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Geology of the country between Durham and West Hartlepool (Explanation of one-inch geological sheet 27, New Series)

By D. B. Smith, B.Sc. and E. A. Francis, B.Sc. with contributions by M A. Calver, MA., A. H. Edwards, B.Sc., G. D. Gaunt, B.Sc., R. K. Harrison, MSc. and J. Pattison, B.Sc.

Natural Environment Research Council. Institute of Geological Sciences

Memoirs of the Geological Survey of Great Britain, England and Wales

Geology of the Country between Durham and West Hartlepool (Explanation Of One-Inch Geological Sheet 27, New Series)

By D. B. Smith, B.Sc. and E. A. Francis, B.Sc. with contributions by M. A. Calver, M.A., A. H. Edwards, B.Sc., G. D. Gaunt, B.Sc., R. K. Harrison, M.Sc. and J. Pattison, B.Sc.

London Her Majesty's Stationery Office 1967. Printed in England. © Crown copyright 1967 Printed and published by Her Majesty's Stationery Office To be purchased from 49 High Holborn, London W.C.1. 423 Oxford Street, London W.1. 13A Castle Street, Edinburgh 2. 109 St. Mary Street, Cardiff. Brazennose Street, Manchester 2. 50 Fairfax Street, Bristol 1. 35 Smallbrook, Ringway, Birmingham 5. 7–11 Linenhall Street, Belfast 2 or through any bookseller

The Institute of Geological Sciences was formed by the incorporation of the Geological Survey of Great Britain and the Museum Of Practical Geology with Overseas Geological Surveys and is a constituent body of the Natural Environment Research Council

(Front cover) Reef dolomite, Black Hall Rocks (continued on (Rear cover))

(Rear cover) Reef dolomite, Black Hall Rocks

Preface

The country between Durham and West Hartlepool was originally surveyed on the six-inch scale by H. H. Howell, who was District Surveyor, and A. G. Cameron. Two of the six-inch whole sheets were published—namely Durham 20 and 35, which appeared in 1871 and 1876 respectively. They were followed in 1881 by publication of both Solid and Drift editions of the Old Series One-inch Map Sheet 103 N.E. Revised editions of the Drift map were printed in 1889 and 1892, but no explanatory memoir was published.

The resurvey of the district was begun in 1954 by Mr. D. B. Smith working on the Permian rocks in the east. He was joined in 1955 by Messrs. E. A. Francis and G. D. Gaunt, who mapped the ground covered by the western and southern parts of the sheet respectively. The field work was supervised by Mr. W. Anderson and was completed in 1958. The six-inch standards were drawn on the National Grid and published during 1963 and 1964. They are listed on p. x. Solid and Drift Editions of the new One-inch Map, Sheet 27, were printed in 1965.

The task of writing this memoir has fallen almost entirely to Messrs. Smith and Francis, who have incorporated contributions from Mr. Gaunt into the chapters on the Permian and Pleistocene and Recent. The fossils obtained from the Coal Measures have been identified by Mr. M. A. Calver, and from the Permian by Mr. J. Pattison, Dr. F. W. Anderson and Sir James Stubblefield. Thanks are due to Dr. A. Logan for permission to use his unpublished revision of the Permian brachiopods and lamellibranchs. Comments on the fauna of the Easington Raised Beach have been made by Mr. D. F. W. Baden-Powell of Oxford University, and isotopic age determinations on shells from this beach have been provided by Drs. Meyer Rubin and Irving Friedman of the United States Geological Survey. Most of the sections on petrography have been written by Mr. R. K. Harrison, but also included in the text are brief descriptions of rocks by Dr. R. Dearnley, myself (when Chief Petrographer) and Dr. J. Phemister. The chapter on mineral products and water supply contains a contribution on rank and quality of coal written by Mr. A. H. Edwards, Coal Survey Officer, National Coal Board, Northumberland and Durham Division. The memoir has been edited by Mr. E. H. Francis.

Assistance obtained during the resurvey and writing of the memoir from officials of the National Coal Board, water works engineers and local government officers is gratefully acknowledged.

This Memoir received final approval from Sir James Stubblefield, F.R.S., as Director before his retirement in December 1966.

K. C. Dunham, Director. Institute of Geological Sciences, Geological Survey Office, Exhibition Road, South Kensington, London S.W.7, 14th March 1967

List of six-inch maps

Published geological six-inch maps included in one-inch Sheet 27 are listed below with initials of the surveyors and dates of survey. The surveyors were: E. A. Francis, G. D. Gaunt and D. B. Smith. Strips of ground inside the western and southern margins of the one-inch map are covered by parts of the following incomplete and unpublished six-inch sheets: NZ22NE, NZ23NE, NZ23SE, NZ24NE, NZ24SE, NZ32 NW, NZ32NE, NZ42NW, NZ42NE, NZ52NW.

Chapter 1 Introduction area and physical features

This memoir describes the geology of the district covered by the Durham (27) Sheet of the One-inch Geological New Series of maps of England and Wales^‡1 . This district (Figure 1) lies entirely within the County of Durham and includes the south-eastern part of the Durham Coalfield. Coal Measures crop out in the west, but elsewhere they are overlain by Permian rocks and these are succeeded in turn by Triassic strata over a small area in the south-east. In much of the district, the solid rocks are obscured by extensive spreads of superficial deposits.

The district can be divided on the basis of topography and geology into four areas, namely western, central, eastern and southern. The western area coincides approximately with the outcrop of the Coal Measures (Figure 2). It lies mainly between 150 and 400 ft O.D. though it falls to as little as 25 ft in the northern part of the entrenched valley of the River Wear. This river, and its tributaries, drain the area and locally flow through gorges which are cut through thick deposits of glacial sands and clays and which form important topographical barriers. The horseshoe-shaped gorge at Durham (Plate 1) forms a fine defensive site for the Castle and Cathedral; and between the city and the northern margin of the district, the river is crossed only by one railway bridge, one footbridge and one road bridge. The area is bounded to east and south by a prominent feature frequently referred to as the 'Permian Escarpment', though in general only the capping rocks are of Permian age. The escarpment is dissected by re-entrant valleys, one of which, at Shadforth, is nearly two miles long and is floored, east of the village, by at least 100 ft of drift. Most of the other re-entrants have also been proved to contain buried valleys and these fall to the main buried valley of the River Wear which lies below present sea-level downstream from near Shincliffe. The escarpment is further breached in the south by the Ferryhill Gap and this too contains a buried valley. The gap links the Wear and Tees drainage basins and provides an easy route for the Edinburgh–London railway.

The central area, lying immediately to the east and south of the escarpment, is formed by a rolling plateau, generally over 400 ft high, and including the highest ground in the district, reaching over 600 ft around Cassop Vale, Raisby Hill, Trimdon, and west of Ferryhill. Drift is mostly thin or absent, though it becomes thicker towards the east.

The eastern area, which lies roughly east of a line through Easington and Embleton, is generally below 400 ft and falls gently eastwards to coastal cliffs north of Black Halls Rocks and to low ground around West Hartlepool. The streams in the northern part drain directly to the North Sea through steep-sided gorges ('dens') which locally cut down through the drift into the Permian rocks. Farther south, the streams flow to the estuary or tributaries of the River Tees. Drift is more than 60 ft thick over much of the area and buried valleys have been located, though their courses are not known in detail.

The southern area lies south of a line through Ferryhill Station and Fishburn, and is largely covered by thick drift. It merges with the eastern area between Butterwick and Embleton. The streams drain mainly into the River Skerne, a tributary of the Tees, and the ground is generally below 350 ft. A feature of the area is the linked series of flats ('carrs') which mark the sites of former lakes. Peat and other organic deposits have been proved in some of these former lake-basins. E.A.F., D.B.S.

Human settlement

The two main centres of population within the district are Durham, in the west, and West Hartlepool, in the east. The distribution of the more important smaller towns and villages is shown in (Figure 2).

Old Durham, which lies nearly one mile east-south-east of the Cathedral, was sited on a well-drained terrace and on glacial sands and gravels above the level of the river alluvium. It was settled at least as early as Roman times, when a villa, said to be the northernmost farming estate of the Roman world, was occupied (Richmond 1949, p. 64). Durham itself flourished as a monastic centre during the Norman period, when the Cathedral and Castle were built. It later became a market town and in the 19th Century was a natural site for a university. It remains the administrative capital of the county, and supports several light industries, which are becoming increasingly concentrated in the Dragonville area. West Hartlepool, though larger, is younger, having expanded mainly in Victorian times as an industrial centre. Its coal-exporting and ship-building activities have declined, but timber-importing and steel-making are still important. In recent years the field of employment has been widened by the introduction of light industries, including a plant, established in 1937, for the extraction from sea-water of magnesia which is used in the manufacture of refractories.

Some of the other settlements, including Shadforth, Easington, Fishburn, Sedgefield, Hett, Cornforth, Hutton Henry and Trimdon, are set around village greens and were originally agricultural. In later times, mining villages such as Sherburn Hill were newly formed from rows of miners' houses erected around local pits, and existing villages like Pittington were rapidly enlarged in the same way.

In the inter-war and post-Second World War years, new housing estates have been built around Durham and West Hartlepool and also at some of the mining villages, such as Thornley and Wheatley Hill. Along the coast, where mining prospects are good, the villages of Easington Colliery, Horden and Blackhall now form an almost continuous settlement about four miles long, and the concentration of population is made greater by the junction with Easington at the northern end, and by the establishment of the new town of Peterlee near Horden. Inland, where the future of mining is less secure, some of the villages have taken on a secondary function as dormitories for Durham and Darlington. Further changes in the distribution of population and light industry are likely to follow from the construction of the Durham Motorway through the western part of the district.

Farming has been influenced to a considerable extent by the development of mining and other industries in the district. There is a large arable acreage which is partly devoted to the production of potatoes and other vegetables. Milk production is also important. E.A.F.

History of mining

The Northumberland and Durham Coalfield was the site of some of the earliest mining for coal and was certainly the first British coalfield to be developed commercially. Although working by the Romans seems to have been confined to the Tyne area, much more widespread exploitation took place during the monastic period from the twelfth to the sixteenth centuries. The earliest mention of coal-mining by the monks of Durham is in 1188, but workings only seem to have become important during the fourteenth century, when a considerable revenue began to be derived. The most important places in the Durham district and the dates mentioned are: Hett (1293), Coxhoe (1327), Ferryhill (1327), Rainton (1347), Moorhousefield (1360), West Rainton (1430), Trillesden, i.e. Tursdale (1447), Cassop (1456). There seems to have been extensive mining from 1402 to 1528 at Moorhousefield (near Moor House), south of West Rainton, associated with Finchale Priory, and at Rainton by the Durham monks from 1351 to 1431. Because there were not more than 60 monks at Durham and Finchale, some of the workings were leased; during 1447 land and a coal pit at Tursdale were let to three or four people by the Prior of Durham in one of the earliest colliery leases on record (Simpson 1910, pp. 589, 595).

Although coal was shipped from the Tyne as early as the thirteenth century, it was mostly burned near outcrops until Elizabethan times. Then, with the depletion of timber resources, and consequent rise in prices, it became economic to transport the easily worked household coal of Northumberland and Durham by sea to London. Thus the coalfield gained a dominant position which was unrivalled until the Industrial Revolution. The collieries which produced the so-called sea-coal were at first mainly near the Tyne and based on the High Main Seam. But by the beginning of the seventeenth century, this seam was apparently nearly exhausted near Newcastle, due to difficulties with water, and though its life was prolonged by the introduction of new methods, including steam-driven pumping, the difficulties became progressively greater, until by 1763 the central part of the Tyne basin was flooded out.

The flooding helped to promote the coal export trade in Durham. It was first based on staithes on the River Wear, near Penshaw and Fatfield, but by 1670 short wagonways were in general use linking these with the nearby pits. Elsewhere in the coalfield there were only a number of landsale pits which worked various seams for local use.

One of the earliest mine-plans of the district refers to Flintoff's Engine Pit, which worked the Hutton Seam 550 yd north of Oswald House, Durham, possibly in the early part of the eighteenth century. The earliest records of bores in the district are those put down on Cornforth Moor in 1748 and in the Coxhoe and Quarrington area between 1750 and 1785. A bore was also put down near Moor House, Rainton, in 1751. By 1800, the system of wagonways leading to the staithes near Penshaw had reached back into the Rainton area on the northern margin of the district, but the record of the earliest sinking within the district, Rainton Adventure Pit, is dated 1816. At the beginning of the nineteenth century, much of the production from the Wear collieries was derived from the Main and Five-Quarter seams, which yielded only a moderate household coal, but a first-class household coal was gained by sinking to the Hutton Seam when the Tyne High Main was finally nearing exhaustion (Smailes 1935, p. 205). The Hutton had, however, beenexploited near Lambton somewhat earlier. The Rainton pits were developed from 1816 to 1823, and at Seaham, just beyond the northern margin of the district, the Marquis of Londonderry built an artificial harbour which began to ship coal from these pits in 1831, and from Murton a few years later.

Before 1820 it was generally thought that no valuable coal existed under the Permian rocks, but in that year a new era opened when Hetton Colliery shafts were sunk through the Magnesian Limestone to the Hutton Seam, which was of comparable thickness and quality to the same seam worked in the Rainton pits. The chief problem in sinking through the Permian rocks lay in the water-bearing Yellow Sands; though only 27 ft thick in the Murton sinking of 1837, these sands introduced 9,000 gallons of water per minute into the shaft (Poole and Raistrick 1949, p. 88).

The development of the railway system was also an important factor in the exploitation of the coal resources of the district (Smailes 1935, p. 206). In 1830, the Clarence Railway and the Middlesbrough extension of the Stockton and Darlington Railway connected the southern part of the coalfield and the Tees estuary. A branch line provided access through the Ferryhill Gap to the Coxhoe area, and the small Bell's Pit sunk in 1827 was superseded by Coxhoe Colliery in 1835. Soon after, the Hartlepool Docks and Railway Company developed Hartlepool as a coal-shipping port and opened a more direct route from this part of the coalfield to the coast. The company also opened a main line to Haswell with a number of branch lines into the surrounding area, so that by 1850 this part of the concealed coalfield was further developed than the exposed coalfield west of Durham City. The Durham and Sunderland Railway (1836) also provided access from the Rainton–Pittington area to the docks which were built at the mouth of the Wear in 1838 and 1840. Many more pits were opened during this period, as for instance, Sherburn Hill (1835), East Hetton (1836), Shincliffe (1837), Houghall (1841), Kepier Grange (1844) and Bishop Middleham (1846).

After the middle of the nineteenth century, London gained access to other coalfields by rail and the household coal trade in this coalfield declined. However, the coking coal trade grew in its stead and in central and east Durham the decline was offset by an increase in demand for gas coal. In this period few pits were sunk in east Durham because of the financial risk associated with the water in the Yellow Sands. These sands are over 100 ft thick at Haswell, and the first attempt to sink a shaft there was abandoned after a loss of £60,000 (Galloway 1898, p. 452). Soon after the beginning of the twentieth century, however, the technique of freezing water-bearing strata during sinking was introduced, and this method was used at Dawdon (1903) and Horden (1904) and also at Easington and Blackhall. In 1905 these coastal collieries were joined by a railway which provided them with access to Seaham and Hartlepool. The last major colliery to be opened in this district was Fishburn in 1912. After the First World War the industry contracted and in the succeeding years, the only expansion of importance took place in the coastal area.

Since nationalization in 1947 there has been reorganization of the collieries that are economically viable and closure of those pits that have either exhausted their resources or are too expensive to maintain. One result of this programme has been the joint running of two or more collieries as a unit, illustrated in this district by the amalgamation of Dean and Chapter and Chilton, and of Elemore, Murton and Eppleton. For the last three, the new coal-drawing Hawthorn Shaft has been sunk, and now produces the largest total in the district, though the takes of Eppleton and Murton lie partly beyond the northern margin of this district.

Including Dawdon, which lies a few yards beyond the northern margin of the district, but draws coal partly from within it, the total production for 1962 was nearly 9 million tons, of which more than half was raised in the north-eastern and coastal collieries. The latter are the collieries with the most assured futures because they have large undersea reserves. Most of the inland pits, by contrast, have only limited reserves of relatively thin seams, and in consequence there has been a movement of labour either to the coastal collieries or to other coalfields. E.A.F.

Geological sequence

The divisions represented on the One-inch Geological map and sections of the Durham district are summarized below:

Superficial Formations (Drift)

Solid Formations

Geological history

Nothing is known of the pre-Carboniferous history of the district and the Carboniferous strata are thought to lie unconformably on older rocks, such as the Skiddaw Slates or Caledonian granite proved in neighbouring areas (Woolacott 1923, p. 60; Dunham and others 1961; 1965). In the adjacent parts of northern England, the pattern of Lower Carboniferous sedimentation is thought to be linked closely with the structure: the Lower Palaeozoic rocks form a block outlined on the north, west and south by faults, and flanked to north and south by troughs in which a much greater thickness of Carboniferous strata accumulated than on the block. According to Bott and Masson-Smith (1957), the Butterknowle Fault (see (Figure 2)), crossing the southern part of the district, marks the line of a hinge to the south of which thick Carboniferous sedimentation took place.

Such differential subsidence seems to have ceased by Coal Measures times, since these beds show no significant difference in thickness across the fault. The Coal Measures seem to represent a complex history of limited intermittent subsidence over a long period interrupted by phases of relative stability, sometimes only local, which permitted the spread of coal-forming vegetation across the depositional surface. It is probable that Upper Coal Measures, as well as the Lower and Middle divisions, were deposited in the district, for they have been preserved from erosion in the district to the north.

During the Armorican orogeny, the Carboniferous rocks were subjected to folding and faulting, and quartz-dolerite dykes and sills were intruded. Then followed a period of erosion during which Upper Coal Measures, and in places older rocks, were removed.

By the end of Lower Permian times, the surface of erosion probably took the form of a low desert plain and on it sands and breccias were deposited. The sands were shifted by wind, and the breccias, in the southern part of the district, were probably redeposited in low fans by occasional floods. Both sand and breccias were probably partly redistributed by the ensuing transgressive Upper Permian or Zechstein Sea in which the Marl Slate was the first undoubted marine deposit followed by carbonates and by sulphates and chlorides to the east.

Permian deposition ended with shallow-water elastic, fine-grained red beds with thin evaporites. The division between them and the later continental sandstones and mudstones of the Trias is entirely lithological and may not be contemporaneous with that drawn in other areas in north-eastern England.

No other deposits are known in the district until the drifts of the Pleistocene. It is certain that the Permo-Triassic rocks of the district were disturbed by later earth-movements, particularly along the Butterknowle Fault and the adjacent anticline. Similar movements, generally held to be Tertiary in age, affected Jurassic and Cretaceous rocks in East Yorkshire, and the present cycle of erosion began when these movements led finally to uplift and tilting of the whole region. Remnants of a surface at about 600 ft above O.D. probably belong to the stage reached during the later Pliocene. The lines of the present major buried river valleys were established, and subsequently these were partly obliterated by the invasion of the great Pleistocene ice-sheets. Upon the melting of the ice great quantities of material were left, mainly in the valleys, and these are at present in process of removal. Erosion was rapid at first, but most of the streams are now fairly well graded and erosion is only significant during abnormal floods, though in places landslides are still active. E.A.F., D.B.S.

References

BOTT, M. H. P. and MASSON-SMITH, D. 1957. The geological interpretation of a gravity survey of the Alston Block and the Durham Coalfield. Quart. J. Geol. Soc., 113, 93–117.

DUNHAM, K. C., BOTT, M. H. P., JOHNSON, G. A. L. and HODGE, B. L. 1961. Granite beneath the northern Pennines. Nature, 190, 899–900.

DUNHAM, A. C., HODGE, B. L. and JOHNSON, G. A. L. 1965. Granite beneath Visayan sediments with mineralization at Rookhope, northern Pennines. Quart. J.Geol. Soc., 121, 383–414.

GALLOWAY, R. L. 1898. Annals of Coal Mining and the Coal Trade. London.

POOLE, G. and RAISTRICK, A. 1949. Extractive industries. Scientific Survey of North-Eastern England, 87–98, Brit. Assoc., Newcastle upon Tyne.

RICHMOND, I. A. 1949. Roman settlement. Scientific Survey of North-Eastern England, 61–8, Brit. Assoc., Newcastle upon Tyne.

SIMPSON, J. B. 1910. Presidential address. Coal-Mining by the monks. Trans. Inst. Min. Engrs., 39, 572–600.

SMAILES, A. E. 1935. The development of the Northumberland and Durham coalfield. Scott. Geogr. Mag., 51, 201–14.

WOOLACOTT, D. 1923. On a boring at Roddymoor Colliery, near Crook, Co. Durham. Geol. Mag., 60, 50–62.

Chapter 2 Upper Carboniferous

General

In the Durham–West Hartlepool district the proved thickness of Carboniferous rocks amounts to over 2000 ft including 400 ft of Millstone Grit Series, 600 ft of Lower Coal Measures and about 1100 ft of Middle Coal Measures. From comparison with neighbouring areas it is likely that a further thickness of about 450 ft of Millstone Grit Series lies at depth and that the full thickness of Middle Coal Measures before erosion was about 1600 ft.

Carboniferous strata are unconformably overlain by Permian over all but the north-western part of the district where Middle Coal Measures crop out in a strip about 9 miles long by about 3 to 5 miles wide. Southward, the Permian oversteps Coal Measures on to Millstone Grit Series, but eastward the Coal Measures continue beneath the younger rocks to form the south-eastern part of the Durham Coalfield. At the time of writing, mining operations in these measures extend for 3.5 miles beyond the coast-line and the coalfield has been proved by deep offshore borings to extend seaward for at least one further mile.

The beds underlying the worked Coal Measures in the Durham district have not been described previously though a general account of the equivalent measures farther west has been given by Dunham (1948). The Coal Measures of Durham and Northumberland have been described in some detail by Hopkins (1954) and those of this district have also been mentioned by Hickling (1949) and Armstrong and Price (1954) in papers dealing with the coalfield farther north in the Sunderland (21) district. The Coal Measures of the south-eastern part of the district are described in a recent paper by Magraw and others (1963).

Classification

The traditional three-fold division of the British Carboniferous into Carboniferous Limestone Series, Millstone Grit Series and Coal Measures has been tacit in Durham for nearly 150 years. The boundaries of the divisions have been defined at different horizons by different authors, though from Conybeare and Phillips (1822) onwards all have agreed on the inclusion in the Millstone Grit Series of the predominantly arenaceous sequence underlying the lowest worked seam of the Coal Measures. This arenaceous sequence was subdivided by the Primary Geological Survey into First, Second and Third grits, in ascending order.

These classifications have been based entirely on lithology and it has been apparent for some time that they do not accord with the standard classification of central and southern England and Wales. In order to reconcile this discrepancy it is proposed in this memoir to use the palaeontological boundaries which are now generally accepted throughout northwestern Europe. Thus the base of the Millstone Grit Series is now placed at the base of the Great Limestone since it is the most convenient mappable horizon approximating to the first appearance of Cravenoceras leion Bisat, at the base of the Namurian (Johnson and others 1962). This limestone lies well below the lowest proved horizon in the Durham–West Hartlepool district. The boundary between the Millstone Grit Series and the Coal Measures, that is the Namurian–Westphalian boundary, is internationally accepted to be the marine horizon with Gastrioceras subcrenatum (Frech). This goniatite has yet to be found in north-eastern England, but there is now indirect evidence (Mills and Hull, in press) to suggest that the equivalent horizon is the lowest of a group of marine bands between the Second and Third grits of the earlier surveyors. The boundary between the Millstone Grit and Coal Measures is consequently drawn at the base of this lowest band.

In other parts of the country the division between the Lower and Middle Coal Measures is now taken (Stubblefield and Trotter 1957) at the base of the marine band characterized by the goniatite Anthracoceras vanderbeckei (Ludwig) and lying near the middle of the non-marine lamellibranch zone of Anthraconaia modiolaris. The Durham equivalent of this bed is the Harvey Marine Band. The top of the marine band characterized by Anthracoceras cambriense Bisat is taken as defining the upper limit of the Middle Coal Measures. In the Sunderland district, to the north, this band lies about 550 ft above the Usworth Coal, but neither it nor the overlying Upper Coal Measures are known in this district.

Lithology

The Carboniferous succession is generally regarded as a sequence of cycles or cyclothems, each of which might be defined ideally as starting at the base with limestone and continuing upwards through marine mudstone, non-marine mudstone, sandstone and seatearth to coal. For reviews of the extensive literature dealing with this aspect of Carboniferous sedimentation the reader is referred to Wells (1960) and Duff and Walton (1962). Limestones are restricted to the cycles below the Coal Measures. In the lower part of the Lower Coal Measures the sandstone phase predominates, but the remainder of the Coal Measures is characterized by thick beds of coal.

The coals of the Durham Coalfield are almost entirely bituminous, though cannels are found locally, particularly at the tops of certain seams. The properties of the principal coals of Durham are described by Mr. A. H. Edwards of the National Coal Board on p. 257. The shales and mudstones, mainly dark grey in colour, pass upwards through paler silty mudstone to siltstone. In the Millstone Grit Series many of these argillaceous bands contain marine faunas, but in the Coal Measures non-marine lamellibranchs or 'mussels' are more common and are best preserved in clay-ironstone nodules. The few marine bands in the Coal Measures are for the most part thin and are found at or near the base of mudstone and siltstone units. The ecological distribution of the Coal Measures fossils is more fully described on pp. 19–22. Here it will suffice to say that ostracods are particularly abundant at specific horizons such as the Hopkins Band in the roof of the Harvey Coal (p. 20 and (Figure 3)), and that 'Estheria' is of similar stratigraphical significance in being more persistent at certain horizons than at others. Fossils of less use as indices include annelid burrows and trails, fish remains and plant debris.

The term siltstone has no universally accepted definition and does not appear in older records. As used in modem borehole logs and sections quoted in this memoir it refers to rocks of grain size between 0.002 and 0.06 mm (cf. British Standard, CP 2001 of 1957). Rocks of this grade occur interlaminated with fine sandstone and also as hard grey massively bedded rocks with conchoidal fracture.

Most of the Carboniferous sandstones in Durham are fine- to medium-grained rocks composed mainly of quartz with subordinate feldspars such as orthoclase, microcline and oligoclase. Among the heavy minerals, zircon, garnet, rutile, tourmaline, apatite, magnetite, chlorite, epidote, ilmenite, sphene and sapphire have been recorded by Kellett (1927) who has suggested that the Durham Coal Measures were derived principally from Cheviot igneous rocks and Silurian, Old Red Sandstone and Carboniferous Limestone sedimentary rocks of the Border district. In some sandstones, muscovite, lying parallel to bedding planes, is so abundant as to impart fissility. Most sandstones, however, are massive and cross-bedded and provide good freestones which have been used extensively in building. Coal Measures sandstones have been used in the construction of Durham Cathedral and Castle, and for walls in the old city. The harder, more compact sandstones are cemented by silica or ankerite, but a more common cement is kaolinite which gives rise to softer, more porous rocks. Where fresh the sandstones are off-white to light grey, but where weathered they are yellow or rusty brown with the iron hydroxide concentrated to form 'boxstones'. In places, particularly in the bottom layers of thick sandstones, conglomerates are seen. The pebbles in these are mainly subangular fragments of siltstone or mudstone, or clay-ironstone nodules dissociated from their argillaceous matrix. Evidence of slumping, sliding and 'balling-up' is most common in interlaminated and interbedded fine sandstones and siltstones, but slumping or overturning of cross-bedding is also seen in relatively homogeneous sandstones. Generally the slumped beds are not appreciably thicker than individual beds in a cross-bedded sandstone, and like these range from about 1 in to 3 ft in thickness, averaging about 12 to 18 in. Their extent is rather limited, although slumping seems to be concentrated at particular horizons.

Seatearths range from soft apparently unbedded brownish or light grey fireclays to hard siliceous ganisters and are characterized by rootlets either penetrating the rock from top to bottom or radiating from Stigmarian rhizomes. Ferruginous concretions are common. Some take the form of sphaerosiderite, which are small spherical grains of iron carbonate, about the size of a large pin-head, usually scattered through the bed. Others are clay-ironstone nodules which are noticeably more irregular than the bedded or sub-spherical varieties found in the mudstones and are commonly concentrated in the lower part of the seatearths. Most of the seatearths contain too much iron to be of use as refractories, but farther west some of the Lower Coal Measures ganisters have been extensively worked and the lateral equivalents of some of these are recognizable in the Durham–West Hartlepool district.

Stratigraphy

Millstone Grit Series

It is inferred, from evidence in other parts of Durham, that the Millstone Grit Series in this district is probably between 900 and 1100 ft thick, though only the uppermost 375 to 400 ft have been proved (Figure 5). The fullest section is given by the Ryal Bore, near Sedgefield, where an 11-ft limestone near the base is correlated with the Upper Felltop Limestone of West Durham. Above the limestone there is no obvious equivalent of the Grindstone Sill, but thin limestones a little higher in the sequence are thought to correspond with marine beds overlying that bed in West Durham. About 115 ft above the supposed Upper Felltop Limestone lies an 11.5-ft limestone which is correlated with a 12.25-ft limestone near the bottom of Littletown Lady Alice Pit Bore. At Bishop Middleham the position of this limestone appears to be marked by a pebbly sandstone.

The remainder of the succession up to the top of the Millstone Grit Series is 250 to 275 ft thick and consists mainly of sandstone with subordinate, probably marine, shales and a few thin limestones. The sandstones in the lower part of this sequence cannot be followed individually from one borehole to another in this district and it is not therefore possible to define the local equivalent of the 'First Grit'. In the upper part of the sequence, however, the 'Second Grit' can be recognized as a persistent sandstone 45 to 65 ft thick. Argillaceous strata underlying the 'Second Grit' include a marine band proved in a boring at Middle Stotfold, just inside the southern margin of the district.

Lower Coal Measures

(Figure 3) and (Plate 3). A marine band interpreted as overlying the 'Second Grit', and therefore marking the base of the Coal Measures as here defined (p. 11), has been proved only in the Middle Stotfold Bore, where it contains fragments of costate Productids. Between this horizon and the Brockwell Coal there are 325 ft of strata including several thin coals. Some of the latter are correlatives of the Gubeon, Ganister Clay, Marshall Green and Victoria coals of other districts, but none has been worked in this part of Durham. A second marine band, the Gubeon Marine Band, lies in the roof of the Gubeon Coal. It has been proved at two localities, and contains Lingula, foraminifera and sponge spicules. Non-marine lamellibranchs are not common below the Victoria Coal, but they have been found about 16 ft below and about 30 ft above the Canister Clay Coal, and between about 6 and 22 ft below the Victoria Coal. The junction between the Anthraconaia lenisulcata and Carbonicola communis zones is taken, tentatively, at the Ganister Clay Coal (p. 23). Persistent 'mussel'-bands forming the lowest well-defined marker bands of the Durham Coal Measures lie in the roof of the Victoria Coal and between about 15 and 30 ft above it. About 40 ft beneath the Brockwell Coal, or at intermediate positions up to that seam, a seatearth commonly underlies one or more thin coals. In places, these thin coals thicken and unite to form a single banded seam, which is as much as 47 in thick in Offshore No. 1 Bore. This seam is known as the 'Bottom Brockwell', but it is regarded here as distinct from the true Brockwell Seam.

The Brockwell Seam has been worked in the south and south-west where it is 4 to 6 ft thick, but in much of the central part of the district it is thin and poor in quality. The roof measures, up to 65 ft thick, include thin coals and the uppermost of these underlies the distinctive Brockwell Ostracod Band, which, in places, especially in the southern part of the district, contains abundant ostracods and non-marine lamellibranchs. The roof of the Three-Quarter Coal—a seam of no economic importance in this district—contains the Fishburn 'Estheria' Band, which is the equivalent of the Low 'Estheria' Band of the upper part of the C. communis Zone in the East Pennine Coalfield. Up to about 60 ft of sandstone overlie the Three-Quarter Coal in some south-western parts of the district, but this is not persistent. Over most of the district, the Bottom and Top Busty coals are distinct seams, but in the west central area they are close together and in places form a single seam 4 to 6 ft thick. A general deterioration in quality sets in eastwards of a north-north-westerly line across the centre of the land-area, and there is a further area of impoverishment trending north-north-east through the north-western portion of the district. The Top Busty Coal is provisionally taken as the top of the C. communis Zone (p. 26).

The strata between the Busty and Harvey seams comprise a complex sequence 70 to 175 ft thick including three or more coal seams which are persistent in the western and south-western parts of the district but are generally absent in central and eastern areas. The nomenclature of these seams is confused, since it has been the custom to name the locally thickest coal the Tilley, after a worked seam of this name in West Durham. Correlation of this part of the sequence with West Durham, however, is uncertain. Thus in some western parts of the district there are three impersistent coals, and the lowest two have been named Bottom Tilley and Top Tilley seams; it is assumed that the highest is equivalent to the Hodge Seam of north-west Durham. The use of the terms Bottom and Top Tilley should not be taken to imply that these seams are splits from the Tilley Seam of the type area, for the possible alternative is that the local Bottom Tilley may correspond with the Hand Seam of West Durham. Both Top and Bottom Tilley seams, as here defined, split into two or more thin coals. In parts of the district where a sandstone up to 106 ft thick overlies the Top Busty Coal, the Bottom Tilley Seam is absent. With the exception of the west-central area the Top Tilley Coal is also impoverished. The measures between the 'mussel'-band over the Top Busty Coal and the Harvey Coal are relatively unfossiliferous.

The Harvey Coal has been extensively worked. In the north-western area it is less than 2 ft thick, and there is also an impoverished belt in the coastal area where thick sandstones appear in the overlying measures. Farther east, in the offshore area, the seam splits into Top and Bottom Harvey coals and the line of split can be traced south-westwards through the Fishburn area at least as far as Windlestone. Where split there is scattered information to suggest that the Bottom Harvey is generally over 2 ft thick and is therefore an important reserve for the East Durham collieries. The Top Harvey is overlain by the Hopkins Band, which is the most persistent ostracod-bearing marker band in the Durham Coal Measures. Non-marine lamellibranchs in this band are representative of the Anthracosia regularis fauna which is typical of the measures somewhat below the marine band in the middle of the Anthraconaia modiolaris Zone. The uppermost widespread member of the Lower Coal Measures is a seat-earth or thin coal horizon.

Middle Coal Measures

(Figure 3) and (Plate 4). The base of the Middle Coal Measures is marked by the Harvey Marine Band, lying near the middle of the A. modiolaris Zone. It is generally thin, and in places absent: well-preserved Lingula are common and Orbiculoidea and Hollinella? have also been recorded. Above the marine band lies an important 'mussel'-band which is over 20 ft thick and forms one of the most persistent marker bands of the Durham Coal Measures.

At Ferryhill, the measures between the marine band and the Hutton coals are about 150 ft thick and consist largely of sandstone. Elsewhere they average about 100 ft and include several thin coals, the most persistent of which is here correlated with the Ruler Seam. Scattered non-marine lamellibranchs in the roof of the Ruler Coal include Anthracosia aquilina (J. de C. Sowerby) associated with A. ovum Trueman and Weir and A. phrygiana (Wright). Shells are not abundant and there is no bed comparable with the Plessey Shell-bed (Hopkins 1929, p. 132; Fowler 1936, p. 67) of the Northumberland Coalfield.

In the northern half of the district, the Hutton is a single 4- to 6-ft seam of good quality which has been widely worked. In the southern half of the district, it is split into Top and Bottom Hutton coals, of which the Bottom is the more valuable, while in the east further splitting results in a number of thin seams of no economic value. The strata between the Top and Bottom Hutton seams are generally 20 to 40 ft thick, and locally contain at the base poorly preserved 'mussels', ostracods and fish remains. The 'mussels' in the roof of the Top Hutton are also poorly preserved. The faunas found at low horizons in the Middle Coal Measures are rather similar, but good collections over a wide area suggest that the assemblages have different dominant forms (p. 27).

The Bottom Brass Thill Coal consists of two thin and impersistent leaves which are, in most places, separated by up to 10 ft of strata from the thicker, more persistent, Top Brass Thill Coal. Near Finchale, however, all three leaves join to form a single seam about 3 ft thick. The overlying Brass Thill Shell-bed is a significant marker band containing an abundant A. beaniana King–A. phrygiana assemblage.]

In the central part of the district, the Durham Low Main Coal is an important worked seam 2 to 4 ft thick, but there are belts in which the coal is thin, for it is more affected by 'washouts' than any other seam in the district. It is separated from the Maudlin Coal by measures which include a sandstone locally over 100 ft thick—the 'Low Main Post'. Towards the northern margin of the district, however, the Durham Low Main and Maudlin coals are united to form a seam which is locally more than 8 ft thick. As noted by Hopkins (1933, p. 216) there is a general relationship between the thickness of the Low Main Post and that of the Maudlin Coal: where the post is thick the coal is thin, and vice versa. There are exceptions, however, as at Trimdon Grange Colliery, where sandstone and coal are both thin, and in the offshore area where there is no obvious relationship between the two. The top of the A. modiolaris Zone is drawn at the Maudlin Coal position (p. 27). In western parts of the district a fairly persistent sandstone overlies the Maudlin Coal; in eastern areas the measures somewhat higher in the sequence, but below the Main Coal, include the Blackhall 'Estheria' Band (Magraw and others 1963, p. 164).

The Main Coal which, as its name suggests, has been one of the richest seams in the district, has been removed by erosion from large tracts in the west. It is 6 to 9 ft thick in the north, but is only 2 ft or less in other parts of the district. Immediately west of Blackhall Colliery it lies less than 2 ft below the Five-Quarter Coal, but the interval increases in other parts of the district to over 100 ft including 70 ft of sandstone at the base. In the northern part of the district, this sandstone unites with another overlying and cutting out the Five-Quarter Coal to make up a combined thickness of over 140 ft. Generally, however, the Five-Quarter Coal is 2 to 7 ft thick and has been widely worked. Over large areas in the central part of the district it is closely overlain by the Metal Coal which contains several bands of dirt. The coal to which the name 'Metal' is now applied by the Geological Survey is locally known as the Three-Quarter, and by the National Coal Board as the Bottom High Main. In order to avoid confusion with the Lower Coal Measures Three-Quarter Coal on the one hand, and to avoid accepting an unproved split in this upper coal from the High Main on the other, the name 'Metal' has been adopted from the Newcastle upon Tyne area. In part of the coastal area the Metal and High Main seams are united to form a thick banded seam which includes about 13 ft of coal, but farther east, in offshore areas, they are again separate.

In central parts of the district a sandstone overlies the Metal Coal and this unites in places with another sandstone overlying the High Main Coal to form a thick bed occupying much of the interval up to the High Main Marine Band. In such areas, therefore, the High Main Coal is absent. Elsewhere it is generally less than 2 ft thick, but it has been worked extensively in the north-eastern part of the district, where it is 5 to 7.5 ft thick and is commonly banded.

A maximum of about 700 ft of Middle Coal Measures above the High Main Coal has been preserved beneath the Permian. In the Durham Coalfield as a whole these measures contain five marine bands, named in upward succession the High Main, Little, Kirkby's, Hylton and Ryhope (Figure 3). Of these only the High Main and Kirkby's marine bands have so far been proved within the district. The High Main Marine Band consists of a few inches of dark shale with Lingula. It commonly overlies a thin coal separated from the High Main Coal either by a sandstone—the High Main Post—which is up to 80 ft thick in the north-central part of the district, or by siltstones and mudstones containing plant debris and sparse non-marine lamellibranchs. The strata between the High Main. Marine Band and the Ryhope Little Coal include three 'mussel'-bands. The Ryhope Little Coal is locally split to form the Top and Bottom Ryhope Little coals. All are thin and therefore unworked. Above the coal a thin bed of dark shale marks the position of the Little Marine Band which has yielded Lingula in adjacent districts.

The next seam above is the Ryhope Five-Quarter Coal which is 2.5 to 3 ft thick and is worked only in a small area near the northern margin of the district. It is immediately overlain by a 'mussel'-band and about 50 ft above it is Kirkby's Marine Band which contains scattered Lingula and abundant foraminifera. The succeeding 100 ft of strata probably include the Hylton and Ryhope marine bands, though for want of modern sections neither band has yet been proved in the district. Near the top of the known sequence of Middle Coal Measures, the Usworth and Hebburn Fell coals are preserved in a restricted area in the north-east. Though thick, both coals are thought to lie too close to the unconformity to be workable. E.A.F., D.B.S.

Reddened Carboniferous strata

Reddened sandstones crop out in the lower part of the escarpment capped by Permian strata, and have been sunk and bored through in the search for coal. Sedgwick's (1829) belief that they were New Red Sandstone in age remained unchallenged until Howse (1857), citing floral evidence, assigned them to the Coal Measures—a view which was supported on other grounds by Daglish and Forster (1864).

More recently Anderson and Dunham (1953) recorded that beneath the Permian of Durham there is a reddened zone. This zone, which is transgressive and in no way attributable to original red minerals in Carboniferous rocks, does not lie directly beneath the Permian, but is separated from it by grey rock. The latter is generally 3 to 10 ft thick, though less commonly it amounts to between 10 and 30 ft, and in extreme cases is absent or, as in a bore near Black Hurworth, as much as 53 ft thick.

This grey zone, especially in its upper part, is in most places pyritic, and it seems reasonable to suppose that it owes its colour, in part at least, to the reduction of secondarily oxidized and reddened Coal Measures by waters percolating down from the Marl Slate sea (p. 96). This explanation is satisfactory where the grey zone is shallow, but where it is deep original non-reddening, rather than reduction, may be responsible. At the top of the grey zone there is commonly what appears to be a leached layer, generally only a few inches thick, but in places extending down to a foot or two. Where the rock at the sub-Permian surface was formerly mudstone it has been changed in places to a very pale grey or whitish dust. The superficial pale grey zone, though apparently leached, is now commonly pyritic. Where mudstone in this zone contains moisture, it resembles certain types of seatearth-mudstone and it has consequently been termed 'seggar' in some old records. In some respects it is indeed comparable, for it seems to be deficient in iron and it may have a rather greasy texture, but it does not contain the characteristic rootlets of normal seatearth, and this enables the distinction to be made.

The reddened zone below the grey zone can be loosely divided into two parts. In the upper of these all the rocks are coloured except where they are near to coals or other beds with a high organic content. Mudstones and siltstones are generally purplish red, clay-ironstones exhibit colour-banding with brownish yellow cores, and coals, in some cases, have been totally oxidized. This subzone extends in places down to about 70 or 80 ft below the unconformity, but it may be as little as 10 ft or even absent. It is underlain by a subzone in which reddening is confined to sandstones. Micaceous partings in these are commonly picked out in bright shades of red, while the body of the rock is only pale pink. In many bores this restricted reddening extends to more than 100 ft below the unconformity, and the maximum depth so far proved is 292 ft in the Dalton Nook Bore, closely approached by 285 ft in Fishburn 'D' Bore.

The origin of the reddening in Durham is thought by Anderson and Dunham (1953, p. 31) to be due to oxidation of pyrite and chalybite in situ and to introduction of red iron oxide along joints and into pore-spaces of sandstones. The pre-Zechstein age of at least some of the reddening can now be demonstrated by the incorporation of fragments of reddened Carboniferous rocks in the Basal Permian Breccias. Since some of the breccias have a general pink tinge, however, the possibility arises that reddening continued while they were being formed. E.A.F.

Palaeontology of the Coal Measures

In the predominantly non-marine environment under which the greater part of the Coal Measures was deposited, the most common inhabitants of the waters of the swamps were non-marine lamellibranchs, crustaceans such as ostracods, and worms and fish. The periodic but short-lived incursions of the sea profoundly affected the endemic swamp fauna, causing it to withdraw from the area during the duration of marine conditions, and in turn introducing a marine fauna of foraminifera, sponges and brachiopods. On the withdrawal of the sea the swamp fauna repopulated the area until driven out by the emergence of the coal-forming forests or further marine invasions. 'Estheria' is found interbedded at intervals in the non-marine facies and also in strata associated with the marine bands; the appearance of these fossils in the sequence is thought to be dependent on the extension of special and somewhat brackish conditions into the swamps (see below).

Non-marine fossils

Lamellibranchs

The non-marine lamellibranchs or 'mussels' are the best known of the Coal Measures fossils; they occur abundantly at certain levels forming characteristic 'mussel'-bands, which are valuable as marker-horizons. The 'mussels' are most commonly found in the roof measures of coals, but they also occur in mudstones in other parts of the sequence. They inhabited the relatively shallow tracts of water which spread over extensive areas with the drowning of the Coal Measures forests. The mutual exclusion of the 'mussels' and typical marine fossils is accepted as evidence that the habitat of the 'mussels' was not marine (Trueman 1946, p. lxii), but whether they favoured fresh-water or brackish conditions is not definitely established. It is evident that the ecological ranges of the different genera varied to some degree, particularly their tolerance of salinity (Weir 1945). In this respect the habitat of Curvirimula, and to a lesser extent Naiadites, approached most closely to near-marine conditions (see p. 28). Carbonicola, from its faunal associations in the Lower Coal Measures, appears to have favoured slightly more brackish conditions than the typical Middle Coal Measures genera Anthracosia, Anthracosphaerium and Anthraconaia. The habitat of Anthraconauta, though not known for certain, was apparently different from that of the other genera and related to the special conditions arising from the withdrawal of marine influence from Western Europe in Upper Coal Measures times (Weir 1960, p. 299).

In the Durham–West Hartlepool district, of the seven genera of Coal Measures non-marine lamellibranchs, only Anthraconauta is not recorded and this can be explained by the absence of the Upper Coal Measures to which it is virtually confined. The distribution of the other six genera is as follows: Carbonicola is characteristic of, and confined to, the Lower Coal Measures. During the resurvey the highest position at which it has been found is in the roof measures of the Top Busty Coal, but in adjacent districts Carbonicola is found up to the band above the Harvey Coal. Anthracosia replaces Carbonicola as the dominant genus, appearing in the highest part of the Lower Coal Measures and continuing up to the beds associated with Kirkby's Marine Band, which is the highest faunal horizon proved in the district. Elsewhere in the Durham coalfield, Anthracosia ranges up to just below the Ryhope Marine Band. Anthracosphaerium is known rarely in the Lower Coal Measures, but is more common in the lower part of the Middle Coal Measures; the highest record obtained during the resurvey is from just below the position of the High Main Marine Band; in other districts the upper limit is similar to that of Anthracosia. Anthraconaia is generally rare in the district but ranges from the beds above the Brockwell Coal to the 'mussel'-band above the High Main Marine Band. Naiadites is known from most of the 'mussel'-bands and also in isolation at numerous intervening horizons. Finally, Curvirimula is typical of the Lower Coal Measures faunal horizons up to the 'mussel'- band 15 ft above the Three-Quarter Coal; it is then absent from the sequence until it reappears in the 'mussel'-band overlying the High Main Marine Band and in the upper part of Kirkby's Marine Band. The inference from this close association with the regressive phase of the marine incursion is that Curvirimula favoured a more saline environment than the other 'mussel' genera (see also Weir 1960, pp. 298–9).

Crustaceans

The commonest crustaceans in the Coal Measures are the ostracods which are mainly found either closely associated with the lamellibranchs or occupying distinct layers within the 'mussel'-bands. The two principal genera are Geisina and Carbonita; the former is characteristic of the Lower Coal Measures, but is absent from the Middle Coal Measures except for rare examples in the regression stage of the High Main Marine Band (p. 28). This distribution of Geisina accords with that found in the other Pennine coalfields, and also with the view that the habitat of Geisina was more brackish than that of Carbonita. The latter genus ranges throughout the British Coal Measures particularly in the higher beds where the marine influence has declined. The two characteristic bands in this district are the Brockwell Ostracod Band (p. 24) containing Carbonita humilis (Jones and Kirkby), C. cf. pungens (Jones and Kirkby) and numerous immature forms, and the Hopkins Band (p. 26) in the roof measures of the Harvey Coal, where Geisina arcuata (Bean) is abundant. C. humilis and C. pungens also occur in the Middle Coal Measures, and there are records of elongate forms comparable with C. scalpellus (Jones and Kirkby) from above the Low Main Post and close below the High Main Marine Band. An elongate ostracod with a finely striated carapace, here referred to as Hilboldtina sp., is known from the 'mussel'-band just below the Hutton Coal and also above the Bottom Brass Thill Coal.

