial aggregate and later porphyroblastic rhombs (0.06 mm). Veins of secondary calcite with siderite cut the specimen.

Dalton Beds

These are characterised by well bedded and thinly bedded dark grey biocalcarenites, and by calcareous shale in the middle part of the sequence. The limestones exhibit a mixture of abundant poorly sorted skeletal bio- and lithoclasts, mainly with interstitial micrite, indicating a low-energy depositional environment, but also in places with sparry calcite. Post-depositional dolomitisation, hematitisation, and microstylolitic reorganisation have considerably modified the sedimentary textures. Pseudobrecciation has also occurred, though this is not obvious in hand specimen.

A specimen (E40025) from 7 m above the base of the formation at Iron Pit Spring Quarry [SD 308 785], is a medium grey, finely crystalline biocalcarenite ((Plate 4).4, p. 43). Prominent crinoid stems and shells are set with other poorly sorted skeletal bioclasts including foraminifera and spines in a partly micritic, partly recrystallised calcite mosaic. Microstylolites carry traces of likely bitumen. More characteristic of the formation is a darker grey, bituminous limestone (E40026), from Plumpton Quarry [SD 310 784], which similarly consists of poorly sorted bioclasts–corals, crinoid stems, plates, foraminifera, ?bryozoa, ?algae, and lithoclasts. The matrix is mainly finely comminuted bioclastic debris with some sparry calcite. Microstylolites carrying bitumen are associated with quartz-silt, and evidently represent a diagenetic re-organisation of the terrigenous material.

Mottled porcellanous pale grey biocalcarenite (E40540), (E40541) from Elliscales Quarry [SD 224 748] consists of abundant skeletal materials including gastropods, ostracods, algal structures and bryozoa, set in a predominantly micrite matrix. Disturbance of the sediment, presumably during diagenesis, resulted in segregation of coarser and finer grained units, to form pseudobreccia. A further specimen (E40542) shows dolomitisation, the dolomite mosaic replacing the micrite matrix, and is veined by hematite.

Park Limestone

For the most part this is a massive, white-weathering, pale biocalcarenite. Bioclasts are generally unoriented and this contributes to the poor bedding. Recrystallisation of the matrix is common, but much micrite remains and, though some of this is secondary, sufficient probable primary micrite remains to indicate mainly low-energy deposition. Nevertheless Nicholas (1968, p. 228) has provided evidence of brief periods of higher energy.

A specimen of a sparry biocalcarenite (E40027) 22 m above the base of this formation at Plumpton Quarry [SD 311 784], shows poorly sorted, randomly oriented, mainly self-supporting, skeletal bioclasts–mainly crinoid remains, foraminifera, gastropods, spines and shell particles, consisting wholly of, or rimmed by, micritic calcite, presumably formed due to recrystallisation (Purdy, 1965, p. 169). The matrix is mainly recrystallised calcite, and patchy development has resulted in pseudobrecciation, with segregations of fossils; lithoclasts include particles of micritic limestone. Euhedral quartz crystals are conspicuous (average 0.3 mm length), and contain inclusions of carbonate and unidentified specks, commonly zonary.

Nearer the top of the limestone, pale grey biocalcarenite (E40028) from Crown Quarry [SD 245 728] is similar to the above specimen with poorly sorted and unoriented skeletal bioclasts and lithoclasts with much micrite and patchy re-crystallised microgranular (less than 5 mm) calcite. At Birkrigg Common [SD 281 747], the micritic (0.002 mm) matrix in a biocalcarenite (E40533) is in places recrystallised, and contains conspicuous authigenic quartz. There appears to have been some replacement of skeletal material by micrite.

In summary, therefore, the proportions of micrite are variable and depend on the extent of recrystallisation, but the evidence indicates low-energy deposition with little winnowing by current or wave action.

Urswick Limestone

The grey to white Urswick Limestone contrasts with the underlying formation in including conspicuous pseudobreccias. Some lithological and depositional continuity is, however, shown with the Park Limestone in that bioclastic limestone, biocalcarenite in particular, predominates, showing variable primary micritic matrix and patchy recrystallisation.

Specimens exhibiting pseudobrecciation were examined from Stainton and Birkrigg Common. At Stainton Quarries [SD 245 728]; [SD 249 728], specimens (E40029); (E40030) respectively from 7 and 35 m above the base of the formation consist of closely packed, poorly sorted, unoriented skeletal bioclasts (averaging 0.3 mm) of foraminifera, crinoids, gastropods, bryozoa and unidentified particles, together with sparse micritic lithoclasts set in a matrix ranging from 0.005 mm (micrite) to about 0.5 mm ( 'recrystallised' calcite). Crinoid stems show syntaxial overgrowths.

The pseudobreccia structure consists of dark grey, randomly distributed irregular rounded patches of biocalcarenite to biocalcisiltite of very variable size. These make sharp contacts in places with the predominantly pale grey biocalcarenite, though the contrast is considerably reduced in thin section. The dark grey patches contain a lower proportion of micrite and a higher content of recrystallised matrix than the remainder of the rock does (Plate 4).5. Fine microfossil debris is plentiful throughout, and in the pale intra-pseudoclast areas there is a marked orientation of the bioclasts. A detailed account of pseudobreccias in general, and these in particular, is given by Nicholas (1968, pp. 233–251).

Examination of fractured surfaces of the limestone under the scanning electron microscope showed a variety of structures in the respective micritic matrices, including crystal aggregates similar to those figured (Plate 4).1. No significant textural differences emerged, however, between the bulk of the rock and the dark grey patches.

The specimens indicate a physical-chemical segregation of the dark pseudoclasts, probably due to selective patchy recrystallisation and partial consolidation of the micritic matrix, followed by soft-sediment movement of the interstitial carbonate ooze presumably during early diagenesis. Dolomitisation does not appear to have been a contributory factor in the present specimens, although the re-organisation of the soft sediment evidently led to microstylolite formation in places. The 'flow texture' noted above, was first described by Garwood (1913), who noted a relation to detrital quartz which appears to be absent in the specimens examined. The reason for the selective recrystallisation is unknown, though this may have been governed by in-homogeneous aragonite-calcite precipitation in the original ooze.

Gleaston Formation

Around Gleaston limestones are subordinate in this unit, being mainly dark, crinoidal or algal with some chert. The specimens examined confirm a range of bioclastic lithologies (biocalcirudites to calcilutites), with variable micritic matrix, sporadic silicification, and impregnation by sapropels and pyrite. Lithologies transitional to arenites show complex mixtures of carbonate and terrigenous materials, with calcitisation and decalcification. The environment of deposition within a developing basin was evidently characterised in part by reducing conditions, with precipitation of silica and deposition of sapropels, giving rise to the dark cherts described below (cf. Marcher, 1962).

A well-bedded biocalcarenite (E40032) from a quarry [SD 264 714] 220 m E of Gleaston Castle, is dark grey and bituminous with a foetid odour on breakage. Dark grey chert forms stratiform replacement lenses and nodules. Bio- and litho-clasts form a partly oriented, poorly sorted, closely packed, skeletal framework with a micritic (less than 0.005 mm) matrix. The bioclasts include foraminifera, bivalves, crinoidal particles, spines, ostracods, collophane needles and probable bryozoa. Veinlets carry calcite and hydrocarbons. Pyrite is common and contributes to the overall dark colour of the rock.

Chertification (E40536) is complex, with an initial silica 'front' selectively replacing the micritic matrix. Replacement of the bioclasts appears to have been random, with complete to partial replacement of selected crinoid stems. This general sequence of replacement is similar to that described by Marcher (1962, pp. 826–827) in the Warsaw Limestone of Tennessee, where large crinoid ossicles were found to be the most resistant to silica replacement. In this process, the fundamental chemical rule that the finer the particle size the easier and more rapid the reaction seems to apply. Dolomitisation has apparently followed silicification, and accompanied the formation of microstylolites. This suggests that silicification occurred at an early diagenetic stage. The evidence indicates low-energy deposition under reducing conditions of restricted circulation, the deeper cooler water favouring the precipitation of silica and sapropels (cf. Marcher, 1962, p. 832).

Coarser bioclastic limestones examined from this formation include a sparry coarse biocalcarenite (E40031) from a quarry [SD 259 730] near Hawkfield in which closely packed bioclasts average 0.6 mm, and include crinoids, gastropods, bryozoa and corals. Some show syntaxial overgrowths, and there are also micritic lithoclasts. The matrix is in part micritic, though in places this has evidently been replaced by clear sparry calcite ((Plate 4).6, p. 43) which gives no clue to the depositional environment. A coarser, very poorly sorted bioclastic calcirudite (E40033) occurs at another quarry [SD 346 770] near Holker Farm. The coarsest clasts are, here, not self-supporting. There has, consequently, been much disturbance of the intraclasts and the fine matrix. Patchy recrystallisation of the micritic component has occurred.

An arenaceous specimen (E40535) from a sewer trench [SD 268 737] near Little Urswick shows extensive replacement by calcite, the original bedding being emphasised by aligned heavy detrital minerals (zircon and leucoxene) and micas. Decalcification and ferruginisation have tended to work along bedding planes. It is apparent that the admixture of arenaceous terrigenous material with precipitated carbonate resulted in chemical exchange, presumably under diagenetic processes including compaction. The overall limestone textures point to sluggish accumulation under low-energy conditions with little or no current action, and the increasing quantities of terrigenous sediment suggest formation in a developing basin.

In the Haverigg Haws Borehole other types of limestone were proved. Towards the base of the formation at 712.02 m a medium grey (N5) biocalcisiltite (E45577) consists mainly of fine-grained bioclasts–chiefly foraminifera, gastropods, plates, spines and other debris–scattered in a finely crystalline calcite cement. At a higher level the limestones are paler. One example (E45576) from 696.78 m is mainly light brownish grey (5YR/6/1). It is a medium-grained bioclastic limestone, with small patches of euhedral dolomite (averaging 0.03 mm) and authigenic quartz set amongst the bioclasts. A medium light grey (N6) fine-grained limestone (E45575) from a depth of 687.64 m contains scattered bioclasts chieflycrinoid plates, foraminifera, gastropods and bryozoa–set in a patchily sparry calcite cement. A little hematite is finely disseminated along microstylolites, and there is again some authigenic quartz. A specimen of pseudo-brecciated limestone (E45574) was examined from a depth of 629.42 m. It is mainly a finely crystalline pinkish light grey (N7) limestone with irregular slightly reddened medium grey (N5) patches, giving rise to the conglomerobreccia appearance. The dark patches consist of concentrated aggregates of closely packed bioclasts mainly preserved in micrite, and the fine grain of the bioclasts together with the micritic texture are the cause of the dark colour. In contrast the main part of the rock consists of coarser less concentrated unsorted bioclasts with subordinate sparry calcite cement. A little quartz is dispersed along strings and some of the cores of fossil fragments are replaced by chalcedony. The segregation appears to be due to both physical and chemical reasons, with reorganisation of the soft sediment and perhaps patchy crystallisation of the matrix. At 588.27 m a medium-grained light brownish grey (5YR6/1) limestone (E45573) includes a light grey (N8) siliceous unit. In the limestone closely packed unorientated poorly sorted bioclasts–including plates, crinoid ossicles and possible bryozoans–predominate, and interclast cement is relatively insignificant. The siliceous band represents almost complete silicification of the limestone, and consists of cryptocrystalline growths of silica with zonary specks of dolomite and remnants of calcite. Its sharp contact with the limestone is variably marked by a narrow selvage of dolomite.

Four specimens of the Roosecote Limestone were examined from the Roosecote Borehole. At a depth of 779.00 m a dark grey (N3) microcrystalline limestone (E41439) showed a laminated structure with pellety laminae aligned roughly along the bedding. The laminae consist of very fine-grained (0.002 mm) and closely packed brownish yellow-stained micritic calcite aggregates charged with aligned, opaque to reddish brown and yellowish brown, microscopic filaments of hydrocarbons, calcite needles and other bioclasts. The intra-pellet cement is microcrystalline (0.03 mm) calcite mosaic and minor constituents include scattered quartz grains (0.03 mm) and specks of pyrite. The other specimens (725.00 m, (E41432); 675.00 m, (E41424); 625.90 m, (E61418) are all basically similar. They are medium dark grey (N4), hard, micro-crystalline limestone, composed of particles of micrite and abundant foraminiferal and other bioclasts set in a mosaic of interlocking microcrystalline calcite. Although the mosaic may be partly primary matrix, the overall texture suggests there has been some recrystallisation. Specks of opaque and brown material scattered throughout are probably bitumen. Patches of replacive undulatory quartz aggregates indicate initial silicification. One specimen (E41432) contained dark pellets up to 2 mm thick aligned roughly along bedding: these represent concentrations of biomicrite, microfossils and aligned calcite needles. RKH

Details of stratigraphy

Millom–Hodbarrow

A sketch map of the geology of this area together with two sections appears in ((Figure 18)." data-name="images/P988102.jpg">(Figure 17)) and (Figure 18). With the exception of a small area at Red Hills and another near Hodbarrow Point the solid rocks are concealed by superficial and glacial deposits that are up to 60 m thick and cover a highly irregular sub-drift surface. Most of the information on which (Figure 18)." data-name="images/P988102.jpg">(Figure 17) is based comes from borehole and mining records, and from underground exposures in Hodbarrow Mine that were accessible during the resurvey: the sites of the geologically more important boreholes are shown on the figure. About 80 of the boreholes were deep enough to reach Basement Beds, and at least 10 entered Basement Beds directly beneath the drift; a few penetrated the Lower Palaeozoic floor. Selected records are summarised in Appendix 1. Cores of those holes sunk after 1924 were examined by the Geological Survey and these have enabled the earlier records to be interpreted. The major faults are also shown on (Figure 18)." data-name="images/P988102.jpg">(Figure 17). Most were formerly exposed underground at several levels, and their positions, dips and amounts of throw are accurately known in the workings. Many of the smaller faults have had to be omitted from the figure.

Most of the useful underground exposures were in haulage levels driven below the main orebody, and revealed sections mainly in the lower part of the sequence. The best exposures in the Basement Beds were in levels connecting the several shafts with the main orebody and in the Red Hills cross-cut. These roadways provided almost continuous sections, but faulting was so intense that the detailed sequence could not be deciphered. The sections, however, demonstrated the extreme variability of the Basement Beds, rapid lateral changes occurring over distances of only a few metres. The passage from the Basement Beds to the Martin Limestone was well exposed in several places, notably in the Moorbank area. Dark grey shales, with thin bands of purple sandstone, conglomerate and impure limestone were noted. Similar beds were seen in Lowther Pit, which passed through the Lowther Fault. Both this fault and the No. 1 Pit Fault were exposed in the lower levels around Lowther Pit and No. 1 Pit respectively. These faults are closely associated with the hematitisation which gave rise to the main orebody at higher levels yet, where seen cutting the Martin Limestone and Basement Beds, they were clean fractures with no trace of hematite. In the Red Hills area the eastern extremities of the two branches of the Red Hills cross-cut provided excellent sections in the Basement Beds and Martin Limestone. They also exposed the 'north-west' faults which carried vein-like hematite orebodies in the Red Hill Oolite above: again these showed little or no trace of hematite in the cross-cut. The Red Hill Oolite was exposed in other cross-cuts connecting the orebodies at higher levels. It was a massive white fragmental limestone, generally dolomitised in the vicinity of the ore.

The Moorbank area of Hodbarrow was the last to be developed. The proved succession, established in several boreholes and in No. 11 Pit, extends upwards from the upper part of the Basement Beds to the lower part of the Dalton Beds. The more important borehole logs are given in Appendix 1, and the fossils obtained from No. 8 and No. 11 Pit are listed (locs. Cl–C3)^‡2  in Appendix 3. The Basement Beds near No. 11 pit-bottom consisted of purplish brown sandy mudstones, commonly with green mottlings and laminations, together with bands of purple and green sandstones and conglomerates. The latter contained pebbles of andesite from the Borrowdale Volcanic Group averaging 5 cm in diameter, but ranging up to 30 cm. Pebbles of igneous rocks comparing closely with the Eskdale Granite and Ennerdale Granophyre have been obtained from cores of Basement Beds from some of the boreholes. A level at −155 m OD connecting No. 11 Pit with the Moorbank South orebody was driven in Martin Limestone, the general dip of the beds being 10°–25° west-south-westwards, although there was much disturbance by faulting. The cross-cut westwards from this level cut through the Moorbank South Fault and entered heavily dolomitised Red Hill Oolite on its downthrow side.

Beyond the Outer Barrier towards Haverigg, Basement Beds were reached in a borehole at a depth of 193 m (SD17NE/73).^‡3  Another hole (SD17NE/74) intersected the Haverigg Fault at a depth of 159.6 m and thence passed through the Red Hill Oolite and the Martin Limestone, entering the Basement Beds on the footwall side of the fault. This borehole and others near Whitriggs Close, north of Haverigg, fix the position of the Haverigg Fault in this area.

The Martin Limestone and Red Hill Oolite are exposed [SD 179 792] in Red Hills Quarry (locs. C9, C22) which for many years supplied limestone for the Millom steelworks. At the time of the resurvey the section was as shown below, but the quarry has since been closed, and the section has become much obscured and difficult of access.

The upper part only of the Martin Limestone is exposed, but the full thickness of the formation is about 40 m in this area, for two boreholes sunk from the main floor of the quarry at about the horizon of the Algal Band have reached the Basement Beds. There is some interdigitation between the lithologies characteristic respectively of the Martin Limestone and Red Hill Oolite near their junction, but the Algal Band marks a broad division into a well bedded sequence of mainly fine-grained limestone and calcite mudstones below, and massive coarse-grained limestones above. Two bands of fine-grained pink-stained dolomite about 10 cm thick occur close below the Algal Band. Dips are generally at 5° to the east, and the quarry faces are cut by prominent vertical joints trending at 330°–335°, parallel to the several faults which give rise to the hematite veins of the Red Hills area. The major joints are about 3 to 4 m apart, and there are many intervening minor ones. The former are heavily stained with hematite and are commonly accompanied by extensive brecciation and minor faulting. The brecciated rock is generally dolomitised and partially hematitised, with some dolomitisation and hematitisation along the joint walls.

The old quarries around Hodbarrow Houses and the cliffs towards Hodbarrow Point provide excellent sections covering about the same horizons as those in Red Hills Quarry. Most of the quarries are now filled in, but the following section (loc. C10, see also loc. C25) was measured in a quarry [SD 182 783] north by west of Hodbarrow Point:

About 10 m of beds at the top of the Martin Limestone and the same thickness of the lowest beds of the Red Hill Oolite, containing cf. Carruthersella compacta (loc. C23), are exposed in the cliffs. The Martin Limestone, forming the lower part of the cliff, consists of thinly bedded, fine-grained and compact limestones and calcite mudstones with a few thin layers of calcareous shales. Some of the limestones are laminated and false-bedded, and have ripple-marked bedding-planes. Near the top there are two 10 cm bands of pink-stained flaggy dolomite similar to those in Red Hills Quarry. The dip is usually steep–up to 40° to the west–probably due to the presence of an important fault off-shore. The Algal Band has not been noted with certainty in these sections, although scattered algal structures are prominent at the top of the Martin Limestone. About 10 m of Red Hill Oolite, consisting of medium-grained oolitic limestone with a poor fauna, were exposed in a quarry (loc. C24), 90 m N of Hodbarrow Point.

These outcrops lie between the Lowther and Old Mine Faults, which contain the adjacent Old Mine orebody (see (Figure 18)." data-name="images/P988102.jpg">(Figure 17)), and they are affected by secondary dolomitisation and hematitisation. The alteration is clearly related to the main joints which trend at 330°–335° and are mostly vertical where seen in the cliffs, where they are 2 to 3 m apart and generally accompanied by brecciation and small-scale faulting. All stages of secondary dolomitisation can be seen from thin replacement selvages on joint faces, through irregular bodies of dolomite spreading out from the joints, to the complete replacement of beds of limestone by dolomite. In certain places, for instance near Towsey Hole [SD 1833 7819], similar stages in hematitisation can be seen, including the conversion of jointbreccias into hematite. Veins of hematite have been worked nearby. These sections illustrate in miniature all the various forms taken by the large hematite deposits of Hodbarrow, in particular the ways in which dolomitisation and hematitisation favour the heavily jointed limestone, and bedding has controlled the lateral spread of mineralisation. Dolomitisation in the well-bedded limestones at the top of the Martin Limestone is seen in the lower part of the cliff and tends to extend laterally as flats. It is less extensive and more irregular in pattern than in the more massive Red Hill Oolite. Though other joint-systems are also present, notably ones trending at 345°–350° and at 250°, there is no obvious alteration along them.

At Hodbarrow Scar (loc. C44) on the old foreshore west of Hodbarrow Houses, 7.31 m of grey limestones, including fine-grained, coarse-rained and crinoidal types are exposed on the downthrow side of the Lowther Fault. They lie near the base of the Dalton Beds with a fauna that includes Caninia sp. cylindrica group, C. sp.subibicina group, P. murchisoni and Delepinea carinata.

The only extensive section of higher beds is that proved by the Haverigg Haws Borehole (SD17NW/2); the details appear in Appendix 1. WCCR

Dunnerholme–Askam

Lower Carboniferous rocks are seen at the surface only at Dunnerholme, where the upper beds of the Martin Limestone and the lower beds of the Red Hill Oolite are well exposed in low cliffs and quarries. Elsewhere the solid rocks are concealed by up to 45 m of superficial and glacial deposits, but boreholes have proved the Basement Beds and probably also part of the Dalton Beds. A sketch map of the solid geology around Dunnerholme is given in (Figure 7) and shows the more important boreholes.

One of these (27NW/323) proved 230.5 m of Basement Beds before entering the Lower Palaeozoic. Its section appears in (Figure 4). A nearby hole proved the top of the Basement Beds at −30.5 m, and their thickness hereabouts is some 244 m, the greatest recorded in the district. Several other holes between Ireleth and Low House proved Basement Beds resting on the Lower Palaeozoic floor at about −45 m OD. One (27 NW/456) passed through 162.6 m of Basement Beds without reaching their base; the recorded lith-o logies are chiefly red shales with limestone bands.

The exposures west and north-west of Dunnerholme House show the highest 18 m of the Martin Limestone comprising calcite mudstone and fine-grained limestone with algal nodules, K. cf. meathopense, K. cf. praecursor, Cleiothyridina glabristria and Composita aff. ficoidea (locs. C12a–e, and C13a), capped by the 1 m thick Algal Band, which is in turn overlain by 21 m of pale grey 'oolitic' and fragmental limestones of the Red Hill Oolite with K. meathopense and K. cf. praecursor (locs. C12f,g and C13b,c). Some of the beds are secondarily dolomitised; this may be associated with the NW faults. The Red Hill Oolite contains caverns partly filled with collapse-breccias, in which the fragments are wholly dolomitised and generally cemented by coarser crystalline calcite. The caverns are overlain by undisturbed and undolomitised limestone. KCD

Roanhead–Park–Sandscale

This area contained some of the largest of the Furness hematite deposits, and consequently has been extensively proved by mining and by exploratory boreholes, of which over 500 have been drilled. Because drift limits solid exposures to a few small outcrops knowledge of the area is wholly dependent on this borehole information and on that obtained from underground sections accessible during the resurvey. There is extensive faulting and some folding, probably even more intense than shown in (Figure 20).

The Basement Beds are not exposed, but have been proved in many boreholes to lie beneath drift between Askam and Park and to be present beneath higher formations throughout the area. None of the holes has bottomed the formation. The greatest thickness recorded was 116.0 m in an underground borehole at Sandys Pit (27NW/451), and 93.4 m was proved in another (27NW/381), where the lithologies were mainly shales with limestone bands. A deeper hole (SD17SE/40) entered the Basement Beds at 372.0 m and one other (SD17SE/35) proved 48.0 m of limestone with beds of shale at the top of the Basement Beds overlying 9.1 m of blue shale.

The Martin Limestone is exposed only in small outcrops at the north end of Park Knotts Hill, and at the north end of Roanhead Crag, where 1 to 2 m of calcite mudstone underlie Red Hill Oolite [SD 2048 7623]. Material from the dumps at Park Knotts trial pit (loc. C14) is from the Martin Limestone immediately above the Basement Beds. In the lower workings of Nigel Sop, Roanhead, the Martin Limestone consisted of greenish grey fine-grained limestone and calcite mudstone, with a bed of shale 0.7 m thick near its top, and several boreholes between Roanhead and Askam passed through the Martin Limestone into the Basement Beds. The evidence suggests that the formation is at least 105 m thick, and perhaps as much as 135 m, at least twice as thick as elsewhere in the district.

Roanhead Crag (loc. C26) is an isolated exposure of about 45 m of much dolomitised Red Hill Oolite, with Caninia subibicina and Linoprotonia sp. hemisphaerica group, dipping south-westwards at 15°. The full thickness is about 60 m in this vicinity. Underground exposures in Nigel Pit indicate that the formation is here about 55 m thick and that, when undolomitised, the beds consist mainly of coarse-grained fragmental pale grey limestone with some beds of calcite mudstone. A borehole (27NW/193) near Burton Pit proved 17.9 m of partly dolomitised Red Hill Oolite underlain by 1.2 m of algal limestones, probably the Algal Band.

Dalton Beds lie directly beneath the drift between Roanhead and Sandscale Haws, their outcrop being shifted to the south in a series of steps by northerly-trending faults. The beds are nowhere exposed at the surface but were examined underground (locs. C45–51) in Nigel, Billy, Rita, Kathleen, Peggy and Violet pits, and along the California Vein; extensive and typical faunas have been collected. The formation was also penetrated in a large number of boreholes, the cores of some of the more recent of which were available for examination. Even so, the thickness of the formation and the details of the succession are not known with certainty owing to faulting. The former is estimated at about 200 m, and the general sequence of lithological types in the higher part of the formation is shown by the following section of Nigel Air Pit [SD 2020 7540]:

Dalton Beds formed the walls of the upper part of Nigel Sop and the lower part of Park Sop (see (Figure 25)." data-name="images/P988109.jpg">(Figure 24)). Between Park Sop and High Wood, boreholes have shown that both the Red Hill Oolite and the Dalton Beds are extensively dolomitised. The Martin Limestone was proved in the 218-yd Level at the foot of Nigel No. 2 Shaft (loc. C11).

The Park Limestone forms the wall-rock of the upper part of Park Sop, and was well exposed in the steep sides of the subsidence formed by the extraction of the orebody before this was flooded. The positions of both the base and top of the Park Limestone in the Park–Roanhead area are accurately known both underground and at surface, and its thickness averages 125 m. The following is an approximate section at Burlington Shaft [SD 2132 7531] at Park, on the southern side of the orebody: Surface +39 m; Drift, to 8 m; Park Limestone, to 135 m; Dalton Beds to 226 m. The Urswick Limestone crops out near the shaft, which thus proves almost the full thickness of the Park Limestone.

The following section of the lower part of the Urswick Limestone is exposed in Park Quarry (loc. C105):

Westwards towards Sandscale the Urswick Limestone has been proved under drift by numerous boreholes, and samples occur in tip material (e.g. Far Oxenclose trial pit, loc. C106). One of the boreholes [SD 204 745] proved the following section:

The Woodbine Shale was not ^-recorded in this borehole or others in the vicinity and presumably dies out south-west of Park.

The many boreholes between Goldmire and Sowerby Wood prove a highly variable sequence in the Gleaston Formation. A guide to their correlation is provided by a unit of some 35 m of sandstone, with sandy shale intercalations but free from limestones. Wherever adequately proved the successions above and below this sandstone are so similar that it seems certain that the latter represents the same single member. In some of the holes its identification is difficult because it lies immediately beneath the Permo-Triassic unconformity and so is stained red and hard to separate from the St Bees Sandstone, particularly where the latter fills hollows on the Carboniferous surface. Nevertheless it is possible to plot the outcrop of the sandstone beneath drift, and this has helped considerably in establishing the structure and succession throughout this tract. The resultant composite section of the formation in this area is given in (Figure 5).

The lowest unit proved is about 14 m of 'limestone with shale beds' resting immediately on the Urswick Limestone (27SW/465), and apparently passing westwards into limestone. Above it, in the same hole, lies 'flinty limestone' (presumably cherty) at least 60 m thick, with one 2 m shale parting. This limestone is exposed on Oxenclose Hill [SD 2126 7465], where 2.4 m of red crinoidal limestone with large nodules of pink crinoidal chert dip south-westwards at 15°, the presence of chert providing strong confirmation of a D₂ age. Similar limestone occurs on nearby spoil heaps, and suggest that it was encountered on the hanging wall of the California Vein (see p. 105) south of California No.3 Shaft, and in the workings of No. 18 Pit, Goldmire. Farther west this limestone probably equates with the 'red gritty siliceous limestones with red shale partings' that are at least 17 m thick (27SW/566).

The sequence appears to be continued upwards by a unit about 50 m thick, that is variously described as 'limestone with shale partings' or 'limestone and shale', and that has been proved in Thwaite Flat No.1 Borehole (27 SW/462) and nearby holes. To the north of Sowerby Wood at least 34 m of alternating shales and limestones have been proved in this position (SD17SE/16), individual shale beds having thickened at the expense of the limestones. Their outcrop may extend beneath drift westwards from here across Scarth Bight to Lowsy Point.

This sequence is overlain by the sandstone member referred to above, which is variously logged as 'grit', 'sandstone' and 'sandstone and sandy shale', the more detailed sections recording discrete shale partings within it. The sandstone is generally stained red and yellow, though thin white and grey bands are recorded. Away from the Triassic outcrops grey colours are more common but, even then, the interbedded shales are red and purple, suggesting that at least some of the coloration is penecontemporaneous in origin. The sandstone is 30 to 35 m thick throughout the area, but it is difficult to trace east of the Yarlside Fault. In the only recent borehole, the British Cellophane No.1 Borehole (SD17SE/63), fragmentary plant debris is recorded from it.

A thin limestone directly overlies the sandstone in Thwaite Flat Nos. 1 and 3 boreholes, and the same limestone is a least 5.5 m thick in Park No. 177 Borehole (27SW/609), sunk in a downfaulted block north of Thwaite Flat. It maintains this thickness at Sowerby No. 10 (27SW/565), though it has thinned to only 2 m thick at Bouth Wood No. 2 (27SW/532). At Sowerby Wood No. 3 (27SW/466) it appears to be cut out by unconformity, but is almost certainly the unit formerly correlated with the Magnesian Limestone at Sowerby Wood No.1 (SD17SE/7), where it is said to have been 17 m thick. In British Cellophane No.1, what appears to be the same limestone has been encountered and, though it was heavily dolomitised owing to its position close beneath the Permo-Triassic unconformity, it contained chert nodules and microfossils of Carboniferous age. This recorrelation of Sowerby Wood No.1 removes a major anomaly from the Permian succession of the district (see p. 61).

At Bouth Wood No.2 and British Cellophane No.1 the limestone is overlain by another sandstone unit 7 to 14 m thick, with intercalations of red mudstone. This passes upwards into red mudstones, and at Sowerby Wood No.1 into shaly sandstone overlain by red mudstone. The position of the Permo-Triassic base is most uncertain, and the presence of gypsum bands in the highest mudstones suggests that these highest strata may lie above the unconformity, though instances are known of secondary gypsum bands occurring within undoubted Namurian strata close beneath the sub-Permian unconformity. KCD, WBE

Park Cottage–Housethwaite Hill–Hagg Hills

In the northern part of this area a complex series of small faults associated with the Park–Yarlside Fault-system breaks up the outcrops of the Basement Beds, Martin Limestone and Red Hill Oolite into discontinuous segments (see (Figure 20)). The faulting is accompanied by extensive dolomitisation of the limestones and much hematite staining. Drift deposits are relatively thin or absent and exposures are good.

At Park Crossing about 20 m of Basement Beds are exposed on the west side of the railway [SD 2158 7537] and consist of conglomerates and reddish brown, purple and green sandstones, siltstones and shales, the latter containing some nodules and nodular layers of yellow dolomitic limestone. There are also several exposures of sandstone and conglomerate south of Park Cottage around [SD 216 752], and of dull red siltstones in the stream northwest of Green Haume. A quarry section in the Basement Beds north-east of Park Cottage is now partially obscured by talus. About 7 m of dull red and greyish green sandstones, conglomerates and siltstones with bands and nodules of yellow dolomitic limestone have been noted. At one point [SD 2179 7538] they appeared to rest unconformably on a weathered surface of High Haume Limestone; elsewhere in the quarry they were faulted against the Skiddaw Group. A sample from the top of the quarry face yielded carbonaceous debris but no spores (loc. C4). Mapping suggests that the Basement Beds were deposited on a highly irregular surface cut across the Skiddaw Group, volcanic rocks and the High Haume Limestone. During subsequent faulting the relatively soft Basement Beds seem to have moved laterally along the unconformity.

In the side of an old tramway cutting [SD 2198 7532] 200 m NW of Green Haume, there are discontinuous sections near the junction of the Basement Beds and the Martin Limestone. The following section (loc. C6) was measured:

In the same cutting immediately south of Green Haume the junction between the Martin Limestone and the Red Hill Oolite, including the Algal Band, is well exposed. The Martin Limestone with the Algal Band at its top is also visible (loc. C15) on the west side of Housethwaite Hill [SD 2183 7522], and the Red Hill Oolite crops out on the top of the hill. The general dip is south to southwestwards at 10° to 20°. Red Hill Oolite, with a rich fauna including K. praecursor, Syringopora spp.and Spiriferellina octoplicata, is also exposed (loc. C27) south-east of Green Haume.

Dark grey limestone typical of the Dalton Beds crops out on the south-western slopes of Housethwaite Hill, and in a quarry (loc. C56) massive dark grey limestone with Caninia sp. cylindrica group, P. murchisoni, Zaphrentis' cf. kentensis and Delepinea carinata, probably low in the Dalton Beds, is faulted against a higher, more shaly, part of the same formation. There are substantial exposures of dolomitised limestone, probably still higher in the Dalton Beds, in old quarries [SD 218 746] west of St Helen's Farm. The upper part of the Dalton Beds is also exposed in an old quarry (loc. C58) north-cast of St Helen's Farm.

Park Limestone, succeeded to the south by Urswick Limestone, occupies the Hagg Hills ridge west of Dalton. The Park Limestone is exposed in the crags (loc. C83) south-south-west of St Helen's Farm, where Lithostrotion minus and Linoprotonia corrugatohemispherica have been recorded from about 6 m of pale grey crinoidal limestone ( ? middle part of Park Limestone); in an old quarry (loc. C84) where 7 m of pale grey crinoidal limestone, dolomitised at the base, contain Clisiophyllum rigidum, Diphyphyllum smithi, P. murchisoni and Megachonetes cf. papilionaceus (lower part of Park Limestone); and in another disused quarry (loc. C85) where 7.6 m of pale grey locally dolomitised limestone have yielded Lithostrotion cf. ischnon, L. minus, L. cf. sociale, and M. cf. papilionaceus (lower part of Park Limestone). At Goldmire Quarry (loc. C86) there is an excellent section exposing about the highest 60 m of the Park Limestone (loc. C86a). D. smithi, Lithostrotion minus, L. cf. sociale, M. cf. papilionaceus and Linoprotonia cf. hentisphaerica have been recorded. The Park Limestone consists of massive jointy pale grey limestone which gives way in the south-east corner of the quarry to the distinctive well-bedded pseudobrecciated and spotted Urswick Limestone with L. pauciradiale (loc. C86b), heavily jointed and hematite-stained along the southern faces. The Park Limestone is also exposed in a small faulted outlier at Hagg Hills Wood [SD 2215 7460].

The southern part of the Hagg Hills ridge is occupied by the Gleaston Formation and is separated from the outcrop of the Urswick Limestone by a W–E fault. The outcrop is wedge-shaped, narrowing southwards through Ruskinville to Billincoat Farm, and it lies between the branches of the Park–Yarlside Fault. Most of the ground is drift-covered, but limestones and shales with a few sandstones have been proved in many shallow boreholes. The only exposure is in the railway cutting (loc. C130) at Mary Bank where black shales with bivalves and orthocone nautiloids, thin sandstones and limestones dip at 15° to the south. KCD, WCCR

Dalton–Lindal Moor–Marton–Pennington

A sketch-map of the geology between Dalton and Crossgates is shown in (Figure 27), and of that around Lindal Moor in (Figure 29). A notable feature of the former area is the large number of small sops of hematite, aligned along NW–SE faults, and mostly lying within the outcrop of the Red Hill Oolite and the lower part of the Dalton Beds. Hematite deposits are also associated with faults around Lindal Moor and Pennington: again they occur mainly within the Red Hill Oolite, though they are here more vein-like.

Several shallow boreholes have proved the Basement Beds beneath drift between Green Haume and Tytup Hall, north of Dalton. A roadway driven from No. 1 Pit, Mouzell Mines [SD 231 754] proved the junction between the Basement Beds and the Silurian rocks on the footwall side of the Mouzell–Berkune Fault. Together with nearby borehole records it suggests that the Basement Beds are about 90 m thick. They are exposed only in Poaka Beck near Holmes Green. About 8 m of conglomerates and thinly bedded micaceous sandstones crop out in the west bank [SD 2325 7604] within a few metres of an outcrop of Brathay Flags to the north. A further small exposure of pale green and dull red coarse conglomerates, sandstones and sandy shales lie in the Beck about 300 m upstream from Holmes Green. The Basement Beds are at least 70 m thick in the Poaka Water-level where they are faulted against Silurian rocks so that the full thickness is not exposed. This level, about 450 m long and driven to assist in the dewatering of mine workings on the Lindal Moor Vein, was still accessible at the time of the resurvey. For much of its length it provides a continuous section in the Basement Beds, and this forms the basis of the section in (Figure 4). Dull red and pale green sandstones, siltstones and sandy shales with prominent beds of conglomerate predominate; thin bands of impure limestone occur near the top. The highest beds and the basal beds of the Martin Limestone are repeated by a NW–SE fault intersected by the level. Some of the mudstone bands in the level contain plant remains, and one (loc. C7) from 180 m SW of Marton has yielded a spore assemblage which is of Tournaisian age (see p. 33).

Boreholes between Dalton and Lindal (27SW/375); (27SW/377-8); (27NW/492), in Lindal (SD27NW/225); (SD27NW/227), and on Lindal Moor (SD27NW/436) have proved Basement Beds resting on the Lower Palaeozoic, and the thickness of the formation is some 80 to 100 m. Its detailed lithology is variable, and correlation of individual beds is not possible even in adjacent boreholes, although in a general way conglomerates tend to be restricted to the lower part of the sequence. In a borehole at Diamond Pit (SD27NE/88) a 0.3 m band of gypsum lies 16 m below the top of the highest conglomerate. On the upthrow side of the main Lindal Moor Vein, Basement Beds formed part of the footwall in the Whinfield and Diamond Pit areas. Between Whinfield and Pennington the ground is drift-covered and the only information available comes from old boreholes with scanty, possibly unreliable records that are hard to interpret. Conglomerates and shales, almost certainly within the Basement Beds, were recorded beneath drift in a borehole (SD27NE/59) north-east of Wellington Inn while the lowest workings of Pennington Mine probably entered Basement Beds, and the upper part of the formation was recorded in nearby boreholes at depths of between 100 and 120 m.

The highest beds of the Martin Limestone, consisting of partially dolomitised fine-grained limestone with shale partings, are exposed around the subsidences of Mouzell Sop, north of Dalton, underlying the Algal Band and the lowest beds of the Red Hill Oolite. The same beds, less dolomitised, crop out at intervals north-eastwards to Tytup Hall. At Mouzell the base of the Martin Limestone was not reached in the mine workings at −6 m OD, so the thickness here is at least 80 m. Near Tytup, however, boreholes show that the thickness has decreased to 60 m. A small quarry (loc. C16) south-east of Marton (previously Martin) is in the higher beds of the formation (see (Figure 29)). The section measured in 1969 is as follows:

This quarry was chosen as the eponymous locality for the Martin Limestone, chiefly because it is one of the few fossiliferous exposures of the formation. The lithology of the beds has been described in detail by Nicholas (1968). Although the section is incomplete its relationship to the top of the Basement Beds, which is seen in Poaka Water-level, suggests that the Martin Limestone is about 55 m thick.

Surface exposures of the Red Hill Oolite are few but small exposures of unaltered coarsely fragmental pale grey limestones, in places laminated and showing current bedding, can be seen (loc. C28, with Clisiophyllum cf. ingletonense) north of Elliscales Quarry; in subsided ground (loc. C30) at Tytup No. 3 Sop, and around Tytup Farm (loc. C31). The Algal Band is exposed in the subsidence at Mouzell No. 1 Pit [SD 2314 7540]; the overlying beds are much dolomitised, but include some unaltered coarsely fragmented and banded limestone. Evidence from mine dumps (e.g. material from Mouzell No. 3 Shaft, loc. C29, which has a rich fauna including C. ingletonense, K. praecursor, M. megastoma and P. murchisoni) confirms that the normal lithology is maintained and that the Algal Band is continuous over much of the ground. Locally, however, the beds are much dolomitised and hematite-stained and on Lindal Moor such alteration is extensive. Beds near the middle of the Red Hill Oolite are exposed in crags (loc. C32) south-east of Marton and Cleiothyridina glabristria and Spirifer cf. furcatus are recorded.

Much of the northern part of the Lindal Moor and Whitriggs mining area is occupied by the relatively broad dip-slope of the Red Hill Oolite. There are a few exposures in the sides of mine-subsidences e.g. at [SD 245 768] and in one or two old and much overgrown quarries south of Marton; there is much dolomitisation and hematitisation.

The best section in the Red Hill Oolite is in Elliscales Quarry [SD 2245 7480], which Garwood (1913, p. 532) considered to establish the presence in Furness of the Camarophoria isorhyncha Subzone of his Michelinia grandis Zone. The section is as follows (loc. C33):

In one face of the quarry prominent reef-knolls lie within the normal bedded limestone. They consist of sharply defined steep-sided masses of unbedded pale grey limestone, up to 4 m in width, extending from the floor up to a height of about 10 m. The largest, occupying a central position in the quarry, has a dome-shaped top, the reef limestone being capped by normally bedded limestone. The limestone of the reefs consists of coarse bioclastic fragments in a matrix of calcite mudstone; algal structures and bryozoa are abundant, with Michelinia megastoma and other corals common. At least three reef-knolls can be seen. Lithologically similar limestone, though not associated with reef forms, occurs in the lower part of the Dalton Beds east of Elliscales Quarry in Poaka Beck where Syringothyris exoleta has been recorded from an exposure on the east bank (loc. C61).