'Estheria' is a small bivalved crustacean related to the water fleas. The isolated valves of the carapace are distinctive fossils and commonly show an iridescent preservation. In such circumstances the precise generic identity cannot always be established and the general term 'Estheria' is employed. The tendency for 'Estheria' to be restricted to discrete horizons of wide lateral extent is comparable to the behaviour of the marine bands with which 'Estheria' is commonly associated. The implication of this distribution is that 'Estheria' was not a member of the swamp fauna, but favoured special conditions found in the brackish regions fringing the marine environment (see also Defrise-Gussenhoven and Pastiels 1957, p. 65). Periodically these brackish conditions extended into the swamps, in some cases as a prelude or aftermath of a marine incursion, and brought in the floods of 'Estheria' which characteristically occur in the initial or regressive phases of a marine incursion. In general, 'Estheria' is not found with other fossils, although at some horizons abundant fish remains are associated with it. In the Durham–West Hartlepool district the main occurrences of 'Estheria' are in the Fishburn 'Estheria' Band in the roof measures of the Three-Quarter Coal, in the Blackhall 'Estheria' Band a short distance below the Main Coal in the offshore bores, immediately below the High Main Marine Band, and associated with Kirkby's Marine Band.

Worms

Although worms are seldom preserved as fossils, their former presence in a sediment is indicated by tubes, trails or burrows. The coiled tubes of the serpulid Spirorbis occur either isolated or attached to 'mussels', notably Naiadites, or to plant remains. The trails and burrows, which are collectively known as 'trace-fossils', are found mainly in the argillaceous rocks; the sinuous trails of Cochlichnus [Belorhaphe] kochi (Ludwig) occur in the non-marine facies, notably in the beds above the Fishburn 'Estheria' Band. The burrows of Planolites ophthalmoides lessen are characteristically found in proximity to marine incursions (see p. 22), but are also found, though less commonly, associated with, or between, layers of 'mussels' such as Curvirimula and Carbonicola. The inference is that the layers containing Planolites represent a slightly more brackish environment than that of the 'mussel'-bands lying higher in the sequence. Such rare occurrences of P. ophthalmoides are known above the Top Marshall Green Coal, above the Victoria Coal and in the 'mussel'-band overlying the Brockwell Ostracod Band.

Fish

Isolated scales, teeth and bones of fish are common in both the 'mussel'-bands and marine horizons. The remains tend to be concentrated at the base of the faunal cycles immediately above a coal or seatearth, indicating that the fish were amongst the first animals to invade the area at the periodic flooding of the coal forests. Complete fish are rare, but their debris is notably abundant at certain horizons such as the Harvey Marine Band and in the beds associated with the High Main Marine Band. The common genera are Elonichthys, Rhabdoderma, Rhadinichthys, Rhizodopsis and Platysomids; all these forms occur in both the non-marine and marine facies, particularly the Lingula phase (see below). It seems possible that these fish were able to live in the shallow coastal waters and estuaries, and also in the swamp facies, but their wide distribution may also reflect transport of disintegrated remains far from their place of death.

Marine fossils

Only five marine bands have been proved in the Durham–West Hartlepool district, namely the band in the Middle Stotfold Bore taken as the base of the Coal Measures (p. 35), the Gubeon a short distance above the base, the Harvey at the base of the Middle Coal Measures, and the High Main and Kirkby's marine bands near the middle of the Middle Coal Measures. Costate Productids are recorded from the basal Coal Measures band, and the remainder contain Lingula. In addition, the fauna of the Harvey Marine Band at one locality (p. 58) includes fragmentary Orbiculoidea and Hollinella?; and the Gubeon and Kirkby's marine bands also contain foraminifera, sponge spicules and Planolites ophthalmoides. The bands are thin and the faunas impoverished and they do not display clearly the sequence of faunal phases found in fully developed marine bands such as those of the central and south Pennines (Calver in Smith and others 1967, pp. 91–4). However, some of the phases can be recognized in the district, particularly when augmented by evidence gained from adjacent parts of the coalfield. An idealized sequence of stages in a marine incursion may be envisaged as a progress from a basal fish phase through layers dominated respectively by P. ophthalmoides (p. 21), foraminifera, and Lingula; the acme of the incursion is represented by the presence of the cephalopod/lamellibranch fauna such as is found in the Ryhope Marine Band farther north in the Sunderland (21) district. The regression stage of the incursion mirrors the advance, except that the equivalent of the basal fish phase is not often present, its place being taken by non-marine lamellibranchs such as Naiadites. In many cases the advance of the marine invasion appears to have been more rapid than the retreat, since the initial phases are condensed or may even be absent, whereas in the regression stage the different phases are thicker and more clearly distinguishable.

The typical lithology for both the Planolites and foraminifera phases is a pale grey to dark grey, smooth or slightly silty mudstone. Increase in carbonaceous matter or arenaceous material inhibited the existence of Planolites and foraminifera and they are seldom recorded from beds of this lithology. These factors probably explain their absence from the Harvey and High Main marine bands as developed in the district. The common foraminifera genera are Ammodiscus, Glomospira and Tolypammina.

Faunal succession

The general sequence of faunas in the Coal Measures of the Durham and Northumberland coalfields has been described in a series of papers by Hopkins (1929, 1930; see also 1954) but no systematic investigation of their detailed distribution in the Durham district had been undertaken prior to the resurvey. A brief reference to fossils from the Fishburn boreholes was made by Trueman and Weir (1946, p. 14) in their discussion of Carbonicola declivis Trueman and Weir, while Magraw and others (1963) have referred to collections made from bores in the Elwick–Hartlepools area.

The application of the non-marine lamellibranch zonal scheme to the local sequence is shown in (Figure 3), which also gives the position of the more important faunal horizons. In the following account the main characteristics of the faunal sequence are described, and interpreted in terms of zonal position. The detailed fauna of individual bands is included in the detailed stratigraphical account (pp. 35–86); representative fossils from the district are figured on (Plate 2).

Lower Coal Measures

In the absence of the characteristic Gastrioceras subcrenatum fauna, the base of the Coal Measures has been taken arbitrarily at the marine horizon containing costate Productid fragments at 942 ft in the Middle Stotfold Borehole. Os noted on pp. 11, 35 this decision is based on indirect faunal evidence, particularly on information gained from adjacent areas, but it accords with the known facies changes affecting the G. subcrenatum horizon in the north Pennines. Apart from this Middle Stotfold band the lowest fossiliferous horizon recorded from definite Coal Measures of the district is the Gubeon Marine Band of the East Hetton Colliery Busty Borehole and Offshore No. 1 Borehole which contains rare foraminifera, pyritized sponge spicules, Planolites ophthalmoides, Lingula mytilloides J. Sowerby, Rhizodopsis sp.and undetermined Palaeoniscid scales. There is insufficient faunal evidence to determine the precise equivalent of this marine band in terms of the standard south Pennine succession, but the presence of foraminifera suggests that this band is unlikely to be lower than the Gastrioceras listed horizon. Although in the absence of non-marine lamellibranchs direct evidence is lacking, by inference the Anthraconaia lenisulcata Zone is represented by these lower measures; the junction with the overlying C. communis Zone cannot be determined with confidence, but it is taken at the Ganister Clay horizon pending further evidence. The lowest fauna referred to the C. communis Zone is that containing Carbonicola cf. communis Davies and Trueman and Curvirimula sp.from 30 ft above the Ganister Clay Coal (see p. 37). There is some resemblance between the Carbonicola and the shells known from the 'mussel'-band which lies between the Albrighton and Lower Three-Quarter coals of the Cumberland Coalfield (Taylor 1961, pp. 7, 20; cf. Trueman and Weir 1947, pl. v, fig. 19) and which is placed in the lower part of the C. communis Zone and correlated with the Carbonicola torus Eagar fauna of the Lancashire Coalfield (Eagar 1956, p. 356).

Between the Top Marshall Green and Victoria coals poorly preserved lamellibranchs have been found at three horizons. The fauna includes ?Anthracosphaerium dawsoni (Brown), a small form of Carbonicola pseudorobusta Trueman, Curvirimula sp.and Naiadites flexuosus Dix and Trueman. This assemblage is not diagnostic but gives the first indication of the incoming of C. pseudorobusta and is therefore likely to be near the base of the middle C. communis Zone, and approximately equivalent to the beds overlying the horizon of the Arley/Kilburn coals of the central Pennine coalfields. The C. pseudorobusta group appears in force above the Victoria Coal. The shells are smaller than typical forms and usually confined to the basal foot or so of the band in which Curvirimula and fish remains are commonly found. At some localities Carbonita humilis and Geisina arcuata also occur but are far less common than in the higher Brockwell Ostracod Band. In the Fishburn series of boreholes the basal layer is overlain by up to 5 ft of pale mudstones in which the shells are small and less common and are interbedded with Planolites ophthalmoides. The Carbonicola shells include C. cf. rhindi (Brown) and C. declivis Trueman and Weir sensu lato (cf. Trueman and Weir 1946, p1. ii, fig. 28).

A higher band overlying the seatearth about midway between the Victoria and Brockwell coals is typically represented by small poorly preserved Carbonicola (cf. Trueman and Weir 1946, pl. ii. figs. 24, 27). Those showing straight ventral margin, posterior truncation and carina are termed C. aff. declivis; others, which form the majority, have curved ventral margin, higher Height /Length ratio, shorter anterior end and lack the carina and truncation, and are therefore compared to stunted forms of Carbonicola cf. acuta (J. Sowerby) and C. cf. communis. This horizon has been referred to as the C. declivis Band (Magraw and others 1963, p1. xix) but it is inadvisable to continue to use this name for this horizon as the acme of typical C. declivis is in the band above the Brockwell. Curvirimula is represented by C. subovata (Dewar) and Naiadites flexuosus is also present. The absence of Carbonita is a further distinction between this horizon and that above the Brockwell Ostracod Band.

The detailed faunal sequence in the Brockwell Ostracod Band provides a readily recognized marker horizon. As its name implies, the characteristic feature of this band over much of the district is the abundance of ostracods in the ferruginous basal layers, where they are associated with Curvirimula subovata and fish remains. Carbonita humilis is the most common ostracod, but C. pungens and undescribed species of Carbonita are also present; the ostracods are in general of small size and immature forms are common; Geisina arcuata is recorded at some localities, but is rare. In the upper part of the band lamellibranchs are dominant, but the fauna varies in different parts of the district. In the Fishburn area, where the band is approximately 6 ft thick, the majority of the. Carbonicola belong to an assemblage of C. declivis, the type of which comes from this band in the Fishburn No. 2 Bore (Trueman and Weir 1946, p. 14, pl. ii, figs. 15, 17, 18; refigured in this memoir, ((Plate 2), fig. 12). Trueman and Weir also figured three specimens from the equivalent horizon in the Fishburn No. 1 Bore as Carbonicola declivis (pl. ii, figs. 21–22) and C. aff. declivis (pl. ii. figs. 25, 26). The type of C. declivis measures 14.5 mm but Trueman and Weir stated (p. 13) in their diagnosis that this species may attain 30 mm, which is about the size of the largest shells occurring in this Brockwell fauna; the implication is that the type of C. declivis is either a juvenile or is stunted. However, certain of the larger shells compare with Carbonicola browni Trueman and Weir which has a similar form to C. declivis, but differs mainly in its greater size, the holotype measuring 54 mm (Trueman and Weir 1946, p1. ii, fig. 8; refigured Lumsden and Calver 1958, pl. iv, fig. 12). Since there is no evidence to link these larger shells ((Plate 2), figs. 14, 15) in a continuous series with the type of C. browni, it seems preferable to include them with C. declivis, although with the emphasis on certain morphological features they could also be referred to as C. cf. browni. Associated fossils include cf. Carbonicola circinata Pastiels, Curvirimula subovata and Anthraconaia fugax Eagar. The latter fossil provides a link with the Yorkshire Coalfield where A. fugax occurs a short distance below the Low 'Estheria' Band, and also with the Burnley Coalfield where the same species is known from above the Blindstone Rider Mine (Calver in Earp and others 1961, p. 200; Eagar 1962, p. 331). In Fishburn No. 1 and 'B' bores a slightly higher band lies 10 ft above the C. declivis fauna and contains a different assemblage. The fossils identified include Spirorbis sp., Carbonicola pseudorobusta, Curvirimula candela (Dewar), C. subovata, Naiadites sp., and fish remains including Elonichthys sp.and Rhabdoderma sp.

Farther east, in the Elwick series of boreholes, e.g. at Low Throston, the fossils in the Brockwell Ostracod Band range over some 13 ft of strata, but C. declivis is absent. A basal layer with fish remains is overlain by a few inches of mudstone with abundant Carbonita humilis and rare Geisina arcuata. The succeeding measures contain a fauna of large shells including Carbonicola pseudorobusta?, C. cf. rhomboidalis Hind, C. cf. robusta (J. de C. Sowerby), Curvirimula candela, C. subovata, Naiadites sp., in addition to Geisina arcuata and fish remains including Elonichthys sp.and Rhadinichthys sp.About the middle of the band are several examples of Planolites ophthalmoides associated with Curvirimula and Carbonicola. This fauna from the Elwick area is therefore more like that of the higher of the two bands recorded in Fishburn No. 1 and 'B' bores (see above).

The generic assemblage from the Brockwell Ostracod Band is similar to that from immediately above the Victoria, although at the latter horizon ostracods are far less common, and the Curvirimula are smaller; on the other hand, Naiadites is rare in the Brockwell fauna, but is recorded at several localities in the measures overlying the Victoria Coal.

Bores in the northern part of the district have shown that two faunal bands occur between the Brockwell and Three-Quarter coals. The lower, which is probably the equivalent of the Ostracod Band of the south, contains small Carbonicola sp., Carbonita spp., Geisina arcuata and fish remains. In the higher band, as proved in Eppleton No. 2 Bore, the fauna comprises Curvirimula candela ((Plate 2), fig. 13), C. subovata, Carbonita humilis, C. cf. pungens and fish remains. In Murton No. 1 Bore, this higher band contains Anthraconaia sp.nov.of A. modiolaris (J. de C. Sowerby) group, Curvirimula candela and C. subovata. The presence of Anthraconaia is of interest for the genus is rarely found in the C. communis Zone, but a comparable record is noted by Hind (1895, p. 163) and Hopkins (1930, p. 103) in a reference to Anthracomya adamsi (Salter) from the Brockwell horizon near 'Wylam' in the Newcastle upon Tyne (20) district.

The records of 'Estheria' in the roof measures of the Three-Quarter Coal at several localities in the southern part of the district justify the term Fishburn 'Estheria' Band (p. 45) for this occurrence. The specimens measure up to 4 mm in length and have the widely-spaced growth lines seen also in examples from the Low 'Estheria' Band of the East Pennine Coalfield. The stratigraphical position of these respective bands in the two areas and their relationship to the non-marine faunas strongly suggest that they are the same horizon, which is a convenient boundary between the middle and upper parts of the C. communis Zone. Preservation of these fossils is generally poor, and pending generic revision, the non-committal designation

'Estheria' is employed for this form. However, the wide spacing of the growth lines can usually be discerned, a feature which distinguishes this form from the Lioestheria vinti (Kirkby) of the Middle Coal Measures. At some localities the pale-coloured mudstones overlying the 'Estheria' Band contain Cochlichnus [Belorhaphe] kochi and cf. P. ophthalmoides.

A 'mussel'-band about 15 ft above the Three-Quarter Coal is known in the Fishburn–East Hetton area and contains Carbonicola pseudorobusta, Curvirimula candela, C. subovata, Carbonita cf. humilis, Geisina arcuata and fish scales including Rhabdoderma. This is the highest band in the district from which Carbonicola pseudorobusta and Curvirimula spp.are recorded. The occurrence of large C. candela recalls the fauna from above the Cannel Mine of West Lancashire and above the Lower Yard Rider Mine of Burnley (Calver in Earp and others 1961, p. 201); on this comparison the zonal position is placed near the top of the C. communis Zone.

Several examples of Anthracosphaerium cf. dawsoni (Brown) ((Plate 2), fig. 11), preserved as internal moulds in ironstone, were found associated with small Carbonicola sp.and Naiadites flexuosus in the roof measures of the Top Busty Coal of the Fishburn No. 3 Borehole. Elsewhere in the district fossils have rarely been found at this horizon; exceptions are Fishburn 'B' Bore and a bore in the Butterwick area where Carbonicola rhomboidalis? is recorded. The A. cf. dawsoni recall the similar forms known as a constituent of the Carbonicola cristagalli Wright fauna at the base of the Anthraconaia modiolaris Zone in several southern Pennine coalfields, including the suite figured by Trueman and Weir (1955, fig. 27) from the roof of the Middle Lount Coal of the Leicestershire Coalfield. Although in the Durham–West Hartlepool district the C. cristagalli fauna is not recognized as such, an equivalent horizon is thought to be represented by this band containing A. cf dawsoni. The Top Busty Coal is therefore taken as the provisional junction of the C. communis and A. modiolaris zones.

The measures between the 'mussel'-band above the Top Busty Coal and the Harvey Coal are relatively unfossiliferous; consequently there is little evidence of the fauna found in other coalfields in measures representing the lower part of the lower A. modiolaris Zone. The next higher fauna which can be assigned to a zonal position is that overlying the Harvey Coal where the Anthracosia regularis (Trueman) fauna becomes dominant, although the genus first appears a short distance below this coal (p. 53). As well as A. regularis the lamellibranchs include rare Anthraconaia modiolaris, Naiadites sp.intermediate between productus (Brown) and quadratus (J. de C. Sowerby), associated with Spirorbis sp., Carbonita sp., Geisina arcuata and Palaeoniscid scales. This assemblage is characteristic of the measures in the upper part of the lower Anthraconaia modiolaris Zone in the majority of the British coalfields. The distinctive faunal profile (see p. 56) described by Hopkins (1929, p. 8) as a feature of this band in the Northumberland and Durham coalfields cannot always be recognized, although the abundance of G. arcuata in the basal layers is characteristic. This abundance is also found in the A. regularis faunal belt of the whole Pennine area including Cumberland (Calver in Taylor 1961, p. 22), the East Pennine Coalfield (Eagar 1960, pp. 146–7) and also in the nearby Midgeholme Coalfield.

Middle Coal Measures

The Harvey Marine Band at the base of the Middle Coal Measures is the equivalent of the Anthracoceras vanderbeckei marine horizon of the British coalfields, but displays the impoverished development characteristic of the coalfields of the north and west of the Pennine Province. The fauna is usually restricted to Lingula mytilloides (up to 6 nun in length) and fish remains such as scales and teeth of Elonichthys, Helodus, Rhadinichthys and Rhizodopsis. In the Elwick No. 3 Bore sponge spicules were found in addition, and in the Hartlepools Lighthouse Point Bore the fauna consisted of fragmentary Orbiculoidea and Hollinella? The fossils occur characteristically in a finely-micaceous, silty mudstane, the maximum thickness of the band not exceeding 6 in. At some localities the Lingula are found with both valves in contact and undamaged suggesting deposition under quiet conditions; elsewhere, e.g. Hartlepool Lighthouse Bore and Offshore No. 2 Bore, the brachiopods are fragmentary and largely confined to the more sandy patches of the core samples, implying erosion and re-deposition. The absence of foraminifera and Planolites ophthalmoides from this marine band can be explained by the prevalence of the silty lithology.

The measures between the Harvey Marine Band and the Maudlin Coal are placed in the upper A. modiolaris Zone, which is conveniently subdivided at the Bottom Brass Thill Coal into upper and lower parts. In the lower part, which includes the 'mussel'-bands above the Harvey Marine Band and those above the Ruler and Hutton coals, the Anthracosia spp.are mainly dominated by A. ovum Trueman and Weir ((Plate 2), fig. 10) and A. aquilina (J. de C. Sowerby) with subordinate A. phrygiana (Wright) and A. subrecta Trueman and Weir. Anthraconaia is represented by A. modiolaris and A. cf. curtata (Brown) in the beds below the Hutton, but above this coal only small or fragmentary Anthraconaia has been obtained. The characteristic Naiadites are N. triangularis (J. de C. Sowerby) and N. quadratus; the Anthracosphaerium species recorded include A. cf. affine (Davies and Trueman), A. exiguum (Davies and Trueman) and A. turgidum (Brown). There is little to distinguish the assemblages from above both the Bottom and Top Hutton coals, and in the absence of diagnostic Anthraconaia the precise position of the Hutton faunas in terms of the upper A. modiolaris sequence of faunas has not been established.

In the highest part of the A. modiolaris Zone the faunal records are largely confined to the 'mussel'-bands above the Bottom and Top Brass Thill coals. These two horizons possess similar assemblages, in which the Anthracosia phrygiana group ((Plate 2), fig. 9), including A. beaniana and A. disjuncta Trueman and Weir ((Plate 2), fig. 8), is more in evidence than in the lower beds. The Anthracosphaerium species are similar to those below except that A. turgidum ((Plate 2), fig. 7) is more common. Naiadites quadratus is the typical species, but Anthraconaia is rare.

The Maudlin Coal is taken as the base of the Lower similis-pulchra Zone largely on the evidence obtained in adjacent areas to the north where the Anthraconaia pulchella Broadhurst fauna is well developed above the coal. An important faunal marker band near the base of the zone is the Blacichall 'Estheria' Band (Magraw and others 1963, p. 164) occurring just below the Main Coal in the Offshore Nos. 1 and 2 boreholes. The 'Estheria' are preserved as iridescent films and are invariably associated with fish debris. A similar 'Estheria' band associated with the Anthraconaia pulchella fauna is known from the base of the Lower similis-pukhra Zone in Lancashire (Magraw 1961, p. 442), in the east Pennines (Calver in Smith and others 1967, p. 173) and in Ayrshire (Mykura 1967, p. 64); the horizon is considered to be the same in all four areas.

In the measures between the Maudlin and the High Main coals, corresponding to the lower part of the Lower similis-pulchra Zone, lamellibranchs are not common. Several horizons contain Naiadites productus and a winged variant, as well as N. aff. alatus Trueman and Weir. The Anthracosia species are largely confined to the faunal bands between the Metal and High Main coals from which A. cf. aquilinoides (Chemyshev) and A. sp. cf. caledonica Trueman and Weir were collected, together with Anthraconaia sp.  nov. cf. wardi (Hind) ((Plate 2), fig. 6) and Anthracosphaerium propinquum (Melville) ((Plate 2), fig. 5).

The important Anthracosia atra (Trueman) group makes its appearance in the 'mussel'-band between the High Main Coal and the overlying marine band where it is associated with Anthracosphaerium radiatum (Wright) and other representatives of the Anthracosia acutella (Wright) concinna (Wright) fauna. This assemblage is similar in many respects to that from a slightly higher horizon overlying the High Main Marine Band in adjacent areas to the north (Hopkins 1933).

A distinctive faunal profile is recognizable in the measures associated with the High Main Marine Band as the following composite sequence illustrates. The seatearth or coal at the base is overlain by abundant fish remains; at some localities Anthracosia cf. atra, Naiadites sp., Carbonita humilis and C. cf. scalpellus are found in addition. This basal layer is succeeded by 1 to 2 ft of mudstone with abundant Lioestheria vinti ((Plate 2), fig. 4) and fish remains, and is in turn overlain by dark silty mudstone containing Lingula sp.The marine band is generally only a few inches thick, but in the Easington E. 11 Underground Bore the Lingula range over 1 ft 7 in. They are up to 4 mm in size and include a broad form of L. mytilloides ((Plate 2), fig. 2); no other marine fossils have been found at this horizon in the district. A thin band with abundant fish debris overlies the marine band and is in turn succeeded by some 10 to 15 ft of mudstone with a characteristic fauna at the top. The fauna includes Anthraconaia sp.nov. cf. wardi, Anthracosia cf. atra, A. cf. simulans Trueman and Weir, Curvirimula sp., Naiadites cf. obliquus Dix and Trueman, N. cf. productus, Carbonita humilis and Geisina sp.Spirorbis sp.is locally abundant at the base. Many of the lamellibranchs are small and possibly stunted, and, coupled with the presence of Curvirimula and Geisina, support the interpretation that the environment at this period was more brackish than that prevailing during the deposition of a typical 'mussel'-band. As noted above (p. 20), both Curvirimula and Geisina are found in the regression stages of the marine bands of the Lower and Upper similis-pulchra zones, although absent from intervening strata (see Calver in Smith and others 1967, pp. 88–9). The typical well-developed 'High Main shellbed' known elsewhere in Durham and Northumberland (Hopkins 1933) has not been noted from the district but it may be represented by the sparse Anthraconaia aff. librata (Wright) ((Plate 2), fig. 3) found in Easington E.11 Bore 25 ft above the marine band.

Kirkby's Marine Band (the highest faunal band so far proved in the district) is distinguished by the close relationship between the marine fossils and non-marine lamellibranchs, and the association with Lioestheria. The fauna obtained from this horizon includes foraminifera, sponge spicules, Planolites ophthalmoides, Lingula spp., Anthracosia cf. atra, Curvirimula sp.and fish debris. From the evidence of the collections from Hawthorn Colliery Shaft and also from bores just to the north of the district, the non-marine lamellibranchs tend to be concentrated in a band between two layers of marine fossils, although both foraminifera and P. ophthalmoides occur on the same bedding plane as the Anthracosia. The basal marine phase occurs in a dark grey, slightly silty mudstone, and contains in addition to Lingula, rare foraminifera and pyritized sponge spicules. The succeeding grey mudstones have Anthracosia cf. atra and foraminifera at the base, but in their upper part the fauna is largely P. ophthalmoides, abundant foraminifera including Glomospira and Tolypammina, and Lingula. In these upper beds, the pyritized strap-like markings and pyrite-filled burrows are possibly atypical preservations of P. ophthalmoides. Some of the foraminifera occur massed in elongated patches in the plane of the bedding; these accumulations may represent mulled burrows or it is possible that the tests have been used for the formation of the walls of worm-tubes similar to the present day Terebelloids. An elongate grouping is also shown by specimens of Lingula forming a chain-like arrangement. Although the majority of the Lingula are referred to L. mytilloides there are several examples which are proportionately narrower and are here compared with L. elongata Demanet ((Plate 2), fig. 1), which is also recorded from the Haughton Marine Band of the East Pennine Coalfield (Calver in Smith and others 1967, p. 184). The presence of Curvirimula associated with foraminifera in the upper part of the band recalls the comments made in the description of the High Main Marine Band (see above). It is also significant that Curvirimula is characteristically found in strata associated with the presumed equivalent Bradford/ Haughton Marine Band in other coalfields of the Pennine province (Calver in Magraw 1960, p. 482; Calver in Smith and others 1967, p. 183.

Lioestheria is present in isolation in grey mudstones; the precise position of this phase in the sequence of Kirkby's Marine Band based on the collections from Hawthorn Colliery Shaft has not been ascertained, but evidence from other areas suggests that the Lioestheria occur in the upper part of the marine band, or immediately overlying it. M.A.C.

Details of stratigraphy

During the long history of mining and exploration in this district about one thousand shafts and bores have been sunk. Representative sections are shown graphically in (Figure 5) (Millstone Grit Series), (Plate 3) and (Plate 4) (Lower and Middle Coal Measures) and (Figure 16) (uppermost Middle Coal Measures). The sites of these are indicated on (Plate 3) and (Plate 4). 1, Eppleton Colliery. *2, Murton No. 2 Bore. *3, Dawdon Colliery. *4, Dawdon No. 3 Bore. 5, Harbour House Drifts. 6, Cocken Drifts. 7, Cocken Colliery. *8, Rainton Colliery, Adventure Pit. 9, Rainton Colliery, Meadows Pit. 10, Rainton Colliery, Hazard Pit. 11, Hetton Colliery. *12, Eppleton No. 2 Bore. *13, Murton No. 1 Bore. *14, Murton Colliery. *15, Easington Colliery No. 11 Bore. *16, Easington Colliery No. 3 Bore. *17, Easington Colliery No. 9 Bore. 18, Framwellgate Colliery. *19, Frankland Colliery, Furnace Pit. 20, Brasside Colliery. 21, Woodside Colliery. *22, Belmont Colliery, Furnace Pit. *23, Rainton Colliery, Lady Seaham Pit. *24, Rainton Colliery, Alexandrina Pit. *25, North Hetton Colliery, Moorsley Winning. *26, Elemore Colliery. *27, South Hetton Colliery. 28, Hawthorn Colliery. *29, South Hetton No. 7 Bore. *30, Murton No. 3 Bore. *31, Easington Colliery No. 5 Bore. *32, Easington Colliery No. 12 Bore. 33, Aykleyheads Pit. *34, Durham Main Colliery. *35, Kepier Colliery, Florence Pit. 36, Kepier Grange Colliery. *37, Grange Colliery, New Winning. 38, Broomside Colliery. 39, North Pittington Colliery, Buddle Pit. *40, North Pittington Colliery, Londonderry Pit, and Littletown Colliery, Engine Pit. *41, Littletown Colliery, Lady Alice Pit. *42, South Hetton No. 6 Bore. *43, Murton No. 5 Bore. *44, Easington Colliery. *45, Horden No. 5 Bore. *46, Horden No. 20 Bore. *47, Horden No. 15 Bore. *48, Offshore No. 2 Bore. 49, Elvet Colliery. 50, Kepier Colliery. *51, Old Durham Colliery. *52, Sherburn Colliery, Lady Durham Pit. *53, Sherburn House Colliery, North Pit and Pit Bore. *54, Sherbum Hill Colliery, East Pit. *55, Ludworth Colliery. *56, Haswell Colliery. *57, South Hetton No. 10 Bore. 58, Mill Hill Reservoir Bore. *59, Horden No. 4 Bore. *60, Harden Colliery. *61, Horden No. I Bore. *62, Horden No. 19 Bore. *63, Horden No. 12 Bore. *64, Blackhall No. 33 Bore. *65, Blackhall No. 43 Bore. *66, Houghall Colliery, and No. 1 Bore. *67, Shincliffe Colliery. *68, Whitwell House Bore. 69, Whitwell Colliery, A' Pit. 70, Whitwell Colliery, C' Pit. 71, Whitwell Colliery, B ' Pit. 72, Cassop Moor Colliery. 73, Cassop Vale Colliery. *74, Thornley Colliery. *75, Wheatley Hill No. 5 Bore. *76, Wheatley Hill Colliery. *77, Wheatley Hill No. 2 Bore. *78, Shotton Colliery. *79, Shotton Colliery No. 7 Bore. *80, Shotton Colliery No. 1 Bore. *81, Shotton Colliery No. 6 Bore. *82, Blackhall Colliery. *83, Blackhall No. 9 Bore. *84, Blackhall No. 16 Bore. *85, Blackhall No. 28 Bore. *86, Blackhall No. 36 Bore. *87, Offshore No. 1 Bore. *88, Low Butterby No. 2 Bore. *89, Butterby No. 4 Bore. *90, Bowburn Colliery, New Pit. *91, Coxhoe, Bell's Pit. *92, Heugh Hall No. 1 Bore. 93, Heugh Hall Colliery. 94, West Hetton Colliery. *95, Coxhoe Colliery, Engine Pit. 96, Crowtrees Colliery. 97, South Kelloe Colliery. *98, East Hetton Colliery, Busty Bore. *99, East Hetton Colliery, North Pit. *100, Cassop Colliery, 'A' Pit. *101, East Hetton Colliery, No. 32 Bore. 102, Kelloe New Winning. 103, Deaf Hill Colliery. 104, Wingate Grange Colliery. 105, Hutton Henry Marley Pit. *106, Hutton Henry Perseverance Pit. *107, Castle Eden No. 1 Bore. *108, Castle Eden Colliery. 109, Thorpe Bulmer Bore. *110, Black Halls Bore. *111, Blackball Nos. 18 and 19 bores. 112, Hart Bore. 113, Croxdale Colliery, Thornton's Pit. *114, Tudhoe Colliery, West Pit. 115, Metal Bridge Drifts. *116, Tursdale Colliery, South Pit. *117, Coxhoe Brickyard Bore. 118, Clarence Hetton Pit. 119, Cornforth Colliery, George Pit. *120, Garmondsway 'B' Bore. 121, Garmondsway Moor Colliery. *122, Trimdon Grange Bore. *123, Trimdon Grange Colliery. 124, Trimdon Colliery. *125, Deaf Hill No. 4 Bore. *126, South Wingate Colliery. 127, Fifty Rigs Plantation Bore. 128, Naisberry Waterworks Nos. 1 and 2 bores. 129, Low Throston Bore. 130, Howbeck Hospital Bore. 131, North Sands Bore. 132, Hartlepool Lighthouse Bore. 133, Tudhoe Grange Colliery. *134, Dean and Chapter Colliery, No. 3 Pit. *135, East Howle Colliery, Catherine Pit. *136, West Comforth Colliery, Thrislington Coke Oven Pit. *137, Thrislington Colliery, Jane Pit. *138, Garmondsway Pit. 139, Fishburn No. 1 Bore. *140, Fishburn No. 2 Bore. 141, Fishburn 'B' Bore. 142, Dropswell Bore. 143, Cotefold Close Bore. *144, Elwick No. 1 Bore. 145, Dalton Piercy Waterworks bores. *146, Dalton Nook Bore. *147, Chilton Colliery. *148, Chilton Colliery, 'E' Bore. 149, Little Chilton Colliery, Cragg Pit. *150, Mainsforth Colliery, East and West Pits. *151, Bishop Middleham Colliery, East Pit. 152, Fishburn 13' Bore. *153, Fishburn Colliery, North Pit. *154, Fishburn No. 3 Bore. *155, Fishburn No. 4 Bore. *156, Murton Blue House Lane Bore. *157, Murton Hall Farm Bore. *158, Windlestone Colliery. 159, South Mainsforth 'J' Bore. 160, Nunstainton No. 2 Bore. 161, Nunstainton No. I Bore. 162, Stony Hall Bore. 163, Ryal Bore. *164, Ten-o'Clock Barn No. 2 Bore. *165, Whin Houses Bore. *166, Whin Houses Farm Bore. *167, Ten-o'Clock Barn No. I Bore. *168, Embleton Old Hall Bore. 169, Tinkler's Gill Bore. 170, Middle Stotfold Bore. 171, Seaton Carew Bore. 172, Rushyford Bore." data-name="images/P991348.jpg">(Figure 4) which also shows the localities of other collieries and bores. Details of the more important coal seams are summarized in (Figure 6), (Figure 7), (Figure 8), (Figure 9), (Figure 10), (Figure 11), (Figure 12), (Figure 13), (Figure 14), (Figure 15), which show the principal lines of split and include isopachs of some of the thicker sandstones.

In many of the older records local terms are used to describe rock types and these are here quoted verbatim. Among these, 'post' generally refers to sandstone, 'metal stone' or 'fakes' to strata consisting of alterations of mudstone, siltstone and sandstone, 'post girdles' to thin bands of sandstone commonly present in 'metal stone', and 'metal' or 'blaes' to mudstone or shale. 'Whin' has been applied to any hard stone including certain sandstones and ironstones, though it is nowadays applied mainly to dolerite. The term 'thill' embraces all types of seatearth, though seatclays approaching fireclay in lithology are more commonly known as 'seggar' or the variants 'sagger' and 'sagre'. Coal of poor quality is called 'splint', and if dirty it is referred to as 'dant'. Cannel or cannelly shale which gives out a 'chattering' sound when burnt has been called 'parrot' and pyrite is usually known as 'brass'. In sections of coal the term 'band' is used for any interbedded layer other than coal and corresponds to the term 'dirt' used in other coalfields; 'banded coal' thus signifies coal with layers of dirt.

Description of outcrop, shaft, bore and mine-plan information is, as far as possible, related to localities shown on the One-inch Geological Map, but the exact positions are indicated either in the text or in Appendix 1 by reference to the National Grid. Records of selected bores drilled since the publication by the Institution of Mining Engineers of the volumes of Borings and Sinkings in Northumberland and Durham have been summarized in Appendix 1, p. 266, which also includes summaries of the full records of older bores and shafts published in those volumes.

Millstone Grit Series

Records of sinkings through the Millstone Grit Series of the district are restricted to a few borers' logs compiled during the nineteenth century. Some are shown graphically in (Figure 5), which indicates tentative correlation with the west Durham sequence.

The site of Ryal Bore (1874), which reaches the lowest stratigraphical horizon in the district, is not accurately known, but its position is thought to be in the vicinity of the swallow-hole [NZ 3633 2976], 300 yd S.W. of Ryal Farm, near Sedgefield. At a depth of 688 ft in this bore there is a limestone, 10 ft 9 in thick, with a 4-in shale band 1 ft 7 in from the top. The limestone is here correlated with the Upper Fell-top Limestone of south-west Northumberland and west Durham (Figure 5). Its lower part is reported to contain cockle 'shells', a term which by analogy with the Cockle Shell Limestone (Dunham 1948, p. 19) may imply Productids.

The Upper Felltop Limestone is overlain in the Ryal Bore by 1 ft 5 in of shale with 'blue beds' (presumably thin layers of calcareous shale or limestone), above which are 14 ft 8 in of interbedded 'post' and 'shale'. The equivalent beds in west Durham comprise up to 50 ft of shale overlain by the Grindstone Sill, a flaggy sandstone 30 to 50 ft thick (Dunham 1948). In the 21 ft of strata above the 'post' and 'shale' are three unnamed limestones, measuring, in upward succession, 5 in, 2 ft 4 in, and 2 ft 2 in. They are correlated here with a group of six thin limestones which lie above the Grindstone Sill in the Woodland Bore in the Barnard Castle (32) district (Mills and Hull, in press). Two further unnamed limestones, 9 in and 11 ft 7 in thick, are recorded 43 and 66 ft higher respectively in the Ryal Bore. The lower limestone may be the equivalent of 10 ft 11 in of 'grey shales with fossils' lying at the bottom of a deep bore at Littletown Lady Alice Pit; the upper thicker bed is here correlated with 12.25 ft of 'blue limestone with shells' lying at a depth of 1538 ft 9 in in the Littletown Bore. This 12.25-ft limestone is immediately underlain by beds of 'dark grey shale with fossils', 3.5 and 2 ft thick and separated by 2 ft of 'grey post'. In the Bishop Middleham Colliery (? East Pit) Bore, the limestone is absent and its position is assumed to lie at or near the base of 52 ft 5 in of white sandstone, the lower 22.5 ft of which is 'full of pebbles'.

The strata succeeding the thick limestones at Ryal and Littletown and the sandstone at Bishop Middleham, consist of 20 to 40 ft of 'shale' and 'post' overlain by about 10 to 20 ft of argillaceous beds which include seatclays. At Bishop Middleham (Figure 5), seatclays are succeeded first by about 5 ft of 'dark grey shale' followed by 5 in of 'cherty or flinty limestone'. This bed is not recorded at Ryal and Littletown but appears to be represented by 10 in of hard dark grey argillaceous limestone in the Woodland Bore.

In West Durham, this thin limestone is overlain by up to 20 ft of generally argillaceous beds, separating it from the 'First Grit', which reaches over 100 ft in thickness. In this district, however, the 'First Grit' is less clearly defined, and in the absence of geologically examined sections, correlation is conjectural In the Ryal Bore, the 'First Grit' may be represented by two sandstones, a lower 48-ft and an upper 47-ft bed being separated by about 13 ft of strata including a 14-in limestone. In the Littletown Lady Alice Pit Bore, 61 ft 10 in of very coarse 'grey post' is recorded with a 7-in 'grey shale' parting 27 ft above the base, but elsewhere most sandstones are less than 40 ft thick.

The sequence above the suggested equivalents of the 'First Grit' (Figure 5), comprises rather varied strata; they are generally 20 to 30 ft thick, but at Ryal consist of about 50 ft of 'shale', 'metal', 'metal stone' and thin sandstone or 'post' bands. In the South Hetton Bore, a 9-in coal was recorded, and limestones 1.5, 3.5 and 5 ft thick have been proved in the Ryal, Hart, Tudhoe Colliery and Bishop Middleham bores respectively. At about the same horizon in the Middle Stotfold Bore, a 1-ft bed of grey shaly mudstone at a depth of 990 ft 1 in yielded, in addition to carbonized plant fragments, the following: Planolites ophthalmoides; Campylites [Sphenothallus] sp.; Lingula mytilloides, Productus carbonarius de Koninck; cochliodont fish tooth.

The 'Second Grit', which is over 100 ft thick in the Woodland Bore is readily recognized in the Durham–West Hartlepool district. In the Littletown Lady Alice Pit Bore it is represented by 66.5 ft of 'very coarse grey post', and in the Rainton Alexandrina Pit Bore nearby it is 63 ft 11 in thick and is made up of 'hard light grey post' 14 ft 14 in, on 'very coarse post' 41 ft, 'fine dark post with shale partings and coal threads near the bottom' 7 ft 7 in, and 'conglomerate' 1 ft at the base. In most other provings within the district, the equivalent sandstone is between 40 and 50 ft thick, though in the Hart and Middle Stotfold bores it is only about 30 ft. At Bishop Middleham, the basal layer consists of 10 ft 4 in of white sandstone, very coarse and full of pebbles overlain by 2 ft of 'dark conglomerate'. The remaining 32 ft comprises grey post, with shale bands.

In the Middle Stotfold Bore, the sandstone considered to be equivalent to the 'Second Grit' is overlain by seatearth–siltstone, which is taken to be the topmost stratum of the Millstone Grit Series. In the older records this seatearth is not recorded, and the boundary is consequently placed at the top of the bed correlated with the 'Second Grit'. E.A.F.

Lower Coal Measures

The base of the Lower Coal Measures is now defined as the base of the lowest of a group of marine bands which overlie the 'Second Grit' in West Durham (Figure 5). In the Durham–West Hartlepool district, the presumed equivalents of these marine bands lie between about 934 ft and 943 ft in the Middle Stotfold Bore, and have yielded Planolites? at 934 ft 2 in, P. ophthalmoides at 937 ft 3 in, and fragments of costate Productids between 941 ft 10 in and 942 ft 1 in, and at 942 ft 5 in. Marine fossils have not been recorded at the same horizon in any other boring in this district, but the generally argillaceous sequence which fills the interval between the 'Second' and 'Third' grits can be distinguished in most of the old logs. The sequence includes a coal which is up to 7 in thick in the Bishop Middleham and South Hetton Colliery bores (Figure 5) and also in the Hart Bore.

Above the coal are sandstones of variable thickness and extent: they are thought to correspond with the 'Third Grit' which in West Durham attains a thickness of 50 or 60 ft. In the Durham–West Hartlepool district, however, a single thick sandstone at this position is exceptional, apart from one of about 40 ft in the Hart Bore, and 30 ft in the Tursdale and Windlestone Colliery bores (Plate 3).

The measures above the 'Third Grit' sequence include ganister in the Rainton Alexandrina Pit and Windlestone Colliery bores. The Littletown Lady Alice Pit Bore passed through 'mild grey post with silica' at this horizon, and in the East Hetton Busty Bore the Gubeon Coal is underlain successively by 1 ft 7 in of ganister and 10 in of hard sandy fireclay. The presence of ganister in these bores supports the correlation with the 'Third Grit', for ganister is otherwise rarely recorded in this district. In Offshore No. 1 Bore the floor of the same coal is a grey-brown rather silty seatearth which passes down into a brown sandy seat-earth with sphaerosiderite.

Gubeon Coal

The Gubeon Coal which underlies the Gubeon Marine Band ((Plate 3) and (Figure 3)), has been proved in many bores in the district, but is everywhere thin. In Offshore No. 1 Bore, it is 18 in thick with a 2.25-in dirt band 12 in above the base; in Ten-o'-Clock Barn No. 1 Bore, it is 17 in; in Rainton Alexandrina Pit Bore, 10 in; and in Littletown Lady Alice Pit Bore, 9 in. The correlation is not certain in the Bishop Middleham and Windlestone Colliery bores, where two thin coals are recorded at about this horizon and where the overlying Gubeon Marine Band has not yet been recognized. In the Bishop Middleham Bore, the lower coal, 7.5 in thick, is separated from the upper 14.75-in coal and bands by about 15 ft of 'grey metal, with post partings'; and in the Windlestone Bore, the lower 11-in coal (with a 4-ft ganister seatearth) is separated from the upper 12-in coal by about 21 ft of 'metal' and 'post' with 1.5 ft of 'seggar' at the top.

Gubeon Marine Band

The Gubeon Marine Band has yielded the following fauna from Offshore No. 1 Bore: foraminifera; Planolites ophthalmoides; Lingula mytilloides; undetermined Palaeoniscid scales, Rhizodopsis sp.In this bore Lingula was recorded at intervals through 7 ft of the shales above the coal, but in the East Hetton Busty Bore Lingula and sponge spicules were found only in the lowest 4 in of 3 ft 9 in of 'bluestone' (i.e. mudstone) forming the roof of the Gubeon Coal. E.A.F.

Measures between the Gubeon and Ganister Clay coals

The measures between the Gubeon and Ganister Clay coals (Plate 3) range from about 40 ft to over 70 ft in thickness. At Rainton Alexandrina Pit, 61.5 ft of strata separate the Gubeon Coal from 4 ft of 'grey shale' at the horizon of the Ganister Clay Coal, and of this, 56.75 ft consists of 'white and grey post' (Figure 5). In Littletown Lady Alice Pit, 1.75 miles to the south, the interval of 46.75 ft includes only 24 ft of 'grey post with shale partings'. However, there is no direct relationship between the thickness of the interval and that of the sandstone, for in the East Hetton Busty Bore (Plate 3) where the interval is 55.5 ft, there are only 17.75 ft of 'tough white micaceous shaly post' at about 7.5 ft above the base and two thin bands near the top. Farther to the southeast, in Ten-o'-Clock Barn No. 1 Bore, the strata comprise 44 ft of mainly argillaceous beds, with a few thin sandy bands bearing plant debris. In some borings, this part of the sequence is so variable that correlation is uncertain. In the South Hetton Bore, for instance, the first seam recognizable above the Gubeon horizon is the Brockwell Coal, and two 60-ft sandstones, separated by about 10 ft of 'blue metal with ironstone', lie between the horizons of the Gubeon Marine Band and the Victoria Coal (Plate 3).

The upper part of the sequence between the Gubeon and Ganister Clay coals in Offshore No. 1 Bore (Plate 3) is:

The Curvirimula sp.from 16 ft below the Ganister Clay Coal is stratigraphically the lowest non-marine lamellibranch yet found in the Coal Measures sequence in this district (see p. 23). E.A.F., D.B.S.

In south-west Durham, an important refractory seatearth underlies the Ganister Clay Coal, but in the Durham–West Hartlepool district this seatearth is not prominent, though thin fireclays and hard sandstones (sometimes called 'ganister-like') are recorded. In Fishburn No. 2 Bore, for instance, 3 ft of 'strong ganister-like post' lies below the coal, but the topmost 1 ft probably consists of fireclay. In Ten-o'-Clock Barn No. 1 Bore, 1 ft 11 in of 'very hard grey sandstone' lies about 5 ft beneath the coal. At other places ganister-like sandstone is present above the coal, as in the East Hetton Busty Bore, where the section (by G. A. Burnett) is:

EAF

Ganister Clay Coal

The Ganister Clay Coal is of no economic importance in this district. It is more than 1 ft thick only in Windlestone Colliery Shaft (17 in) and Fishburn No. 2 Bore (15 in). In Murton Blue House Lane Bore it is 12 in thick, and in South Wingate Colliery and Offshore No. 1 bores 9 in thick. In Littletown Lady Alice Pit an upper 6-in coal is separated from a lower 4-in coal by 2 in of 'grey shale'. Elsewhere the coal is either an inch or two thick or it is absent.

Measures between the Ganister Clay and Marshall Green coals

The measures between the Canister Clay and Marshall Green coals range from about 30 ft to 90 ft in thickness, averaging about 55 ft. In most of the twenty or so bores which have proved this part of the succession, the strata are predominantly arenaceous, with argillaceous beds at the base and top. An exception is the East Hetton Busty Bore where these measures largely consist of 'bluestone' with many 'iron ribs and balls'. This bore is also exceptional in providing the only record of non-marine lamellibranchs from this part of the succession. In Fishburn No. 2 Bore the roof measures of the Ganister Clay Coal contain Rhadinichthys sp.and pyrite-filled burrows; the lithology is that of a typically marine sediment, but no marine fossils were found. In addition to the crushed shells above the Ganister Clay Coal split (see above), Carbonicola cf. communis and fragmentary Curvirimula sp.were identified from 9 in of 'black bluestone with ironstone ribs' and the base of the overlying 'sandy Bluestone' about 30 ft above the Ganister Clay Coal and 19 ft below the Marshall Green Coal. In Offshore No. 1 Bore, the roof of the Ganister Clay Coal consists of 9 in of 'grey sandy shale' with Annularia radiata Brongniart.