The Dalton Beds are thickest around Dalton-in-Furness where they total about 150 m. The wide outcrop around the town extends north-eastwards towards Lindal and Ulverston. Several exposures can be seen on the western and northern sides of Dalton, notably at Cat Crag (loc. C59), Church School Quarry (loc. C60) and in quarries and railway cuttings between Dalton and Lindal. They are mostly in the lower part of the formation, which consists of well-bedded dark grey limestones with thin shale partings. Similar beds have been recorded in boreholes near Maidenlands and Lindal. The section in Maidenlands Quarry (loc. C62) is as follows:

In Tunnel Quarry (loc. C63) the lower to middle part of the formation is present:

About 10.66 m of dark grey limestone with shale partings are present in Eure Pit Quarry (loc. C52) and are in the lower part of the Dalton Beds with C. subibicina, C. sp. cylindrica group and D. carinata. Dalton Beds fossils have also been collected from a trial pit (loc. C53) south-south-west of Lindal, with Michelinia megastoma, and from Frank Pit (loc. C54) south-east of Marton, with C. cf. ingletonense and K. praecursor.

Between Lindal and Whinfield the lower formations may be seen only in a few small exposures, but they have been penetrated by several mine shafts (e.g. Martin Limestone with algal nodules from tip material at loc. C17) and boreholes. South-east of the railway line between Lindal and Dalton the drift cover is extensive, and largely masks the upper part of the Dalton Beds. Several shafts, for instance Lindal Cote No. 4 Pit (loc. C55), and boreholes show this to consist mainly of calcareous shales with some thin limestones below, and thickly bedded dark grey limestones above. KCD, WCCR

Ulverston

Between Pennington and Ulverston the ground is heavily drift-covered and the detailed geology is locally uncertain. An exposure of the Basement Beds [SD 2729 7849] in Barn Beck at Rosside shows reddish brown and green micaceous sandstones and shales dipping to the SSE at about 10°. They are also exposed in a small down-faulted wedge in Gill Banks Beck [SD 2823 7872] on the outskirts of Ulverston. The beds are exposed for a few metres in the beck and on its eastern bank (p. 74). They consist of dull red, green and grey sandstones and mudstones with a few thin bands of impure nodular limestone. Pennington No. 2 Shaft [SD 2654 7675] probably entered the lower part of the Red Hill Oolite beneath about 22 m of drift, and passed through the full thickness of the Martin Limestone before entering Basement Beds. According to Smith (1919, p. 154) the Lower Carboniferous rocks rest upon a floor of 'Coniston Grits and Flags' which slopes ESE at 13° in part of the mine.

In a small disused quarry at Tarn Close [SD 2770 7870] about 9 m of fine-grained dark grey limestone and calcite mudstone of the Martin Limestone can be seen; the rocks show much dolomitisation and hematite staining probably associated with the Stone Cross Fault, the course of which lies only a few metres to the east.

A wide tract of ground occupied by Dalton Beds between Whinfield, Ulverston and Bardsea Park is largely drift-covered, and exposures are small and rare. Two or three shallow disused quarries (locs. C64 and C65) near Edge Hill worked coarse- and fine-grained dark grey limestones with shale partings and there are scattered exposures of fine-grained limestone, partly dolomitised, with some calcite mudstone in Levy Beck [SD 2857 7729]. In Gasgow Quarry (loc. C66) there was, at the time of the resurvey, an excellent exposure of about 39 m in the upper part of the Dalton Beds. Dips average 15° south-eastwards and the Park Limestone crops out about 6 m above the highest beds exposed. The section was as follows:

The quarry is now disused and the section is rapidly becoming obscured by refuse.

Around Ulverston information is particularly meagre and even the positions of the Stone Cross Fault and the base of the Carboniferous are somewhat uncertain. The only information about the Lower Carboniferous around South Ulverston comes from a recent (1951) borehole (37 NW/4), which started in the lower part of the Dalton Beds and continued to the underlying Silurian strata. The topmost 30 m of limestone (loc. C34b) yielded a limited fauna with C. sp. cylindrica group and P. murchisoni indicative of the Dalton Beds, and it is likely that the borehole passed through most of the Red Hill Oolite (loc. C34a), but without yielding a diagnostic fauna, before entering the Silurian. Martin Limestone is not identifiable with certainty, but although the lower part of the core was crushed and stained with hematite, a thin representative of the Basement Beds was recorded near the base of the hole.

The greater part of the Red Hill Oolite and of the Dalton Beds, and about 36 m of the Park Limestone can be seen in the old quarries near Plumpton Hall, 2 km E of Ulverston. The geology of this area is shown in (Figure 32). The Lower Carboniferous rocks dip generally to the ESE at 12°–15°. The Plumpton hematite vein follows a down-south fault of about 45 m. It is continuously exposed along the line of an old tramway connecting the quarries south-west of Plumpton Hall, and old workings on it can be seen at the north end of Iron Pit Spring Wood [SD 3078 7868] in the Red Hill Oolite. The Red Hill Oolite crops out (locs. C35 and 36) on the north side of the wood, giving rise to a small escarpment. The fauna here includes C. aff. ingletonense, cf. K. meathopense and Stenoscisma isorhyncha. The formation also crops out in the wood west of Plumpton Hall, on the footwall side of the Plumpton Vein, where it is much dolomitised (loc. C37) on the north side of the old tramway. The base of the Red Hill Oolite and the Martin Limestone below are not seen at Plumpton, but the former is probably about 60 m thick.

In Iron Pit Spring Quarry (loc. C67) about 6.1 m of the upper part of the Red Hill Oolite (loc. C67a) lies in the lower part of the main quarry face; it is a massive, pale grey or brownish grey, fragmental limestone, weathering white. About half-way up the face the limestone becomes noticeably darker in colour and bedding planes appear. The division between the Red Hill Oolite and the Dalton Beds has been drawn at the first appearance of dark limestone, though there is some interbedding of light grey and dark grey limestone for a few metres above. Fossils are rare in the Red Hill Oolite. About 6.1 m of well-bedded dark grey limestones (loc. C67b) with shale partings–lithologies typical of the Dalton Beds–can be seen in the side walls of the quarry and in an old tramway cutting at its entrance. They carry a rich fauna including Caninia sp. cylindrica group, Clisiophyllum multiseptatum, K. meathopense, P. murchisoni and 'Z.' kentensis. Delepinea carinata is common in the lower part of the sequence. The middle part of the Dalton Beds underlies a grassy hollow extending southwards between Iron Pit Spring Wood and Plumpton quarries. The beds are poorly exposed, but consist mostly of dark grey calcareous shales with bands of dark grey crinoidal limestone. The upper part of the Dalton Beds is seen in the following two quarries:

The junction between the Dalton Beds and the Park Limestone is seen in another old quarry (loc. C72), where the section is:

The Dalton Beds are also exposed north of the old tramway cutting along the line of the Plumpton Vein (see loc. C73 with Syringothyris exoleta; loc. C74 with Caninia subibicina, C. sp. cylindrica group, K. aff. praecursor and D. carinata; and loc. C75 with Caninia densa and Composita aff. ficoidea).

The Dalton Beds are extremely fossiliferous, particularly the more thinly bedded layers in the lower part of the formation. The Park Limestone is less fossiliferous, but a rich fauna including Lithostrotion minus and Linoprotonia cf. corrugatohemispherica is present in the higher beds of the formation, on the shore (loc. C99) of Plumpton Bight. Exposures on the shore south of Old Pier and in old quarries nearby (loc. C98) show the Park Limestone to be cut by closely spaced joints, often several per metre, trending 320°–325° with accompanying minor brecciation and hematite staining.

A small isolated exposure in an old quarry [SD 3223 7985] at Ashes Point shows about 4.5 m of thickly bedded calcite mudstone (Martin Limestone) overlain by the lowest beds of the Red Hill Oolite. The junction between the two formations is taken at a prominent 30 cm band of purplish grey and slighly nodular marly shale, similar to a bed at this same horizon at Hazelhurst Point (p. 53), but the Algal Band is not present. WCCR

Stainton–Newton–Gleaston–Barrow

The full thickness of the Park Limestone was exposed underground [SD 2276 7135] in cross-cuts in the No. 1 Pit, Yarlside, its base being cut 930 m N of the shaft and its top 69 m E of the shaft. It was also encountered in the lower levels of Newton Mine, and the Urswick Limestone was driven through in higher levels. These workings entered the Gleaston Formation so the thickness of the Urswick Limestone here can be shown to be 117 m. The Woodbine Shale was exposed in many parts of the mine and was about 4.3 m thick, its base lying 29 m above the base of the Urswick Limestone. The Urswick Limestone was also extensively exposed in the workings of Yarlside and Stank mines beneath the Gleaston Formation, and those from No. 11 Pit, Yarlside [SD 2267 7077] probably entered the Park Limestone.

About 18 m of spotted and white limestones above the horizons of the Woodbine Shale are exposed in an old quarry [SD 2363 7219] south of Woodbine Pit, but the best exposures are at Stainton, where over 150 m of limestone, comprising approximately the upper half of the Park Limestone and much of the Urswick Limestone, are exposed in a large quarry complex. The eastern part of the quarry, formerly Devonshire Quarry (loc. C110), is in the Urswick Limestone, and was once an important source of ornamental stone. The western part was called Crown Quarry (locs. C87 and 109) and is mainly in the Park Limestone. The two quarries are now continuous. The Park Limestone is remarkably uniform in lithology. Its junction with the Urswick Limestone is well exposed, and the upward change from massive cream-white to thickly bedded, grey, pseudobrecciated limestone is abrupt, and accompanied by the incoming of a typical D, fauna including Dibunophyllum bourtonense. The junction lies about 30 m below the Woodbine Shale, which is well exposed and about 4.6 m thick. The lithology of the Urswick Limestone above the Woodbine Shale is more variable than smaller natural exposures would suggest. The detailed section in the combined quarries is given below: above the Woodbine Shale the section is taken from Devonshire Quarry (loc. C110), and from the Woodbine Shale to the base of the section it is that exposed in Crown Quarry (locs. C87 and 109).

Two other sections have been measured and collected in Crown Quarry. Mr S. W. Hester's section (1937) across the Park Limestone–Urswick Limestone junction is as follows (loc. C87):

In 1969 Mr J. Pattison measured the following section (loc. C109) on the east side of the roadway into Crown Quarry base of section at [SD 2474 7289]:

To the north of Stainton, Park Limestone is present in several trial pits (e.g. locs. C91 and C92).

About 18 m of the middle part of the Urswick Limestone with the Davidsonina septosa Band is exposed in Woodbine Quarry (loc. C107). P. murchisoni and D. septosa have been collected from this locality. The D. septosa Band is also exposed in broken ground (loc. C108) above No. 3 Vein workings north-west of Newton Mine.

There are no surface exposures of the Gleaston Formation between Stainton and Yarlside but the shafts, boreholes and workings yield much detailed information about the succession (see (Figure 33)). The lower beds show rapid variations in their thickness, and individual members of limestone and shale, and less commonly sandstone are recorded. Several, if not all, of the Stank pits (see locs. C131–135 for collections from the lower part of the Gleaston Formation) passed through the Girvanella Nodular Bed, specimens of which can be collected from their spoil, and entered the Urswick Limestone. The Girvanella Nodular Bed was also noted in a cross-cut (Lindal Tunnel, loc. C136) driven north-east from Woodbine Pit, Newton Mines. This cross-cut yielded the following section:

East of Stainton, dark grey limestone at the base of the formation contains the Girvanella Nodular Bed; a higher exposure of similar limestone, but with Saccamminopsis sp., is exposed northwest of Redman Hall (loc. C140). Purplish brown sandstones overlain by coarsely crinoidal grey limestones probably about 45 m higher in the sequence are exposed in the crags on the north-east side of the road, immediately north of Hawkfield (loc. C137). The sandstone is about 6 m thick, and forms a strong feature but seems to die out rapidly to the east. Crinoidal limestones with chert are typical of the lower part of the Gleaston Formation, and one such limestone is exposed in an old roadside quarry (loc. C138) at Bolton Chapel. It is underlain by a sandstone, and these two beds are probably the same as those at Hawkfield. The section of the limestone at Bolton Chapel is:

The brachiopod fauna from bed b is of reefy aspect and suggests a low D₂ age for this bed. Between Bolton Chapel and Great Urswick the Gleaston Formation is concealed beneath drift, but shales and limestone have been recorded at shallow depths near Little Urswick, and dark grey limestones with some sandstone were proved in St Mary's Churchyard, Great Urswick. Beds low in the Gleaston Formation crop out west of Little Urswick (loc. C139, with the Girvanella Nodular Bed; and loc. C140, with abundant Saccamminopsis sp.). Beds probably a little higher in the sequence were exposed south-east of Stainton and Little Urswick in

a sewer-trench (loc. C143). One length [SD 2650 7320], near Skeldon Moor, was in dark grey calcareous shales, with posts of grey limestone up to 1 m thick, both lithologies yielding a rich coral-brachiopod fauna of D₂ age. Thinly bedded yellow and grey calcareous sandstone with bands of siliceous limestone were also exposed. Similar strata were dug between Stainton and Beckside [SD 2530 7240].

On the eastern flank of the Urswick Syncline a borehole (2 7 SE/44), between Holme Bank and Scales, proved 29 m of limestone and black shale beneath drift, and then entered the Urswick Limestone. Urswick Limestone with dark grey limestone overlain by pale grey oolitic limestone is exposed in a small quarry (loc. C113) north-west of Scales Park. Fossiliferous dark grey limestone of the Gleaston Formation with Saccamminopsis sp.[abundant], Amplexizaphrentis derbiensis, Aulophyllum pachyendothecum, Dibunophyllum bipartitum, Diphyphyllum lateseptatum, Lithostrotion junceum, L. martini, Gigantoproductus edelburgensis and Pugilis pugilis is present in another quarry (loc. C144) west of Scale Park. The abundance of Saccamminopsis sp.suggests that the exposure is low in the Formation, probably just above the Girvanella Nodular Bed.

Two old quarries near Gleaston Castle expose dark grey, mostly fine-grained and bituminous limestones of the Gleaston Formation yielding rich D, faunas. The quarry (loc. C141) south of Gleaston Castle exposes the following section:

The section in the other quarry (loc. C142) east of Gleaston Castle is:

The dip in both quarries is 10°–15° to the WSW. These limestones are faulted against black mudstones, probably Namurian, which have been proved near the old Gleaston Mill, between Gleaston and Beacon Hill.

The succession in the upper part of the Gleaston Formation was proved by the IGS Gleaston Castle Farm Borehole (SD27SE/51). The borehole passed through the correlative of the Cravenoceras leion Band and proved the highest 40 m of the Gleaston Formation. These comprised alternations of thinly bedded crinoidal limestone and dark grey shaly mudstone, both of which lithologies were fossiliferous. The detailed log and faunas are given in Appendix 1. The sequence is duplicated and continued downwards to the Urswick Limestone by the closely adjacent Harbarrow No. 1 Borehole (SD27SE/37), and another good section is provided by Windhills No. 1 Borehole (SD27SW/14). Details of both holes appear in Appendix 1.

Knowledge of the Roosecote Mudstones comes practically wholly from boreholes, and in the case of the older holes there are no recorded faunas to help in correlation. Consequently the Gleaston Castle Farm Borehole was drilled by the Institute to establish the position of the base of the Namurian in the type-area of the former Gleaston Group. Although none of the key goniatites was found, the succession of marker bands enabled a correlation to be made with the Roosecote sequence (see below). The significance of the failure of the goniatite faunas is uncertain for the landward margin of the basin lay well to the east. A thin limestone marks the position of the C. leion Band and others lie immediately beneath and above the position of the E. pseudobilingue Band. Otherwise the sediments in the upper part of the hole are mainly mudstones, though with a 7.6 m sandstone that is unrepresented farther west, while interbedded siltstones and thin sandstones appear above the upper C. malhamense horizon. The sequence can be continued upwards in the Windhills No. 1 Borehole, where sandstones become more common upwards from about 129 m above the likely base of the Roosecote Mudstones. Several shallow boreholes near Gleaston have proved thick mudstones in the lower part of the Namurian succession, and there are a few poor exposures of shaly mudstone in the banks of Gleaston Beck. A thin limestone is recorded within these mudstones and it may represent one of the bands yielding C. malhamense at Roosecote.

Of the older boreholes the Gleaston No. 4 Borehole (SD27SE/33) proves one of the thickest Namurian sequences in the district. At the base of the hole some 8.5 m of limestone were encountered without being penetrated, and because no limestone of this thickness is known from the Namurian in the other provings, the C. leion Band seems likely to lie in or close above it. The succeeding 227 m are wholly mudstones and sandy mudstones, and presumably correlate with much of the lower half of the Namurian sequence at Roosecote. Sandstones are common in the overlying strata and there is a crude apparent correlation with the higher sandstone units at Roosecote. A porphyritic dolerite or 'greenstone' is recorded and is probably related to an olivine-dolerite dyke exposed at Gleaston Green.

The Roosecote Borehole (SD26NW/19) was drilled by the Institute to elucidate the thick sequence penetrated in the Gleaston No. 4 Borehole. It proved 455.18 m of Namurian strata from 158.13 to 613.31 m, and continued in Dinantian rocks to its base at 800.88 m.^‡4  An abridged log with the contained faunas is given in Appendix 1. The Dinantian strata were a monotonous sequence of dark grey, finely granular limestones with thin mudstone partings at 10 to 50 cm intervals and sporadic thin bands and nodules of black chert: the basal 30 m were argillaceous and patchily dolomitic.

Thin partings of green pyritic mudstone at 615.59 m and between 692.30 and 704.91 m may be of volcanic origin. Bioclastic limestones were confined to a 2.27-m bed at 682.94 m and to the uppermost 4 m of the sequence. Zaphrentoid corals and chonetoid brachiopods were the main constituents of the dispersed fauna. The records of Rotiphyllum costatum above 683 m and of Michelinia parasitica at 720.65 m suggest an equation with P₁ and P₂ strata elsewhere. The sequence is, however, so different from the lithology of the Gleaston Formation in its type-area that it has been given separate formational status as the Roosecote Limestone.

The base of the Namurian has been drawn at the base of a mudstone unit that contains a fauna representative of the C. leion Band, though the basal 4.46 m of the unit was unfossiliferous. The C. leion (E_1a) and E. pseudobilingue (E_1b) zones are respectively 25.65 and 29.66 m thick. The rocks are mainly dark grey silty mudstones, calcareous in parts, though two thin (22 and 25 cm) beds of barren dark grey, finely granular, limestone occur close beneath the E. pseudobilingue Band. Above the latter the mudstones became siltier and carry a few pale grey siltstone stripes. The base of the Cravenoceras malhamense (E_1c) Zone is taken at the base of the lower of two bands both containing C. malhamense. An abrupt lithological change takes place 29.8 m above the top of the upper of these bands, and the mudstones are succeeded by a thick alternating sequence of mudstones, siltstones and sandstones that continues to the base of the Permian. In detail the lithologies vary rapidly, but overall this part of the sequence is characterised by belts of thinly interlaminated dark grey muddy siltstones, pale grey coarse-grained quartzose siltstones, and fine- to medium-grained sandstones. Directional sole-markings on the bases of these latter are characteristic of turbidites. These belts can be grouped into units, with sharp bases resting on silty mudstone and gradational tops. They mark a rude megacyclicity, apparently indicating surges of turbidites passing into the basin. A detailed account of the borehole is at present in preparation.

Of the older holes at Barrow both the Davy Street (SD26NW/10) and the Rampside (SD26NW/31) boreholes entered Namurian rocks beneath the Permian. The thicker section is at Rampside where the presence of beds of sandstone suggests that the strata lie above the C. malhamense Band. No more precise correlation is feasible. A notable feature is the presence of a bed of 'greenstone'–probably a dolerite–within the sequence. It is not possible to say whether it is a sill or a lava-flow. It may represent the same episode that was responsible for the igneous rocks at Gleaston (see below). KCD, WCCR, WBE

A small intrusion of olivine-dolerite into dark grey Namurian mudstone occurs on the eastern outskirts of Gleaston, and is probably a dyke intruded along a fracture associated with the Gleaston Fault. During the resurvey it was exposed in a small quarry [SD 2584 7073] on the southern bank of Gleaston Beck, and there was a smaller exposure on the northern bank. Both exposures are now obscured. The intrusion was first described by Binney (1868), who quotes three partial analyses of the rock, and it was also mentioned by Aveline (1873). KCD

Specimens from the dyke show a variable degree of alteration. In the least altered samples (E727), (E17693) turbid plagioclase laths, averaging about 0.9 x 0.2 mm, form a framework with euhedral to subhedral pseudomorphs of chlorite and iron oxide after olivine, the pseudomorphs amounting to about 25 per cent of the total volume. The plagioclase ranges from andesine to labradorite, and occurs as both slender laths and stouter interstitial anhedral plates showing undulose extinction. Much of the chlorite forming the olivine pseudomorphs has pleochroism X = pale yellow, Z =deep green. Some of the opaques appear to be magnetite, but there are also granular clusters of hematite associated with interstitial calcite-chlorite.

In the more altered samples (E17694) the feldspars are albitised, the olivine pseudomorphs are broken down into aggregates of clay minerals, and quartz is common in interstitial patches together with calcite and chlorite. It is not possible to estimate the degree of alteration respectively due to deuteric, autometasomatic or post-emplacement processes, but weathering seems to have been the least important. RKH

Urswick–Bardsea–Baycliff

The Urswick Limestone is well exposed around the nose of the Urswick Syncline at Great Urswick (loc. C115 with D. bourtonense) and Hagg End, where it characteristically gives rise to grikes. There are other good exposures on Little Urswick Crags on the western limb of the Urswick Syncline, where the 'slack' formed by the Woodbine Shale can be traced along the crags. At the north end of Little Urswick village, Long Rigg Quarry (loc. C112) shows the following section:

The dip is 8° to the south-east and the highest bed exposed is at, or very close to, the top of the formation. Along the east side of the Urswick valley, the limestone is exposed immediately east and north-east of Holme Bank (locs. C114 and C116) where the beds dip at up to 40° westwards towards the centre of the syncline, though the amount of this dip may be partly a result of proximity to NW–SE faults. The normal south-easterly dip of 10° to 12° is resumed about 450 m E of Holme Bank, thus fixing the position of a sharp anticlinal axis trending approximately NE–SW, parallel to the axis of the Urswick Syncline. Locally there is strong hematite staining and impregnation which appear to be associated with several NW–SE faults, and there are old trial shafts for hematite in Holme Bank Plantation [SD 274 737]. Limestones within 15 m of the base of the Urswick Limestone are exposed in the crags (loc. C117) west-north-west of Sunbrick and C. vaughani, D. bourtonense and P. murchisoni have been collected here.

The drift-free ground of Birkrigg Common provides excellent exposures of almost the full sequence of the Park and Urswick limestones, and the junction between them is marked by a sharp feature. The general dip is 10° to 12° in an easterly direction. The Park Limestone, forming the face of the escarpment, is visible in several disused quarries (e.g. locs. C93 and C94) between the summit of the Common and the crossroads to the north-west. Its lithology is normal, and the common fossils include Lithostrotion portlocki, Gigantoproductus sp., Linoprotonia corrugatohemispherica and Megachonetes cf. papilionaceus. The junction between the two formations is best seen just south of the highest point of Birkrigg Common, and is exposed sporadically to the north as far as the Green Lane Fault. The section in the low crags and old quarry on Birkrigg Common (loc. C95) is:

The change from massive creamy limestone (Park Limestone) below to darker grey pseudobrecciated limestone (Urswick Limestone) above is sharp, though there is no indication of penecontemporaneous erosion or even of any significant pause in deposition. The lowest bed of the Urswick Limestone is marked by the incoming of the typical D, coral fauna. Eastwards from the summit of Birkrigg Common the Urswick Limestone forms a grike-covered dip-slope extending to the coast at Sea Wood. An old quarry (loc. C118) east of the summit yields a coral fauna including Aulophyllum redesdalense, C. vaughani, D. bourtonense, Lithostrotion martini and L. pauciradiale.

A narrow hollow, which runs several hundred metres northwards from Sunbrick [SD 2879 7381], may indicate the outcrop of the Woodbine Shale. The higher beds of the Urswick Limestone can be seen in quarries at Wellhouse Wood [SD 2945 7385] and in low cliffs along the shore at Sea Wood; they include thick beds of pale grey bioclastic limestone, which is pseudo-oolitic in places. In the shore section [SD 296 733] this lithology passes laterally into pseudobrecciated limestone.

The outcrop of the Urswick Limestone continues southwards towards Aldingham and again gives rise to grike topography at Baycliff Haggs and Scale Haggs. Again a slack, shifted by NW–SE faults, is present along the outcrop of the Woodbine Shale. The higher beds are exposed in old quarries south-west and north of Baycliff [SD 283 718]; [SD 287 727], and include much creamy, partly pseudo-oolitic limestone. The last-mentioned quarry was once well known as a source of good-quality ornamental stone.

To the north of the substantial Green Lane Fault, the outcrops of the Park and Urswick limestones are stepped about 1.6 km to the east, and both formations are again well exposed on Bardsea Park golf-course. The junction between the two formations is seen in an old quarry (loc. C96), where the section is as follows (see also locs. C90 and C97 for the top beds of the Park Limestone):

The base of the Park Limestone can be traced along the western edge of the Park, following approximately the dry valley known as White Gill. An old quarry (loc. C89) exposes 7.62 m of pale grey oolitic limestone about 6 m above the base of the Park Limestone with P. murchisoni [exceptionally large diameter, 60+ mm], Linoprotonia corrugatohemispherica, L. cf. hemisphaerica and Megachonetes cf. papilionaceus. The base of the Urswick Limestone forms a prominent feature, which runs northwards through the golf-course immediately below the Monument [SD 2974 7512]. An old quarry (loc. C111) 180 m N of the Monument shows the beds within 1.52 m of the base of the Urswick Limestone with K. cf. O, Lithostrotion martini, L. cf. sociale, P. murchisoni, Delepinea comoides, Linoprotonia cf. hemisphaerica and M. cf. papilionaceus. The junction with the Park Limestone is almost continuously exposed from near the Bardsea end of White Gill Lane [SD 299 748] northwards for about 540 m to Priory Park. The Stone Cross Fault, and a smaller branch fault, repeat the outcrops of the Park and Urswick limestones so that both, including their junction, are also exposed at Hermitage Hill.

An old quarry (loc. C119) 500 m N 15°E of Bardsea church exposes beds close above the Woodbine Shale and contains Lithostrotion martini, P. murchisoni and Linoprotonia cf. hemisphaerica. The crags (loc. C123) to the south are in limestones below the Shale.

Around Baycliff and near Manor House the ground is again almost entirely drift-covered. Dark grey limestones with black mudstone bands were temporarily exposed during 1971 in an excavation near Baycliff [SD 2875 7219], and a small exposure of dark grey limestone was visible on the shore [SD 2925 7264] during the resurvey. A section on the foreshore at Bean Well Bank [SD 2920 7224] shows dark grey limestones overlying pale grey pseudobreccias of the Urswick Limestone. The Girvanella Nodular Bed can sometimes be seen cropping out below high-water mark (loc. C145); the dip is about 12° to the east and the bed lies about 4 m above the top of the Urswick Limestone. W C C R

Roudsea Wood–Holker

There are extensive natural exposures in the low cliffs and ridges bordering the eastern shore of the Leven Estuary. Dips are generally to the east at 10°–15°. The outcrops are shifted by several south-westerly downthrowing NW–SE faults, whose courses are commonly hidden beneath alluvium (see (Figure 8)).

In the Roudsea Wood Nature Reserve the Martin Limestone forms the lower part of a westerly-facing escarpment capped by Red Hill Oolite that forms a prominent feature through the central part of the wood. Its junction with the Silurian rocks, beneath the western part of the wood, is not naturally exposed, but a short trench through the contact was dug by Nicholas (1968) and proved the absence of the Basement Beds and the lower part of the Martin Limestone, a thin representative of the latter with a basal 0.15 m sandy bed which failed to yield any spores (loc. C19) resting unconformably on Silurian rocks. The trench [SD 3336 8166] was reopened for the Institute in 1969. About 25 m to the south another contact was exposed during the 1938 resurvey (loc. C20) [SD 3336 8164], but the junction here was locally faulted, and it was then wrongly assumed that the contact was faulted throughout Roudsea Wood (Eastwood, 1940). The Martin Limestone has a maximum thickness of 25 m in the wood, and is well exposed in several places, consisting of thinly bedded fine-grained limestones and calcite mudstones with some shale partings, typical of the upper part of this formation farther west. The Red Hill Oolite is exposed in many places along the eastern side of the wood, and in cliffs at its southern end (locs. C41 and C42), where it is cut by several small dip-faults accompanied by some hematitisation and staining. The best exposure (loc. C40), however, is in an old quarry at the northern end where about 19 m of the lower beds with P. murchisoni and Composita ambigua can be seen.

The cliffs at Skelwith Hill, Little Arrad and Hazelhurst Point provide fine sections in the highest beds of the Martin Limestone and the lowest beds of the Red Hill Oolite. In general the junction between the two formations lies at or near high-water mark. At Skelwith Hill [SD 3310 8088] a prominent brecciated bed, 0.3 to 1.0 m thick, marks the junction between the formations, and consists of rounded and subangular blocks of dark grey limestone up to 5 cm in diameter set in a marly and dolomitic matrix locally pink-stained. A similar, but less prominent, bed marks the junction at Ashes Point (p. 48) and at Hazelhurst Point. The following section was measured at Skelwith Hill (loc. C18).

The Algal Band recorded farther west has not been seen, although some algae occur in the lowest beds of the Red Hill Oolite. The lithology of these sections has been described in detail by Nicholas (1968), who considered the breccia to be indicative of penecontemporaneous erosion and of a depositional pause. The beds in the cliff sections at Skelwith Hill are much jointed and crushed; the normal easterly dip steepens to 45° and locally to 60° at the northern end of the section suggesting that there is a fault close off-shore parallel to the cliff line. At Little Arrad about 22 m of the Red Hill Oolite crop out in cliffs and old quarries.

At High Frith the lower horizons of the Dalton Beds are well exposed, and an old quarry (loc. C80) yielded Caninia caninoides, P. murchisoni and Delepinea carinata. These beds resemble the Red Hill Oolite, but are thickly bedded rather than massive, while the limestone is slightly darker in colour than it is in the former. The Dalton Beds are also assumed to underlie the drift-covered ground of Deer Dike Moss and Stribers Moss.

A small fault-bounded patch of limestone occurs near Stribers [SD 3524 8108], but is not now exposed, though it is said to have been worked for lime in the last century. An exploratory shaft for hematite nearby [SD 3529 8103] recorded crushed, dolomitised and hematitised limestone. Debris from this shaft has been provisionally identified as Red Hill Oolite.

The Red Hill Oolite with P. murchisoni is exposed on the shore (loc. C38) near Frith Hall, and is overlain southwards by the lower part of the Dalton Beds which, during the resurvey, was exposed on the shore (loc. C77) south-west of Low Frith where D. carinata has been recorded. The low cliffs to the south of Low Frith provide a section in ascending sequence southwards through the upper part of the Dalton Beds into the Park Limestone. The continuity of the beds is broken by minor faulting which obscures the relationships of the Dalton Beds and the Park Limestone. The dip is to the ESE at 12°–15°. The composite section (loc. C78, base at [SD 3395 7955]) is as follows:

The Park Limestone is exposed on Reake Hill (locs. C100–102 with Lithostrotion minus) and in the quarry (loc. C78 m to o) at its southern end. The formation is here about 120 m thick.

The base of the Urswick Limestone probably follows the eastern margin of Reake Wood and presumably underlies part of Reake Moss and the alluvial ground to the south. An isolated outcrop of the higher part of the formation with the Davidsonina septosa Band occurs in Waitham Wood where there are several exposures in a line of small crags. The following is the section in an old quarry (loc. C122):

The best sections are, however, in the cliffs from Barker Scar to the southern end of Old Park Wood, which provide an excellent and almost continuous section from the upper part of the Dalton Beds at Barker Scar to the lower part of the Urswick Limestone; there are also several exposures of the Park and Urswick limestones nearby in Old Park Wood. The section at Barker Scar (loc. C76) is as follows:

At the southern end of Old Park Wood the junction between the Park Limestone and the Urswick Limestone may be seen in the centre of the face of an old quarry (loc. C121). The dip is 15°–20° east-south-eastwards.

The Park Limestone is a massive pale grey to cream-coloured bioclastic limestone. It is succeeded by well-bedded compact grey Urswick Limestone bearing some darker spots. Beds higher in the Urswick Limestone are exposed in old quarries south of Old Park [SD 3405 7755] and in crags close to the north. Other outcrops of Urswick Limestone, dipping to the east at 15°, lie below high-water mark at Black Scars [SD 327 770] on Cartmel Sands. They are separated from those in the cliffs by a major NW–SE fault. Another similarly dipping outcrop of Urswick Limestone forms Chapel Island (loc. C120), and the formation has also been proved at depth beneath the estuary in two boreholes [SD 3225 7796]; [SD 3305 7625].

The Gleaston Formation is best exposed on the western edge of Holker Park, southwards from Godderside Gate to Black Myre Stile and Quarry Flat, and in scattered sections to the north and east of Holker Farm. The lowest beds crop out at Godderside Gate (loc. C148), where the section is:

The fossils from the limestones include Antiquatonia cf. antiquata, A. sulcata, Avonia cf. youngiana and Schizophoria resupinata. They suggest a horizon low in the formation and are indicative of back-reef conditions (see p. 35). A little to the south there is a further exposure [SD 3460 7718], probably lying higher in the sequence though its relationship to the above sections is uncertain. Its detailed record is:

This section is in turn succeeded southwards to Black Mire Stile by outcrops of sandstone, sandy shale and crinoidal limestone, dipping at from 15°–20° to the south-south-east, but the detailed sequence is complicated by several small faults. The crinoidal limestone is best exposed in a quarry (loc. C147) west of Holker Farm, but contains only a sparse fauna. The section is:

Crinoidal limestone (3.65 m) is also present in the crags (loc. C149) north-east of Holker Farm where the fauna includes Aliteria panderi, Avonia cf. youngiana, Krotovia spinulosa and Spirifer trigonalis, and also (4.57 m) in an old quarry (loc. C151) 350 m E of Holker Farm where Chaetetes radians and Cyathaxonia cornu have been recorded. The mudstones exposed in a temporary drainage trench (loc. C150) 230 m ESE of Holker Farm yielded a poor fauna of brachiopods, including Lingula sp.and Productus sp., with the bivalves Leiopteria sp.[juv.] and Streblopteria?.

The highest beds exposed round Holker Park are in an old quarry and a cliff section [SD 3455 7690] south-west of Holker Farm, at Quarry Flat [SD 3470 7685] from where some of the stone used in the construction of Cartmel Priory is said to have come, and in a ditch (loc. C146) close to, and parallel with, the railway embankment between these two places. A little coal was obtained at Quarry Flat. A combined general section for all three localities is:

Two old boreholes near Cark have recorded a sequence of mudstones with appreciable bands of sandstone. Their correlation is most uncertain, but it seems reasonable to assume that they lie within the lower part of the Namurian. The thickest sequence is in Cark No. 2 Borehole (37 NE/2), and is illustrated in (Figure 6). The correlation of other boreholes close to the east of Cark is in even more doubt. Sandstones and shales have been encountered, but since they are highly reddened it is not practicable to distinguish them from the Permo-Triassic conglomerates of Roughholme Point, though the absence of recorded conglomerates suggests their Namurian age. NVCCR

Cartmel–Humphrey Head–Grange-over-Sands

The lower part of the sequence, striking north–south with an easterly dip of around 10°, underlies the heavily drift-covered Cartmel Valley; there are few exposures. The Basement Beds have not been proved, but 13 m of Martin Limestone are exposed beneath the Red Hill Oolite in an old quarry (loc. C21) at the north end of Fiddler Hall Wood, 1.5 km N of the district, and the formation is probably present at depth. Between Cark and Barber Green the Red Hill Oolite is faulted against Bannisdale Slates, as are locally the Dalton Beds near Cartmel (see (Figure 8)).

The only exposure of the Red Hill Oolite is close to the east of Middle Birkby (loc. C39) where pale grey bioclastic limestones and calcite mudstones underlie the Dalton Beds. There are several small exposures of the latter in narrow strike ridges around Birkby Hall (loc. C79) and Hesketh Wood. They consist chiefly of well-bedded, dark grey, commonly crinoidal limestones, but include some pale grey limestones in Hesketh Wood. The hollows between the ridges probably follow shale partings. Beds exposed in old quarries (loc. C43) at Field Broughton lie at the junction between the Red Hill Oolite and the Dalton Beds. They are thickly bedded grey and dark grey crinoidal limestones that are commonly pseudo-oolitic; extensive secondary dolomitisation follows strong joints trending at 35°. The section is:

The Dalton Beds are also exposed (loc. C81) north from Merlin's Wood, Field Broughton.

Northwards from Allithwaite to the eastern margin of Hesketh Wood the base of the Park Limestone is mostly concealed by drift, but the Park and Urswick limestones form the drift-free ground of Newton Heads, Hampsfield Fell, and Wart Barrow, north-east of Allithwaite. The outcrops are faulted against Silurian rocks between Lindale and High Newton. A good exposure of the Park Limestone occurs in a quarry [SD 3987 8298] 1 km S of Head House, High Newton, where about 19 m of massive, creamy white limestone is overlain by some 6 m of Urswick Limestone. The Park Limestone forms the lower part of the western slope of Hampsfield Fell and is exposed in Haggs Quarry [SD 3891 7812], north-west of High Fell Gate. Other exposures are small but many large blocks of pale grey limestone litter the surface. In contrast, the Urswick Limestone higher up the slope, crops out in a continuous line of crags, its base being marked, at about the 600ft contour, by the lowest of these. The beds near the junction between the two formations are best exposed at Newton Heads [SD 399 818], and in low crags and in an old quarry (loc. C103) on Wart Barrow where the section is:

The change in lithology is abrupt both here and at Newton Heads, though there is no indication of penecontemporaneous erosion nor even of a pause in deposition. The Urswick Limestone is exposed in an old quarry north of Middle Fell Gate (loc. C125) and the following section has been measured:

The western side of Humphrey Head, with its high cliffs of Urswick Limestone, marks the course of the eastern branch of the Humphrey Head Fault (p. 75); the fault-plane stained with hematite is exposed on the cliff face near Holy Well. At the foot of the cliff just south of Holy Well there is a small exposure (loc. C152) of rocks of the Gleaston Formation on the downthrow side of the fault. They consist of black cherty limestones with some white and reddish purple medium-grained sandstones and dull red and green shales. The fauna from the limestone includes Aulophyllum pachyendothecum, Diphyphyllum lateseptatum and Lithostrotion junceum. This outcrop forms part of a narrow wedge-shaped strip of the Gleaston Formation lying between the eastern branch of the Humphrey Head Fault and the western branch which brings in the Permo-Triassic brockram of Roughholme Point.

The eastern shore of Humphrey Head between Wyke House and the southern point of the promontory provides an excellent section of the highest part of the Urswick Limestone and the lower beds of the Gleaston Formation. It is best visited at low tide. It includes an extensive exposure of the Girvanella Nodular Bed, described by Garwood (1913) as the best in the north of England. The beds dip eastwards at 20°–30° and the junction between the two formations, striking parallel to the coastline, crops out approximately at HWMMT at a point 500 m S of Wyke House, Urswick Limestone occupying the low cliffs and higher part of the beach and Gleaston Formation most of the rest of the beach and foreshore. The junction is displaced by small NW–SE faults at several places, and towards the southern end of the promontory strikes across the foreshore, the whole of the section being in the Urswick Limestone. The section (loc. C127) is as follows base at [SD 3906 7469]:

The exposure of Urswick Limestone immediately south of where Pigeon Cote Lane joins the beach (loc. C126) also contains abundant specimens of Linoprotonia hemisphaerica, and may be the same horizon as bed b of the main section.

The alluvial tract between Wyke House and Kirkhead is underlain by part of the Gleaston Formation, another small exposure of which can be seen at Castle Haw [SD 3898 7571], the section being as follows:

The limestones are much stained with hematite and the exposure is adjacent to a small trial shaft for hematite sunk last century near the course of the Kirkhead Fault (see below).

The foot of the western slope of Kirkhead marks the line of the Kirkhead Fault, throwing about 80 m down west and bringing in Urswick Limestone on the upthrow side. Excellent exposures of the upper part of the Urswick Limestone (above the Davidsonina septosa Band), and the lowest beds of the Gleaston Formation, are seen also in the Kirkhead railway cutting south-west of Kents Bank Station and in the cliffs northwards from Kirkhead End. The section in the railway cutting (loc. C124) is as follows:

The dip of the beds averages 30° to the east but both sections are traversed by several faults and the Urswick Limestone is much crushed towards the south-west end of the sections as the Kirkhead Fault is approached.

The NW–SE fault through Abbot Hall, throwing down about 100 m to the south-west, shifts the Urswick Limestone/Gleaston Formation junction offshore, but the north–south strike probably brings this horizon just below HWMMT 300 m N of Kents Bank

Station for dark grey shaly limestones overlie grey pseudobreccia fed. limestones in exposures on the shore.