Marshall Green Coal

Because of insufficient evidence, the correlation of the Marshall Green Coal and associated measures is uncertain in some places. In the East Hetton Busty Bore the coal is 6 in thick lying about 43.5 ft above the thin coal taken to be a top split of the Ganister Clay Coal. In the Windlestone Colliery Shaft two 8-in coals at the Marshall Green position are separated by 6.75 ft of strata, and though a split has not been proved, it seems reasonable to name these coals Top and Bottom Marshall Green. In Offshore No. 1 Bore, the supposed Bottom Marshall Green consists of an upper 4-in, a middle 1-in and a lower 8-in coal lying in 8 ft 2 in of generally arenaceous measures; the 14-in Top Marshall Green Coal lies 37.5 ft higher. The thickest single seam recorded at the Marshall Green position in this district is one of 18.5 inches in Littletown Lady Alice Pit, and even this contains a 3.5-in 'shale' band 5 in above the base. A few scattered records show coal of about 12 inches in thickness. E.A.F.

Measures between the Marshall Green and Victoria coals

The measures between the Marshall Green and Victoria coals are again not known in detail, but it is clear that they vary considerably in lithology (Plate 3). Where the supposed Top Marshall Green Coal is found, the measures both below and above it commonly include grey, medium- to coarse-grained feldspathic sandstone bearing pebbles in many places. The immediate roof of the Top Marshall Green is, however, commonly composed of mudstone, ranging in thickness from a few inches to about 15 ft. The base of this bed is thought to be the horizon of the Stobswood Marine Band of the Northumberland Coalfield (see 6-in published sheet NZ 27 NE). Although Planolites ophthalmoides, Curvirimula sp.and fish remains have been found in the Fish-bum area, no marine fauna has yet been found in Durham. Non-marine fossils have been found at two higher levels in the East Hetton Busty Bore where the succession (recorded by G. A. Burnett) is:

In Ten-o'-Clock Barn No. 2 Bore, the positions of the two 'mussel'-bands are marked by thin coals, but no fossils were recorded from their argillaceous roofs. Coals up to a few inches thick occur at similar horizons in other scattered localities, but elsewhere this part of the sequence is commonly occupied by sandstone. E.A.F., D.B.S.

Victoria Coal

The Victoria Coal is everywhere too thin in this district to hold much prospect of it being worked. The maximum proved thickness is in Ten-o'-Clock Barn No. 1 Bore where it is 22 in, including a 0.5-in 'dirty rib' 12 in above the base. This record, however, is exceptional, for over most of the western and southern parts of the district the coal is only 3 to 12 in thick. Farther east it is less than 3 in, and in some places absent, its position being marked only by seatearth.

Measures between the Victoria and Brockwell coals

The measures between the Victoria and Brockwell coals are between about 40 and 85 ft thick and include two 'mussel'-bands, one at the base and the other nearly mid-way up the sequence. The basal band, forming the roof of the Victoria Coal, is persistent throughout the district, though the abundance and preservation of the fauna is variable. In the East Hetton Busty Bore, for instance, preservation is poor and the fauna, together with macro-spores, is restricted to the lower part of 5 ft 8 in of 'bluestone', the upper part of which is sandy. Around Fishburn, however, the band is nearly twice as thick, as in Fishburn No. 1 Bore where 9 ft 8 in of shales overlie the Victoria Coal. This band contains: Planolites ophthalmoides; Carbonicola aff. declivis, C. pseudorobusta, C. cf. rhindi [juv.], C. sp. cf. cristagalli, Curvirimula subovata, C. trapeziforma; Carbonita humilis, Geisina arcuata. Other borings nearby have yielded Naiadites sp.E.A.F., D.B.S.

Similar forms have been obtained from Elwick No. 1, Dalton Nook and Low Throston bores. In Offshore No. 1 Bore P. ophthalmoides is restricted to a 9-in band 1 ft 9 in above the base of the bed of shales, where it is intercalated with layers containing 'mussels'. Fish remains including an Acanthodian spine, Elonichthys sp., Rhadinichthys sp.and Rhizodopsis sp.were found with a similar fauna of lamellibranchs and ostracods in Offshore No. 2 Bore.

The 'mussel'-band in the roof of the Victoria Coal is overlain successively by sandstone and seatearth. In the East Hetton Busty Bore the sandstone, about 21 ft thick, is hard and contains thin bands of 'sandy bluestone' close to the base and top. Around the Fishburn area it generally ranges between 10 and 25 ft in thickness, though exceptionally it is reduced to 2 or 3 ft. The same sandstone can be traced through the Elwick series of bores and is distinguishable in Offshore Nos. 1 and 2 bores, though in the latter it is only 2 ft thick. The overlying seat-earth consists of 8 in of 'dark fireclay with soft bands' in the East Hetton Busty Bore, and is persistent over much of the southern and offshore parts of the district, but is not recorded in the north-western part. It is thought to be the equivalent of a prominent fireclay or fireclaymudstone which forms the roof of the Victoria Coal in parts of West Durham.

The seatearth is overlain by a bed of mudstone up to 16 ft thick and containing non-marine lamellibranchs in the lower part. This is the Upper Victoria Shell Band or 'declivis Horizon' of Magraw and others (1963, pp. 197–203; pl. xix) though it is now clear (p. 24) that the latter term has been misapplied and should be discontinued. The fauna is distinctive in consisting mainly of small poorly preserved Carbonicola by means of which the band can be traced over most of the district. A representative faunal list obtained from Fishburn Nos. 1 and 2 bores is as follows: Carbonicola cf. acuta [small], C. cf. communis, C. aff. declivis, Naiadites flexuosus; Carbonita?, Geisina arcuata; Elonichthys sp.In addition to these Curvirimula subovata, Carbonicola cf. polmontensis (Brown) and Pleuroplax sp.[tooth] were obtained from the band in Offshore No. 1 Bore and Spirorbis sp.[large] from No. 2 Bore of the same series.

Between this ‘mussel’-band and the Brockwell Coal are up to 85 ft of strata which include a median bed of seatearth. In places this seatearth is missing, as in Elwick No. 1 Bore where the whole of the interval is occupied by 43.5 ft of cross-bedded sandstone overlain by 12 ft of interbedded sandstone, siltstone and mudstone. In other places the seatearth is overlain by a coal which is normally thin, though in Offshore No. 1 Bore it is as much as 47 in thick and has been named 'Bottom Brockwell' (Magraw and others 1963, pl. xix). Although in the Nunstainton No. 1 and Stonyhall bores this seam lies so close beneath the County Brockwell Coal as to form with it a single banded section of up to 107 in, it is in most other places separate from the latter.

(Figure 6) illustrates this separate identity of the 'Bottom Brockwell Seam' in the southern and south-western parts of the district, and shows that the coal worked as Brockwell Seam around Dean and Chapter Colliery and at Chilton Colliery lies at a higher stratigraphical level. Farther east the 'Bottom Brockwell', in six leaves, reaches a thickness of 31 inches in South Mainsforth 'J' Bore [NZ 3104 2933], 650 yd W.N.W. of Nunstainton East Farm, where it lies 9 ft 8 in below the Brockwell Coal. In three bores respectively 400 yd S.S.E., 200 yd S.S.W. and 200 yd W.N.W. of Hope House (Mainsforth Underground Bores A, B and C, in Fig 6), it is respectively 21 in, 17 in and 20 in thick lying at intervals below the Brockwell Coal of 13 ft, 22.5 ft and 44.5 ft. It is probable that the 31-in ‘Bottom Brockwell’ of the South Mainsforth 'J' Bore includes thin coals which develop in the strata between the County Brockwell and ‘Bottom Brockwell’ of the Mainsforth Underground bores. In the Bowburn, Shincliffe, Sherburn, Low Grange and Rainton areas, the ‘Bottom Brockwell’ is represented by a thin coal, which only exceeds 7 inches in a bore [NZ 3052 3786] 130 yd S.E. of Bowburn D.C. Pit, where it reaches 16 in.

Brockwell Seam

The Brockwell Seam (Figure 6) and (Figure 7) is the lowest worked in the district, but the workings are restricted to two areas in the south-west and south. The larger of these is around Chilton Colliery and Ferryhill, extending northwards to Croxdale Hall and eastwards to Mainsforth Hall; the smaller occupies an isolated area south of Fishburn, between Holdforth, Weterton House and Bridge House. In these areas, the coal is generally 3.5 to 4.5 ft thick, locally increasing to over 5 ft, but reserves of this thickness have now been exhausted and mining is now being extended only at Fishburn Colliery, east-south-eastwards from Bridge House, where the coal is between 2 and 3 ft thick. E.A.F.

The seam may be similarly 2 to 3 ft thick over an area of about 35 square miles east of Easington, south of Cold Hesledon and north of Hart Station, extending seawards at least as far as Offshore Nos. 1 and 2 bores, but in this large area, it has so far been proved only in 7 bores. D.B.S.

The Brockwell Seam has been worked from Chilton, Dean and Chapter, and East Howle collieries in the south-western area as a good quality coal 40 to 65 in thick, in which bands are absent or very thin. To the east, the coal becomes too banded for profitable mining, and the line along which workings have terminated for this reason has been traced between Croxdale Hall, Broom Hill and Cookson's Green (Figure 7). Immediately to the east of this line, the thickness of the banded seam is maintained in a narrow zone, but still farther to the east, the thin leaves of coal die out and in some places only one survives. A typical section through the banded seam at the limit of workings [NZ 2801 3768], 2.5 miles N.N.W. of East Howie Colliery, is coal 15 in, on band 3 in, coal 5 in, band 7 in, coal 4 in, band 7 in, coal 9 in.

Farther south, the banded zone broadens between Windlestone, Mainsforth and Bishop Middleham and the direction of deterioration is from south to north. Within the zone there are small areas in which the banded coal is more than 24 in thick and one of these has been worked south of Mainsforth Colliery shafts. Near Hope House, three Mainsforth Colliery underground bores (Figure 6) illustrate the progressive deterioration first by the incoming of a band, and finally by the reduction in thickness of the individual leaves of coal.

The Brockwell Coal attains its maximum unbanded thickness of 63 inches in the southern part of the Fishburn area at a locality [NZ 3616 3128], 550 yd E. of Lizards Farm. Towards the southern limit of working, between 450 yd N.W. and 250 yd N.N.W. of Weterton House, its thickness is reduced first to between 38 and 46 in and then to 18 in. The termination of the workings coincides with a line of impoverishment which has been proved eastwards by borings for over 2 miles (Figure 7), and which has been interpreted as the margin of a washout, though alternatively, since its trend is subparallel to the outcrop on the sub-Permian surface, the absence of the seam farther south may be a result of post-Carboniferous pre-Upper Permian oxidation (see also p. 18). In Fishburn D Bore (Figure 6), the coal is 66 in thick including an 11-in band 19 in above the base of the seam. There is no record of a band in the log of Fishburn Colliery North Shaft, where the seam is 55 in thick, nor within a limited area between the colliery shafts and Holdforth, but a thin band is generally included in the seam west and north-west of the shafts. A typical section at a locality [NZ 3508 3201], 1150 yd W.N.W. of the North Shaft, is coal 33 in on band 3 in, coal 13 in. At another locality [NZ 3387 3352], 300 yd E. of Mahon House, the seam comprises coal 6 in, on band 0.25 in, coal 4.5 in, band 0.5 in, coal 5.25 in, band 2 in, coal 0.25 in, band 0.5 in, coal 9 in, splint coal 7.25 in. Still farther north, beyond the banded zone, few of these thin coals persist; thus in a bore [NZ 3427 3561], 1 mile S.S.W. of East Hetton Colliery, the section reads coal 18 in, on dark grey seatearth-mudstone with pyritic partings 14 in, coal 7 in. A thickness of 41 in of coal with bands, proved in the East Hetton Busty Bore, 1200 yd farther north, is exceptional for this part of the district.

North-east of Fishburn, impoverishment is again evident. The coal is 34 in thick in a bore [NZ 3672 3258], 550 yd N.N.E. of Fishburn crossroads, and only 24 in 250 yd farther to N.N.E. Workings were terminated 50 yd still farther to the north where the seam is 20 in thick. In Fishburn No. 1 Bore, 1300 yd N.N.E. of Fishburn crossroads, the coal is 25 in thick, but in Fishburn No. 2 Bore and Fishburn 'B' Bore, farther to the northeast, it is only 16 in and 17 in thick respectively. Seam thicknesses recorded from other bores in this area are as follows: bore [NZ 3803 3234] 700 yd W. of Humble Knowle, 24 in; Fishburn No. 4, 27 in; Whin Houses, 23 in; Embleton Old Hall, 28 in (with a 2-in band 15 in above the base); Murton Hall, 20 in.

Over much of the central and western parts of the district, the Brockwell Seam ranges in thickness from 0 to 24 in, though exceptionally in Grange New Winning Bore, north of Camille, it is said to be 37 in. E.A.F.

Between Elwick and West Hartlepool (Figure 7), the coal forms the lower leaf, 20 to 43 in thick, of a composite seam separated by 5 to 8 in from an upper leaf 29 to 40 in thick. This upper leaf is represented farther west by one or more thin coals (Brockwell roof coals of (Figure 6)) lying between the Brockwell Seamand the overlying Brockwell Ostracod Band. In Offshore No. 1 Bore the roof coals consist of coal 32 in, on band 22 in, coal 3 in, and are separated from the County Brockwell by 57 in of strata. The 32-in roof coal is correlated with the Three-Quarter Seam by Magraw and others (1963, pl. xix).

At Dean and Chapter, Chilton and Windlestone collieries there are one or two thin roof coals separated from the worked coal by a thin band. Northeastwards from Dean and Chapter, this band becomes thicker, as in the East Hetton Busty Bore, where the sequence is:

Elsewhere the intervals containing the thin coal or coals between the worked seam and the ostracod band may be as little as a few inches or as much as 65 ft. The latter value was recorded in Fishburn 'D' Bore, where the intervening strata comprise 40 ft of coarse gritty micaceous sandstone, succeeded by 18 ft of dark grey micaceous sandy shale with plant debris and 7 ft of grey sandy fireclay with ironstone nodules. In other bores south of Fishburn shafts and near Weterton House, the interval is 40 to 50 ft, largely filled by sandstone, with seatearth and with a coal 1 to 4 in thick at the top. In Fishburn No. 1 Bore near Trimdon, the interval is reduced to 26.25 ft of which only 2 ft consists of 'post' and this has shaly partings, but in Fishburn 'B' Bore, the equivalent strata are 61.25 ft thick including about 34.5 ft of sandstone overlain by about 18 ft of sandy shale and sandstone with shaly bands. To the southeast of Fishburn shafts, in Fishburn No. 3 Bore (Figure 6), the thin coal underlying the Ostracod Band is represented by 4 in of black cannelly shale, but an additional 9-in coal is present a little lower in the sequence. The appearance of this additional coal is the first indication of the incoming of the Brockwell roof coals in south-east Durham. In Fishburn No. 4 Bore, farther east, another thin coal is found at a still lower level so that three Brockwell roof coals are present. Still farther to the east, in the Embleton Old Hall Bore, the two lowest are split to form a total of five thin coals in this part of the sequence. The roof of the Brockwell Seam in both these bores consists of mudstone with Curvirimula sp.In the Murton Hall Farm Bore there is no split and the strata between and below the lower two roof coals are thinner than in Fishburn No. 4 Bore. In Elwick No. 1 Bore the band separating the roof coals from the Brockwell Seam is further reduced to only 5 in and the lower two of the roof coals are combined into one 30-in seam. Farther east, in the Dalton Nook and Low Throston bores, all the roof coals are united and lie close above the true Brockwell, forming with it a single composite seam, 76 to 83 in thick with one 7- or 8-in band. In the Hartlepool Lighthouse Bore the whole of the composite seam is missing, and its position is marked only by a seatearth. The Brockwell is absent also in the North Sands Bore, but the roof coal is 24 in thick. Although these two bores penetrate quite a different type of sequence from that proved in the bores between Embleton and West Hartlepool, a sequence more comparable to the latter is found in Offshore No. 1 Bore (see above).

Brockwell Ostracod Band

The Brockwell Ostracod Band, which is a useful and widespread marker band, consists of a few feet of shaly mudstone from which the following composite fauna has been obtained: Gyrochorte carbonaria Schleicher, Spirorbis sp.[large], Planolites ophthalmoides; Anthraconaia aff. fugax, Carbonicola cf. browni, cf. C. circinata, C. declivis, C. cf. martini Trueman and Weir, C. pseudorobusta?, C. cf. robusta, Curvirimula candela, C. subovata, C. trapeziforma; Carbonita humilis, C. pungens, Geisina arcuata; and fish remains.

The measures between the Brockwell Ostracod Band and the Three-Quarter Coal

The measures between the Brockwell Ostracod Band and the Three-Quarter Coal vary in thickness and lithology. Where the Ostracod Band forms the roof of the Brockwell Seam, the measures may be as much as 50 ft, but elsewhere the interval is reduced and is locally as little as 10 ft. In the East Hetton Busty Bore, the sequence begins at the base with 'bluestone' and sandstone 6.5 ft, overlain successively by seatearth 2 ft, coal 10 in, plant-bearing bluestone and sandstone 10.5 ft, and hard coaly fireclay-shale 15 in. In South Mainsforth 'J' Bore, the succession is as follows:

The 3-in coaly base of the mudstone 8 ft above the Brockwell Ostracod Band in this bore is equivalent to a 4-in coal lying 20 to 25 ft above the Brockwell Coal at Chilton and Dean and Chapter collieries. The 4-in coal higher in the bore has also been proved at those collieries, and at Dean Pit it is 11 in thick. Farther north-east, at East Howle Colliery, the two coals beween the Brockwell and Three-Quarter coals are closer together (Plate 3), the lower 7-in coal being separated from the upper 4-in coal by only 4 ft 7 in of 'white post' and dark fireclay.

In Tursdale South Shaft, these thin coals are thought to be represented by two bands of 'black stone', the lower 22-in band being separated from the upper 18-in band by 2.5 ft of grey 'metal'. There is no evidence that these intermediate coals are splits from the higher Three-Quarter Seam and the records suggest that they come in when the interval between it and the Brockwell Coal exceeds about 40 ft. E.A.F.

The 4-in coal of the South Mainsforth ‘J’ Bore can be traced through Mainsforth and Bishop Middleham collieries into the Fishburn area and it attains 20 inches in the Green Lane Cottages Bore [NZ 4095 2993]. The fauna in its roof includes: Spirorbis sp.; Carbonicola pseudorobusta, Curvirimula candela, C. subovata, Naiadites cf. flexuosus and fish remains. Non-marine lamellibranchs have been recorded from the same horizon in Fishburn Nos. 3 and 4 bores, and farther east, in Embleton Old Hall and Murton Hall bores. Fragmentary ‘mussels’ are also recorded above a 6-in coal at this horizon in a bore [NZ 3442 3853] 650 yd south-west of Dene House Farm, near Cassop Colliery. In Elwick No. 1 Bore, the position of the same coal is marked by roof shales containing macrospores, large fragmentary Curvirimula sp.and indeterminate Palaeoniscid scales. No fossils were found in this part of the sequence in the Dalton Nook Bore, where the interval between a 23-in coal containing a median 9-in band and the Three-Quarter Coal is largely filled by 42.5 ft of sandstone. In the Low Throston Bore, this interval amounts to only 7 ft 7 in, and the lower coal is only one inch thick. In the North Sands Bore, it is represented by coal 9.5 in, band 2 in, on coal inferior 2 in, lying about 50 ft below the assumed position of the missing Three-Quarter Coal. E.A.F., D.B.S.

Three-Quarter Seam

The Three-Quarter Seam (Plate 3) is 17 to 19 in thick at Dean and Chapter Colliery, but only 4 in thick at Chilton Colliery. At East Howle Colliery, it is a 16-in seam overlain by 27 in of 'black stone' upon which rests 9 in of 'fireclay' forming the floor of an unnamed 6-in coal. At Croxdale Thornton Pit in the Wolsingham (26) district, the Three-Quarter Seam comprises 18.5 in of coal separated by a 1.5-in band from an overlying 4-in seam. A staple-pit near Tursdale South Shaft proved a similar section in which an upper 4-in coal is separated from a lower 12-in coal by a 6-in ‘slaty band’. In the nearby shaft, the Three-Quarter Seam is represented by 26 in of ‘coal and bands’, while in Tudhoe West Pit, just beyond the western margin of the district, it is a banded coal 36 in thick.

Traced into the north-western part of the district, from the adjacent Wolsingham district, the seam undergoes an eastward deterioration. In two bores near Bishop's Grange it is 39 in and 26 in with bands respectively, while other records to the south-south-east are Kepier Florence Pit, 21 in; Elvet South Engine Pit, 16.5 in; Old Durham Colliery, 24 in; and Shincliffe Colliery, 5 in. In the Sherburn and Rainton areas, the Three-Quarter Coal does not exceed 15 in. E.A.F.

In the eastern part of the district, the Three-Quarter Coal is commonly 18 in or less in thickness and locally it is absent. The coal is 14 and 19 in thick respectively in the Dalton Nook and Hartlepool Lighthouse bores, and in the Low Throston Bore it comprises coal 3 in, on band 7 in, coal 10 in. Though only 8 in thick in Offshore No. 1 Bore, the seam amounts to 34 inches in No. 2 Bore. D.B.S.

At Bishop Middleham Colliery and Fishburn No. 4 Bore, the coal is only 1.5 in and 3 in thick respectively, and in the Embleton Old Hall, Murton Hall Farm, Elwick No. 1 and North Sands bores, it is absent, its horizon being marked by silty beds or seatearth. It is also absent in a bore [NZ 3442 3853] 650 yd S.W. of Dene House Farm, and in the East Hetton Busty Bore it comprises clean coal 8 in, on coaly fireclay 1 in, dirty coal with pyrite rib 3 in. E.A.F.

The roof of the Three-Quarter Coal locally contains 'Estheria', and is thought to be the equivalent of the Low 'Estheria' Band of the East Pennine Coalfield (p. 25). It has been proved at several places in the district and is here named the Fishburn 'Estheria' Band (Figure 3). In Fishburn No. 4 Bore, the band, only 1 ft 10 in thick and overlain by sandstone, contains only 'Estheria' sp.In Fishburn 'D' and No. 3 bores, however, where the thin Three-Quarter Coal is overlain respectively by 16 ft 11 in and 18 ft 8 in of shale and shaly mudstone with ironstone ribs and nodules, 'Estheria' sp.is found near the base and non-marine lamellibranchs above. The presence of 'Estheria' and a non-marine lamellibranch fauna in the Offshore No. 1 and North Sands bores assists in identifying the position of the Three-Quarter Coal, close below the Busty coals, and the correlation is consequently different from that in Magraw and others (1963, pl. xix). E.A.F.

In Fishburn No. 3 Bore the following were identified: Carbonicola pseudorobusta, Curvirimula subovata; Carbonita cf. humilis, Geisina arcuata; and fish remains. Cochlichnus kochi was obtained 3 ft above 'Estheria' in Hartlepool Lighthouse Bore. The top of this 'mussel' band in Fishburn 'D' and No. 3 bores lies only 6 ft 8 in and 22 ft 3 in respectively below the Bottom Busty Seam. In South Mainsforth 'J' and Fishburn No. 4 bores, by contrast, this interval includes nearly 60 ft of sandstone. This bed reaches a maximum of 94 ft at Croxdale Thornton Pit, just beyond the western margin of the district, but it is about 70 ft thick at East Howie Colliery and ranges from 40 to 70 ft over much of the south-western part of the district (Plate 3). E.A.F.

In an underground bore [NZ 3658 3617], 550 yd N.N.W. of Trimdon Grange East Shaft, the sandstone is 70 ft thick extending down, with no trace of the Three-Quarter Coal, to the roof of the thin coal about the Brockwell Ostracod Band.

Top and Bottom Busty coals

The Top and Bottom Busty coals (Figure 8) are normally separate and distinct, and in most places the Bottom Busty has been the more extensively worked. In three areas, however, the two coals form a single, usually banded, seam. Two of the areas are extensions from adjacent districts. Between Hetton le Hole and Murton Moor East Farm, this single seam is currently being worked southwards from Eppleton Colliery in the Sunderland (21) district, where a typical section measured in the workings [NZ 3624 4716] is coal 19 in, on band 2 in, coal 3 in, band 6 in, coal 24 in. The composite seam extends, in similarly banded form, around New Hesledon and has been proved in an underground bore [NZ 4117 4669] 300 yd W. of Cold Hesledon. D.B.S.

The Top and Bottom Busty coals are again close together in the extreme northwest of the district between Crook Hall and Ford Cottage, and the combined seam has been worked from the west. A bore [NZ 2750 4742], 2.5 miles N. of Durham Main Colliery, proved top coal 24 in, on band 12 in, bottom coal 27 in. To the east of this bore the coals become thinner and the band increases to over 3 ft. At the limit of workings 750 yd E. of the bore, the section is Top Busty 28 in (coal 21 in, on band 4 in, coal 3 in), band 3 ft 10 in, Bottom Busty 17 in. Farther south, at a locality [NZ 2757 4633], 250 yd N.of Red House, the combined seam comprises coal 19 in, on band 14 in, coal 24 in; but 425 yd E.N.E. of Red House, it is coal 21 in, on band 2 ft 10 in, coal 19 in; and this is close to the limit of workings. Between two localities [NZ 2763 4460] and [NZ 2778 4420], 0.75 mile and 0.5 mile N. of Durham Main Colliery, the band increases from 2 to 15 ft, ana as both top and bottom coals are there only 19 to 21 in, the workings have not been continued to the east. Immediately north of the colliery, the line of split follows a course generally sub-parallel to the 24-in isopach of the Bottom Busty Seam (Figure 8). To the east of the colliery, the course of the line of split is more conjectural, but some evidence is provided by the Kepier Florence Pit section in which the whole Busty comprises top coal 0.75 in, band 22 in, bottom coal 20 in; and by the Grange Pit section, in which it is top coal 22 in, strata about 22 ft, bottom coal 19 in.

The main area of combined Busty coals lies in a triangle between Shincliffe Colliery, Trimdon and East Howle. The composite seam has been worked from Bowburn Colliery, where the Downcast (West or New) Pit proved 54 in of unbanded coal. The same thickness was proved in a bore [NZ 2986 3639], 640 yd N.E. of Broom Hill. To the north of Bowburn, bands come in near the middle of the seam, and a bore [NZ 3003 3921], 190 yd S.E. of Shincliffe Station, proved coal 24 in, on plate band 1.75 in, coal 4 in, seggarclay band 3 in, coal 25.5 in. To the south of Bowburn also, the composite seam becomes banded as shown by the following section in a bore [NZ 2911 3659], 550 yd S.S.W. of Tursdale House: good coal 5.5 in, on black shale with coal scars 1.75 in, good coal 3.5 in, grey metal shale 2.25 in, coal with danty partings 4 in, good coal 6 in, brown band 0.5 in, good coal 2.5 in, rather danty coal 2 in, good coal 22.5 in. This is close to the western limit of workings beyond which the single seam is impoverished.

Mine plans show the Busty Seam to be washed out in two areas to the northeast of Bowburn (Figure 8). One area, about 350 yd N.N.E. of Bowburn Downcast Pit, is about 1300 yd long by 300 yd wide trending in a north-westerly direction. A larger area of ‘nip-out’ measuring 1800 by 400 yd and elongated in the same direction, lies about 0.75 mile N.E. of the same pit. At the north-western limit of this area [NZ 3067 3938], 800 yd E. of Shincliffe Station, the seam is recorded as diminishing in thickness from 24 in to 4 in over a distance of 60 yd from west to east. Farther north, towards Shincliffe Station and Shincliffe Colliery the thicknesses of the worked Busty seams range as follows: top coal 13 to 24 in, band 12 to 26 in, bottom coal 21 to 23 in. On the western side of this area, the top coal decreases from 24 to 18 in near High Grange, and on the eastern side the bottom coal is reduced to 18 in near Whitwell Beck. It would therefore seem that the Busty split develops at these extremities.

In the Busty workings [NZ 2950 3824] 1050 yd W.N.W. of Bowburn Downcast Pit, the 23-in top coal is separated from the 16-in bottom coal by a 4-ft band. At South Grange, nearby, the section is top coal 5 in, band 14 in, bottom coal 31 in; and the workings are limited to the west by a ‘nip-out’. Between 100 and 350 yd N.E. of Shincliffe Colliery the seam comprises top coal 22 to 24 in, band 3 to 8.5 ft, bottom coal 19 to 22 in. The increase in thickness of this band and reduction of both coals to less than 2 ft has precluded mining farther north.

To the west and north-west of Bowburn lies an area in which the Busty is impoverished and unworked. Throughout this area, extending from Skibbereen north-north-eastwards through High Croxdale, Shincliffe, Old Durham, Gilesgate Moor and Carrville to Leamside, the Busty Seam consists generally of a single coal less than 18 in thick. Thus, two bores [NZ 2806 3832] and [NZ 2754 3875], 2 miles and 1.5 miles W.N.W. of Bowburn Colliery, proved 9 and 18 in of coal respectively. At Old Durham, however, a 3-ft band separates an upper 8 in from a lower 18-in coal, suggesting that the Busty split inferred at the limits of the Shincliffe workings extends this far north.

The Busty Seam has also been worked north-east of Bowburn in a narrow zone bounded on the west by the Heugh Hall ‘nip-out’. The northern boundary is marked by cindered coal. Thus in the workings [NZ 3232 3914], 1.25 miles N.E. of Bowburn Upcast Pit, the coal is 33 in thick, but 100 yd farther to the north-north-east, 15 in of cindered coal lies on 9 in of uncindered coal and the seam is overlain by 18 in of 'whin' (dolerite). At the northward end of a 250-yd exploration [NZ 3197 3938] within the limit of cindering, the section is cindered top coal 19 in, band 37 in, 'whin' (dolerite) 22 in, cindered bottom coal 24 in. This cindered zone lies on the south side only of the Ludworth Dyke (p. 189) and is 700 to 1000 yd wide in this area lying to the east of the Heugh Hall nip-out. The last section also demonstrates a split in the seam, which widens north-eastwards so that in a bore [NZ 3354 3929], 2 miles E.N.E. of Bowburn Colliery, the 39-in Bottom Busty is separated from the Top Busty coals by about 22 ft of strata.

South-east of Bowburn in the area around Coxhoe Hall, bands are present in most sections of the Busty Seam, which ranges in thickness from 44 to 71 in. In the workings 750 yd N.N.E. of the Hall, a top coal, 27 in thick, is separated from a bottom 31-in coal by an 8-in band, but 500 yd N.E. of Low Raisby, the top coal is reduced to 22 in and the bottom coal to 27 in, while the separation is as much as 4.5 ft. This and other records between Quarrington Hill and Trimdon indicate the approximate course of the 3-ft isopach on the Busty split and the continuation of the south-easterly trend from the Cassop Moor area (Figure 8).

The southern boundary of the area of composite Busty Coal lies between Trimdon and Skibbereen. In a bore [NZ 2857 3506] 0.75 mile N.N.W. of East Howle, it consists of coal 23 in, on 'brown metal mixed with coal' 3 in, coal 9 in, 'white metal' 2 in, 'white post' 16 in, coal 20 in. Another bore [NZ 279 341], 475 yd N.E. of Skibbereen, proved Top Busty Coal 30 in, ‘grey metal’ 5 ft 10 in, Bottom Busty Coal 24 in. At East Howle, the 28-in Top Busty and 31-in Bottom Busty coals are 15 ft apart. Farther east, at Thrislington Florence Pit, the Top Busty is 35 in thick, and the Bottom Busty Seam, 6 ft 9 in below, consists of coal 21 in, band 28 in, on coal 6 in.

The Bottom Busty Seam has been worked extensively in the south-western part of the district, where it is now largely exhausted. In the Dean and Chapter Colliery shafts, the Bottom Busty is 32 in thick and is separated from the 35-in Top Busty by 5 to 10 ft of strata. At Chilton, the interval is reduced to 3 ft, between a 27-in bottom coal and a 14-in top coal. To the east, a band noted in the Bottom Busty at Thrislington persists to Mainsforth, the shaft section being coal 32 in, on band 11 in, coal 15 in. The Top Busty, 22 in thick, lies 16.5 ft higher. Farther east between Thrislington, Mainsforth, Garmondsway and Bishop Middleham, the Bottom Busty is generally 42 to 56 in thick, though it is locally less, as at Bishop Middleharn itself where it amounts to only 31 in. At Bishop Middleham the 16.5-in Top Busty lies 32.5 ft above the Bottom Busty, but to the north this interval decreases and at Garmondsway Pit the whole Busty section is coal 43 in, on band about 12 in, coal 55 in. At an intermediate locality [NZ 3374 3314], 400 yd S.S.E. of Mahon House, it is coal 37 in, on band 24 in, coal 53 in. This section evidently lies close to the line of split as do the following: [NZ 3445 3286] coal 20 in, on band 4 in, coal 29 in; [NZ 3465 3309] coal 29 in, on band 3.5 ft, coal 41 in; [NZ 3495 3330] coal 30 in, on band 6 in, coal 30 in; [NZ 3479 3360] coal 8 in, on band 1 in, coal 7 in, band 6 in, coal 34 in.

The Bottom Busty Seam has been extensively worked at Fishburn Colliery and is still being developed in the Butterwick Moor area. Near the south 'crop' between Weterton House and Butterwick, the interval between the Top and Bottom Busty is 20 to 30 ft. The Bottom Busty around Fishburn shafts is generally 3 to 4.5 ft thick, but locally it increases to over 5 ft, as in a bore [NZ 3646 3079], 400 yd N.E. of Weterton House, where the whole Busty sequence is Top Busty (coal 0.5 in, on seatearth-mudstone 0.5in, on coal 27 in), black carbonaceous shale 3 in; sandstone and siltstone 22 ft 9 in; Bottom Busty (coal 67 in, on seatearth-mudstone 4 in, inferior shaly coal 3 in). To the east-north-east between Cowburn and Butterwick Moor, the thickness of the Top Busty is maintained at 20 to 30 in, but the Bottom Busty decreases to about the same range. Concomitant with this deterioration, the Busty split is reduced from over 20 ft to a few inches. Thus, in Fishburn No. 3 Bore, the section is Top Busty (black parroty shale 2 in, coal 18 in, on pyritic splint 1 in), ‘post’ with sandy shale above and below, and with sandy fireclay-shale at top 22.5 ft, Bottom Busty (coal 33 in, on splint and coal 5.5 in, coal 2.5 in, splint 1 in). About 350 yd S.E. of Bridge House the Bottom Busty is 36 in thick, and in Fishburn No. 4 Bore, 650 yd farther N.N.E., the section is Top Busty Coal 28 in, ‘post’ and sandy fireclay-shale 7 ft, Bottom Busty Coal 24 in. In workings 200 yd N.E. of this bore there is a composite Busty section of coal 29 in, on band 3 ft, coal 26 in, and at a further locality [NZ 3887 3180], 450 yd N.W. of Butterwick Moor, it is coal 26 in, on band 2 ft, coal 27 in. At 100 yd farther to the north-west the band is only 6 in thick and separates top coal 28 in from bottom coal 26 in, and a comparable section [NZ 3887 3211], 300 yd S.E. of Humble Knowle, is coal 30 in, on band 6 in, coal 24 in.

To the north-east of Fishburn, a similar decrease in the thickness of both the Bottom Busty Seam and the strata separating it from the Top Busty Seam can be detected. In a bore [NZ 3672 3258], 550 yd N.N.E. of Fishburn crossroads, the section reads: Top Busty Coal 18 in, on ‘grey metal stone’ 28.5 ft, ‘dark blue metal’ 1.5 ft, Bottom Busty Coal 42 in; and at a locality [NZ 3498 3258], 250 yd E. of this bore, Top Busty (coal 28 in, on band 1 in, coal 7 in) on 'black shale' 17 in, ‘blue metal’ 5 ft 10 in, Bottom Busty Coal 38 in. At two other localities [NZ 3681 3274]; [NZ 3670 3277], 225 yd N.N.E. and 250 yd N. of the same bore, the separation is 6.5 ft and 4 ft respectively, and the Top Busty is 33 in thick. The evidence in the Humble Knowle and Hope House areas suggests that the area of composite Busty Coal north-west of Trimdon might extend into the northeastern side of the Fishburn Colliery take as far south-east as Cowbum (Figure 8). E.A.E.

Between Butterwick and Elwick, beyond the present Fishburn workings, bores indicate a split of between 5 and 25 ft in the Busty Seam. Around Whin Houses, West Murton Blue House, Murton Hall and Embleton Old Hall, the Top Busty Coal is 20 to 28 in thick, and the Bottom Busty Seam is generally over 3 ft thick, but tends to include one or more bands. Thus, in the Embleton Old Hall Bore, the bottom seam comprises coal 17 in, on seatearth-mudstone 5 in, coal 20 in; and in the Murton Hall Farm Bore: coal 15 in, on seatearth-mudstone 23 in, coal 5 in, seatearth-sandstone 10 in, coal 11 in. These records indicate a northwards impoverishment, for the Whin Houses Bore proved 53 in coal and the West Murton Blue House Bore proved 37 in coal. Farther east, in Elwick No. 1 Bore, the bottom seam is only 24 in thick, and still farther east, in the West Hartlepool area, neither leaf is thicker than 19 in. E.A.F., D.B.S.

The Bottom Busty Coal has been widely worked in the Sherburn Hill area where the Top Busty, generally less than 20 in thick, is locally absent. The interval between the two seams is generally 15 to 30 ft, but this decreases rapidly to the west between Belmont and Whitwell. Thus, a bore [NZ 3104 4060], 2 miles S.W. of Sherburn Hill Colliery, recorded black stone (Top Busty position) 3 in, 'white post' and 'grey metal stone' 17 ft 10 in, Bottom Busty Coal 19.25 in; and a second bore [NZ 3058 4038], 560 yd farther to the south-west, proved the combined seam to be coal 10 in, on 'black stone with coal threads' 1 in, coal 20 in. Over most of the area between Sherburn Hospital, Pittington, Ludworth and Old Cassop, the Bottom Busty is 2 to 3 ft thick. Near Pittington, bands of unspecified thickness are recorded in a 34-in seam. Along a 950-yd line trending north-west from Littletown Colliery, the workings terminate against the western margin of a ‘nip-out’, but the width of this is not known. About 450 yd E. of Sherbum Hill Downcast shafts, the Bottom Busty workings stopped where the thickness of the seam decreased to 15 in, and the 24-in isopach can be traced (Figure 8), thence roughly eastwards to a locality [NZ 3524 4198], 650 yd S.S.W. of Haswell Moor and on to Thornley, Trimdon Grange and Trimdon. E.A.F.

With the exception of the areas in the north, the Busty seams in the whole district east of a line joining Pittington, Ludworth, Thomley and Trimdon are impoverished. Even where the thickness of either seam increases to over 24 in, as in the approximately circular offshore area, 3 miles in diameter, beyond Black Halls Rocks, the coal is generally banded. Over the whole of this southeastern part of the district both of the Busty seams are commonly less than 18 inches in thickness. Near Thomley, the interval between them increases to over 30 ft; 32 ft is recorded in a bore [NZ 3898 3767], 880 yd N.N.W. of Wingate Grange. Over most of this part of the district the seams are separated by sandstone, though 'metal stone' is not uncommonly mentioned in the old records. In the offshore area the interval is 6 to 20 ft, and the coals are both thin and banded. D.B.S.

Measures between the Busty or Top Busty Seam and the Bottom Tilley Seam

In the south-western part of the district the measures between the Busty or Top Busty Seam and the Bottom Tilley Seam consist of 20 to 35 ft of strata variously recorded as 'post', 'metal stone' or 'metal'. The interval is increased to 50 ft at Garmondsway Pit but is only 14 to 35 ft farther east in the Fishburn area (Plate 3). In Fishburn No. 3 Bore the Top Busty Coal is overlain by 9 ft of shale with Anthracosphaerium cf. dawsoni, preserved as internal moulds in ironstone, small Carbonicola sp.[juv.] and Naiadites flexuosus. Shells have been recorded at the same position in Ten-o'-Clock Barn No. 2 Bore and from borings in the Embleton area, while Carbonicola rhomboidalis? was obtained from this position in a bore [NZ 3807 3040] in the Butterwick area and from Fishburn 'B' Bore.

Just beyond the western margin of the district, the Bottom Tilley Coal lies 29.5 ft above the Busty in Aykley Heads Pit. The interval amounts to 31 ft in a bore [NZ 3003 3921], 190 yd S.E. of Shincliffe Station, but is only 13.5 ft in Littletown Lady Mice Pit. Just beyond the northern margin of the district, between Great Lumley and Chilton Moor, the interval is 20 to 35 ft, but over much of the north-central part of the district, between Elemore, Coxhoe and Castle Eden, the Bottom Tilley Seam is absent and a thick sandstone occupies this part of the sequence (Plate 3). This bed reaches a recorded maximum of 106 ft 5 inches in a bore [NZ 3312 4313], 550 yd S.S.E. of Hallgarth church, where it consists mainly of medium- and fine-grained pale grey sandstone, generally massive, but 'wispy. bedded' with silty and micaceous bands and partings in the top 14 ft. Siltstone and shale pellets are so abundant in a 3.5-ft layer, 25 ft above the base of the bed, as to form a breccio-conglomerate, and they are also scattered through a thickness of 30 ft of the overlying sandstone. Coal scars are recorded at about 10 ft and 50 ft above the base of the bed, and poorly preserved plant debris and rootlets from the top 10 ft. The sandstone is overlain by 6 ft 8 in of grey shaly mudstone with scattered rootlets, the top lying only about 5 ft below the Harvey Coal. Sandstone, 94 ft thick, was proved in two bores [NZ 3263 4362]; [NZ 3201 4357], 250 yd W.N.W. and 900 yd W. respectively of Hallgarth church. Between Pittington and Sherburn Hill, and between Hetton le Hill and Shincliffe Colliery, the sandstone is generally over 60 ft thick, and a similar thickness is proved between Shincliffe Station and East Hetton, and around Dene House Farm and Ludworth. The sandstone may be continuous eastwards beyond Haswell Plough, with thicknesses of 65 to 85 ft extending north-eastwards at least as far as Easington and New Hesledon. To the west the sandstone extends to Kepier Florence Pit, where it amounts to 87 ft, and thence through Durham City, Grange Colliery and Low Newton to Rainton Adventure Pit where a thickness of 70 ft is recorded (P1 III).

Bottom Tilley Seam

The Bottom Tilley Seam, where present, consists generally of one or more thin coals, though one of these reaches a thickness of between two and three feet. At the western margin of the district, in Tudhoe West Pit, the seam section is coal 3 in, on band 24 in, coal 2 in, band 26 in, coal 10 in. In the surrounding area, the seam comprises either a single coal or two parts separated by up to about 8 ft of strata. To the south-east, in the Ferryhill area, the second alternative is typical, but traced from Tudhoe to Mainsforth the coals become closer, thin, and finally die out. Thus, at East Howie Catherine Pit, the Bottom Tilley comprises coal 18 in, on 'dark fireclay' 11 in, coal 3in, fireclay' 30 in, 'blue metal' 33 in, 'post' 28 in, coal 5.5 in, 'fireclay' 17.5 in, coal 13 in; at Dean and Chapter No. 3 Pit, coal 14 in, on 'black stone' 2.5 in, coal 17 in, 'seggar' 26 in, coal 5.5 in, 'seggar' 6 in, coal 7 in, 'seggar' 34 in, coal 18 in; at Dean Pit, coal 12 in, on 'hard seggar-clay' 25 in, coal 17 in; at Chilton Colliery coal 6 in, on band 9 in, coal 15 in; at Windlestone Colliery, coal 18 in; and at Mainsforth Colliery, coal absent. E.A.F.

Farther east in the Fishburn area, at Fishburn North Downcast Shaft, the Bottom Tilley is a single seam, 26 in thick, and in a bore [NZ 3672 3258], 350 yd S.S.E. of Hope House, it is 29 in thick. The best section in this area is proved in Fishburn No. 3 Bore: upper leaf 30 in, on fireclay 30 in, grey fireclay-shale with ironstone nodules 16 in, rather coarse micaceous sandstone 10 in, lower leaf 23 in. In the Ten-o'-Clock Barn, Embleton and Elwick areas, the Bottom Tilley Seam generally comprises two or three thin coals separated by a few inches to 5 ft of strata. In the Dalton Nook Bore, one of these leaves attains 29 in in thickness, but elsewhere in these areas 20 in is the maximum and 4 to 10 in normal. Spirorbis sp.and Naiadites sp.[juv.] were obtained from the roof of the Bottom Tilley Seam in the Hartlepools Lighthouse Bore. E.A.F., D.B.S.

Bottom Tilley Seam

The Bottom Tilley Seam is less persistent in the north-western part of the district than in the south-west and south. At Aykley Heads Pit, just beyond the western margin of the district, the lower leaf comprises 18 in of coal, and the upper leaf is absent, though its seatearth lies 14 ft higher. At Durham Main Pit, 400 yd to the north-east, both leaves are present and are 14 in and 3 in thick respectively, but at Old Durham Colliery Upcast Pit there is only a single Bottom Tilley coal, 20 in thick, and at Shincliffe Colliery and in a boring near Shincliffe Station, the single seam is only 7 and 10 in thick respectively. Further to the east, in a bore at Sherburn Lady Durham Pit, the Bottom Tilley comprises 4 in of 'coal mixed with stone', but is absent in a bore said to be put down about 30 chains due east of this pit. At Littletown Lady Alice Pit, the Bottom Tilley consists of 'coal and black stone' 3 in, on 'grey shale' 5 in, coal 7 in. Just beyond the northern margin of the district, between Great Lumley and Chilton Moor, the seam is represented in borings by one thin coal or two leaves separated by a band up to 26 in thick. E.A.F.

Around Murton, in the offshore area east of Harden, and also to the south of Thornley, the Bottom Tilley is formed by one or more thin or banded coals. The seam is absent over much of the north-central part of the district between Elemore, Coxhoe and Castle Eden, where a thick sandstone occupies this part of the sequence (p. 50). D.B.S., E.A.F.

Top Tilley Seam

The Top Tilley Seam is a variable, banded coal which is of economic importance only in the western part of the district between Sherburn Hill, Trimdon, Whitwell and Wingate. Sections near the western margin of the worked area illustrate the degree of lateral variation. In the Sherburn Hill and Sherburn House shafts no coals are recorded between the Busty and Harvey seams, but in a bore [NZ 3370 4127], 500 yd S.S.W. of Crime Rigg, the Top Tilley Seam consists of coal 12 in, on band 7 in, coal 17 in; and it is represented by a single 21-in coal in a second bore [NZ 3321 4106], 575 yd farther to W.S.W. To the south-east many, though not all, sections are highly banded. Thus, a bore [NZ 3402 4089], 200 yd W.S.W. of the western end of Shadforth, proved coal 3 in, on band 2 in, coal 2 in, band 2 in, coal 3 in, band 9 in, coal 10 in, band 1 in, coal 2 in, band 0.5 in, coal 1 in. By contrast, a bore [NZ 3385 4085], only 200 yd farther to west-south-west, proved coal 9 in, on band 8 in, coal 19 in. A zone in which Tilley coals are absent extends through Fatclose House, Strawberry Hill and Old Cassop, and separates this area of banded coal around Shadforth from the main area of worked Top Tilley Seam to the south and east: it seems to trend parallel to a similar zone through Sherburn House and Sherburn Hill. E.A.F.

The Top Tilley Seam is of most economic importance between Thomley and Garmondsway, Cassop Moor and South Wingate, where it is 3 to 5 ft thick, including four or more bands, and has been worked from East Hetton, Thomley, Wheatley . Hill, Deaf Hill, Wingate Grange, Trimdon Grange, South Wingate, Trimdon, and Hutton Henry collieries. Typical sections are: [NZ 3516 3732], 425 yd E.S.E. of Hole House (East Hetton), coal 10 in, on band 3 in, coal 5 in, band 7 in, coal 10 in, band 3 in, coal 11 in, total 49 in; in a staple [NZ 3714 3975], 700 yd E.N.E. of Thomley Colliery, coal 25 in, on band 4 in, coal 16 in, band 28 in, coal 15 in; [NZ 3983 3455], 300 yd W. of White Hurworth, coal 16 in, on band 1 in, coal 14 in, band 2 in, coal 16 in, total 49 in. In some of the workings, part or all of the uppermost leaf of the seam is inferior and is not mined. D.B.S., E.A.F.

The Top Tilley seems to be united with the Bottom Tilley in a small part of the Wheatley Hill area, but elsewhere in the eastern part of the worked area, the Top Tilley is up to 30 ft above the thin Bottom Tilley. To the north, between South Hetton and Murton collieries, the interval is again small, and at Hawthorn Colliery Shaft, the following section was measured: Top Tilley Seam (coal 18 in, on band 6 in, coal 7.5-in, band 6 in, coal 10 in), seatearth and siltstone 9 ft 7.5 in, Bottom Tilley Seam 5 in. D.B.S.

Beyond the southern margin of worked Top Tilley, the seam is absent in the Thrislington area. To the east, a bore [NZ 3538 3313], 800 yd S.S.W. of Catley Hill, proved coal 14 in, on 'dark metal' 3 ft 7 in, on coal 15 in. In Garmondsway Moor Pit, about 1150 yd to the north, the Top Tilley is typically banded: coal 10 in, on band 2 in, coal 10 in, band 6 in, coal 28 in, band 4 in, coal 19 in. In a bore [NZ 3038 3313], 800 yd S.S.W. of Catley Hill, the Top Tilley comprises foul coal 5 in, on 'grey metal scared with coal' 24 in; and in another bore [NZ 3672 3258], 350 yd S.S.E. of Hope House, it is only 4 in thick. E.A.F.

In the coastal and offshore areas, additional splitting is characteristic of the Tilley coals and their clear distinction becomes difficult (Plate 3). It is possible that the Top Tilley is absent in this area, but the data are too scattered for correlation to be reliable. Between South Wingate and Hutton Henry collieries, the Top Tilley closely underlies the Harvey, with a thin coal between. The section at Hutton Henry Perseverance Pit reads: Harvey Seam (coal 45 in, on band 1.75 in, coal 20 in) on seggar 34 in, coal 7.5 in, seggar 41 in, Top Tilley Seam (coal 18 in, on band 4.5 in, coal 11 in, band 2.5 in, coal 8.5). The intermediate 7.5-in coal is thought to represent the Hodge Seam of north-west Durham.

Measures between the Bottom Tilley and Harvey coals

In the south-western corner of the district, the measures between the Bottom Tilley and Harvey coals range in thickness from 50 or 60 ft (as at Tudhoe) to 101.5 ft (at Thrislington Jane Pit) and to 123 ft (at Garmondsway Pit). Farther north, at Durham Main Pit, these coals are 85 ft apart and this interval again increases to east and south-east so that at Old Durham Colliery Upcast Pit, at Shincliffe Colliery and in a boring 190 yd S.E. of Shincliffe Station, it is 96, 97 and 101 ft thick respectively. It reaches 112 ft in a bore at Sherburn Lady Durham Pit. In much of this area, the Top Tilley Seam is missing. The interval between the Top Tilley and Harvey coals is commonly between 30 and 50 ft in the western part of the district. E.A.F.

In other areas where the Top Tilley is present, the range is from 7 to 70 ft corresponding respectively with lithologies consisting mainly of seatearth, as at Hutton Henry, and sandstone as in the undersea areas off Blackhall, Horden and Easington. Sporadic non-marine lamellibranchs are found in a shaly mudstone or shale commonly lying at the base of this sandstone: they include fragmentary Anthraconaia sp.and Naiadites sp.obtained 35 ft below the Harvey Coal in Eppleton No. 2B Underground Bore [NZ 3677 4816]. It is not clear whether this band is more closely associated with an upper leaf of the Bottom Tilley or with the Top Tilley group. Where the thin coal thought to be the equivalent of the Hodge Seam of north-west Durham is present (see p. 15 and below) the strata between it and the Harvey are generally dominantly argillaceous, and in places its seatearth seems to merge with that of the Harvey, the section at Hutton Henry being an example approaching this extreme. D.B.S., E.A.F.

Along the western border of the district, west of the worked area of Top Tilley, the only coal between the Busty and Harvey seams, with the exception of a sporadic thin Bottom Tilley Seam, is 2 to 6 in thick and lies 14 to 27 ft below the top of the sequence. This thin coal is presumed to be the Hodge Seam of West Durham, because as it is traced westwards the Tilley Coal is found 9 to 30 ft below it. A thin coal representing the Hodge Seam can be recognized around Whitwell and Hallgarth. For instance, it is 5 in thick, 14 ft below the Harvey Seam, in a bore [NZ 3058 4038], 420 yd N.W. of Whitwell House, and in another bore [NZ 3104 4060], 525 yd N.N.E. of Whitwell House, it is represented by 18 in of 'black partings' 17 ft below the Harvey, while a 6-in coal 49 ft below the Harvey in the same bore can be correlated with the thicker Top Tilley Seam farther east. Similarly, a bore [NZ 3189 4407], 850 yd N. of Broomside House, proved a 6-in coal about 17 ft below the Harvey, with no trace of coal or seatearth in the measures immediately below, while in a bore [NZ 3201 4357], 350 yd N.N.E. of Broomside House, a seatearth marks the position of the Top They lying 21.5 ft below the Harvey and 6.5 ft below the Hodge which is represented by coal 2 in, on seatearth-mudstone 1 in, inferior coal 1 in. Fossils have been obtained from between the Hodge and Harvey coals only in Easington No. 5 Bore where they include Spirorbis sp., Anthracosia aff. regularis, cf. Carbonicola venusta Davies and Trueman, and Naladites sp.

Harvey Seam

The Harvey Seam (Figure 9) is one of the most important in the district. It has been exploited most extensively in the south-central and south-western areas where it is generally over 3 ft thick. At Chilton and Hutton Henry, and between Thrislington and Garmondsway Moor, it exceeds 5 ft. At Chilton, however, the seam, 68 in thick, includes an 8-in band 3 in from the top, and a 5-in band 40 in from the base. The lower of these bands persists as far as Fishburn. Thus, the section at Mainsforth is coal 19.5 in, on band 4 in, coal 38 in; and at a position [NZ 3415 3313], 1160 yd S.E. of Garmondsway Pit, it is coal 16 in, on band 1 in, coal 45 in. At Windlestone, in the southwestern corner of the district, the band has thickened to 11 in, the top coal being 14 in and the bottom coal 30 in thick. The Harvey Seam has been worked in the area east of Chilton East House, and at the southern limit of workings [NZ 3127 3055] is recorded as being 23 in thick. This probably refers to the Bottom Harvey alone for the evidence of borings suggests that the parting, only inches farther north, is here much thicker. Thus in Nunstainton No. 2 Bore, the 30-in Bottom Harvey Coal is separated from a 12-in Top Harvey Coal by 17.5 ft of strata; and in Windlestone 'E' Bore [NZ 2875 2896], just over 1 mile S.S.E. of Chilton Colliery, the Top Harvey Seam (shaly coal 1 in, on black shale 0.5 in, shaly coal 2 in, seatearth-mudstone 29.5 in, coal with pyritous partings 6 in) lies 26 ft above the Bottom Harvey Seam (coal 9 in, on seatearth-mudstone 2 in, coal 4 in, seatearth-mudstone 6 in, coal 8 in). The line of split seems to have a west-southwesterly trend in this area, but there is only scattered information relating to its course to the east. It must, however, lie to the north of a bore [NZ 3243 3039], 1050 yd S.S.W. of Bishop Middleham church, where the section is Top Harvey Coal 9 in, strata 24 ft, Bottom Harvey Coal 28 in. The parting must also increase in thickness immediately to the north of Bishop Middleham East Pit where the 37-in Top Harvey is separated by 5.5 ft of strata from the 33-in Bottom Harvey.

Farther east, in the Fishburn area, the Harvey Seam is again thick and affected by splitting. At Fishburn North and South shafts, it is 75.5 and 78 in thick respectively. In a bore [NZ 3552 3251], 1000 yd N.W. of the shafts, it is 55 in thick, but at the northern limit of workings [NZ 3593 3301], 700 yd N.B. of the bore, a 2-in band intervenes between top coal 14 in and bottom coal 34 in. In other bores [NZ 3672 3258]; [NZ 3653 3228], 1000 yd N.N.E. and 650 yd N.N.E. of Fishburn Colliery, unbanded sections of 59 in and 58 in respectively were recorded, but a 12-in band separates top and bottom coals, each 30 in thick, in workings [NZ 3536 3170] 0.5 mile W. of Fishburn South Shaft. At two places [NZ 3509 3145]; [NZ 3534 3145], 1200 yd and 950 yd W.S.W. of the same shaft, however, the worked coal is only 26 in and 32 in thick respectively, and it is thought to be Bottom Harvey alone. A 27-in seam worked [NZ 3651 3159], 500 yd E.S.E. of the shaft is similarly taken to be Bottom Harvey alone. In the area north of Galley Law, the Bottom Harvey, 28 to 30 in thick, is separated by a band, 4 to 15 in thick, from the Top Harvey, which is 26 to 32 in thick including, locally, a 3- to 6-in band near the top. At a locality [NZ 3758 3197], nearly 1 mile E. of Fishburn Colliery, only the Bottom Harvey, 29 in thick, has been worked, but at another place [NZ 3697 3218], 500 yd to E.N.E. the section is coal 25 in, on band 27 in, coal 27 in. These records suggest that the line of Harvey split (Figure 9) traced from Windlestone to Bishop Middleham Colliery continues south of Holdforth and southeast of Fishburn Colliery and thence a short distance north of Galley Law.

To the south-south-east of the major line of split, only the Bottom Harvey Seam is generally worked, but along a narrow strip, about 20 yd wide, the Top and Bottom seams are united, and have been worked together across the Fishburn take (Figure 9). The reduction in thickness of the parting is abrupt. For instance, it is 21 ft 5 in thick in a bore [NZ 3703 3139], 1100 yd E.S.E. of the colliery, but only a few inches thick 125 yd to the south-south-east. Within the strip, the Harvey Seam is over 6 ft thick, with a band ranging from 1 to 18 in. A typical section measured near to the middle of the strip [NZ 3731 3131], 1400 yd E.S.E. of the colliery, is coal 49 in, on band 8 in, coal 35 in. To the east of the strip, the Top and Bottom Harvey coals are again separated by up to 20 or 30 ft of strata and the

Bottom Harvey alone is worked, its thickness between Cowburn and Fishburn No. 3 Bore being 28 to 30 in. In the latter bore, the interval is 25 ft and the Top Harvey 33 in, but in Fishburn No. 4 Bore (Plate 3) the Top Harvey is absent and its seatearth lies 30 ft above the 33-in Bottom Harvey Seam. E.A.F.

The Bottom Harvey Coal is 42 in thick in workings [NZ 3903 3103], 2 miles E.S.E. of Fishburn Colliery, and bores show it to be over 3 ft thick to the north-east and south-east of the workings. However, this area is limited to the north and south by the outcrop of the seam on the base of the Permian, and to the east bores in the Whin Houses area show the Bottom Harvey to be between 2 and 3 ft thick. Still farther east, beyond Embleton Old Hall, the thickness of this seam is generally less than 2 ft, except in the Dalton Nook Bore, where it is 29 in. E.A.F., D.B.S.

The Harvey split can also be traced in the eastern part of the district. It is proved in the workings south of Hutton Henry, between Catlaw Hall and Sheraton Hill, and in bores between Thorpe Bulmer and the coastline two-thirds of a mile N.W. of the mouth of Crimdon Beck. Beyond the coastline the line of split is thought to turn northwards so as to lie 2.5 miles offshore from Easington Colliery (Figure 9). Seawards of this line, the Bottom Harvey is generally 2 to 3 ft thick and comprises an important reserve. The Top Harvey, up to about 30 ft higher, is thought to deteriorate to the east, for the offshore bores proved only 6 to 12 in of coal at this horizon.

To the north and west of the line of split in the coastal and offshore region and as far inland as a line joining Sheraton Hill and New Hesledon, the single Harvey Seam is generally less than 2 ft in thickness. In the area between the line of split and Blackball Colliery, however, the seam is over 2 ft thick, increasing to more than 3 ft in a small area offshore (Figure 9). In the Hesleden and Horden areas, the impoverished area is about 2.5 miles wide; at Easington Colliery, it is about 4 miles wide, and east of New Hesledon it seems to be about 5 miles wide. Beyond about 3miles east of the coastline in the northern part of the district, the seam is generally 2 to 3.5 ft thick, though records of over 3 ft are rare. In the impoverished area as a whole, the Harvey is rarely absent, and typical sections were recorded at Castle Eden Colliery, 18 in, at Hot-den Colliery, 14 in, and at Easington Colliery, 3 in. D.B.S.

In the north-central part of the district there is an irregular zone in which the Harvey Seam is more than 2 ft, and in places over 3 ft thick (Figure 9). In the north-eastern part of this zone, the seam has been worked from Murton Colliery on a restricted shale south and west of the shafts. Farther to the west, around Hetton le Hole and Rainton, the coal is again over 2 ft thick, but is reduced to 23 in at Rainton Alexandrina Pit. At Rainton Adventure Pit, it is 27 in thick, but dirty. Beyond these pits and throughout the north-western part of the district, the Harvey Coal is less than 2 ft thick and is commonly dirty and sulphurous; locally, as at Old Durham, the seam is absent. This area of impoverishment extends beyond the district to affect the Harvey Seam over much of central Durham. E.A.F., D.B.S.

Strata between the Harvey Seam and the Harvey Marine Band

The strata between the Harvey Seam and the Harvey Marine Band constitute the highest part of the Lower Coal Measures. Over much of the district, where the Harvey is a single seam, the Harvey Marine Band lies between about 20 and 50 ft higher in the sequence, and the intervening strata generally consist of mudstone, siltstone or sandstone with silty bands (Plate 3). In eastern and north-eastern parts of the district, however, where the interval is filled largely by sandstone, it is over 50 ft, and exceptionally over 70 ft thick. Where the Harvey is split, these measures seem to remain thick, but sandstone is generally absent. D.B.S., E.A.F.

The roof of the Harvey Seam constitutes an important faunal marker band, distributed widely in the Durham and Northumberland Coalfield. It contains a distinctive fauna of non-marine lamellibranchs and ostracods, and was originally described by Hopkins (1928, p. 6; 1929, p. 8) as the Ostracod Band. In order to avoid confusion with other ostracod bands discovered later, however, Armstrong and Price (1954, p. 977) renamed it the Hopkins Band (Figure 3). Hopkins traced the band into this district as far as Bowburn and Tudhoe collieries, but did not detect it in the south-east at Wheatley Hill and Thornley. According to Hopkins (1929, p. 8) the " band, wherever it is found, shows a constant three-fold division, as follows:

1.  An upper division composed of Carbonicola and Naiadites with occasional Anthracomya;

2.  A middle division composed of numerous Spirorbis with a few Carbonicola and ostracods; and

3.  A basal division composed entirely of ostracods "Beyrichia arcuata (Bean)" Hopkins continues: " It should be noted that it is not the presence of the ostracods that makes the band distinctive, but the assemblage and order of deposition of ostracods, annelids and mussels ". This is broadly supported by some borings in the northern, north-western and western parts of the district where the Harvey Seam is directly overlain by a thin black or dark grey shale or shaly mudstone with abundant ostracods and sporadic fish debris, above which is mudstone in which ostracods are less abundant and non-marine lamellibranchs are common. However, so many exceptions to the generalization are found in this district that it is concluded that the Hopkins Band is subject to marked local variations in character and thickness. Thus, in a bore [NZ 2895 3817], 1 mile W. of Bowburn, the band consists of a mere 2 in of dark grey shaly mudstone with 'mussels' and ostracods interposed between the 16-in Harvey Coal and 29 ft of sandstone which underlie the 8-in seatearth-mudstone forming the floor of the Harvey Marine Band. In another bore [NZ 2888 3877], 0.333 mile farther north, at High Butterby, the argillaceous sequence forming the roof of the Harvey Coal is:

In a bore [NZ 3312 4313], 550 yd S.S.E. of Hallgarth church, the basal layer of the band contains  'mussel' fragments and ostracods, with poorly preserved 'mussels' above. Another bore [NZ 3470 4127], 250 yd W.N.W. of Hill House, Shadforth, includes a basal layer, 1 in thick, with fish scales and spines, and above this both ostracods and 'mussels' are found. Close by, in a bore [NZ 3466 4188], 750 yd N.N.W. of Hill House, the basal layer, 2 in thick, consists of black, very shaly mudstone containing coalified comminuted plant fragments, with ostracods and fragmentary Naiadites above, and other 'mussels' in the upper part of the band, the total thickness being here about 11 in. On the extreme northern margin of the district, a bore [NZ 3256 4768], 1100 yd W. of East Rainton church, proved the Hopkins Band divided into two, as follows:

The Hopkins Band is less persistent to the south, south-east and east of Shadforth. It has been proved in a bore [NZ 3445 3764], 400 yd N.E. of Hole House, East Hetton, where it is 2 ft thick, consisting of grey shaly mudstone with 'mussels' (including Anthracosia) at the top, with ostracods and 'mussels'— in the lower half, and with poorly preserved coalified plant debris in the bottom 3 in. The band here rests on a seatearth-mudstone about 10 ft above the Harvey Seam goaf. In another bore [NZ 3442 3853], 650 yd S.W. of Dene House Farm, near Cassop Colliery, the roof of the Harvey Seam cavity consists of about 4 ft of seatearth-mudstone. This is overlain by shaly mudstone with rootlets 2 ft, seatearth-mudstone 11 in, siltstone 1 ft 4 in and 'mussel'-bearing mudstone 16 ft, sandstone 6 ft, seatearth-mudstone 2 ft 4 in and coal 2 in. No ostracods were recorded in this bore, nor in a bore [NZ 4016 3532], 1.25 miles E.S.E. of Trimdon Colliery, where the 39-in Harvey Seam is overlain by 1.5 ft of mudstone which contained only doubtful fragmentary shells at the base.

To the south and east of the line of Harvey split, the Hopkins Band, where present, lies in the roof of the Top Harvey Coal. A bore [NZ 3243 3039], 1050 yd S.S.W. of Bishop Middleham church, proved Top Harvey overlain by 8 in of barren mudstone and the overlying Hopkins Band consists of 8 in of grey shaly mudstone with a few ostracods at the base and 'mussels' including Naiadites above. The barren mudstone contains 'abundant, light buff, flattened small angular silty (? clay-ironstone) inclusions', which were also found above the Top Harvey in a bore [NZ 2875 2896], 650 yd W.S.W. of Standalone, Chilton. In the Fishburn area the roof of the Top Harvey is generally barren, apart from local plant debris. E.A.F.

In Offshore No. 1 Bore the 6.5 in Top Harvey Coal has a dark grey shaly mudstone roof, 2 ft 3.5 in thick, containing: Anthracosia regularis, Naiadites sp.intermediate between productus and quadratus associated with Spirorbis sp.; Geisina arcuata; and fish remains including Palaeoniscid scales. Only fragmentary 'mussels', identified as Anthracosia?, were collected from an inch of shaly mudstone forming the roof of the 6-in Top Harvey Coal in Offshore No. 2 Bore. D.B.S.

The strata between the Hopkins Band and the Harvey Marine Band are variable in this district. The sequence in places includes one or more seatearths, locally carrying thin coals. In some areas, a thin coal underlies the horizon of the marine band, but it is rarely more than a few inches thick. In the eastern and north-eastern parts of thedistrict the sequence includes a thick sandstone which reaches 65 ft in a bore [NZ 4773 3981] about 1.25 miles E. of Blackhall Colliery station. Except in the extreme north-east, in the undersea area off Dawdon and Easington collieries, the presence of the thick sandstone has little effect on the thickness of the interval between the Harvey Seam and the Harvey Marine Band, which maintains an average of around 55 ft over most of the eastern part of the district. In the south-western part of the district another thick sandstone is present and reaches 52 ft in Little Chilton Cragg Pit. This sandstone extends from near Croxdale Wood House south-south-eastwards to Mainsforth, where it may unite with the sandstone of the Tudhoe area. Above the sandstones and equivalent strata, is a widespread seatearth which forms the floor of the impersistent coal immediately underlying the Harvey Marine Band and forming the top of the Lower Coal Measures (Plate 3). E.A.F., D.E.S.

Middle Coal Measures

Harvey Marine Band

The Harvey Marine Band, at the base of the Middle Coal Measures (Figure 3); (Plate 4), is a black or dark grey micaceous shale or mudstone, rather silty in places, lying between 20 and 70 ft above the Harvey or Top Harvey Seam. It is generally thin and in some places it is absent. The fauna is usually restricted to Lingula mytilloides (up to 6 mm in length) and fish scales and teeth, but other fossils recorded from it include sponge spicules, Orbiculoidea sp., and Hollinella?.

The band seems to have been first recorded in the Northumberland and Durham Coalfield by G. A. Burnett during examination of a staple pit sunk in 1929–30 at Harton Colliery in the district covered by the Sunderland (21) Sheet. It was subsequently noted in the Bates Sinking in the Tynernauth (Sheet 15) district by Hopkins (1934, p. 186; 1935, pp. 5, 9). At both localities the recorded fauna consists of Lingula mytilloides alone. Since then, the band has been recognized in numerous bores. In some places it seems to be represented solely by a film of black shale with numerous well-preserved brown L. mytilloides. Generally, the Lingula are scattered over the bedding plane or planes, but occasionally they are found in a vertical position. Lingula was proved in 13 in of very dark grey finely micaceous shale in a bore [NZ 3868 3051], 900 yd W.N.W. of Ten-o'-Clock Barn, and in 5 in of shale in a bore [NZ 4015 3473], about 200 yd N. of White Hurworth. Trechmann (1941, p. 314) recorded a 4-ft black bed 'with well preserved Lingula mytiloides and traces of fish bones " at a depth of 1,000 ft in the Thorpe Bulmer Bore, and this is here identified as the Harvey Marine Band.

In the Hartlepool Lighthouse Bore the band contains fragments of Orbiculoidea sp.associated with pyritized specimens of Hollinella?, and fish remains including scales of Rhadinichthys sp.and Rhizodopsis sp.The marine band is there composed of 3 in of dark micaceous silty and shaly mudstone, and the fragmentary nature of the fossils suggests that they have been transported and redeposited. Pyritized sponge spicules have been found in 4 in of black slightly silty finely micaceous mudstone in the Dalton Nook Bore, together with L. mytilloides and a tooth of Helodus sp. In Offshore No. 2 Bore the basal 2 in of a bed of black silty shale at the Harvey Marine Band position contain fish debris, while the overlying 4 in contain juvenile and fragmentary Lingula sp., fish remains including Rhadinichthys sp.and pyritized strap-like markings sometimes referred to as 'fucoids'. The fossils again appear to have been transported. In Offshore No. 1 Bore, 2.5 in of black shale at the marine band position contains no specifically marine forms, though they have yielded conspicuous fish remains including Megalichthys?, an indeterminable Palaeoniscid and Rhizodopsis sp.together with Spirorbis sp.and Naiadites? In many places the marine band is between 4 and 10 in thick, and there are a few records of it exceeding 12 in. One of these is in a bore [NZ 4979 4104], 2.5 miles E. of Dene Mouth, where abundant Lingula lie in 14 in of black shale, overlain by black splintery non-marine shale. E.A.F., D.B.S.

Measures between the Harvey Marine Band and the Hutton Seam

The measures between the Harvey Marine Band and the Hutton Seam (Plate 3) range in thickness from about 75 ft in the Fishburn area to about 150 ft at Ferryhill, where they consist mainly of sandstone. Their average thickness in the district is 90 to 100 ft, which is divided by three relatively persistent seatearths, of which the middle one carries a thin coal here correlated with the Ruler Seam of north-west Durham.

The strata between the marine band and the lowest of these seatearths are generally 30 to 50 ft thick, including near the base one of the thickest and most persistent 'mussel'-bands in the district. The following is a typical section through this sequence as logged in Offshore No. 2 Bore:

The 'mussel'-band near the base of the sequence is rarely less than 10 ft thick and serves to fix the position of the base of the Middle Coal Measures where the marine band is absent. Towards the base of the bed the 'mussels' are associated with fish debris, while Spirorbis sp.is also common and ostracods and 'Planolites'have been recorded locally.

The band is well developed in Fishburn No. 3 Bore, where 3 ft of mudstone some 35 ft above the Top Harvey Coal contain the following typical fauna: Spirorbis sp.; Anthraconaia modiolaris, Anthracosia aff. aquilina, A. lateralis (Brown), A. ovum, A. subrecta, Naiadites aff. quadratus and N. triangularis. Species recorded elsewhere in the district include: Anthraconaia cf. curtata, Anthracosia aff. phrygiana, A. cf. regularis, Anthracosphaerium cf. affine, A. aff. exiguum, A. turgidum, Naiadites sp.[marked posterior wing]; Carbonita humilis; scales of Rhabdoderma sp., Rhizodopsis sp., and of indeterminate Palaeoniscids. Locally, the band is divided into two by barren measures of the order of 10 to 15 ft including, in some areas, a thin seatearth. The shells in the upper part are commonly of large size, as in the South Hetton Nos. 6 and 7 bores from which the following assemblage was obtained: Spirorbis sp.; Anthraconaia cf. curtata, A. sp. cf. salteri (Leitch) [cf. Wright 1938, fig. 5a], Anthracosia cf. ovum, A. aff. phrygiana, A. subrecta, Anthracosphaerium exiguum, Naiadites sp.; and Carbonita humilis. A similar fauna was present in the Blackhall Colliery No. 36 Underground Bore at 226 ft.

The seatearth, which forms the top of this sequence, locally carries a thin coal which reaches 8 in at Croxdale Thornton Pit and 9 in at Aykley Heads Pit just beyond the western margin of the district. Exceptionally, there are two seatearths at this position, as for instance, in Offshore No. 1 Bore where they are separated by 2 in of black shale containing Anthracosia ovum and rootlets. The overlying 20 to 30 ft of measures up to the next relatively persistent seatearth (here taken to be the floor of the Ruler Seam) are argillaceous below and sandy or silty above. 'Mussels' are common at the base and include Anthracosia ovum and ?Anthracosphaerium exiguum. In Offshore No. 1 Bore, there are 'mussels' at two levels within this part of the sequence as follows:

The thin persistent coal tentatively correlated with the Ruler Seam of northwest Durham is 20 in thick in a bore near Framwellgate Moor, just beyond the western margin of the sheet, but in the shafts at Framwellgate Moor Colliery it is reduced to between 8 and 10 in. The seam is generally at its thickest in the southern part of the district. In Fishburn Colliery North Shaft, where it has been mistaken for the Bottom Hutton Coal, it comprises coal 6 in on band 2.5 in, coal 1.5 in, band 2 in, coal 11 in, band 3 in, coarse coal 12 in. In a nearby bore [NZ 3672 3258], it is made up of coal 6 in, on band 2 in, coal 12 in, band 1 in, coal 10 in. At Bishop Middleham Colliery to the west, it is 20 in, and at Mainsforth East Pit, still further west, it is 13 in thick. To the east of Fishburn, in the Dropswell and Fishburn No. 4 bores, the seam is represented by black carbonaceous shale, but farther to the east, banded coal comes in again and the maximum thickness for the seam in the district is recorded in a bore [NZ 4091 3100], 280 yd W.S.W. of Embleton Old Hall, where it comprises coal 7 in, on seatearth-mudstone 14 in, coal 11 in, seatearth-mudstone 2 in, coal 12 in. Elsewhere in the district, the Ruler Coal is generally less than 1 ft in thickness.

The measures between the Ruler Seam and the Bottom Hutton are thinnest in the Fishburn area, where they are 15 to 30 ft thick and are not divided by a seatearth. Elsewhere in the district, there is another relatively persistent seatearth with or without a coal up to 9 in thick between the Ruler and the Hutton. At present the relationship between this thin coal and the Ruler and Hutton coals is not clear: it is possible that it unites, in places, with one or other of them. Where all three relatively persistent seat-earths can be recognized between the Harvey and Hutton coals the roof of the Ruler, in contrast to the roofs of the other thin coals above and below it, tends to be barren of non-marine lamellibranchs. However, in Shotton Colliery No. 6 Bore [NZ 4201 3929], 0.5 mile S.E. of Shotton village, both the Ruler and the higher thin coal are overlain by musselbands. E.A.F., D.B.S.

The faunal list from the roof of the Ruler in South Hetton No. 6 Bore includes: Spirorbis sp.; Anthraconaia sp.of A. modiolaris group, large Anthracosia shells including A. ovum, and Naiadites sp.Elsewhere in the district Anthraconaia cf. curtata, Anthracosia sp.of phrygiana/subrecta affinities, N. quadratus and N. triangularis have been collected.

In Offshore No. 1 Bore this 'mussel'- band is absent, but from a bed of sandy and silty mudstone, 3 to 11.5 ft above the seam, Dr. W. G. Chaloner has identified Neuropteris attenuata Lindley and Hutton, and N. tenuifolia Schlotheim. Above the higher thin coal in the same bore, 4 in of mudstone contain: Spirorbis sp.; Naiadites aff. quadratus; and fish remains including a Palaeoniscid scale. The same horizon in Blackhall Colliery No. 33 Underground Bore yielded a fauna similar to that from above the Ruler position: Spirorbis sp.; Anthracosia cf. Ovum, A. aff. phrygiana, A. sp.intermediate between phrygiana and ovum, Naiadites cf. triangularis; and fish remains. In Easington Colliery E. 3 Bore, this band contained, in addition to Anthracosia and Naiadites, several ostracods including Carbonita humilis and Hilboldtina sp.

Hutton Coal

The Hutton Coal (Figure 10) is the lowest worked seam of the Middle Coal Measures. To the north of a line between Shincliffe Colliery and Horden, it is a single seam, but to the south of this line, it is represented by the Top and Bottom Hutton seams. E.A.F., D.B.S.

In the north-western part of the district, the single Hutton Seam is generally a high quality coal, 3 to 5 ft thick, locally including near the base a band which lies lower than the horizon of the main split. West of the outcrop along the buried valley of the River Wear, between Bishop's Grange Farm and Durham city, the seam is 3 to 4 ft thick, and at a locality [NZ 2769 4689], 200 yd E. of the farm, the section is coal 48 in, on band 3 in, coal 15 in. A similar section is recorded 150 yd farther south [NZ 2768 4675], but the bottom coal is here inferior and only 8 in thick. East of the buried valley, the single Hutton Seam is generally 4 to 5 ft thick, and it reaches 65 in at Grange Colliery where two bores of uncertain position record a 2- to 4-in band 8 to 12 in above the base of the seam. Farther south, at Old Durham Colliery, the section is coal 47 in, on band 5 in, coal 8 in. At Whitwell ‘A’ Pit and Shincliffe Colliery Shaft, the seam is 70 to 73 in thick with a 0.5-in band lying 20.5 in from the base. The main split appears in the higher part of the seam in the southernmost workings of the Whitwell and Shincliffe collieries. At Whitwell ‘B’ Pit, the section is coal 23.5 in, on ‘stone’ band 15 in, coal 39 in; and sections at the southern limit of Shincliffe Colliery workings variously prove coal 25 to 30 in, on band 13 to 39 in, coal 18 to 24 in. The main split can also be traced near the western margin of the district. Thus, at a locality [NZ 2721 3884], 1.5 miles W.S.W. of Shincliffe Colliery, the section is coal 22 in, on band 30 in, coal 23 in; and a bore [NZ 2754 3875], 375 yd to the E.S.E., proved Top Hutton Coal, with 'brass' near bottom, 15 in, on grey shale 31 ft, white 'post' 15 ft 2 in, on Bottom Hutton Seam, consisting of coal 20 in, dark shale 3 in, coarse coal with shale partings and brass 8.5 in. E.A.F.

In the north-central and north-eastern parts of the district, the single Hutton Seam is generally thicker than 5 ft. It is 70 in thick at North Pittington Colliery, 61.5 in at Rainton Alexandrina Pit, and 64.5 in, including a 0.5-in band 20 in from the base, at North Hetton Moorsley Winning. The unbanded seam, 5 to 6 ft thick, extends eastwards in a narrow strip from Sherburn Hill to Warren House near Horden and thence 2.5 miles offshore. At the southern margin of the strip the major split can again be traced from a band in the upper part of the seam, while at the northern margin a thinner band appears near the base of the seam: both bands are present in parts of the offshore area. Typical sections illustrating the lower, thinner band in the northeastern part of the district are: Hetton Lyons Pit, coal 56 in, on band 4 in, coal 15 in; Easington Colliery, coal 48 in, on band 2 in, coal 15 in; Murton Colliery shafts, coal 60 in, on band 12 in, coal 15 in. Sections which show the upper, principal splitting along the southern margin of the strip are seen in Thornley Hutton workings as follows: [NZ 3339 4008] coal 25 in, on band 6 in, coal 39 in; [NZ 3456 4010] coal 24 in, on band 25 in, coal 38 in; [NZ 3424 3990] coal 26 in, on band 3.5 ft, coal 37 in. Half-a-mile southeast of Ludworth, the single Hutton is 72 in thick, but 1000 yd S.E. of the colliery the section is coal 25 in, on band 6 in, coal 38 in, while 300 yd farther south the band is 3 ft thick. West of Acre Rigg (west of Horden) the band is less than 3 ft thick extending in a belt about one-third of a mile wide, but to the east this belt increases to nearly 2 miles wide in the area north of Black Halls Rocks. D.B.S., E.A.F.

Where, in parts of the offshore area, the Hutton Seam includes both bands (Figure 10), examples are as follows: [NZ 4623 4659] coal 34 in, on band 2 in, coal 19 in, band 2 in, coal 19 in; [NZ 4809 4581] coal 20 in, on band 1 in, coal 24 in, band 27 in, coal 38 in. Farther to the east, just beyond the limit of workings, two bores record only 23 in of coal at the level of the Hutton Seam, and still farther east, Easington No. 9 Bore [NZ 4969 4649], 3.5 miles E. of Chourdon Point, proved only 15 in. of coal. However, sections near the northern margin of the district about 2 miles E. of the coastline show unbanded coal 77 in thick. Farther south, at a locality [NZ 4926 4358], 3.5 miles E. of Easington Colliery, the seam includes three bands as follows: coal 28 in, on band 20 in, coal 3 in, band 3 in, coal 3 in, band 28 in, coal 28 in; but 570 yd to the E.N.E., Horden No. 15 Bore [NZ 4974 4374] proved only 14 in of coal. Further evidence to suggest that the Hutton is thin or banded beyond the present limit of workings in the offshore area is provided by Offshore No. 2 Bore, which proved coal 6 in, on band 6 in, coal 15 in, at this horizon. D.B.S.

Bottom Hutton Seam

The Bottom Hutton Seam is generally over 2 ft thick and in two bores [NZ 2906 3154] and [NZ 4201 3929] near Chilton and Castle Eden, it measures as much as 63 in. Elsewhere, theseam approaches a thickness of 4 ft only in the area east of Fishburn Colliery, between Bridge House, Butterwick and Ten-o'-Clock Barn, where it locally contains a band. In a bore [NZ 3679 3123], 0.5 mile S.W. of the Colliery it is 46 in thick. Farther east, Fishburn No. 4 Bore proved coal 24 in, on band 3 in, coal 21 in, and still farther east, the seam is 27 in thick in the Whin Houses Farm Bore.

The seam is more than 3 ft thick adjacent to the line of split in the area extending between Cassop Moor and the coast, and again in a small area east of High Butterby. It is of comparable thickness between Monk Hesleden and Eden Vale, but is probably impoverished to the south-east, beyond Hulam, being only 30 in thick in a bore [NZ 4349 3653], 570 yd W.S.W. of Hulam, and absent in the Thorpe Balmer Bore. E.A.F., D.B.S.

In the south-western part of the district the seam is locally about 40 in thick as in bores [NZ 3003 3921] and [NZ 3048 3923] 1450 yd N.N.W. and 1450 yd N. of Bowburn Colliery respectively. North-west of the colliery, a bore [NZ 2888 3877] at High Butterby, proved coal 18 in, on band 3 in, coal 10 in, band 5.5 in, coal 0.5 in. The coal exceeds 3 ft in thickness in workings near the western margin of the district, about 800 yd W. of High Butcher Race, in Chilton 'E' Bore [NZ 2825 3036], 620 yd S.E. of Chilton Colliery, and in another bore [NZ 2745 2883], 0.5 mile W. of the inn at Rushyford. It might also be as thick over a limited area between West Close and Ferryhill Reservoir, but information is inadequate both here and in the area to the north and east of Bishop Middleham: theonly recent bore [NZ 3433 3211], 1150 yd N.E. of Bishop Middleham Colliery, proved 45 in of Bottom Hutton, though at the Colliery itself, it is only 36 in. However, the seam is relatively close to the Permian unconformity in much of this ground.

In the remainder of the district, the Bottom Hutton Seam is generally between 2 and 3 ft thick. West of Bowburn and Broom Hill, it includes one or more thin bands, and is subject to variation over relatively short distances. Thus, at Bowburn Colliery Downcast Pit it comprises 25 in of coal, but in a bore [NZ 2978 3796], 680 yd to the west, the section is coal 24 in, on band 1 in, coal 13 in; and in a bore [NZ 2929 3787], 560 yd farther W.S.W., it is coal 18.5 in, on black shale band 1.5 in, coal 13 in. This band is generally 2 in or less in thickness, except in a bore [NZ 2806 3832], 1.5 miles W.N.W. of Bowburn Colliery, where the section is coal 17.75 in, on 'black stone with coal threads' 4.25 in, coarse bottom coal 3 in. The seam is 18 in thick in a bore [NZ 2939 3591], 0.5 mile W. of Tursdale Colliery, but nearby, in three other borings [NZ 2981 3602], [NZ 2960 3646] and [NZ 2986 3639], it is 54, 21 and 37 in thick respectively.

The seam is less than 2 ft thick (Figure 10), in a belt trending south-south-west through Cassop Moor Pit (20 in), Bowburn Upcast Pit (22 in) and Tursdale Colliery (17 in). Farther to the south this impoverished belt seems to divide, one branch extending to Chilton (22 in) and the other via East Howle to Chilton Colliery (12 in). The seam is less than 2 ft in a. small area between Trimdon Colliery and Hurworth Bryan and in a narrow belt adjacent to its northern outcrop in the area east of Fishburn. In the Dalton Nook Bore, it is probably represented by a 13-in coal at a depth of 767.75 ft.

Strata between the Bottom and Top Hutton seams

The strata between the Bottom and Top Hutton seams range from 13 ft in thickness, as at Wingate Grange Colliery, to 43 ft, as proved in two bores [NZ 3981 3555] and [NZ 4016 3534], 400 yd W. and 240 yd S. of Woodlands Close respectively. Elsewhere the interval is generally between 20 and 40 ft, except in the area of impoverished banded Hutton extending from south-east of Tweddle Black Halls to Offshore No. 1 Bore. E.A.F., D.B.S.

The lowest part of this sequence, forming the roof of the Bottom Hutton Seam, consists of mudstone containing non-marine lamellibranchs, though these are usually few and fragmentary. In the Dalton Nook Bore, Spirorbis sp., Anthracosia ovum and Naiadites quadratus were obtained at this horizon. In the two offshore bores, where the Hutton sequence is complicated by further splitting, there are two additional fossiliferous bands. In Offshore No. 1 Bore, the Bottom Hutton is probably represented by an upper 2-in and a lower 13-in coal. The lower coal is overlain by seatearth which carries a mudstone with shell fragments. The roof of the upper leaf is the normal Bottom Hutton shell-bed and contains Anthraconaia sp. [juv.], Anthracosia cf. ovum [pyritized], A. aff. phrygiana, Anthracosphaerium cf. turgidum, Naiadites quadratus and fish debris. The higher additional band occurs immediately beneath the Top Hutton and is represented by a cannelly shale containing coalified plant fragments, together with fish remains, including Elonichthys sp.and ostracods. In Offshore No. 2 Bore, the roof of the Bottom Hutton contains only poorly preserved, indeterminable non-marine lamellibranchs, but the upper fossiliferous band contains: Spirorbis sp.; Naiadites sp.[fragments]; Carbonita humilis, C. sp.; fish remains including Megalichthys sp., indeterminate Palaeoniscid and Platysomid scales, Rhadinichthys sp.and Rhabdoderma sp.In Deaf Hill No. 4 Bore [NZ 4016 3534] and Park Farm Bore [NZ 3900 3440], the following were obtained from 25 ft above the Bottom Hutton: Spirorbis sp.; Anthraconaia cf. pumila (Salter), Anthracosia cf. ovum, A. phrygiana, A. cf. subrecta, ?Anthracosphaerium turgidum, Naiadites quadratus; and Carbonita humilis.

No pattern of distribution can be inferred for the strata above the mudstone roof of the Bottom Hutton. Sandstones are commonly interbedded with the higher mudstones and siltstones, but they are not persistent apart from a bed which occupies most of the interval between the Bottom and Top Hutton immediately south of the major split at Bowburn, Cassop Moor, Cassop, East Hetton, Thornley, Wheatley Hill and Blackhall collieries. This sandstone is exemplified in a bore [NZ 2929 3787], 1100 yd S.S.E. of High Butterby, where the Bottom Hutton roof comprises 2.5 ft of mudstone with clay-ironstone and 'mussel' fragments, overlain by 25 ft of light grey, very fine-grained sandstone, with dark micaceous partings in the bottom 3 ft and silty laminae in the top 1 ft, on which rests 2.5 ft of light grey seatearth-mudstone forming the floor of the Top Hutton Seam. In a bore [NZ 2888 3877], 40 yd E. of High Butterby, the sandstone makes up the whole of the sequence between Bottom and Top Hutton seams.

Top Hutton Seam

The Top Hutton Seam is of less economic importance than the Bottom Hutton. Its thickness is very variable, ranging up to 2.5 ft, especially between Bowburn, Wheatley Hill and Garmondsway Moor. Where it is thicker it generally includes one or more bands or becomes shaly. Thus, in a bore [NZ 3433 3211], 0.75 mile N.E. of Bishop Middleham Colliery, it comprises coal 15 in, on band 12 in, coal 12 in, band 2 in, coal 4 in; and at the colliery itself the 33-in seam includes a 10-in band 4 in above the base. A bore [NZ 3142 3004] at Thrundle, 1250 yd E.S.E. of Chilton East House proved the Top Hutton to be divided into two 13-in leaves by 3 ft 4 in of strata. South of Bowburn Colliery, between Hett and Park Hill, it attains a maximum thickness of over 50 in, but is banded as it is also south of Hett, where the seam is over 2 ft thick. Around Croxdale Hall, though free from bands, it is generally less than 18 in. Between Bowburn and Kelloe Law, it is generally 2 to 3 ft thick and has been worked in places, though many of the thicker sections include a band of up to 5 in.

At Thornley Colliery Shaft, it measures only 11 in, but it has been worked over a small area farther south where it is about 2 ft thick. Other small areas have been worked north and south of Wheatley Hill, where it is only 19 to 21 in thick as compared with a shaft thickness of 24 in. Farther to the east, the coal is thin and variable and only rarely exceeds 2 ft, while in the offshore area, further splitting takes place. D.B.S.

Measures between the Hutton and Bottom Brass Thill coals

The measures between the Hutton and Bottom Brass Thill coals range in thickness from less than 8 ft up to perhaps as much as 94 ft, and include several sandstones. The most persistent is found in the north-eastern part of the district where the interval between the two coals is greatest (Plate 4). This sandstone at Hetton Lyons Pit is 24 ft thick, at Elemore Colliery 33 ft, at Murton Colliery 19 ft, at Haswell Colliery 31 ft, at Horden Colliery 37 ft, at Easington Colliery 19 ft, at Dawdon Colliery 38 ft, at Blackhall No. 36 Underground Bore 71 ft, at Offshore No. 1 Bore 68 ft, and in a bore [NZ 4201 3929], 0.5 mile S.E. of Shotton, 25 ft Another such sandstone, generally less than 25 ft thick, lies between the Top Hutton and Bottom Brass Thill west of a line joining Old Cassop and Bishop Middleham, but it is impersistent between Tursdale House and Dean Bank. In the remainder of the district, this part of the sequence consists of mudstone and siltstone with sandy bands, as in a bore [NZ 3442 3853] near Cassop Colliery:

Locally a thin bed of shaly mudstone at the base of the sequence contains non-marine lamellibranchs, but the shells are generally sparse and poorly preserved. E.A.F., D.B.S.

The assemblage from above the Top Hutton is best represented by the collections from 437 to 442 ft in Fishburn No. 4 Bore. The identifications include: Anthraconaia sp.[large], Anthracosia sp. cf. caledonica A, ovum, A. aff. phrygiana, A. sp.intermediate between ovum and phrygiana, Naiadites quadratus; Carbonita humilis; and fish.

Brass Thill coals

The Brass Thill coals of the Durham district are splits from the single seam of that name in the Sunderland (Sheet 21) and Barnard Castle (Sheet 32) districts to the north and south-west respectively. The primary split is into Bottom and Top Brass Thill coals, of which the Top is generally the thicker and more persistent, while the Bottom Brass Thill is commonly subject to further splitting (Plate 4). The primary split is smallest in the Cocken area where locally only a thin band separates the two leaves. The seam was worked from Cocken Drift as a single section [NZ 2897 4697], 700 yd W.S.W. of Finchale Priory, and consists of coal 15 in, on band 3 in, coal 15 in. Other sections proved in the workings and in bores in the surrounding area demonstrate that the band increases to over 10 ft within 0.25 mile, as in a bore [NZ 3023 4745], 700 yd E.N.E. of the Priory, where the two coals, each 12 in thick, are separated by 10 ft 5 in of strata. On the left bank of the River Wear the following section [NZ 2[NZ 2868 4689], 1025 yd W.S.W. of the Priory, is exposed:

The Brass Thill coals are proved in a small area worked from Harbour House Drift, where the band is up to 3.5 ft thick, separating the Bottom Brass Thill, 8 to 10 in, from the Top Brass Thill Coal, 29 to 36 in.

Traced to the east of Finchale Priory, the Bottom Brass Thill splits, as in a bore [NZ 3092 4707], 0.5 mile N.W. of Leamside Station where the section is Top Brass Thill Seam (cannel 5 in, on bright coal 11 in, cannel 7 in), on seatearth-mudstone 4 in, sandstone 10 in, mudstone 3.5 ft, Bottom Brass Thill Seam (coal 8 in, on seatearth-mudstone 11 in, coal 6 in). However, farther to the east and throughhout the Rainton area, there are only two thin coals each 7 to 12 in thick and about 1 to 3 ft apart. To the north, beyond Rainton Meadows Pit, in the Sunderland (Sheet 21) district, these coals reunite, and at Rainton Plain Pit, just over 0.5 mile N.N.W. of the Meadows Pit, there is a single Brass Thill Coal 40 in thick. Farther to the east, at Houghton Pit, also in the Sunderland district, and at North Hetton Colliery, the Top and Bottom seams are again distinct. In the North Hetton Upcast Shaft, the Bottom Brass Thill comprises two thin coals 7 and 10 in thick, but in the nearby Moorsley Winning these are united in a single 22-in coal.

In the west-central part of the district between Pittington, Sherbum Hill, Bowburnand Kepier Grange collieries, the Brass Thill coals are all thin. The Top Brass Thill reaches a local maximum of 18 in at Kepier Grange, but at Kepier Colliery it is 14 in thick and the Bottom Brass Thill consists of two 4-in leaves of coal. At Whitwell 'A' Pit, however; the sequence is Top Brass Thill Seam foul coal 4 in, on 'post' and 'metal' 10 ft 10 in, Bottom Brass Thill Seam (coal 9 in, on 'grey metal' 2 ft 9 in, coal 5 in). At Old Durham Colliery, the Top Coal seems to be represented only by 5 ft of 'black stone' about 6 ft above the Bottom Seam, here represented by coal 10 in, on 'dark grey metal' 4 ft, coal 7 in. Farther west, at Elvet South Engine Pit, three coals, comprising, from the top, seams of 10, 11 and 6 in thick respectively, are separated by intervening strata comparable with those of Whitwell 'A' Pit. One mile to the north-north-west of Elvet, at Aykley Heads Pit just beyond the western margin of the district, there is again a three-fold sequence, but here the Top Brass Thill is split and comprises coal 13 in, on fireclay 5 in, coal 15 in, separated by 4 ft of fire-clay from the 6-in Bottom Brass Thill Coal. At Framwellgate Moor Pit, one mile farther north, an unhanded 30 in Top Brass Thill is separated by 3 ft 10.5 in of 'grey metal' from an 8-in Bottom Brass Thill.

In the extreme north-western corner of the district, a 15- to 34-in Top Brass Thill Coal lies up to 6 ft above the 4- to 12-in Bottom Brass Thill Coal. To the southeast of this, the Bottom Brass Thill splits so that a three-fold sequence is recorded at Frankland Furnace and Engine pits. However, local variations are exemplified in a third Frankland Pit which records a 21-in Top Brass Thill and a single 7-in Bottom Brass Thill, while an old bore (Borings and Sinkings 1467) of uncertain site in the Newton Hall Estate proved foul coal 10 in, on 'grey metal' 6 in, coal 18 in, 'grey metal' 4.25 ft, coal 4 in, a section closely comparable with that at Aykley Heads Pit. E.A.F.

In the eastern part of the district, the Top Brass Thill Coal is as much as 3.5 ft thick at South Hetton Colliery and 2.5 ft in Easington Colliery No. 5 Bore, but has not been worked. The Bottom Brass Thill Coal, though proved to be 20 and 26 in thick respectively at Eppleton Colliery and Horden No. 15 Bore, 3.25 miles E. of Fox Holes, Easington Colliery, is also not worked. In some eastern parts of the district, further splitting takes place to form up to 5 thin seams, some of the lower of which, as in Blackhall No. 36 Bore are locally absent (Plate 4). D.B.S.