The summit of Hampsfield Fell and its eastern and south-eastern slopes to Lindale and Grange-over-Sands provide extensive exposures of dip-slopes of Urswick Limestone with typical grike topography. The D. septosa Band fauna has been collected from the excavation for a small reservoir (loc. C129) east of Merlewood Farm (Dibunophyllum bourtonense, P. murchisoni, Davidsonina septosa and Delepinea comoides). The general dip is eastwards at an average of about 15° in the Grange area, swinging to ENE at about the same angle west of Lindale. This ground is traversed by several dip-faults with a south-westerly downthrow, their general effect being to widen the outcrop of the formation; nevertheless in this area the thickness of the Urswick Limestone has increased from its usual 120 m farther west to about 150 m. Exposures north and south of the Bathing Pool on the shore at Grange show typical thickly bedded grey spotted and pseudobrecciated limestones, with one prominent band of white limestone. The following section (loc. C128) has been measured along the shore south of the bathing pool:

WCCR

References

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BATHURST, R. G. C. 1971. Developments in sedimentology, 12: Carbonate sediments and their diagenesis. New York. 620 pp.

BINNEY, E. W. 1868. Description of a dolerite at Gleaston in Low Furness. Mem. Lit. Philos. Soc. Manchester, Vol. 7, pp. 148–154.

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GARWOOD, E. J. 1913. The Lower Carboniferous succession in the North-West of England. Q. J. Geol. Soc. London, Vol. 68, pp. 449–586.

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Chapter 5 Permian and Triassic rocks

Introduction

There are few exposures of the Permian and Triassic rocks within the district. The earliest published reference to them is one by Sedgwick (1836), who described an outcrop of Magnesian Limestone near Holbeck together with one of brockram at Roughholme Point, and outlined the distribution of St Bees Sandstone around Barrow. Binney (1847) also described the Holbeck exposure and included an analysis of the Magnesian Limestone in his account. The occurrence of cemented breccias of rounded limestone boulders, which were frequently found resting on the Carboniferous Limestone in quarry and mine sections, and which were known locally as 'crab rock', also occasioned early interest. They were noted by Murchison and Harkness (1864), and considered by them to be the equivalent of the Lower Brockram of the Vale of Eden. This view was not upheld by W. T. Aveline and A. G. G. Cameron when, shortly afterwards, they carried out the Primary Survey of Furness, for neither did they map the crab rock as Permian nor did Aveline mention it in the short memoir on Old Series Sheet 91NW (1873). At about this time J. D. Kendall (1875) suggested that the crab rock was cemented boulder drift of glacial origin, and the resurvey has supported this interpretation.

Deep boreholes drilled since these early writings added substantially to the knowledge of the local sequence. Their results have been summarised by Dunham and Rose (1949). Few of these holes were, however, examined by geologists, and the cores of even these few had commonly been disarranged before examination. Two recent boreholes—one near Sowerby Wood, the other the Institute borehole at Roosecote—have provided modern sections through the succession, and their results have led to minor changes in the correlation and interpretation of certain of the older sections.

There are not sufficient boreholes to enable a reliable reconstruction of the pre-Permian land surface to be made. It was probably an uneven pediment with low ridges and hollows scattered across it. Initially deposition was restricted to accumulations of breccia in the hollows, and possibly of an extremely thin lag breccia more generally over the surface; the Lower Permian sands so widespread over much of northern England are not present. Very probably the pediment ended northwards against steeply rising ground a little south of the present margins of the Fells, as happens along the margins of modern arid basins such as those of western North America. The pediment was cut across a variety of rocks. West of Millom this surface probably extended on to Lower Palaeozoic outcrops; between here and Haverigg Haws it cut across almost the entire Dinantian sequence; and at Roosecote it lay on beds some 450 m above the base of the Namurian. The rocks beneath it were commonly reddened, the Lower Permian date of this reddening being established in those areas where the reddened zone is overlain by Upper Permian strata still in a reduced condition.

This breccia-strewn pediment was briefly submerged by the advancing Upper Permian sea and a thin sequence of dark mudstones and siltstones—the Grey Beds (Smith, 1924)—was laid down. Thin dolomitic bands lie within the Grey Beds, and a marginal dolomite, the Magnesian Limestone of this district, overlies them. The environment soon became more saline and the overlying St Bees Shales comprise a red mudstone and siltstone sequence with substantial beds of anhydrite towards the base, much of which appears to have formed in a playa lake or on the surrounding sabkha surface marginal to it. Towards the uplands, fans of brockram become increasingly common, particularly in the upper part of the St Bees Shale and locally appear to replace the bulk of it. It has proved impractical to subdivide the sequence into St Bees Evaporites and St Bees Shales as has been proposed at Whitehaven (Arthurton and Hemingway, 1972), and the latter term is used in its original sense (Smith, 1924).

There is a gradual upward transition into the St Bees Sandstone, a unit of red sandstones up to 750 m thick, that is probably largely fluviatile in origin. Its base is probably diachronous but it has arbitrarily been taken as the base of the Triassic System in this area since it forms the only practicable mapping line in the relevant part of the sequence.

In the west of the area the St Bees Sandstone is succeeded by a sequence of dominantly red mudstones containing thick beds of rock-salt. At their base lies a thin unit of grey mudstones, reminiscent of the Grey Beds at the base of the Zechstein but without their undoubted marine fauna. The bulk of the overlying mudstones, like the St Bees Shales, seems to have formed on a sabkha surface ephemerally flooded to a shallow depth, and many of the salt beds are a product of this same environment.

The sequence clearly equates with the British 'Keuper Series'. The strata are, however, almost certainly wholly of Scythian and Anisian–Ladinian age and equivalent to the Upper Bunter and Muschelkalk of European sequences. There is thus considerable confusion because of the different use of the same terminology to denote both lithological groups and chronostratigraphic series. A working party of the Geological Society of London will shortly recommend changes of nomenclature to clear up this confusion, and their major proposals have been communicated verbally to that Society (J. Geol. Soc. London, Vol. 129, p. 653). They involve the introduction of two new terms, the Sherwood Sandstone Group and the Mercia Mudstone Group, to cover respectively the dominantly arena ceous strata previously referred in Britain to the Bunter and the lower part of the Keuper Series, and the dominantly argillaceous strata formerly assigned to the higher part of the Keuper Series. We have accepted this proposal and nomenclature in the following account and its application is illustrated in (Figure 10) and (Figure 11)." data-name="images/P988094.jpg">(Figure 9). Sections of individual provings of the Permian strata and of the Mercia Mudstones appear respectively in (Figure 10) and (Figure 11).

General stratigraphy

The Basal Breccia is the lowest member in the sequence. Its maximum recorded thickness is 26 m at Haverigg Haws (SD17NW/2), though generally it is much thinner and locally absent.

Above it lies a distinctive unit of 10 to 20 m of grey mudstones and siltstones that have been called the Grey Beds at Kirksanton (Dunham and Rose, 1949). Where the Basal Breccia is absent the Grey Beds rest directly on reddened Carboniferous rocks and, in the absence of positive evidence, the base of the Permian has been taken at this colour change in some of the older sections. The Grey Beds seem strictly comparable with the Saltom Siltstone (Arthurton and Hemingway, 1972), which like them contains fragmentary plant remains. Thin impersistent limestones are known from the unit, but the record of a substantial Permian dolomite beneath it (Smith, 1924) is now in doubt. In the extreme south there is some evidence that the sediment grade becomes coarser and muddy sandstones replace the finer-grained rocks.

Around Holbeck, the Grey Beds are succeeded by the Magnesian Limestone, which is some 20 m thick at outcrop nearby and in boreholes north-eastwards towards Gleaston. The dolomite thins rapidly away from this area. At the Roosecote Borehole (SD26NW/19), barely 1 km to the SSW it has thinned to 4 m and was not recorded in the Rampside and Davy Street holes (SD26NW/31); (SD26NW/10) still farther south and west. In a similar fashion it is present, though only some 3 to 6 m thick, in holes near Kirksanton, but is not recorded at Haverigg Haws about 1.2 km to the south. This distribution suggests strongly that the dolomite formed around the margin of the Zechstein Sea, for it would be unreasonable to assume that it has been eroded in all the off-shore provings but preserved at its landward extremities. It contains a typical Permian fauna. Bakevellia (Bakevellia) binneyi (Brown), Permophorus costatus (Brown), Pseudomonotis speluncaria (Schlotheim), Schizodus obscurus (J.Sowerby), cf. Cyclobathmus? permianus (King) and cf. Naticopsis sp.have been recorded at Kirksanton, and Bakevellia (Bakevellia) binneyi, Schizodus obscurus, foraminifera and gastropods from Roosecote. The overall assemblage suggests a Zechstein 1, or less probably a Zechstein 2, age (Pattison, 1970).

Above the Magnesian Limestone lies a variable sequence of red mudstones, thin limestones and sandstones, and beds of anhydrite, which has been termed the St Bees Shales. It varies from some 80 to 215 m thick across most of the area. South-westwards from Gleaston the basal member is a bed of anhydrite, which ranges between 5 and almost 40 m in thickness, swelling out south-westwards as the Magnesian Limestone thins. West of the Duddon the same change takes place, for at Haverigg Haws a 15-m anhydrite takes the places occupied in the Kirksanton sequence by the Magnesian Limestone. Above this anhydrite red gypsiferous mudstones dominate. At Roosecote (SD26NW/19) another thin dolomite with a few Bakevellia represents a second marine transgression, possibly to be equated with Zechstein 2, at the base of these red mudstones. Like the main Magnesian Limestone below, it is succeeded by a bed of anhydrite. Local bands rich in anhydrite occur well above this horizon, notably some 100 m above the base of the St Bees Shales at Davy Street, and about 70 m and again at 95 to 125 m at Haverigg Haws. Thin beds of sandstone, and at Kirksanton of limestone, lie within the mudstones. Northwards towards the high ground of the Lake District lenticular breccias and conglomerates (brockram) appear, though some of these may be nodular cornstones. At Haverigg Haws these conglomerates are interdigitated with mudstones throughout much of the top 100 m of the formation, while at Kirksanton a 'conglomeratic' unit seems to occupy much of the upper part of the St Bees Shales.

In contrast to this normal succession, the Grey Beds, the Magnesian Limestone, and much of the St Bees Shales appear to be absent in a general area stretching westwards from Dalton-in-Furness to the sea. Here numerous boreholes prove a sequence of alternating red gypsiferous mudtones, limestone 'conglomerates', and thin sandstones and breccias, averaging 60 m thick and separating the St Bees Sandstone above from the Dinantian rocks below. Reddening of the Carboniferous strata beneath the unconformity, coupled with faulting and the local presence of sandstones directly beneath the unconformity, make the sequence difficult to decipher in the older boreholes. Indeed it was formerly thought that the Magnesian Limestone was present in several of these holes (e.g. De Rance, 1899), but a recent borehole makes it practically certain that the bed so correlated is a reddened and dolomitised limestone high in D₂ (see below). Northwards the sops at Roanhead and Park have central cores composed of broken masses of red sandstone with no visible brockram and very little red shale. This strongly suggests that the whole of the underlying Permian sequence has here been overstepped by the St Bees Sandstone. It is difficult to understand why the Grey Beds, so uniform in their development over much of northern England, should fail in this restricted area, and it is at least possible that local intra-Permian erosion is responsible for their absence.

There is a transitional upward passage from the St Bees Shale, both in its normal and its conglomeratic facies, into the St Bees Sandstone. The junction is probably diachronic, though the absence of faunal control makes this difficult to establish with certainty.

The Sherwood Sandstone Group, here comprising the St Bees Sandstone, is preserved as a narrow strip along the West Cumbrian coast south of St Bees Head, and the southeastern extremity of this belt enters the area near Haverigg. Otherwise the formation is confined to the extreme south of the area, around Barrow. Surface exposures are restricted to the sides of the glacial drainage channel in which Furness Abbey stands and to a small area around Hawcoat, but boreholes at Barrow starting within the sandstone have proved it to a thickness of 667 m. The bulk of the sequence is composed of well-bedded, but not markedly cross-bedded, red sandstones with regular, but extremely thin, intercalations of red mudstone. The environment of deposition was probably an alluvial plain, liable to regular sheet flooding and crossed by shifting stream courses. The top of the sandstone has been encountered in a few boreholes and is variously described as red or grey. In one borehole the grey sandstone contained hydrocarbon traces, and it seems likely that the grey colour is due to secondary reduction caused by local accumulations of hydrocarbons. Microscopic examination shows that the quartz grains within the sandstone are mostly sharp and angular. There is little feldspar present, but cloudy orthoclase and plagioclase, commonly andesine, have been noted. Rounded plates of white mica, some of chlorite, and a biotite-like mica occur. Heavy concentrates show that zircon, tourmaline, rutile, anatase, leucoxene and ilmenite are ubiquitous. Apatite and dolomite are only locally relatively abundant, and the 'metamorphic' minerals are remarkably rare. The cement is in some cases ferruginous, probably limonitic, and more rarely siliceous. Some secondary overgrowth of quartz has turned initially rounded grains into angular ones.

The Mercia Mudstone Group is restricted to Walney Island and to a narrow coastal strip at Barrow. There are no surface exposures, and the borehole records are so few, and, for the most part, so old, that the sequence, particularly in the north of the Island, is still in doubt. Some 550 m of strata are preserved. The basal member is a grey mudstone or sandy mudstone some 15 to 20 m thick, that equates with the recently named Hambleton Mudstones (Evans and Wilson, 1975) on the southern side of Morecambe Bay. Above it there is a sequence of 300 to 400 m of mudstones, red in their lower part (Singleton Mudstones) and alternately red and green above (Kirkham Mudstones), that also matches well with the succession on the Fylde coast. Thin salt beds have been proved within these mudstones, but details are scanty. The highest strata present appear to be a 100 m salt formation proved near Biggar, where it gave rise to a small industry, and 50 m or so of overlying red mudstone, likely by analogy with Cheshire (Taylor and others, 1963) to be collapsed strata above a wet rock-head. There seems little doubt that the salt equates with the Preesall Salt across Morecambe Bay. The correlation of a salt formation proved in a single borehole at Lenny Hill in the north of the Island remains uncertain. It has been assumed to be the Preesall Salt (Evans, 1970), but it remains possible that it is at a lower stratigraphic horizon (Dunham and Rose, 1.949). By analogy with Preesall—and the comparison in the south of the Island is a close one—the lower part of the Mercia Mudstone Group is probably of Scythian age, and the Scythian/Anisian boundary lies high in the mudstones beneath the Preesall Salt. The highest strata present may range upwards into the Ladinian. WBE, KCD

Details of stratigraphy

The detailed succession in the more important provings are given in Appendix 1, and many other logs may be consulted in the Institute's records at Leeds. The following comments are restricted, for the most part, to explanations of the decisions implicit in the mapped positions of the formational boundaries.

Kirksanton

Although Kirksanton lies outside the district here considered, the sequence is pertinent to the other localities. It has been summarised in (Figure 10). Previous accounts have recorded a thick 'Magnesian Limestone' beneath the Grey Beds—a situation that would be unique in north-western England—and anomalously thick provings of 'Permo-Triassic' shales and conglomerates, variously ascribed to banks built up at the foot of a buried cliff or to collapses into swallow holes. The anomalies lie in a belt where the sub-Permian and sub-Carboniferous unconformities converge, and the boreholes in question can be more satisfactorily interpreted as having entered reddened and dolomitised Carboniferous limestones resting on red shales and conglomerates that lie at the local base of the Dinantian sequence. The only possible evidence of a Permian age for these strata is a Permian fauna recorded (Dunham and Rose, 1949) from Kirksanton No. 6 Borehole (SD19SW/5). None of the fossil-bearing specimens in question is depth-labelled, presumably because the cores had been disturbed prior to examination. However, the fauna is preserved in dark grey limestone and, since the only grey limestones recorded in the log lie above the Grey Beds, it is concluded that the specimens came from above, not below, this latter unit. Specimens of red and yellow dolomitised limestones agreeing with the descriptions of the limestones below the Grey Beds are unfossiliferous. Apart from this modification the published account (Dunham and Rose, op. cit.) summarises the available data. WBE

Sowerby Wood–Barrow

The difficulty in identifying the base of the Permo-Triassic in the holes between Sowerby Wood and the Yarlside Fault has already been discussed (p. 44). In the west, at Sandscale No. 17 Borehole (SD17SE/22) 27.4 m of St Bees Sandstone are underlain by 4.9 m of conglomerate, presumably a basal breccia, which rests directly on Dinantian strata and, farther east, Thwaite Flat No. 4 Pit [SD 2109 7425] has proved 18 m of breccia, probably in the same position. In this same general area, Sowerby Wood No. 3 (SD27SW/466) and Bouth Wood No.2 (SD27SW/532) boreholes both record some 20 m of limestone conglomerates low in the sequence. If these represent the basal breccia then underlying red mudstones with gypsum bands probably lie near the Dinantian–Namurian boundary; alternatively they represent part of the St Bees Shales.

The Davy Street Borehole about 5 km to the south at Barrow has proved a full Permian sequence, as have those at Gleaston and Rampside (see (Figure 10)). In both latter holes the base of the Permian has been taken at a downward colour change from grey to red, thus involving minor readjustments of its position from those given in previous accounts of the holes.

The St Bees Sandstone is exposed immediately south of Goldmire, and a trial level driven south from the floor of Goldmire Quarry entered it after passing through the Sandscale Fault. There are good exposures on both sides of the glacial drainage channel followed past Millwood by Goldmire Brook, and these continue at intervals along the Vale of Nightshade to Furness Abbey. West and south of the Abbey there are disused quarries, which are said to have been the source of the stone of which Furness Abbey is built. East of the Abbey several of the Yarlside shafts were sunk through the St Bees Sandstone on the west (hanging wall) side of the Yarlside Fault, and the sandstone, somewhat softened by circulating ground-water, was formerly dug for moulding sand in workings from No. 3 (New) Pit [SD 2264 7135] and from levels driven into the fault zone from near Park House [SD 224 711]. The beds were mainly slightly loamy laminated red sandstone with subordinate beds of yellow, grey and red loam. An analysis is quoted by Dunham and Rose (1949).

The sandstone is probably near the surface beneath much of the high ground south of Sowerby Wood and west of the Vale of Nightshade. It has been worked for building stone at Hawcoat Quarry [SD 199 716], and most of the older buildings in Barrow are built from stone from this site (see (Plate 5.2)). About 50 m of sandstone are exposed. The sandstone is flaggy for about 3 m below the top of the quarry face, but otherwise it forms massive beds, varying somewhat in their shade of red. Conspicuous micaceous layers occur in places, and thin beds of white sandstone recur at intervals of 3 to 5 m.

Numerous borings at Barrow have proved the sandstone beneath drift. There is, however, only one further exposure intermittently visible at low tide at the base of the cliffs north of Rampside. KCD, WBE

Walney Island

Details of the major provings are indicated in (Figure 11) and other logs appear in Appendix 1. Rather different interpretations of some of the sequences have previously appeared (Dunham and Rose, 1949; Evans, 1970) and it is still not possible to correlate the strata in all the holes. Southwards from Biggar, however, the succession is now well established and compares so well with that recently proved by the Institute near Fleetwood on the southern side of Morecambe Bay that it is feasible to employ the same nomenclature that has recently been introduced there (Evans and Wilson, 1975). This nomenclature is summarised in (Figure 10) and (Figure 11)." data-name="images/P988094.jpg">(Figure 9).

The St Bees Sandstone has been entered in Walney No. 1 Borehole (SD26SW/1), where its topmost 124 m was grey. The full sequence of the overlying Mercia Mudstones has not been drilled through in any one hole, but can be obtained by combining the records of a group of holes at Biggar (see Appendix 1) with that of the recent British Gypsum No. 1 Borehole (SD16NE/12), the log of which appears in Appendix 1 by kind permission of British Gypsum Limited. The distinctive grey unit of the Hambleton Mudstones is at least 12 m thick at Walney No.1, and the standard of the logging is such that it could be up to 37 m thick: British Gypsum No. 1 was terminated after penetrating 10 m of the formation. The overlying Singleton Mudstones are some 150 to 180 m thick, and dominantly red mudstones. In Walney No. 1, bands of rotten marl suggested the presence of penecontemporaneous solution breccias in the general position of the Rossall salts and the Mythop salts of the Blackpool area (Evans and Wilson, op. cit.), and British Gypsum No. 1 recorded beds of rock-salt, both in the position of the latter–where they were mostly of haselgebirge type–and at several lower horizons, the lowest of which probably equates with the salt horizons at Rossall. The lower salts in Walney No. 2 (SD16NE/7) are also probably equivalents of the Mythop salts. The Singleton Mudstones are overlain by about 100 m of alternations of red and green mudstone which correlate well with the lower part of the Kirkham Mudstones of Blackpool. Towards the middle of the unit there are a few thin beds of salt, and a 4.58 m bed of 'shale with rock-salt' lying 270.96 m above the top of the St Bees Sandstone in Walney No. 1 probably correlates with this horizon rather than with the main Walney salt as formerly tentatively suggested (Dunham and Rose; Evans, op. cit.).

In British Gypsum No. 1 the colour-banded Kirkham Mudstones are overlain by a thick breccia, representing the solution breccia of a major salt formation. The salt is preserved around Biggar, where it is at least 100 m thick, and seems certain to represent the Preesall Salt of Blackpool. It has a wet rock-head throughout the area, and its full thickness is thus nowhere proved. Brine from its wet rock-head was formerly pumped at a group of holes near Biggar, and piped to a salt plant at the south of the Island, but the industry is long since defunct. At first sight the occurrence of salt near to an established port appears to offer a favourable site for production, and the presence of thick salt deposits at tide-water might allow the production of solution cavities for underground storage without raising the problems of brine disposal that occur in inland sites away from chemical plants. Unfortunately the salt-field is small—less than 5 km² on land—and the wet rock-head conditions make controlled solution-mining impracticable. Salt production would therefore have to be by brining, with a concomitant risk of surface subsidence that might prove unacceptable in such a low-lying area, or by conventional mining of the lower beds of salt, an undertaking that would be expensive with such a small available take.

The highest beds in the local sequence are some 40 m of collapsed red and green mudstones, and represent the higher part of the Kirkham Mudstones. By analogy with the Blackpool area the strata up to about the base of the Kirkham Mudstones are of Scythian age, and so would be regarded as 'Bunter' in Germany; the remainder are mostly Anisian but may range up into the Ladinian, both stages being represented in Germany by the Muschelkalk.

In this southern part of the Island the mapped lines, while conjectural, are based on a number of provings. North of Biggar the situation is more speculative. Walney No. 5 Borehole (SD17SE/2) proves a thick sequence of salts and saliferous mudstones that, while it does not match in detail the provings around Biggar, is much thicker than any of the salts as yet proved in the Singleton Mudstones. For this reason it is considered to represent the Preesall Salt, though further exploration could revise this conclusion. At Walney No.6 Borehole (SD17SE/57), in the extreme north of the Island, the sequence is anomalous. A unit of 105 m of red shaly sandstone apparently lying towards the base of the Mercia Mudstones is unmatched in any other proving of these strata in the region and, accordingly, the accuracy of the record is somewhat suspect. Beneath the shaly sandstone 63 m of marls are recorded, and beneath these 8 m of bluish grey shale that rest directly on the main mass of the St Bees Sandstone and may represent the Hambleton Mudstones. This correlation has been tentatively adopted as being the most reasonable one presently possible.

Because the structural interpretation adopted in this area depends very largely on the correctness of the correlations adopted, many uncertainties remain. The interpretation adopted on the map implies the existence of an elongate syncline trending NNW–SSE beneath Walney Channel. The western limb of this syncline seems to be well established west of Biggar, but the extension of the fold into the northern half of the Island depends on the correctness of the correlation of No. 5 Borehole. The eastern limb is wholly conjectural. The postulated fold, though tectonically unique in South Cumbria, is very similar to the Preesall Syncline (Evans and Wilson, op. cit.), and could represent either an extension of this fold, or an en-echelon replacement of it. The Walney Fault, or a branch of it, must lie between Walney No. 5 Borehole, and Barrow Haematite No. 2 Borehole (SD17SE/52) on the mainland close to the east, where the Hambleton Mudstones, some 14 m thick, lie at shallow depth. Its southward extension is less certain and it may replace the postulated eastern limb of the fold.

Gleaston–Rampside

The only recorded exposure of Permian and Triassic rocks in this area is the one near Old Holbeck [SD 2342 6967]. At present barely 1 m of yellow cellular dolomite can be seen but formerly 19 m of thickly bedded compact dolomite were noted, with lines of cellular structures running parallel to the bedding. The Magnesian Limestone rests on black shales with plant debris, once considered to be Carboniferous in age. By analogy with the Roosecote section these shales are now assigned to the Permian.

Boreholes between Gleaston and Leece have entered the St Bees Sandstone, and Gleaston No. 4 Borehole (SD27SE/33) has provided a good section through the Permian strata (see (Figure 10)). It establishes the presence of the Grey Beds and the Magnesian Limestone, though this latter has thinned to 19.8 m. Immediately above it 10 m of 'jasper' are recorded, and this bed is assumed to represent the anhydrite that has been proved at Rampside, and consequently is likely to underlie some 10 km², with a comparatively small cover east of the Yarlside Fault. There is a marked thinning of the overlying St Bees Shales, which may be in part accounted for by diachronism of the base of the St Bees Sandstone.

The Institute's Roosecote Borehole (SD26NW/19) provides a modern section through the lower part of the St Bees Shales. It is particularly valuable in demonstrating the presence of the Grey Beds in this area and the existence of two closely associated anhydrite horizons. A full account of the stratigraphy of the hole is to be published separately: meanwhile the log is given on p. 134.

It has been generally assumed that a steady south-easterly dip continues from Holbeck to the shores of Morecambe Bay. Recently, however, Moss Side Borehole 1A (SD26NE/2), although an uncored hole, obtained chippings of red marl directly beneath drift some 1.5 km SSE of Leece. These appear to be of St Bees Shales. As a result of this proving the Applied Geophysics Unit of the Institute conducted a seismic refraction survey along the line of Sarah Beck, draining south-eastwards from Old Holbeck to the coast, the work being carried out by Mr E. M. Andrews and Mr R. M. Carruthers in August 1973. The results of the survey were ambiguous, but suggested the presence of a synclinal axis lying north of the Moss Side Borehole. This interpretation has been adopted in constructing the map, and it is assumed that the fold results from post-Triassic movement along the approximate position of the Urswick Syncline. As a further result of this proving it is thought likely that the Yarlside Fault lies to the east of the Rampside Borehole rather than to its west as was formerly believed. Information beneath this heavily drift-covered area is, however, far too scanty for even the present interpretation to be put forward with confidence, and modification of the map may well prove necessary should any further drilling take place.

Humphrey Head

To the west of the head there is a low cliff of Permo-Triassic breccia, showing strong southerly-directed cross-bedding (Plate 5.1). The Humphrey Head Borehole (SD37SE/1) was put down by the Institute in 1973 to determine its thickness. The log of the hole, produced by Dr N. Aitkenhead, is given in Appendix 1. The 257 m of Permo-Triassic conglomerates and sandstones contained a few very thin bands of fibrous gypsum and some loose aggregates of crystalline gypsum and anhydrite, and rested on Carboniferous sandstones and mudstones. At shallow depths the pebbles were almost all limestones, but olivine-dolerites and vesicular basalts appeared at 26 m and formed 95 per cent of the clasts below 157 m. They may well come from a suite that includes the 'greenstones' encountered within the Namurian sequence at Gleaston and Rampside.

It is not possible to date the conglomerates other than to assign them to the Permo-Triassic. Some 5 km to the south Dr Warrington (personal communication 1974) has identified a late Scythian to early Anisian micro-floral assemblage in red shales drilled into by an offshore borehole [SD 3894 6917] sunk in connection with the proposed Morecambe Bay Barrage. This suggests that the Mercia Mudstones extend well up the Bay, and makes it likely that the conglomerates at Roughholme Point lie high in the Permo-Triassic sequence rather than at the base of the Permian. W B E

References

ARTHURTON, R. S. and HEMINGWAY, J. E. 1972. The St Bees Evaporites–a carbonate-evaporite formation of Upper Permian age in West Cumberland, England. Proc. Yorkshire Geol. Soc., Vol. 38, pp. 565–589.

AVELINE, W. T. 1873. The geology of the southern part of the Furness district in north Lancashire. Mem. Geol. Surv. G.B. 13 pp.

BINNEY, E. W. 1847. A glance at the geology of Low Furness, Lancashire. Mem. Lit. Philos. Soc. Manchester, 2nd Ser., Vol. 8, pp. 423–445.

DE RANCE, C. E. 1899. The occurrence of anhydrite in the north of England. Trans. Inst. Min. Eng., Vol. 17, pp. 75–84.

DUNHAM, K. C. and ROSE, W. C. C. 1949. Permo-Triassic geology of South Cumberland and Furness. Proc. Geol. Assoc., Vol. 60, pp. 11–37.

EVANS, W. B. 1970. The Triassic salt deposits of north-western England. Q. J. Geol. Soc. London, Vol. 126, pp. 103–122.

EVANS, W. B.  and WILSON, A. A. 1975. Outline of Geology on Sheet 66 (Blackpool) of 1: 50,000 Series: Geol. Surv. G.B.

KENDALL, J. D. 1875. The haematite deposits of Whitehaven and Furness. Trans. Manchester Geol. Soc., Vol. 13, pp. 231–283.

MURCHISON, R. I. and HARKNESS, R. 1864. On the Permian rocks of the north-west of England and their extension into Scotland. Q. J. Geol. Soc. London, Vol. 20, pp. 144–165.

PATTISON, J. 1970. A review of the marine fossils from the upper Permian rocks of Northern Ireland and north-west England. Bull. Geol. Surv. G.B., No. 32, pp. 123–163.

SEDGWICK, A. 1836. On the New Red Sandstone Series in the basin of the Eden and north-western coasts of Cumberland and Lancashire. Trans. Geol. Soc. London, 2nd Ser., Vol. 4, pp. 383–407.

SMITH, B. 1924. On the West Cumberland brockram and its associated rocks. Geol. Mag., Vol. 61, pp. 289–308.

TAYLOR, B. J., PRICE, R. H. and TROTTER, F. M. 1963. Geology of the country around Stockport and Knutsford. Mem. Geol. Surv. G.B.

Chapter 6 Structure

Introduction

South Cumbria has had a complex geological history. Generally this reflects that of the Lake District area as a whole; it is a history of repeated periods of intense earth movements separated by long ages during which profound erosion was followed by the accumulation of thick sequences of sedimentary rocks resting with marked unconformity on the older rocks below. Little evidence is available in the small area under description about possible movements of early Ordovician age, but three later tectonic periods are well substantiated, both by structures affecting the different rock groups and by profound unconformities between them; the three periods may be related to the Taconic (post-Llanvirn–pre-Bala), Caledonian (end Silurian), Armorican (late Carboniferous–early Permian). There is also abundant evidence of movements of post-Triassic age but in the absence of Jurassic, Cretaceous and Tertiary rocks in the area their precise dating is not practicable. Some of these movements may have been initiated during the Kimmerian ( Jurassic) period of movement which has recently been clearly demonstrated by studies of the submarine geology of north-west Europe and they may have been reactivated during the Alpine (late Cretaceous–Tertiary) orogeny; others may be either of Kimmerian or of Alpine age.

The first period (Taconic) closely followed the cessation of Borrowdale vulcanicity. It involved folding and possibly also faulting; in the ground bordering the Duddon Estuary this structural event and the period of erosion that followed are clearly marked by a pronounced unconformity beneath the Ashgillian rocks.

The second episode affected the whole of the Lake District and much of Britain, giving rise to major folding, faulting, igneous intrusion and cleavage. In the present area the Lower Palaeozoic rocks bear full testimony to these movements, although only minor igneous intrusions associated with them are known (p. 22). The effects of the Caledonian movements, particularly the nature of the subsidiary folding and the extent of the erosion which succeeded them, are highlighted by the angular unconformity at the base of the Lower Carboniferous rocks, which is the most prominent geological feature of the area. The structural style of the Lower Palaeozoic rocks beneath this unconformity is in sharp contrast with that of the newer rocks above.

The third period of major earth movements occurred at the close of Carboniferous time. South Cumbria was not, at this period, in the main track of an orogeny, but uplift was accompanied by faulting on a substantial scale and by gentle folding. The Armorican movements are marked by the unconformity beneath the Permo-Triassic rocks. The structures are nevertheless not always easy to separate from those resulting from the post-Triassic movements. For example, a late significant phase in the structural history of the area was the development of a swarm of major and minor faults, mainly of north-west or north trend. It is unclear how many of these originated in the Armorican movements and how many are of post-Triassic date. The distribution of the more important of these is indicated on (Figure 12); some are certainly post-Triassic and most of them played a significant part in the emplacement of the hematite deposits.

Although most of the folds and the main faults recorded in the area can be assigned with confidence to one of the episodes of movement described above, this is not always possible. Exposures are poor especially in the lower ground where the solid rocks are masked by thick drift deposits, and borehole information, though plentiful, is rarely informative in this respect. Moreover, in some cases repeated movement undoubtedly occurred along the same structural lines. Nevertheless, within the limitations of the data, three broad general conclusions emerge. The first is that most of the observed structures in the Lower Palaeozoic rocks are either of pre-Bala or end-Silurian age, predominantly the latter. The second is that after the Caledonian movements the Lake District massif, now containing a large granite batholith (Bott, 1974), acted as a relatively rigid block. The margins of the block were eventually deeply fractured by faults of Armorican and later age, but in general those that reach the present outcrop of the older rocks die out within a short distance after entering them. Any imprint of Carboniferous or later folding on the older rocks, if it exists, has not been recognised in the present area. The south or southwest tilt due to the doming of the Lake District in Tertiary times (Moseley, 1972), perhaps resulting from its low-density granitic core, cannot be separated from stronger elements of dip imparted by more local movements. The third conclusion is more tentative. All the major faults and most of the minor ones (except a few in the Roanhead area—see p. 73) which affect the Carboniferous and Permo-Triassic rocks throw down to the south-west and west and, taken in conjunction with other evidence, this suggests a foundering of the Lower Palaeozoic basement towards the Irish Sea and Morecambe Bay. This started in Carboniferous times and continued intermittently until late in the Tertiary period. It could be argued that the effect is consistent with the tensional situation arising from the opening of the Atlantic.

The following description of the structure concentrates chiefly on the exposed basement, the iron-ore field, and the Permo-Triassic cover. The first part concerns the structures that affect the Lower Palaeozoic rocks, the second those influencing the Carboniferous and later rocks. Since they form the framework for the hematite mineralisation, the second group of structures are described more fully. The structure of the Duddon Estuary, perhaps to be regarded as an area worthy of exploration for hematite, is discussed separately.

Structures of the Lower Palaeozoic basement

Possible early Ordovician movements

The soft mudstones of the Skiddaw Group, occupying the core of the Stewnor Anticline (see below), are tightly folded and cleaved, and appear to have a different structural style from the later Ordovician and Silurian rocks. The chief exposures, however, are close to the intrusive volcanic rocks of Greenscoe and Ireleth where the rocks are much crushed and disturbed. For this reason such structural evidence as they provide is suspect.

Indirect evidence relating to an early-Ordovician orogeny is meagre and inconclusive. The volcanic necks intruding the Skiddaw Group are of 'Borrowdale' age (p. 6); they lie close to the crest of the Stewnor Anticline (Figure 13), which might point to the early presence of a line of weakness along the axis of this end-Silurian fold. Another volcanic neck is similarly situated along the line of another end-Silurian fold at Bank House [SD 233 812] near Soutergate, just north of the district. Perhaps more significantly, a poor cleavage predating the strong end-Silurian cleavage, is present locally in the Skiddaw Group mudstone; it usually appears to be roughly parallel to the main cleavage but dips at a steeper angle. Its precise dating, however, is uncertain. Direct evidence of a pre-Borrowdale cleavage event comes from slate clasts in a tuffaceous breccia (E38066) exposed in the Greenscoe neck. Mr R. K. Harrison reports that the slate exhibits a second cleavage (across the principal one) which predates incorporation in the breccia. Nevertheless the clasts are not necessarily from the Skiddaw Group; they could be much older and brought up from depth by volcanic activity.

Mid-Ordovician (pre-Bala) movements

The end of Borrowdale volcanicity in the Lake District region was followed by folding and uplift, and then by a period of profound erosion. It has been shown that the younger Ordovician sediments that resulted from the subsequent marine transgression in Caradocian and Ashgillian times rest with marked unconformity on the rocks below (Aveline and Hughes, 1872; Smith, 1924a; Mitchell, 1956a,b). The degree of unconformity increases southwestwards from Coniston to Duddon Bridge, cutting out successively older formations of the Borrowdale Group (Mitchell, 1956a), and also southwards towards the present district where Ashgillian rocks rest on Skiddaw mudstones along the east side of the Duddon Estuary. Unfortunately the few exposures of contacts between these two groups which are found near Greenscoe (Figure 1) are disturbed by faulting and elsewhere the junction is obscured by drift, so that there is no direct evidence of the position or trend of pre-Bala folding; it is possible that some of the folding in the Skiddaw Group mudstone may be of this age. It is quite clear, however, that a pre-Bala uplift of considerable dimensions must have occurred in the Soutergate–Greenscoe area and that, during the period of erosion that followed, the whole of the Borrowdale volcanic sequence which presumably once existed was removed, exposing the volcanic necks in the Skiddaw mudstones, before Ashgillian rocks were deposited. West of the Duddon a thick volcanic sequence is preserved beneath the unconformity immediately north of Millom; the overstep of the Borrowdale Volcanic Group by the Ashgillian rocks must therefore have taken place beneath and towards the eastern side of the estuary where the uplift occurred. This is discussed further on page 71.

End-Silurian movements

This is the main structural episode that affects the Ordovician and Silurian rocks. In a broad sense the entire district lies on the southern limb of the Skiddaw Anticline, which is the main structural feature caused by these movements, so that the regional dips are mostly steeply to the south-east. In detail, however, this relatively simple structure is complicated by strong subsidiary folding and faulting in the western part of Furness and around the Duddon Estuary, by other smaller folds north-west of Ulverston and round the northern part of the Leven Estuary, and by belts of minor folding in the Bannisdale Slates of the Cartmel Peninsula. Almost without exception the trend of the fold axes is between NE and ENE, and many of the faults have a similar trend.

The movements also gave rise to a strong regional cleavage which becomes locally intense in the Duddon area where even the coarse agglomerates of the Greenscoe vents are strongly cleaved. Over the whole area most of the Ordovician and Silurian mudstones and some of the siltstones are cleaved; some of the more competent rocks (e.g. greywackes) are commonly roughly jointed or sheared parallel to the cleavage. The cleavage post-dates all the folding mentioned in the last paragraph, and is clearly the final significant structural feature of the movements.

(a) Folding

Subsidiary folding occurs in the region of Askam where a sharp anticline (Stewnor Anticline) with a core of Skiddaw mudstones, and a syncline (Rebecca Syncline) are responsible for the prominent zig-zag outcrop of the Ashgill and Stockdale shales. A parallel anticline, again with a core of Skiddaw mudstones, runs through Soutergate, just north of the district. These folds all trend approximately north-east and initially plunged gently in that direction. The apparent reversal of plunge of the Stewnor Anticline south-west of Greenscoe is due to post-Carboniferous movement. The traces of the axes of the Stewnor and Rebecca folds are well defined around the places from which they take their names and can readily be followed north-eastwards towards Osmotherley beyond the border of the district. To the south-west, however, that of the Stewnor Anticline is uncertain owing to lack of exposures, and the Rebecca Syncline runs into the faulted margin of the Ireleth volcanic neck beyond which it is not recorded. It seems possible that the Stewnor and Soutergate anticlines were intensified by the buckling of the Skiddaw mudstones and their post-Borrowdale cover near the volcanic necks, for these lie along the anticlinal axes. Much of the tight folding in the soft Skiddaw mudstone cores of the anticlines probably formed along with the major folds. The structure of the Stewnor Anticline and Rebecca Syncline is indicated in (Figure 2); it is further complicated by faulting (see below).

Several sharp but much smaller north-easterly trending open folds can be seen in Silurian rocks in Rathmoss Beck [SD 256 793], around Hasty Gill [SD 271 797] and Gameswell Hill [SD 274 795], in the latter two cases accompanied by faulting of similar trend. Sharp reversals of dip from south-east to north-west indicate local folding in the Bannisdale Slates near Tridley Point [SD 318 787], Old Hough Wood [SD 320 803] and Roudsea Wood [SD 327 825], but the extent of the folding and the exact position of the axes are not certain. On a still smaller scale belts of strong minor folding occur throughout the two main outcrops of the Bannisdale Slates in Cartmel; the axes of these folds trend NE or ENE and their usual particular feature is a steep plunge in that general direction.

(b) Faulting

A complicated series of faults of general NE to ENE trend break up the outcrop of the higher Ordovician and Silurian formations north and north-east of Ireleth. The existence of several of these faults is demonstrated by the shift of the outcrop of the massive High Haume Limestone and to a lesser extent by that of the Stockdale Shales along the flanks of the Stewnor Anticline and Rebecca Syncline. There seems little doubt that the folding and faulting are associated. Two important faults–one along each limb of the Stewnor Anticline–converge at Stewnor Park [SD 239 786], enclosing a wedge-shaped outcrop of Skiddaw mudstones with a small intrusion of volcanic breccia at its apex. This ground is not well exposed, however, and the structure may be more complex than suggested in (Figure 2). The main effect of these two faults is to eliminate an outcrop of High Haume Limestone that would otherwise be present round the nose of the anticline. The position of the northernmost can be fixed near Bankfield House, 500 m NE of Ireleth, where the crop of the High Haume Limestone abuts against an andesitic rock of the Ireleth neck; exposures of both rocks can be seen [SD 2253 7803] within a few metres of each other. A south-westward continuation of the southernmost fault is judged to be necessary to explain the structure between Stewnor Park and Far Old Park, but the ground is again badly exposed. The line of fracture continues to High Haume and Greenscoe but becomes more complex and is interrupted by cross-faults. Its effect at Greenscoe is to repeat, at least twice, the outcrop of the High Haume Limestone, and to introduce a wedge of Skiddaw mudstone and some volcanic material from the Greenscoe neck between two of the steeply dipping and faulted limestone outcrops. An earlier interpretation of the structure (Green, 1913) was that the High Haume Limestone (' Coniston Limestone' of Green) forms a folded sheet. This is not accepted. Evidence obtained during the resurvey, including that from new exposures and temporary trenches, suggests that there is a combination of parallel normal and reversed faults and NW-trending cross-faults, probably of the same age (Figure 1). The varying amounts of displacement of the High Haume Limestone suggest differential lateral movement along the cross-faults, perhaps influenced by the relative rigidity of the Greenscoe and High Haume volcanic necks.