In the south-western part of the district, there is again considerable variation in the Brass Thill coals, but the Bottom Brass Thill is generally less than 1 ft thick where single, and where double, the individual leaves rarely exceed 10 in. South-east of Bowburn, three leaves are present, but the Bottom Brass Thill coals are both thin and the Top Brass Thill is generally less than 12 in. None of these coals was recorded at Coxhoe and East Hetton collieries. South-west of Bowburn, the Top Brass Thill Coal exceptionally reaches 22 inches in a bore [NZ 2960 3646], 550 yd N.N.E. of Broom Hill, and south of High Butcher Race a number of bores record the Top Brass Thill as having thicknesses ranging from 9 to 21 in, though the upper leaf of the Bottom coal is only 8 to 10 in and the lower leaf 2 to 8 in thick. Still farther south, at Dean and Chapter Colliery, the Top Brass Thill is only about 18 in thick, but it increases to 27 in farther east in the Cleves Cross No. 2 Bore [NZ 2946 3264] and in the Wood Lane Bore [NZ 2937 3293]. At Chilton Colliery the Top Brass Thill is 24 in thick, and though one bore [NZ 2867 3120] at West Close proved only 1 in of coal at this position, it is consistently 21 to 31 in thick in other bores in the area. To the east of Chilton the Top Brass Thill is variable in thickness, but is generally over 2 ft in the area south of Thrislington Plantation and Highland House, and reaches its local maximum of 34 in in a bore [NZ 3234 3105], 550 yd S.W. of Bishop Middleham church. In another bore [NZ 3278 3126], 20 yd N. of the church, however, the coal, though comparable in thickness, contains a thin band: coal 11 in, on band 3 in, coal 18 in. To the north around Thrislington and Garmondsway, the thickness decreases, so that at Thrislington Colliery, it is only 22 in, and in the Garmondsway bores, it ranges from 10 to 18 in. E.A.F.

In South Hetton No. 6 and Shotton No. 7 bores, non-marine lamellibranchs were recorded from the roofs of both Bottom and Top Brass Thill Coals. The  'mussel'-band overlying the lower coal is the less persistent and has yielded the following: Anthraconaia salteri?, Anthracosia beaniana, A. cf. ovum, A. aff. phrygiana, A. aff. retrotracta (Wright), A. sp. nov.[truncate], A. sp.intermediate between aquilina and ovum, Anthracosphaerium cf. exiguum, A. turgidum, Naiadites quadratus; Carbonita humilis, C. pungens, Hilboldtina sp.; Rhabdoderma sp.and Rhizodopsis sp.The assemblage from the roof measures of the Top Brass Thill includes: Anthraconaia sp., Anthracosia beaniana, A. disjuncta, A. cf. ovum, A. aff. phrygiana, A. retrotracta?, A. sp.nov.[truncate], A. sp.intermediate between aquilina and ovum, Anthracosphaerium aff. affine, A. exiguum, A. aff. turgidum, Naiadites quadratus; Carbonita humilis; and Eurypterid fragment.

The roof of the Top Brass Thill Coal generally consists of shaly mudstone with abundant non-marine lamellibranchs—the Brass TM Shell-bed. This is one of the most persistent  'mussel'-bands of the Coal Measures sequence in the district and resembles the band overlying the Harvey Marine Band in the variety and abundance of its fauna—in marked contrast to the other shell-beds in the lower part of the Middle Coal Measures. However, it rarely exceeds 10 ft in thickness. In the Butterby bores, between Bowburn, High Butterby, Croxdale Wood House and High Croxdale, the shell-bed ranges from 5 to 8.5 ft in thickness, and this range may be taken as typical.

In the same bores the Brass Thill Shell-bed is successively overlain by 10 to 15.5 ft of mudstone and siltstone, 6 to 10 ft of sandstone and siltstone, and 1 to 3.5 ft of seatearth forming the floor of the Durham Low Main Coal. This sequence is fairly typical of the district, though in the area around Durham City the sandstone and siltstone lie immediately above the ‘mussel’-band. In south-western parts of the district the interval between the coals is increased and is largely occupied by a thick sandstone. At Chilton Colliery the sandstone, 70 ft thick, extends from the roof of the Top Brass Thill up to a 2.5-ft bed of 'fireclay' forming the seatearth of the Durham Low Main Coal.

A small form of Anthraconaia compared with A. pumila (Salter) was found 16 ft below the Durham Low Main Coal in Shotton No. 6 Underground Bore and at a similar horizon in Blackball No. 36 Underground Bore.

Durham Low Main Coal

The Durham Low Main Coal (Figure 11) has been widely worked in the district. It crops out within the buried valley system of the River Wear north-west of Shincliffe and north-east of Hett, and along the northern side of the Butterknowle Fault in the western part of the district. It is absent from a large part of the southern and south-eastern area of the district as a result of pre-Upper Permian erosion. The average thickness of the seam is 3 ft, but it reaches a maximum of about 7.5 ft in Offshore No. 2 Bore where, however, the lower part is banded (see below). Such banding is only locally recorded in this seam. Its distribution is shown in (Figure 11), together with the position and extent of long narrow belts of abnormally thin coal and washouts, which are more abundant in the Durham Low Main than in any other seam in the district. E.A.F., D.B.S.

The seam is more than 5 ft thick in the north-eastern part of the district in a narrow zone extending eastwards from Cold Hesledon. About 0.25 mile E.S.E. of Chourdon Point, the thickness recorded on mine plans is 54 in, but this may not include the uppermost part of the seam which is locally inferior and unworked. About 2.5 miles E. of Chourdon Point, however, the whole seam becomes thinner as the top inferior coal decreases from 14 out of 72 in to 4 in out of 67 in, and then to 2 in out of 60 in. To the north a thin band appears, as at a locality [NZ 4842 4758], 3 miles E. of the coastline, where the seam consists of coal 2 in, on band 5 in, coal 60 in. In most other eastern parts of the district, the seam exceeds 3 ft except in an irregular area extending from Easington through Warren House south-eastwards for over a mile beyond the coast; within it is a smaller, narrow zone where the coal is either less than 2 ft thick, or absent because of washout (Figure 11). In the offshore area, it is likely that substantial reserves in this seam remain to be won, judging from Offshore No. 1 Bore which proved 43 in of unbanded coal, and by Offshore No. 2 Bore which proved coal 59.5 in, on band 1 in, coal 13 in, seatearth 2 in, coal 1 in, seatearth 10 in, coal 2 in.

Between Murton and The Castle, at Castle Eden, the upper part of the Durham Low Main Coal includes a band which rarely exceeds 18 in, though in South Hetton Colliery Shaft it reaches the exceptional thickness of 7 ft 3 in. Another band occurs low in the seam in an area between Easington Lane and Easington. The two areas overlap between Easington and South Hetton, giving seam sections as follows: coal 2 to 6 in, band 9 to 13 in, coal 16 to 23 in, band 1 to 4 in, coal 16 to 23 in. Farther north, the Durham Low Main Seam lies within 2 ft of the Maudlin Coal, thus forming a compound seam, locally over 8 ft thick which has been worked from Eppleton Colliery just beyond the northern margin of the district. The interval is as little as 4 in near Carr House (see also p. 71). D.B.S.

West of a line joining South Hetton, Shotton and Castle Eden the Durham Low Main Seam is generally between 2 and 4 ft thick, and is traversed by several belts of thin coal and washouts, some of which have a north-westerly to north-north-westerly trend corresponding with similar belts near the coast (Figure 11). One of these crosses the northern margin of the district between Hetton le Hole and Carr House and continues as far south as South Hetton. E.A.F., D.B.S.

A much longer one extends from close to the northern margin of the district, about 0.5 mile N.W. of Finchale Priory, for over five miles south-eastwards and then turns southwards for more than a further two miles to Cassop Colliery. Sections measured along the margin of this belt show that impoverishment is caused by erosion in some places, but by thinning or banding in others. Although the impoverishment is of more than one kind, its occurrence within a single belt suggests a causal relationship. The northern part of this belt can be seen at outcrop [NZ 2873 4788], 1250 yd N.W. of Finchale Priory, in the steep left bank of the Bow Burn, where the Durham Low Main Coal, 12 in thick, is overlain by 19 ft of sandstone. It can be followed downstream for about 75 yd until the coal is cut out by the sandstone close to the confluence of the burn with the River Wear. The coal is absent too, in the right bank of the River Wear gorge for about 400 yd upstream from this confluence as far as an old adit [NZ 2864 4746], about 1,100 yd W.N.W. of Finchale Priory. The adit was put in at the level of the seam, though no section is now visible. The belt can be traced south-eastwards first by a bore [NZ 2897 4755], about 825 yd N.W. of the Priory, where the seam is absent, and thereafter by mining information (Figure 11). E.A.F.

To the south and east of Thomley Colliery, this belt is linked with other belts of washout, some having a northwesterly trend, while others trend eastwards, so that in places islands of coal are surrounded by washouts. D.B.S.

The westernmost extremity of the main east–west washout is proved by two stone drifts, respectively 320 and 420 yd long, about 0.25 mile E. of Quarrington Hill crossroads, and in a bore [NZ 3184 3747], 200 yd S.S.W. of Heugh Hall Row. There is evidence to show that from the westernmost extremity of washout a north-westerly belt of thin coal continues towards Durham City. At Shincliffe Colliery, the section is coal 29 in, on band 7 in, coal 11 in, but the limit of workings lies only 70 yd to the west of the downcast pit and trends generally north-north-west from near Shincliffe Station, where a bore [NZ 3003 3921] proved the coal to be only 7 in thick. The limit of workings probably represents the line along which the coal thickness falls below 2 ft. If the north-west trend is continued, this belt of thin coal should pass through Elvet South Engine Pit where the Durham Low Main seems to be represented by an 11-in coal 103 ft 9 in above the Hutton (Dunham and Hopkins 1958, p. 2). The record of an 'old shaft near Durham Grammar School' (Borings and Sinkings No. 2652), however, shows the Durham Low Main to be 30 in thick at 75 ft 3 in above the Hutton. Although the precise position of this old shaft is not known, it appears to mark the southern edge of the north-westerly belt of thin coal. The northern margin probably passes south of Crook Hall High Pit [NZ 2728 4314], which is thought to be the site of a bore (Borings and Sinkings No. 927) proving the Durham Low Main Coal to be 30 in thick, and thence close to Aykley Heads Pit where the coal is 26 in thick. Thus, much of the Durham gorge lies within the belt of thin coal. Recent information suggests that the thin coal which underlies the sandstone upon which the Cathedral is built is the Durham Low Main, as proposed by Holmes (1928), and not the Maudlin as shown on the new One-Inch Map, nor the Brass Thill as proposed by Hindson and Hopkins (1947) and by Dunham and Hopkins (1958). The north-westerly belt is joined to the south-east of Shincliffe Colliery by a similar belt of thin coal which extends southwards through Hen. In one bore [NZ 2774 3827] sited along this belt the coal is 11.5 in thick.

In much of the western part of the district, the Durham Low Main Seam is unhanded, but bands occur locally near impoverished zones. In a bore [NZ 3371 3942] at Old Cassop, the section is coal 0.5 in, on sandstone with large coal scar 8 in, coal 1 in, sandstone 1 in, coal 15 in, seatearth-siltstone 11 in, coal 3 in, and this may indicate proximity to a washout or belt of thin coal extending at least as far as a bore [NZ 3264 3952], 0.75 mile to the west, where the section is coal 13 in, on band 1 in, coal 5 in. Other banded sections were measured in workings [NZ 3487 3562] and [NZ 3452 3514], 1.75 miles E. and 1.5 miles E.S.E. of Coxhoe, where the seam consists respectively of coal 18 in, on band 8 in, coal 3 in; and coal 30 in, on band 10 in, coal 3 in. A bore [NZ 3164 3584], 0.33 mile W. of Coxhoe proved coal 8 in, on band 2 in, coal 31 in. The Durham Low Main, like the Busty Seam (p. 48), is cindered over a smaller area to the north of the Ludworth Dyke than it is to the south where it extends at least as far as a bore [NZ 3166 3879], 300 yd E. of Cassop Grange, which proved cindered coal. 21 in, on band 7 in, cindered coal 5 in.

South of the Butterknowle Fault, the Durham Low Main Seam exceeds 4 ft near Garmondsway and Famless, and decreases to about 1 ft south-westwards. Near Garmondsway, bores proved coal up to about 5 ft in thickness on the northern limb of the anticline, though it is only 29 in thick in a bore [NZ 3426 3453], 0.66 mile N.E. of Garmondsway Pit. Some of the sections may reflect minor tectonic thickening, but this is unlikely to account for the thickness of 50 in proved. in a bore [NZ 3362 3243], nearly 1 mile south of the pit. Still farther south, in a bore [NZ 3386 3168], 0.25 mile N.N.E. of Bishop Middleham Colliery, the 43-in seam includes a 4-in band 7 in above the base, and this band is also proved in several bores around Bishop Middleham church, reaching its maximum in a bore [NZ 3234 3105], 550 yd S.W. of the church where the section is coal 30 in, on band 4 ft 5 .in, coal 4 in. The same band is proved in a bore [NZ 2996 3275], 1 mile N.N.W. of Mainsforth Colliery: coal 28 in, on band 3 in. coal 5 in. The seam measures 42 inches in a bore [NZ 2937 3293], l.25 miles N.W. of the colliery, but this thickness is locally exceptional for the 24-in isopach of the coal runs south-eastward through the Mainsforth Colliery shafts and the seam consists of only 12 in of shale and coal at Chilton Colliery shafts. A small outlier of the coal, 36 in thick, was proved in the Embleton Old Hall Bore, but it lies too close to the base of the Permian to be of economic value. E.A.F.

Measures between the Durham Low Main and Maudlin seams

The measures between the Durham Low Main and Maudlin seams range in ,thickness from 4 in near Carr House to about 115 ft at Littletown Engine Pit. Except in ‘some northern, south-western and farthest offshore areas this interval is dominated by thick sandstone-the Low Main Post-which reaches 105 and 104 ft respectively at Hutton Henry Colliery and Littletown Engine Pit. The 30-ft isopach in the sandstone is plotted on (Figure 11) from which it can be seen that there is 8 direct relationship between most of the washouts affecting the Durham Low Main Coal and the overlying sandstone. An exception is the ‘washout east of Easington Laner for close to its southern tip only 5 ft of sandstone is present in the roof of the Durham Low Main Seam at South Hetton Colliery, and to the west of the washout at Hetton Lyons Pit the sandstone is only 11 ft thick, and lies 18 ft above the coal. E.A.F., D.B.S.

Farther west, at Elemore, Rainton Alexandrina, Meadows, Adventure and Resolution pits, the 40 to 70 ft interval between the Low Main and Maudlin seams consists mainly of ‘grey metal’ and ‘blue stone’ with no thick sandstones. In a bore [NZ 3092 4707], 650 yd W. of the Adventure Pit, the Durham Low Main Coal is overlain by a thicker, more sandy sequence, comprising about 60 ft of sandstone in five bands interbedded with siltstone with sandy partings, and overlain by &bout 20 ft of silty and shaly mudstone topped by the Maudlin seatearth-mudstone. The records suggest that as the succession between the Durham Low Main and Maudlin coals is traced southwards through the area separating Leamside and Elemore Colliery, further bands of sandstone appear, and that these thicken and eventually. coalesce into the single thick bed farther south. In places, however, bands of mudstone or siltstone survive. Thus, whereas at Broomside Colliery 89 ft 4 in of ‘strong jointy white post’ rest on 3 ft 2 in of ‘soft blue metal’ forming the roof of the Durham Low Main, ‘Grange New’ Winning proved the following contrasting sequence:

The immediate roof of the Durham Low Main Coal consists locally of black mudstone or shale with crushed, usually indeterminate, non-marine lamellibranchs. The shale is in most places only a fraction of an inch thick, but reaches 2.5 in at outcrop [NZ 2717 3748], just beyond the western margin of the district During the resurvey, the stratigraphically higher bed beween the coal and the undulating base of the Low Main Post was examined in the workings south of Sherburn Hill Colliery, where it consists of up to 5 ft of grey silty mudstone and siltstone with sandy partings and abundant clay-ironstone nodules. These argillaceous beds seem to be absent in the areas of true washout in the Durham Low Main Coal, where the overlying Low Main Post presumably descends to or below the floor of the seam.

Durham Low Main Post

The Durham Low Main Post crops out along the gorge of the River Wear downstream from Frankland Farm. On the left bank [NZ 2881 4698], 875 yd W.S.W. of Finchale Priory, the lowest 20 ft of the post, containing thin coal partings near the base, rest directly on the Durham Low Main Coal (p. 68), and are overlain by boulder clay. On the opposite side of the river between about 800 yd W. and 500 yd W.N.W. of the Priory, up to 40 ft of sandstone are exposed. In the western part of the section up to 10 in of Durham Low Main Coal are seen and are overlain by up to 9 ft of conglomeratic sandstone, the lower part of which contains lenticular masses of sandstone. At Cocken Rock [NZ 2896 4727], 700 yd W.N.W. of the Priory, at least 6 ft of breccio-conglomerate is exposed and the fragments consist of masses of sandy siltstone or silty mudstone generally 3 or 4 inches in length, but ranging up to 3 ft long by 1 ft thick. These fragments, which are set in a matrix of clean white sandstone, are generally angular or subangular, but mixed with them are many small round lumps of clay-ironstone or 'boxstone', a few inches in diameter. The coarse detritus is collectively reminiscent of the bed lying between the Durham Low Main Coal and Post in Sherburn Hill Colliery (see above): its imbrication suggests transport from the north-west To the west, thin beds of sandstone come in in the upper part of the breccio-conglomerate which is succeded by an impersistent massive bed of sandstone up to 2.5 ft thick. This is overlain by about 40 ft of cross-bedded, fine-grained sandstone which contains thin layers of small nodules of ironstone, many weathered to boxstone

These exposures lie along one of the north-westerly belts in which the Durham Low Main Coal is thin. Not all of the attenuation, however, has resulted from erosion at the base of the sandstone. At Littletown Lady Alice Pit, within the same belt, for instance, the sandstone, 87 ft thick, is separated from the 16-in coal by 8.5 ft of ‘grey metal stone with post girdles’ (Plate 4).

At the southern margin of the Durham Low Main Post, between Hett and Low Butcher Race, the sandstone splits into separate beds which become thinner and eventually wedge out. To the south-west, though the sandstone reaches 30 ft at Chilton Colliery, it is generally thin or absent, and the interval up to the Maudlin Seam contains mostly siltstone and mudstone. In places, a thin impersistent coal is present below the Maudlin (Figure 12). In this south-western area and in the outlier penetrated by the Embleton Old Hall Bore, non-marine lamellibranchs have been recorded locally in the roof of the Durham Low Main Coal. E.A.F.

In some places where the Low Main Post is split or absent ‘mussel’-bands, thin coals and seatearths divide the sequence, as in Horden No. 20 Bore (Figure 12). Less commonly, as in Shotton No. 7 Bore (Figure 12), a ‘mussel’-band with Naiadites productus and Spirorbis sp.locally overlies a thick Low Main Post. In a bore [NZ 3120 3597], 1100 yd E. of Tursdale Colliery, Carbonita sp. cf. scalpellus was recorded in addition from this position. D.B.S., E.A.F.

Maudlin Coal

The Maudlin Coal is generally thin and unworkable over most of this district, though in the ground to the north covered by the Sunderland (21) Sheet, it is a consistent seam of good quality with an average thickness of over 4 ft. This order of thickness persists across the northern margin of the district and the seam has been worked as far south as Rainton Adventure Pit, Middle Rainton and East Rainton in the north-west, Hetton le Hole and Carr House in the north-centre (where it is locally united with the Durham Low Main Coal, p. 68) and Chourdon Point in the north-east. D.B.S., E.A.F.

Sections in the Rainton area commonly include a band 1 to 3 ft thick and 12 to 24 in above the base of the seam. The band exceeds 5.5 ft just beyond the northern margin of the district at Prior's Close, 1600 yd N.W. of Adventure Pit, and the top coal is heavily banded as follows: coal 2.5 in, on band 0.25 in, coal 4.75 in, band 0.5 in, coal 2.75 in, band 0.25 in, coal 5 in, band 0.5 in, coal 2.25 in, band 5.25 in, coal 5 in, band 5 ft 8 in, splint 2.5 in, coal 18 in. Traced to the south and southwest of Resolution Pit, the median band thins and eventually disappears, and the whole seam concomitantly becomes too thin to work. Seam thicknesses in this area are as follows: two bores [NZ 3133 4676] and [NZ 3092 4707], 625 yd W. and 400 yd S.W. of Adventure Pit, 22.5 to 24 in, with a median 0.5-in band; in bores [NZ 3023 4745] and [NZ 2997 4741], 700 yd E.N.E. and 450 yd N.E. of Finchale Priory, 36 in; at Cocken Pit and in a bore [NZ 2937 4745], 425 yd N.W. of Finchale Priory, 30 in. E.A.F.

In broad terms, the deterioration of the Maudlin Coal corresponds to a thickening of the measures between it and the underlying Durham Low Main Coal (Figure 12). Thus, between Resolution and Adventure pits, the seam is reduced from 4 to 3 ft corresponding to an increase from 44 to 70 ft of the underlying strata. Similarly the 48 in of ‘bad’ Maudlin Coal, 45 ft above the Durham Low Main at Alexandrina Pit, deteriorates further to 6 ft of 'soft black metal stone and coal pipes' 67 ft above the Durham Low Main at North Hetton No. 2 Upcast Pit, while at the North Hetton Moorsley Winning and Lady Seaham Pit, it is absent. It is absent too at Belmont Furnace Pit where its seatearth is separated from the Durham Low Main by 97 ft of 'white post'. Farther south-east, where the ‘white post’ is of comparable thickness, the Maudlin is represented by 6.25 ft of 'black stone' at North Pittington Londonderry Pit, by 3 ft 4 in of 'black stone and sulphur' at Littletown Engine Pit, and by 3.5 ft of ‘coal or black stone’ at Littletown Lord Lambton and Lady Alice pits. In places, however, both the Maudlin Coal and Low Main Post are thin as at Trimdon Grange Colliery (Figure 12), and there is no obvious relationship between the Maudlin coals and Low Main Post in the offshore area. E.A.F., D.B.S.

Southward deterioration of the Maudlin Seam can be traced between Hetton le Hole and Carr House. At Houghton Pit, just beyond the northern margin of the district, the Maudlin is a single coal 61 in thick, but at a locality [NZ 3637 4805], 1200 yd N.N.E. of Hetton Colliery, it is represented by coal 25 in, on band 3 in, coal 26 in, band 9 in, coal 6 in. At a locality [NZ 3675 4779], 1200 yd N.E. of Hetton Colliery, the section is coal 14 in, on band 5 in, coal 6 in, band 4 in, coal 13 in, and close to the limit of workings [NZ 3669 4764], 1000 yd N.B. of the same colliery, it is coal 16 in, on band 9 in, coal 9 in, inferior coal 25 in, band 16 in, coal 18 in. At Hetton Lyons Pit, beyond the limit of workings, two coals survive: they are 14 and 4 in thick, lying 58 and 53 ft respectively above the Durham Low Main Seam.

Workings from the Seaham and Dawdon collieries extend southward into the district and in the ground between Hawthorn and Murton collieries the seam is split and only the Top Maudlin is extracted. The split persists into the offshore area, where several bores penetrate a Top Maudlin coal lying up to 50 ft above two relatively persistent coals considered here to be a split Bottom Maudlin. The lower leaf of the Bottom Maudlin is generally 12 to 24 in thick but is as much as 35 inches in Easington No. 20 Bore [NZ 4625 4667]: the upper leaf, lying some 10 to 20 ft higher, is commonly 12 to 18 in thick, reaching a maximum of 22 inches in Easington No. 12 Bore (Figure 12). The Top Maudlin is the most consistent of the three coals, and reaches thicknesses of 48 inches in Horden No. 1 Bore [NZ 4657 4206] and 30 inches in Easington No. 12 Bore [NZ 4728 4560]. East of Horden and Blackhall Colliery the Top Maudlin deteriorates with the incoming of a median band up to 1.5 ft thick.

In the north-central part of the district, between Elmore Hall and Hawthorn, and to the south-east through Shotton Colliery to Oakerside and Blackhall Colliery, the Maudlin coals are absent and correlation between the eastern and western parts of the district is therefore difficult. D.B.S.

In the western part of the district, between Sherburn Hill and Thrislington, there are commonly one or two thin coals 60 to 110 ft above the Durham Low Main Coal. The upper is the more persistent and generally the thicker of the two and is here correlated with the Maudlin Seam of the Rainton area. In the south-western part of the district, beyond Thrislington, this thickens and in a bore [NZ 3226 3215], 250 yd N.N.E. of Hope House, it is 5.5 ft thick, comprising coal 45 in, on band 5 in, coal 16 in. At 12 ft 8 in below is 1.25 ft of black coaly shale, which passes laterally into a thin, relatively persistent coal—the lower of the two coals proved farther north. It is possible that these two coals are the equivalents of the Top and Bottom Maudlin coals of the northeastern part of the district, but in view of the lack of evidence in the intervening north-central area (see, for instance, (Figure 12)) the lower coal in the western area is here regarded as separate and has not been named on the maps.

In a small area north of Mainsforth, the thick Maudlin Coal generally includes more than one band as in a bore [NZ 3112 3200], 650 yd N.W. of Mainsforth Hall, which proved coal 28 in, on band 2 in coal 14 in, band 1 in, coal 4 in, band 1 in, coal 9 in. Farther south-west, at Mainsforth Colliery (Figure 12), the Maudlin is an unbanded seam 48.5 in thick, but still farther south-west as at Chilton Colliery, the seam is again typically banded as follows: coal 26.5 in, on hand 9.5 in, coal 10.5 in, band 6 in, coal, 8 in. Around Ferryhill, this thick banded seam splits, and in the Dean Pit the Section is coal 5 in, on 'seggar-clay' 5 in coal 11 in, 'black stone' 1 ft 8 in, 'grey metal' 5 ft 3 in, coal 19.5 in. The upper split fails nearby and the seatearth is traceable for only a short distance before it too fails. Concurrently, the lower split thin and can be traced into the impoverished Maudlin of the western area. E.A.F.

Strata between the Maudlin Coal and the Main Coal

The strata between the Maudlin Coal and the Main Coal range from about 25 ft in the Eden Bore to about 80 ft at Chilton Colliery (Figure 12). The sequence can be subdivided into a lower, thinner part topped by an impersistent seatearth and thin coal, and an upper part which includes an important  'mussel'-band either just above the thin coal or below the Main Coal seatearth. The band consists of dark grey or black mudstone or shale containing fish fragments and non-marine lamellibranchs. In some places, as in Offshore Nos. 1 and 2 bores, 'Estheria' has been found and the band has been named the Blackhall 'Estheria' Band (Magraw and others 1963, p. 164). The 'Estheria' are preserved as iridescent films and are associated with fish debris including Diplodus sp., Megalichthys sp., Platysomid scales, Rhabdoderma sp., Rhadinichthys sp.and Rhizodopsis sp.Other fossils obtained from the band are as follows: megaspores; Spirorbis sp.; Naiadites cf. angustus Trueman and Weir, N. cf. obliquus, N. productus; Carbonita sp. cf. scalpellus.

Main Coal

The Main Coal (Figure 13) is thickest in the northern part of the district. It is 6 to 7 ft thick in workings as far south as South Hetton and Low Moorsley and reaches a maximum of 107 in at Rainton Adventure Pit. Between Low Moorsley and Rainton Adventure Pit it contains a band (not plotted in (Figure 13)) which is generally only 1 to 2 in thick, though exceptionally as much as 13 in at a locality [NZ 3202 4644], 0.75 mile N. of Belmont Colliery. The band divides the seam into a 15- to 21-in top coal and a 40- to 55-in bottom coal. A thin band lies at a comparable position in the seam east of Murton and Great Coop House, and this thickens south-eastward to more than 3 ft just off shore from Easington Colliery and to 25 ft still farther east in Horden No. 19 Bore [NZ 4738 4258], where the Top and Bottom Main coals are 8 and 27 in thick respectively (Plate 4). The Main Coal has been exhausted in most of this northern part of the district except for a small area around Easington village, where extraction is in progress at the time of writing.

South of a line through South Hetton and Low Moorsley the seam is thinner.

Across the central part of the district, west of Horden, is a zone in which it is less than 2 ft thick and locally only 4 in as in a bore [NZ 4184 4058], 1000 yd N.E. of Shotton. In the ground to the west of Shotton Colliery it is absent in three bores between Harehill Farm and Low Crow's House and a line of 'washout' was proved in the workings 2000 yd S.W. of the colliery shafts. E.A.F., D.B.S.

The seam is absent also farther west, in bores [NZ 3450 4019]; [NZ 3400 3966] 1.5 and 2 miles S.W. of Ludworth Colliery respectively, where about 70 ft of sandstone were proved above the expected horizon of the coal. A similar absence is recorded in a bore [NZ 3361 4063], 1.25 miles S. of Sherburn Hill Colliery. In two other bores [NZ 3317 4105] and [NZ 3303 4101], about 1 mile S.S.W. of the colliery, the Main Coal is 8 in and 12 in thick respectively, and at Sherburnhouse Colliery it is 15 in. A smaller zone of impoverishment trends in parallel through Sherburn Hill Colliery where coal thicknesses of 6 in and 8 in are proved in the East and West pits respectively. At the limit of workings [NZ 3275 4285] on the south side of this zone, the coal is 16 in thick, having decreased from 24 inches only 70 yd to S.S.E.

An outlier of Main Coal has been mapped east of Kepier Pit, in the Carrville–Gilesgate Moor area (Figure 13) on the basis of rock-head calculations. The area is not known to have been penetrated by bores or shafts and since it is in line with the impoverished belt, the coal, if present at all, is probably thin and close to rockhead. E.A.F.

The Main Coal thickness also decreases to less than 2 ft in an area east of a line two miles offshore from Dene Mouth and Blackball Colliery shafts. Two bores [NZ 4981 4104] and [NZ 4916 4045], 2.75 miles and 2.25 miles E. of DeneMouth, record thicknesses of 11 and 16 in respectively, and it may be absent in a third bore [NZ 4924 3939] 1.5 miles E.N.E. of Blackhall Rocks station. The impoverished area does not extend as far as Offshore No. 1 Bore which proved 34 in of coal at this position. North of the zone of impoverishment, borings and undersea workings in the offshore area have proved a thin band near the base of the lower leaf of the Main Coal (or Bottom Main where the split is more than 3 ft). Below this thin band, the coal is of inferior quality. Between the offshore zone of thin Main Coal and Blackhall Colliery, several borings have penetrated a thin banded coal a short distance below the lower leaf of the seam. It seems possible that this banded coal is so near to the Main Coal as to have been worked with it as a composite seam in parts of Blackhall Colliery workings. Alternatively the banded coal may be the seam underlying the Blackball 'Estheria' Band (p. 75).

West of Blackball Colliery the Main and Five-Quarter coals are so close as to have been worked together from Shotton Colliery in a belt elongated southeastwards (Figure 13) and (Figure 14). Within this belt the seams are less than 2 ft apart in contrast with over 50 ft in the surrounding area. They are 3 ft apart in Shotton No. 6 Bore [NZ 4201 3929], 730 yd S.E. of Shotton Hall, and 7 ft apart at Blackhall Colliery shafts. D.D.S.

In the remainder of the southern part of the district, south of the central belt of impoverishment, the Main Coal is split into Top Main and Bottom Main. The Bottom Main is generally over 3 ft thick and has been worked under the name 'Main'. Specimen sections are as follows:

The band reaches 24 ft in a bore [NZ 3220 3942], 1150 yd N.E. of Cassop Grange, where the Bottom Main comprises coal 3 in, on band 1 in, coal 14 in, band 3 in, coal 33 in, and the Top Main consists of 33 in of coal and bands.

At Coxhoe and Wingate, the Top and Bottom Main coals are united as follows: Wingate 61 in; Coxhoe Bell's Pit, coal 34 in, on band 2 in, coal 48 in; bore [NZ 3348 3480], 1075 yd S.S.E. of Coxhoe East House, coal 20 in, on band 15 in, coal 55 in. E.A.F., D.B.S.

Two small outliers of Main Coal remain at Hett. The southernmost has been explored by opencast drilling which proved a thickness of over 4 ft. North of the railway line, opencast bores have proved pillars of coal, up to 6 ft high, in old workings which were probably entered from a drift [NZ 2890 3710] still visible 825 yd N.N.E. of Hett church. E.A.F.

Most of the Main Coal has been worked out west of Castle Eden, but to the east, considerable reserves of coal remain, particularly around. Hesleden. D.B.S.

Measures between the Main and Five-Quarter coals

The measures between the Main and Five-Quarter coals range in thickness from less than 2 ft west of Blackhall Colliery to at least 115 ft, including 72 ft of sandstone, in a bore [NZ 3361 4063], 0.5 mile S.W. of Shadforth. The sandstone exceeds 30 ft in thickness over large areas of the district (Figure 13), And, where the Five-Quarter Coal is washed out, unites locally with a higher sandstone to form a bed up to 142 ft thick as at South Hetton Colliery Engine Pit (Plate 4). E.A.F., D.B.S.

Where sandstone does not form the roof of the Main Coal, argillaceous beds containing rare non-marine lamellibranchs have been recorded. In Easington Colliery No. 12 Bore the coal is overlain by a thin black shale with 'Estheria', and in other bores nearby, fish debris has been obtained from the same bed. Plant remains are common at this horizon. In Offshore No. 1 Bore, the Main Coal is overlain by 6 ft of mudstone containing many pinnuks, mainly of Neuropteris, with abundant Calamites in the basal 1 ft. Finely comminuted plant debris is also preserved in the overlying 10 ft of mudstone. D.B.S.

At some places, and especially in the south-western part of the district, a thin coal lies between the Top Main and Five-Quarter coals. It is 8 in thick in East Hetton North Pit, 15 inches in Coxhoe Engine Pit and 21 inches in Mainsforth Colliery (Plate 4). E.A.F.

Five-Quarter Seam

The Five-Quarter Seam (Figure 14) is 2.5 to 6 ft thick and has been worked widely in the district. It is normally unbanded, but impersistent bands are recorded locally and one of these thickens to form a split of as much as 21 ft in Shotton Colliery No. 10 Bore [NZ 4067 4125], 1.5 miles N.N.W. of Shotton.

In a number of bores at Blackball and Horden collieries, the seam is composed wholly or partly of thin alternations of coal and carbonaceous shale. Farther west, the Five-Quarter Coal is recorded as being just over 6 ft in bores in the Garmondsway area, near to its outcrop beneath the Permian, but it lies in a narrow zone of steeply dipping strata on the south side of the Butterknowle Fault. The coal is absent between Middle Rainton, Low Moorsley, Easington Lane, South Hetton and Shotton Colliery, where a thick sandstone occupies this part of the sequence (see above).

Measures between the Five-Quarter and Metal

The measures between the Five-Quarter and Metal coals range in thickness from a few inches to over 80 ft. In the Little-town area, the thickness variation is as follows:

Where the interval is large, fossils have been obtained from the roof of the Five-Quarter Coal: they include Naiadites aff. alatus from Offshore No. 1 Bore and plants including Alethopteris sp.from Offshore No. 2 Bore. A specimen of A nthrapalaemon, associated with megaspores, was obtained from 20 ft above the Five-Quarter Coal in Easington No. 7 Bore. Where the interval is small, as it is in much of the west-central part of the district, the two coals unite to form a composite seam exemplified in a bore [NZ 3350 3480], just over 0.5 mile N. of Garmondsway Pit, where the Metal Seam comprises coal 32 in, on band 28 in, coal 9 in, band 13 in, coal 1 in, band 6 in, coal 15 in, band 3 in, coal 3 in, band 6 in, coal 19 in, separated by a 7-in band from the 77-in Five-Quarter Seam (corrected for high dip to 74 in). In a zone stretching from Littletown to Deaf Hill collieries through Ludworth and Thornley collieries (Figure 14), the records, which are few and old, show the Metal component of the composite seam to be unbanded and 3 to 7 ft thick, but banding is again recorded farther east at Wheatley Hill and Wingate collieries. Still farther east, where the Metal Seam is separated from the Five-Quarter, banding persists and the seam, up to 6 ft thick, has been worked only in the north-eastern part of Shotton Colliery take. Here, at least, two bands are present, but farther south the number increases, and in Shotton Colliery No. 5 Bore [NZ 4149 4028], 600 yd N. of Shotton Hall, seven bands totalling 25 in were proved in a seam section of 68 in. Eastwards from Shotton and Castle Eden the coal seems to thin rapidly, and in the coastal and undersea areas it is generally thin. Exceptionally, as in Offshore No. 1 Bore, it reaches 42 inches in thickness. In the Buddle Pit, the Metal Seam lies approximately halfway between the Five-Quarter and High Main coals.

In a zone between Middle Rainton and Shotton Colliery, the Metal, like the Five-Quarter, is thin or absent (pp. 78 and (Figure 14)).

Measures between the Metal and High Main coals

The measures between the Metal and High Main coals are up to 100 ft thick and consist mainly of sandstone in the western part of the district, but in the east, between Easington and Blackhall, the two coals are close together and form a composite seam. E.A.F., D.B.S.

In Easington No. 7 Bore, the roof measures of the Metal Coal yielded poorly preserved Anthracosia spp., Naiadites aff. alatus and N. cf. productus [juv.];and at 30 ft higher, a specimen of Anthracosia cf. aquilinoides. Another ‘mussel’ band is locally recorded close below the High Main Seam. In Shotton Colliery No. 6 Bore it contained: Spirorbis sp.; Anthraconaia sp.  nov. cf. wardi, Anthracosia sp. cf. caledonica, Anthracosphaerium propinquum, Naiadites cf. productus; Carbonita humilis; and fish remains including Rhabdoderma sp.

High Main Coal

The High Main Coal (Figure 15) the uppermost widely worked coal of the Durham Coalfield, is over 5 ft thick in the northern and eastern parts of the district, but it is generally banded and has been mined only from the collieries near the northern margin of the district and on a small scale from Blackhall and Horden collieries. The seam is more than 7 ft thick over an area of several square miles to the north of Haswell and Easington collieries, and is over 8 ft thick at some localities around Rainton and Low Moorsley. In many areas, two or more bands are present of which the highest and most persistent is commonly three to eight inches thick, locally increasing to 18 in around Easington and Easington Colliery. The top leaf of the seam, above this band, is commonly about 10 in thick, increasing to 18 in at Elemore and North Hetton collieries. Other, lower bands in the seam are thin, and are only persistent in the area south of South Hetton and Hawthorn shafts, where they aretwo or three in number. In the coastal region between Easington and Blackball, the High Main is joined by the Metal Seam, but the band separating the two cannot always be identified and the High Main, as worked in this area, may locally include part of the Metal Seam. The margin of the united seam (Figure 14), (Figure 15) must therefore be regarded as approximate and it is possible that the area extends considerably farther north-westwards. D.B.S.,

Where present in the south-western part of the district, the seam is unbanded and thinner. It reaches a thickness of only 20 inches in Coxhoe Bridge No. 1 Bore. In the central part of the district, it is impoverished over roughly the same area as that in which the Metal and Five-Quarter coals are close together. Here the High Main Coal is generally less than 18 in thick and is absent in places where the overlying High. Main Post joins the sandstones overlying the Five-Quarter and Metal coals (see below). E.A.F., D.D.S.

Measures between the High Main Coal and the High Main Marine Band

The measures between the High Main Coal and the High Main Marine Band range in thickness from 41 ft in Shotton Colliery No. 6 Bore to 102 ft in Murton Shaft (Plate 4). There is no clearly defined pattern of variation in thickness, but the interval tends to be least in the central part of the district, corresponding with the area in which the High Main Coal is thin or absent, and greatest north of a line joining East Rainton, Hetton le Hole, South Hetton and New Hesledon.

The roof of the High Main Coal is generally a dark mudstone or shale, from which a sparse fauna of fish fragments and non-marine lamellibranchs has been collected. The following were obtained from Offshore No. 2 Bore: Anthraconaia?, Anthracosia spp.including A. cf. elegans (Van der Heide), Naiadites spp.In the extreme north-western part of the district, beyond Low Moorsley, Rainton Alexandrine Pit and Rainton Meadows Pit, the succession above the High Main Coal remains dominantly argillaceous, and this is also true of the eastern area beyond Shotton and Murton collieries where the sequence up to the High Main Marine

Band consists of siltstone and mudstone with abundant plant debris, and subordinate sandstone. In the intervening ground the siltstone and mudstone gives way to a thick sandstone, the High Main Post, which reaches a maximum thickness of over 80 ft at Hawthorn and Hetton Lyons collieries. However, it is only 31 ft at Elemore Colliery, and 27 and 22 ft respectively in the two shafts of North Hetton Colliery. D.B.S., E.A.F.

At Pittington, the High Main Post is 55 ft thick, and a 40-ft face of cross-bedded sandstone is exposed in a disused quarry [NZ 3265 4430], 800 yd S.S.E. of Pittington Station. Farther south, in the Littletown and Sherburn Hill Colliery areas where the High Main Coal is absent, the High Main Post loses its separate identity and becomes vertically continuous with the sandstone overlying the Metal and Five-Quarter coals. South of Sherburn Hill, between Sherburnhouse Colliery and Shaiiforth, about 70 ft of High Main Post overlies about 4 ft of argillaceous beds forming the roof of a very thin High Main Coal. Between Shadforth and Heugh Hall, however, where the High Main Coal is again absent, a thick sandstone separates the Metal Coal from the horizon of the High Main Marine Band, and this sandstone reaches 105 ft in a bore [NZ 3401 3966], 350 yd N.E. of Old Cassop. The High Main Post is absent in bores southwest of Old Quarrington, and in one of these [NZ 3185 3747], five-sixths of a mile N.W. of Coxhoe Colliery, the High Main Coal is separated from the High Main Marine Band by only 48 ft of strata, which include two thin coals, the uppermost being 14 in thick. At Coxhoe Colliery Engine Pit, the correlative of this 14-in seam is 38 in thick with a median 2-in band, but there is no record of comparable thickness elsewhere at this horizon. In bores near Coxhoe Bridge there is a thin sandstone above the High Main Coal, and the interval between this coal and the High Main Marine Band in Coxhoe Bridge No. 1 Bore is nearly 116 ft, though this figure is not reliable because of faulting and dips up to about 30°. The thin sandstone is overlain by siltstone and seatearth, followed in turn by mudstone which comprises a well-developed 'mussel'-band lying at about 43 ft above the High Main Coal. The fauna is represented by: Spirorbis sp.; Anthracosia acutella, A. atra, A. cf. aquiline Trueman and Weir (non J. de C. Sowerby), A. cf. caledonica, A. concinna, Anthracosphaerium radiatum; Carbonita sp.; and indeterminate Platysomid scales. At Thrislington Coke Oven Pit [NZ 3043 3405], 400 yd S.S.W. of Cornforth Station, the interval is 89 ft, and no High Main Post is recognisable from the record (Plate 3). However, sandstone certainly comes in to the west, for it has been observed during the resurvey in and near the lane 400 yd W. of Ferryhill Reservoir. Red micaceous cross-bedded sandstone seems to occupy the greater part of the interval between the Five-Quarter and Ryhope Little coals at this locality, but grey mudstone is present in the ditch by the reservoir approach road less than a quarter of a mile to the east, indicating that the thick sandstone does not continue in this direction. In the area between the reservoir and Thrislington Coke Oven Pit, the Coal Measures outcrop is covered by Permian rocks and drift.

High Main Marine Band

The High Main Post and its lateral equivalents are generally succeeded by a seatearth and by a coal which is usually thin, but exceptionally is 22 in thick at Elemore Colliery Isabella Pit. The overlying High Main Marine Band consists of a few inches of black shale containing small specimens of Lingula mytilloides. In the eastern part of the district the band is commonly separated from the roof of the coal by up to 6.5 ft of mudstone and shale, in which fish fragments have been found near the base, while Lioestheria vinti, in places abundant, is distributed throughout, together with sporadic non-marine lamellibranchs. To the west the High Main Marine Band has been found in Heugh Hall No. 1 Bore where 22 ft of black shale and mudstones containing Lingula in the bottom 1 ft rest directly on grey sandy seatearth, and in Coxhoe Bridge No. 1 Bore. The marine band is absent in some areas and there are two explanations of this: (i) penecontemporaneous erosion, now indicated by records and exposures showing this part of the succession to be occupied by sandstone, or (ii) non-deposition, for in several recent bores no marine fauna has been identified in spite of careful search. In the second case the position of the marine band can usually be recognized by the associated non-marine fauna which includes: Spirorbis sp.; Anthraconaia spp.including A. aff. librata and A. sp.nov. cf. wardi (Hind pars), Anthracosia cf. atra, A. sp. cf. atra, A. sp. cf. fulva (Davies and Trueman), cf. A. planitumida (Trueman), A. cf. simulans Trueman and Weir, cf. Anthracosphaerium radiatum (Wright), Curvirimula sp., Naiadites alatus, N. cf. obliquus; N. cf. productus, Carbonita sp.including C. humilis and C. cf. scalpellus, Geisina sp.; Elonichthys sp., Palaeoniscid scales, Platysomid scales, Rhabdoderma sp, Rhadinichthys sp., Rhizodopsis sp., Stemmatias sp.[tooth].

Measures between the High Main Marine Band and the Ryhope Little Coal

The measures between the High Main Marine Band and the Ryhope Little Coal, in all but the central part of the district between Coxhoe Bridge, Thrislington and Old Quarrington, generally include two thin coals, each overlain in some areas by shale or mudstone, containing fish debris and non-marine lamellibranchs at base. D.B.S., E.A.F.

At Cassop ‘A’ Pit the lower of these two seams is 22 in thick, including a 2-in band 2 in above the base; the upper consists of 21 in of unbanded coal. At North Pittington Colliery Londonderry Pit these two coals are 12 and 20 in thick, and at North Hetton Moors-ley Winning they are 15 and 18 in respectively. A surface drift [NZ 3246 3860], 450 yd E.N.E. of Hill Top Farm (Cassop cum Quarrington), for which no records have been traced, is thought to have been put into the uppermost of these two seams, here overlain by reddened sandstone which has been worked in a small quarry 175 yd to the west. This sandstone, though virtually absent at Cassop ‘A’ Pit, thickens westwards and northwestwards along the sides of Cassop Vale, and is exposed in quarries at the tips of the spurs to the north and south of the Vale. At the western end of the northern spur the sandstone is about 50 ft thick, and is seen to be massive and cross-bedded with small quartz pebbles in a quarry [NZ 3294 3933], 600 yd W.S.W. of Old Cassop. This quarry provided stone for St. Paul's Church, Quarrington Hill. Near Hill Top Farm, around the western end of the southern spur, about 20 ft of cross-bedded sandstone can be seen, but the original thickness is unknown as a result of pre-Upper Permian erosion. On the southern flank of this spur the sandstone seems to wedge out eastwards. E.A.F.

In Coxhoe Bridge No. 1 Bore the strata above the High Main Marine Band contain a coal 24 in thick. The supposed correlative of this coal at Thrislington Coke Oven Pit is 26 in thick. At Hawthorn Colliery (Figure 16) the whole of the interval between the High Main Marine Band and the Ryhope Little Coal is filled by sandstone. E.A.F., D.B.S.

Ryhope Little Coal

The Ryhope Little Coal lies near the top of the sequence of productive coals of the Durham Coalfield and is worked at Ryhope, 4 miles N. of Murton, as a single seam about 3 ft thick. It is not, however, worked anywhere in the Durham–West Hartlepool district. East of a line joining Murton and Shotton collieries, two coals 10 to 20 ft apart are present in this part of the sequence over wide areas (Figure 16). Although it is possible that the lower seam is the correlative of a thin coal lying 18.5 ft below the Ryhope Little Coal at Ryhope, there is some evidence that the two coals are splits from the worked seam and they are therefore shown on the maps as the Top and Bottom Ryhope Little coals. The Top Ryhope Little Coal is a consistent seam, 1.5 to 2.5 ft thick, generally free from bands, and traceable over much of the eastern part of the district. The Bottom Ryhope Little Coal is present in the area east of the line joining Murton and Shotton collieries, and it is commonly about 1 ft thick, though locally it reaches 2 ft. The interval between these two coals is generally occupied by argillaceous strata, and in some places fish debris has been recorded from the roof of the lower coal. D.B.S.