The NE–SW fault crossing the reservoir 1 km N of Pennington, has a south-easterly downthrow which cuts out part of the Harlock Grits and Horrace Flags. Its trace ends against the post-Carboniferous Lindal Moor Fault (p. 74): whether it continues south-westwards in the Silurian basement is uncertain. The NW–SE fault along the west side of Gameswell Hill [SD 274 795] has a downthrow to the northeast and is probably of end-Silurian age. It appears to continue south-eastwards as the post-Carboniferous Stone Cross Fault (p. 74), the throw of which, however, is to the south-west; this may be due to a recurrence of movement along the old fault-plane.

The probable existence of an important tear fault (Kirkby Tear Fault) extending in an ENE–WSW direction across the Duddon Estuary is discussed below (p. 71).

(c) Cleavage

Over most of the area the strike of the strong regional cleavage varies only marginally from east-north-east, its dip being usually 75°–90° north-north-west. The main exception is in the neighbourhood of the Stewnor and Rebecca folds and near Greenscoe where the strike swings to north-east and the steep dip reverses to southeast. In this area the cleavage is locally more intense; as already noted, the coarse agglomerates and tuffs of the Greenscoe and Ireleth vents are strongly cleaved and only the andesitic lavas seem to have resisted the effects of cleavage entirely. Over the area as a whole cleavage is strongly developed in the High Haume Mudstones, the Ashgill Shale, Skelgill Shales, Brathay Flags, and Horrace Flags; surprisingly, the compact mudstones of the Brow-gill Beds are little cleaved. In the turbidite lithologies of the Harlock Grits, Coniston Grits and Bannisdale Slates cleavage is usually restricted to the slate bands and to some of the siltstones; some of the greywackes locally show a crude cleavage or joint-system parallel to the main cleavage.

The sub-Carboniferous platform

The end-Silurian period of earth movements was followed, in Devonian times, by profound erosion which resulted in the production of a platform of folded, faulted and cleaved Lower Palaeozoic rocks sloping gradually southwards and westwards from a mountainous region to the north. Some information about the attitude of this platform is given by boreholes which have reached it through Lower Carboniferous rocks and by the present distribution and thicknesses of the earliest Carboniferous sediments deposited on it as it became submerged beneath the advancing Lower Carboniferous sea. Mention has been made (p. 27) that there was a deep depression in this platform in the Duddon Valley region–perhaps a Devonian erosional feature determined partly by the Kirkby Tear Fault (Figure 13). Around Hodbarrow and Millom the platform on the western side of this depression probably sloped south-westwards towards the Duddon shore. Boreholes near Ireleth, Dunnerholme and Askam indicate a westward slope towards the Duddon from the present outcrops of the Lower Palaeozoic rocks. Near Park Cottage [SD 217 753] conglomerates of the Lower. Carboniferous Basement Beds appear to be banked against small outcrops of High Haume Limestone and, although the relationships between the two formations may be partly due to post-Carboniferous faulting, the High Haume Limestone may have stood out as a feature on the Carboniferous sea floor above the Skiddaw Group mudstone until covered by the conglomerates of the Basement Beds. At that time it is possible that the high ground between Ireleth, Dalton and Ulverston formed a ridge of older rocks above sea level which may not have been submerged before 'Martin Limestone times'. On the eastern side of this ridge several boreholes penetrating the base of the Lower Carboniferous rocks indicate that the platform of Lower Palaeozoic rocks slopes gently south-eastwards.

Structures of the Carboniferous and Permo-Triassic rocks

The main faults are shown in (Figure 12). In the west of the area the structure is dominated by the Haverigg Fault, previously called the Boundary Fault (Dunham and Rose, 1941), its probable extension southwards at Barrow, and the complex Park–Yarlside fault-complex. These faults have a westerly downthrow which can be estimated in places as amounting to at least 700 and 450 m respectively. To the east the Gleaston Fault, the Lindal Moor–Green Lane Fault, the Stone Cross Fault and the Plumpton Fault, all of general NW–SE trend, also have substantial southwesterly downthrows.

Numerous smaller NW–SE faults, in some places linked with W–E faults, occur throughout the area; most have south-westerly downthrows. Exceptionally the downthrow is in the opposite direction producing fault-troughs, the positions of some of which appear to have influenced subsequent hematitisation (p. 87).

Few of the major faults shown in (Figure 12), and none of the smaller faults, can be traced far into the Lower Palaeozoic rocks, although in one or two instances (Kirkby Fault, Stone Cross Fault) there is some evidence that they represent further movement along lines of Caledonian faults (see above). The structural picture in the Carboniferous and Permo-Triassic rocks is, therefore, of a series of roughly parallel tensional fractures along the margin of the Lower Palaeozoic massif of the Lake District producing tilted fault blocks stepped down successively and with increasing displacement towards the Irish Sea; in Cartmel the down-faulting is towards Morecambe Bay.

The age of the main movement of several of the major faults is demonstrably post-Triassic and there is no reason to suppose that the age of many of the smaller faults seen only to affect Lower Carboniferous rocks is not the same. Nevertheless the interpretation adopted of the area east of Sowerby Wood requires both pre-Permian and post-Triassic movement on the Park–Yarlside fault-system. In Cartmel, the N–S trend of the Ellerside fault, coupled with its lack of effect on the Permo-Triassic outcrops, suggests it is primarily an Armorican structure, and the same may be true of the Cartmel and Humphrey Head faults. On general grounds, however, the post-Triassic movements are regarded as the more important, and they are linked with downwarping in the Irish Sea area.

Folding is subordinate in importance to faulting. In Furness the Urswick Syncline and the complementary Scales Anticline, both of which plunge gently to the SSW, are small flexures which nevertheless have an important effect on the surface outcrops. They die out between the Green Lane and Stone Cross faults; south-westwards they can be traced to the Gleaston Fault and, although information is scanty, they appear to affect Permo-Triassic rocks south of Leece. Several NW–SE faults cross and presumably post-date these structures. Unfortunately there is insufficient subsurface evidence to enable the contemporaneous movements which, as in the Craven country, may well have been in progress here during the deposition of D₂ strata, to be deciphered. Nevertheless, the Gleaston Formation shows variations so rapid that they were almost certainly structurally-controlled. Summarising, therefore, it is probable that contemporaneous movements occurred in D₂ times, after the long period of remarkably stable conditions evidenced by the thick limestone succession from the C₂S₁ to the D₁ zones; there is no doubt that major uplift occurred in late Carboniferous times, with accompanying faulting in N–S, and possibly other, directions; but the structure as it is now displayed is to a large extent the product of post-Triassic movements.

Special attention must be directed to the Haverigg Fault at Hodbarrow, and its possible continuation southwards adjacent to the Walney Channel. As a result of additional subsurface information at Walney, and of experience gained in the Preesall district by Mr W. B. Evans along the same belt on the opposite side of Morecambe Bay, it is now considered that a deep, narrow syncline elongated NW–SE, axially underlies the Walney Channel and that the Haverigg Fault may replace, in part, its eastern limb. The structure is unique in this district, but can be matched in tectonic style with the very similar one at Preesall. WCCR KCD

Details

Hodbarrow area

The main faults are shown in (Figure 18)." data-name="images/P988102.jpg">(Figure 17). The position of the Haverigg or 'Red Sandstone' Fault has been fixed by boreholes south-east of Haverigg and around Whitriggs, Close Bridge and Waingate Bridge; one of these [SD 1629 7848] has apparently passed through the fault plane. Its throw in this area is thought to be at least 700 m. Farther north near Kirksanton (about 5 km NW of Millom) the position of the Haverigg Fault is believed to have been proved at Whicham hematite mine where the Whicham Vein dips at 45° to 60°, and is thought to throw Urswick Limestone and Park Limestone against mudstones of the Skiddaw Group. About 800 m NW of Whitriggs Close the Langthwaite Fault, a cross-fault of NE–SW trend, has been inferred from borehole records; it may intersect, and slightly shift, the Haverigg Fault.

East of the Haverigg Fault the Lower Carboniferous rocks are cut by a series of NW–SE faults. Most are in part followed by mineral veins, or have acted as feeders to the larger hematite deposits. Although the area is mostly concealed beneath thick drift deposits, the position and throw of most of these faults is known from mine workings and borehole evidence. With two exceptions their downthrow is to the south-west.

The two branches of the Moorbank South Fault converge to the south; their combined throw is about 50 m. Underground the fault plane of the western branch dips at 50° to 60° to the south-west; that of the eastern branch dips at the same angle but to the northeast and is thus a reversed fault. The fault shown in (Figure 18)." data-name="images/P988102.jpg">(Figure 17) immediately to the east is one of the exceptions where the throw is about 15 m to the north-east. There is a fault-trough between it and the Moorbank North Fault which throws down to the south-west by about the same amount. The other fault with a north-easterly downthrow is the No. 1 Pit Fault, with a throw of 25 m. It forms the margin of another and larger fault-trough bounded to the east by the Lowther and Old Mine Faults, with combined throws of 48 m. All the above faults converge north-westwards towards Oxenbows and Waingate Bridge.

At Red Hills, several NW–SE faults, which are also partly mineral veins, all throw down a few metres to the south-west; they were exposed underground at several levels.

The general 10°–15° south-westerly dip of the Lower Carboniferous rocks over most of the area swings to a north-easterly direction around Red Hills, suggesting the presence of a shallow anticline, the axis of which approximately coincides with the line of the Old Mine Fault. The change in dip may, however, be due to tilting between faults. A sudden steepening of the dip and a change in its direction at Hodbarrow Point may mark proximity to the inferred fault along the Duddon Estuary (see below).

Duddon Estuary

A map showing a possible interpretation of the geology of the southern part of the estuary and a note on the structure were published in Wartime Pamphlet No. 16 (Dunham and Rose, 1941). This study was concerned primarily with the Lower Carboniferous rocks and with the prospects of further deposits of hematite being concealed beneath the Duddon. During the revision of the Lower Palaeozoic areas more information has come to light bearing on the structure of the estuary as a whole and the main conclusions are here summarised. New and extended sketch-maps have been prepared (Figure 13) and (Figure 14), one dealing with the interpretation of the geology of the Lower Palaeozoic rocks underlying the northern part of the estuary and their extension at depth southwards and westwards, and the other with the Lower Carboniferous and later rocks.

Dealing first with the Lower Palaeozoic geology, north-easterly trending folds of end-Silurian age between Askam and Soutergate, on the east shore of the Duddon, have already been described; the axis of the Soutergate Anticline is shown extending into the estuary on (Figure 13). West of the Duddon, the steep dips in the Coniston Limestone Group observable 1 km N of Millom are apparently reversed in small exposures of a member of that Group and of the Brathay Flags at Holborn Hill, Millom. This suggests the presence of a synclinal axis trending NE–SW through the town of Millom and plunging to the north-east towards the estuary. The evidence for the extension of the outcrop of the Coniston Limestone Group towards Hodbarrow Point, beneath a cover of Lower Carboniferous rocks (Smith, 1924) comes from an old borehole [SD 179 794] recording 'limestone with brown and blue shale' (tentatively correlated with the High Haume Limestone) at a depth of 183 m and from boreholes on the Duddon shore near Hodbarrow Point in some of which similar lithologies were recorded. Records of other boreholes in the Hodbarrow area suggest that the Skiddaw Group, and not the Borrowdale Volcanic Group, underlies the Coniston Limestone Group in this vicinity. If this interpretation of the sketchy borehole records is correct, the structural relationships are similar to those around Greenscoe in Furness, and a pre-Bala uplift must have extended across the Duddon to the Hodbarrow area. The disappearance of the whole of the Borrowdale Volcanic Group in less than 3 km is difficult to explain wholly by the overstep of the Coniston Limestone Group, and the pre-Bala uplift may have been accompanied by a pre-Bala fault of considerable magnitude, throwing down to the west and extending from Millom north-eastwards towards the head of the estuary.

It is likely that the striking discontinuity between the outcrops of the Coniston Limestone Group on the east and west sides of the Duddon Estuary (near Soutergate, just north of the district, and near Millom respectively, see (Figure 13)) was caused mainly by a major WSW–ENE tear fault (or faults) extending from the vicinity of Hodbarrow Point across the Duddon to Soutergate and Kirkby-in-Furness and beyond (Kirkby Tear Fault). Some of the end-Silurian folding may have contributed to the displacement, but can hardly have been the cause of the whole of it. There is evidence for extensive faulting in the Bank House Beck area [SD 233 811] near Soutergate, at Beckside [SD 236 823] and near Grizebeck [SD 250 850]. A continuation of this general line of displacement through Kirkby-in-Furness could link up with a tear fault extending from Subberthwaite to Blawith described by Norman (1961). Movement along the fault (but not necessarily lateral movement) may have recurred, at least in the lower part of the estuary, in post-Carboniferous times, and it is even possible that the entire movement occurred at this later period though the apparent association of the faulting with the ENE end-Silurian folding makes it probable that the postulated lateral shift along the estuary is of end-Silurian age.

The suggested geology of the Lower Palaeozoic floor of the estuary is shown in (Figure 13). Coniston Grits probably occupy most of its northern part, with the older Silurian formations appearing towards Millom. South-east of the Kirkby Tear Fault the floor is composed largely of the Skiddaw Group, most of which, however, is now concealed by a cover of Lower Carboniferous rocks. The only information from boreholes concerning the floor beneath the Lower Carboniferous rocks near Hodbarrow and west of the believed outcrop of the Coniston Limestone Group is that 'slate' was recorded in one or two cases. There is no evidence of the presence of the Borrowdale Volcanic Group, and it is suggested that, as on the Furness side of the estuary, the Coniston Limestone Group rests unconformably on the Skiddaw Group.

Since the resurvey a limited revision has been made of the map of the Lower Carboniferous geology of the estuary published in Wartime Pamphlet No. 16 and the results are shown in (Figure 14). One of the changes is confined to the Furness side where the strike of the rocks between Sandscale and Roanhead is now thought more likely to be NW–SE than W–E. The effect is to lengthen slightly the extensions into the estuary of the outcrops of the Martin Limestone and Red Hill Oolite. Another change is to omit the supposed outcrop (beneath drift) of Lower Palaeozoic rocks which was indicated on the original map between Askam and Hodbarrow Point; the existence of a deep depression occupying the Duddon Estuary region in Devonian times (p. 2 7), subsequently filled by thick deposits of the Basement Beds, makes it more likely that the estuary would be floored by Basement Beds in this area.

The main structures in the Lower Carboniferous rocks on both sides of the estuary are the series of north-west faults which break up the outcrop. An important difference, however, is that whereas the faults on the western side mostly throw down to the south-west those between Sandscale and Dunnerholme mostly throw in the opposite direction. Whether this structural difference is associated in any way with a possible post-Carboniferous movement along the general line of the Kirkby Tear Fault, or more particularly with any further lateral movement along it if that occurred, is a matter of speculation. However, steep dips in the Martin Limestone and Basement Beds in the cliffs near Hodbarrow Point may suggest a post-Carboniferous fault in the same general direction and a recent gravity survey over the estuary by the Institute also indicates the presence of such a fault. WCCR

Askam–Park–Roanhead–Sandscale

Most of this area is covered by superficial deposits, chiefly glacial in origin, up to 60 m thick. Knowledge of the structure and stratigraphy of the solid rocks therefore comes almost entirely from boreholes and from such of the underground workings as were accessible during the resurvey. The information is necessarily incomplete and faults additional to those shown are almost certainly present.

There are three principal directions of faulting, see (Figure 12) and (Figure 20). The most prominent varies from N–S to NW–SE; part of the Park–Yarlside fault-system has this direction. A second direction runs W–E. Faults following both these directions appear to be normal. In addition there is a narrow belt of faults trending along the 50°–60° azimuth between Roanhead and Park Mines (shown as a single fault in (Figure 20)), which comprises several parallel high angle reverse faults.

Considering first the N–S and NW–SE group, the Park Fault complex is a linked system of fractures; some of the branches display a tendency to run NNE. The main fault forms the boundary between the Lower Carboniferous and Lower Palaeozoic rocks between Park Mines and High Bridge House (3 km N of Askam).

On the east side of the Park Sop this fault is joined by two NW–SE faults, and the single fracture so formed was known locally as the Park Boundary Fault with a very substantial downthrow to the west. It was proved in mine workings to a depth of–250 m, the footwall being Skiddaw Group (see (Figure 25)). Southwards to Goldmire the displacement is again distributed among a number of branches in the neighbourhood of Chapel Hills and Housethwaite Hill; this ground is well exposed and together with numerous borehole records it is possible to trace the branchings of the fault with fair accuracy. South of Goldmire a simple fracture only is present, bringing St Bees Sandstone against Urswick Limestone and linking the Park Fault complex with the Yarlside Fault to the south.

The California–Woodhead Vein, throwing down to the east, forms a fault-trough about 500 m wide with the Park Fault complex; this trough extends from Askam in the north to Thwaite Flat and Goldmire. The course of the vein is accurately known over most of the distance between Woodhead and Thwaite Flat since several orebodies were worked along it. In the vicinity of California Mines the throw is about 125 m, decreasing northwards. Near Thwaite Flat the California Vein is joined on its western side by two converging NW–SE faults that cross the Roanhead area; both were encountered in workings in the Nigel–Rita area.

Two important faults of N–S to NW–SE trend cross the ground between Roanhead and Sandscale Haws. The more easterly of these (Wet Meadow Fault) runs northwards from near Sandscale Farm [SD 195 738], splitting into two branches before reaching the Duddon Estuary. Several boreholes near the northern part of its course confirm its presence and establish an easterly throw of about 200 m. The more westerly fault (Warren Fault) is known from boreholes near Sandscale Farm and from others farther north on Sandscale Warren. The throw is again down to the east and is estimated at 100 m.

Prominent among the W–E faults is the Sandscale Fault (Figure 20) which was mapped during the Primary Survey as extending from Sandscale across the Furness Peninsula to Aldingham but is now known to continue only as far east at Highfield [SD 245 740], southeast of Dalton. Kendall (1921) doubted its existence but new borehole evidence and mine workings have confirmed its position at two places. Boreholes in the vicinity of Sowerby Wood show that the throw of the fault is not less than 30 m, and workings at Goldmire Mine disclosed a W–E fault which brought high Dinantian limestones into contact with Permo-Triassic sandstone; in this area the fault is apparently shifted southwards by an extension of the Park Fault. West of Sowerby Wood the position of the fault across Sandscale is conjectural. Another W–E trending fault forms the boundary between the Skiddaw Group and the Basement Beds near Park Cottage and terminates against the Park Fault; it extends eastwards towards Mouzell and Lindal. A W–E fault was proved in Askam and Greenscoe mines; it appears to shift a member of the Park Fault complex. The throw of all the W–E faults is down to the south.

The narrow belt of reversed faults running NE–SW along the margins of Rita and Park Sops appears to be unique in the district.

Several of the shafts sunk along this line penetrated the fault-belt and mark its course (Figure 20). The combined effect of the belt is a throw of about 150 m down SE, and the production of a southeasterly facing monocline broken by reverse faults, the planes of which dip to the north-west (see (Figure 21)). Stratigraphically the effect is to truncate the succession in the upper part of the Dalton Beds and the lower part of the Park Limestone. KCD

Dalton–Lindal Moor–Pennington

This area lies between the Park–Yarlside fault-system on the west and the Lindal Moor–Green Lane Fault on the east. The Lower Carboniferous rocks dip generally south-eastwards at 10° to 15°, resting on the Lower Palaeozoic platform (p. 68). The main structures between the two major faults are a series of NW–SE dip-faults which break up the outcrop of the Lower Carboniferous formations (Figure 27) and (Figure 29). Although of no great size some of these faults can be traced south-eastwards across the Urswick Syncline to the shore of the Leven Estuary. North-westwards they cannot be traced into the Lower Palaeozoic outcrops. In the Dalton area northerly-trending branches of the NW–SE faults occur. The fault pattern is completed by the presence of intersecting W–E faults which commonly, but not invariably, shift the NW–SE faults. The most conspicuous of the W–E faults identified extends from Park Cottage (where it terminates against the Park Fault) eastwards for nearly 6 km to the Green Lane Fault near High Carley. In the Lindal Moor area a conjugate system of NW–SE and W–E faults springs from the downthrow side of the Lindal Moor Fault. The general effect of the Lindal Moor–Green Lane Fault and these associated fractures is to shift the outcrop of the Lower Carboniferous rocks nearly 2 km south-eastwards against a footwall of Silurian rocks. The throw is about 150 m down to the south-west.

With the exception of the faults through Mouzell and Eure Pits, and the branched fault at Whitriggs the throw of the NW–SE faults is down to the south-west and that of the W–E faults down to the south. KCD, WCCR

Newton–Yarlside–Stank

Much of the information about the structure comes from mine workings and boreholes. The dip of the Lower Carboniferous rocks on the upthrow (east) side of the Park–Yarlside fault-system is generally to the south-east and averages 15°; that of the St Bees Sandstone on the downthrow side is probably to the south at 10°–12°.

The principal faults are shown in (Figure 33). South of Dalton the two branches of the Park–Yarlside fault-system, here trending approximately N–S converge and become the Yarlside Fault. Near Abbots Wood they are intersected by a WNW–ESE cross-fault, and the Yarlside Fault is apparently shifted about 200 m E on the south side of the cross-fault. South of Yarlside Mine another cross-fault (Stank Main Vein) shifts the Yarlside Fault about 20 m. Workings for hematite along the Yarlside Fault northwards from Yarlside Mine and from West Newton Mine and records from several boreholes have revealed that the fault is complex in character in this part of its course. The fracture is enlarged into a zone, up to 20 m wide in places, between the footwall of Lower Carboniferous limestones and the hanging wall of St Bees Sandstone. The fault-zone consists largely of brecciated Carboniferous shale, with broken limestone, sandstone and hematite. The structure has been described by Smith (1924b), who suggested that it was produced either by pre-Triassic faulting followed by post-Triassic movement along the fault, or by two periods of post-Triassic movement. The evidence is not conclusive, but a wholly post-Triassic age for the fault seems the more probable, at a time when the Gleaston Formation extended over all the ground east of the fault. The footwall of the fault adjoining the fault-zone is highly irregular; this may be due to subsequent underground solution. The throw of the Yarlside Fault is estimated at not less than 450 m; the plane of the fault dips west at about 60°.

Between Stank and Stainton a series of NW–SE and W–E faults of relatively small throw traverse the Carboniferous outcrops. In the south these faults cannot be traced west of the Yarlside Fault–though they may be present in the Carboniferous strata–except in the case of the Stank Main Vein referred to above. Others farther north, in the Newton–Stainton area, converge southeastwards probably to join the Gleaston Fault (see below). Most of these faults have a southerly throw; however, two or three near Newton Mine throw down to the north-east, and one of these (between North Stank and Newton), together with a W–E fault with a northerly throw converging with it westwards, gives rise to a complicated fault-trough between these faults and others near Stainton.

Boreholes in the neighbourhood of Gleaston prove that a NW–SE fault (Gleaston Fault) with a substantial downthrow to the south-west separates rocks of the Gleaston Formation and the overlying Namurian from Permo-Triassic rocks. Gleaston No. 4 Borehole (SD27SE/33) south of Gleaston proved about 450 m of Namurian rocks beneath the Magnesian Limestone, which indicates a throw of about 500 m. North-west of Gleaston the amount of the throw rapidly decreases; the fault splits into two branches the combined throw of which is less than half that recorded farther south. A small doleritic intrusion exposed in Gleaston village (p. 51) appears to be associated with the Gleaston Fault.

Ulverston

A major fault of north-west trend on the western outskirts of the town (the Stone Cross Fault of (Figure 12)) locally separates the outcrops of the Silurian and the Lower Carboniferous rocks. It throws down to the south-west and shifts the outcrops of the Lower Carboniferous formations 2 to 3 km to the north-west on the down-throw side. The fault lies between exposures of the Martin Limestone [SD 2768 7870] near Tarn Close and sections in the Coniston Grits [SD 2817 7872] east of Heaning Wood. Farther south where the ground is mostly drift-covered, its course is less certain but can be inferred from a few old boreholes around Dragley Beck [SD 292 775], which variously record either 'Carboniferous Limestone' or 'Slate' beneath drift. To the south it probably splits into two branches. The more westerly branch with the smaller throw, causes a sharp displacement of the Park Limestone outcrop near Conishead Priory [SD 303 758]; the main branch reaches the Leven shore about 500 m N of the Priory and continues into the estuary south of Chapel Island where Urswick Limestone is exposed on its upthrow side.

The Stone Cross Fault can be traced north-westwards into the Silurian outcrops, and it gives rise to a strong feature at Gameswell [SD 273 795]. Its throw in the Silurian rocks, however, is almost certainly down to the north-east (p. 68), and the fracture may represent an end-Silurian fault along which renewed, but reversed, movement took place in post-Carboniferous times. Alternatively the fault may be entirely of post-Carboniferous age, but of the hinged type, reversing its throw near the margin of the present Carboniferous outcrop.

The structural relationships of a small outcrop of Basement Beds in Gill Banks Beck [SD 282 787] are obscure. The outcrop is entirely surrounded by Silurian rocks and seems to be a narrow wedge bounded by two faults of north-easterly trend; the latter cannot, however, be traced far into the Silurian rocks.

The series of north-west faults stepping the outcrop of the Lower Carboniferous rocks between the Stone Cross Fault and Pennington has been largely inferred from borehole information but the exact position and trend of the individual faults is by no means certain. The ground is thickly drift-covered except for a small exposure of Basement Beds at Rosside (p. 47) and one of Martin Limestone at Tarn Close (p. 47).

A WNW–ESE fault (Plumpton Fault) running through Plump-ton Hall separates Silurian and Lower Carboniferous rocks. It has a comparable effect on the Carboniferous outcrops to that of the Stone Cross and Lindal Moor faults, and the amount of its southwesterly downthrow is probably of the same order. It may join up across the estuary with a fault near Capes Head (see below). A smaller parallel fault exposed in the Plumpton quarries carried a hematite vein (p. 47).

The Cartmel peninsula

The north–south Ellerside Fault (Figure 12), which separates the outcrop of the Lower Carboniferous rocks along the low-lying ground of the western shore of the peninsula from the Bannisdale Slates forming the central ridge, gives rise to an impressive fault-line scarp the base of which is closely followed by the road from Haverthwaite to Holker. At Stribers [SD 353 813] the direction of the main fault changes to NW–SE but a branch of it continues northwards into the Bannisdale Slates along Stribers Beck; a small kersantite intrusion has been recorded in the Slates along this line (see p. 22). A wedge of much hematitised limestone believed to be Red Hill Oolite (p. 53) is enclosed within a split in the fault at Stribers. The Lower Carboniferous rocks throughout the Cartmel peninsula dip steadily eastwards at 10°–15°, the principal effect of the Ellerside Fault being to repeat the Lower Carboniferous outcrops. Its estimated throw depends partly on the throw of the Cartmel Fault (see below), but it could be over 1000 m. A fault of this magnitude might be expected to continue south of Cark towards Morecambe Bay, but little is known of the geology of the solid rocks underlying the thick drift deposits of this ground and such an extension of the fault has not been proved. As stated below, however, part or all of the displacement may be taken up by the Cark Fault, as shown in (Figure 8) and (Figure 12).

A group of NW–SE and W–E faults that cuts the Lower Carboniferous rocks at Holker, Frith Hall and Roudsea Wood mostly throw down to the south-west and south respectively. A NW–SE fault and its branches north of Frith Hall originate as a branch from the Ellerside Fault; others farther south around Holker Park and Capes Head converge eastwards and join the main W–E Cark Fault.

North of Cartmel the Cartmel Fault (Figure 12) is postulated to explain the apparent absence of the lowest units of the Dinantian sequence. The ground is largely drift-covered and the fault has not been proved. The alternative possibility that the Martin Limestone rests unconformably on Bannisdale Slates as in Roudsea Wood farther west (p. 52) cannot be ruled out. South of Cartmel, however, there is little doubt that the junction is faulted along a NE to SW line, and that the fault terminates against the Cark Fault at Bank Top. Two branches of the Cartmel Fault between Cark and Allithwaite trend N–S and repeat the outcrop of the Red Hill Oolite and part of the Dalton Beds. Near Cartmel the Cartmel Fault is probably shifted by two NW–SE faults that can be traced south-eastwards across the outcrop of Lower Carboniferous rocks to Grange-over-Sands. The southern of these two faults has a throw of about 60 m down to the south-west at High Fell Gate.

The Lindale Fault compares closely with the Ellerside Fault: it has a similar substantial westerly downthrow of Lower Carboniferous rocks against Bannisdale Slates leading to a further repetition of the limestone outcrops in the Meathop–Witherslack area east of Lindale. Its throw is estimated at around 1000 m. The fault-plane is exposed in Lindale village close to the church [SD 4147 8036] and a fault-line scarp runs north-westwards from Lindale to High Newton.

The low-lying and drift-covered ground south of Cark and Flookburgh, and west of Humphrey Head, is structurally a down-faulted block of Carboniferous and Permo-Triassic rocks bounded by the Cark Fault in the north and the Humphrey Head Fault in the east. The total throw of the Cark Fault is not known but must be substantial. At Cark the fault is joined by the Ellerside Fault which probably takes up most of the displacement; the throws of two branches of north-westerly trend extending to Old Park and Capes Head are estimated at 150 and 250 m respectively. At its eastern end near Allithwaite the Cark Fault splits into three branches, the main one of which turns south to join the Humphrey Head Fault. A second branch (Kirkhead Fault) turns SSE from Laneside; the westerly throw of about 180 m brings the Gleaston Formation against the lower part of the Urswick Limestone along the western side of Kirkhead. The third branch (Abbot Hall Fault) continues eastwards to Abbot Hall (Kents Bank) where its throw is about 100 m down to the south.

The Humphrey Head Fault south of Wraysholme Tower has two parallel branches. One of these closely follows the western cliff face of the Head, the fault-plane being exposed in one or two places near Holy Well accompanied by hematite staining on the Urswick Limestone footwall. The throw of this branch is at least 90 m because a small outcrop of limestone and some associated sandy marl within the Gleaston Formation can be seen on the shore near Holy Well on its downthrow side. The main displacement, however, occurred on the western branch which separates the outcrop of Permo-Triassic brockram of Roughholme Point (p. 65) from the high Dinantian strata between the two branches. The amount of the displacement is uncertain.

A group of small closely spaced faults of WNW trend can be seen in the Urswick Limestone outcrops along the eastern shore of Humphrey Head; some throw down to the south, and others to the north, but the displacements rarely exceed 3 m.

On general grounds the age of all the faults in the Cartmel peninsula mentioned above might be expected to be post-Triassic but the N–S trend of the large Ellerside and Humphrey Head faults suggests that they, and perhaps others, might have been initiated during the Armorican earth movements, displacement being renewed in post-Triassic times. WCCR

References

AVELINE, W. T. and HUGHES, T. McK. 1872. The geology of the country between Kendal, Sedburgh, Bowness and Tebay. Alem. Geol. Surv. G.B. (2nd Edition, revised by A. Strahan, 1888.)

BOTT, M. H. P. 1974. The geological interpretation of a gravity survey of the English Lake District and the Vale of Eden. Q. J. Geol. Soc. London, Vol. 130, pp. 309–328.

DUNHAM, K. C. and ROSE, W. C. C. 1941. Geology of the iron-ore field of South Cumberland and Furness. Wartime Pamphlet Geol. Surv. G.B., No. 16. 26 pp.

GREEN, J. F. N. 1913. The Older Palaezoic Succession of the Duddon Estuary. London. 23 pp.

KENDALL, J. D. 1921. 'Flats' and 'Sops' in Furness. Min. Mag., Vol. 24, pp. 145–150.

MITCHELL, G. H. 1956a. The geological history of the Lake District. Proc. Yorkshire Geol. Soc., Vol. 30, pp. 407–463.

MITCHELL, G. H. 1956b. The Borrowdale Volcanic Series of the Dunnerdale Fells, Lancashire. Liverpool Manchester Geol. J., Vol. 1, pp. 428–449.

MOSELEY, F. 1972. A tectonic history of northwest England. Q. J. Geol. Soc. London, Vol. 128, pp. 561–590.

NORMAN, T. N. 1961. The geology of the Silurian strata in the Blawith area, Furness. Unpublished Ph.D. thesis. University of Birmingham.

SMITH, B. 1924a. The unconformable base of the Coniston Limestone Series in the Lake District. Geol. Mag., Vol. 61, pp. 163–167.

SMITH, B. 1919. 2nd Ed. 1924b. Iron Ores: Haematites of West Cumberland, Lancashire and the Lake District. Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B., Vol. 8. 182 pp.

Chapter 7 Hematite ore deposits

Relationship with limestone

All the hematite deposits worked in the district filled space previously occupied by consolidated limestone. A century ago, J. D. Kendall (1875) established that many of the deposits came into existence by the replacement of the calcium carbonate of limestone by ferric oxide. His evidence included: (i) the continuation of thin shale beds from the wall rocks through the hematite fillings of the veins (Askam); (ii) the existence of included beds of shale (Askam) or of limestone with shale (Lindal) inside large ore-bodies in attitudes exactly paralleling the strike and dip of the limestones; (iii) the presence of corals, crinoid ossicles and brachiopods, now partly or wholly composed of hematite, within the ore. These facts leave no room for doubt that metasomatism–molecule for molecule, in non-stoichiometric proportions–has been a major factor in the emplacement of these large deposits. Extended reference is made to this conception, long accepted by all workers familiar with the deposits, because of the attacks which have been made in recent years upon the status of metasomatism in ore-genesis by a continental school of ore-geologists,^‡5  and because it is fundamental to the understanding of this mineral field.

Nevertheless, not all the deposits originated in this way. Kendall recognised that, in certain cases, pre-existing caverns and solution-features in the limestone have been filled with ore. This especially applies to the sop deposits described below, where pre-mineralisation collapse of the roof can be demonstrated though, even in these, mineralisation was not solely a matter of filling pre-existing space. The large flat deposits, however, some of which, like Hodbarrow, cover many hectares, cannot be explained by the infilling of pre-existing caverns for their limestone roofs could not have remained unsupported. It follows that, since the hematite is certainly not an original sedimentary facies, these deposits are wholly metasomatic in origin.

All the deposits have been found in limestones of Lower Carboniferous age with only one exception, the small Waterblean deposit [SD 175 825] 2 km N of the district at Millom, which is in a limestone of the Coniston Group. In several of the stronger veins, however, Lower Palaeozoic or Permo-Triassic rocks have formed one wall of the deposit, with limestone on the other.

The deposits occur in three main forms: (a) veins, generally along faults, and 'ginnels', along joints; (b) flats, conforming more or less exactly with the strike and dip of the limestone; (c) 'dish-like' deposits (Kendall, 1875), pots (Smith, 1919) or sops (the traditional name among the Furness miners, reaching the literature in Greenwell's 1866 paper). While the fiats are concordant with the bedding of the limestones, the other two types are markedly discordant. All the evidence combines to show that the deposits were epigenetic, that is, they were introduced into the limestones after the host rocks had become consolidated. The most extensive and productive of the vein deposits were those of Lindal Moor and the Stank–Yarlside region in Furness, and the Red Hills and Moorbank areas of Hodbarrow. The main orebody at Hodbarrow, from which was produced over 25 million tons of hematite, provides the best example of a true flat. The sops are confined to Furness; the largest was the famous Park Sop, discovered in 1849, which yielded about 17 million tons of ore.

All hematite mining has now ceased in the area, the last mine to close being Hodbarrow in 1968. At the time of the resurvey of the mining areas in 1937–38 the large Roanhead (Nigel) Sop was still being worked in Furness, as were vein deposits both there and at Newton Mine, but work in both these places ceased soon after World War II. At Hodbarrow, Roanhead and Newton, therefore, opportunities were available underground for the study of the three types of deposits and their geological relationships. For the greater part of the mining areas in Furness, however, and for parts of the older workings at Hodbarrow, information comes from mining records and the writings of earlier workers. A description of the deposits of all the mining areas has been given by Smith (1924) , and references in this chapter to mines closed before the resurvey will be confined to such new information about their geology as has been brought to light.

Form of oreshoots

Veins

The vein orebodies follow either NNW or north faults with inclinations varying from near vertical to 45° (Lindal) or 55° (Stank), or vertical joints having little or no displacement. As already noted, the smaller faults trend NW and west, but parts of the large NNW to north faults are also mineralised. The ginnels (the local name for passages), which were narrow oreshoots up to 5 m wide with irregular walls on both sides, are considered to have followed joints and some may have filled pre-existing caverns. The larger vein oreshoots in most cases had a well-defined wall on one side, most frequently the upthrow or footwall side. The hanging-wall in such cases was highly irregular, so that the oreshoot was subject to pinches and swells, the latter reaching as much as 35 m wide at Red Hills and Moorbank (Hodbarrow) and Lindal Moor (Furness); widths of up to 10 m were common elsewhere in Furness. Such orebodies clearly result from the replacement of the hanging-wall limestones. In a small number of cases, the fault lay on the hanging-wall side, and irregular metasomatism has proceeded in the footwall; Yarlside and Stank veins provide examples. In some cases a plexus of closely spaced faults provided a locus for replacement, as was plainly evident from Kendall's (1882, pl. 43) section of Lindal Moor, and as our structural studies at Moorbank and Newton have demonstrated. Vein oreshoots mainly of metasomatic origin reached a length of 600 m at Red Hills and over 200 m at Lindal Moor, with vertical extensions of up to 250 m in the Stank Main Vein and the Whitfield–Lowfield section at Lindal, and 180 m at Crossgates. At the last-mentioned mine, two oreshoots exhibit an axial plunge to the south-east steeper than the dip of the limestone, but this effect is not common.

With the exception of the Stank veins, which underlie D, and Namurian sediments, all the remaining vein oreshoots reach the surface of the massive C₂S₁ to D₁ limestones. All die out downwards, very few extending as far as the top of the Basement Beds on the hanging-wall.

Flats

These deposits, as their name implies, are flat or tabular in form and were developed by the more or less complete replacement of favourable beds of limestone by ore. They are invariably associated with faults which presumably acted as feeders, and all stages exist between flats and the bulging type of deposit which replaces the limestone of the hanging wall of a vein or fault. The main orebody at Hodbarrow was the largest example of a true flat ever recorded; it had an area of approximately 350000 m² and an average thickness of 20 m, though reaching 35 m in places. It was formed essentially by metasomatism in the lower part of the Red Hill Oolite and the upper part of the Martin Limestone, and rested on the lower, more shaly, part of the latter formation or locally upon the Basement Beds. In general flats were of much less importance in Furness than sops and veins. Nevertheless small flats are recorded from the Lindal Moor region (although replacement of limestone was here frequently incomplete), at the Askam–Sandys Mine (p. 98), at Lindal Cote (p. 108), and at Goldmire (p. 106). Small flats spread into the footwalls of veins at Stank and Newton.

Sops

These deposits are a unique feature of Low Furness, without any counterpart elsewhere in Cumbria. They lie around the nose of the Park Anticline. Fundamentally they are large dissolution hollows in the Lower Carboniferous limestone. The three largest, Park, Rita and Nigel, are illustrated in plan and section in (Figure 22), (Figure 23), (Figure 25)." data-name="images/P988109.jpg">(Figure 24), (Figure 25). Park was 420 m long, 20 to 180 m wide, and reached a maximum depth of 180 m. Each of the three seems to have formed by the union of two adjacent hollows. In detail the sides were found to show many irregularities, as the sections indicate. From these large bodies, there was a gradation in size down to sops only 30 m wide and less than 30 m deep. The smaller examples lie mainly to the east of the Park–Yarlside fault-system, and for the most part occur in Red Hill Oolite, while Park and Rita sops start in Park Limestone, and Nigel in Dalton Beds.

A definite sequence of linings is found in the hollows (Dunham and Rose, 1949), though all members are not necessarily found in each case. In the bottom of the hollow lies a 'rubble', consisting of rounded and water-worn blocks of limestone up to 1 m across, each with a white 'decalcified' crust. Where the orientation of the bedding in these blocks can be measured it is random, and the deposit plainly results from collapse during the dissolution process, in part predating the introduction of hematite. The limestone rubble is normally mixed with clay, which may be either a dark brown cave-earth variety (probably the insoluble residue of the dissolved limestone), or a pale grey, white and pink clay known as 'hunger', or a nearly black manganiferous 'black muck'. At Nigel, where the bottom lining was thickest (Figure 22), some blocks of sandstone resembling St Bees Sandstone were also found, while at Tytup the main lining was clay (Kendall, 1875, pl. 31).

The second layer, 10 cm to 1 m thick is known as the 'casing'.

It consists of bright red clay containing angular fragments of hematite, and separated the rubble from the ore. It is heavily slickensided, showing that movement has taken place between the ore and the outer layers. The sop orebody, forming the next layer consists of a broken-up mass of fragments and blocks of iron oxide minerals with quartz and in some places manganese oxides, set in a red powdery hematite matrix or enclosed in 'black muck'. Finally, in the largest sops, a central core of 'sand' is present, made up of large broken blocks of sandstone indistinguishable from the St Bees Sandstone. Few, if any, of these blocks can be seen now, but at the time of the resurvey when the Roanhead and Park mines were being kept pumped out to −180 m OD, many were visible in the subsidence hollows. The outer parts of the blocks were softened, but their hearts were hard unaltered St Bees Sandstone.

All the sops came to outcrop with the surrounding limestone, or were covered with boulder clay. None has, however, been found under Permo-Triassic rocks, for reasons to be discussed later (p. 88). It is quite clear, nevertheless, that St Bees Sandstone at one time rested directly on the Carboniferous Limestone over the area where the sops occur, with little or no intervening St Bees Shale, breccia or Magnesian Limestone (Dunham and Rose, 1949); and that it has subsided into the dissolution hollows (Figure 15). At least two hollows contain sand but no ore.

There is a certain parallel between the sops and the 'pocket deposits' worked for industrial sand in the Carboniferous Limestone of north Derbyshire. These dissolution features have preserved the Neogene Brassington Formation (Walsh and others, 1972) far below its original level. For example, the subsidence feature at the Bees Nest Pit is about 150 m wide, but it is claimed that the Neogene strata have subsided 498 m below their original position. Subsidence outliers preserving probable Neogene sediments in Carboniferous Limestone are also recorded from Staffordshire, Flint–Denbigh, and Carmarthen–Brecon, but none of these contains iron ore. The nearest parallel to the sop deposits of Furness is to be found in the sink structures of the Ozark Plateau in Missouri (Grawe, 1945). These occur in the Ordovician Gasconade and the Cambrian Eminence dolomites, and are related to a mid-Ordovician erosion surface overlain by the highly permeable Roubidoux Sandstone. The sink structures are believed to have developed by caverns in the dolomite extending up to the base of the sandstone, causing the latter to sag into the sinks. As this process proceeded, mineralisation with pyrite and a number of minor associated sulphides was taking place, and the Roubidoux Sandstone was in part prevented from subsiding to the floor of the sink by the growing mineral body. Eventually erosion re-excavated the sub-Roubidoux surface, the sinks were exposed, and the pyrite was oxidised in part or whole to hematite. The largest example in 1945 (Chemy Valley No. 2g) was 300 x 200 x 50 m; the Moselle No. 10 was 100 x 50 x 62 m. These dimensions are comparable with those of the Furness sops, the evolution of which will be further discussed after the mineralogy and ore controls have been considered.

Ore textures

The following three distinct types of texture were recognised by Kendall and comprise a useful classification.

1. hard bluish purple ore, with visible quartz in small ramifying filled cavities; this type was typical of the best run-of-mine ore from veins and flats.
2. soft dull red massive or broken-up hematite, commonly in a red 'smit' matrix; this occurred in some veins and sops.
3. dark or black broken-up ore mixed with 'black muck'; this was typical of the bottom part of sops.

Representative analyses of the first two types appear later in (Table 8) (p. 84), analysis 1 representing the hard bluish purple ore and analysis 2 the soft red ore; representative analyses are also given in (Table 12) (anals. 3–5). The third category covers a wide range of compositions, from admixtures with manganese (for example Kendall's 1893, p. 116, analysis, showing 12 per cent manganese oxide) to admixtures with residual black shale, perhaps from the Dalton Beds. Electron micrographs of the three types are shown in (Plate 7).

The fragmented nature of the sop ores (see p. 80) is due to subsidence in the hollows continuing after mineralisation, a conclusion substantiated by other kinds of evidence. KCD

Mineralogy of ores

At first sight the ore deposits of Furness, like those of West Cumbria, seem remarkable as examples of monomineralic concentrations. In fact, they are not quite as simple as this, but the mineral suite is very restricted indeed compared, for example, with that of the non-ferrous deposits of the Lake District or the Northern Pennine Orefield. The very simplicity of the iron deposits of the north-west coast is, in itself, a geochemical problem.

Iron oxides

Hematite (αFe₂O₃) is the principal ore mineral. The botryoidal or kidney form from this district, consisting of radiating fibrous crystals elongated perpendicular to the c-axis (Bradshaw and Phillips, 1967), is very well known. It was found chiefly along the sides of the veins and flats, where cavities developed making free crystal growth possible. Specularite, the 'micaceous' tabular form, was also found in cavities, though much less frequently than kidney or 'pencil' ore. Greg and Lettsom (1858, p. 246, fig. 2) figure a fine specularite crystal from 'near Ulverston'. The characteristic colour of this variety is lustrous black, while the botryoidal form is dark reddish brown, both having a characteristic bright red streak. The bulk of the hematite, however, is not fibrous or micaceous, but is either in dull, blue, hard and massive, or in red to reddish brown and soft varieties. There is generally some admixture with bright red 'smit', a greasy-feeling fine powdery variety. KCD

The colour of the ores varies considerably and may be masked or enhanced according to the lustre of the hematite. The compact microcrystalline variety (e.g. (MI35258)) is dull, greyish blue (near 5PB5/2) to pale greyish purple (5P4/2) on freshly broken surfaces, passing to pale reddish brown (10R5/4) on outer crusts, which rarely exceed 1 to 2 mm thickness. Botryoidal hematite commonly has a metallic to splendent lustre that modifies the body colour, which may, however, be described as a dark reddish brown to very dusky red (10R2/2); earthy, scaly hematite is nearer pale reddish brown (10R5/4). The earthy 'smit' type of ore (MI35254), which is highly friable and adheres readily to surfaces in contact with it, is near greyish red-purple (5RP4/2).

In form the hematites vary considerably, but are generally very finely crystalline. As a function of form, and particularly of microscopic texture, they range widely in hardness and crushing strength. Massive microcrystalline pure, though porous, hematite has a Mohs' hardness of about 3.5. Where reinforced by silica impurity the hardness rises to near 7.0. Kidney ore has a hardness of about 6.0 externally, and of 6.5 internally on a radial segment. Reddish brown, dull crusts to both kidney and massive hematite have a hardness near 4.5. Bowie and Taylor (1958) found that the Vickers Hardness Number of hematite (VHN 733–1062) varied with the degree of crystallinity. Specific gravities were measured (by Mr C. R. Wheatley) on compact hematites with the following results: massive porous bluish purple ore, 4.69; kidney ore, 4.99.

Because of its very fine crystallinity and porous texture, the massive hematite (MI35224); (E44797P) takes a poor polish. Kidney ore, on the other hand, is not so porous and takes an excellent polish. Under normally incident, plane polarised illumination, the massive variety appears as aggregated sheaves of minute crystallites, which appear to be mainly fibrous to scaly. These are more resolvable around the abundant pores and vughs, where the individual crystals attain 0.02 x 0.004 mm. The sheaves appear to be randomly arranged and interpenetrating, and coalesce into a microporous aggregate away from the pores.

Natural fracture surfaces of the main hematite varieties were examined under the Stereoscan scanning electron microscope by Mrs A. E. Tresham. These comprised: a radial segment of a kidney ore from Roanhead Mine (MI35292); bladed hematite from a botryoid fragment in breccia (MI35255); soft, radially fibrous, reddish brown hematite from a similar botryoidal clast; massive bluish purple hematite ore (MI35258), (MI35261); the reddened 'weathered' surface of similar ore (MI35266); and friable earthy hematite (MI35254). A selection of the electron micrographs is shown in (Plate 6), p. 78. Radial blades from the kidney ore are resolved at a magnification of 2500 as sheaves of minute, parallel, elongated, closely packed to coalescing crystallites ((Plate 6).4). Though the individual crystals are insufficiently well developed to be discernible clearly in the present electron micrographs, their platy arrangement along the segment axis and the crystal edges developed on those plates tend to confirm visually the orientation found by X-ray studies. Reddish brown, radially fibrous hematite (MI35235) shows under low magnification ( X 200: (Plate 6).5) a marked alignment of micaceous plates not dissimilar to the hard kidney ore described above. Under high magnification, however ((Plate 6).6), the mica-like crystallites are only loosely aggregated, thus accounting for the friability of this variety. Crystal faces are rarely visible in these aggregates. The most friable of all the hematites, the earthy 'smit' ore (MI35254), shows at a magnification of 2500 ((Plate 6).8), randomly arranged sheaves of hexagonal micaceous platelets averaging perhaps 7[1 across, with no evidence of interlocking texture. Under light pressure these aggregates form a shiny coating due to the alignment of the platelets. In marked contrast the massive, bluish purple microcrystalline hematite ore (MI35224), (MI35256), (MI35258), (MI35261) has a relatively high crushing strength. Under the scanning electron microscope ((Plate 6).1 and 6.2) it shows a minutely cellular texture of closely packed sheaves of hematite flakes complexly interlocking and fusing together. Though minor quartz is present in stringers and vughs in these specimens, it is not thought to contribute to the strength of the hematite, which is most probably accounted for by this complex microtexture. RKH

Though there is no doubt that the major part of the iron in the South Cumbrian deposits is present as hematite, it is necessary to consider whether hydroxides are also present. The ores, in bulk, showed a substantial water-content; summarised works analyses (Dunham and Rose, 1941, table iii), representing millions of tons of production show H₂O ranging from 4.71 to 18.93 per cent, with the mean probably in the lower part of this range. Accepting that these figures included a high proportion of free water, there is evidence here, as in the Whitehaven–Egremont district, that water retained above 105°C is present (Table 8), (Table 11) and (Table 12). Of the three possible iron hydroxides, turgite (2Fe₂0₃.11₂0) was thought by Smith (1919, pp. 28, 29) the most likely to be present in view of its red colour, though he recognised that goethite also occurred. KCD

Turgite was at one time considered to be an authentic mineral species; the alternative name hydrohematite which according to Hey (1955) has priority, is also used. However, since the studies of Posnjak and Merwin (1922) it has appeared more likely that hydrohematite is a variety of hematite with adsorbed water. They demonstrated that hematite and 'turgite' have the same ultimate structure, and connected the water-content with the fibrous structure of the 'turgite'. Bohm (1928) noticed a broadening of X-ray diffraction lines in hydrohematite and suggested that this effect was related to crystallite size.

For both the analysed hematites in (Table 8), showing respectively 0.32 and 0.40 per cent 'combined water', X-ray powder data show sharp lines throughout, with the high-angle Ka-doublets well resolved. This is not, however, the case in a number of other hematites investigated, includ ing kidney ore from Roanhead (MI35275) and Ulverston (MI14991), a radial-fibrous microbotryoidal variety from Stank–Yarlside (MI35325), radial-bladed ore (MI35255) from Lindal Moor, and bluish purple microcrystalline ore (MI35261) also from Lindal Moor. In all these the Kocdoublets are poorly resolved; this may be due to fine crystallinity, with a corresponding increase in surface area, and to micropore space, where water might be more or less tightly held by adsorption. To test this possibility six extra samples were analysed by the Laboratory of the Government Chemist, using the most rigorous methods for 'combined water'. The results (Table 13) show only marginally higher H₂O+ than in the well-crystallised specimens of (Table 8), and appreciably lower values than those from a fibrous hydrohematite (Nevill Coll. No. 885) from Germany. Nevertheless, water is present in significant amount, too great to enable the view to continue to be held that the ore-mineral is exclusively anhydrous iron oxide.

The presence of goethite, x(FeO.OH), in yellowish brown material associated with the gangue minerals in many specimens was established by X-ray powder photography (X6995), (X7017A,), (X7017B), but the impression was gained that its deposition was independent of that of the hematite–hydrohematite. Interbanding of goethite and calcite occurs (MI35216) but no alteration of hematite to goethite could be proved. Goethite is, on the basis of the field evidence, only a minor constituent of the deposits, and the quantities present are quite insufficient to explain more than a small fraction of the water-content of the ores.

The possibility that some maghemite (γFe₂O₃) might also be present was suggested by the successful use of the vertical-force magnetometer as a tool for locating concealed orebodies during the resurvey (Hallimond and Butler, 1940; Dunham and Rose, 1941), for hematite is normally regarded as having low magnetic susceptibility. A laboratory investigation was accordingly made of massive microcrystalline hematite from Lindal Moor. Following crushing and wet sieving through 240-mesh BSS, this was put through the Cook Electromagnetic separator at varying amperages and a constant cross-slope (forward tilt 17.5°, side 13.5°). The hematite showed magnetic suceptibility,

starting at 0.5 amp and persisting to the maximum of 2.4 amps, which should be regarded as indicating moderate, rather than low, susceptibility. Nevertheless no iron oxide other than hematite was detected in X-ray patterns from the magnetic fractions. The non-magnetic fraction consisted of composite grains of hematite with quartz and calcite. Thus if a magnetic iron oxide is present, its quantity is below the limit of X-ray detection. Maghemite is not the only possibility, for the analyses in (Table 12) show very small amounts of FeO which cannot be accounted for by the observed minerals, but which might point to a very minor proportion of magnetite (FeO.Fe₂O₃) being present in the ore. It must be emphasised, however, that neither magnetic iron oxide has been proved to be present. BRY

Manganese oxides

As in most iron ore deposits, subordinate amounts of manganese are generally present, the quantities varying from a trace up to several per cent. A few bodies of manganese ore were worked, notably at the Woodhead sop at Roanhead (p. 99). Smith (1919, p. 27) states that manganite, x(MnO.OH), is the oxide present, but hausmannite (Mn₃O₄) has also been mentioned from this district. Good quality material was no longer available at the time of the resurvey and we have not been able to carry this matter further.

Quartz

As the analyses show, silica is rarely absent, even in what appears to be pure hematite. It is in the form of quartz, and no iron silicate has been found. The commonest mode of occurrence of the quartz is as an infilling, generally complete, of small macro-cavities in the iron oxides; much of it was deposited after the hematite (MI35239), (MI35240), (MI35241), (MI35242), (MI35264), (MI35265). In very siliceous ores, the individual quartz crystals in the interlocking aggregates may reach as much as 5 mm across. Chalcedony may also be present (MI35252), (E44883). Euhedral authigenic quartz occurs in association with carbonate gangue and breccia. Some quartz-predominant gangue ((MI35238), Stank–Yarlside) consists of an aggregate of slightly pinkish brown-stained mica-like plates, colourless under the microscope, containing disseminated hematite. The thinly tabular habit suggests pseudomorphism after baryte.

Carbonates

The carbonates calcite and dolomite complete the assemblage. During the field survey a careful search was made for the iron carbonates siderite (FeCO₃) and iron ankerite, but none was discovered. The absence of these minerals has further been confirmed by measurements of the refractive index in 60 specimens, from seven localities, representative of the carbonate gangue minerals, as reported below. RKH

Thus it certainly cannot be established that the hematite was formed by oxidation of siderite, as J. A. Phillips (1884) suspected. Indeed the refractive index measurements by Mr Harrison showed no values greater than 1.684, the figure for the dolomite end of the ankerite series (MgCO₃ CaCO₃–FeCO₃ CaCO₃). For this reason, the classification of the Cumbrian coast deposits as 'Bilbao type' adopted in a recent United Nations Survey (1968, p. 15) is open to considerable question, the definition of this type being: 'Massive iron oxide deposits derived from the weathering of underlying iron carbonate. Iron deposits of irregular shape occurring as iron carbonate below the water table and as goethite and hematite above. Examples: Bilbao, Spain; Cumberland, England; Erzberg, Austria.' There is, indeed, a very striking contrast in the mineralogical style between the deposits of the present district, where hematite-hydrohematite is the primary mineral, and the Northern Pennine iron deposits where, as at Bilbao, the protore is a mixture of siderite and ferriferous ankerite, and the oxidised ore is goethite.

Dolomite might be regarded as the wallrock mineral of the hematite deposits, but it must be admitted that its distribution is very patchy, and iron ore is commonly directly in contact with limestone that has escaped dolomitisation. It could even be argued that the dolomite belongs to early New Red Sandstone times, predating the main mineralisation. KCD

Dolomite is generally finely crystalline and variable in colour; specimens from Hodbarrow are pale green, elsewhere the usual brownish colour is found. None has been found in vughs. The occurrence of dolomite-hematite breccia (MI35225), cemented by later dolomite and minor calcite, shows that not all the dolomite is pre-ore. Banded dolomite (MI35218) consists of grey-ochre microcrystalline dolomite charged with gaseous micro-inclusions, intercalated with dolomite carrying dispersed specks of hematite, and bounded by white dolomite in crystals up to 4 mm across. All these dolomites have refractive index n_ω = 1.684 ± .002. However in one specimen from Lindal Moor (MI35267) a lower index, n_ω = 1.676 ± 0.002, is found in coarse yellowish buff cleavage-plates, associated with earthy hematite and calcite. This carbonate is assumed, following Winchell and Winchell (1951, p. 114), to be very close to the magnesian end-member of the dolomiteankerite series. Two further examples were discovered from Lindal (MI35270), (MI35273), but none from other localities.

Calcite is ubiquitous as a gangue mineral though it never forms more than a small proportion of the deposits. It occurs in a considerable variety of forms, colours and crystal habits. At least three generations show in some specimens, the earliest being very fine grained and admixed with goethite (MI35216, (MI35226), (MI35227), (MI35228): an X-ray film failed to show siderite in this. It is commonly veined by pale or colourless calcite, and vughs generally carry colourless or white crystals. Other calcites are black, various shades of brown, pale orange and olive-grey; some are markedly colour-zoned. All have the same refractive index, n_ω =1.658 1.002. Generally this mineral appears to have been the last to crystallise. RKH

Sulphides

These are very rare constituents and the sulphur-content of the ores was remarkably low. Only at Anty Cross, south of Dalton, was sulphide found in more than trace amount. Here there were small lenses of chalcopyrite (CuFeS₂) and chalcocite (Cu₂S) enclosed in the hematite. Works analyses of the time showed up to 0.085 per cent Cu in the ores shipped in 1925. A few tons of copper ore were picked out and sold from this mine, but this is the only recorded production of non-ferrous ore from the district. A small copper vein has, however, been found in the Urswick Limestone in Sea Wood, Bardsea.

Other minerals

Occasional pseudomorphs in hematite after a cubic mineral—probably, from its twinning, fluorite—and also after baryte have been found (Rudler, 1905), but the spectacular crystals of these minerals familiar from cavities in hematite in the Egremont district have not been reported here. Kendall (1893) mentions the presence of baryte in the Waterblean deposit, and it has also been recorded from the Lindal Moor Vein. The very low sulphur and phosphorus contents in the South Cumbrian ores are noteworthy, and were one of their chief merits.

Chemistry of ores

The analyses of Gillbrow hematite by A. Dick and of 'Lindale, near Ulverstone' ore by J. A. Spiller quoted in the first Geological Survey memoir on iron ores (Smyth, 1856) are the earliest published. Kendall (1893) and Smith (1919, 1924) both record a number of others. During the resurvey, the Barrow Haematite Steel Company and the Millom & Askham Company placed at our disposal the records of their analytical laboratories, covering a long period. Average works analyses for most of the mines in the district were given in Wartime Pamphlet No. 16. However, it was clearly desirable to make modern analyses for major and trace elements. KCD

Two full analyses of hematite ore specimens, one from Hodbarrow Mine (MI35224), the other from the Daylight Hole Vein, Lindal Moor (MI35254), were made by the Laboratory of the Government Chemist. The results are presented in (Table 8), where they are compared with analyses of other hematite samples from this district and elsewhere. The present analysis of the Hodbarrow hematite ((Table 8), anal. 1) shows it to be very nearly pure Fe₂O₃, the atomic ratios on a basis of three oxygen atoms being Fe³⁺_1.999    Fe²⁺_0.001  Ti_0.002 Mn_0.0002 O₃. Because of its minutely porous nature, the measured density (4.99) is lower than the theoretical density D_calc=5.27₂ based on the cell dimensions obtained by Mr Young of a 5.034₇Å, c 13.74₈Å. In these calculations it has been assumed that, since calcite, quartz and clay mineral impurities occur in other nearby hematites, the other oxides reported are due to mineral impurities, although these must be mere specks. The second analysis, of 'smit' ore ((Table 8), anal. 2), bears out the microscopic examination, in containing considerably more impurities, particularly quartz and calcite.

Partial chemical analyses of five specimens of massive ore from the district, and one of hematite-quartz rock, were also made by the Laboratory of the Government Chemist. They appear in (Table 9), where they are compared with the results obtained from a sample of hydrohematite from Prussia.

A spark source, mass spectrographic survey analysis was carried out on a sample of hematite by the Analytical Research and Development Unit, Applied Chemistry Division, Atomic Energy Research Establishment, Harwell. The sample ((MI35224), from Hodbarrow Mine) was selected because no mineral impurities had been detected in polished section or by X-ray diffraction, and a sub-sample was also analysed for major and trace elements, the latter by optical spectrography (Table 10). The mass spectrographic analysis, however, amplifies optical spectrography because theoretically it is possible to look for the majority of elements in the Periodic Table. In the present analysis Be, F and Al could not be detected or determined because of interfering mass lines, and rare gases, H, C, and 0 were not specifically sought. The results otherwise show that elements with atomic number above 26 were, with the exceptions of As, Sb, Ba and Pb, all less than 6ppm, but there may have been interference by complex ions, suspected or known. The major impurity Ca is, together with Mg, probably due to discrete carbonate impurity although none was detected. Indeed the problem of deciding whether or not the trace elements reported lie in such discrete mineral phases or are within the hematite lattice is probably insoluble because methods of identifying mineral phases in sub-microscopic particles are too insensitive. However, alpha-hematite can contain up to 5 per cent TiO ₂ (Basta, 1953, in an unpublished Ph.D thesis, University of Bristol), and Mn may also be held in the hematite lattice having been reported commonly in hematites of this area (Smith, 1924, p. 48). Apparently no sulphide phase is present. RKH

Using X-ray fluorescence techniques, a group of 85 massive microcrystalline and 10 botryoidal hematite samples from the Millom and Furness areas were analysed for their major and trace element components at the Department of Geological Sciences, University of Durham (Shepherd, 1975). The samples were prepared as powder briquettes and were compared with synthetic standards made from a spectrographically pure ferric oxide base. Deviations from linearity due to matrix effects were minimised by choosing materials physico-chemically similar to the samples. Cases of spectral overlap were resolved by measuring the interference directly on single-element standards. All detection limits were calculated at the 3- significance level. The results in (Table 11) give unscreened statistical averages. The most striking feature is the enrichment in arsenic; there is also a slight enrichment in lead compared with crustal averages; copper, nickel and zinc are however below average. A significant trace of titanium is present, as noted from the mass spectrographic results. The distribution of elements resembles that in the West Cumbrian hematites, and also those in iron oxide fractions from the Skiddaw Group, the Borrowdale Volcanic Group and the Eskdale Granite. Tjs

The bulk compositions of the ores are represented by analyses 1, 2, 6, 7 and 8 in (Table 12), each one being averaged from samples taken at the mine or works and representing millions of tons of production. These are compared in the table with J. D. Kendall's three main ore types (analyses 3–5) which we accept as a reasonable classification (p. 81). The quality of these analytical data is not, of course, to be compared with that in (Table 8), but the results are nevertheless worth placing on record. The various analyses are sufficient to emphasise the siliceous nature and the low phosphorus content of the South Cumbrian hematites. There is a suggestion that ores from veins and flats tend to carry more unreplaced limestone than those from sops. The data given in Wartime Pamphlet No. 16, table iii, include many other works analyses, and suggest that phosphorus increases as the Gleaston Formation is approached. The water figures include part of the 'free' water as well as combined water. Four tolerably complete analyses of Furness ores are given in (Table 13); they are of individual samples rather than long runs of shipments as in (Table 12). If the analyses in (Table 13) were interpretable in terms of mixtures of anhydrous hematite and the hydroxide goethite, the ratio Fe₂O_3: Fe₂O₃. H₂O would vary between 80.8: 2.7 and 55.2:11.9. However, as already indicated, even if the combined water figures could be relied upon, such an interpretation would greatly over-emphasise the quantity of goethite actually present. The fact appears to be that much of the tightly bound water is adsorbed in the hematite, especially where this is fibrous in character.

Summarising the chemistry of the ores as mined, the average iron-content for works analyses covering the period 1891–1938 (Dunham and Rose, 1941) was 47 per cent (compared with 69.9 per cent in pure Fe₂O₃). The ores were predominantly iron oxide with some adsorbed water, but with only minor quantities of hydroxide; silica as quartz was generally less than 10 per cent in veins and flats and over 10 per cent in sop ores, and calcium carbonate was significantly higher in veins and flats than in the sops. Magnesium carbonate and alumina figures were rarely over 1 per cent, indicating only a slight admixture of dolomite and clay minerals. Manganese rarely exceeded a fraction of 1 per cent save in some black ores from the bottom parts of sops. Phosphorus and sulphur were very low. KCD

Fluid inclusions

The modern technique of investigation of fluid inclusions in thick microsections has been found applicable to calcites intimately associated with the hematite. The following homogenisation temperatures have been recorded for calcites overgrowing botryoidal hematite:

Subject to a small pressure correction, which might raise the figure by a few degrees, these temperatures indicate the conditions in the closing stages of the mineralisation. Separation of the included liquid enables some impressions to be gained of the composition of the fluid which introduced the minerals. Salinity measurements for inclusions in the Hodbarrow samples give a range from 14 to 23 weight per cent equivalent NaCl, representing salinities 4 to 6 times that of sea water. The calcites were thus deposited from hypersaline brines and it is a reasonable conclusion that this also applied to the iron oxides and the quartz.

Compared with fluids trapped in minerals of the nonferrous suite, those of the present district were markedly richer in potassium compared with sodium. The range of Na/K here is from 3:1 to 10:1, a mean of 8 analyses showing 8:1. In contrast, the Mississippi Valley lead-zinc deposits, where the medium is believed mainly to be connate water show 20:1, while in the Northern Pennines (Sawkins, 1966) the range is 12:1 to 20:1. Using gas mass spectrometry, an attempt has been made to analyse the gases present in the fluid inclusions: the paucity of inclusions has prevented fully quantitative results from being obtained, but it can be stated that CO₂ N₂ and CH₄ are all present in amounts less than 0.2 per cent, presumably dissolved in the aqueous phase when the inclusions were homogenised.

In freezing the inclusions for salinity measurements they were found to exhibit a marked degree of super cooling, ice nucleation requiring two hours at liquid nitrogen temperatures. This suggests a complete absence of heterogeneous nuclei in the inclusion fluids, brought about by ultrafiltration. The gangue minerals were, therefore, deposited from very slow-moving fluids, a conclusion well in accord with the observed important role of metasomatism. TJS

Controls of mineralisation

Structural controls

All the vein orebodies occupy fissures which may be faults or, less commonly, joints. In several of the areas where vein-like deposits predominate, for example the Lindal Moor, Whitriggs, and Newton mining districts of Furness and the Red Hills and Moorbank districts of Hodbarrow, controlling faults are generally separated by parallel smaller faults or joints, the fracture system as a whole giving rise to complicated vein-like deposits which merge to form large irregular masses according to the degree to which replacement has occurred. Clear evidence shows both that the fissures were in existence prior to mineralisation and that there was no marked subsequent movement along them. Thus many instances have been noted underground where the original slickensided surfaces of fault-planes in limestone have been replaced by hematite in all details save for the original polish, and where masses of hematite kidney ore crystallised on vein-walls show no sign of disturbance.

Both at Hodbarrow and in Furness the dominant system of post-Carboniferous NW–SE faults has provided the main structural control for all the important vein-like deposits though, locally in Furness, some large faults trending more nearly N–S—for instance, the Park–Yarlside fault-system have been equally important. Some W–E fractures have also carried notable vein deposits in parts of Furness, and a linked system of these and the NW faults controlled emplacement of the orebodies in the southern part of Lindal Moor and at one or two other places. At Lindal Moor in particular the intersection of the two sets of fractures frequently proved to be the locus along which vein deposits swelled out into large irregular replacement deposits or small flats.

There is strong evidence that the existence of fault-troughs influenced ore deposition especially–where stratigraphical controls (see below) were also favourable–the formation of the larger orebodies and flats, the boundary faults of the trough acting initially as feeders. This is well illustrated in the case of the main orebody at Hodbarrow by the section in (Figure 19). Another example is the Askam Flat (p. 98) , which occupies one side of a fault-trough crossed by a W–E fault. Again the large irregular orebody at Moorbank North, Hodbarrow (p. 97), is contained within a fault-trough, and the extensive system of small veins and irregular deposits in the Whitriggs area of Lindal Moor lies within a much fractured downfaulted block, while several large orebodies, including the Park Sop, are situated along the downfaulted area between the California and Park faults, as shown in (Figure 20) and (Figure 25).

Structural control over the distribution of the Furness sops is less obvious than in the case of veins and flats, but is nonetheless clear in many instances. An association between these solution hollows and the belts of fracturing is suggested by the NW–SE and N–S alignment of several small sops north and north-east of Dalton (Figure 27) , especially at Elliscales and Eure Pits, and the presence of faults following lines of sops has indeed been proved in several cases, those at or near the margins of some of the larger sops around Park and Roanhead having been confirmed underground. It seems clear that faults and fractures influenced the initiation of the solution hollows and may later have acted as feeders for the mineralising solutions, as in the case of the California Vein (p. 105), though no further tectonic movement along the faults has been proved subsequent to the infilling of the hollows with ore.

Stratigraphical controls

The subdivision of the Lower Carboniferous rocks into the formations shown in (Table 6) has made possible a detailed study of the distribution and form of the orebodies in relation to stratigraphy. All the replacement deposits–whether flats, irregular deposits or veins–occur in limestones, and the more massive beds of limestone are in general much more favourable host rocks than those which are thinly bedded or contain shaly partings. In contrast the Basement Beds, consisting mainly of conglomerates, sandstones and shales, are devoid of replacement deposits, although some veins have been productive where the formation lay in the footwall of a controlling fault. Even veins of the infilled type, however, seem to be restricted to those fractures where at least one wall consists of limestone. Similarly the distribution of many of the sops appears to have been controlled by the presence of a limestone formation known in other parts of the area to have been favourable for replacement by hematite. Presumably the same chemical and physical properties that allowed the development of solution hollows in particular limestones also facilitated their replacement by mineralising solutions.

Replacement deposits have been found throughout the Martin Limestone, but they are generally restricted to its upper part which is largely devoid of shale. The overlying Red Hill Oolite is by far the most favourable formation for hematite mineralisation. The greater parts of all the large Hodbarrow deposits lie within it (Figure 19), as do many of the replacement deposits and sops in Furness (Figure 28). Two physical characteristics of the formation may have contributed to its suitability as a host rock for large replacement orebodies. The limestone, although mainly massive, is always severely jointed, and it is a calcarenite of relatively coarse grain: both of these factors may have facilitated permeation by mineralising fluids. The lower part of the Dalton Beds, consisting mainly of limestone, contains a number of small sops north of Dalton (Figure 27), and the formation has formed the higher part of the wallrock of veins in the southern end of the Lindal Moor field, including Lowfield and Lindal Cote, where there is a small flat in its upper part. The middle part of the Dalton Beds, with a higher proportion of shale, is mainly devoid of deposits. The Park Limestone, although forming the wallrock in the upper part of two of the largest sops–Park and Rita in the Roanhead district–has nevertheless proved disappointing elsewhere, notwithstanding its lithological similarity to the Red Hill Oolite. Extensive trials in it at Yarlside and Newton, beneath veins productive in the Urswick Limestone above, met with little success. The Urswick Limestone is perhaps second in importance to the Red Hill Oolite as an ore carrier and numerous large veins in the Stank–Newton–Stainton area (Figure 33) have been very productive in that part of the formation above the Woodbine Shale. Only one orebody of importance–Goldmire [SD 218 739]–has been found in the Gleaston Formation, which is generally unfavourable to mineralisation on account of its thick beds of shale. No orebodies are known where Permo-Triassic rocks form both walls of a fissure, but some large orebodies have been worked on the Yarlside Fault at Yarlside (p. 113) where St Bees Sandstone forms the hanging wall.

Depth control

All the evidence in the district points to the fact that the orebodies have only a limited vertical range beneath the surface. In many cases, of course, a limit is set by an unfavourable stratigraphical horizon being reached at depth, as at Hodbarrow where the main orebody bottoms on the Basement Beds. But, even in those cases where structural and stratigraphical controls still appear favourable, most of the important orebodies have been proved either to terminate, or to show conclusive signs of so doing, at depths of around −180 m OD. The deepest trials were at Park Mine where the sop was bottomed at −187 m. The neighbouring Rita and Nigel sops extended to −196 and −183 m respectively. The Stank South Vein oreshoot terminated at −192 m, and that of the North Vein at −172 m. The Low-field section of the Lindal Moor Vein was worked to a depth of −180 m, where it was found to be dying out. In the Moorbank South section at Hodbarrow, working continued to about −150 m, the orebody being still within the Martin Limestone but showing signs of pinching out, and at Whicham Mine, 4 km NW of Hodbarrow, the base of the orebody was reached at about the same depth. Most of the smaller orebodies were exhausted much nearer the surface. WCCR

Control of pre-Triassic surface

The presence of large quantities of St Bees Sandstone in the cores of the larger sops with only minor amounts of white, grey and red shale, can be understood only if it is accepted that this sandstone locally overlapped the Zechstein deposits on to a land surface of massive Carboniferous limestones. The lateral changes in the Permian and Triassic strata, and the overlap of the former by the latter, have been illustrated by Dunham and Rose (1949, fig. 3) and, despite subsequent minor modifications, this picture remains unchanged. The largest hematite deposits in Furness have been generated within a belt where the highly permeable St Bees Sandstone directly overlay the massive limestones, and where the pre-Triassic land surface had been re-exposed by erosion prior to the Quaternary glaciations. It is impossible to say whether the same was true at Hodbarrow, but nothing in the evidence precludes it. In a similar fashion Trotter (1937) concluded that the West Cumbrian ore deposits, where they have been followed beneath Permo-Triassic strata, are restricted to those areas where the permeable Brockram rests directly on Carboniferous limestones; where shale intervenes, whether of Carboniferous or Permian age, no deposits are found.

The conclusions for the two hematite districts are thus perfectly in accord; a clear control of mineralisation was the existence of free passage for fluids between permeable members of the Permian or Triassic sequence and the thick limestones of the Carboniferous. Because the latter had been uplifted and exposed during later Carboniferous and early Permian times, karst solution-features had probably already begun to develop on their surface before they were buried under Permo-Triassic sediments. KCD

Ore genesis

Historical summary

The origin of the hematite deposits, their age, and the source of the iron concentrated in them have been subjects for controversy over the past 120 years. A very brief summary is given here of the principal hypotheses previously advocated, recognising that any hypothesis which may be acceptable for the Millom–Dalton–Ulverston field must also account for the Egremont–Whitehaven field.

Sedgwick (1836) and Binney (1847, 1855) advocated an origin from waters associated with volcanic activity, and a pre-Permian age. Wurzburger (1872) and Shaw (1880) considered that the iron was derived from the old slaty rocks. Kendall (1876) in his first essay on the hematites thought that the iron was derived from the Coal Measures, but the discussion on his paper (1876, pp. 288–304) attracted contributions from Binney on the volcanic hypothesis, from Brockbank who believed that volcanic iron had been contributed to the Permian sea, and from Plant who advocated a metamorphic origin from limonite. Kendall later (1882) modified his views and advocated ferric chloride solutions associated with volcanism as the mineralisers, eventually coming to the view (1920) that the hematite field could be regarded as the outer zone of the Lake District copper-lead-zinc province. Macdonald (1925) also advocated an origin from magmatic solutions.

Goodchild (1890) proposed a totally different hypothesis. In his view, the iron was derived from the New Red Sandstone, and had been carried down into the limestone by infiltering meteoric waters in Triassic or later times. Bolton (1906) cautiously supported this, and the descendent view found a wholehearted advocate in Bernard Smith (1919, 1924, 1928), who nevertheless realised that the mineralising solutions 'could not be described as ordinary meteoric waters' (1928, p. 35). Dixon (1928), while admitting that many of the deposits in Carboniferous Limestone were beyond question deposited from downward percolating water, nevertheless believed that the source of the water was igneous and hydrothermal, rising in West Cumbria through veins in the Loweswater Flags of the Skiddaw Group and directly entering the limestone in some places, while in others travelling to the limestone through the New Red Sandstone. Trotter (1937, p. 70) stated that in the Egremont district 'borings are sufficiently numerous to enable us to delimit the underground extension of the St Bees Shales and it has been proved that the deposits... either lie outside, or close to the limits of the St Bees Shales. It would appear therefore that the St Bees Shales tended to act as an impervious barrier, and in areas where they are thick prevented the descending mineralised water from reaching the Carboniferous Limestone.' Trotter had thus developed further the notion of the association of the mineralisation with the overstep of Permo-Trias across Carboniferous Limestone, already recognised by Goodchild, Smith and Dixon. Nevertheless, after a careful examination of the reddened Carboniferous beds in the Carlisle Basin and Edenside, Trotter (1939) came to the conclusion that 'the theory of the origin of the West Cumberland haematites by meteoric waters descending from the New Red Sandstone finds no support in the reddened Carboniferous strata'. He later (1945) produced convincing evidence for the post-Triassic age of the West Cumbrian mineralisation, for some orebodies actually cross post-Triassic faults without being displaced. He now argued strongly that the mineral suite could not have been produced by meteoric waters, but required magmatic waters to be supplied to the Brockrams and thence to descend into the Carboniferous limestones.

At first sight, no reconciliation of these conflicting views is possible; but we believe that each has some element of the truth in it, and that a new hypothesis which will meet all the data can now be formulated.

Volcanic-sedimentary solutions

At the present time the only high-iron concentrations that can be observed in process of formation are the bog ores (where bacteria are important) , the laterites, and a number of submarine mineralisations in some of which volcanoes play an essential part. The ideas of Sedgwick, Binney and Brockbank must not therefore be dismissed out of hand. In the Andes, 290 km E of Antofagasta, Chile, a recent volcanic flow has been found to consist entirely of magnetite and hematite with a little apatite and quartz (Park, 1961). Externally the flow looks like basalt. Since temperatures of the order of 1500°C must have been involved, this observation is not relevant to Cumbria, save as showing that concentration of iron by magmatic differentiation, a process for which petrologists—for example the late L. R. Wager—have for long argued, undoubtedly occurs. Fumaroles associated with many volcanoes produce FeCl₃ (Mizutani, 1962), but more relevant to the present problem is the new volcano of Nea Kameni which erupted in 1952 in the centre of the great flooded caldera of Santorini in the Aegean Sea. Here a hematite sediment is actively forming, probably from sea water passing through the hot andesitic dacite (Butuzova, 1966). A bright orange layer 40 to 60 cm thick of Fe₂O₃ gel has formed, incorporating opaline silica pellets; beneath this a dark greenish layer contains ferrous corn-pounds where it is affected by H₂S from the volcano. According to Chukhrov (1973) the springs are at 30 to 40°C and the iron comes down as ferrihydrite (2.5Fe₂O₃ 4.5H₂O), which has a structure very like that of hematite and, provided the reaction proceeds fast enough, turns readily into that mineral. Another similar case is the Eseko Volcano which discharges ferriferous solution into the Okhotsk Sea (Zelenov, 1959). In the hot, hypersaline brine pools at the bottom of the central trench in the Red Sea (Degens and Ross, 1969) the deposits according to Chukhrov (op. cit.) are amorphous iron hydroxide, formed at 65°C; but at 115°C this changes into hematite. The Discovery Deep contains ferrihydrite. Chukhrov thinks that in all these cases, the volcanic contribution is principally heat, the metals being derived from adjacent or distant rocks by leaching.

Returning now to Furness, there are two obvious difficulties in the way of the volcanic-sedimentary hypothesis. The first is the absence from Cumbria of any substantial volcano or igneous intrusion of late Carboniferous or early Permian age that might have furnished the heat. The nearest volcano of this date is in the Midland Valley of Scotland; the nearest major intrusion the Whin Sill, east of the Vale of Eden, for the scale of the small basaltic sheet or sheets in the Namurian (p. 51) is quite out of keeping with the magnitude of the iron deposits. Secondly, there is the epigenetic character of the orebodies, a difficulty that Binney (1847) recognised when he remarked... 'whether the iron was injected into the place where it is now met with through the fissures immediately below, or was mingled with the waters of the sea which then flowed through the fissures and caverns of the limestone and gradually filled them up with the metallic matter, held partly in solution as Professor Sedgwick thinks, is difficult to determine'.

It is therefore necessary to conclude, albeit reluctantly, that a volcanic-sedimentary origin in the Stephanian–Zechstein interval is the least acceptable hypothesis. Nevertheless, igneous heat had its contribution to make, as will emerge later.

Descending meteoric waters

Introduction of iron oxides, including hematite, into the rocks beneath the basal Permian unconformity is very widespread in the north of England. Trotter (1939) reviewed the evidence in the north-west and showed that the staining of normally grey strata took place before the basal conglomerates of the Permian were deposited, and that water-worn pebbles of hematite were incorporated in these basal strata. In many cases, white or grey Zechstein sediments—for example the Grey Beds of Kirksanton—rest on highly stained Carboniferous beneath. In north-east England, a similar zone of red staining, averaging 8 m deep below the unconformity, affects the rocks almost irrespective of their lithology (Anderson and Dunham, 1953), and is covered by unstained Yellow Sands, the basal member of the local Permian sequence. Thus red iron oxide was filtering into the rocks of the Armorican uplands prior to their submergence under the Zechstein lagoon, but it is not possible to identify any concentrations formed at this time that have proved workable as iron ore. Although Trotter (1939) quoted E. B. Bailey's idea of the deep penetration of desert conditions, we do not regard hematitisation as a characteristic of deserts (Dunham, 1952), but instead suggest that extensive lateritic profiles developed at the end of Carboniferous times in hot wet climates similar to those of the hot tropics today. Where sufficient humic acid was available, some iron oxide was exported downwards from the profiles along with other elements removed in the lateritisation process (for examples see Borchert, 1960) , and deposited by reaction with underlying rocks, but not enough, in this area, to produce ore concentrations. It should be noted, however, that the widespread production of thick laterite soils and reddened rocks at this time created the reserve of red oxide which was to supply, throughout later Permian and Triassic times, the red pigment that coats the sand-grains and clay minerals of the St Bees Sandstone, the St Bees Shales, and much of the Keuper succession (Dunham, 1952). The normal Fe₂O₂ content of the local St Bees Sandstone, according to analyses quoted by Dunham and Rose (1949, p. 28) varies between 2.3 and 3.4 per cent: its approximate thickness is 1 km. Thus every km³ of the sandstone, if our figures are representative, contains 2.6 (assumed density) x 2.5 (assumed Fe₂O₃ content) x 10⁷ tonnes = 65 million tonnes of disseminated hematite.