AtNorth Hetton No. 2 Shaft, the Ryhope Little Coal consists of 3.5 ft of coal with bands. There are no records of this seam in the area around East Rainton, about 1 mile to the north, but it is likely to be present, although probably thin or banded. About a mile south-east of Low Moorsley, however, at Elemore George Pit, the Ryhope Little Seam consists of three leaves: the Top Ryhope Little, a 28-in coal, is separated by a band, 3 ft 9 in thick, from the Bottom Ryhope Little comprising coal 21 in, on band 13 in, coal 23.5 in. A line of split thus lies between Low Moorsley and Elemore and this is thought to continue north-eastwards to join that assumed between Murton and Ryhope. The southward trend of the line of split is obscure due to the paucity of records and difficulty of interpretation. A bore [NZ 3293 4175] in Sherburn Quarry, 1200 yd S.F. of Sherburn crossroads, records a section thought to represent the Ryhope Little Coal: coal 4 in on 3 ft 8 in of seatearth, on coal 2 in. To the south, a 15-in coal at Cassop 'A' Pit has been correlated with this seam. To the west of the district, around Westerton, a 2.5- to 3-ft coal now identified as the Ryhope Little Seam has been proved, and on the assumption that this coal extends eastwards, the outcrop has been inserted on the maps north-west of Ferryhill. The line at which impoverishment takes place has not however, been established.

Measures between the Ryhope Little and Ryhope Five-Quarter coals

The measures between the Ryhope Little and Ryhope Five-Quarter coals range in thickness from about 35 ft to nearly 70 ft. To the west, at Westerton South Pit, the interval is near the minimum of this range and about half, i.e. 18 ft, consists of 'post', separated from the underlying coal by 2 ft 9 in of 'blue metal'. In the field immediately east of the northern end of the lane between Ferryhill and East Howie, red micaceous sand in the soil is thought to mark the outcrop of the 'post' above the Ryhope Little Coal. In Coxhoe Bridge No. 1 Bore, a seatearth close beneath the base of the Permian strata may belong to the bed underlying the Ryhope Little Coal. Over most of the area lying to the north of the Butterknowle Fault, the strata between the Ryhope Little and Ryhope Five-Quarter coals are composed consistently of white sandstone, though a variable thickness of argillaceous beds lies above this sandstone in some localities. The interval is generally between about 45 and 60 ft. In most places the sandstone lies directly on the roof of the Top Ryhope Little Coal which is nevertheless rarely affected by washouts. At some localities, a thin shale lies in the roof of the coal and presumably is equivalent to the Little Marine Band or its associated non-marine phase. Near the northern edge of the district, the sandstone was formerly worked in a small quarry [NZ 3359 4738], 450 yd S. of East Rainton church, but neither sandstone nor associated strata are now exposed. In this area the sandstone is less constant than in most of the central and eastern parts of the district and is missing from the 30 ft of strata proved above the Ryhope Little Coal at North Hetton No. 2 Shaft, three-quarters of a mile S.S.E. of the quarry near East Rainton. At Elemore George Pit the sandstone is separated from the coal by 16 ft of blue metal with ironstone 'balls'. E.A.F.

Ryhope Five-Quarter Coal

The Ryhope Five-Quarter Coal, the highest worked seam in the district, is worked only at Murton Colliery (Figure 16) near the northern margin, where it is an unbanded coal of good quality between 2.5 and 3 ft in thickness. The coal is present in much of the north-eastern sector of the district and is commonly 1.5 to 3 ft thick with only slight lateral variations in thickness. The outcrop of the seam has been inferred on the maps of the spur and vale country between Low Moorsley and Quarrington Hill, but no details of its thickness are available. There is a similar lack of information in the narrow zone of steeply dipping strata along the southern side of the Butterknowle Fault, and as no sign of coal was seen at the appropriate horizon during resurvey north of Ferryhill, the outcrop has been omitted from the maps in that area. In the South Pit at Westerton, the Ryhope Five-Quarter Seam, known as the Westerton High Main, has the section coal 22 in, on band 4 in, coal 33 in, and this seam may extend eastward for a short distance crossing the western boundary of the present district. D.B.S., E.A.F.

The Ryhope Five-Quarter Coal is generally overlain by mudstones. Above the mudstones is a sandstone, up to 28 ft thick, followed by a succession including two or three thin coals, the highest of which underlies Kirkby's Marine Band. This band has the characteristic interleaved structure found in sections examined in the Sunderland (21) district to the north where non-marine fossils commonly occur between strata containing marine fossils. In a trial borehole at the site of Hawthorn Colliery Shaft, the section is as follows:

Fossils were identified from this sequence in the borehole and shaft as follows: plant fragments; foraminifera [abundant] including Ammonema sp.and Tolypammina sp.; sponge spicules [pyritized]; Planolites ophthalmoides; Lingula cf. elongata [3.0 mm], L. mytilloides [ 5.0 mm]; Anthracosia cf. atra, Curvirmuda [rare]; Lioestheria sp.; fish remains including Diplodus tooth; pyritized strap-like markings C fucoids Kirkby's Marine band has not been identified at other localities, but its position can generally be recognized in older records by the presence of up to 30 ft of argillaceous strata. The overlying sequence includes two more thin coals, the upper being overlain by dark grey mudstone and shale, up to 10 ft thick, marking the position of the Hylton Marine Band. This band is known from several recent bores in northern Durham and south Northumberland, but no recent opportunity of examining the horizon in the present district has arisen. The mudstones and shale are generally overlain by a thick sandstone, which reaches a maximum thickness of 100 ft 40 yd N. of the district at Dawdon Shaft (Figure 16) in the Sunderland district, but thins rapidly southwards. Above it are two thin coals, succeeded by mudstone believed to contain the Ryhope Marine Band, which also has not been proved in this district. The mudstone extends up to a thin coal lying about 10 ft below the Usworth Coal, and this sequence reaches over 120 ft in thickness at Dawdon Colliery (Figure 16).

Usworth Coal

The Usworth Coal (Figure 16) is restricted to the area immediately south of Dawdon Colliery, where the shaft section is 59 in with a median 4-in band. The coal is present offshore, but cannot be regarded as workable anywhere within this district because of its limited extent and thin cover to the base of the Permian.

Hebburn Fell Coal

The Hebburn Fell Coal is even less extensive than the Usworth Coal, and inland it never lies more than 30 ft below the base of the Permian. Although this figure is exceeded offshore, the coal is thought to be too close to the unconformity to be workable. At Dawdon Colliery (Figure 16), it lies about 48 ft above the Usworth Coal and is 52.5 in thick. D.B.S.

References

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ARMSTRONG, G., and PRICE, R. H. 1954. The Coal Measures of North-East Durham. Trans. Inst. Min. Eng., 113, 973–97. Also discussions in: 1955, Trans. Inst. Min. Eng., 114, 83–6 and 111–14.

BORINGS AND SINKINGS. 1878–1910. An account of the strata of Northumberland and Durham as proved by borings and sinkings. North of England Inst. Mining and Mech. Eng.

CONYSEARE, W. D., and PHILLIPS, W. 1822. Outlines of the geology of England and Wales. London.

DAGLISH, J., and FORSTER, G. B. 1864. On the Magnesian Limestone of Durham. Trans. N. of England inst. Min. Eng., 13, 205–13.

DEFRISE-GUSSENHOVEN, E., and PASTIELS, A. 1957. Contribution á l'étude biométrique des Lioestheriidae du Westphalien supérieur. Publ. Assoc. Etud. Paleont. Strat. Houill., 31, 1–71.

DUFF, P. McL. D., and WALTON, E. K. 1962. Statistical basis for cyclothems: a quantitative study of the sedimentary succession in the East Pennine Coalfield. Sedimentology, 1, 235–55.

DUNHAM, K. C. 1948. Geology of the Northern Pennine Orefield. Vol. 1. Tyne to Stainmore. Mem. Geol. Surv.

DUNHAM, K. C. and HOPKINS, W. 1958. Geology around the University Towns: Durham area. Geol. Assoc. Guide, 15.

EAGAR, R. M. C. 1956. Additions to the non-marine fauna of the Lower Coal Measures of the North-Midlands Coalfields. Liv. and Manch. Geol. 1., 1, 328–69.

EAGAR, R. M. C. 1960. A summary of the results of recent work on the palaeoecology of Carboniferous non-marine lamellibranchs. C.R. 4me Cong. Strat. Carb. Heerlen, 1958, 1, 137–49.

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

EARP, J. R., MAGRAW, D., POOLE, E. G., LAND, D. H., and WHITEMAN, A. J. 1961. Geology of the country around Clitheroe and Nelson. Mem. Geol. Surv.

FOWLER, A. 1936. The geology of the country around Rothbury, Amble and Ashington. Mem. Geol. Surv.

HICKLING, H. G. A. 1949. The prospects of undersea coalfield extension in the North-East. Trans. Inst. Min. Eng., 109, 659–74.

HIND, W. 1895. A monograph on Carbonicola, Anthracomya and Naiadites. Pt. 2, 81–170. Palaeontogr. Soc.

HINDSON, G., and HOPKINS, W. 1947. The relationship of the Coal Measures to the 'Wash' between Shincliffe Bridge and Harbourhouse Park, Co. Durham. Trans. Inst. Mining Eng., 107, 105–17.

HOLMES, A. 1928. The foundations of Durham Castle and the geology of the Wear Gorge. The Durham University Journal, March issue, 1–8.

HOPKINS, W. 1928. The distribution of the mussel bands of the Northumberland and Durham Coalfield. Proc. Univ. Durham Phil. Soc., 8, 1–14.

HOPKINS, W. 1929. The distribution and sequence of the non-marine lamellibranchs in the Coal Measures of Northumberland and Durham. Trans. Inst. Min. Eng., 78, 126–44.

HOPKINS, W. 1930. A revision of the Upper Carboniferous non-marine lamellibranchs of Northumberland and Durham and a record of their sequence. Trans. Inst. MM. Eng., 80, 101–10; and discussion, 254–57.

HOPKINS, W. 1933. Impoverished areas of the Maudlin and Busty seams in the Durham Coalfield. Trans. Inst. Min. Eng., 85, 212–22.

HOPKINS, W. 1934. Lingula horizons in the Coal Measures of Northumberland and Durham. Geol. Mag., 71, 183–89.

HOPKINS, W. 1935. A record of the Upper Carboniferous non-marine lamellibranchs from the Bates Sinking, Blyth, Northumberland. Trans. Inst. MM. Eng., 89, 48–56.

HOPKINS, W. 1954. The coalfields of Northumberland and Durham, in Trueman, A. E. The coalfields of Great Britain. London.

HOWSE, R. 1857. Notes on the Permian system of Northumberland and Durham. Ann. Mag. Nat. Hist., (2) 19, 33–52, 304–12, 463–73.

JOHNSON, G. A. L., HODGE, B. L., and FAIRBAIRN, R. A. 1962. The base of the Namurian and of the Millstone Grit in north-eastern England. Proc. Yorks. Geol. Soc., 33, 341–62.

KELLETT, J. G. 1927. A petrological investigation of the Coal Measures sediments of Durham. Proc. Univ. Durham Phil. Soc., 7, 208–32.

LUMSDEN, G. I., and CALVER, M. A. 1958. The stratigraphy and palaeontology of the Coal Measures of the Douglas Coalfield, Lanarkshire. Bull. Geol. Surv, Gt. Brit., No. 15, 32–70.

MAGRAW, D. 1960. Coal Measures proved underground in cross measures tunnels at Bradford Colliery, Manchester. Palaeontology by M. A. Calver. Trans. Inst. Min. Eng., 119, 475–92.

MAGRAW, D. 1961. Exploratory boreholes in the central part of the south Lancashire coalfield. Min. Eng., 6, 432–48.

MAGRAW, D., CLARKE, A. M., and SMITH, D. B. 1963. The stratigraphy and structure of part of the south-east Durham coalfield. Proc. Yorks. Geol. Soc., 34, 153–208.

MILLS, D. A. C., and Hum., J. H. In press. The Geological Survey Borehole at High Kays Lea Farm, Woodland, Co. Durham (1962). Bull. Geol. Surv. Gt. Brit.

MYKURA, W. 1967. The Upper Carboniferous rocks of south-west Ayrshire. Palaeontology by M. A. Calver and R. B. Wilson. Bull. Geol. Surv. Gt. Brit., No. 26, 23–98.

SEDGWICK, A. 1829. On the geological relations and internal structure of the Magnesian Limestone, and the lower portions of the New Red Sandstone Series in their range through Nottinghamshire, Derbyshire, Yorkshire and Durham, to the southern extremity of Northumberland. Trans. Geol. Soc. (2), 3, 37–124.

SMITH, E. G., RHYS, G. H., and EDEN, R. A. 1967. The geology of the country between Chesterfield, Matlock and Mansfield. Mem. Geol. Surv.

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

TAYLOR, B. J. 1961. The stratigraphy of exploratory boreholes in the West Cumberland Coalfield. Palaeontology by M. A. Calver. Bull. Geol. Surv., Gt. Brit., No. 17, 1–74.

TRECHMANN, C. T. 1941. Borings in the Permian and Coal Measures around Hartlepool. Proc. Yorks. Geol. Soc., 24, 313–27.

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WEIR, J. 1960. A monograph of British Carboniferous non-marine Lamellibranchia. Pt. 10, 273–320. Palaeontogr. Soc.

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Chapter 3 Permian and Trias

Introduction

Classification and distribution

Subdivision of the Permian and Triassic rocks was first attempted by Sedgwick (1829) and later successively refined by Howse (1848, 1857), King (1850), Kirkby (1860) and Woolacott (1912). The classification adopted here (Figure 17) is a modified version of that proposed by Woolacott, in which the base of the Middle Magnesian Limestone was defined as coincident with the base of the reef. ^‡2  In Woolacott's classification, the base of the Middle division could not be recognized directly where reef is absent, and to overcome this difficulty Smith (in Magraw and others 1963, p. 172) has redefined the base of the division at the base of a loosely defined group of transitional beds which underlie the reef and can also be recognized in lagoonal and basin areas.

The greatest recorded thickness of Permo-Triassic rocks at any locality in the district is 1,382 ft in the Seaton Carew Bore (Bird 1888, p. 570), near West Hartlepool, but each of the lithological divisions shows marked lateral variation with a general tendency for divisions above the Lower Magnesian Limestone to thicken eastwards. The maximum recorded thickness of Magnesian Limestone is 991 ft in N.C.B. Offshore No. 2 Bore (Magraw and others 1963, pp. 202–3), six miles north of Hartlepool. Over most of the district, the average dip at the base of the Permian rocks is about 125 ft per mile (Plate 15), but this tilt is partly tectonic and partly primary and higher beds have a somewhat lower average dip.

The distribution of the Permian and Triassic rocks in the district is depicted on (Plate 5) which shows that no strata higher than the Upper Magnesian Limestone crop out on land north of the West Hartlepool Fault. However, their former presence is indicated by fragments of red and green mudstones of Upper Permian Marl Ethology in many collapse breccias in the Middle and Upper Magnesian Limestone in coastal sections, and the succession is probably complete a few miles out to sea. The Permo-Triassic rocks are largely overlain by drift, especially in the south-eastern part of the district where information is derived mainly from boreholes. Elsewhere most exposures are in narrow belts along the western escarpment, along the coast, and in a number of narrow ravines in the eastern part of the district. Where not overlain by drift the limestones and dolomites give rise to an undulate topography with thin light soils utilized mainly for pasture. Even where buried by drift the underlying rock in many areas exercises a broad topographic control, as for instance, in the case of the drift-covered ridge by which the course of the reef of the Middle Magnesian Limestone is traced between exposures.

Conditions and history of deposition

Immediately prior to Permian deposition, the gently folded Carboniferous rocks of the district had been eroded to a low-lying plain, reddened at and below the surface by the oxidation of pyrite and siderite in situ and by the introduction of red iron oxide along joints and into pore-spaces of sandstones (Anderson and Dunham 1953). The plain, broken by a few scattered hills, had a gentle slope to the east and was bounded by higher ground to the south and possibly also to the west. The small-scale relief of the plain would also appear to have been low judging from the inclination of the plane of the Carboniferous–Permian unconformity in borings and at the few surface exposures.

In the southern part of the district the earliest Permian deposits are breccias and sandstones and widespread patination and the presence of scattered dreikanter suggest that the breccias may have formed part of a stony desert pavement. Many of the fragments are of Carboniferous Limestone, presumably derived from areas a short distance to the south and west. In the northern part of the district (Plate 15), sands form the characteristic basal deposit. These are mainly aeolian, but are thought to have been partly redistributed subaqueously over wide rock pediments interspersed among the original dunes.

Opinion on the age of the basal deposits is divided. Many writers on the Zechstein of continental Europe, for instance, assign the basal sands and breccias (the Weissliegende and Zechstein Conglomerate respectively) to the Upper Permian. It is here suggested, however, that both these deposits and their equivalents in Durham are more likely to be of Lower Permian age by analogy with the type area of Russia (Nalivkin 1937), where continental beds are assigned to the Kungurian stage of the Lower Permian and the base of the Upper Permian is taken at the base of the marine Kazanian.

Transgression by the Zechstein Sea ended the continental phase, and began a prolonged period of marine conditions. After the transgression, most of east Durham lay in the marginal shelf zone of the Zechstein Sea, and deposits here bear evidence of cyclic sedimentation similar to that which characterizes the Zechstein beds of continental Europe. In England, Sorby (1856), Ramsay (1871) and Green (1872) were the first to recognize that there was an upwards impoverishment in the Magnesian Limestone fauna which could be related to concentration by evaporation, and Bird (1881), Wilson (1881), Lebour (1902), Woolacott (1912) and Trechmann (1913) each reported supporting evidence. Sherlock (1926, p. 59) further supposed that the concentrating water was diluted 'two or three times' and Hollingworth (1942, p. 145) discerned two cycles of 'partial desiccation', followed by a third partial cycle represented by the Upper Anhydrite.

Ideally, the deposits of a complete evaporite cycle should consist of a basal elastic member, followed in lateral and vertical succession by carbonates and sulphates and ending with the precipitation of halite and highly soluble salts of potassium and magnesium. Such cycles are rarely complete in marginal parts of evaporite basins, and this is true of the Permian shelf deposits of Durham where the bulk of the succession is formed by the carbonate phases of three main evaporite cycles corresponding with the main lithological divisions of the Magnesian Limestone. In each of the lower cycles, but especially in the second, the early carbonate deposits contain a relatively rich shelly fauna which becomes impoverished in the later beds. Dolomitization is generally more complete in the later stages of each cycle, and this agrees with observations in equivalent beds in north-east Yorkshire (Dunham 1948, p. 219) where the carbonate directly associated with evaporites is almost exclusively dolomite, some of which may be primary. The margin betweenshelf and basin in the lowest cycle appears to have lain at about the longitude of West Hartlepool, but in subsequent cycles it followed the outer slope of the reef in the Middle Magnesian Limestone (Plate 5).

The first cycle begins with a fish-bearing bituminous silty carbonate phase, the Marl Slate, followed by up to 250 ft of relatively pure fine-grained carbonate beds which appear, like the Marl Slate, to have been deposited in tranquil water some miles from the shoreline. Sulphate and later phases of this cycle are present in eastern parts of Yorkshire, but in this district are believed to have been relatively minor and have now been removed by solution.

Except in the area south of the West Hartlepool Fault the second cycle is represented in the shelf area entirely by carbonates. The fauna, the rapid lateral variation of Ethology, and the widespread oolitic, algal and reef rocks within this cycle suggest deposition in shallow water. The development of a barrier reef near the present coastline defined the margin between shelf and basin more clearly than before, and to the east of this margin deposition of barren carbonates, probably partly chemically precipitated, was followed later in the cycle by precipitation of thick sulphates. The presence south of the West Hartlepool Fault of red elastic deposits of late Middle Magnesian Limestone age suggests a nearly complete infilling of this part of the Zechstein Sea so that by the end of this second evaporite cycle, the depositional surface in Durham and north Yorkshire was almost flat and virtually emergent.

The third cycle commenced with widespread inundation of this surface and the subsequent deposition of the laminated, impure flexible Limestone which is in many respects similar to the Marl Slate. Higher beds are relatively pure carbonate rocks, which show little lateral variation and, like those of the Lower and Middle Magnesian Limestone, contain very little terrigenous material. Although correlation of the Magnesian Limestone north and south of the West Hartlepool Fault is not yet certain, it appears that the Upper Magnesian Limestone is directly succeeded by the Billingham Main Anhydrite which, east of Billingham (6 miles south of West Hartlepool), is overlain by thick halite.

After the deposition of the Billingham Main Anhydrite the area was covered by red gypsiferous mudstones and siltstones—the Upper Permian Marls—now found in situ only south of the West Hartlepool Fault. These marls contain near their base a relatively thin sulphate bed, the Upper Anhydrite, which is extremely persistent and may be traced at least as far south as Scunthorpe (Lincolnshire). The significance of the Upper Anhydrite within the evaporite sequence is not fully understood, since it is not associated with a well-developed carbonate phase in the Durham district. It may, however, have been deposited in the shelf areas following a relative rise in sea level during a fourth cycle whose carbonate and later phases are restricted to the centre of the basin. Wood (1950, p. 332) notes a westward thinning and increase in the dolomite content of this bed. In the upper parts of the overlying mudstone sequence, sulphate beds become progressively less important and thin beds of red siltstone and sandstone become increasingly prominent. By an increase in the proportion of sandstone the Upper Permian Marls pass gradually upwards by alternation into the Bunter Sandstone, the base of which is almost certainly diachronous in this area. Neither the upper part of the Bunter Sandstone nor the Keuper Marl have been proved in this district, but their presence is inferred from structural evidence.

Earlier writers on the Permo-Triassic have inferred that the climate was arid, and have taken the absence of fossils in the basal deposits to indicate that the land surface was essentially barren. These conclusions are supported by palaeomagnetic evidence (Runcorn 1956, Nairn and Thornley 1961), which suggests that during Permian times, northern England lay within the belt of east-north-easterly trade winds, a direction independently attested by the trend of dunes in the Yellow Sands (Figure 18) and by aeolian cross-bedding in the Permian Penrith Sandstone in Cumberland (Shotton 1956). At this time a large land mass lay to the east of England and, with easterly winds and high ambient temperatures (Quiring 1954, estimated an average surface temperature of 23°C in the late Permian of Europe), desert conditions are almost axiomatic.

The presence of abundant plant debris in the lower parts of the Lower, Middle and Upper Magnesian limestones suggests that after each transgression, an amelioration of conditions took place around the margins of the Zechstein Sea. It may be supposed that moisture was brought onshore by easterly winds, permitting recolonization of the marginal area by plants with a consequent decrease in the rate of erosion and the formation of a soil cover. Temporary reversions to aridity are suggested by lack or paucity of plant remains in the later stages of each cycle, when deposition took place in water of increasingly high salinity. This does not necessarily imply that temperatures at these times were higher, for it has been shown (d'Ans 1947) that for a given temperature and humidity, evaporation (and therefore subsequent precipitation potential of winds) from concentrated brine is smaller than from water. Depletion of vegetation cover around the margins, presumed to be due partly to this effect and partly to shrinkage of the sea, is reflected by an increased supply of detritus which formed red mudstones and siltstones towards the end of each evaporite cycle. Final infilling of the basin resulted in the shrinkage and disappearance of permanent bodies of open water, and the restoration over the entire area of arid conditions as represented by the barren Upper Permian Marls and Bunter Sandstone. D.B.S., E.A.F.

Correlation with Yorkshire

In south Durham and north Yorkshire, understanding of the Permian is complicated by intraformational overlap and widespread drift. Borehole evidence (Fowler 1944; 1945) shows that the whole succession is condensed and contains non-sequences and red elastic beds indicative of an approach to the limit of marine deposition.

Still farther south, in central Yorkshire, two facies, each showing clear evidence of cyclic deposition, can be distinguished. One of these in the ground to the west of York and Selby is represented by shelf deposits similar to those in Durham. In the other, to the east, sediments are basinal and Stewart (1954) and Lotze (1958) have recognized three main cycles as well as a possible fourth which is incomplete. Correlation between the two facies is difficult, particularly since there is a scarcity of comparative faunal data. The similarity of the shelf deposits of Yorkshire and Durham, however, has been recognized by workers from Sedgwick (1829) onwards. A revised correlation in terms of evaporite cycles is shown in Table 1.

The transition from the first to the second evaporite cycle in central Yorkshire is marked by the sporadic occurrence of thin contemporaneous breccias and beds of red and green mudstones (presumably extending westwards over the shelf from the thick evaporites being deposited penecontemporaneously in the basin farther east). The transition appears to coincide with the well-known and widespread lithological change from compact well-bedded dolomitic limestones to granular, minutely cellular, wedge-bedded dolomitic limestones at about the middle of the Lower Magnesian Limestone. Contrary to earlier belief (e.g. Edwards and others 1940, p. 123) field evidence suggests that reef limestones are not randomly scattered vertically throughout the Lower Magnesian Limestone of Yorkshire, but are concentrated a few feet above the base of each of the two lithological (cyclic) subdivisions. D.B.S.

Palaeontology

The fauna of the Magnesian Limestone of East Durham is typical of the marginal shelf areas of the enclosed or nearly enclosed Zechstein Sea. It is comparable as a whole, and in its vertical distribution, with that of the Zechstein beds of Thuringia. Although individuals are locally numerous, the restricted character of the fauna is demonstrated by the small number of species present and the rarity of cephalopods and corals. These facts, together with the absence of fusulinids, rules out direct faunal comparison with the marine Permian deposited outside the Zechstein basin.

The lowest fossiliferous beds are those of the Marl Slate with a fauna almost limited to fish and inarticulate brachiopods and a flora consisting mainly of algae and primitive conifers. In the Lower Magnesian Limestone brachiopods are the most prominent fossils, although foraminifera, ostracods and cryptostome polyzoa are also fairly common. The fauna of the Middle Magnesian Limestone varies with the facies. The reef contains a relatively rich fauna in which brachiopods, lamellibranchs and polyzoa generally dominate, but gastropods, foraminifera and ostracods are not uncommon. Calcareous algae contributed largely to the building of the reef, especially in the upper parts. The beds immediately adjacent to the east and west sides of the reef contain fossils which were either the remains of living assemblages influenced by the proximity of the reef or which were derived from it. Otherwise, the fauna of the lagoonal beds west of the reef consists mainly of lamellibranchs, ostracods and foraminifera. The basinal beds east of the reef are not well known and have yielded little more than brachiopods, foraminifera and ostracods. In the Upper Magnesian Limestone the fauna is more restricted and the only fossils commonly found belong to two lamellibranch genera and algae. However, gastropods, ostracods and other lamellibranchs also occur at some localities. J.P., D.B.S.

Basal Permian sands and breccias

The Basal Permian deposits of the district consist of sands, sandstones and breccias. North and west of a sinuous east-north-easterly line extending from Rushyford to Blackhall Colliery (Plate 15) the typical deposits are incoherent sands. To the south and east breccias and sandstones predominate. Because of this distribution the Basal Permian deposits at outcrop consist entirely of sands and these are best exposed at Crime Rigg and Sherburn Hill Sand Pits, at Old Quarrington Quarry and in the railway cutting north of Ferryhill Station. The breccias and sandstones do not crop out and are known only from boreholes and shafts. At some localities neither sand nor sandstone and breccia are present and Marl Slate rests directly on Coat Measures.

Basal Permian Sands

The traditional name 'Yellow Sands' was applied to the deposits because, as noted by Sedgwick (1829, p. 65), at outcrop they normally consist of yellow incoherent coarse 'siliceous sand'. In fact, patches of white or light grey sand can also be seen in the large sections now open to view, and below the zone of oxidation grey is the characteristic colour. Studies by Hodge (1932) and Davies and Rees (1944) show that the deposits consist of 85 to 94 per cent of silica, predominantly in the form of quartz and quartzite and with up to 5 per cent of feldspar, commonly microcline. They infer an aeolian origin from the bimodal grain size distribution and from the content of 'frosted', well-rounded millet-seed grains in the coarser fraction. Samples from outcrop contain up to 1 per cent of iron mainly in the form of limonite coating the quartz grains; its distribution is irregular, some of the grains being well coated, others almost clean. Woolacott (1919) suggested that this limonite, which is responsible for the yellow colour at outcrop, resulted from the oxidation of pyrite. During the resurvey, it was noted that while pyrite is absent from the Basal Sands at outcrop, it is abundant in the grey sand at depth; in the latter, limonite seems to be virtually absent. The pyrite may have been formed by reducing waters percolating from the sea bottom when the Marl Slate was being deposited. This would explain why the surface of the sub-Permian Coal Measures is similarly grey and commonly pyritiferous, and also why the reddening associated with this surface often begins some inches or feet below it.

Although the Basal Sands are normally incoherent and lack any cementing material other than limonite, some beds—the so-called 'sand rock' contain a high proportion of interstitial carbonate, generally identified as calcite. Such beds are well exposed in the railway cutting north of Ferryhill Station. The sands normally lying immediately beneath the Marl Slate are also characteristically cemented in this way, and then locally contain the 'small spherical calcareous concretions' noted by Sedgwick.

From the suite of heavy minerals Hodge (1932) concluded that the sands were derived partly from the Carboniferous sandstones in the immediate vicinity, and party from an area to the north in which sandstones and some granitic and metamorphic rocks were undergoing erosion. In addition to the petrographic evidence of aeolian transport within the Durham district, the bedding too shows features typical of wind-deposited sands. For example the deposit may be divided into distinct lenticular units within which the cross-bedding tends to be in the form of curves with the concave side facing upwards; curves with the convex side facing upwards are absent.

The Basal Permian deposits are so variable in thickness that a pattern can only be made out where there are a number of closely spaced borings as in the Chilton–Raisby Hill area (Figure 18). The sands attain a thickness of at least 134.5 ft and may be as much as 161 ft according to a possibly unreliable record near Easington Colliery. The amount of variation over small areas can be demonstrated at Sherburn Hill: a bore in the quarry at the western end of the spur proved only 12 ft of sand, but at Crime Rigg (only 1350 yd to the east) about 120 ft are exposed in the sand pit (Plate 7A), while at Ludworth Colliery, 2500 yd farther to the east, the thickness has decreased to 30 ft. A similar variation can be traced from 0 ft at Thrislington Colliery to 94 ft near Thrislington Plantation, and back to 5 ft a short distance north of Bishop Middleham.

It was formerly thought (Lebour 1902; Hodge 1932) that the sand accumulated in hollows on the eroded surface of the Carboniferous rocks. At the present day, however, aeolian sands often form dunes, particularly in flat featureless country, and if, as seems likely, the Basal Sands were aeolian deposits in this type of environment they also might be expected to include dune forms. In most areas information is too scattered to allow of the location of such forms, but between Raisby Hill and Chilton, a number of relatively closely-spaced bores (Figure 18) have indicated a ridge of sand which seems to extend west-south-westwards to Chilton Colliery. A secondary spur projects from the area of maximum thickness towards Mainsforth, and it is possible that this is actually more pronounced than shown because the 30 ft of deposits immediately south of the boundary between the sand and breccia facies are tentatively thought to include up to 24 ft of dune sand. The elongated form of this mass of sand is reminiscent of a modern longitudinal or seif dune, examples of which are known to reach a height of up to 300 ft in Egypt. Bagnold (1941) explained the development of seif dunes from isolated barchans (crescentic dunes) by postulating two alternating wind regimes. His illustration (op. cit., fig. 78d) strikingly resembles the form of the deposit between Raisby Hill and Chilton Colliery, which, according to Bagnold's hypothesis, might have been formed under the influence of a prevailing wind blowing from a point E. 10° N. and an alternating subordinate wind blowing from a point E. 40° N. Such winds by analogy with present-day conditions suggest a tropical latitude and this agrees well with palaeomagnetic evidence (p. 44). It nevertheless seems likely that during the ensuing transgression of the Zechstein Sea, the dune form was modified and that some sand was redeposited subaqueously in interdune areas.

Basal Permian breccias and sandstones

The breccias contain rock fragments up to about 3 in long, which are embedded either in a matrix of smaller fragments and a variable proportion of sand, or entirely in sandstone. Although the largest fragments are generally mudstone or sandstone derived from the Coal Measures, by far the greatest number of fragments in many samples consist of Carboniferous Limestone which probably were transported from outcrops in south Durham or north Yorkshire.

Many of the limestone fragments are crinoidal,- and separated columnals and portions of stems are common. With the exception of these derived organic remains, most of the fragments are markedly angular or subangular.

'Dreikanter' pebbles with three well-marked faces and with clean edges have been noted, and these generally have soft leached interiors and hard black skins. Some pebbles in desert areas at the present day exhibit similar characters; the hard black skin, termed 'desert varnish', consists of iron and manganese oxides deposited from evaporating moisture drawn to the surface of the pebbles by capillary action. In the sand matrix, the coarse grains are well rounded and generally 'frosted', and tend to be more abundant in the upper part of the breccia sequence. Much of the sand matrix consists of subangular to angular fine to medium sand and in places this forms beds of sandstone in which breccia fragments are subordinate or absent. Some of these beds contain relatively high proportions of mica and could be mistaken for Coal Measure sandstones. Pyrite is common throughout.

The variation in thickness of the breccia-sandstone facies is pronounced, but is not so great as in the sand facies. The greatest thicknesses proved are 44.25 ft in Elwick No. 1 Bore (Magraw and others 1963, pp. 168, 197) and 41.5 ft in a borehole a mile south-e4st of Trimdon Colliery. Apart from these and several records of about 30 ft of breccia with interbedded sandstones in the Bishop Middleham area, the range in thickness is between 0 ft and 20 ft. The information in the Durham district is too scattered for conclusions to be drawn about detailed distribution and thickness variation. E.A.F., D.B.S.

Details

Basal Permian Sands

In Moorsley Banks, between Coal Bank [NZ 345 464] and High Moorsley Quarry [NZ 335 456], the sands are about 20 to 30 ft thick, but wedge out in the vicinity of High Moorsley Quarry. Exposures are small and are of typical incoherent yellow sand. Old diggings mark the outcrop along the slopes up to 600 yd north of Elemore Hall [NZ 351 442], but the only section now open comprises a few feet of brownish yellow sand in a disused pit 100 yd N.B. of the Hall. A maximum of 20 to 30 ft may be present locally. Up to 2 ft of typical yellow sand were seen at the time of resurvey in a number of small temporary excavations made in the upper slopes of White's Wood, near Littletown Colliery. A section [NZ 3425 4332] showing up to 12 ft is accessible in the east bank of a small glacial drainage channel 500 yd E.S.E. of the colliery.

The best exposures in the district are at Sherbum Hill. The original pit [NZ 3397 4174] immediately north-east of Crime Rigg Farm is now largely filled with debris, but a large pit (Plate 7A) adjacent to it on the eastern side has a face nearly 300 yd long, with a maximum thickness of Yellow Sands of about 120 ft. Directly beneath the Marl Slate, some cementation has taken place, but the cemented layer rarely exceeds 2 to 3 ft. It is characterized by the small spherical calcareous concretions observed by Sedgwick (1829). Elsewhere, the sands are uncemented, except in some thin layers near the base which have developed iron-pan. In a bore [NZ 3293 4175], 1100 yd W. of Crime Rigg Farm, the Yellow Sands were no more than 12 ft thick. In another bore [NZ 3361 4063], 1200 yd S.S.W. of Crime Rigg Farm, 19 ft of Yellow Sands were recorded. At Sherburn Hill Sand Pit [NZ 344 418], 450 yd E.N.E.of Crime Rigg Farm, over 80 ft of Yellow Sands have been worked and considerable reserves remain. A bore [NZ 3473 4059], 500 yd. S.S.E. of Shadforth proved 23.5 ft of soft sandstone, interpreted as Yellow Sands, under 84.5 ft of drift.

Yellow Sands crop out [NZ 335 380] on the northern side of the valley 375 yd E. of Cassop Vale Colliery, but they appear to have wedged out within 300 yd to northwest. They seem to be absent, too, on the southern side of the Vale [NZ 3228 3856], 300 yd N.E. of Hill Top Farm, but are certainly present from the Quarrington Hill–Cassop Moor road eastwards to at least as far as Cassop Colliery. Up to 7 ft of typical Yellow Sands are visible in an old quarry [NZ 339 383], 1250 yd S.W. of Dene House Farm, where they are immediately overlain by the Magnesian Limestone. Since this locality lies on the 500-ft contour and a nearby bore at Cassop 'A' Pit Shaft is presumed to have cut the base of the Yellow Sands at about 385 ft 0.D., their total thickness hereabouts is probably over 100 ft.

At the top of an old quarry [NZ 3191 3854], 200 yd N.W. of Hill Top Farm, the Yellow Sands are only about 6 ft thick. Half a mile to east-south-east, at the northern end [NZ 3256 3815] of Quarrington Quarry, 50 ft of Yellow Sands were measured between the Marl Slate and light grey Coal Measures mudstone. The thickness appears to decrease along the escarpment towards St. Paul's Church [NZ 3347 3792], but in a quarry [NZ 3325 3742], 500 yd W. of Quarrington Hill cross-roads, up to 30 ft of typical Yellow Sands were exposed during the resurvey. Judging from borings at quarries between Quarrington Hill and Coxhoe, the thickness again decreases towards the south-west; and between these quarries and the western end of Raisby Hill Quarry, the Yellow Sands are evidently thin or completely absent. In Raisby Hill Quarry 3 ft of Yellow Sands are exposed in a small cutting [NZ 3403 3552] 950 yd E.S.E. of Coxhoe East House.

Yellow Sands up to 6 ft thick are exposed on the southern side of the railway cutting [NZ 2796 3355], 0.25 mile S.E. of Skibbereen. A bore [NZ 2855 3378], 1000 yd E. of Skibbereen, proved 10.25 ft of ‘soft and coarse sandstone’ which is interpreted as Yellow Sands. The soil contains abundant grains of YellowSands in two patches respectively 900 yd S. and 950 yd S.S.W. of Skibbereen, but there are no sections hereabouts. E.A.F.

In the Ferryhill Gap at an exposure [NZ 3004 3295], 780 yd S.W. of Thrislington Hall, Coal Measures are separated from Marl Slate by fine sand, 0.5 to 1 in thick. Within this sand, in an almost vertical position, a small indeterminate shell was found. The sands thicken gradually to the south, and 40 ft are exposed in the eastern face of the railway cutting between 350 and 550 yd north of the road bridge at Ferryhill Station. The deposit is largely dune-bedded, but the upper part is either level-bedded or very gently cross-bedded, suggesting aqueous deposition. Small outcrops also occur round the sides of the spur immediately east of this exposure. G.D.G.

Basal Permian Sands have been proved in numerous bores and shafts, and thicknesses have been inserted on the maps (Plate 15) and (Figure 18).

Basal Permian breccias and sandstones

All records are from bores or rarely from shafts; the following are cited as examples of the thicker sections proved.

In Elwick No. 1 Bore [NZ 4531 3117], 0.75 mile S. of Elwick, 15 ft 1 in of breccia, containing fragments tending to be roughly flat-lying in the top half and to dip at about 30° in the bottom half, are underlain by 29 ft 2 in of grey and grey-brown sandstone with coarse rounded grains and with subordinate breccia fragments and crinoid columnals. D.B.S.

A bore [NZ 3433 3210], 1000 yd E.S.E. of Farniess, proved 30 ft 9 in of Basal Permian deposits as follows:

A bore [NZ 3142 3004] at Thrundle proved 29 ft 8 in of Basal Permian sandstone and breccia:

A bore [NZ 3385 3168], 1000 yd E.N.E. of Bishop Middleham church, proved 28 ft 9 in of sandstone and breccia:

Marl Slate

The equivalence of the Marl Slate to the Kupferschiefer at the base of the Upper Permian (Thuringian) of north-west Europe was established by Sedgwick (1829, p. 75), the name being an anglicized version of Mergelschiefer ( = Kupferschiefer). It is a silty dolomitic shale or shaly dolomite^‡3 , usually finely laminated and generally somewhat bituminous. At outcrop it is yellowish brown in colour, but in its unweathered state it is a hard compact rock, usually consisting of alternating grey and black laminae. Freshly broken cores commonly have a strong bituminous odour and have a characteristic flecked appearance (Smith in Magraw and others 1963, p. 169). The deposit is minutely uneven at the base, especially where resting on breccia (Plate 7C), which it locally penetrates. Laminae in the lower part of the Marl Slate conform to irregularities of the base, but are generally smooth and level in the upper part of the deposit. Locally, thin beds of millet-seed sand are present near the base. The upper surface is generally smooth and makes a sharp contact, though in places, especially in southwestern parts of the district, thin beds of Marl Slate lithology are interbedded with the lowest beds of Lower Magnesian Limestone. Evidence of contortion by slumping has been noted in several bores.

The Marl Slate reaches a maximum thickness of 18 ft in a bore west of Rushyford, and elsewhere in the area west of Fishburn and Sedgefield it locally exceeds 12 ft (Figure 19). In most of the district, however, its thickness is 2 ft or less and in bores in the offshore area and at Hartlepool, West Hartlepool and Seaton Carew, the Marl Slate is absent.

The proportions of the main constituents show a fairly wide range from place to place and from bottom to top of the deposit. Aeolian sand grains have been noted in the basal layers both in field exposures and boreholes, and Browell and Kirkby (1866, pp. 209–12) show that whereas the lowest parts of the deposit contain up to about 55 per cent of non-carbonate matter, this proportion generally decreases upwards until the uppermost laminae are composed of almost pure carbonate. This trend is also shown in analyses of specimens of Marl Slate from Blackhall Colliery shaft (Trechmann 1914, p. 249). Proximate calculations of the carbonate fractions show that dolomite is the main carbonate present in all but one of the specimens analyzed by Browell and Kirkby and by Trechmann and this is confirmed by microscopic examination. The non-carbonate fraction, apart from incorporated aeolian sand, consists of angular and subangular quartz grains ranging in grade from silt to fine sand, with mica (mainly muscovite), microcrystalline pyrite, bituminous material, and clay minerals. The pyrite is present mainly in the form of enormous numbers of spheres (Deans 1950, p. 348; Love 1962, p. 354) ranging from 3 to 120μ, in diameter and in some cases amounting to over 4 per cent of the total volume of therock. The spheres are intimately associated with delicate films of organic tissue, and these, together with widely distributed black carbonaceous films, account for the high (up to 14 per cent) content of bituminous matter shown in some analyses. Pyrite is also present in megascopic form: form the time of Sedgwick (1829) onwards it has been recorded as coating bedding planes and joints in association with sphalerite and galena. Deans (1950) and Dunham (1960, 1961) postulated a syngenetic origin for the bulk of the metallic sulphides in the Marl Slate, whilst agreeing that subsequently a certain amount of diagenetic redistribution took place. Schouten (1946) and Love (1962) maintained that, in the Kupferschiefer, only the iron sulphide is actually syngenetic and that the remaining metallic sulphides are diagenetic replacements of the primary pyrite.

Deans (1950, p. 349) has demonstrated that the Marl Slate of Durham contains a trace-metal assemblage similar to that in the Kupferschiefer. He points out that while the copper content is normal for sapropel shales, there is a high concentration of lead but little zinc. According to Deans, the Marl Slate carries base-metal concentrations over 100 times greater than normal geochemical background values.

The initial transgression of the Zechstein Sea appears to have been relatively rapid, and resulted in some redistribution of pre-existing aeolian sand (the thin beds of such sand noted above may be evidence of this but are thought more likely to indicate continuing movement of sand around the margins). Subsequent deposition of the Marl Slate took place in a euxinic environment free from bottom scavengers, in water estimated (Love 1962, p. 362) to be 300 to 600 ft deep. The deposition of the Marl Slate is thought (Oelsner 1959, p. 109) to have taken about 17,000 years. Reviews of the conditions of deposition of this deposit are given by Love (1962) and by Hirst and. Dunham (1963), who also give much new petrographical and analytical data.

The Marl Slate is well known for its fauna of fossil fish which has been described by Westoll (1941) as including bottom-dwelling elasmobranchs, deep-bodied Platysomids, and large Palaeoniscids. In the past well-preserved specimens were collected from localities such as the Ferryhill Gap, but in recent years few good specimens have been obtained, though scattered scales and spines are recorded from many outcrops and borings. Lingula credneri Geinitz is fairly common in the western part of the district and reaches 12 mm in length in Mainsforth No. 5 Bore. About two miles to the south-west, 'Nautilus freieslebeni' Geinitz and 'Myalina hausmanni' Goldfuss have been recorded (Howse 1890) from Middridge Quarry in the north-eastern part of the Barnard Castle (32) Sheet.

Plant remains are more abundant. The railway cutting north of Ferryhill Station is the type locality of 'Mixoneura huttoniana' (King); and from other railway cuttings nearby Calvert (1884) has recorded Ullmannia frumentaria (Schlotheim) and Pseudovoltzia liebeana (Geinitz). The Marl Slate at the western end of Raisby Hill Quarry yielded a branch of Ullmannia bronni Goppert nearly 35 cm long (Hickling 1931). A description of plants from the Marl Slate and overlying beds has been given by Stoneley (1958). The assemblage appears to represent the remains of land plants washed into the sea. E.A.F.. D.B.S.

Details

Exposures of Marl Slate are comparatively rare along the escarpment but good sections may be examined at the following localities: cutting at roadside [NZ 334 457], High Moorsley; Sherburn Hill Sand Quarries [NZ 3435 4175] and [NZ 3415 4165]; old quarry [NZ 3395 3825] west of Cassop Colliery; Quarrington Quarry [NZ 327 379]; Coxhoe Bank Quarries [NZ 329 368]; Raisby Hill Quarry [NZ 3402 3521]; railway cutting [NZ 3084 3230] north of Ferryhill Station; road cutting [NZ 285 328] at Ferryhill. E.A.F.

Marl Slate crops out at several places on the flanks of the Ferryhill Gap. At one locality [NZ 3004 3296], 780 yd S.W. of Thrislington Hall, a 10-ft section comprises dark grey to black, laminated, fissile, dolomitic siltstone which contains sporadic fish scales in the lower beds and which becomes more calcareous towards the top where it passes gradually up into rather silty flaggy limestone. G.D.G.

A thin section (E21046) ^‡4  of a representative specimen of Marl Slate from a depth of 518 to 519.5 ft in Ten-o'-Clock Barn No. 2 Bore [NZ 3916 3035] near Fishburn is described by Dr. K. C. Dunham as follows:

“An argillaceous sandy magnesian limestone, dark brownish grey in hand specimen. The rock is composed of crystalline carbonate of average grain-size 0.015 mm, the bulk of which is dolomite with refractive index ω = 1.680. Some calcite, with ω = 1.658 is, however, present, forming groups of crystals coarser than the average. These groups have rounded outlines and may represent organic remains. The bedding of the rock is marked by ramifying layers of a brownish translucent or opaque substance up to 0.05 mm thick, spaced about 0.2 mm apart. A few flakes of mica are associated with these layers. Subangular grains of quartz up to 0.05 mm diameter are scattered through the rock.”

This rock has been analysed by Mr. G. A. Sergeant (Lab. No. 1450) as follows (figures in percentages):

SiO₂ 21.79, Al₂O₃ 8.12, Total Fe as Fe₂O₃ 4.88, MgO 10.21, CaO 17.28, Na₂O 013, K₂O 1.68, P₂O₅ 0.06, TiO₂ 0–44, MnO 0.18, BaO 0.07, Cl trace, F trace, LiO, trace, SO₃ (in loss-on-ignition residue) 5.00, loss on ignition 30.03^‡5 ; total 99.87.

From this analysis percentage mineral composition is calculated to be: dolomite 46.9, calcite 4.9, siderite 2.1, gypsum 0.6, baryte 0.1, pyrite 41, quartz 12.3, muscovite 14.3, kaolinite 6.5, limonite 4.0, organic carbon 4.8.

Dr. Dunham adds: “The richness of the Marl Slate in organic compounds is noteworthy. The dark layers mentioned in the petrographical description evidently consist of bituminous material, mixed with finely divided mica and clay minerals, and with some detrital coarse muscovite. The quantity of the coarse mica, as seen in thin section, is considerably less than 14 per cent ”

The sample was further analysed for metallic trace elements (Deans 1950 p. 348), as follows (figures in parts per million): vanadium 950, lead 500, molybdenum 310, nickel 230, copper 120, cobalt 30, zinc variable but around 20, and chromium 13. Similar figures were obtained by Deans from a specimen of Marl Slate from Blackhall Colliery shaft, and by Dunham (1960, p. 293) from Marl Slate at 546 ft in Elwick No. 1 Bore.