As Trotter (1945) has shown from analyses of groundwater from the Bunter Sandstone, there is no possibility that any appreciable amount of this iron oxide could be transported by present groundwaters. The groundwaters of the Stephanian–Zechstein interval were probably more effective by virtue of their humic acid content, but nevertheless not effective enough to produce orebodies, and in any case could not explain temperatures of formation in excess of 100°C (see p. 87).

Igneous-hydrothermal waters

The objections to the correlation of the hematite deposits with the rather sparse non-ferrous mineralisation of the Lake District are several: (a) the complete lack of hematite in any Lake District lead, zinc or copper vein; (b) the greater geochemical complexity of the copper-lead-zinc deposits; (c) the lack of any paragenesis transitional between the two groups of deposits. The single copper occurrence, and the minor recorded amounts of baryte (which is blue and unlike the typical Lake District baryte) and fluorite (normally absent in the Lake District non-ferrous ores), in no way help the case. Moreover, there are considerations of age which need not be entered into here that are also unfavourable. Thus, even if we accepted a magmatichydrothermal origin for the non-ferrous ores (which we do not), we would not regard that as applicable here. Nevertheless Kendall, Dixon and Trotter were right in maintaining that the hematites formed at considerably above the normal temperature of 10 to 15°C now observed in the workings. How could this be achieved without invoking the residual fluids from crystallising magmas?

Formation waters

The answer lies in the fact that permeable sediments beneath 650 m depth, where they have been penetrated in the English Midlands (Downing, 1967) as elsewhere in the world, contain groundwater that is, in effect, hypersaline brine with up to six times the NaCl and KCl contents of normal sea water. These waters, because of the opportunity they give to form chloride complexes, are excellent solvents for those metals able to form complexes, especially at elevated temperatures (Dunham, 1970). It is almost certain that the subsidence of the St Bees Sandstone into the Irish Sea Basin was sufficient to bring it to depths where the temperatures exceeded 100°C; for example in the Portmore Borehole in Northern Ireland, the temperature in Bunter Sandstone at 1372 m depth had reached 62.8°C (measured by Dr W. Bullerwell). The gradient, 38.5°C/km, would give a temperature of over 100°C at 2.5 km depth. There appears to be an area, even today, of higher than normal heat-flow around the northern Irish Sea. For example, the Institute's Archerbeck Borehole, in Roxburgh, showed a temperature gradient of about 36°C/km (Bullerwell, 1961). If, by the time the tectonic events of late Cretaceous and Tertiary times occurred, the permeable St Bees Sandstone with its formation water had subsided to over 2.5 km, as Bott's (1964) and Bott and Young's (1971) gravity surveys suggest, the tectonic pressures could have driven the waters upward. There is also a WNW-trending magnetic anomaly observed by the Institute (Wright and others, 1971, fig. 8) commencing at about 25 km WSW of Barrow which might be interpreted as a substantial igneous intrusion of Tertiary date, and which might have started convective circulation of the waters: the cause of this anomaly, however, remains to be proved. (Figure 16) gives a speculative interpretation of what may have happened.

Thus, if it is accepted that in the Cumbrian hematite fields the mineralisers were hypersaline fluids driven up from the Irish Sea Basin between Furness and the Isle of Man, the source of the iron would be the New Red Sandstone. Leaching of these fluviatile deposits, which had received their iron from laterite being weathered on the surrounding iron-rich Carboniferous uplands, could readily yield the required quantities of iron. The effects of leaching would not of course be visible in Furness, but might appear at deeper levels below the Irish Sea. There are good, though small, examples of leached zones accompanying fracture belts in the New Red Sandstone in north-west England; George Gill, near Appleby, shows this very well. Confirmation of the validity of the suggested process would be provided if we were able to indicate that leaching of St Bees Sandstone would yield the very simple solutions, more or less free of non-ferrous metals, that are required, but we have not been able to do the necessary experimental work.

When the warm ferriferous brines rising up-dip in the Permo-Triassic rocks reached places in west and south Cumbria where they had free access to already existing fractures, to replaceable limestones, and probably to karst features, they are believed to have descended into the limestones (Figure 16). Here, if the process began in Triassic times, there may have been a very low water-table in response to the now arid conditions (Dunham, 1952); a depth as great as 600 m below surface is quite possible. In that case, limestone solution would be very active, and not only would replacement attack the hanging wall of the veins, but in places old swallow holes would be greatly enlarged to produce the sops, while a low water table would also facilitate the outflow of the spent fluids. It is emphasised, however, that sop-formation took place beneath a cover of St Bees Sandstone, which eventually collapsed into the hollows (Figure 15) in much the same way as that postulated for the Ozark Plateau pots. If this is true for the sops, then the veins and flats were also mineralised under cover.

Some contribution of iron from leaching of the basement rocks cannot, perhaps, be ruled out. In an interesting study, T. J. Shepherd (1973) has concluded, on both structural and geochemical grounds, that the source-rock of the iron in the West Cumbrian field was the Eskdale Granite, the underground extent of which can be deduced from the gravity survey of M. H. P. Bott (1974). The geochemical argument comes from the enrichment in arsenic of both hematite ores and granite. While there is a similar enrichment in the South Cumbrian ores, no major granite is suggested by the gravity results, though there may be a small intrusion into the basement below Dunnerholme and the presence of a concealed intrusion beneath Silurian rocks near Soutergate and Ireleth has been suggested by Bott (1974). It is possible that the Skiddaw Group or the Borrowdale Group might have been leached of arsenic, but the structural evidence in South Cumbria does not suggest that the sub-Carboniferous basement is the main source of the iron, unless this was transported from elsewhere into the St Bees Sandstone.

The period of mineralisation must be placed as either late Triassic or as late Cretaceous–Tertiary; we favour the latter view. It was of definite duration, and had ceased before Tertiary erosion exposed the deposits to further denudation during Pleistocene times. Solution of the limestone, however, went on after mineralisation ceased. Unmineralised cavities, such as could be seen during the resurvey beneath Rita and Nigel sops, and the broken-up state of all the sop ores, proves that the sops continued to collapse, and perhaps were still imperceptibly moving downward when mining commenced. KCD

Details of mineralisation

Hodbarrow area

The distribution of the main orebodies is shown in (Figure 18)." data-name="images/P988102.jpg">(Figure 17) and sections across the area appear in (Figure 18). Prior to about 1860 the only occurrences of hematite known were those in the vicinity of the Old Mine, immediately north of Hodbarrow Point. In this area the Red Hill Oolite and Martin Limestone crop out at the surface, and guts and stringers of ore along joints and small faults prompted the start of an opencut near Towsey Hole perhaps as early as the end of the 17th century. The Old Mine at Hodbarrow was established about 1855 when veins followed north-westwards at shallow depth from near Hodbarrow Houses were found to widen out into a large irregularly shaped orebody which had the general form of a flat. The deposit was subsequently found to narrow and become thinner as development proceeded westwards and it appeared to terminate against the Lowther Fault. However, in 1860 boreholes to the west of the fault proved a substantial body of ore at a deeper level and the vast extension of the Old Mine deposit to the west and north was disclosed. Subsequent exploration proved further extensions of the orebody southwards.

During and immediately after World War I, when most of the ore had been extracted, an intensive borehole campaign resulted first in the discovery of vein orebodies in the Red Hills area, north of the Old Mine, and, a few years later, of the two relatively large orebodies at Moorbank. The shallow Red Hills veins were opened up by means of a cross-cut at −61 m OD from No. 6 Pit [SD 1772 7892] on the eastern margin of the main orebody, but the situation and greater depth of the Moorbank deposits necessitated a new shaft, No. 11 Moorbank [SD 1668 7880], west of Steel Green. This was completed in 1931 to a depth of 175 m and a drainage level (Moorbank Adit) was driven from it at—108 m OD to connect up with the main orebody workings; this level was subsequently sealed on safety grounds, so that the new workings would be isolated from the rest of the Hodbarrow area in case of flooding.

In the early days of mining the extraction of the main orebody was constantly hampered by inrushes of water usually accom panied by mud and silt. Although these hazards were to some extent reduced by the construction of the Inner Barrier, and in 1905 of the Outer Barrier, major inundations still occurred as development proceeded southwards under the old foreshore of the Duddon towards the Seawards area (see (Plate 7.1)). It was eventually realised that the top-slicing method of mining in use, in conjunction with the geological conditions, was the main cause of the trouble. This method involved the removal of the ore by pillar and stall, working from above downwards and allowing the roof to collapse as extraction proceeded. Where the ore lay directly beneath boulder clay this method worked reasonably well as the roof subsided evenly and gently without fracture, thus maintaining the seal between the mine workings and any accumulations of water in the superficial deposits. But farther south, where the ore dipped beneath a thickening limestone cover, subsidence resulted in sudden fracturing of the roof and of the drift deposits above, which in this area included thick beds of sand and silt heavily charged with water. In 1922 a more costly but safer method of mining involving hydraulic stowing ('sand filling') was tried out and soon became standard practice. The method has been described in detail by Jones (1932) and more recently by Holland (1962). Major inundations due to subsidence were thereafter largely controlled, although troublesome inrushes of sea water continued to occur in the Seawards Area. In the new workings at Moorbank large water-filled cavities in the limestone and hollows on the sub-drift limestone surface caused several inrushes accompanied by mud and silt during the development of the ore deposits.

In 1938 the average quantity of water dealt with by Cornish pumps at No. 8 and No. 10 pits, serving the workings of the main orebody and the Red Hills Area was 700 to 1000 gpm. The Cornish pumps, one of which had been in use since 1878, were eventually replaced by electric pumps. The electric pumps at Moorbank No. 11 Pit dealt with an average of 300 gpm, increasing in later years to 500 gpm.

A useful summary account of the history of Hodbarrow Mine is given by Smith (1924), and more recently the full story of this remarkable mine, from its earliest days to 1968, when the pumps finally ceased operation, has been told by Harris (1970).

The chief orebodies in the Hodbarrow area and their geological relationships are described below.

The Main Orebody

The boundaries shown in (Figure 18)." data-name="images/P988102.jpg">(Figure 17) are based on the maximum outline in plan as proved during mining operations; because most of the margins of the orebody were steeply inclined, the outline did not vary greatly level by level. The maximum width of the ore-body from east to west was about 540 m excluding the Old Mine deposit, and that from north to south about the same figure excluding the Seawards Area. The maximum thickness was about 33 m, with an average of 20 m in the central part. The geological features of this large flat are shown in (Figure 19). It lay mainly within the downfaulted trough between the Old Mine and Lowther faults on the east and the No. 1 Pit Fault on the west. Over the greater part of its extent hematitisation was concentrated within the lower part of the Red Hill Oolite and the upper part of the Martin Limestone (Figure 18) and (Figure 19).

In detail the horizon of the base of the orebody varied slightly, probably due to differences in the ratio of shale to limestone in the Martin Limestone. For instance on its eastern side, in the Old Mine, and in the Seawards Area, the base lay near the middle of the Martin Limestone whereas in the north and west it was closer to the top of the Basement Beds. In the central part and in the Old Mine a few so-called roots were found to an otherwise flat base but none of these persisted far in depth, and none penetrated to the Basement Beds (Figure 18).

The general dip of the beds and of the orebody is to the south-south-west at an average angle of 5°. In its northern part the ore-body cropped out at rock-head beneath a drift cover of up to 60 m, suggesting that a considerable quantity of hematite was removed by erosion either before or during Glacial times. Southwest of a line approximately corresponding with the old coastline the orebody had a limestone cover which increased gradually with the dip to about 30 m in the Seawards Area; it was overlain by up to 55 m of drift.

On parts of its western and eastern sides the orebody terminated abruptly against the footwalls of the No.1 Pit and the Lowther faults respectively, where the ore-bearing horizon was thrown against the lower part of the Martin Limestone and the Basement Beds. Both faults were exposed underground at different levels and, where seen below the orebody, were clean-cut fractures showing little or, more often, no trace of hematite-staining, and thus afforded no evidence that they acted as feeder channels from below. Extensive exposures of the Martin Limestone and Basement Beds in levels driven beneath the orebody similarly were free from any significant traces of hematite.

In the southern part of the Seawards Area mineralisation became more patchy as the Outer Barrier was approached, the ore tending to be concentrated in veins or ginnels with a NW–SE trend separated by blocks of partially replaced limestone. Further trials southwards indicated that the deposit was dying out in that direction although exploration beyond the Barrier was limited to one unsuccessful borehole (Figure 19).

Exposures of the orebody underground, and especially of unfaulted contacts between ore and limestone, provided clear evidence of the replacement of limestone in situ by mineralising solutions. At one locality on the −255ft Level, 75 m E of No.1 Pit, thinly bedded fine-grained limestone with scattered thin shale partings (upper beds of Martin Limestone) passed sharply into hematite through a vertical contact. Although the hematite was in the form of small kidney ore, bedding planes and joints could be traced into the hematite, and some shale partings extended across the contact into the hematite. Some cases were noted underground where massive hematite contained traces of the original bedding planes showing the regional dip of the host rock. Numerous specimens of fossils replaced by hematite have been recorded. Where the margin of the orebody was determined by a fault, or where replacement of limestone traversed by minor faults had occurred, the ore was commonly much broken suggesting the replacement of a fault-breccia. Where not determined by a fault the orebody tended to terminate abruptly against a steeply inclined or vertical limestone face, probably marking an original major joint.

A small section of the workings in the Old Mine known as Lowther Stopes was still accessible during the resurvey. This was situated on the upthrow side of Lowther Fault close to Lowther Pit. The ore occurred in large irregular pockets, uniting in places to form a flat-like deposit at the base of the Red Hill Oolite. Many upward extensions from the flat several metres in width extended up to the boulder clay roof. Contacts between ore and host rock were sharp, but the limestone was commonly dolomitised for up to 2 m from the ore and contained some minor hematite impregnations.

Apart from a marginal zone up to 2 m wide of small kidney ore which was invariably present, the main orebody consisted of 'hard blue' hematite with only very few lumps of 'stone' (unreplaced limestone or dolomite). Large kidneys of hematite were occasionally found, usually lining cavities, but were more common in the Old Mine and were up to 0.5 m in diameter. Many of them were accompanied by ore encrusted with calcite crystals. Some pencil ore was also found in the Old Mine, as were cubes of hematite that were clearly pseudomorphous after either fluorite or pyrite.

Red Hills Veins

These deposits were discovered by boreholes in the neighbourhood of the small outcrop of Red Hill Oolite in this area, which shows extensive signs of hematitisation along joints and small faults where exposed in a large quarry. One borehole (SD17NE/94) proved a series of bands of ore in the Martin Limestone, the ore in aggregate amounting to about 5 m. The lowest band occurred near the base of the formation, which is here about 30 m thick. A crosscut was driven at about −60 m OD from No.6 Pit: it started in the Basement Beds and entered the mineralised ground in the Martin Limestone near the above-mentioned borehole. Further development disclosed four principal veins (see (Figure 19)). The general dip of the beds in this area varies from 5°–15° east to north-east, the veins being located along NW–SE faults throwing down to the south-west and thus tending to counteract the effect of the dip. The throw of the Main Vein fault is about 30 m, that of the others considerably less.

Although the oreshoots were essentially vein-like, considerable replacement had occurred, usually along the hanging-wall, and had given rise to irregularly shaped orebodies having the character of flats in places. The oreshoots had their greatest lateral development where the Martin Limestone and the lower part of the Red Hill Oolite formed the hanging-wall; that of the Main Vein was nearly 180 m in length, and that of the others somewhat less. In the lower parts of the workings the oreshoots ended abruptly against the footwall of the vein where it was formed of Basement Beds and the lower shaly part of the Martin Limestone, but in the higher levels adjoining veins coalesced in places, the width of the oreshoot increasing from the normal 5 to 10 m to over 25 m. Most of the oreshoots were proved to extend up to the sub-drift surface. Where exposed underground the footwalls of the veins dipped south-westwards at 45°–50°.

The ore deposits of this area showed abundant evidence, similar to that described above in the case of the main Hodbarrow ore-body, that they were formed by the replacement of limestone by hematite, and that this was controlled by faults in the limestone which acted as feeder channels for mineralising solutions descending from above.

Unlike the ore from other Hodbarrow workings that from Red Hills usually contained a little silica in the form of small grains of quartz mixed with the ore. A particular type of partially hematitised siliceous limestone known to the miners as 'red rat' was found in places on the margins of the oreshoots.

Moorbank South

The first indication of the presence of an ore deposit below the western part of the area enclosed by the Outer Barrier was obtained in 1924 (SD17NE/58). Further boreholes and the subsequent development of the deposit from No. 11 Moorbank shaft, showed that it consisted of a highly irregular vein-like oreshoot elongated in a NW–SE direction and dipping south-west at about 45° (Figure 19). It is clearly closely associated with the Moorbank South Fault, which has a downthrow of about 20 m to the southwest, but several smaller parallel faults to the south-west (not all shown in (Figure 18)." data-name="images/P988102.jpg">(Figure 17)) give rise to a fault belt across which replacement of limestone has taken place to varying degrees; it is the cornbined effect of the faults which was responsible for the irregular form of the deposit. The main fault was exposed at several places in the workings and most of the smaller faults in development headings. Towards the western margin of the deposit two or three of the smaller faults appear to throw down to the north-east suggesting that the position of the orebody may be determined by a shallow fault trough, but the evidence is less conclusive than in the case of the main orebody and that of Moorbank North.

The host rock is the lower part of the Red Hill Oolite, the general dip of which is 10°–20° WSW, although the direction appears to change locally to a more north-westerly one in the southern part of the mineralised ground. Boreholes indicate that mineralisation did not extend down into the Martin Limestone as elsewhere at Hodbarrow, and this was confirmed in the workings. Although the exact course of the Moorbank South Fault could not be traced through the workings it would seem that replacement of Red Hill Oolite also occurred on the footwall side leaving no clean-cut footwall boundary to the oreshoot. Contacts between ore and country rock along most margins of the deposit were, however, usually sharp. The ore terminated mostly against either steeply inclined to vertical walls or relatively flat surfaces in limestone or dolomite, which in many cases could be shown to be joints and bedding planes respectively, suggesting that these latter usually provided the final limit to the spread of the mineralising fluids.

Except for occasional 'horses' of dolomitised limestone near the margin of the deposit the Moorbank South ore was remarkably free from impurities. Apart from the normal marginal zone up to 1 m wide of small-sized friable kidney ore the orebody consisted of rubbly and blocky 'blue' ore in a matrix of fine granular hematite. It was almost silica-free and of a higher grade than the ore from the main orebody and Red Hills; indeed it exceeded in qualify any of the other hematites of Furness and West Cumbria. An average analysis covering the period 1933–37 was as follows: Fe 57.23; SiO₂ 1.02; CaO 4.02; H₂O 7.30; P 0.004.

Moorbank North

This deposit was discovered by boreholes soon after Moorbank South, and was also opened up by a heading (at–102 m OD) from the new shaft at Moorbank. The general form of the orebody is indicated in (Figure 19). It is another irregular vein-like deposit controlled by NW–SE faults, but with a more pronounced elongation along them than in the case of Moorbank South. The central part of the orebody was up to 45 m in width, however, and had more obviously the form of a flat. At its extremities to the north-west and south-east the oreshoot was found to split up into wide vein-like extensions, the maximum length of the main oreshoot exceeding 270 m. There are two chief controlling faults of opposite throw, which give rise to a small fault trough within which the mass of the orebody was found. Exposures in development headings indicated that the ground within the trough is traversed by several smaller parallel faults. The straight north-eastern margin of the deposit is determined by the footwall of the Moorbank North Fault.

The hematitisation was largely within the lower part of the Red Hill Oolite but extended a short distance into the Martin Limestone in some of the vein-like extensions to the south-east. The general dip of the beds in this area is 10°–20° to the south-west. In several places the ore was proved to extend up to the sub-drift surface, and in one instance a serious inundation of the workings occurred when a rock-head hollow filled with water-laden clay, silt and stones was unexpectedly breached. At lower levels in the workings similar difficulties were caused by water-filled caverns and fissures in the limestone.

The boundaries of the orebody were less well defined than at Moorbank South; they were commonly marked by belts of incompletely mineralised ground containing lenticular and wall-like 'horses' of limestone (many dolomitised) separated by steeply inclined narrow ginnels of ore parallel to the general elongation of the orebody and probably representing replacement along joints.

The ore from Moorbank North was similar in character to that of Moorbank South and of comparable grade and quality. WCCR

Askam–Roanhead–Park

A sketch-map of this area showing the stratigraphy, the principal faults, and the location of the ore deposits appears in (Figure 20). The mineralised areas are distributed over the low ground underlain by Lower Carboniferous rocks, between the high ground of the central part of the Furness peninsula and the Duddon Estuary; they extend from Askam southwards to a line through Goldmire and Sandscale, beyond which Permo-Triassic rocks crop out, and include the largest individual hematite deposits worked in Furness. The most important mines or groups of mines are discussed individually below.

Surface exposures of the solid rocks are confined to the ridge running from Housethwaite Hill to Hagg Hills, and to the immediate vicinity of the deep glacial channel whose course is followed by the railway line from Barrow to Askam. There is a small isolated exposure of Red Hill Oolite and Martin Limestone at Roanhead Crag beside the estuary. The rest of the ground is covered by superficial deposits, chiefly glacial in origin, up to 60 m in thickness (Figure 37). All the major ore deposits lie within this concealed area and were mostly discovered by boreholes. Knowledge of the solid geology thus comes largely from the interpretation of borehole information supplemented by evidence from such underground workings as were accessible for examination during the resurvey: it is, therefore, of necessity incomplete. While the general succession, distribution and structure of the Lower Carboniferous formations is now well known, there are almost certainly more faults present than have been positively identified and shown on (Figure 20).

All three of the main types of orebodies—veins, flats and sops—are represented, but the importance of this area as a hematite producer was mainly due to deposits of the latter type, the largest known sops in this country being those of Park, Rita and Nigel.

The general structure of the area is described in Chapter 6. The mineralised ground, with the minor exception of the Green Haume group of mines near Housethwaite Hill (p. 108), was bounded to the east by the Park Fault and its associated fractures. The footwall of the main fault, bringing in the Skiddaw Group, forms the eastern limit of the Park Sop, the westerly throw of the fault at this place being of the order of 750 m. Between the Park Fault and the Duddon Estuary the mineralised ground is traversed by several roughly parallel, but smaller, faults all of which have an easterly downthrow. The most important of these, from the point of view of the influence of structure on the distribution of hematitisation, is the California–Woodhead Vein (Figure 20) that, with the Park Fault to the east, gives rise to a fault trough, extending roughly north–south through the area, within which several of the larger orebodies were deposited. The Park Sop occupied the whole width of the trough. Two other faults, branching from the west side of the California Vein near Thwaite Flat, extend northwestwards through the Roanhead mining area and the positions of the large Rita and Nigel sops are in some degree related to one or both of them. The fault shown in (Figure 20) running ENE along the margins of Rita and Park sops, and which is intersected by the north-west faults, is another major structure and is unique in the area. It is, in detail, a narrow belt of parallel reversed faults associated with a southward-facing monocline; the combined effect is the equivalent of a throw of 150 m down to the south, bringing in almost the whole thickness of the Park Limestone against the Dalton Beds to the north (see section, (Figure 21)). The position of the structure, in close relation to that of the two sops mentioned, suggests that it also must have had some important control over their formation. The ENE-trending fault shown along the margin of the Sandscale Sop may be a similar structure.

The influence of stratigraphical controls on ore deposition is no less striking, most of the orebodies being found only at particular horizons in the Lower Carboniferous sequence. All the formations of the latter are present in the area and their outcrops may be regarded as forming the much-faulted western limb of the Park Anticline. The dip of the beds is generally to the south-west at 10°–20° so that the lower formations crop out in the north around Askam with the newer formations coming in successively to the south, the outcrop of the Gleaston Formation being limited on its southern side by the Sandscale Fault bringing in Permo-Triassic rocks. In the north the Greenscoe–Sandys orebody, the Woodhead Sop and veins, and the Burton Pipe all occurred in the much-faulted outcrop of the Martin Limestone and Red Hill Oolite; the large sops of Sandscale, Rita and Park, and some of the California deposits, were mainly in the Park Limestone. Nigel Sop, exceptionally, was within the Dalton Beds in its higher levels but extended down to the base of the Red Hill Oolite. Farther south the Urswick Limestone carried a few small orebodies along the California Vein but, like the Dalton Beds, was generally unfavourable to ore deposition in this area. The orebodies worked at Thwaite Flat and Goldmire occurred in the Gleaston Formation–probably at horizons within it where limestone predominated over shale.

Evidence from the sops in this area together with the general form and distribution of the ore deposits, show more clearly than in the other mineralised areas of South Cumbria that the hematite mineralisation was related to an eroded platform of gently-folded and much-faulted Lower Carboniferous rocks which approximated to the present sub-glacial surface.

Greenscoe–Sandys

The form of this orebody more closely resembled those of the Hodbarrow area and of West Cumbria than any other in Furness. It lies within the northern part of a fault trough formed by the Park Fault (which in this part has a western branch) and the California–Woodhead Vein. Parts of the Greenscoe section approached very close to the surface and in places may have cropped out. The orebody consisted, essentially, of a series of flats, formed at the junction of a W–E fault with two major N–S to NW–SE members of the Park complex (see (Figure 20)). The stratigraphical control of its position is very evident, for it was formed at or near the base of the Martin Limestone, resting on the Basement Beds. Its shape in Greenscoe mine was highly irregular, and a series of

NNW-trending ginnels were followed from both sides of it. These seem to have been formed by the direct replacement of limestone along joints, for Kendall (1882) recorded the discovery of a shale bed which passed from the limestone through the ore in one of them. The thickness of the flat in the Greenscoe mine was calculated by G. C. Greenwell (1866) to be 671 ft (20.6 m), and to him belongs the credit for having first recognised the form of the deposit, a conclusion which Kendall resisted for some time before accepting.

The beds here dip to the south-west at 15°–20°, and near the boundary with the Sandys section of the mine the deposit was under a substantial cover of limestone, as shown by the section of Sandys No.2 Pit (SD27NW/489) sunk directly to the flat. It continued to dip south-westwards until the western branch of the Park Boundary Fault was encountered. This branch here comprises two distinct parallel fractures, known as the Charity and Poverty ginnels, the effects of which were to throw the beds about 16 m down to the west. The flat continued westwards for about 100 m still resting on the Basement Beds, but at a greater depth due to the fault. The dip of the beds and of the flat increased to 26°, the base of the flat reaching a maximum depth of–139 m OD on top of the Basement Beds, where the dip of the beds abruptly flattened in the central part of the fault trough in which Sandys Mine is located. An unreplaced bed of limestone seems to have split the flat into an upper and lower part in this portion. On the flat bottom of the fault-trough, the quality of the ore in the flat greatly deteriorated and, although the deposit is said not to be exhausted at this level, the workings were abandoned in 1923 after at least 75 years of continuous production.

On the west side of Charity ginnel the main flat is bounded to the north by a W–E fault that extends eastwards across the Greenscoe section of the orebody. East of the ginnel, however, the flat extended across the fault and, in addition, there is an irregular subsidiary flat following the course of the Park Boundary Fault north-westwards from the main flat. In places the ore ran up into the limestone, but above the main level of the flat. The last ore-shoot worked in the Greenscoe mine was such an extension according to a report by J. D. Kendall.

It seems clear that the Greenscoe–Sandys orebody was formed almost entirely by direct replacement of limestone, and it is not surprising, therefore, that the ore was of the massive hard blue variety, similar to that of parts of the Hodbarrow deposit and those of the West Cumbrian mines, but of a different type from the broken-up material in the sops.

An attempt to discover a continuation of the flat southwards from Greenscoe property was not successful. A little ore was obtained in Knotts Pit [SD 2138 7648] on N–S and NW–SE faults running south from the flat, but further trials and many deep bore-holes to the south and east failed to find any continuation of the orebody. It seems questionable, however, whether the western branch of the Park Fault has been explored adequately in that part lying about midway between Sandys and Park Mines (Figure 20).

At the Greenscoe mine the orebodies were worked from eleven shallow shafts, the workings extending from Ordnance Datum to about–39 m OD. The deepest level was at −48 m OD, running west-south-west from No.10 Pit [SD 2138 7661]. Beyond the northern limit of the orebody, a single shaft, B3 [SD 2111 7677], gave access to the workings on the Chapman's Lot royalty, the deepest level being the 84-yd Level (−47 m OD). A cross-cut at this level explored the ground for 90 m N of the shaft, while another cross-cut, in limestone, ran 120 m WSW at the 64-yd Level (−29 m OD). There were five shafts on the Sandys royalty; three were sunk directly into the orebody, Shaft S3 [SD 2129 7647] to the south of it, and Shaft S5 [SD 2093 7661] to its west.

Woodhead Vein

The main fault-trough is bounded to the west by the Woodhead Vein. This has been worked from four levels: 59yd (–33 m OD), 71yd (-45 m OD), 88yd (−60 m OD), and 105yd (−76 m OD). The vein dips to the east at 45°–50°. The greatest length of stoped ground lies between the 71- and 88-yd levels, where the oreshoot is 550 m long. The stopes extend only two 'heights' (about 3 m each) below the 88-yd Level and were never carried down to the 105-yd Level, the ore at this level being considered too poor to work. Over much of its length the vein seems to have been little broader than the normal width of a level, but in the neighbourhood of Woodhead No. 3 Pit [SD 2086 7621] the oreshoot swelled out and in places reached a width of 13 m. There was another wide place in the vein near Woodhead No. 5 Pit [SD 2077 7645].

Martin Limestone forms the footwall of the oreshoot; Red Hill Oolite and Martin Limestone the hanging-wall. Adjacent borings suggest that on the footwall side, the top of the Basement Beds must have been encountered on the 105-yd Level about 60 m NNW of No. 3 Pit but confirmation of this is lacking. The throw of the vein at this point is probably about 60 m.

The oreshoot pinched out both to the north and south. Borings on the estuary north of the vein failed to prove any substantial continuation of the orebody in this direction, while borings to the south have found only iron-stained dolomitised limestone on the supposed course of the vein. Some ore remains below the lowest stopes but it is of a poor quality.

The main operating shafts were Woodhead Nos. 1 [SD 2077 7625] and 2 [SD 2074 7621] on the footwall side. Other shafts were sunk on the hanging-wall side and entered the vein at depth. Cross-cuts joining No. 1 Shaft to the levels in the vein were continued beyond the hanging wall at the 71- and 105-yd levels, and proved two subparallel veins or joints of ore, one of which may be continuous with that proved from the surface by Woodhead No.7 Shaft [SD 2098 7606], farther south. Neither proved sufficiently productive to justify stoping of the ore.

Woodhead Sop

This is the northernmost sop in the area and lies west of the Woodhead Vein. The orebody occupied a depression in the Martin Limestone about 110 m long, 30 to 45 m wide and 44 m deep, extending from −26 m OD to −70 m OD. The orientation of its long axis was west-north-west, parallel to the strike of the host rock. Its outline was irregular. Apart from a thin lining of clay between the limestone walls and the ore, the filling of the depression consisted of good quality hematite, associated on the south between −53 m and −70 m OD with manganese ore, the mineralogical nature of which is not known.

The sop was worked from Woodhead Nos. 1 and 2 pits. From No. 2 Pit a cross-cut was driven W17°S for 210 m, proving a WNW-trending ginnel 142 m from the shaft. The cross-cut appears otherwise to have been in limestone.

Burton Pipe and Ginnels

The pipe was found by boring and is about 16 m in diameter. It was worked from–10 m to–41 m OD. Near the bottom it splits into two roots. It lies entirely within the Red Hill Oolite, which has in this neighbourhood been extensively dolomitised. Burton Shaft [SD 2068 7593] lies 48 m W of the pipe, which is reached by levels at −16 m OD and −35 m OD. Both these levels were continued east of the orebody, but failed to find other workable bodies though many reddened joints occurred in the dolomite. The joints strike N25–30°W, and most dip to the east. Several have been explored by vein workings north and east of the pipe at −25 m OD. A prominent joint which was discovered near the shaft on the level at −11 m OD has been explored both north-west and south-east of this level. To the south-east small orebodies of the ginnel type, lying between limestone walls which had been much worn by water action, were discovered on and parallel to the line of this joint. The ore here resembled that in the sops in consisting of broken fragments of hematite. These were set in a matrix that contained clay, with rounded pieces of limestone and fragments of chert. The chert is considered to have come from the middle part of the Dalton Beds, not less than 90 m above, indicating a substantial mechanical movement of material within the ginnel.

Roanhead–Sandscale

The great Nigel Sop worked from the Nigel shafts [SD 2025 7554 and 2032 7561] was discovered in 1902 and was worked until soon after World War II. The depression in the limestone is at least 300 m long and up to 150 m broad, and proved to be nearly 180 m deep. In plan it is ellipsoidal though irregular in detail. A cross section (Figure 22) suggests that the depression may have been formed by the union of two very large cone-shaped swallow holes, the eastern one being the deeper.

The country rock ranges from the upper shaly part of the Dalton Beds, which was encountered in the highest workings on the south side, to the top of the Martin Limestone. Apart from the small thickness of shaly beds at the top, the section consists of bedded and massive limestones, oolitic limestones and, near the bottom, intercalated calcite mudstones. Patchy dolomitisation occurs, especially in the Red Hill Oolite.

The outer lining of the depression consisted of a conglomeratic mass of subangular and well-rounded limestone blocks in a matrix of brown stiff clay, known as the 'rubble'. Since this material lay between the orebody and the limestone walls of the depression, the precise limits of the depression were not proved for the workings ceased where they entered the rubble. The blocks in the rubble were almost all of limestone, each one having a soft white crust of partly decomposed material a few millimetres thick. Chert fragments were abundant, and Smith (1924) recorded some of grit and sandstone, presumably from the Gleaston Formation, though none was found during the resurvey. 'Black muck', consisting in part at least of decomposed black shale, and 'hunger' (clay formed from reconstituted shaly material of a paler shade) were found in places. No red sandstone or sand of the St Bees Sandstone type was found, nor was there any record of such material from the rubble. A borehole made to test the ground in the centre of the depression proved 137 m of rubble, but as shown on the section (Figure 22) this borehole must have gone down near the junction of the two supposed swallow holes. As far as the evidence goes, the lining of rubble was continuous, even in the very steep-sided western part of the depression where the walls of the orebody are almost vertical. Where seen, the contact between the rubble and the country rock was also steep, and the limestone walls were commonly much water-worn and contained joints filled with clay.

Between the rubble and the orebody there was a more or less continuous lining of bright red clay, from a few centimetres up to 3 m thick, known as the 'casing'. There were strong indications of movement throughout this clay in the form of vertically-striated slickensides, grooved where fragments of ore had been dragged along. The clay was mixed with hematite fragments adjacent to the orebody.

The next shell within the depression was the orebody itself. This lay in both parts of the composite depression, and at the highest working level—the 60-yd Level (–36 m OD)—a continuous sheet of ore extended between the two. Below this level, however, a ridge of rubble separated the orebody into two parts which continued separately in depth. The western part was elongated north-west, and did not extend far below the 138-yd Level (–102 m OD). The eastern part was more nearly circular in plan and extended to nearly–180 m OD.

Enclosed within each of the two parts of the orebody there was a core of red sand and sandstone, with a little red clay. Apart from their darker and richer colour, due to impregnation with hematite, the sandstone blocks were identical texturally with the St Bees Sandstone farther south. Within the core the blocks lay in a haphazard orientation, indicating that the sandstone was not laid down in its present position. In the eastern part of the orebody the sand extended down to −50 m OD. The texture of the ore, the striated casing and the broken-up sandstone blocks all point to considerable downward movement of the several linings of the depression. Within the orebody the occurrence of large masses of solid ore was rare, the normal texture being a breccia of fine particles of hematite. The ore proved to be pure and of good quality in much of the orebody, and any admixture of clay was small. Thin quartz veins, terminating at the edges of the fragments, were common, and there was a general tendency for the amount of silica in the ore to increase towards the sand core, whether due to admixture with sand or an increase in quartz-veining could not be ascertained. The downward movement of the orebody since its formation has not only been responsible for the breaking up of the ore, but also for the admixture of ore with rubble and for the tendency of the orebody to run out in salients into the rubble, which was a feature of the most recent working heights near the 191-yd Level.

The first shaft sunk [SD 2025 7554] was Nigel I Pit, and from this the 60-yd Level was worked. It proved, however, to be too near to the subsiding ground, and another shaft, Nigel II [SD 2032 7561], was sunk farther north, well outside the depression. An air shaft [SD 2018 7537] was sunk south of the orebody, and the ore was extracted by means of top-slicing methods from the surface downwards, the ore being trammed to the shaft along a series of main levels between Nigel II Pit and the Air Pit, as shown on the section, (Figure 22). In the course of driving the upper levels a small oreshoot, the Nigel ginnel, trending NW between Nigel I and II shafts, was discovered and worked. Although there were obvious indications of movement on the fracture associated with this ginnel, it died out at depth.

East of Nigel Sop two small replacement orebodies in the middle part of the Dalton Beds have been worked at Billy Pit [SD 2046 7550]. These are reminiscent, on a small scale, of the Red Hills Veins at Hodbarrow. In part they were transgressive to the bedding, dipping at about 45'; upon encountering a thin chert bed, however, one flattened out and followed the bedding above the chert at 15°–25° to the south. These orebodies were worked on and above a level at −25 m OD. An attempt was made to find their continuation in depth at the 80-yd Level ( −49 m OD), but here the cross-cut, which ran SSW from the shaft, encountered what is believed to be the northward continuation of the Violet Fault (Figure 25) at 76 m from the shaft. Striae on one of the walls of the fault dip SE at 70°.

Billy Pit was sunk primarily for exploratory purposes on the site of a borehole which proved ore and limestone. On the 53 yd 2 ft- Level a drift was driven 52 m from the shaft, and from a chamber at the end a fan of horizontal boreholes was put out to explore the ground within a radius of about 120 m round the shaft. Several boreholes inclining downwards were also made. The horizontal holes to the south-west and south-east encountered the shaly upper Dalton Beds, and one to the south-west probably passed through the Violet Fault, though this carried no ore. Other exploration levels from this shaft gave unpromising results.

A highly irregular orebody–the Sandscale Sop–has been worked from Peggy [SD 2017 7512] and Ethel [SD 2021 7518] pits and a western extension of it was wrought from Sandscale No. 1 Pit [SD 2003 7525]. It lies in the lowest beds of the Park Limestone and in the uppermost Dalton Beds. The exact nature of the body is in some doubt but it is probably the bottom part of a sop that, before erosion, covered a greater vertical range. It may be noted in passing that this orebody terminates downwards at much the same stratigraphical horizon as the great Park and Rita sops though this horizon lies much nearer to the surface at Sandscale No. 1 Pit. The workings are shallow on both sides of the boundary. No definite sand core was found, but the ore from the Sandscale workings is said to have been highly siliceous and not of good quality. Exploratory crosscuts were put out to the west and south from the base of Sandscale No.1 Pit at about −66 m OD and, although driven over 150 m in each direction, no further deposits were found.

Comparable in size with Nigel, the Rita Sop of the Roanhead group of mines provided a substantial part of their production for the years 1875 to 1925 when it was exhausted. It resembled the Nigel Sop in having apparently been formed by the union of two large swallow holes, though here the western was the deeper (see (Plate 7.2)). The country rock was Park Limestone and the underlying upper part of the Dalton Beds. The Violet Fault ran into the middle of the depression (Figure 23), with the Betty Fault adjacent to its western margin; the northern side of the depression was bounded by an ENE-trending monocline and reverse fault-system (p. 98), which was cut by two shafts (Rita and Kathleen) sunk on this side of the orebody. A study of the southern margin of the depression revealed a number of linear NW-trending offshoots comparable with, though less well developed than, the one that marks the course of the Violet Fault. These may follow the lines of small faults, but critical data of any displacement are lacking.

There was no separate lining of rubble to the sop, but where the ore was in contact with the limestone it was in places of poor quality and associated with black muck (Smith, 1924). It was not possible to establish whether this was equally true where the country rock was Park Limestone and where it was Dalton Beds; it seems much more likely to have been so in the latter case. The muck is said to have been not unlike the clay of the rubble at Nigel Sop but was blacker, as might be anticipated from the greater thickness of shaly Dalton Beds here involved.

The orebody consisted of two shells of hematite lining the two former swallow holes, linked by a bridge of ore across the separating rock barrier. The eastern and western parts of the orebody were completely separated at −78 m OD, the ore having been worked down from −21 m OD. In the eastern part the ore was bottomed at −143 m OD; in the western at about −196 m OD. The bottom of the eastern part corresponds closely with the base of the Park Limestone, but in the western part the depression penetrates deeply into the Dalton Beds.

There are two central masses of sand and sandstone, forming a core to each part of the depression. More clay seems to have been present in the cores than at Nigel, and a plan showing the distribution of clay and sand in the cores at a depth of 80 yd has been published (Smith, 1924). Since it was not the practice here to extract the sand core in mining, the details of this plan may be inaccurate. Blocks of sandstone identical with those of Nigel Sop can be seen on the dumps of the shafts which worked this orebody. An oreshoot on the Violet Fault was worked from −2 3 m to −115 m, reaching 76 m from the outside of the sop at −60 m OD.

A flat-like extension westward from the fault was worked at–20 m OD. Another satellite orebody lay on the south-western side of the sop near Betty Pit [SD 2060 7497]. This apparently passed down into a linear structure at −93 m OD, and may be on the line of a small fault.

Access to the upper levels working the sop was from Roanhead No. 2 [SD 2090 7520] and Roanhead No. 3 [SD 2094 7519] shafts on the east, and from Betty Pit on the south-west. Wilfred Pit [SD 2075 7505] gave access at −93 m OD. Three deeper shafts, Violet [SD 2070 7496], Rita [SD 2060 7522] and Kathleen [SD 2072 7530] pits are all sunk to the 233-yd Level (−200 m OD), which served the deeper levels. The underground workings from these three shafts were accessible during the resurvey and geological information obtained is included in (Figure 23). The position of the Violet Fault on the 233-yd Level indicates that its dip increases northwards.