The rock from Elwick No. 1 Bore has been analysed by Pattinson and Stead and the following figures (in percentages) are from Hirst and Dunham (1963):

SiO₂ 34.60, Al₂O₃ 13.90, FeO 1.00, MgO 1.10, CaO 12.45, Na₂O 0.14, K₂O 1.63, P₂O, 0.14, TiO₂ 0.55, MnO 0.14, SO₃ 0.12, BaO 0.18, V₂O₃ 0.05, F 0.28, CO₂ 10–80, FeS, 6.45, H₂O+ 4.84, Organic C 11.51, less 0 for F 0.12; total 99.76.

A selection of details from representative borehole sections of Marl Slate is given below:

(1)          [NZ 2745 2882] at Mill Cottages, Windlestone, 1000 yd W. of Rushyford: 18 ft of brownish grey, very hard shale; black and slightly more fissile in bottom 6 in; fish scales at 11.5 ft above base.

(2)          [NZ 3361 3242] 175 yd N.E. of Farnless: 14 ft of dark grey, very hard, finely laminated dolomite, with silty partings; becoming softer towards base with some obscure fish remains.

(3)          [NZ 3349 3479], 1100 yd S. of Coxhoe East House: 7.5 ft of grey, dolomitic, finely laminated shale with finely mottled partings; hard at top, but softer, black and highly fissile from 2 ft to 2.5 ft above base; fish scales from 1.5 ft to 3 ft above base.

(4)          [NZ 3890 4584] on site of Hawthorn Colliery Shaft: 5 ft 1 in of grey, finely laminated, silty, argillaceous, bituminous, dolomitic limestone with many small cavities in uppermost part and with scattered mica, a few fragments of poorly-preserved plant debris and scattered fish scales.

(5)          [NZ 3717 3052] 1000 yd S. of Mill House, Fishburn: 2 ft of black, fissile shale, with fine grey mottling on bedding planes and with scattered fish scales, on 3 in of hard grey, siliceous, pyritic limestone.

(6)          [NZ 4145 3185], at Murton Hall, EmbIeton; shale, grey, dolomitic, hard, finely laminated 9 in, on dolomitic limestone 2 in, shale as above, sandy near base 7 in, shale, greenish grey, dolomitic, softer than above, with fish scales 5 in.

E.A.F. D.B.S.

Lower Magnesian Limestone

The outcrop of the Lower Magnesian Limestone is restricted to a relatively narrow belt (Plate 5) along an escarpment, 100 to 200 ft high, between Hetton le Hole and Ferryhill. Farther east these rocks are known only in shafts and boreholes. In some places, where the lower slopes of the escarpment are formed by older strata, only the lower beds of the Lower Magnesian Limestone are found in the quarry sections, and exposures of the upper beds are confined to valleys and to quarries down-dip from the escarpment. Stone from the lower beds was used in the construction of many of the early farms and settlements, but these rocks are now used mainly as refractories for which they are intensively quarried between Quarrington Hill and Mainsforth.

The thickness of the Lower Magnesian Limestone in the district ranges from 40 ft in Offshore No. 1 Bore (4 miles north of Hartlepool) to 245 ft in a bore at Mill Hill, Easington. It may be about 250 ft thick around Dalton Piercy in the southern part of the district also, but the scanty evidence there is ambiguous and is disregarded in (Figure 19) which shows the broad trend of thickness to range from less than 125 ft in the south and east to over 225 ft between Fishburn and Easington.

At outcrop the Lower Magnesian Limestone falls naturally into three main lithological units distinguished by differences in colour, texture, and type and thickness of bedding. The lowest unit comprises 4 to 12 ft of beds which are individually 6 to 12 in thick and which have a granular or finely crystalline texture; analyses show them to range from dolomite to almost pure limestone. Laminated argillaceous layers are widespread in the lower part of these beds in the area between Ferryhill and Kelloe, where there is a passage by alternation from the underlying Marl Slate (p. 102). Small quantities of galena, pyrite and sphalerite are common near the base, and in some places persist for some distance upwards.

The middle division, up to 120 ft thick, is predominantly thin-bedded in layers of 2 to 4 in, grey to buff in colour, and very finely crystalline with grains ranging from mud- to fine silt-grade. Analyses (Table 2) indicate a predominance of dolomite, though samples from Raisby Hill Quarry and the Cotefold Close and Sheraton bores (Woolacott 1919a, b) are partly or wholly calcitic. The bedding, though even and regular in general aspect, is often very uneven and nodular in detail (Plate 8B), especially in unweathered sections and borehole cores; many bedding planes have become stylolitic and bear thin films of argillaceous carbonaceous residue. A nodular structure, first described by Sedgwick (1829, p. 76), is closely associated with grey and buff mottling, in which discrete or interconnected rounded, pale crystalline patches are enveloped in undulant irregularly laminated darker films. Thin sections (E30183), (E30187), (E30188) show that, apart from a slight concentration of carbonaceous material in the darker bands, the mineral composition of these is the same as that of the pale patches. This is confirmed by chemical analysis (Trechmann 1914, p. 247) of specimens from Blackhall Colliery Shaft. Trechmann (op. cit., p. 255) considered that the mottling reflects a slight segregation or concentration of calcite, and that the nodular structure is due to 'internal bending' brought about by the removal of parts of the more dolomitic portion. An alternative view (Woolacott 1919a, p. 164) is that the nodular bedding planes are due to pressure-solution, and the common association between thin darker bands and bedding planes with stylolites strongly supports this suggestion. In addition to stylolites arranged sub-parallel to the bedding, steeply inclined varieties have been noted in a number of borings. The abundance of stylolites varies greatly from place to place, but there is no apparent relationship between their frequency and the total thickness of beds. In some exposures and bores thin layers of brown leathery clay, often bituminous, occur on non-stylolitic bedding planes low in this middle subdivision and these appear to be original sedimentary deposits.

At slightly higher levels widespread incipient to advanced autobrecciation, accompanied by a complex network of carbonate veinlets, gives rise to a characteristic hackly fracture. Brecciated horizons, first noted by Woolacott (1919a, p. 166), occur towards the top of these beds at Raisby Hill Quarry and in a number of borings in the south-eastern and south-western parts of the district. Woolacott (op. cit., p. 167) suggested that much of the brecciation is contemporaneous, but since gypsum is reported (Woolacott 1919b, p. 456) in geodes at Raisby Hill Quarry and in stratified breccias from boreholes at Embleton and Hartlepool (Smith in Magraw and others 1963, pp. 172, 207) it is possible that the breccias are due to collapse following the solution of interbedded sulphate-rich horizons.

The beds of the middle division of the Lower Magnesian Limestone pass laterally in places into lenticular masses of shelly limestone. The most notable in this district is at Raisby Hill Quarry and is 90 ft thick. Trechmann (1914, p. 259; 1921, p. 539) suggested that both this mass and another at Thickley Quarry, 3 miles S.W. of Rushyford, in the Barnard Castle (32) district, were of primary limestone which had for some reason escaped dolomitization.

The upper division of the Lower Magnesian Limestone comprises 40 to 100 ft of buff to brown uneven or lenticular beds up to 1.5 ft thick. The rock is generally granular in texture and is composed of dolomite grains of silt-grade with small amounts of interstitial calcite. Stylolites and autobrecciated patches are less common than in the underlying division, and bedding planes are more regular. At Raisby Hill Quarry a group of transitional beds, consisting of interbedded limestones and dolomites, lies at the base of the upper division. Somewhat higher, in boreholes in the Fishburn area and also in Chilton Quarry, Fowler (1943; 1956) recorded widespread baryte and fluorite, mainly in veins and cavities, but also in small amounts disseminated throughout the rock.

The general threefold Ethological subdivision of the Lower Magnesian Limestone persists eastwards for 5 or 6 miles from the scarp, but is difficult to recognise in boreholes in the Elwick–West Hartlepool area. D.B.S., E.A.F.

The Lower Magnesian Limestone has a limited fauna, and in many places is almost barren. In all, less than 40 invertebrate species have been recorded from the whole of Durham and some of these were collected outside the limits of the present district. In general, shelly fossils are restricted to the lower 100 ft or so, and are most concentrated in the lowest 20 to 30 ft. Brachiopods, of which the most common are Strophalosia morrisiana King and Horridonia horrida (J. Sowerby), and crinoid columnals, are virtually confined to the basal beds and to the lenticular masses of shelly limestone. Here, too, are found several species of polyzoa–Acanthocladia anceps (Schlotheim), Batostomella crassa (Lonsdale) and the cryptostome species described later (p. 181)—not previously recorded from these beds. Higher beds contain only a scanty fauna of lamellibranchs, ostracods and coiled tubular foraminifera. Amphibia and fish are recorded from other parts of Durham (Hancock and Howse 1870, p. 219; Howse 1890, p. 247) but are not known in the present district. Plant remains, many of them obscure, are widespread in lower beds of the division. D.B.S., E.A.F.,

Details

Hetton le Hole to Shadforth

The Lower Magnesian Limestone is overlain by thick drift at Hetton le Hole and the most northerly exposure is in a railway cutting [NZ 357 465] 850 yd N. of Elemore Colliery, where 4 ft of cream, very finely crystalline, autobrecciated dolomitic limestone ^‡6  are seen. To the south-west 9 ft of thinbedded ^‡7  dolomitic limestone are exposed at Coal Bank Quarry [NZ 346 464]; and at

Low Moorsley Quarry [NZ 342 462] the section is:

Beds in both these quarries are near the base of the Lower Magnesian Limestone, as are 12 ft of thin-bedded dolomitic limestone exposed in Moorsley Banks Quarry [NZ 3362 3591]. The base itself is seen in a roadside section [NZ 3342 4569] 500 yd W.S.W. of High Moorsley, where thin-bedded, finely crystalline dolomite is intercalated with Marl Slate. The sequence at High Moorsley Quarry [NZ 334 455] is similar to that at Low Moorsley: 42 ft of brown dolomitic limestone are thick-bedded in the lowest 9 ft and thin-bedded above. Haematite and dolomite are abundant on joint faces and in veins on part of the north-west face. The thick-bedded limestone seen at the base of several of the above exposures is over 12 ft thick in an old quarry [NZ 3331 4520] 200 yd S. of High Moorsley Quarry, and is overlain by 60 ft of more flaggy dolomitic limestone in Pittington Quarry [NZ 332 447]. Thin-bedded dolomite and dolomitic limestone are also seen in the following exposures along the escarpment east and south-east of Pittington Quarry: Warren Quarry [NZ 333 445], Cobbler's Quarry [NZ 345 449], Hetton le Hill Quarry [NZ 348 450], Hetton le Hill Wood Quarry [NZ 3500 4495], and in several small old quarries between Elemore Hall [NZ 351 442] and Hastings House [NZ 3449 4331]. In thin section (E16136) a specimen from Cobbler's Quarry is seen to be a calcitic dolomite of silt grade, containing a few small angular quartz grains. E.A.F.

East of the escarpment, Lower Magnesian Limestone is exposed in the sides of a glacial drainage channel now occupied by the Coldwell Bum, and at a number of old quarries near Low Haswell. Exposures alongside Coldwell Bum are mainly small and overgrown, and are mostly of thin-bedded, fine-grained, cream, dolomitic limestone. The following is the section in an old quarry [NZ 3658 4451] 850 yd N. of High Haswell: dolomitic limestone, cream-buff, massive, hard, semi-porcellanous, autobrecciated, cavernous 10 ft, on dolomite, cream, thin-to thick-bedded, finely granular, with thin bands of semi-porcellanous partly autobrecciated dolomite 10 ft. Autobrecciation is also seen in 7 ft of thin- and medium-bedded sub-porcellanous dolomitic limestone exposed in a small quarry [NZ 3656 4463] 130 yd farther north, and again at three localities about 600 yd S.W. of Low Haswell. At one of these, an old quarry [NZ 3612 4368], the rock is finely granular dolomite and dolomitic limestone in which large irregular patches are unbedded and autobrecciated, whilst the remainder of the rock shows well-defined bedding including traces of original small-scale cross-bedding. In some softer parts of the granular dolomite, a felted texture (p. 123) is developed as a result of the intersection of large numbers of platy dolomite crystals up to 4 mm across. This texture is taken to indicate a position at or near the top of the Lower Magnesian Limestone, for it is not found at lower horizons. D.B.S.

Scattered exposures between Sherburn, Shadforth, Haswell and Ludworth are all in thin-bedded dolomitic limestone, as follows: old quarry [NZ 346 425] at Black Banks; old quarry [NZ 352 422] at Limekiln Hill 12 ft; old quarry [NZ 335 423] at Sher-burn Hill 3 ft; Sherbum Hill Sand Pit [NZ 344 418], 0–10 ft, overlying Marl Slate; Crime Rigg Sand Pit [NZ 341 416] 12–20 ft (in 1956) overlying Marl Slate; Crime Rigg Quarry [NZ 339 419] 10–15 ft; old quarries [NZ 345 414] 400 yd E.N.E. of Shad-forth Church; and old quarry [NZ 3560 4125] at Ludworth Tower. The lowest exposed beds at Sherburn Quarry [NZ 328 418] are 12 ft of thick-bedded dolomitic limestone containing ferruginous bands. An old quarry [NZ 3575 4125] 100 yd E.S.E. of Ludworth Tower gives the following section:

The base of the middle unit of the section is somewhat uneven and rests on a bed at the western end of the quarry which is 4 ft higher in the sequence than the bed underlying it at the eastern end. The lithology of the lowest unit is like that previously noted near the base of the Lower Magnesian Limestone. D.B.S., E.A.F.

Shadforth to Garmondsway

The most northerly outcrop between Shadforth and Garmondsway is in a small quarry [NZ 3572 4066] 700 yd S. of Ludworth Tower, where 3 ft of grey-cream sub-porcellanous partially autobrecciated dolomitic limestone are exposed. The bedding is generally thin, but extremely uneven. Similar rock is exposed in a group of small quarries in Shadforth Dene, 800 yd farther west. The beds at both localities are about 80 to 100 ft above the Marl Slate. Along the escarpment, the northernmost exposure of any importance is at Running Waters Quarry [NZ 334 404], where 30 to 40 ft of thin-bedded dolomitic limestone are visible. Thicker bedding in the lowest part of the section indicates proximity to the base of the division. Thin-bedded dolomitic limestone is 20 ft thick in a quarry [NZ 3353 4018] 350 yd N.W. of Cassop Smithy, and forms small outcrops at Strawberry Hill [NZ 342 400], and on both sides of a deeply-incised valley [NZ 351 399], 1000 yd E. of Strawberry Hill. Farther south exposures are confined almost entirely to the following localities on the scarp: old quarry [NZ 3415 3965] 500 yd N.E. of Old Cassop, thin-bedded dolomitic limestone 18 ft; old quarry [NZ 3315 3933] 500 yd. W.S.W. of Old Cassop, thin-bedded dolomitic limestone 10 ft; old quarry [NZ 3387 3866] 670 yd N.W. of Cassop Colliery church, thick-bedded white 'limestone' 7 ft; old quarry [NZ 3464 3870] 350 yd S.W. of Dene House Farm, massive dolomitic limestone 10 ft; old quarries [NZ 339 382] 500 yd W. of Cassop Colliery church, thin-bedded dolomitic limestone 25 ft, over thick-bedded dolomitic limestone 11 ft, resting on Basal Permian Sands; three old quarries [NZ 329 386] 950 yd E.N.E. of Hill Top Farm, thin-bedded dolomitic limestone spanning the lowest 50 ft of Lower Magnesian Limestone; old quarry [NZ 3204 3844] at Hill Top Farm, Old Quarrington, thin-bedded dolomitic limestone 15 ft; and Quarrington Quarry [NZ 327 379], thin-bedded dolomitic limestone 12 ft, resting on Marl Slate.

A boring [NZ 3323 3815] 0.5 mile N.W. of Quarrington Hill proved rubbly buff dolomite 36 ft, on bedded dolomite and dolomitic limestone (with autobrecciation between 45 ft and 48 ft from top) 101 ft, on Marl Slate. Analyses show CaO to decrease sharply between depths of 41 ft and 57 ft from the surface, though it remains constant at between 31 and 35 per cent (calcitic dolomite) throughout the remaining 80 ft of beds down to the Marl Slate. Fossils found at depths between 20 and 36 ft may indicate that the highest beds in this bore are Middle Magnesian Limestone. E.A.F., D.B.S.

Over a mile to the east of the scarp Lower Magnesian Limestone is exposed in the flanks of a system of glacial drainage channels near East Hetton Colliery. Here, two old quarries [NZ 3600 3700] and [NZ 3592 3710] each show about 30 ft of thin-bedded, cream, finely granular, cavernous dolomitic limestone, overlain in the southernmost quarry by flaggy dolomite of the Middle Magnesian Limestone. A third quarry [NZ 3580 3725] contains 20 ft of hard, thin-bedded, cream-brown, sub-porcellanous autobrecciated dolomitic limestone lying 20 to 30 ft lower in the succession, and similar rock is intermittently exposed in the valley sides north and west of Town Kelloe. D.B.S.

Exposures along the scarp south of Quarrington Hill are dominated by the large quarries at Coxhoe Bank and Raisby Hill. About 130 ft of dolomite, thin-bedded except in the lowest 10 to 18 ft, are exposed in Coxhoe Bank Quarries [NZ 325 362]. Thin laminated layers are present near the base of the section. Trechmann (1945, p. 339) records 'Productus horridus' J. Sowerby [Horridonia horrida] 'in plenty' at these quarries.

Analysis (E. G.Radley in Thomas and others, 1920, p. 82) of a specimen representative of the lowest beds exposed in Coxhoe Bank Quarries shows that these beds are composed of calcitic dolomite. Beds above, shown by three analyses of representative specimens to be of only slightly calcitic dolomite, are relatively uniform in composition. Thin sections (E11747), (E11748), (E11749), (E11750) show the analysed rocks to be composed of fine-grained aggregates of dolomite crystals (0.03 mm), with a small amount of interstitial calcite in (E11748). Cavities are most common in the highest beds.

Analyses of rocks from closely spaced bores sunk by United Steel Co. Ltd. for the Steetley Company Limited in the ground between Coxhoe Bank Quarry and Kelloe, show a slightly calcitic dolomite down to a level 20 ft above the Marl Slate; below that level impurities increase sharply.

Raisby Hill Quarries (Plate 8A) yield a complete section through the Lower Magnesian Limestone, mainly in the mile-long north face. A thick lenticular mass of limestone occurs near the base of the division in the central part of the north face, but thins rapidly westwards and is absent in the most westerly faces. The margins of this mass are irregular and diachronous, each component bed passing laterally from limestone to dolomite. Basal beds are exposed in a cutting [NZ 3403 3532] in the floor of the central part of the quarry where 10 ft of thin-bedded dolomite or dolomitic limestone overlie 6 ft of dolomitic limestone interbedded with rock of Marl Slate lithology. The following section is exposed [NZ 347 352] midway along the north face: thin-bedded dolomitic limestone 80 ft, on alternating beds of limestone and dolomitic limestone 30 ft, on light grey compact limestone 90 ft. The base of this lowest bed probably lies at about, or slightly above, the beds exposed in the cutting. The following have been collected from the lower part of the 90 ft bed of the above section: 'Adhaerentina' permiana Paalzow, 'Glomospira'pusilla (Geinitz), uniserial chambered foraminifera; Acanthocladia anceps ((Plate 6), fig. 13), Batostomella sp., Fenestrellina retiformis (Schlotheim), Polyzoan, ?Gen. et sp.nov.((Plate 6), fig, 10) [also from Fishburn No. 4 Bore 330 to 357 ft—see note on p. 181]; Dielasma elongatum (Schlotheim), Horridonia horrida [several forms—Eisel's varieties, hoppelana, initialis, ?auritula], ?Neochonetes davidsoni (Schauroth), Pterospirifer alatus (Schlotheim). ((Plate 6), fig. 14), Strophalosia niorrisiana, Strophaloslid juv. [?S. parva King; flat, circular, ventral valve with spines]; Schizodus rotundatus (Brown), Streblochondria pusilla (Schlotheim); nautiloid septa; ostracods. E.A.F. At the eastern end of the main face the section [NZ 3516 3509] is:

The lowest 35-ft unit of this section corresponds with the upper part of the lowest (90 ft) member of the previous section. Analysis of a specimen from near the base of this bed (Trechmann 1914, p. 248) shows it to be a slightly dolomitic limestone (calculated calcite 95.27 per cent, dolomite 3.2 per cent), whilst analysis (Thomas and others 1920, p. 82) of a specimen from about the middle of the sequence shows it to be calcitic dolomite (CaCO₃ 56.12 per cent, MgCO₃ 38.16 per cent). Similar analyses are given by Woolacott (1919a, p. 167), who also records (1919b, p. 456) gypsum crystals from cavities in this quarry. It is possible that the cavernous, autobrecciated beds noted some 50 ft above the base of the sequence represent collapse caused by the removal of earlier interbedded sulphates. It is notable that whereas the lower 55 ft of beds in the east of the quarry are even and of uniform dip, those above this level are slightly undulate (see (Plate 8A)). The uppermost 10 to 20 ft of beds are probably of Middle Magnesian Limestone age. D.B.S.

A number of small exposures between the eastern end of Raisby Hill Quarry and the railway line are all in highly brecciated dolomite and dolomitic limestone, and malachite and chalcopyrite occur in the most southerly of these. The breccia lies close to the position of the Butterknowle Fault. G.D.G.

Further small exposures of thin-bedded dolomitic limestone are seen in one old quarry [NZ 3292 3585] near Coxhoe Hall and another [NZ 3460 3610] at Low Raisby. Thin-bedded dolomitic limestone is also seen overlying massive beds of similar composition in an old quarry [NZ 3257 3579], 550 yd W. of the ruins of Coxhoe Hall. E.A.F.

South of Garmondsway

Raisby Hill Quarries are bounded on the south side by the Butterknowle Fault, beyond which the outcrop of the Lower Magnesian Limestone is shifted westwards. Although its thickness decreases to less than 150 ft in places, the Lower Magnesian Limestone outcrop is over 2 miles wide around Ferryhill (Plate 5); (Figure 19), and this reflects topography and an anticlinal structure. The most northerly exposure is an old quarry [NZ 330 348], 1350 yd S. of Coxhoe Hall, which shows 20 ft of cream fine-grained or porcellanous thin-bedded dolomite lying a short distance below the top of the division. A more complete section is seen at West Cornforth Quarry [NZ 318 345] where 80 ft of dolomite are exposed. Lower beds here are mainly thin-bedded, fine-grained or porcellanous dolomitic limestone. whilst upper beds are paler, thick-bedded, softer and more dolomitic. A thin section from the latter (E21138) is described by Dr. K. C. Dunham as a 'yellow fine-grained rock, composed of crypto-crystalline dolomite traversed by thin veinlets of coarser carbonate'. A borehole in the floor of the quarry proved a further 63 ft of thin-bedded dolomitic limestone on 10 ft of slightly dolomitic, finely crystalline massive limestone overlying Marl Slate. The only exposure around Cornforth is an old quarry [NZ 309 341], 800 yd N.N.W. of Thrislington Hall, where 15 ft of thin-bedded dolomitic limestone show extensive incipient autobrecciation. South of Corn-forth, beds high in the division are exposed in an old quarry [NZ 318 324] in Thrislington Plantation, where soft fine-grained cream dolomite overlies hard grey-buff finely crystalline dolomitic limestone. Adjacent boreholes show that the Marl Slate lies at a depth of about 130 ft hereabouts. Finely crystalline dolomitic limestone, 15 ft thick, is seen at a second quarry [NZ 316 328] nearby. In both quarries the bedding is of uneven thickness and is undulate, as it is at the same horizon at Raisby Hill Quarries (p. 111). South-west of Cornforth there are old quarries on both sides of the Ferryhill Gap. To the west, in Ferryhill Cliff Quarry [NZ 300 330], thin-bedded dolomitic limestone with argillaceous partings is evenly laminated in the lower part and passes down to Marl Slate. Baryte and galena occur at several places in this quarry and are also present in a group of small exposures [NZ 3000 3321] 200 yd farther north. Loose fragments of flaggy dolomitic limestone from the latter yielded 'Ammodiscus' roessleri (Schmid). Some 10 ft of thin-bedded contorted and brecciated dolomitic limestone containing plant debris are exposed 40 yd farther north. An old quarry [NZ 334 329] on the east side of Ferryhill Gap shows 32 ft of thin-bedded cavernous dolomitic limestone.

Of several exposures in the lowest beds of the Lower Magnesian Limestone near Ferryhill Station, the best are at Mainsforth Lime Works Quarry [NZ 305 321], Rudd Hill Quarry [NZ 302 321] and in a railway cutting [NZ 303 323]. At each of these localities about 30 ft of thin-bedded fine-grained and sub-porcellanous dolomitic limestone are seen. The underlying Marl Slate and Basal Permian Sands are exposed on the east face of the cutting. Farther east, two quarries [NZ 308 329] and [NZ 309 328], 700 yd S.S.E. of Thrislington Hall, have recently been opened in an area where boreholes have proved about 100 ft of thin-bedded fine-grained and porcellanous cream dolomitic limestone. Poikilitic calcite was noted in some of the early faces. South of Ferryhill Station excellent sections about 80 ft high are afforded at Chilton Quarry [NZ 300 314] where the lower beds are hard thin-bedded grey dolomitic limestones and the upper are softer grey-brown calcareous dolomites containing hard grey ?calcareous nodules. In thin sections (E20615), (E20616), (E20617), (E20618), (E20619), (E20620) from this quarry, both slightly dolomitic limestone and slightly calcitic dolomite can be seen, often in the same specimen and separated by a sharp junction. The occurrence of baryte, fluorite and sphalerite at this locality has been discussed at length by Fowler (1957, pp. 258–60). A borehole [NZ 3030 3091], 450 yd S. of the quarry, proved 130 to 150 ft of Lower Magnesian Limestone, its top coinciding approximately with the top of the sequence exposed in Chilton Quarry. G.D.G.

In the south-western part of the district dolomitic limestones at or near the base of the Lower Magnesian Limestone are seen at the following localities: old quarries [NZ 2945 3357] 350 yd S.S.W. of East Howie Post Office, thin-bedded 12 ft on thick-bedded 2 ft; railway cutting [NZ 279 336] 350 yd S.S.E. of Skibbereen, thin-bedded 2 ft on Marl Slate 9 ft; Pickering Quarry [NZ 274 229], thin-bedded 6 ft; old quarry [NZ 2751 3276] 300 yd W. of Low Hill House, Dean Bank, thin-bedded 11 ft over thick-bedded 7 ft; and road-cutting (285 327] Ferryhill, thin-bedded with some finely laminated bands towards base 34 ft.

East of the outcrop

East of Hetton le Hole and Shadforth, in the northern part of the district, most of the shaft and borehole records are old and unreliable, but Hawthorn Colliery Shaft and Mill Hill Bore, Easington can be taken as representative of more modern sinkings.

The shaft section shows:

Details of the Lower Magnesian Limestone of Offshore Nos. 1 and 2 bores are given by Magraw and others (1963). The uppermost 48 ft of the division are exposed [NZ 4268 4436] in a cross-measures drift leading down from the western end of a tunnel at Easington Colliery, and consist of thin-bedded, fine-grained and sub-porcellanous dolomitic limestone. There is partial autobrecciation near the top of this sequence, which is conformably overlain by granular dolomite of Middle Magnesian Limestone age.

East of Shadforth and Kelloe the Lower Magnesian Limestone has been cut in a number of bores and shafts, but it has been examined in detail only at Blackhall Colliery South Shaft where Trechmann (1913, p. 213) recorded it as 240 ft thick. The uppermost beds of the division are described as 'yellow, bedded friable limestones' containing plant and polyzoan debris. Under the classification used here, however, these are referred to the Middle Magnesian Limestone. Trechmann (1914, p. 247) gave 5 analyses from the 'Lower Magnesian Limestone' at Blackhall Colliery; all are of slightly calcitic dolomite. The lowest bed analysed, a hard dark grey rock with carbonaceous partings, contains 4–52 per cent CaCO₃ in excess of the molecular proportions of dolomite, and this calcite is visible in thin sections of the rock. Although most of the records of the remaining bores and shafts east of the outcrop area are generalized and unreliable, many show a twofold sub-division into yellow and brown 'limestone' overlying harder grey, dark grey or blue 'limestone ', the latter often 30 to 40 ft thick. D.B.S.

South of the Butterknowle Fault modern borings are more numerous, particularly in the Ferryhill–Embleton area. Records between Ferryhill and Bishop Middleham indicate great lateral variations of lithology, but prove a widespread general triple subdivision of the Lower Magnesian Limestone similar to that noted at outcrop (pp. 106–8). A generalized section is:

It is apparent from analyses (abstracted by kind permission of the Steetley Company Limited) that although Woolacott (1919a, p. 166) recorded 100 ft of 'highly calcareous rock' from equivalent beds in the Cotef old Close Bore, 2 miles N.N.E. of Embleton, there is no local thick development of calcitic rock low in the sequence as there is at Raisby Hill Quarry. On the contrary, some of the higher beds of the division are fractionally more calcitic than the lower. In the lowest of the three units there is a downward increase to up to 10 per cent of non-carbonate matter. The middle and upper units, however, consist mainly of slightly calcitic dolomite with between 1 and 2 per cent of non-carbonate matter.

Where mottling is well developed in the middle unit, bedding surfaces are markedly knobbly or even semi-stylolitic and bear thin black films of carbonaceous calcareous clay. Thin sections (E27634), (E27635), (E27636), (E27637), (E27638), (E27639) of representative specimens from depths between 109 and 131 ft (4 to 26 ft above the base of the division) in Mainsforth Low Main Series No. 9 Bore [NZ 3202 3305] are described by Dr. R. Dearnley as dolomite siltstone, consisting almost entirely of a mosaic of silt-grade dolomite grains with scattered coarser 'patches'. Collapse-breccias were seen 108 ft above the Marl Slate in a bore [NZ 3141 3230] 900 yd N. of Mainsforth.

Fossils are rare and are found mainly in the lowest 20 to 30 ft of the division. They include Horridonia horrida and Lingula credneri from Mainsforth No. 2 (1955) Bore [NZ 3112 3200], and small ?brachiopods from Mainsforth No. 4 Bore [NZ 3227 3215]. A short distance south of the district, in a borehole [NZ 2791 2830] near Rushyford, brachiopods including Lingula sp.and foraminifera occur in the lowest beds of the division, and foraminifera, polyzoa and plant debris are recorded about 50 to 65 ft higher. Exceptionally, ostracods are found 115 ft above the base of the division in Mainsforth No. 7 Bore [NZ 3282 3186].

Boreholes east of Bishop Middleham are less closely spaced than those to the west, and many were cored only in the lower part of the Lower Magnesian Limestone. In this area the division reaches a maximum thickness of over 225 ft, but thins to less than 125 ft near the southern margin of the district (Figure 19). The triple lithological subdivision recognized west of Bishop Middleham persists throughout the Fishburn–Embleton area, though the lowest member locally becomes progressively more difficult to recognize towards the east. The middle member of the sequence is characterized by pronounced mottling, associated with stylolites and knobbly (semi-stylolitic) bedding planes—features previously described in the ground east of Embleton (Woolacott 1919a, p. 164; Smith in Magraw and others 1963, p. 171). The lower part of the middle member of the sequence tends to be calcareous as at Raisby Hill Quarry (p. 111), and this is illustrated in Table 2 (p. 116) where an analysis (Lab. No. 1451) from Ten-o'-Clock Barn No. 2 Bore shows only 0.21 per cent MgO to contrast with approximately 18 to 20 per cent measured in other beds in the bore.

Thin sections of the analysed rocks are described by Dr. K. C. Dunham as follows:

• (E21051). Yellow fine-grained calcitic dolomite, composed of dolomite rhombs (average 0–06 mm) with calcite cement.
• (E21050). Yellow fine-grained dolomite, composed of dolomite grains (average 0.02 mm). Pore spaces (empty) reach 0.8 X 0.3 mm.
• (E21049). Grey fine-grained dolomite, composed of dolomite grains (average 0–03 mm) and a little calcite. Small pore spaces.
• (E21048). Light grey dolomite composed of rhombic dolomite grains (average 0.03 mm) with many small empty pores aad some pyrite.
• (E21047). Grey fine-grained calcite mudstone, composed of even-grained calcite grains averaging 0–01 to 0.015 mm.

Quartz is present in small quantities in slides (E21047), (E21048), (E21049), (E21050). It is also seen in thin sections (E19806)-(E19807), (E19809), (E19810) of fine-grained compact limestone from equivalent beds 7, 11.5, 17.5 and 24.75 ft respectively above the base of the division in the Whin Houses Bore. Minerals such as baryte, fluorite, pyrite, chalcopyrite and sphalerite recorded from the higher beds of the Lower Magnesian Limestone in the Ten-o-'Clock Barn, Whin Houses and other bores in the area (Fowler 1943, pp. 41–51; 1957, pp. 251–65), have been found also in many of the more recent bores.

Fossils collected from Ten-o'-Clock Barn No. 1, Fishburn No. 3, Fishburn No. 4, Fishburn ‘D’, and the Whin Houses bores are listed on pp. 173–6. Most of them are from the lower 50 ft of the Lower Magnesian Limestone, but in Fishburn 'B' Bore, where the division is about 190 ft thick, fossils (chiefly lamellibranchs and foraminifera) extend upwards to within 70 ft from the top.

Boreholes east of Embleton show a continuation of the general lithological sequence noted above, but the lowest unit becomes distinguishable only with difficulty from the middle unit of the division, and in the extreme east of the district even the middle and upper units tend to lose their separate identities. Details of the Lower Magnesian Limestone in these boreholes are given by Magraw and others (1963). D.B.S., E.A.F.

Middle Magnesian Limestone

Middle Magnesian Limestone beds occupy most of the outcrop of Permo-Triassic formations north of the West Hartlepool Fault (Plate 5), a circumstance arising mainly from a combination of a low easterly dip and the gradual easterly fall of the land surface. The division as a whole is interpreted as comprising the deposits of a single major evaporite cycle, although chemical precipitation probably commenced in Durham only at a fairly late stage.

The earliest deposits of the Middle Magnesian Limestone are a relatively thin group of fine-grained calcitic dolomites, here referred to as transitional beds (p. 90, (Figure 17)). The junction of these beds with the underlying Lower Magnesian Limestone is usually indistinct, indicating a gradual and irregular dilution of the highly saline water in which the uppermost part of the Lower Magnesian Limestone is thought to have been deposited. D.B.S.

The earliest transitional beds are barren, but with increasing dilution a limited shelly fauna developed in central and western parts of the district. This fauna is characterized by Astartella vallisneriana (King) [(Plate 6), fig. 12], and includes also species of Bakevellia, Permophorus and Schizodus, as well as foraminifera and ostracods. The later transitional beds, deposited under nearly normal marine conditions, contain a more varied fauna which includes, in addition to the above, a number of species not previously recorded from this part of the sequence. These include the brachiopods Horridonia horrida and Streptorhynchus pelargonatus (Schlotheim). Also present, mainly as isolated randomly oriented tubes, is the alga Tubulites permianus (King), hitherto regarded as an index fossil of the Upper Magnesian Limestone. D.B.S., J.P.

Perhaps under the influence of longshore currents, shells accumulated in the eastern part of the district in sufficient numbers to form an elongate bank (reef 'A' of Trechmann 1925, p. 139), which subsequently became the locus of reef formation. The fauna of this shell-bank is notable for the abundance of such brachiopods as H. horrida, Orthothrix excavata Geinitz, Dielasma elongatum and Stenoscisma schlotheimi (von Buch), lamellibranchs including Bakevellia antiqua (Munster) and B. ceratophaga (Schlotheim); and the presence of cryptostome polyzoa such as Acanthocladia anceps, Fenestrellina retiformis, Synocladia virgulacea (Phillips) and Thamniscus dubius (Schlotheim). Here too are found rarer fossils, including reef-sponges, echinoids, the lamellibranch Solemya biarmica de Vemeuil and the gastropod Macrochilina symmetrica (King).

The formation of the shell-bank and superincumbent reef brought about a fundamental change in depositional environments on their western and eastern sides, so that three distinct and contrasting facies–lagoonal, reef and basinal—can be recognized above the transitional beds (Figure 20). These facies are not recognized in the highest beds of the Middle Magnesian Limestone which are basinal dolomites deposited over the reef-flat after the latter had become submerged.

On the protected, western lagoonal side of the reef, accumulation in shallow water of a varied sequence of granular oolitic and pisolitic carbonates, now dolomitized, lagged little behind the rapid upward growth of the reef. This is indicated by the widespread shallow-water depositional features, especially current-bedding, in most of the lagoonal deposits, and by the interdigitation of these sediments with the uppermost, largely algal, deposits of the reef. In contrast, deposition in deep water on the eastern (basinal) side of the reef was comparatively slow except in the immediate vicinity of the reef front, where fore-reef talus forms a wedge-shaped apron. This relatively slow accumulation can be inferred in a series of tunnels (p. 136, (Figure 21)) driven through the Middle Magnesian Limestone at Easington Colliery, where detrital off-reef beds are only 30 to 50 ft thick as compared with over 250 ft of equivalent reef rock some 200 to 400 yd to the west. Corresponding lagoonal deposits probably exceeded 200 ft in thickness.

During the early stages of reef formation, growth was predominantly upward, and the lower parts of the reef are composed of massive biohermal dolomitic limestones and dolomites containing a prolific fauna of stenohaline brachiopods, lamellibranchs and polyzoa, together with scattered poorly preserved stromatolitic (algal) incrustations. The lower part of the reef appears to have been built mainly by cryptostome polyzoa, but it is thought (Smith 1958) that marine calcareous algae also contributed. As the reef was built upwards shallower water encouraged more rapid growth of calcareous algae, and at the same time increasing salinity first led to stunting, and then to gradual extinction of many of the earlier faunal elements (Trechmann 1913, p. 203). Consequently the uppermost parts of the reef are almost wholly of algal origin and contain a wide variety of growth-forms (Smith 1957), of which good examples are seen in Hesleden Dene and in Whelly Hill Quarry, Hart. Growth-forms similar to some of these are found today in Shark Bay, Western Australia (Logan 1961), where they are being formed by fixation of calcareous sediment in the intertidal zone of hypersaline lagoons. D.B.S.

During the process of extinction of the shelly fauna, the rare forms (p. 117) found in the initial shell-bank were the first to die out. Amongst brachiopods, species such as Pterospirifer alatus and Cleiothyridina pectinifera (J. de C. Sowerby) were the earliest casualties, followed by Horridonia horrida, Stenoscisma schlotheimi and Orthothrix excavata. The most adaptable was Dielasma which survived almost until the end of reef-formation. Lamellibranchs, less abundant than brachiopods at first, became relatively more prominent later, although the number of species was reduced. The more durable forms include Bakevellia antiqua, B. ceratophaga, Pseudomonotis speluncaria (Schlotheim) and Parallelodon striatus (Schlotheim). The number of gastropod species also became reduced, although in the later stages of reef-growth the remaining species achieved considerable prominence and locally dominated the fauna. J.P.

In addition to the vertical changes noted above, there is marked lateral variation in the faunal assemblages of the reef. The rocks deposited near the lagoonal margin of the reef, for instance, contain a fauna dominated by gastropods and lamellibranchs; they are best seen farther north, in the Sunderland (21) district. Those formed at the reef-crest also contain many lamellibranchs, but they are associated with pedunculate brachiopods, with only rare gastropods and retiform polyzoa. Faunas of the reef-slope, by contrast, are dominated by retiform polyzoa, crinoids, lamellibranchs and larger brachiopods. The distribution of these assemblages appears to be comparable with that found in the Capitan Reef of the Guadalupe Mountains (Newell and others 1953, fig. 79).

The varied growth forms of stromatolites also reflect different environments. Those formed on the upper part of the reef-slope and at the reef-crest are large and complex, those formed on the reef-flat are generally small and uniform, whilst those formed at the lagoonal margin are of intermediate size and complexity and are similar to modern lagoonal and bay-head forms. Stromatolites on the reef-slope form steep sinuous sheets which persist to at least 40 ft below the reef-crest. At lower levels they are progressively less prominent and are almost unrepresented in the talus at the foot of the reef-slope. The precise conditions of formation of a group of large growth forms on the reef-flat in Hesleden Dene is in some doubt, as there appear to be no modern analogues, but it seems possible that they formed in a high energy zone on a newly submerged reef platform. Oncolites are found mainly in the lagoonal deposits near the reef, but also form lenticles within the reef-flat deposits.

The vertical distribution of faunas in the lagoonal environment reflects the same increasingly unfavourable conditions as those of the reef. Forms found in the upper part of the transitional beds at the base of the Middle Magnesian Limestone survive in the overlying lagoonal beds, but show a progressive upwards impoverishment, and are virtually extinct about 80 ft above the base of the division. Exceptions are found only near the reef and these seem to be derived from the reef itself, for they are found nowhere else in the lagoonal beds. The presence in the lagoon of only euryhaline forms and the paucity of stenohaline brachiopods, polyzoa and crinoids, points to a less hospitable (metahaline to hypersaline) environment than that found in corresponding parts of the reef, and the evidence suggests that for a considerable period after the indigenous lagoon fauna became extinct a restricted shelly fauna continued to survive on the reef. However, throughout the period of reef-growth, quantities of derived bioclastic material accumulated in the lagoonal deposits adjacent to the back-reef, forming a narrow belt of coquinas and detrital calcarenites which thin rapidly westwards. Deposits of this type are well exposed in Hesleden Dene and also occur in the Mill Hill Bore, Easington. The middle and later periods of reef-growth are represented in the lagoon predominantly by oolitic rocks, which contain abundant compound pisoliths (oncolites) concentrated chiefly in a belt a few hundred yards wide behind the reef. Similar pisoliths are reported (Newell and others 1953, p. 120) from lagoonal beds adjacent to a reef in the Carlsbad formation of New Mexico and western Texas where they are believed (Johnston 1942, p. 213) to be of algal origin.

The well-defined margins of the preliminary shell-bank and early reef were partially modified as the lagoon filled with sediments, and it is clear that reef growth at times extended both backwards over lagoonal sediments and forwards over talus derived from erosion of early reef-rock. As a result of the differing rates of sedimentation behind and in front of the reef, a sharply asymmetrical form was produced, with back-reef and lagoonal deposits of low surface relief being separated from a steeply-plunging reef-front by a reef-top platform up to a mile wide (Figure 20).

Interdigitation at the margins of the reef, particularly on the lagoonal side, suggests that reef formation may have been intermittent and that the reef might more properly be regarded as a composite structure built up of a succession of reefs formed, in general, at much the same place. In boreholes in Hesleden Dene, however, the superimposition of basinal and lagoonal beds suggests that here the reef-front during the late stages of reef growth may have lain west of its earlier position. The course of the reef-front (Plate 5), as inferred during the resurvey, is typical of many present-day reefs, with wide embayments, and in some places, prominent spurs projecting seawards. It is not known whether the reef is a continuous mass or is divided wholly or partially by channels of varying depth and width, but the form of the outcrops from Horden northwards suggests that at least the higher parts of the reef sequence are locally absent. A deep debris-filled cleft in reef-rock at Fox Cover Quarry, Dawdon, is interpreted as a former reef-channel.

Available evidence suggests that reef formation may have continued longer in central and southern parts of the district than in the north. For example, algal rocks of reef-facies appear to persist to a higher horizon in the south, and only a few miles north of the district Burton (1911, p. 301) records wind-blown sand grains in reef-limestones at Tunstall Hills, near Sunderland. This may have been due to a gentle southerly tilting of the whole area, bringing about a gradual emergence of the northern parts of the reef and continuing subsidence of central and southern parts. With subsidence, reef-growth continued until the tolerance of calcareous algae was exceeded, either by increasing salinity or by descent of the reef-top below the light compensation level. The uniformity of the bedded algal reef-rocks south of Castle Eden indicates formation on a wide slightly emergent platform rather than on an exposed reef-flat, however. Eventually increasing salinity and too-rapid subsidence may have operated concurrently in bringing reef-formation to an end. Subsequent temporary returns to more favourable conditions are indicated by algal rocks interbedded with post-reef granular carbonates overlying the reef at a number of eastern and southern localities.

The extent of the reef southwards from West Hartlepool is uncertain. However, indirect evidence yielded by a gravity survey (Bullerwell 1961, pp. 41, 60), and by borings, suggest that the reef may continue as far south as Seaton Carew where, as suggested by Trechmann (1942, p. 320), it seems likely that the reef has a more subdued relief than farther north and that it interdigitates with normal carbonate sediments around its southern margin. South and west of Seaton Carew, the Middle Magnesian Limestone was probably laid down in semi-open shelf conditions rather than in a lagoonal environment, and this would account for the difficulty experienced in distinguishing lower beds of the division from the shelf deposits of the Lower Magnesian Limestone in boreholes at Throston and Brierton. Similar difficulty is experienced east of the reef in more northerly parts of the district.

During the formation of the reef, contemporaneous erosion gave rise to wedge-shaped talus fans at the foot of the reef-front. These were progressively buried as the reef advanced seawards so that the detrital limestones and talus fans now exposed in front of the reef are mainly derived from erosion of the latest reef-growth. Excellent examples of reef talus are exposed at Black Halls Rocks (Plate 12) and in Crimdon Beck. No examples of detritus fans of early reef-growth are seen at the surface in the district, but shelly dolomite of this facies is present in underground sections at Easington Colliery and in boreholes at Hesleden Dene and Hartlepool. In the boreholes at Hartlepool these beds contain fragments of black fossiliferous siltstone (see p. 146), a rock-type found nowhere else in the Permian of Durham. D.B.S.

The fauna of the basinal beds of equivalent age to the reef changes with increasing distance from the foot of the reef slope. Near the latter, as seen in the underground sections at Easington Colliery, the fauna is closely comparable with that of the contemporaneous reef from which is is presumably derived. Farther away, as in the boreholes at Hartlepool, species found in the reef are common but there are also uniserial, chambered foraminifera and fish debris which are rare or unknown in the reef. The indigenous fauna of the basinal beds is known only from Offshore No. 1 Bore, 3 miles from the reef; here Chonetids and coiled, tubular and uniserial, chambered foraminifera are the commonest forms. J.P., D.D.S.

It is inferred from the high rate of reef-growth compared with that of accumulation of off-reef material that the front (eastern) face of the reef was ultimately over 200 ft high with a slope of between 30° and 85°. It effectively limited subsequent major sediment deposition to the basinal areas to the east until over 200 ft of sediments had accumulated. Because of the lack of features common to both reef and basin environments, it is not yet possible to equate any basinal bed with the end of reef-growth. However, the virtual absence of a shelly fauna in the highest parts of the reef implies a high salinity and it is thus possible that chemical precipitation of carbonates or even sulphates in adjacent deep water was synchronous with the latest stages of reef growth (Hickling and Holmes 1931, p. 255). The post-reef beds in the basin area comprise fine-grained barren dolomites succeeded by a thick series of evaporites in which interbedded carbonates and sulphates deposited alongside the reef wall pass eastwards into thick anhydrite with subordinate dolomite. Immediately east of the reef these beds are represented by 70 to 140 ft of collapse-brecciated granular and oolitic dolomites. The former presence of anhydrite in this group of strata was inferred by Trechmann (1913, p. 195) from the evidence of the collapse-breccias and of widely disseminated traces of sulphate, and strong supporting evidence comes from the position of the base of the Upper Magnesian Limestone which in places appears to be over 100 ft lower than when originally deposited. The western edge of the collapse-brecciated beds is marked by an adjustment zone of faults and mechanically brecciated rocks which lies immediately east of the reef front (Figure 20). Borehole evidence (Figure 22) shows that the zone of interbedded carbonates and sulphates is narrow or absent at West Hartlepool, but appears to widen to 3 to 5 miles in the northern part of the district and in adjacent parts of the Sunderland district. Farther east (Magraw and others 1963) boreholes at Hartlepool and in the offshore area show that the horizon of these beds is occupied by the Hartlepool Anhydrite which is 500 ft thick in N.C.B. Offshore No. 2 Bore. Fowler (1944, p. 205) has suggested that the anhydrite has been formed mainly by replacement of dolomite and there is evidence of such replacement at many localities. It is believed, however, that this process is of relatively minor importance and that on the basis of form and relationship the anhydrite should be regarded as a largely primary deposit. Geophysical evidence (Figure 23) coupled with boreholes at Hartlepool show that the lateral transition from the predominantly carbonate to the predominantly sulphate phase is fairly sharp, and at Hartlepool the transitional zone is clearly traceable by a marked gravity gradient. A comparable gradient underlies Seaton Carew, and may indicate that the anhydrite which is 35 ft thick and lies at the top of these beds in the Seaton Carew Bore thickens rapidly eastwards.