Park

Several small orebodies lie between the Rita and Park sops. The largest of these is worked from Garden Pit [SD 2102 7526] and from some of the shafts serving Rita. The sop seems to have been entirely in Park Limestone, and it had a flat bottom on, or very near to, the top of the Dalton Beds. At this horizon (−47 m OD) a small flat spread out westwards from the sop. There was no sand core in this sop, and the ore is said to have been of good quality. Here the conditions more closely suggest direct replacement of limestone than do those in the larger sops, but it was unfortunately not possible to ascertain the textural nature of the ore, which was exhausted.

The Park Sop, the largest example of this type of orebody, was discovered in 1849 and was exhausted by 1921, having yielded ore which has been estimated at 12 to 17 million tons. It is perhaps significant that this great orebody lies at the intersection of the two major structural trends of the district–the fault trough between the California–Woodhead Vein and the Park Fault, and the ENE reverse fault–monocline (p. 98). At rock-head, the sop occupies almost the full width of the fault trough, but the sides of the depression diverged from the faults in depth (Figure 25). The reverse fault–monocline lies on the north side of the body, 30 m from the north wall at its nearest point. The long axis of the depression runs, like that of the Rita Sop, parallel to this fault system, and is 450 m long. The greatest width of the depression is 240 m. There seems to be good reason to suppose that this depression was formed by the union of several large swallow-holes, and remains of the partly dissolved barriers between these are evident from the accompanying plans and sections (Figure 25)." data-name="images/P988109.jpg">(Figure 24) and (Figure 25). The broad depression was bottomed near the 106-fathom Level (−150 m OD), but a funnel-shaped continuation near its centre was followed down to the 124-fathom Level (−185 m OD). Its depth is thus comparable with those at Nigel and Rita. Parts of its outer walls, in Park Limestone, were exposed in the subsidence over the worked-out orebody before this was flooded. They showed the usual evidence of solution action. The depression occupied the whole thickness of the Park Limestone and extended, over a restricted area, into the shaly Dalton Beds below. Slate of the Skiddaw Group on the footwall of the Park Fault was reached on the east side in the upper levels, but in depth there was a mass of limestone between the ore and the fault.

There seems to have been little or no rubble on the sides of the depression, but such material was recorded at the bottom, though there is too little evidence to indicate its limits on the plans. Much of the ore from the bottom levels was black and poor in quality, no doubt due to admixture with rubble derived from the shaly Dalton Beds. Clay or muck from a few centimetres to two metres in thickness separated the orebody from the walls of the depression.

The orebody was highly irregular in outline, and included within it some large masses of unreplaced limestone. On the south side a number of salients ran into the walls of the depression, perhaps controlled by bedding planes in the Dalton Beds. The ore seems to have been of the fragmental type common in sops.

The sand core was continuous at the surface but split up into several funnel-shaped masses in depth. Between the orebody and the core there was a discontinuous lining of clay, the distribution of which on the 50-fathom Level has been figured by J. D. Kendall (1921). The sand is said to have been quite free from ore, but there was some admixture of ore with the clay. However, Kendall (op. cit.) states that the junction between clay and ore was sharp and well defined. His eye-witness account of the sand core in the upper levels at Park is worth quoting: 'At the 60-fathom level the sand was mainly white, but some of it was red. That immediately adjoining the red was mottled. Both red and white were in places quite hard and bedded; the red there looked exactly like St Bees Sandstone. It seemed as if the binding material was being decomposed through exposure. Blocks that were quite hard in the centre became softer outwards and ultimately quite incoherent.... 'Many of the blocks of sand and clay are nearly plumb, and on their side adjoining the ore, are in parts more or less vertical.' It appears from sections of the orebody that there were masses of sand completely enclosed within ore, generally with a layer of clay between ore and sand. Sand from the core was mined for use as moulding sand.

On the south side of the orebody there are three satellitic pockets of ore, one of which near Burlington Pit [SD 213 253] was pipe-like in form. They were shallow only.

The orebody was worked from a series of shafts sunk outside the depression, and from levels at 40, 50, 60, 70, 82, 94, 106 and 124 fathoms. The main drawing shafts were Burlington Pit, Quarry Pit [SD 2143 7525], No. 1 (Plunger) Pit [SD 2098 7545] and No. 16 Pit [SD 2089 7534], which was later deepened to −157 m OD to give access to the deepest part of the orebody. This was, however, never reached owing to trouble with water, and it is possible that some ore remains on and above this level on the Roanhead side of the deposit.

For about 300 m N of Park Sop the ground occupied by Dalton Beds was extensively explored by boreholes and by some cross-cuts from exploratory shafts, especially in the vicinity of the western branch of the Park Fault, but no promising indications of ore were discovered.

California Sops and Vein

A line of three sops runs southwards from the Garden Sop. These are: California No. 1 Sop, Plevner Sop and California No. 3 Sop. The fact that they lie on a line parallel to the California Vein suggests that jointing parallel to this fracture may have influenced their formation, but there is no evidence of a more direct connection. The vein is nowhere in contact with the sops, and it dips away from them.

As noted by Smith (1924), there was a general southerly decrease in the proportion of ore to sand in the filling of these depressions. There was no sand core in the Garden Sop; California No. 1 contained a moderate sized core that extended almost to the bottom of the depression; in Plevner Sop there was much more sand than ore; and in No. 3 Sop the ore was only a thin discontinuous lining between the walls of the depression and the core.

The most productive of the California sops was No. 1. This was worked from the base of the glacial drift, near Ordnance Datum, to the 66-fathoms Level ( −99 m OD). The depression was shaped like a clover-leaf at the surface, but at the 50-fathoms Level, where the depression passed from Park Limestone into Dalton Beds, the orebody was elongated roughly parallel to the strike of the country rock. The ore of the Plevner Sop, which averaged only 3 to 6 m wide, was not of good quality and was very much mixed with black muck. The walls of the depression, which lay entirely in Park Limestone down to the 50-fathoms Level (about −60 m OD), were slightly decomposed, but showed no trace of dolomitisation. Solution action was, however, very evident. In the core, pale sandstone predominated, in places containing green clay galls. Very large blocks occurred in a matrix of sand and white or coloured clay; even where undisturbed by mining operations, it was evident from their orientation that they had been broken up and had collapsed. They were, however, sharply angular, and it does not seem possible that they were transported by water action.

The No.3 Sop is the only example of an orebody of this kind lying in the Urswick Limestone (see (Figure 26)). Like the Plevner Sop, it has not been worked to the bottom, and this is not surprising in view of the poor quality and thinness of the ore. It has been explored from the 19-fathom Level (OD), and from levels at −16 m and −28 m OD. A vertical boring from the level at −16 m OD near the centre of the sop recorded:

From the south side of the Park Sop the California Vein has been followed from the California No.1 Pit [SD 2108 7508], the chief levels being the 28-fathoms (−29 m OD), the 34-fathoms (−40 m OD) and the 50-fathoms (−70 m OD). Two principal oreshoots were proved. One with a maximum length of 210 m extended southwards from near No. 1 Pit; another extended southwards up to 109 m from No. 3 Pit [SD 2108 7470]. The former has been worked down to the 50-fathoms Level, although the ore was poor above the 28-fathoms Level. A series of underground borings proved that the oreshoot continued in depth for at least 43 m below the 50-fathoms Level, but further development in hand at the time of the resurvey was not long continued. The bottom of payable ore in the other shoot seems to have been reached at −41 m OD, but there was some tendency for this shoot to pinch southwards.

The dip of the vein in the California stretch averages 60°–65°, and is thus steeper than in the Woodhead portion; the dip decreases in the shaly Gleaston Formation. The country rock is, on the footwall, Dalton Beds, Park Limestone and the lower beds of the Urswick Limestone; the Gleaston Formation and the Urswick Limestone form the hanging-wall. The reason for the upward pinching of the northern oreshoot seems to have been the oncoming of shales of the Gleaston Formation on the hanging-wall. On the other hand the southern oreshoot was highly productive where the Gleaston Formation lay on the hanging-wall, but this seems almost certainly to have been due to the local presence of thick crinoidal limestones in that formation (see p. 44). There is evidence from an underground borehole of a shale bed below the northern oreshoot (presumably on the hanging wall), and this may be the Woodbine Shale. It lies about 90 m below the top of the Urswick Limestone, and may limit the extension of the ore-shoot in depth.

The ore in the vein is said to have been of the hard blue variety and not broken up as in the sops. Where accessible for inspection on the 50-fathoms Level, however, it was very broken, but these workings had been re-opened in collapsed ground. In this part of the vein the ore has a variable, and at times highly unfavourable, phosphorus content. Many hundreds of feet of exploratory crosscuts were driven on both the hanging-wall and the footwall of the vein. A small W–E vein encountered in limestone 39 m SW of No. 3 Shaft at the 28-fathom Level contained a few centimetres of baryte and malachite.

Thwaite Flat

A trial shaft was sunk about 120 m south of California No. 3 Pit in search of a southward continuation of the California Vein. The fracture was located at +8 m OD, but no oreshoot was found. A drift to the south on the hanging-wall side proved red shale dipping south-westwards, and a cross-cut into the footwall proved only limestone, presumably the Urswick Limestone. About 250 m farther south a small oreshoot on the California Vein was worked from Thwaite Flat Nos. 1, 3 and 4 pits [SD 211 743]. Permo-Triassic rocks form the hanging wall of the vein along this southern part, and Thwaite Flat No. 4 Pit was sunk in brockram underlying drift. Adjacent to the orebody, red sandstone dipping south-westwards was recorded. The footwall seems to have been the upper beds of the Urswick Limestone beneath the Gleaston Formation, and the oreshoot pitched southwards with the dip of the beds. It was followed from +6 m to −29 m OD.

Farther east, flanking the railway line about 150 to 200 m SE of Thwaite Flat Farm [SD 216 744], a number of small vein-like orebodies were worked from shallow shafts. These lay on the western branch of the Park fault-complex running N–S and on a linked NW–SE branch.

Goldmire

Three orebodies were worked beneath the alluvial flat west of Goldmire Quarry [SD 219 740]. These evidently lay within the complex of faulted ground that extends southwards from Park. The country rock is the Gleaston Formation and, though conclusive proof is lacking, it is suspected from an examination of borehole records and of the material on the dumps that these oreshoots were located where the coarse crinoidal limestone seen on Oxen-close Hill (p. 44) farther north came into contact with mineralising fractures. A N–S vein, dipping west, was worked from −1 m to −8 m OD from Nos. 4, 15 and 19 pits [SD 217 740] on the vein, and Nos. 1 and 2 pits [SD 218 739] 60 m E of the footwall. The vein was also tried at the 88-yd Level (−13 m OD). The outcrop of the Gleaston Formation is limited to the south by the Sandscale Fault which brings in the St Bees Sandstone. A flat-like body lying on the north side of this fault was worked from Nos. 7 [SD 2175 7388] and 14 [SD 2168 7392] pits. This dipped with the beds from +4 m OD on the east side to −27 m OD west of No. 14 Shaft; a little ore continued to the bottom level at −34 m OD which was otherwise in limestone. This oreshoot is considered to have replaced the crinoidal limestone of the Gleaston Formation referred to above. The Sandscale Fault, bringing sandstone against this limestone, was proved on the bottom level, 73 m SSW of No.14 Shaft.

A level running south from the floor of Goldmire Quarry proved the Sandscale Fault, here bringing the St Bees Sandstone against the Park Limestone. No ore was found at the junction.

Farther north an irregular oreshoot in the Gleaston Formation was worked from No. 18 Pit [SD 2170 7416] between two N–S faults which are the continuation of the Goldmire Vein. The workings were at −3 m and −11 m OD.

Other boreholes and shafts

Intensive boring of the area between Dunnerholme in the north and Sandscale–Goldmire in the south started around 1850 and continued until shortly after World War II. Journals and sites of over 650 boreholes are in the Institute records. In addition, there are numerous sites and partial records of other boreholes and trial pits. Space does not permit even a summary of the journals of all these boreholes to be published here; and indeed, because the orebodies usually lie directly under drift, most of the borings merely prove rockhead. From the data so obtained, however, contoured rock-head maps have been constructed and are more accurate than would be feasible in many other districts. These maps (Figure 36) and (Figure 37) thus summarise the results of most of the borings that prove only unmineralised limestone below superficial deposits.

In the Roanhead area a programme of deep boreholes designed to test for deposits at the base of the main limestones was carried out between 1906 and 1922. Though the programme met with little success, the results are important in fixing the position of the top of the Basement Beds between Askam and Nigel Pit and along the northern margin of Sandscale. Many of the holes merely enter the Basement Beds; others (e.g. (SD27NW/360), (SD27NW/451), (SD27NW/491) prove up to 116 m of the formation. KCD, WCCR

Dalton–High Crossgates

Sketch-maps showing the geology of most of this area and the location of the chief ore deposits appears in (Figure 27) and (Figure 29). It is notable that in the ground north and north-east of Dalton the deposits are almost exclusively sops, whereas farther east towards Lindal veins predominate. Whether in the form of sops or veins, however, it is clear that most of the deposits are associated with faults and are concentrated within the outcrop of the Red Hill Oolite and the lower part of the Dalton Beds. South and east of Dalton a few orebodies (Anty Cross, Highfield, Dalton and Lindal Cote) occurred in the upper part of the Dalton Beds, here mainly massive limestones, and in the Park Limestone. It is noticeable that the outcrop of the middle, more shaly, part of the Dalton Beds, which extends north-eastwards from Dalton towards Lindal, is mostly devoid of ore deposits.

The general trend of the faults is north-westerly, but faults of N–S and W–E trend also occur. It seems probable that, as in the case of the faults associated in the Park Fault system farther west and those of Lindal Moor, all the faults are part of a linked system of fractures and not of different ages.

None of the many sops that have been found and worked north and north-east of Dalton compared in size or in economic importance with those of Roanhead and Park, but several were over 100 m in diameter and were worked to a depth of over 100 m. An indication of the relative size of the sops in this ground and of their stratigraphical relationships is given in (Figure 28). The influence of faults on the distribution of the sops is well displayed at Elliscales, Mouzell and Eure Pits.

The area included in (Figure 27) is largely drift-covered and most of the deposits were discovered by boreholes; where the drift was thin some were found by sinking shafts along the likely extensions of faults known elsewhere to be associated with mineralisation.

The search for sops north and north-east of Dalton was more indiscriminate; it developed into one of the most intensive borehole campaigns on record in Britain, several hundred shallow boreholes being put down to rock-head within an area of only about a square kilometre.

In the years 1910–13, after most of the workings had been abandoned, three deep exploratory boreholes (SD27SW/375), (SD27SW/376), (SD27SW/378) were sunk to test the possibility of mineralisation at depth along lines of known orebodies to the south-east, but no promising indications were found, though they confirmed the general stratigraphy in the area and proved the platform of underlying Lower Palaeozoic rocks. The only new deposit of economic significance found in more recent years was that at Anty Cross near Dalton (see below).

Anty Cross

A vein deposit was discovered at Anty Cross by boreholes and developed during World War I; the mine was in production for a few years prior to World War II. An account of the vein as exposed underground has been given by Smith (1924). It was worked from two shafts in close proximity [SD 229 736], but although its width was up to 6 m in places and its length nearly 600 m it had little extension in depth. Workings were not carried below the 35-fathom Level ( +1 m OD); in a deeper trial level at −35 m the vein was proved but values were poor. The vein followed a WNW fault having a southerly downthrow that brings the Park Limestone against the Dalton Beds along the longer section of the vein lying east of the shafts. In the short, but highly productive, section west of the shafts the upper part of the Dalton Beds forms the hanging-wall with lower horizons of that formation on the footwall. An unusual feature of the vein was the common occurrence of copper ore (chalcocite) mixed with the hematite. A cross-cut at about +27 m OD was driven southwards for about 450 m with the dual objectives of exploring the ground and of connecting with a heading driven northwards from West Newton Mine; the project was not completed and no significant discoveries were made. Elsewhere in the vicinity of the vein the ground has been extensively drilled.

Green Haume

A small circular sop [SD 222 758] about 45 m across occurred in the Red Hill Oolite at Green Haume; it may be related to NW–SE faults in its immediate vicinity. It was worked beneath a thin boulder clay cover, first by means of an open cut and later from a shaft [SD 2225 7498] to a depth of about 35 m + 40 m OD). Small flats immediately west of the sop were discovered by boreholes in 1876, and this prompted further exploration by boreholes during World War II to test a NNW–SSE fault that flanks the eastern side of Housethwaite Hill; no deposits were found.

Dalton and Highfield

These mines worked small pockets of ore connected by vein-like bodies that are associated with a small ENE fault crossing the outcrop of the upper part of the Dalton Beds. Traces of copper ore have been recorded from these mines also. At Dalton Mine, workings from the main shaft [SD 2397 7381] reached a depth of about 78 m (−19 m OD) and the length of one body was about 270 m; the Highfield workings were much shallower and the orebody much smaller. The ground around the mines was explored by several short cross-cuts and by many boreholes.

Elliscales and Mouzell

A group of relatively large sops at Elliscales and Mouzell occurred within the Red Hill Oolite; some occurrences extended down into the Martin Limestone and a few, including the most northerly of the Mouzell deposits, lay wholly within the Martin Limestone. The sops are related also to a linked system of NW–SE and N–S faults, with the former probably exercising the greater control, and the W–E Mouzell–Berkune Fault may have had some influence over the northernmost Mouzell sop. Much of the ground between the known deposits was explored by boreholes and by cross-cuts at different levels.

To the south of these mines several smaller sops were worked in the lower part of the Dalton Beds; most were associated with the extensions of the NW–SE and N–S faults proved to the north.

Crossgates, Eure Pits and Tytup

A series of irregular sops in the lower part of the Dalton Beds and in the Red Hill Oolite was worked at Crossgates and Eure Pits. The deposits showed a marked concentration along NW–SE faults, especially near the intersections of these with the W–E Mouzell–Berkune Fault. The alignment of the string of Eure Pits sops along a NW–SE fault is strikingly shown by the subsidences into the old workings about 1 km N of Dalton on the road to Holmes Green. At the intersection of the Mouzell–Berkune Fault with the most westerly of the NW–SE faults, vein-like orebodies were worked to a depth of over 100 m (−32 m OD) for a short

distance along both faults from Colorado Pit [SD 2343 7536]. Several small sops were also worked from this pit. One or two of the sops at Crossgates and Eure Pits were of the order of 75 m deep, being bottomed at around +25 m OD, the depth of the others varying from 30 to 50 m; some of the larger sops had sand cores. The smaller scattered sops around Tytup also lay within the Red Hill Oolite, but their connection with faulting is less certain. Tytup No. 5 Pit [SD 2377 7556] was about 65 m deep; it also served two of the Eure Pits deposits.

High Crossgates and Backguards

These mines worked a vein of hematite along the WNW–ESE High Crossgates Fault, which has a throw of about 60 m down south. The vein, though not continuously mineralised, was proved over a length of about 1 km (Figure 29) with a dip of 45°–50° to the SSW. Over most of its length Dalton Beds occupy the hanging-wall, and Red Hill Oolite the footwall, but the latter formation comes in at depth on the hanging wall around No.2 Pit [SD 2414 7575], and it is in this section that the oreshoot was richest. Workings from this pit reached a depth of over 195 m (about −100 m OD) and the oreshoot plunged gently to the east-southeast probably in conformity with the general dip of the beds.

The eastern section of the vein was worked by headings driven from Backguards Pit [SD 2475 7586]; in these the oreshoot was thinner and, though it was followed to a depth of 135 m (−59 m OD), it died out before the workings reached the Mouzell–Berkune Fault. The expected continuation of this vein with one of those worked at Lindal Cote on the south side of the fault was never established.

The orebodies at Whitriggs Mines, the southern extensions of which were also worked from Backguards Pit, are described in the next section (Lindal Moor).

Lindal Cote and Grievson

The main vein worked from Grievson No. 1 Pit [SD 2495 7457] was along a NW–SE fault throwing down to the south-west. The ore-shoot was productive mainly near the pit, where the fault brought the upper part of the Dalton Beds and the lowest beds of the Park Limestone, on the hanging-wall, against a Dalton Beds footwall. Subsidiary veins and vein-like deposits were also worked on the hanging-wall side, probably associated with minor fractures and joints roughly parallel to the main vein. The vein was proved over a length of more than 700 m, the deepest workings being about 130 m deep (−50 m OD) from Grievson No. 1 Pit.

The vein worked at Lindal Cote North was along a parallel fault, both footwall and hanging-wall of which were in the Dalton Beds. The oreshoot was worked to about the same depth as at Grievson Pit, but had considerably less lateral extent. Another parallel fault about 60 m to the east carried a small irregular vein-like orebody in Dalton Beds; this was worked to a depth of 90 m (−15 m OD) from No. 2A Pit [SD 2512 7497] and other nearby shafts.

Drainage of all the Lindal Cote workings, which were heavily watered, was facilitated by a water level driven in 1855 at about + 35 m OD to Urswick Tarn, a distance of 2 km. Ventilation shafts for this level are said to have proved an interglacial lacustrine deposit (p. 118).

Berkune

The vein orebody worked at this mine occurred partly along the Mouzell–Berkune Fault and partly along a NW–SE fault which joins it from the south. About 225 m farther west, a NW–SE fault, carrying a vein with poor values, leaves the Mouzell–Berkune Fault on its northern side. The two NW–SE faults may be the same fracture, in which case there is a sinistral shift along the Mouzell–Berkune Fault; alternatively they may be distinct and independent fractures. Park Limestone formed the hanging-wall of the vein in the upper levels of the mine, both on the W–E and the NW–SE faults, with Dalton Beds on both footwalls. The vein was worked to a depth of 82 m (−22 m OD) from Pit No. 11 [SD 2556 7543], and to 136 m (−76 m OD) from Pit No.2 [SD 2578 7534]. KCD, WCCR

Lindal Moor–Whitriggs–Lowfield–Ulverston

This area contained the greatest concentration of vein-like hematite deposits in Furness. The distribution of these and their relationship to structure and stratigraphy is shown in (Figure 29). The chief structural controls were provided by the north-westerly trending Lindal Moor fault-system with its subsidiary W–E faults, referred to as 'cross-faults' by the miners, and the slightly more southerly Whitriggs group of faults, trending between Lindal Moor and Crossgates. The two fault-systems converge near Marton, where mineralisation was extensive; farther south they were separated by stretches of barren ground near Lindal-in-Furness. The mineralised parts of the intricate Lindal Moor fault-system, with which the largest deposits of the area were associated, are shown in (Figure 29), as are those of the faults of the Whitriggs group. Although the NW–SE faults appear to be shifted by the W–E faults, it is believed that both comprise a conjugate system and are of the same age. The general effect of the Lindal Moor fault-system as a whole is to shift the Carboniferous outcrops about 1500 m to the south-east on its north-eastern upthrow side, thus bringing the lower formations against a footwall of Silurian rocks between Poaka Open Works and Whinfield. Farther south-east, near GB4 Pit, Carboniferous Basement Beds form the footwall and Dalton Beds the hanging wall, and the south-westerly downthrow of the system is about 250 m. Three of the NW–SE faults of the Whitriggs group throw down in the opposite direction, giving rise to a shallow fault-trough within which lay the more valuable deposits of the Whitriggs area.

A notable feature of the Lindal Moor area was that, although deposits on the NW–SE faults were more continuous and generally more productive than those on W–E faults, replacement was frequently most complete and extensive at the junctions between the two sets: some of the richest parts of the oreshoots worked around Whinfield and Diamond Pit were so located.

It will be seen from (Figure 29), (Figure 30), (Figure 31) that mineralisation was richest within the upper part of the Martin Limestone, the Red Hill Oolite and–south-east of Whinfield and High Crossgates–in the lower part of the Dalton Beds; all these horizons are characterised by massive limestones and the absence of shale. Most deposits tend to die out as the veins enter the lower, more shaly, part of the Martin Limestone. At Lindal Moor replacement was most widespread in the Red Hill Oolite, especially its lower part. Accordingly the workings were shallow in the north-west where the oolite crops out and the first discoveries were made here: as the veins were followed south-eastwards the main ore-bearing horizon became deeper because the beds dip south-eastwards. At Whinfield and Lowfield some of the veins were productive in the Dalton Beds up to rock-head, but lower parts of these veins, mainly in the Red Hill Oolite hanging-wall, were richer, and were worked to depths of −120 m at Diamond Pit and −180 m at Lowfield.

Information about the general form of the orebodies comes chiefly from existing mine-plans, and from the records and publications of Kendall (1882, 1893, 1921), Schneider (1885), Wurzburger (1872) and Smith (1924). Typical examples of ore-bodies seen in cross-section, based partly on information drawn from the above-mentioned sources, are shown in (Figure 30) and (Figure 31). Their vein-like character and connection with the main faults are clear but, in detail, the deposits varied greatly in size and shape.

The lateral spread of mineralisation at favourable stratigraphical horizons on the hanging-wall side of veins was almost certainly easier where blocks of limestone between faults were broken up by minor fractures and joints. In such cases the vein swelled out to give rise to large irregular orebodies, some of which approached flats in form where replacement was complete; orebodies of this type up to 50 m in cross-section were worked on Lindal Moor. In the area between Lindal Moor and Whitriggs much of the ground between the main veins was partially mineralised in the form of thin veins, stringers and small irregular orebodies and flats.

The oreshoots associated with the NW–SE faults of the Lindal Moor fault-system were referred to generally by the miners as the Lindal Moor Vein (see (Plate 7.3)). Mineralisation along the main fault separating Lower Carboniferous and Silurian rocks was more or less continuous from Poaka Open Works to Lowfield, making the oreshoot more than 2000 m long. At Poaka, where the vein was first discovered beneath shallow drift, the deposit was said to be more sop-like than vein-like in character ((Figure 30)A–B), and was in the Martin Limestone bounded by a footwall of Silurian rocks. South-eastwards along the main fault and its branches, the ore-body developed into typical veins of the replacement type within the Red Hill Oolite, with bulging lateral extensions into the hanging-wall. Throughout the whole of its length, mineralisation on the main vein and on most of the branches commonly extended from rock-head downwards to the upper part of the Martin Limestone, with the largest deposits occurring in the Red Hill Oolite. At Lowfield, where the deepest working level was at about −150 m OD, the vertical range of the mineralisation was nearly 300 m.

Most of the ground traversed by the Lindal Moor fault-system has been explored by cross-cutting at various depths from the workings of the many shafts particularly those between Lindal Moor and Lowfield. There is little doubt that all major deposits of economic value have been found and worked out. The deeper workings from Diamond Pit and Lowfield were heavily watered and this was an important factor leading to closure, although evidence suggests that the deposits were dying out south-eastwards in depth.

Only fragmentary information exists about the amount of ore raised from the Lindal Moor Vein, but total production must have been several million tons. The earliest operations date from about 1758 (Smith, 1924, p. 4) and mining ceased in the early years of the present century.

The group of veins in the Whitriggs area, though generally narrower and less productive than those of Lindal Moor, were nevertheless once of much importance. Mining at Whitriggs probably started about 1714 (Smith, 1924, p. 4), almost certainly in the north towards Marton where the main ore-bearing horizon of the Red Hill Oolite was near outcrop and could be opened up by adits. This area was known as 'the Peru of Furness'. The main deposits were associated with faults forming a shallow fault trough within which the veins swelled out into small irrregular orebodies and flats at or near the base of the Red Hill Oolite. As in the case of the Lindal Moor Vein the more productive parts of the veins became deeper with the dip of the beds, and thinned both laterally and in depth south-eastwards towards Lindal-in-Furness.

Pennington

The orebodies worked from Pennington No.2 Pit [SD 2654 7673], 1.3 km E of Whinfield, were vein-like deposits lying along a W–E fault, with five smaller deposits associated with faults branching northwards from the main fracture. The direction of throw of these faults is not known, and the amount of throw is probably quite small. According to Smith (1924, p. 188), the W–E fault dipped northwards at 80° in the lower levels of the mine but in the higher levels became vertical and then dipped at 45° to the south nearer the surface.

With the exception of a small exposure of dolomitised limestone (probably the Martin Limestone) in the railway cutting west of No. 2 Pit, the whole of the ground is drift-covered to a depth of 10 to 25 m and details of the solid geology can be inferred only from the borehole and mining records. It would appear that No.2 Pit entered solid near the base of the Red Hill Oolite through about 20 m of boulder clay, and probably intersected parts of the Martin Limestone and the Basement Beds before entering Silurian strata at about −40 m OD. According to Smith (1924, p. 188) the Silurian floor sloped ESE at 13°, and the dip of the limestone was 10°–20° in the same direction.

Evidence from the mine tip which still existed at the time of the resurvey suggested that the veins were mostly worked at or about the horizon of the upper part of the Martin Limestone and the lower part of the Red Hill Oolite. Replacement of the wall-rock was evidently extensive, giving rise to irregular flat-like masses of ore. The mine-plans show that the productive horizon followed the dip of the beds, becoming deeper in an ESE direction; workings around the shaft were mainly about at Ordnance Datum, but reached to a depth of about −40 m OD farther east. The deposits, apparently quickly died out about 250 m E of No. 2 Pit and although exploration was continued for a further 100 m in the level at–39 m OD, no more ore was found. In the workings between No.2 Pit and the railway the ore extended up to rock-head, but exploration west of the railway along the continuation of the main fault yielded little ore, although farther west at Rawlinson No. 1 Pit [SD 2619 7682] a small deposit on the same vein had previously been worked.

Ulverston

A small, but interesting, hematite vein at Plumpton, about 2 km E of Ulverston (Figure 32) has been described by Smith (1924, p. 205). The vein is associated with a WNW fault crossing the largely drift-free outcrop of the Red Hill Oolite, Dalton Beds and Park Limestone. Its chief interest lies in the fact that it is one of the very few cases in Furness where the course of a hematite vein can still be seen at the surface, and where the relationship of hematitisation to stratigraphy readily demonstrated.

The vein was probably worked at least as long ago as about 1220 (Smith, 1924, p. 4) which puts it among the earliest records of hematite mining in Furness, but it was not until the eighteenth and nineteenth centuries that sustained operations took place. Unfortunately no plans are available and the total production is not known, although the maximum annual output was probably about 7000 tons, a figure recorded in 1873.

The best exposure of the vein is in an old open cut in Iron Pit Spring Wood, and there are also good exposures along the old tramway to the quarry on the shore at Plumpton Bight. Immediately south of Plumpton Hall a small branch vein is thrown off on its southern side. The footwall of the main vein is composed of Red Hill Oolite at surface along its western end, and is of Dalton Beds to the south-west of Plumpton Hall. The hanging-wall is also Red Hill Oolite at the extreme western end, but of Dalton Beds at Iron Pit Spring Quarry and Park Limestone south of Plumpton Hall. The southerly downthrow is about 45 m. At the western end the footwall is recorded as Silurian slate in the workings at a depth of 30 to 45 m (Smith, 1924). Most of the ore was obtained from the workings in Iron Pit Spring Wood, where some replacement of the Red Hill Oolite hanging-wall evidently took place, the vein being several metres wide. Farther east the vein was narrower and less productive, for the Dalton Beds forming the hanging-wall is less favourable to replacement. There is no indication on the surface, or from records, of the productivity of the vein at its extreme eastern end. Throughout its exposed length there is extensive dolomitisation on the walls of the vein, as there is also over much of the outcrop of the Red Hill Oolite on the footwall side of the vein. Several small parallel veins in the Red Hill Oolite have been recorded between the vein and a major WNW fault at Plumpton Hall which brings in Silurian rocks, but they have been worked on only a very small scale.

Elsewhere near Ulverston the only other noteworthy indication of hematitisation is around the small outcrop of Martin Limestone at Tarn Close [SD 277 788], where two or three small trials were made years ago, evidently with little success. So far as is known none of these tested the main Stone Cross Fault (p. 74) in the area west of Stone Cross where the Red Hill Oolite probably abuts against a footwall of Silurian rocks. WCCR

Yarlside–Stank–Newton–Stainton

Most of the ore deposits worked in this area were veins, and as will be seen from (Figure 33) their distribution is closely related to the geological structure and the stratigraphy of the Lower Carboniferous rocks. Most of the mines closed before World War I but production at Yarlside and Stainton continued on a small scale for a few years after 1918. Newton Mine continued in production until shortly after World War II, and was the last hematite mine in Furness to close. The best years of Yarlside and Stank, which were the largest mines, were towards the end of last century when their combined production reached the order of 70 000-80 000 tons per annum.

Except for a small area near Newton Mine the solid rocks are everywhere concealed by drift, usually 10 to 20 m thick but up to 30 m in places. Most of the larger ore deposits were discovered initially by boreholes, most of which were put down during the latter part of the last century; the intensity of the search can be judged from the fact that the journals and sites of over 250 bore-holes are in the Institute records. Ground in the vicinity of operating mines was also explored by long cross-cuts, and many smaller veins were discovered in this way. A considerable amount of geological information has thus been made available, and the structure of the area and details of the Lower Carboniferous sequence are now known with fair accuracy.

The general dip of the Carboniferous rocks is 10°–20° to the south-east, so that the outcrops of the different formations strike NE–SW, abutting obliquely against the southern part of the Yarlside Fault and successively forming its footwall. The structure is dominated by the Yarlside Fault which is the southern extension of the Park fault-system to the north. In the vicinity of Yarlside Mine its throw exceeds 300 m, bringing St Bees Sandstone on the west against Lower Carboniferous and, in the extreme south, Namurian rocks. A series of faults of W–E and WNW–ESE trends springs off the upthrow side of the main fracture and traverses the outcrop of the Lower Carboniferous rocks as dip faults; the throw of the component faults is to the south, and does not exceed 15 m. At least one of these, Stank Main Vein, shifts the Yarlside Fault, and probably all of them comprise a linked system with the latter, as in the case of the faults associated with the Park Fault farther north (p. 98). When traced northwards the Yarlside Fault is again stepped by a WNW–ESE fault running north of Newton; thence it continues northwards in two branches which join up with the Park fault-system west of Dalton. Between Newton and Stainton a complicated pattern of W–E, WNW–ESE and NW–SE faults has been proved; individual throws are mostly small although those of some increase rapidly in the Namurian outcrops towards Gleaston.

All of the faults mentioned above including the Yarlside Fault acted to some extent as channels for mineralising solutions over parts of their courses. The concentration of mineralisation to form economic hematite orebodies occurred, with very few exceptions, where the faults cross the outcrop of the Urswick Limestone. In the Newton Mine area the stratigraphical control has been shown to be even closer, the veins being productive only in the upper part of the Urswick Limestone above the Woodbine Shale. Where the Urswick Limestone lies at rockhead, therefore, or where it is exposed near Newton and Stainton, the ore deposits are fairly shallow but die out quickly in depth. In the case of the Stank Veins, however, the veins were productive at considerable depth, the Urswick Limestone having dipped beneath the Gleaston Formation.

Most of the veins were of the replacement type and commonly swelled out into small irregular or flat-like deposits. That on the Yarlside Fault, however, appears to have been, in part at least, a unique example of an infilled vein.

Yarlside

The hematite occurred as vein-like masses or irregular pockets along that part of the Yarlside Fault where the footwall, either at rock-head or beneath a cover of the Gleaston Formation, is composed of Urswick Limestone. It was worked from several shafts, the most important of which were No. 3 [SD 2265 7215], near the northern end of the workings about 300 m WNW of Bowesfield, No. 10 [SD 2265 7106], and No.11 [SD 2257 7077] farther south. The structure of the fault is highly complex in this part of its course and several explanations as to its formation and that of the orebodies along it have been put forward (Kendall, 1921; Smith, 1924). The hanging wall of the fault, composed of St Bees Sandstone, is separated from the footwall by a 'fault zone' up to 30 m wide, which is composed largely of black shale derived almost certainly from the Gleaston Formation. The general dip of both walls of the fault is 50°–55° west. The shale is reported to have been crushed and broken, and evidently slipped in or was dragged down the fault plane. The orebodies were distributed irregularly between the shale and the footwall, but a few small ones were formed between the shale and the red sandstone of the hanging-wall. Some mixing of ore and black shale occurred. Another unusual feature of the fault was thatthe footwall, while maintaining the overall general dip mentioned above, was highly irregular in detail showing broad undulations and sharp re-entrants both laterally and in depth; there was some evidence that this may have been a result of water erosion and solution subsequent to movement of the fault and, in part at least, prior to ore deposition.

The general character of the ore along this vein and the form of some of the orebodies indicated infilling rather than replacement; however, some replacement may also have occurred especially in the case of irregular veins and ginnels parallel to the main vein, which were worked in the footwall. Concentrations of ore in the fault-zone and in the footwall occurred where the W–E Stank and Bowesfield veins joined the Yarlside Vein.

Where the Urswick Limestone abuts against the footwall in the northern section of the vein the orebodies were relatively shallow and reached rock-head; south of the Bowesfield Vein, where the Gleaston Formation is against the fault, the values came in at depth where Urswick Limestone again occupied the footwall. Thus the orebodies were worked to a depth of only 57 m OD near No. 3 Shaft, to −102 m near No. 11 Shaft, and to nearly −150 m farther south at the junction with the Stank South Vein.

The northern extension of the Yarlside Fault west of Newton where its footwall is in the Park Limestone was tested by workings along the fault-zone for about 100 m; a little ore was proved between shale in the fault-zone and the footwall, but values were poor. Still farther north a heading from West Newton Mine (see below), which intersected the fault, proved the fault-zone to be 20 m wide, but to be composed entirely of black shale. In the south the orebodies in the vicinity of the junction with the Stank South Vein died out rapidly southwards, and boreholes farther south found no extension of the mineralisation.

Stank Main Vein and South Vein

The Main Vein is associated with a WNW–ESE fault which crosses the sub-drift outcrop of the Gleaston Formation about 250 m S of Bowesfield. At its western end this fault apparently shifts the Yarlside Fault. Mineralisation is of the replacement type and is confined to that part of the fault which is within the Urswick Limestone at depth (Figure 34). The lateral extent of the oreshoot was about 650 m from the Yarlside Fault eastwards to the region of Stank Farm [SD 254 705], where it rapidly died out. It was worked to about–170 m OD in the western part from No. 3 Shaft [SD 2298 7082], and to about −153 m OD in the east from No. 1 Shaft [SD 2325 7076] and No.5 Shaft [SD 2315 7088]. The ore-shoot (see (Figure 34)) had a gentle easterly dip, probably influenced by the dip of the beds. The width of the vein is said to have varied from a few centimetres up to 10 m, and in its wider stretches included lenticular masses of limestone which split the oreshoot into narrow vein-like orebodies. In the upper levels near No. 3 Shaft some replacement on the hanging-wall gave rise to a small flat. The average dip of the vein was 45° to the south.

The South Vein, apparently marking the position of another W–E fault, was discovered by means of a cross-cut driven at–157 m OD from the Main Vein workings near No. 1 Shaft. This intersected two narrow veins which converged westwards to form a single, much wider, vein. This was eventually proved to extend to the Yarlside Fault, where irregular orebodies associated both with the vein and the fault were worked between −90 and −150 m OD. The development of the South Vein from No. 1 Shaft necessitated an air shaft—No. 12 Shaft [SD 2296 7062]—which entered Urswick Limestone beneath the shales and thin limestones of the Gleaston Formation at a depth of 130 m (−60 m OD). The oreshoot was worked from −90 m to −190 m OD and lay entirely in the Urswick Limestone. The dip of the vein was about 55° to the south.

Much of the ground between the Stank Main Vein and the Bowesfield Vein to the north has been explored by cross-cuts in the Urswick Limestone between the workings on both veins. Several small veins were found mostly parallel to the Yarlside Vein, but did not lead to any important workings. One small irregular orebody, found by this means near Nos. 3 and 5 shafts, had little extension in depth. Much exploratory cross-cutting was done from levels at −153 m and −170 m OD in the ground between No. 1 Shaft and Stank Farm [SD 234 705] where the Main Vein and the South Vein appeared to converge; several small veins were found but none was very significant. Exploration by cross-cutting at depths down to −250 m OD in this area met with little success. It was carried out by sinking winzes from the lowest level served by No. 1 Shaft, and driveages were extended as far as a point about 250 m SE of Stank Farm, mostly following small veins thought to be continuations of the Main or South veins or of a small vein intersected in the Urswick Limestone by a cross-cut at −150 m OD driven south from No. 12 Shaft. Records of these deep trials show that the country rock was dark limestone and shale, indicating that the Gleaston Formation had been brought down to this level by the prevailing dip.

Bowesfield Vein

This marks the course of a W–E fault throwing down about 20 to 25 m to the south, which brings in the Gleaston Formation against the Urswick Limestone on the footwall side. The vein was traced eastwards for about 370 m from where it abuts against the Yarlside Fault. Mineralisation was patchy in the western and eastern sections of the vein. The best oreshoot, worked from No.8 Shaft [SD 2286 7111], extended laterally for about 100 m immediately south-west of Bowesfield and vertically from about +42 m OD (close to rock-head) to −90 m OD where values became poor.

Workings on smaller oreshoots at the eastern end of the vein and others on a parallel vein were connected to Stank No. 5 Shaft by cross-cuts.

Several small W–E and WNW–ESE faults have been proved by cross-cuts and boreholes in the outcrop of the Urswick Limestone between the Bowesfield Vein and Newton. Most of these were mineralised to some extent but the few workings were on a small scale. The possible eastwards extension of some of these veins at greater depth was tested by cross-cuts from Stank Nos. 6 and 7 shafts [SD 2342 7218], [SD 2345 7139]; one of these was driven over 600 m NNE to North Stank Mine (see below) but no useful deposits were found. A cross-cut south-westwards from Stank No. 6 Shaft driven in the Urswick Limestone at −85 m OD did not find any continuation of the Bowesfield Vein.

West Newton

The main shaft [SD 2284 7189] from which several small orebodies were worked is situated between a WNW–ESE fault, trending through the village of Newton, and throwing down to the north, and a parallel fault about 300 m to the north which throws in the opposite direction. Vein-like orebodies were associated with both faults, those on the northern one being the more important, and several small pockets and ginnels of ore occurred in the fault-trough where the controls were probably minor faults and joints. Most of the orebodies lay in the lower part of the Urswick Limestone but did not persist far in depth on entering the Park Limestone. The West Newton Shaft was connected to Yarlside workings near Bowesfield by a cross-cut about 500 m long driven at about +34 m OD mainly in the Park Limestone. It disclosed only a few small veins, none of which was of much value. This cross-cut was continued northwards from the shaft for about 450 m with the intention of connecting with the Anty Cross heading (p. 108).

North Stank

Two veins, each along a WNW–ESE fault, were worked from New Pit [SD 2371 7191], which was sunk between the faults on the outcrop of the lowest beds of the Gleaston Formation. The pit entered Urswick Limestone at a depth of about 15 m ( +50 m OD). An oreshoot on the vein north of the shaft was worked for a distance of about 100 m eastwards from the shaft and to a depth of about −43 m OD in the Urswick Limestone; the dip of the vein was 45° to the SSW. The vein south of the shaft was first proved in the long cross-cut mentioned above connecting the workings of this mine with Stank Nos. 6 and 7 shafts, and was followed westwards from the cross-cut for about 300 m in the Urswick Limestone. The ore-shoot sloped from west to east. Workings were very shallow at the western end of the vein but were carried to a depth of −23 m OD in the eastern section beneath a cover of Gleaston Formation. A cross-cut from New Pit driven NNE in the Urswick Limestone intersected several small veins of general WNW–ESE trend, some of which were worked farther west in Newton Mine.

Newton Mine (Old North Stank) and North Newton

A number of vein-like orebodies were worked in this area, all of which appear to be directly related to a series of linked NW–SE and W–E faults. A great deal of information about the geology of these mines and the ground between Newton and Stainton is available from many boreholes and from underground sections in Newton Mine, which was working during the resurvey. Woodbine Pit [SD 2361 7235] was the main shaft. Immediately north of this shaft two W–E faults about 60 m apart provide the main structural control for mineralisation, with NW–SE faults being more important to the east and north-east of the mine. The general dip of the beds is 15°–20° ESE, and it has been established that all the oreshoots worked north and east of Woodbine Pit are confined to the upper part of the Urswick Limestone above the Woodbine Shale. Within the outcrop of the Urswick Limestone most veins reached, and were worked up to, rock-head, and workings were accordingly shallow. Where traced eastwards at greater depth under a cover of Gleaston Formation, the orebodies seemed quickly to die out. The Woodbine Shale, which was exposed in many places underground, provided a most useful marker horizon in resolving details of the structure.

At North Newton shallow veins were worked for short distances along extensions westwards from Woodbine Pit of two W–E faults. At Goldhills Pit [SD 2317 7240] the best vein was known as the Schneider and Hannay Vein. The oreshoots on this vein, and on one worked 200 m to the north-east, were in the Park Limestone. Each had a lateral extent of about 100 m but died rapidly in depth. Exploratory cross-cuts both north and west from Goldhills Pit at about +26 m OD did not reveal any important orebodies.

Many of the veins worked at Newton Mine were discovered by cross-cutting in the Urswick Limestone, mostly at +20 m OD. As a result of the conclusions reached during the resurvey a magnetic survey was carried out over an area of ground south-west of Minikin Hall [SD 241 729] where the outcrop of the upper part of the Urswick Limestone above the Woodbine Shale was known to be crossed by NW–SE faults (Hallimond and Butler, 1940). The results were encouraging enough for one of the cross-cuts from Woodbine Pit to be continued into this area and several more small vein deposits were proved.

Stainton

The workings at Stainton Mines, some of which are of great antiquity (Smith, 1924), are located along a W–E fault which runs immediately south of the large Stainton limestone quarry. This fault throws down to the south, bringing the Gleaston Formation against the Park and Urswick limestones. The vein has offshoots running north-westwards in the Urswick Limestone. The ground is largely drift-free near the vein, which was originally worked at the surface. Many shafts were sunk along it over a distance of about 600 m, but the greatest depth recorded is about 40 m. The vein was said to be nearly vertical.

Crown Quarry Pit [SD 2427 7276] was situated on a small NW–SE fault branching off the main W–E vein, and along which the Park Limestone and Gleaston Formation were thrown together. It was sunk on a vertical vein to a depth of 22 m, but little ore was found. WCCR, KCD

Cartmel

Several small trials for hematite have been made in the outcrops of Lower Carboniferous rocks in the Cartmel peninsula, mostly in the last century or earlier, but no discoveries of importance have been made. Generally the stratigraphy of the Lower Carboniferous rocks is similar to that in Furness so that the lithological conditions appear favourable to hematitisation. However, the usual indications of hematite deposits, such as extensive hematite staining and dolomitisation, are rare. Some instances of reddening along the NW–SE and N–S faults that affect the Lower Carboniferous rocks have been noted, and these occurrences have provided the reason for the trials in most cases.

Three small trials have been made in the western part of the area. One of these [SD 3525 8194] near Stribers, 2.5 km N of Holker, was located on or close to the Ellerside Fault (p. 53), where a small outcrop of limestone is enclosed between the main fault and a branch of it. A shaft, perhaps 10 to 15 m in depth, was sunk probably early in the last century and, judging from the tip material visible at the time of the resurvey, entered brecciated limestone with traces of hematite, the limestone probably being Red Hill Oolite. Both the shaft and the tip are now obscured. The other trials, both very small, were made on small faults at the south end of Roudsea Wood [SD 333 814] and at the south end of Old Park Wood [SD 3380 7750], the former at the base of the Red Hill Oolite and the latter at the junction of the Park Limestone and Urswick Limestone. Farther east, near Cartmel, a small orebody was worked opencast in Hesketh Wood [SD 3852 7850] on a NW–SE fault cutting the Dalton Beds. The orebody gave out at shallow depth and boreholes in the neighbourhood failed to find an extension.

Mention has already been made that one condition favouring the occurrence of hematite may have been the occurrence of Triassic sandstones directly overlying Carboniferous limestones. It was suggested by Dunham and Rose (1941) that such conditions might exist between Allithwaite and Cark, but this is now thought unlikely. WCCR

Future prospects

The prospects of the district were considered in detail in Wartime Pamphlet No. 16 (Dunham and Rose, 1941) under the heading 'Explored and unexplored areas'. At that time it was thought that further prospecting could be recommended, at least as a wartime measure, in a few selected localities. Most of the localities were adjacent to mines then in operation, or in areas close to orebodies that had been worked and where geological controls were favourable to mineralisation. Since the Pamphlet was written little more geological information has become available to affect the conclusions about prospects then reached. These conclusions, however, have been affected by changing economic conditions. The remaining mines have now closed, and a new mining venture would have to face heavy capital expenditure and contend with very different conditions from those of 1941. Even the largest of the mines of the district would now be regarded as a relatively small undertaking, and its potential contribution to national requirements of iron ore would be small. Against such an economic background it would have been unrealistic until recently to regard any of the localities listed in the Pamphlet (with the one possible exception of the Duddon Estuary) as promising from the point of view of exploration. Nevertheless present import costs are such that this assessment may prove far from final.

Duddon Estuary

As stated in the Pamphlet, the presence of Carboniferous Limestone strata on both sides of the estuary near its mouth has long lent attraction to the suggestion that undiscovered orebodies might occur beneath the estuary, especially as this area lies between Hodbarrow to the north-west and Park–Roanhead to the south-east, the two areas where the largest ore deposits occurred (Shaw, 1903). At the time of the resurvey, however, the general conclusions about the prospects of finding new orebodies beneath the Duddon were pessimistic. Apart from three relatively restricted areas close to the shore–two on the west side of the estuary and the other off Furness–it was thought that favourable geological conditions were unlikely to be found and that, in particular, there was probably not a continuous outcrop of limestone between Hodbarrow and Roanhead. Little new geological information has become available since 1941 but a re-appraisal of the geology of the surrounding district and of the possible structure beneath the estuary has been made, and some geophysical work has been undertaken over the estuary. It is now thought that the conclusion reached in 1941 may have been too extreme, and that the possibility of the existence of orebodies–even large ones–beneath the estuary ought not to be rejected out of hand on the basis of the meagre information available.

A revised sketch-map of the geology of the estuary is shown in (Figure 14). The position of outcrops and faults is still necessarily conjectural and the map should be regarded only as a now preferred alternative to that shown in Wartime Pamphlet No. 16. A change has been made in the likely strike of the faulted outcrops of the Red Hill Oolite which project into the estuary between Askam and Sandscale. The main effects of this change are to suggest that, contrary to the view expressed in the Pamphlet, there could be more extensive outcrops of the Red Hill Oolite beneath the estuary between the Hodbarrow sea-wall and Sand-scale, and that other areas of limestone may occur. A subsidiary effect of this change is to increase slightly the areas of Red Hill Oolite believed to lie immediately offshore near Askam and Roanhead; the positions of the NW faults separating these outcrops are plotted from known positions onshore and remain unaffected. Another change on the revised map is the omission of an area of Lower Palaeozoic rocks; for the reasons stated on p. 71 it is instead concluded that the area is underlain by the Basement Beds. The NE–SW fault along the estuary may help to explain the difference in the general direction of throw of the NW faults on one side of the estuary from those on the other (p. 71), but its exact position, its structural characteristics and effects, and its possible implications as regards mineralisation are unknown. The potentialities of the small areas west of the Hodbarrow sea-wall and offshore from Borwick Rails are unaffected by the revision and remain as stated in Wartime Pamphlet No. 16; both probably include faulted outcrops of Red Hill Oolite but details of the structure and stratigraphy are unknown.

It is clear that, even on the assumptions made in constructing the revised map of (Figure 14), large areas beneath the central part of the estuary are likely to be occupied by Basement Beds and thus of no interest from the point of view of ore deposits. The areas where limestone outcrops are most likely to occur lie between Hodbarrow and Sandscale.

Several faults probably traverse this area so that potentially favourable conditions for ore deposition may occur. This conclusion, based as it is on extremely limited information, must be treated with due reserve. It must also be weighed against two other factors. The first is that mineralisation at Hodbarrow was clearly dying out southwards, and intensive boring along the coastal strip near Roanhead and Sandscale failed to find any worth-while deposits; the second is that the estuary is floored by superficial and drift deposits, possibly up to 90 m in thickness in places, so that glacial erosion may well have removed substantial thicknesses of solid rocks including any contained hematite. If the prospects of the estuary as a possible source of hematite are to be re-examined in future the first step should be drilling to secure more geological information. If the stratigraphy proved favourable, seismic geophysical surveys might then be conducted in an attempt to build up a more reliable picture of the geology before considering a more intensive exploratory programme.

A gravity survey over the Duddon Estuary was carried out in 1973 for the Institute by Mr P. M. Howell. It augments the regional survey of the Lake District and the Vale of Eden by Bott (1974). Generally the results support the existence of an important NE–SW fault along the estuary in about the position shown in (Figure 14), and it is suggested that this fault is related to the north-west boundary of a concealed intrusion near Ireleth and Soutergate. In more detail the survey has revealed the presence of a sharp positive residual anomaly beneath the estuary near Askam, but more work would be necessary before it could be inferred that this might be caused by a concealed body of hematite. WCCR

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SMITH, B. 1924. Iron ores: Haematites of West Cumberland, Lancashire and the Lake District. Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B., Vol. 8 2nd edition.

SMITH, B. 1928. The origin of Cumberland haematite. Summ. Prog. Geol. Surv. G.B. for 1927, pp. 33–36.

SMYTH, W. W. 1856. The iron ores of Great Britain. Part I-The iron ores of the north and north-Midland counties of England. Mem. Geol. Surv. G.B.

TROTTER, F. M. 1939. Reddened Carboniferous beds in the Carlisle Basin and Edenside. Geol. Mag., Vol. 76, pp. 408–416.

TROTTER, F. M. 1945. The origin of the West Cumbrian haematites. Geol. Mag., Vol. 82, pp. 67–80.

TROTTER, F. M. HOLLINGWORTH, S. E., EASTWOOD, T. and ROSE, W. C. C. 1937. Gosforth District. Mem. Geol. Surv. G.B.

UNITED NATIONS, DEPT. OF ECONOMIC AND SOCIAL AFFAIRS. 1970. Survey of World Iron Ore Resources. New York. 479 pp.

WALSH, P. T., BOULTER, M. C., IJTABA, M. and URBANI, D. M. 1972. The preservation of the Neogene Brassington Formation of the southern Pennines and its bearing on the evolution of Upland Britain. J. Geol. Soc. London, Vol. 128, pp. 519–559.

WINCHELL, A. N. and WINCHELL, H. 1951. Elements of optical mineralogy. Part II. 4th Ed. New York. 551 pp.

WRIGHT, J. E. 1975. The geology of the Irish Sea in Symposium on Canada's continental margins and offshore petroleum exploration. Mem. Can. Soc. Pet. Geol., No. 4.

WRIGHT, J. E. HULL, J. H., MCQUILLIN, R. and ARNOLD, S. E. 1971. Irish Sea investigations 1969–70. Rep. Inst. Geol. Sci., No. 71/19.

WURZBURGER, P. 1872. The haematite iron deposits of Furness. J. Iron Steel Inst., No. 1, pp. 135–142.

ZELENOV, K. K. 1959. On the discharge of iron in solution into the Okholsk Sea by thermal springs of the Ebeko volcano (Paramushir Island). Dokl. Akad. Nauk. SSSR, Vol. 120, pp. 1089–92. English translation by Consultants Bureau Inc. 1959. New York. pp. 497–500.

Chapter 8 Quaternary deposits

Introduction

The whole of the area shows abundant evidence of intensive glaciation. Over much of the ground glacial deposits of varying thickness—chiefly boulder clay, for which the local term 'pinner is often used—obscure the solid while in the relatively small drift-free areas glacial striae and roches moutonnees evidence the effectiveness of glacial erosion. The glacial deposits have been described by several workers notably Mackintosh (1869, 1871), Kendall (1900), Grace and Smith (1922) and Gresswell (1962), and a recent reexamination of the Barrow area has been carried out by Grieve and Hammersley (1971). Much of the evidence bearing on the direction of ice-movement and on the detailed sequence is generally agreed in these publications, and is briefly summarised below.

East and north of a line drawn south from Ireleth to the vicinity of Furness Abbey and then approximately east through Leece to Newbiggin on Morecambe Bay the glacial deposits consist almost entirely of a greyish brown or yellow boulder clay, very variable in thickness, that has been termed the Low Furness Till (Grieve and Hammersley, 1971). Its erratic content shows that it was derived from the fell country around Coniston to the north. The direction of ice-movement appears to have been almost due south around Ulverston and to have swung to the south-southwest towards Gleaston. This is deduced from striae, roches moutonnees and the crest alignments of a drumlin swarm occupying much of the lower ground south of Dalton. There are some large tracts of drift-free ground between Dalton and the shores of Morecambe Bay, and others on the Lower Palaeozoic outcrops in the north, particularly in Cartmel where deposition is largely confined to the N–S valley running through Cartmel.

West and south of the line mentioned the glacial deposits are thicker and, in places, more complex in lithology. This area lies within the influence of the Irish Sea glacier that brought with it erratic material derived mainly from West Cumbria–Eskdale Granite erratics being prominent–and also from south Scotland. An admixture of these erratics and those characteristic of the South Cumbrian ice marks the confluence of the major ice-streams. It becomes noticeable around Hodbarrow, extends as far north as Askam, and continues through the south-western end of the Furness peninsula around Barrow. Boreholes have proved that the glacial deposits attain a thickness of nearly 90 m in places in the Millom–Hodbarrow area, and nearly 60 m along the Duddon shore near Roanhead. The deposits include thick beds of sand and gravel that locally divide the boulder clay into a lower and upper member. The upper boulder clay is generally the sandier and more incoherent of the two and contains a high proportion of Irish Sea erratics. Even so the two boulder clays cannot be separately identified where sand is absent, as it is south-east of Sandscale Farm and beneath much of Walney Island. Nevertheless a tripartite drift sequence was described in this area by Mackintosh (1869), and has been demonstrated in individual sections by most subsequent workers. It has been generally interpreted as indicating two distinct ice-advances represented by the lower and upper boulder clays, separated by an ice-free period when outwash sands and gravels—the 'middle sands'—were laid down. For the most part, however, the sands in the individual surface sections and in boreholes are not laterally persistent and it is by no means certain that they represent a single depositional episode. In a general way the more substantial beds lie within rock-head depressions.

The most extensive surface outcrop of sand lies between Roose and Rampside and clearly represents material that has debouched from a complex glacial drainage system that funnels southwards into the Furness Abbey channel and lies near the western limit of the Low Furness Till. The sand is capped by small patches of thin boulder clay. Nevertheless the surface topography developed on it, and the freshness both of the feeding channel and of an earlier distributary running through Moss Side make it unlikely that any major ice-advance has covered the area since the sands were deposited. It seems more probable that, as suggested by Gresswell (1962), this particular sand body represents out-wash laid down between the two major confluent ice-sheets and does not equate with the sands present at depth around the Duddon.

None of the surface exposures shows any positive evidence of multiple glaciation; in particular there is no record of more than one lodgement till in any one section. The freshness of the surface topography almost certainly dates the bulk of the deposits as late-Devensian (Weichselian).

Nevertheless it is possible that the products of earlier glaciations are present locally at depth. This is most likely in the thicker sequences recorded on either shore of the Duddon Estuary and on Walney Island. The relationship of these thicker sequences to the exposed drifts is, however, not clear.

Much of the difficulty in precise dating of the sequence results from the paucity of organic horizons. One unconfirmed record of peat beneath boulder clay is from a borehole [SD 1819 7045] at North Scale, Walney, but no samples have been preserved. Another record comes from a series of shafts sunk near Lindal-in-Furness, where a peaty deposit containing insects, leaves and diatoms, and overlain by up to 30 m of boulder clay was described by Bolton (1862), and Hodgson (1863), though the latter doubted whether the material was interglacial and believed it to be the recent infilling of a subterranean drainage course. The most convincing description of an organic deposit is that by Kendall (1881), who described an area of 'at least 34 acres' to the south-west of Lindal, within which numerous bore-holes have proved a peaty deposit, up to 7 m thick, which is overlain by up to 30 m of boulder clay and underlain by up to 7 m of boulder clay, sand and clay. It seems likely that the deposit is the infilling of a pond within a solution hollow in the surface of the underlying limestone, and that earlier glacial deposits are also preserved in this hollow. Unfortunately a recent Institute borehole failed to prove organic material and is presumed to have penetrated a pinnacle within the solution hollow. In general, however, the spread of Flandrian marine alluvium masks the underlying Quaternary deposits over the lowest ground.

When the ice-cover melted from the district, sea level was appreciably lower than it is to-day, and gradually rose as the melt spread northwards (Tooley, 1974). Evidence of this period of low sea level was obtained when Barrow harbour was excavated during the 1870s. W. B. Kendall (1900) recorded the section in the channel wall near the entrance gates of the harbour: it showed a stream channel, about 100 m wide and lined with up to 3 m of peat, the lowest exposed level of which lay at –33 m OD. The peat rests on river gravels and freshwater clays, the valley being cut in glacial sands overlying a lower boulder clay. The peat is overlain by black silty clay with marine shells, indicating a subsequent rise of sea level from at least –33 m OD.

This rise of sea level was responsible for an extensive spread of marine alluvium, with local beaches, that now covers the glacial deposits over much of the lowest ground. Blown sand is also locally extensive. The details of the various stages of this complex and intermittent inundation are beyond the scope of the present study. WCCR, KCD

Details: glacial deposits

Millom–Hodbarrow

Glacial deposits cover most of the area, and are overlain on the lower ground by marine alluvium and blown sand. Rockhead contours are shown in (Figure 35). These show that the limited Carboniferous outcrops at Hodbarrow Point and near Red Hills are culminations at about +15 m ( + 50 ft) OD of a broad swell in the rockhead. A similar, but much lower swell, lies around Steel Green with culminations at about −30 m ( −100 ft) OD. A wide N–S channel, apparently ungraded and falling to at least −66 m ( −218ft) OD, separates these two areas. A deeper channel dropping to at least −83 m ( −272 ft) OD runs NNW–SSE through Haverigg; and other smaller channels cut across the two areas of relatively high rockheads, making it uncertain whether these latter represent cut platforms of any real significance. North of the main cluster of boreholes there are two records of particularly thick drift [SD 1757 7950]; [SD 1675 7944]. These holes may lie along the centreline of two distinct N–S channels: alternatively it is possible that both lie in a W–E channel that carried sub-marginal drainage beneath Millom. The apparently ungraded profiles of most of the channels and the steepness of their walls makes it probable that they were cut by sub-glacial meltwaters.

At surface the glacial deposits consist mainly of a reddish brown boulder clay containing erratics derived chiefly from the Borrow-dale Volcanic Group and the Eskdale Granite, a suite suggesting an admixture of ice from the Duddon valley with the main flow of Irish Sea ice. A few small patches of sand and gravel are exposed, and are both overlain and underlain by boulder clay. A section at Red Hills Quarry, recorded in 1938, reads: red sandy boulder clay 1 m; medium–coarse, pale brown sand with thin seams of gravel 3 m; stiff purplish brown boulder clay 1 m + (base not seen). A similar section in the railway-cutting [SD 163 798] west of Millom shows about 4 m of sand and gravel beneath some 3 m of sandy boulder clay.

The many boreholes establish the presence at depth of a thick complex of sands and gravels and boulder clays in those areas where the drift is thickest and the presence of thick beds of waterlogged sand above parts of Hodbarrow Mine led to inrushes of water during mining (Harris, 1970; Smith, 1919). Nevertheless even in this small well-drilled area, it is not possible to correlate individual beds of sand and till with any certainty, nor to establish how this sequence is related to the thinner one present over the areas of high rockhead. At the Haverigg Haws Borehole the sequence is even more complicated, and includes four beds of sand and gravel with intervening boulder clays in a total glacial thickness of some 51 m. The age of this complex is similarly uncertain. It may all represent the products of the late-Devensian glaciation, or its lower part may have been deposited during an earlier glaciation. WCCR

Dunnerholme–Sandscale

The rockhead contours in this area are shown in (Figure 36) and (Figure 37). Broadly the deposits thicken towards the coast. At Sand-scale over 60 m have been recorded in one borehole, while between Askam and Dunnerholme the thickness varies from 15 to 55 m, the higher figures being recorded near the Duddon shore. On this lower ground, blown sand and marine alluvium cover the glacial deposits, Dunnerholme standing up like an island through the resultant flat. Rockhead is above Ordnance Datum from near Askam to Thwaite Flat, and both here and at Roanhead Crag there are small drift-free outcrops.

The surface glacial deposits are mainly boulder clays, although laminated clay–possibly formed in a glacial lake–has been recorded near Tippin's Bridge [SD 225 793] (Grieve and Hammersley, 1971). North of Askam the boulder clay is brown or greyish brown, and its contained erratics consist almost exclusively of Silurian greywackes and tuffs and lavas from the Borrowdale Volcanic Group, all derived from ice moving down the Duddon Estuary. South of Askam Carboniferous limestones and scattered Eskdale Granite boulders are added to the suite. In the extreme south between Sandscale and Thwaite Flat the colour of the till changes to reddish brown over the Triassic outcrops and St Bees Sandstone becomes a conspicuous erratic. Only small patches of sand and gravel are exposed. In the walls of the subsidences over Rita and Park Sops [SD 207 752]; [SD 215 755] up to 4 m of sand and gravel are overlain and underlain by boulder clay, and have been referred by Grieve and Hammersley to the 'Middle Sands'. The deposit seems to extend at surface towards Greenscoe [SD 220 764].

At depth knowledge of the sequence is dependent on borehole records and some broad conclusions can be drawn from their results. Northwards from Roanhead Crag the deposits consist almost entirely of boulder clay, except for thin included beds of sand and gravel that occur at various depths beneath a belt extending south-east from the coast through Askam to the line of the Furness railway and are apparently associated with a rockhead depression. Around Roanhead and westwards and southwards as far as Sandscale Farm a thick complex of boulder clays, sands and gravels extends downwards to some 30 or 40 m below OD. The highest member of this complex is normally a boulder clay and where examined is brown and sandy with erratics from the Borrowdale Volcanic Group and the Ennerdale Granophyre together with Silurian greywackes and St Bees Sandstone. Thick beds of sand and gravel recorded near the coast at the north-eastern extremity of Sandscale Haws may predate the late Devensian glaciation. They are overlain by 20 to 30 m of boulder clay, and some of the holes prove an underlying boulder clay.

Many of the logs note a concentration of large boulders at the base of the glacial sequence. Towards Sowerby Wood the sands fail as rockhead rises and an indivisible mass of boulder clay results.

A prominent glacial drainage channel extends southwards from Askam to Goldmire, and continues beyond it through the Vale of Nightshade to Roose (Plate 8.2). It is cut deeply into solid rock over much of its course, and because it is not filled with glacial deposits and is topographically so fresh is taken to be a product of the latest glaciation. KCD

Walney Island–Barrow–Gleaston

With the exception of small areas between Newton [SD 230 715] and Old Holbeck [SD 234 696], around Hawcoat and Furness Abbey, and near Gleaston, glacial deposits are ubiquitous though covered by Recent deposits on the lower ground. Drift thicknesses in selected boreholes appear in Appendix 1.

Permanent sections in the boulder clay are rare, though formerly glacial clays were worked for bricks and tiles in small pits in the Ormsgill and Hindpool areas of Barrow.

Cliff sections at Hare Hill [SD 204 630], at Beacon Hill [SD 230 663], and in the sand-pits [SD 225 688] at Roosecote all expose sands, both overlain and underlain by boulder clay; they have been described recently by Grieve and Hammersley (1971). The Hare Hill section showed about 1 m of reddish brown gravelly boulder clay overlying up to 6 m of sand preserved within a steep-sided channel cut into a lower boulder clay. The section at Beacon Hill shows up to 3 m of upper boulder clay resting on some 8 m of sand, with a lower boulder clay beneath characterised by a thin limonitic and manganese-rich layer at its top.

The large outcrop of sand and gravel which occupies much of the surface between Roosecote, Rampside and Roosebeck probably correlates with that seen at Beacon Hill; it is well exposed in workings of the Roosecote sand-pits [SD 224 688] where it reaches 25 m in thickness and where a thin overlying boulder clay is locally present (Plate 8.1). In the Roosecote Borehole [SD 2304 6866] the proved section reads: sand 8 m; boulder clay 5.5 m; sand with layers of gravel 7.1 m; boulder clay 15.2 m; on solid. The obvious relationship of this extensive spread of sand and gravel to the Askam–Goldmire–Furness Abbey–Roose glacial drainage channel has already been mentioned.

Several small outcrops of sand, probably overlain by a thin boulder clay, occur along the Walney shore of the Walney Channel, and shallow boreholes [SD 179 692] near Vickerstown proved about 7 m of boulder clay overlying at least 8 m of sand and gravel. For the most part, however, the Walney drift is dominantly boulder clay. Walney No. 5 (SD17SE/2) at Lenny Hill, North Scale, recorded about 20 m of boulder clay overlying 13 m of stony sand itself underlain by 5.5 m of boulder clay. Even less sand is recorded at Walney No. 6 Borehole (SD17SE/57) where out of 50.3 m of glacial drift all is sandy 'pinnel', apart from two bands of sand and gravel, respectively 1.2 and 1.5 m thick. In Walney No. 4 Borehole (p. 124) 5.2 m of loamy sand separate 30 m of boulder clay above from 20.1 m of a lower boulder clay, but nearby holes show the sand to be impersistent.

Temporary trenches and excavations in 1970–72 for a sewage scheme between Stainton, Gleaston and Newbiggin showed the Low Furness Till, here overlying Carboniferous rocks, to be dark grey when fresh, weathering to yellowish brown; it contained frequent blocks and boulders of Carboniferous limestones which were angular, in contrast to other erratics which were smaller and usually rounded. Over the Permo-Triassic outcrop south-west of Gleaston the colour of the boulder clay changes to reddish brown. An excavation [SD 264 690] near Newbiggin exposed about 10 m of reddish brown plastic clay with silty patches and only rare stones; this passed up into reddish brown boulder clay. Drumlins are common between Dalton, Gleaston and Rampside, where much of the surface is occupied by boulder clay. The general alignment of the long axes of the drumlins varies between NNE–SSW and NNW–SSE though, as Grieve and Hammersley have shown, there are notable exceptions to this. KCD, WCCR

Dalton–Aldingham–Ulverston

Boulder clay covers much of the ground between Dalton and Ulverston, and between Stainton and Aldingham. It generally ranges between 5 and 10 m in thickness inland, increasing to about 20 m in the cliffs between Sea Mill [SD 270 695] and Aldingham. At one point [SD 281 705] on the coast a thin sandy boulder clay overlies a bed of sand 2 m thick, with a stiff grey boulder clay below. The erratics in the latter include large boulders of Urswick Limestone together with smaller stones from the Gleaston Formation, the Borrowdale Volcanic Group, and the Silurian.

In the cliff at Wadhead Scar [SD 308 745] near Bardsea, the following section has been recorded:

A small deposit of sand and gravel is exposed on both sides of the valley of Poaka Beck, about 1 km N of Dalton, and can be seen in old pits. It is up to 6 m thick and is overlain by yellowish brown boulder clay. Irregular patches of sand and gravel, loamy in parts, occupy areas around Kilner Park, Three Bridges and Stone Cross, on the western outskirts of Ulverston. Exposures in old pits near Three Bridges showed, at the time of the resurvey, that the deposit there was up to 6 m thick, that it was underlain by boulder clay, and that an overlying sandy boulder clay, up to 2 m thick, was also present.

Boulder clay covers most of the ground between Urswick and Ulverston and probably reaches a maximum thickness of about 5 m. Boreholes in the alluvial tract east of Ulverston proved up to 16 m of boulder clay resting on solid.

A terrace-like deposit of earthy gravel with boulders, rising about 1 m above the alluvium on both sides of the stream (Gleaston Beck) draining southwards from Urswick Tarn, is believed to be of fluvioglacial origin. KCD, WCCR

Cartmel

Glacial deposits in this area are mainly confined to the low ground of the wide valley extending northwards from Cartmel towards Windermere, and to the coastal region south-west of Cark and Flookburgh. In the Cartmel valley boulder clay, mostly giving rise

to well-defined drumlins, occupies much of the surface. It is usually a greyish brown sandy clay, and the erratics in it are almost entirely Silurian greywackes with only scattered stones from the Borrowdale Volcanic Group. Its thickness may reach 15 m under some of the higher drumlins but is usually much less. The alignment of the drumlins is N–S in the ground north of Cartmel, swinging to NNE–SSW between Cartmel and Cark. No bedded sand and gravel has been recorded, although some small mounds of gravelly morainic drift occur at Cark [SD 367 764] and near Holker [SD 365 770].

Two boreholes at Sandgate Marsh [SD 353 760], west of Cark, proved about 18 m of glacial deposits described as mainly 'stony clay and gravel'. A small cliff section at Lenibrick Point [SD 349 752], 1 km to the south, shows about 6 m of stiff red boulder clay with erratics of Silurian greywackes, Borrowdale volcanic rocks, Carboniferous limestones and reddish purple sandstones probably of Namurian age. Another borehole on Winder Moor [SD 575 752] recorded 20 m of stony clay with thin gravel beds beneath marine alluvium. WCCR

Details: Recent deposits

The post-Glacial deposits comprise marine and fluviatile alluvium, beach deposits, blown sand and peat.

Marine alluvium (warp) occupies extensive areas of the low coastal strip on both sides of the Duddon Estuary, and around Barrow, Walney Island, and the shore of Morecambe Bay between Rampside and Newbiggin. In most of these localities it consists of a grey or pale greyish brown clay, which may be silty in parts and which is commonly peaty at the surface. Elsewhere in the area large spreads of marine alluvium are found east and north-east of Ulverston, on the Cartmel side of the Leven Estuary between Roudsea Wood and Holker, and south and south-east of Flookburgh. Between Ulverston and Greenodd, and around Flookburgh the deposit is more commonly a pale greyish brown silt, while north of Holker it is a stiff grey clay, very peaty at the surface, and enclosing areas of peat (see below).

The height of most of the larger tracts of marine alluvium varies from about 5.5 to 6.7 m OD, distinctly higher than the high-water mark of ordinary tides today (about 4.3 m OD). In places it is separated from the present day marine alluvium by a minor step of up to 1 m. In other places, however, there is no such dividing line; for instance, the large tract south-east of Flookburgh varies from about 6.7 m OD on its inland side to about 4.9 m OD as the shore is approached. Near Biggar and around South End, Walney Island, an intermediate level of marine alluvium at 4.6 to 5.2 m OD can be recognised. For the purposes of the map all marine alluvium above about 4.5 m OD has been termed Older Marine Alluvium; it is regarded as marking a slightly higher sea level than the contemporary one.

The beach deposits of sand and shingle at Sandscale and Walney Island, and those along the shore of Morecambe Bay between Rampside and Newbiggin vary in height from about 6.7 to 7.9 m OD: some are clearly related to the sea level denoted by the Older Marine Alluvium; others are covered by blown sand, but probably formed before sea level reached its maximum. The name Older Beach has been used for these, rather than Raised Beach with its connotation of uplift. Smaller occurrences and traces of Older Beach Deposits have been noted at Haverigg and east of Red Hills, east of Ulverston, and south of Flookburgh. The deposits of Walney Island, especially those at North End and South End, and those of Sandscale are much obscured by blown sand and are probably more extensive at depth than is shown on the map.

Both the Older Beach Deposits and the contemporary storm beaches have been worked extensively for gravel, particularly at South End Haws [SD 224 620]. It has been estimated that between 1895 and 1905 well over a million tons of gravel was removed from this area (Smith, 1907). The influence of these workings on coastal accretion and erosion has been discussed in a recent paper (Phillips and Rollinson, 1971) and the raised warps and beaches of the Barrow area have been the subject of a study by Grieve and Hammersley (1971).

The only extensive deposit of peat in the area is at Deanholme Moss [SD 345 805], east of High Frith, on the Cartmel side of the Leven Estuary. The peat is mostly brown and has been proved to be at least 3 m thick in parts, resting on Older Marine Alluvium. It has been worked sporadically between Holker and Roudsea Wood.

Blown sand covers considerable areas on Walney Island, especially at the North and South ends, and at Sandscale, where some of the dunes reach to over 15 m OD; smaller dunes are present along the Duddon shore between Askam and Dunnerholme.

The fluviatile alluvium of the few small streams in Furness consists mainly of earthy and bouldery gravel in the upper reaches, grading down into silty clay on the lower ground where it merges into Older Marine Alluvium; the dividing line between the two deposits shown on the map is mostly an arbitrary one. KCD, WCCR

References

BOLTON, J. 1862. On a deposit with insects, leaves, etc, near Ulverston. Q. J. Geol. Soc. London, Vol. 18, pp. 274–277.

GRACE, G. and SMITH, F. 1922. Some observations on the glacial geology of Furness. Proc. Yorkshire Geol. Soc., Vol. 19, pp. 401–419.

GRESSWELL, R. K. 1962. The glaciology of the Coniston Basin. Liverpool, Manchester Geol. J., Vol. 1, pp. 57–70.

GRIEVE, W. and HAMMERSLEY, A. D. 1971. A re-examination of the Quaternary deposits of the Barrow area. Proc. Barrow Nat. Field Club, (New Series), Vol. 10, pp. 5–25.

HARRIS, A. 1970. Cumberland Iron: the story of Hodbarrow Mine 1855–1968. Truro. 122 pp.

HODGSON, E. 1863. On a deposit containing diatomaceae, leaves, etc. in the iron-ore mines near Ulverston. Q. J. Geol. Soc. London, Vol. 19, pp. 19–31.

KENDALL, J. D. 1881. Interglacial deposits of West Cumberland and North Lancashire. Q. J. Geol. Soc. London, Vol. 37, pp. 29–39.

KENDALL, W. B. 1900. Glacial deposits in Furness and district. Proc. Barrow Nat. Field Club, Vol. 3, pp. 25–30.

KENDALL, W. B. 1900. Submerged peat mosses, forest remains and post-Glacial deposits in Barrow Harbour. Proc. Barrow Nat. Field Club, Vol. 3, pp. 55–62.

MACKINTOSH, D. 1869. On the correlation, nature and origin of the drifts of North-West Lancashire and a part of Cumberland, with remarks on denudation. Q. J. Geol. Soc. London, Vol. 25, pp. 407–431.

MACKINTOSH, D. 1871. On the drifts of the west and south borders of the Lake District, and on the three great granitic dispersions. Geol. Mag., Vol. 7, pp. 564–568.

PHILLIPS, ADA W. and ROLLINSON, W. 1971. Coastal changes on Walney Island, North Lancashire. University of Liverpool Research Paper. 36 pp.

SMITH, B. 1919. Iron ores: Haematites of West Cumberland, Lancashire and the Lake District. Spec. Rep. Miner. Resour. Mem Geol. Surv. G.B.

SMITH, J. W. 1907. In The Royal Commission on coast erosion and the reclamation of tidal land from the sea in the United Kingdom. Vol. 1, Part 2.347 pp.

TOOLEY, M. J. 1974. Sea-level changes during the last 9000 years in north-west England. Geogr. J., Vol. 140, pp. 18–42.

Appendix 1 Boreholes and shafts

Abbreviated logs of a selection of the stratigraphically more significant boreholes and shafts are given below, together with a few closely adjacent to the district. The National Grid reference of each site is also given. Most records referred to in the text are included. With the exception of those bore-holes sunk since 1971 all depths were originally recorded in Imperial Units. They have been converted to their metric equivalents to the nearest centimetre.

The records are grouped according to the six-inch sheets on which the boreholes lie: within each such group the order is that of the Institute's Borehole Record Collection at Leeds.

Sheet SD 16 NE

Walney Island No. 2 (SD16NE/7)

Surface level about +3.05 m OD; National Grid ref. [SD 1940 6612]. Date 1887.

Walney Island No. 3 (SD16NE/8)

Surface level +5.79 m OD; National Grid ref. [SD 1984 6596]. Date 1887.

Walney Island No. 4 (SD16NE/9)

Surface level about 5 m OD; National Grid ref. [SD 1995 6552]. Date: 1887.

British Gypsum No. 1 (SD16NE/12)

Surface level about +5 m OD; National Grid ref. [SD 1906 6503]. Date: 1971. Log by A. A. Wilson and R. S. Arthurton.

Sheet SD 17 NW

Haverigg Haws (SD17NW/2)

Surface level about +7.8 m OD; National Grid ref. [SD 1473 7858]. Date: 1938–39. Log by W. C. C. Rose.

Sheet SD 17 NE

Sandscale; Kennedy Bros. No. 38 (SD17NE/22)

Surface level +9.14 m OD; National Grid ref. [SD 1978 7564]. Date: 1910.

Sandscale; Kennedy Bros. No. 40 (SD17NE/24)

Surface level +10.67 m OD; National Grid ref. [SD 1966 7565]. Date: about 1910.

Sandscale, Kennedy Bros. No. 48 (SD17NE/29)

Surface level +3.05 m OD; National Grid ref. [SD 1964 7576]. Date: about 1915.

Bourkes No. 1 (SD17NE/36)

Surface level about +4.6 m OD; National Grid ref. [SD 1604 7844]. Date: ?1875.

Bourkes No. 2 (SD17NE/37)

Surface level about +610 m OD; National Grid ref. [SD 1549 7956]. Date: ?1880.

Langthwaite No. 1 (SD17NE/53)

Surface level + 6.10 m OD; National Grid ref. [SD 1569 7971]. Date: 1918–19.

Hodbarrow No. 109 (SD17NE/54)

Surface level -1.5 m OD; National Grid ref. [SD 1739 7786]. Date: 1920–21.

Hodbarrow No. 111 (SD17NE/56)

Surface level about + 1.46 m OD; National Grid ref. [SD 1680 7864]. Date 1924.

Hodbarrow No. 113 (SD17NE/58)

Surface level +0.45 m OD; National Grid ref. [SD 1684 7840]. Date: 1924–25.

Hodbarrow No. 123 (SD17NE/68)

Surface level +6.60 m OD; National Grid ref. [SD 1669 7897]. Date: 1926.

Hodbarrow No. 128 (SD17NE/73)

Surface level 0.8 m OD; National Grid ref. [SD 1660 7839]. Date: 1927–28.

Hodbarrow No. 129 (SD17NE/74)

Surface level +2.38 m OD; National Grid ref. [SD 1632 7851]. Date: 1927–28.

Hodbarrow No. 90 (SD17NE/94)

Surface level +5.3 m OD; National Grid ref. [SD 1818 7900]. Date: 1917.

Duddon Estuary No. 4 (SD17NE/100)

Surface level about +1.5 m OD; National Grid ref. [SD 1842 7818]. Date: 1866.

Hodbarrow No. 47 (SD17NE/109)

Surface level +5.28 m OD; National Grid ref. [SD 1761 7899]. Date: 1889–90.

Massicks No. 1 (SD17NE/126)

Surface level 12.5 m OD; National Grid ref. [SD 1675 7944]. Date: ?1882.

Hodbarrow No. 85 (SD17NE/153)

Surface level +15.82 m OD; National Grid ref. [SD 1692 7911]. Date: ?1917.

Lord Lonsdale's No. 4 (SD17NE/171)

Surface level about + 8 m OD; National Grid ref. [SD 1747 7839]. Date: ?1880.

Hodbarrow No. 86 (SD17NE/172)

Surface level 5.6 m OD; National Grid ref. [SD 1757 7950]. Date: ?1917.

Sheet SD 17 SE

Walney Island No. 5 (SD17SE/2)

Surface level about +10 m OD; National Grid ref. [SD 1820 7045]. Date: unknown.

Sowerby Wood No. 1 (SD17SE/7)

Surface level about +28 m OD; National Grid ref. [SD 1983 7332]. Date: 1891.

Sandscale Meadow No. 6 (SD17SE/16)

Surface level +6.10 m OD; National Grid ref. [SD 1958 7389]. Date: about 1870.

Sandscale; J. D. Kendall's No. 17 (SD17SE/22)

Surface level about +15 m OD; National Grid ref. [SD 1977 7420]. Date: about 1871.