Whilst anhydrite was being deposited in the eastern part of the district, sediments on the submerged reef-platform were largely of granular and oolitic carbonates which are indistinguishable from the highest lagoonal beds to the west of the reef. In the southern part of the district the lagoon appears to have been wider and deeper than farther north, and to have opened out into a shelf area where sulphates were deposited in alternation with carbonates. These sulphates extend from adjacent parts of the Stockton (33) district into the southern margin of this district and may represent an extension round the southern end of the reef of parts of the thick anhydrite laid down in the basin. In this southern area anhydrite beds are especially common at the top of the Middle Magnesian Limestone, where, west of Billingham, they are interbedded with red mudstone (Hollingworth 1942) and are together thought to correspond with the Middle Permian Marls of Yorkshire (p. 95). There is no evidence that sulphates ever formed primary deposits in the more restricted northern parts of the lagoon, although abundant cavities testify to the former presence of disseminated sulphates (Guy 1911). Chemical precipitation of both carbonates and sulphates was eventually halted by an influx of fresher water under which the widely distributed impure Flexible Limestone at the base of the Upper Magnesian Limestone was laid down. D.B.S.

Details

In the following account, lagoonal, reef and basin facies are treated separately, but details of the transitional group are included with those of the overlying facies for these beds are generally thin and the junctions at top and bottom are gradational. Details of Middle Magnesian Limestone beds overlying the reef are included in the section dealing with the basin facies. Where possible, faunal lists are included in the text, but some longer lists from exposures and from boreholes are given on pp. 169–72.

Lagoonal facies

Beds of lagoonal facies occupy most of the outcrop of the Middle Magnesian Limestone. They consist of a thick series of granular, oolitic and pisolitic carbonate rocks which are almost universally dolomitized. In most of these rocks the dolomite forms rhombs of silt- to sand-grade, but is widely distributed irregular patches the dolomite has recrystallized into platy crystals up to 5 mm across arranged in sheath-like and semi-radial aggregates with a loosely cemented matrix of smaller rhombs. This recrystallization texture, which will henceforth be referred to as 'felted', is virtually confined to the lagoonal beds of the Middle Magnesian Limestone.

Murton

Two small outcrops occur at New Hesledon, 0.5 mile E. of Murton Colliery shafts. The more northerly [NZ 4095 4772] is beside the A.19 (Murton to Easington) road, 350 yd N.N.W. of the Water Works, and comprises about 20 ft of thin- and medium-bedded cream-white finely granular calcitic dolomite in units alternately poorly laminated and finely brecciated, most of the breccia fragments being apparently structureless. The other exposure [NZ 4103 4711] is in an old quarry at the north end of the Water Works; it consists of about 20 ft of thin- and medium-bedded cream saccharoidal calcitic dolomite, with a wedge of brecciated dolomitic limestone near the western edge of the quarry. Outcrops [NZ 4125 4648] and [NZ 4140 4636] of similar lithology flank the A19 road 520 yd S.S.E. of the Water Works, and 200 yd farther S.E. in the eastern side of a glacial drainage channel. Poorly developed irregular lamination is common, and beds and lenses of breccia occur throughout. All these outcrops lie close to the eastern limit of the lagoonal facies, and some of the laminated beds may be partly algal in origin.

South Helton

Three small exposures occur near South Hetton Station. In an old quarry [NZ 3765 4524], 190 yd W.N.W. of the station, about 6 ft of gravel overlie soft cream finely granular vuggy dolomite, which contains a thin pisolitic bed near the base. A second old quarry [NZ 3759 4507], 270 yd W.S.W. of the station, contains about 14 ft of cream, thin-bedded friable finely granular dolomite and dolomitic limestone, overlain by about 8 ft of gravel. The dolomite and limestone of the second quarry are probably younger than the dolomite of the first and are composed largely of sand-grade dolomite rhombs commonly strongly cemented into sub-spherical aggregates; irregular patches with a strongly 'felted' texture are common. At the south-eastern end of this quarry a zone of harder, more calcareous rock is slightly brecciated and has numerous cracks and widened joints. The third exposure [NZ 3744 4515] lies on the north side of the channel, 420 yd W.; of the station, and contains about 30 ft of highly weathered soft cream granular dolomite similar to that in the quarry first described.

High Haswell

The main exposures around High Haswell are in the sides of the road north-east of the village and on the hillside 500 yd to the south. The roadside section [NZ 368 438] includes about 30 ft of hard thin-bedded cream-grey fine-grained dolomitic limestone, which contains patches of saccharoidal dolomite and scattered traces of small concentric structures which may be recrystallized ooliths. The hillside section [NZ 366 434] consists of a number of small outcrops in which about 40 ft of massive cream finely granular dolomite are exposed. Beds at several of these outcrops are highly recrystallized in parts and excellent examples of coarsely saccharoidal (aggregated) and 'felted' dolomite occur. In some cases the matrix of fine dolomite rhombs has been removed by subaerial weathering and only the framework of platy dolomite crystals remains.

Haswell to Pesspool Hall

In road and railway cuttings and an old quarry at the north end of Haswell village, a total of about 30 ft of bedded calcitic dolomite are visible. The rock is thinly but irregularly bedded and many layers are lenticular; it is cream in colour, and of granular texture, varying from silt to coarse sand in grade. Cavities occur throughout, and vague traces of cross-bedding are seen in places. About 15 ft of beds of similar lithology are exposed in an old quarry [NZ 3794 4307], 400 yd S.S.E. of Haswell Station, though parts of the beds are harder and more calcitic than at the previous locality. Abut 7 ft of calcitic dolomite with both saccharoidal (sand grade) and 'felted' textures are exposed in the sides of a large swallow hole [NZ 3815 4319] about 80 yd S. of Pesspool Hall.

At Tuthill Quarry [NZ 390 423], 1 mile S.E. of Haswell Station, about 130 ft of beds are seen. The uppermost 100 ft consist of a varied sequence of calcitic dolomites ranging from mud to sand in grade, in which an original oolitic texture is preserved in scattered less-altered patches. Cross-bedding is well exhibited in these patches and is also recognizable in many beds which now have a granular texture and are composed almost entirely of dolomite rhombs. Differential cementation into sub-spherical aggregates of dolomite rhombs is common, as at South Hetton and elsewhere in the lagoonal facies, and ‘felted’ texture (E29448) is locally well developed. A bed of oolitic dolomite of silt-grade, containing many compound ooliths and pisoliths, occurs near the top of the section; small amounts of free calcite have been noted. Samples of oolitic and granular rock from this quarry were analysed (Trechmann 1914, p. 246) and were found to be of dolomite with only 2 to 4 per cent CaCO₃ in excess of that required by the molecular proportions of pure dolomite.

The lowest part of the quarry is in bedded cream finely granular dolomite, containing no traces of cross-bedding nor of ooliths. About 10 ft of carbonate silts and sands, cross-bedded but non-oolitic, form a transitional group between the upper 100 ft and the lower 20 ft of beds. A number of indeterminate shells were found in this lower 20 ft during the resurvey; they are taken to indicate an horizon near the base of the division. Trechmann (1914, p. 246; 1945, p. 352) also recorded the presence of fossils at this locality but he named only 'Astarte vallisneriana'.

A feature of the beds at and near Tuthill Quarry is a marked solution-widening of some joints and the formation of large solution cavities in a prominent faulted zone. Several such cavities occur at the south end of the quarry, and other may be located beneath large sink holes in adjacent fields.

Shotton Colliery

Shotton Quarry [NZ 399 418] 1050 yd N.E. of Shotton Colliery Station, contains about 25 ft of thin-bedded cream and grey oolitic calcareous dolomite of silt-grade with a few poorly preserved lamellibranchs. Cross-bedding is conspicuous in some beds, but no preferred orientation of fore-set laminae is apparent. One bed in the middle of the quarry face contains large numbers of compound ooliths and pisoliths, mostly of irregular shape and of apparently random distribution and orientation. This rock closely resembles that at South Hetton and near the top of Tuthill Quarry. In thin sections (E29438), (E29439) the ooliths are seen to be largely replaced by fine-grained dolomite, the original texture being almost completely obliterated. Small amounts of free calcite have also been determined.

Similar rocks are exposed in the sides of a small glacial drainage channel some 300 yd N. of the quarry, but much of their original structure has been obliterated by the growth of aggregated coarsely crystalline dolomite. Sections at the base of the railway cutting north and south of Shotton Colliery Station show a few feet of thin- and medium-bedded cream finely granular and granular calcitic dolomite similar to that found 20 to 30 ft above the base of Tuthill Quarry.

The most complete section of these beds in the Shotton area is in the Mill Hill Bore, Easington; starting beneath reef limestone, it comprises:

The uppermost 39 ft of these beds show close lithological and faunal affinities with reef dolomites located immediately to the east. The lowest 23 ft represent the transitional group at the base of the Middle Magnesian Limestone.

Ludworth

Middle Magnesian Limestone is poorly exposed near Ludworth in small quarries [NZ 3709 4140] and [NZ 3709 4098], respectively 400 yd W.N.W. and 500 yd S.W. of Harehill Farm. Both are largely overgrown, and contain cream and grey, thin- and medium-bedded granular unfossiliferous calcitic dolomite and dolomitic limestone.

Wheatley Hill

Dolomite with a marked 'felted' texture occurs in the sides of a sink-hole [NZ 3768 4008] in an alluvial flat 780 yd W. of Low Crow's House. The dolomite is thin-bedded, except near a zone of movement planes where it has a saccharoidal texture and is harder and more massive. In a railway cutting [NZ 3844 3991] about 100 yd S. of Low Crow's House, about 8 ft of thin-bedded cream saccharoidal (sand-grade) calcitic dolomite are present. An old quarry 40 yd S.E. of Low Crow's House is now filled, but rock obtained from it and built into local walls is of similar lithology to that in the cutting. Another small old quarry [NZ 3802 3942] immediately north of Wheatley Hill is in about 9 ft of soft cream thin-bedded calcitic dolomite. Most of the rock is oolitic and unfossiliferous, but a thin non-oolitic bed about the middle of the section has yielded: Tubulites permianus; 'Adhaerentina' permiana, Ammodiscus?, 'Glomospira' gordialis (Jones and Parker), 'G' milioloides (Jones, Parker and Kirkby), 'G.' pusilla; Astartella sp., Bakevellia antiqua, Permophorus sp.; ostracods.The section also includes an 8-in bed containing ooliths and pisoliths similar to those described from Shotton, Haswell and South Hetton. In thin section (E29440) this rock is seen to be largely recrystallized and to contain dolomite both as rhombs and as small platy crystals in the cores of ooliths and in the matrix. The origin of the compound ooliths is uncertain, but it appears likely that the platy dolomite crystals represent the early stages of the development of the 'felted' texture noted earlier.

Castle Eden

Rocks of lagoonal facies crop out intermittently in Castle Eden Dene from about 450 yd E. of the main Easington–Castle Eden road to Ivy Rock, midway between Dene House and Dene Leazes, where they are overlain by massive dolomites of reef fades. The lowest exposed beds are about 125 ft above the base of the division, so that most sections are stratigraphically higher than those at Wingate and Haswell, These lower beds constitute a uniform, relatively evenly bedded series of slightly calcitic dolomites, cream to grey in colour and generally finely saccharoidal (mainly silt-grade) in texture. Small flattened cavities are widespread. The dolomite at many of the outcrops is highly altered and most original sedimentary structures have been obliterated, but traces of current-bedding are common, especially in coarser-grained intercalations. In thin section (Trechmann 1914, p. 246) these beds are seen to be composed of loosely packed subhedral and anhedral dolomite grains, with scattered traces of calcite. Two analyses (loc. cit.) indicated an almost pure dolomite, having calculated calcite percentages of only 0.21 and 1.65 respectively; insoluble residues of 0.16 and 0.05 per cent are typical of Middle Magnesian Limestone lagoonal beds, all of which are remarkably free from detrital inorganic material. These beds are particularly well exposed in the valley sides near Gunner's Pool [NZ 419 388] and in the Trossachs [NZ 417 388], a spectacular gorge excavated along a fault plane.

Despite recrystallization and brecciation of the rock, moulds of small lamellibranchs, and a number of species of foraminifera, gastropods and ostracods are common in some beds. The most characteristic lagoonal form, Astartella vallisneriana, is plentiful ((Plate 6), fig. 12), associated with Schizodus sp.and Permophorus costatus (Brown). Small tubular rod-like fossils, thought to be Tubulites permianus, have also been noted. Trechmann (1964, pp. 215–6) further record Bakevellia ceratophaga, and species of 'Serpula', Spirorbis and 'Vermilia' from this locality. A total thickness of about 120 ft of these beds is exposed in the Dene, with a gentle overall easterly dip which carries them below the valley floor between Ivy Rock [NZ 435 396] and Craggy Bank [NZ 438 398]. They are overlain by 20 to 25 ft of irregularly bedded hard cream-grey lagoonal dolomite, which has a sub-porcellanous appearance when fresh, but which weathers to show its constituent sand-grade dolomite rhombs, with some ooliths and highly comminuted shell-debris. Where these beds first appear, at the top of Seven Chambers [NZ 431 394], access is difficult, but it becomes easier eastward down towards Ivy Rock. The section there is:

The oolitic bed has a markedly nodular-weathered surface, and is largely recrystallized; the pisoliths near the base are coarse, ranging up to 7 mm, and are similar to those of suspected algal origin in Gilleylaw Quarry, near Sunderland (Smith 1958, p. 75).

Wherever the base of the reef dolomite is seen in Castle Eden Dene it forms an irregular plane transgressing 6 to 8 ft of underlying beds. Lateral passage into reef-rock probably takes place shortly to the east for there are no beds of lagoonal facies in strata of the same age penetrated by Blackhall Colliery Shafts (Trechmann 1913, p. 213), 1.5 miles E. of Ivy Rock.

Thornley to Kelloe

In the area between Thornley and Town Kelloe, drift is predominantly thin, and exposures collectively include more than 100 ft of the sequence already described at Tuthill Quarry, Haswell. The most northerly, at Gore Hill [NZ 361 400], are of massive cream fine-grained calcitic dolomite. Some 12 ft of thin-bedded cream soft granular calcareous dolomite are exposed in a small quarry [NZ 3567 3981], 650 yd W. of Gore Hall, and flaggy beds of similar lithology crop out on a hillside about 130 yd S.S.W. of the quarry. Further beds of this kind are 12 ft thick in a cutting on the disused Cassop Wagonway, 500 yd E.N.E. of Halfway House Inn, and 6 ft thick in a field [NZ 3588 3935], 125 yd N. of the cutting. Shallow cuttings along the main Durham–Hartlepool road near to Halfway House Inn contain soft flaggy calcitic dolomite with a well-developed though somewhat patchy 'felted' texture, and similar rock is found in numerous fragments in the soil and in scattered outcrops south and south-west of the Inn. In an old quarry [NZ 3544 3827], 920 yd S. of the Inn the 'felted' rock is 12 ft thick: it is also seen at natural exposures [NZ 3561 3838] and [NZ 3565 3828] respectively 220 yd N.E. and 230 yd E. of the quarry.

Most of the good exposures in the Thornley area are in the sides of glacial drainage channels (p. 222). Of the several exposures of thin-bedded granular and 'felted' calcitic dolomite in the main valley the biggest is a 30-ft sequence [NZ 3647 3894], 810 yd N.N.E. of Thornley Hall. Unfortunately most of the of the other exposures are now covered by colliery waste, but 12 ft of soft cream 'felted' dolomite are still to be seen [NZ 3656 3872] 270 yd S. of the above locality. A small exposure [NZ 3689 3859] on the south side of a tributary valley, about 50 yd S. of White House, contains 10 ft of thin-bedded soft cream calcitic dolomite, in which traces of foreset cross-bedding laminae dip towards the east. This rock is completely recrystallized and granular with patchy 'felting'. Similar beds are also exposed in an old quarry [NZ 3682 3842], 260 yd S.S.W. of White House, where the section is:

All three lithological units of this section are highly weathered and contain pockets of soft cream-white powdery dolomite. Similar pockets are seen in thin-bedded, cross-laminated dolomite in a group of quarries about 600 yd E.S.E. and 350 yd E.N.E. of Thornley Hall where the texture range from finely saccharoidal to coarsely 'felted' and where parts of the rock adjacent to open joints and movement planes are harder, more massive and more calcitic.

Further exposures of thin-bedded, cream, granular or 'felted' calcitic dolomite, commonly with traces of cross-bedding, extend along the glacial drainage channel south of Thornley Hall. Original textures are largely obliterated by re-crystallization, but beds of oolite and pisolite are preserved [NZ 3633 3776] 500 yd N.N.W. of Kelloe Law. Oolite lying close to the base of the subdivision and containing some compound ooliths and pisoliths crops out high on the valley side [NZ 3585 3739] 760 yd W. of Kelloe Law and at the top of an old quarry [NZ 3602 3702] 750 yd W.S.W. of Kelloe Law.

Old Wingate

The Middle Magnesian Limestone has been extensively quarried around Old Wingate. In all there are over two miles of quarry face ranging up to 60 ft high and spanning a sequence of about 90 ft of beds just above the base of the subdivision. Most of the typical lithologies are represented, but undoubted ooliths are rare and no pisoliths were noted. Granular textures predominate, but 'felting' is common and dedolomitization adjacent to widened joints and to a prominent fault system has produced zones of hard massive fine-grained calcareous rock. The southernmost quarry contains, near its base, thin beds of fairly hard cream-brown fine-grained dolomitic limestone which contain scattered traces of small-scale cross-bedding and appear to be less altered than others in the vicinity. Seen in thin section (E3439) this rock is composed of silt-grade calcite with patchy recrystallization of dolomite.

A mile farther east, an isolated quarry [NZ 3933 3789] contains about 20 ft of thin-bedded saccharoidal (silt- to fine-sand grade) calcitic dolomite with small-scale cross-bedding, and small flattened cavities (?shell-casts) throughout. There are local dedolomitized zones and many irregular patches of powdery fine-grained dolomite from which the calcite cement has been leached.

Hesleden

Beds of lagoonal facies, represented by 20 ft to 30 ft of thin- and medium-bedded soft cream-grey shelly dolomitic calcarenite, lie between dolomites of reef-facies at several places in Hesleden Dene, west of Monk Hesleden. Excellent natural exposures occur on the north side of the stream [NZ 4358 3783], 700 yd W. of Hesleden Station, at Hairy Man's Hole [NZ 4416 3776], 150 yd S. of the station, and at several points between this locality and Jack Rock [NZ 4463 3762], 450 yd E.S.E. of the station, where reeffacies limestones overlying the lagoonal beds dip south-eastwards beneath the stream. A gradual and very irregular easterly thinning is apparent from the above sections, and these beds are thin or absent in the core of an anticline 500 yd S.W. of Fillpoke, 1.5 miles farther east. They appear to be about 9 ft thick in a borehole [NZ 4672 3696], 620 yd S. of Benridge. The irregularity of the eastwards thinning is due to the presence of prominent domes up to 20 ft high (Plate 10A) on the upper surface of the underlying reef limestones. Cliffs [NZ 4416 3776] at the side of Hairy Man's Hole provide the most complete single section, although the lowest beds are absent:

The lowest member of this section is essentially a shelly calcarenite of detrital origin, and though individual fossils are common they are stunted and restricted to a few species of euryhaline gastropods and lamellibranchs, Those collected during the resurvey include: Cyclobathmus? permianus (King), Straparollus permianus (King), ?Naticopsis leibnitziana (King), N. minima (Brown), Omphalotrochus helicinus (Schlotheim), O. taylorianus King), O. thomsonianus (King), Pleurotomaria?, Strobeus?; Bakevellia antiqua, Cardiomorpha modioliformis King [(Plate 6), fig. 9]; coprolites. Trechmann (1913, pp. 215–6; 1925, p. 136) records the following from this part of Hesleden Dene, but does not specify the horizon, so that some forms (especially the brachiopods) may have been collected from autochthonous reef rock: Epithyris elongate (Schlotheim), E. sufflata (Schlotheim), Strophalosia goldfussi (Munster); Macrocheilus sp., Natica leibnitziana King, ?N. minima Brown, Pleurotomaria antrina (Schlotheim), P. tunstallensis King, ?Rissoa gibsoni Brown, ?R. leighi Brown, R. obtusa Brown, Turbo helicinus (Schlotheim) T. mancuniensis Brown, T. permian us King, T. taylorianus King, T. thomsonianus King; B. antique, B. ceratophaga, ?B. tumida King, Pleurophorus costatus (Brown), ?Schizodus truncatus King, S. rotundatus; Peripetoceras freieslebeni Geinitz; ostracods ". Lagoonal beds below those of Hairy Man's Hole are seen near the base of cliffs [NZ 4448 3773], 350 yd farther east on the north side of the stream, where they fill hollows between domes and where their average thickness had decreased to about 11 ft.

The following fossils were collected from beds corresponding approximately to those of the Hairy Man's Hole section in a bore [NZ 457 361], situated about 330 yd N.W. of Thorpe Bulmer Farm: Tubulites?; 'Adhaerentina'permiana, 'Ammodiscus' roessleri (Schmid); Neochonetes? dayidsoni; Astartella vallisneriana, Bakevellia antique, Schizodus sp.

Trimdon

Lagoonal beds crop out at many localities in the area around Trimdon Grange, Trimdon Colliery and Trim-don, and have been proved in a number of boreholes farther east. At outcrop these beds are as texturally variable as they are in the Thornley–Kelloe area, but in boreholes they are composed mainly of finely cross-bedded carbonate rocks of sand-grade and oolites, generally approaching dolomite in overall composition.

About 40 ft of thin-bedded, granular and finely granular calcitic dolomite are exposed in two old quarries [NZ 368 361] immediately north of Trimdon Grange, where bedding is thin, uneven and lenticular. Small scale cross-bedding has fore-set laminae dipping generally at less than 15° without noticeable preferred orientation. Recrystallization has produced a saccharoidal texture in most beds with grain size ranging from silt- to sand-grade. In another old quarry [NZ 3735 3613], some 500 yd farther east, about 12 ft of similar strata include thin oolitic beds and have incipient 'felted' texture. Cross-bedded, cream, granular and oolitic dolomite is exposed also in old quarries [NZ 383 359] and [NZ 383 358] 1250 and 1050 yd N. of Park House, Trimdon Colliery. At the south side of the latter quarry the oolite is coarse, and some individual bodies are of pisolith grade (>2 mm). The most westerly exposure of lagoonal beds is at Raisby Hill Quarry [NZ 340 350], where they form the uppermost 20 ft of the section (p. 111). A thin section (E29452) of flaggy rock from a small exposure [NZ 3523 3505] at the eastern end of this quarry is described by Dr. R. Dearnley as "a limestone of silt-grade consisting of a relatively homogeneous mass of calcite and dolomite grains (0.025 mm) ". This rock appears to be an altered oolite. D.B.S.

About 25 ft of dolomite are exposed in a quarry [NZ 361 353], 600 yd W.N.W. of The Grange; it has a predominantly 'felted' texture, but is otherwise like the rock north of Trimdon Grange. Similar 'felted' dolomite is 15 ft thick in a railway cutting [NZ 364 353] nearby, where fore-set cross-bedding laminae are preferentially orientated eastwards. Less highly recrystallized finely granular dolomite with small-scale cross-bedding is exposed in a small quarry [NZ 3704 3506] 430 yd E. of The Grange. About 60 ft of cream-buff calcitic dolomite, largely recrystallized, are seen in Grange Quarry [NZ 363 346], 600 yd S.W. of The Grange, where cross-bedding and other structures are indicative of an originally granular deposit. In thin section (E29927) this rock is seen to consist of a porous aggregate of silt-grade rounded and subhedral dolomite crystals (0.02 mm) with small quantities of interstitial calcite. Dips of up to 20° at the north end of Grange Quarry are probably related to the proximity of the Butterknowle Fault, some 200 yd to the north.

About 25 ft of yellow-buff granular calcitic dolomite, mostly thinly cross-bedded, is seen in a small quarry [NZ 3600 3392] 800 yd W.S.W. of Trimdon Cross Roads. This rock is lustre-mottled in hand specimen and appears to be undergoing dedolomitization. An unusual rock (E29926) occurs in patches on the west side of the quarry; it consists predominantly of an aggregate of equigranular, rounded and subhedral calcite grains of silt- and fine sand-grade, with a poikilitic calcite matrix and with large calcite porphyroblasts (up to 0.25 in diameter). Cross-bedding and wedge-bedding are ubiquitous in Harap Quarry [NZ 3554 3351], 1450 yd S.W. of Trimdon Cross Roads, where 30 ft of granular, oolitic and pisolitic calcareous dolomite and dolomite limestone are to be seen. Some beds contain a mixture of pisoliths and ooliths, many of the former being very irregular. In thin section (E29924) the shells of ooliths and pisoliths are seen to be almost pure fine-grained calcite while the interiors are either empty or contain sparry calcite, which also fills most of the interstices. Some ooliths and pisoliths are seen also in a 35-ft section of mainly thin-bedded fine-grained rock exposed in an old quarry [NZ 361 336] 600 yd E. of Harap Quarry.

A number of the old quarries in the ridge west of Trimdon contain calcitic dolomites similar to those at Harap Quarry. Massive granular dolomite, 12 ft thick, is exposed at the Hare and Hounds cross-roads [NZ 3323 3401], and a similar thickness is seen in an old quarry [NZ 3397 3395], 750 yd farther east, where the dolomite is extensively recrystallized, and where many pisoliths have been removed by solution. Garmondsway Moor Quarry [NZ 349 333], 900 yd S.E. of the cross-roads, contains 35 ft of well-bedded calcareous dolomite, parts of which have a coarse saccharoidal texture. About 12 ft of fine-grained dolomite are exposed in a small quarry [NZ 3473 3331] 900 yd farther east where thin interbedded layers contain excellent examples of a mixed oolith/pisolith assemblage, with many multiple ooliths and with a matrix of sparry calcite. These and all other beds exposed west of Trim-don are near the base of the Middle Magnesian Limestone.

East of Trimdon, an old quarry [NZ 3772 3336], 800 yd W. of Trimdon East House. contains 15 ft of massive silt-grade saccharoidal calcitic dolomite. Sections measured in Cope Hole Quarries, 200 to 400 yd W. of Trimdon East House, include up to 35 ft of compact to porous granular limestone, with cross-bedding and with scattered ooliths. In thin section (E29925) it can be seen that the rock consists of about 60 per cent uniformly sized ooliths and pseudo-ooliths with cores and matrix of sparry calcite. Farther east a number of boreholes through thick drift prove the eastward continuation of thick predominantly oolitic dolomites succeeded by predominantly granular non-oolitic beds. Approximately 240 ft of the lagoonal Middle Magnesian Limestone were penetrated in the Cotefold Close Bore, 430 yd S.S.E. of Pudding Poke, and 270 ft were met in the Fifty Rigs Plantation Bore, 1070 yd N. of Sheraton Grange (Woolacott 1919a, p. 165). Lamellibranchs including Bakevellia ceratophaga are recorded by Trechmann (in Woolacott 1919a, p. 164) from the lower part of the subdivision in the latter bore: recently they have also been found in equivalent beds in a water borehole, 100 yd W.N.W. of the Cotefold Close Bore. The transitional beds at the base of the division in the water bore are 55 ft thick, and consist of hard fine-grained dolomite and dolomitic limestone.

Mainsforth to Bishop Middleham

A belt of disused quarries, trending north-north-westwards for a distance of about 2000 yd from the east end of Bishop Middleham, is traversed by a fault-zone adjacent to which the beds are hardened and dedolomitized, giving rise to a prominent ridge. About 60 to 70 ft of beds similar to those west of Trimdon are exposed in the quarries. They are predominantly well bedded, granular dolomitic limestones and calcitic dolomites, with abundant traces of cross-bedding and with prominent beds and lenses of coarse oolite or pisolite. As at Trimdon, Haswell and elsewhere, some pisoliths are of bizarre form, and occur in a matrix of ooliths, but unlike those of Haswell and Wheatley Hill they are found in layers displaying current-bedding. Pockets of incoherent silt-grade dolomite and patches of dolomite with 'felted' textures are scattered throughout the quarries. The lowest beds in these quarries lie in the transitional zone at the base of the division.

Beds from the same part of the succession as the quarries are also seen in a number of smaller exposures near Bishop Middleham: old quarry [NZ 3447 3200], 560 yd N.N.E. of East House, 6 ft; west bank of stream [NZ 3480 3137], 630 yd E.S.E. of East House, 12 ft; valley side [NZ 3334 3154], 950 yd W. of East House, 18 ft; excavation [NZ 3334 3003], 1920 yd S.S.W. of East House, 12 ft; excavations [NZ 3345 3013], 1770 yd S.S.W. of East House, 6 ft; valley side [NZ 3275 3035], 2090 yd S.W. of East House, 5 ft; and old quarry [NZ 327 318], 650 yd E. of Hope House, 15 ft. A borehole [NZ 3282 3186] in the floor of the last-named quarry proved 37 ft of dolomite and dolomitic limestone before reaching Lower Magnesian Limestone. The uppermost 7.5 ft of this 37 ft were of lagoonal facies, the rest falling into the transitional beds. Another borehole [NZ 3030 3091], 390 yd N.W. of Chilton East House, penetrated 60 ft of Middle Magnesian Limestone, including 30 ft of lagoonal facies. Lagoonai beds are also proved in a number of boreholes in the Rushyford–Sedgefield area.

Fishburn, Sedgefield and Embleton

In this area, where exposures are uncommon, lithologies are similar to those described from the Trimdon area, though oolitic rocks appear to be less common. About 25 ft of hard well-bedded and fine-grained dolomitic limestone are exposed in an old quarry [NZ 367 326], 350 yd S.S.E. of Hope House, and traces of cross-bedding are preserved at the west end of the quarry. Cross-bedding is also apparent in 12 ft of yellow, hard, massive, and extensively brecciated limonitic limestone exposed in a railway cutting [NZ 3620 3182] east of Fishburn Colliery. A similar thickness of massive limonitic calcite rock of silt-grade is exposed in another cutting [NZ 3578 3163], 460 yd N.N.E. of Lizards. The most southerly exposure in this area is in an old quarry [NZ 350 309], 730 yd W.S.W. of Lizards, where over 25 ft of yellow thin-bedded compact dolomitic limestone occur. G.D.O., D.B.S.

The Middle Magnesian Limestone has been completely cored only in a few of the coalfield boreholes drilled in the area east of Fishburn and Sedgefield. The sequence is similar to that met in boreholes east of the Trimdons, consisting of up to 210 ft of essentially granular barren dolomites overlying 100 to 300 ft of oolitic, pseudo-oolitic and pisolitic dolomites which are shelly towards the base. In a borehole [NZ 4157 3054] at Tinkler's Gill, 910 yd N.N.W. of Embleton Church, the lower 50 ft of the 210-ft division yielded numerous lamellibranchs including Astortella vallisneriana, Schizodus obscurus (J. Sowerby) and species of Bakevellia. Transitional beds in this bore appear to be only about 2 ft thick. From several boreholes between Sedgefield and Embleton, Mr. A. Fowler has obtained the most complete fauna yet collected from the lagoonal beds of the Middle Magnesian Limestone. The faunal list (quoted in full on pp. 173–6) includes brachiopods such as Horridonia, Neochonetes? and Strophalosia, together with polyzoa previously thought to be confined to rocks of reef-facies, and Tubulites permianus. A specimen of rock from a depth of 300 ft (about 30 ft above the base of the division) from Ten-o'-Clock Barn No. 2 Bore [NZ 3916 3035], Fishburn, has been analysed by G. A. Sergeant (Lab. No. 1456), with the following result (figures in percentages): SiO₂ 0.32, Al₂O₃ 0.16, Fe₂O₂ 4.27, FeO nil, MgO 16.04, CaO 33.84, Na₂O 0.02, K₂O 0.01, H₂O+105° 0.90, H₂O 105° 025, TiO₂ nil, P₂O₂ 0.01, MnO 0.30, CO₂ 43.87, SO₃ 0.12, Cl trace, F trace, FeS₂ 0.07, C 0.02, Ba calculated as BaSO4 0–47, total 100–67. A suggested mineral composition for this rock is dolomite 73.7 per cent, calcite 20.0 per cent and limonite 5.4 per cent. In thin section (E21052) it is seen to be composed of pseudoooliths which have outer rims of heavily pigmented dolomite and cores of sparry calcite; the matrix is of fine-grained dolomite with abundant limonite. D.B.S.

Elwick, Naisberry and West Hartlepool

Thick drift covers most of this area, but Permian beds of lagoonal facies crop out near Naisberry at two localities. One is an old quarry [NZ 477 333], 650 yd S.E. of Naisberry Farm, where there are about 20 ft of cross-bedded granular and oolitic dolomitic limestone. Thin sections (E29917), (E29918), (E29919), (E29920), from these beds are of highly recrystallized oolitic and pseudo-oolitic calcarenite, with a matrix of sparry calcite, which also forms the cores of many ooliths. Some non-oolitic beds are of crystalline silt-grade limestone (sometimes dolomitic), with a matrix of poikilitic calcite. About 15 ft of bedded dolomitic limestone are exposed in the other quarry [NZ 4749 3330], 430 yd S.E. of Naisberry Farm. G.D.G., D.B.S.

Water boreholes, 610 yd W. of Naisberry Farm, penetrated an interbedded sequence of calcitic dolomites of reef and lagoonal facies, representing a zone of interdigitation on the landward side of the reef. Upper strata in these boreholes are comparable with those exposed in Hesleden Dene, with alga-laminated beds overlying about 12 ft of bedded granular and oolitic dolomite of lagoonal facies containing debris of stunted shells (mostly lamellibranchs and gastropods). These beds are underlain by about 85 ft of bedded and massive shelly and polyzoonal dolomite of reef facies, which pass down by interdigitation into 155 ft of cross-bedded granular, oolitic and pisolitic dolomites similar to those cropping out in the Trimdon area. About 45 ft of transitional beds lie at the base of the division at this locality. Six boreholes around Dalton Piercy waterworks [NZ 465 315] penetrated a maximum thickness of 300 ft of predominantly oolitic dolomite, in which a fragment of Astartella vallisneriana was noted 30 ft above the base of the division. This form together with Streptorhynchus pelargonatus, species of Permophorus, Bakevellia (especially B. ceratophaga) and Schizodus, is found also at a similar horizon in the Dalton Nook Plantation Bore one mile farther east, and is recorded in Elwick No. 1 Bore, 995 yd S. of Elwick Church. A somewhat richer fauna, including lamellibranchs, polyzoa and foraminifera, was met in the Middle Stotfold Bore.

In the partially cored Dalton Nook Plantation and Low Throston bores and also in a bore [NZ 4473 5276] 2 miles S.S.E. of Dalton Piercy there appears to be no clear lithological break at the base of the Middle Magnesian Limestone. In the bore south-south-east of Dalton Piercy the upper part of the lagoonal dolomites contains several beds of anhydrite which may be extensions from the thick Hartlepool Anhydrite, the main mass of which lies in the basin 2 to 3 miles to the east. Farther south, anhydrite becomes increasingly abundant and in a bore at Norton, 4 miles south of Embleton, in the Stockton (33) district, it forms the bulk of the lagoonal deposits, together with subordinate beds of dolomite and red mudstone. D.B.S.

Reef facies

Dolomites and dolomitic limestones of reef-facies crop out in a sinuous belt (Plate 5) extending south-south-eastwards from near Murton to West Hartlepool, although for much of this distance drift is thick and the reef is known only from boreholes and scattered exposures in deep quarries and ravines. In the West Hartlepool area the reef is overlapped by basinal beds of the Middle Magnesian Limestone and by higher strata.

Murton to Cold Hesledon

The most northerly outcrops of reef-limestone in this area are found in a cutting [NZ 408 477] on the Murton to Easington road, 800 to 1000 yd N.N.W. of the Water Works, New Hesledon, where A. canthocladia anceps, Fenestrellina retiformis, Stenoscisma schlotheimi, ?Strophalosia morrisiana, Bakevellia ceratophaga and Pseudomonotis speluncaria were collected from hard massive calcitic dolomite. Similar rock is exposed [NZ 4082 4767] slightly farther up the hill side in an old quarry and yielded: ‘Adhaerentina’ permiana; Acanthocladia?, Batostomella crassa, Fenestrellina retiformis; Dielasma elongatum, D. elongatum sufflatum (Schlotheim), Orthothrix excavata; Bakevellia antiqua, B. ceratophaga, Pseudomonotis speluncaria; Peripetoceras freieslebeni; and ostracods.

Stromatolitic structures occur throughout the rock in the cutting and the quarries, and a number of extensive steeply inclined stromatolite sheets are also present. Much of the shell debris is highly comminuted.

At the time of the resurvey a rich fauna of polyzoa, brachiopods, gastropods and lamellibranchs was collected from Fox Cover Quarry [NZ 426 478], 700 yd N.W. of Hesledon East House, where poorly bedded reef-dolomites, 80 ft thick, are now obscured by urban waste. Fossils identified include: algal filaments; 'Adhaerentina' permiana; Eudea tuberculata King; crinoid stems; Acanthocladia anceps, Batostomella crassa, Fenestrellina retiformis, Synocladia virgulacea, Thamniscus dubius; Dielasma elongatum, D. elongatum suffiatum, Horridonia horrida, Orthothrix excavata, Spiriferellina cristata (Schlotheim) multiplicata (King), Stenoscisma globulina (Phillips), S. schlotheimi, Strophalosia morrisiana; Naticopsis cf. leibnitziana (King), gastropod with three whorls in low-angled spire and numerous fine spiral striae; Bakevellia antiqua, B. aff. antiqua [beak almost in centre of hinge line], Palaeolima?, Parallelodon striatus, Permophorus costatus, Pseudomonotis speluncaria, Schizodus?; ostracods. The reef-rock in this quarry appears to be naturally disposed in a number of large, mutually interfering, dome-shaped bodies, some of which are over 60 ft high and as much in diameter. Dips on the flanks of such bodies measure up to 85°, and appear to be primary. Spaces between the domes are filled by rubbly reef-detritus, consisting largely of shell-debris, with local coarse breccias of penecontemporaneously eroded reef-rock.

An analysis of a specimen of fossiliferous rock from this quarry (Woolacott 1912, p. 264) shows it to contain 58.02 per cent CaCO₃ and 38.33 per cent MgCO₃. At the south-east corner of the quarry a 50-ft cleft filled with carbonate sands and breccias of derived reef material appears to be an infilled reef-channel.

Dolomitized limestones of reef facies crop out in a railway cutting [NZ 418 473], 1350 yd W. of Hesledon East House, where three distinct sub-facies are recognized. The first is a massive shelly reef-rock similar to that in Fox Cover Quarry: it is exposed at the north-eastern end of the cutting and contains: algal pellets and filaments; Acanthocladia anceps, Fenestrellina retiformis; Dielasma elongatum; indet. gastropods; Bakevellia ceratophaga, Pseudomonotis speluncaria; and ostracods. The second fades is represented by roughly horizontal and southwestwards dipping bioclastic dolomite, with interbedded alga-laminated sediments and lenses of granular, oolitic and pisolitic dolomite. These deposits yielded Acanthocladia anceps, Dielama sp., indet. gastropod and Parallelodon striatus. The third facies, exposed at the southwestern end of the cutting, is a dolomite composed of a confused mass of mutually interfering small (up to 3 ft diameter) irregular algal colonies (Smith 1958, pl. vib) with interstitial pockets of contemporaneous breccias composed of alga-laminated fragments and algal? pellets. A sparse shelly fauna consisting chiefly of small gastropods and rolled crinoid columnals occurs in parts of this rock, which appears to represent a local backreef deposit. In a lane [NZ 4136 4740], 500 yd W. of the railway cutting, temporary exposures through 4 ft of unbedded cream reef-dolomite contained a rich fauna of polyzoa, brachiopods, gastropods and lamellibranchs. Deep subsidence cracks [NZ 4220 4735] some 400 yd E. of the cutting reveal dolomite composed entirely of an assemblage of small (less than 1 in) concentrically laminated algal bodies. The remaining exposure of reef-facies in this area comprises 8 ft of finely laminated crystalline dolomitic limestone in a small quarry [NZ 4148 4695], 450 yd S.W. of the railway cutting. The laminae are broadly undulant and in part closely crenulated, and appear to be of algal origin.

East of Cold Hesledon, boreholes have proved a maximum thickness of over 100 ft of massive reef-facies dolomite containing a limited fauna of small brachiopods (chiefly Dielasma), gastropods and small lamellibranchs with a few retiform and straggling polyzoa. Fossils identified from this bed in three of the holes include: algal filaments; ?Acanthocladia an-ceps, Batostomella crassa, Fenestrellina retiformis; Dielasma elongatum, Orthothrix cf. lewisiana (de Koninck), Spirifereilina cristata multiplicata, Strophalosia morrisiana; Naticopsis leibnitziana; ?Pseudomonotis speluncaria; and ostracods. In two of the holes [NZ 4206 4607]; [NZ 4249 4656] shelly reef-limestone was overlain by irregularly laminated dolomite in which algal structures have been recognized in thin section (E26238) and (E26239). It is probable that in other bores of this group original alga-lamination has been obscured by recrystallization. In five of the bores the shelly reef-rock is overlain by granular and oolitic bedded dolomite which is interbedded with alga-laminated dolomite in the lower part. These interbedded deposits form part of the lagoonal sequence, but beds above the uppermost algal intercalations are regarded as lagoonward extensions of post-reef basinal deposits.

Hawthorn

Dolomite of reef facies crops out in Hawthorn Quarry [NZ 437 463], and in the eastern part of the valley of Hawthorn Burn. The former is the only quarry still operating near the Durham coast, and is cut into about 80 ft of reef and superincumbent granular calcitic dolomite. Reef-facies dolomite forms the lower 30 to 35 ft of the main quarry face, and is a hard, irregularly thick-bedded or massive rock, with scattered poorly preserved fossils, generally similar to those seen in the Cold Hesledon boreholes. They include: 'Adhaerentina' permiana, 'Glomospira' gordialis; Acanthocladia anceps, Batostomella crassa, Thamniscus dubius; Dielasma elongatum, D. elongatum sufflatum [(Plate 6), figs. 4, 5], Orthothrix cf. excavata; Stenoscisma schlotheimi, Strophalosia morrisiana, Naticopsis sp., Omphalotrochus thornsonianus, Straparollus sp.; Bakevellia antiqua, B. ceratophaga, Liebea squamosa (J. de C. Sowerby), Permophorus sp., Pseudomonotis speluncaria; and ostracods. The uppermost reef-limestones are irregularly alga-laminated, the laminae at some exposures showing marked small-scale asymmetric crenulations resembling current ripple-marks. The approximately horizontal bedding in the uppermost part of the reef in the main quarry is interrupted in a small neighbouring quarry [NZ 4366 4642], now filled, by a number of prominent dome structures. The largest of these is about 50 ft in diameter and 20 ft high, and has a massive apparently structureless core overlain by alga-laminated deposits similar to those in the main quarry. Dips on the flanks of this and other domes reach 70 to 80°, and are thought to be primary. The top of the reef persists as a relatively flat plane throughout the small quarry and all but the eastern end of the main quarry, where the outer shoulder of the reef is seen trending north-north-west-wards and where bedded reef-flat dolomites grade laterally into steeply-dipping massive beds of the reef-front. The north face of the main quarry is now largely obscured, but formerly individual horizontal beds deposited on the reef-flat could be seen to pass over the reef-crest and thicken rapidly (Plate 9) before dipping at angles of up to 80° down the seaward side of the reef. A fault-zone, reversed at the surface but normal in underlying coal workings, lies parallel with the reef-crest and truncates the most easterly beds of the reef-front (equivalent to the highest beds of the reef-flat). Analyses of the reef-rock, though variable, show it to be a calcitic dolomite, with about 28 per cent MgCO₃, but evidence of extensive dedolomitization was noted.

A short distance to the south, dolomitic reef-limestones are continuously exposed for about 300 yd in Hawthorn Burn [NZ 436 458]. Pockets in the limestones contain varied and abundant faunas comparable in age with that obtained from off-reef beds at Chourdon Point (p. 145), but older than that found in Hawthorn Quarry. The easternmost exposure is in the south bank of the stream, and takes the form of a number of small (3 ft to 6 ft high) mutually interfering domes each composed of a complex of hard smaller rounded masses of dense reef-rock up to about 9 in across. These masses appear to be piled haphazardly, and may represent contemporaneously eroded material accumulated on the reef-front slope. Each mass is enveloped by laminated stromatolitic dolomite, and irregular sheets of similar material ramify throughout and around the domes. Pockets of detritus, some with much shell material, occur between the domes.

This type of lithology continues upstream, but bedding gradually becomes more distinct and regular until, at the western end of the outcrop, the reef-rock is relatively evenly bedded, has only a few low domes and contains a more varied and abundant fauna. Here the following were collected from an outcrop [NZ 4338 4575] on the south bank of the Burn, 890 yd upstream from the mouth: 'Adhaerentina' permiana, 'Glomospira'pusilla; Acanthocladia anceps, Thamniscus dubius; Dielasma elongatum, Stenoscisma? [juv.]; Bakevellia antiqua, B. ceratophaga; ostracods. The proportion of stromatolitic material remains roughly constant, at 30 to 50 per cent, to about 700 yd upstream from the railway bridge, but thereafter decreases progressively westwards. It is still, however, an important constituent of the rock at the western end of the outcrop.

Easington Colliery

The steep outer face of the reef runs southwards from Hawthorn Quarry and, except around Shippersea Bay, lies a short distance west of the railway line. The hard dolomitic limestone and dolomite of the reef-wall give rise to a marked topographical feature, and have been quarried on a small scale at several localities between Hawthorn Burn and Easington Colliery. The most northerly exposures [NZ 4381 4579] are in and around a footpath on a wooded slope, 450 to 490 yd N.N.W. of Beacon House, where a few feet of hard dolomite contain a fauna characteristic of a fairly late stage of the period of reef growth, and include: 'Adhaerentina' permiana, 'Glomospira'gordialis; Acanthocladia anceps, Fenestrellina retiformis, Thamniscus dubius; D. elongatum, especially D. elongatum sufflatum; indet. gastropods; Bakevellia cf. antiqua, Pseudomonotis speluncaria; and ostracods. Shells and shell debris make up a high proportion of the rock, but the number of species is relatively small. Some shells have thin concentrically laminated stromatolitic envelopes. Stromatolitic material in the form of closely packed concentrically laminated bodies forms most of the hard dolomite exposed in a small excavation [NZ 4395 4564], 180 yd N. of Beacon House, and several larger sheets of laminated stromatolitic dolomite similar to those in the bed of Hawthorn Burn also occur. Some polyzoan and shelly material was also noted. Similar dolomite from the reef-flat sub-facies, near the top of the reef and about 150 yd west of the reef-crest, is found in a small overgrown quarry [NZ 4407 4539], 50 yd E. of Beacon House. Specimens from this quarry contain the remains of algal colonies resembling Girvanella, Ortonella and Bevocastria (F. W. Anderson in Smith 1958, p. 81, pl. viii). Many excellent examples of stromatolitic structures from the same locality are seen in the walls of Beacon House and around adjacent fields.

Massive steeply dipping beds of the outer reef-slope, equivalent to those 50 yd E. of Beacon House, form 80-ft faces on the west side of the Beacon Hill railway cutting. As at the eastern side of Hawthorn Quarry, primary dips commonly reach 70°, and the beds are arranged in a series of massive, confluent, asymmetrical domes in which the main convexity is eastwards. Many domes are defined by extensive thin steeply dipping sheets of laminated dolomite of algal origin. Towards the base of the cutting these become progressively less common and the proportion of detrital shelly reef-talus increases. Small pedunculate brachiopods are common throughout the cutting, but deeper water forms such as crinoid columnals and retiform polyzoa are abundant only at lower levels. From these lower levels the following have been identified: 'Glomospira'milioloides, 'G.' pusilla; crinoid stems; Miocidaris keyserlingi (Geinitz); Acanthocladia anceps, Batostomella crassa, Fenestrellina retiformis, Thamniscus dubius; Dielasma elongatum, Orthothrix excavata, Spiriferellina cristata multiplicata, Stenoscisma schlotheimi, Strophalosia morrisiana; Omphalotrochus sp.; Bakevellia antiqua [juv.], B. aff. ceratophaga, Parallelodon striatus, Pseudomonotis speluncaria, Streblochondria pusilla; and ostracods. Because the original dip of the beds exceeds the slope of the exposure, beds near the base of the Beacon Hill cutting are younger than those at the top. The high dip clearly continues in depth, for 100 ft below the floor of the cutting and 50 yd to the east, bedded brecciated reef-top alga-laminated dolomites are seen at the foot of the cliffs at the western end of Shippersea Bay. These brecciated beds are overlain by an interbedded sequence of crossbedded dolomitic oolites and alga-laminated dolomites, the highest of which is conspicuously laminated and locally contains complex algal growths or is broken down into a mass of large stromatolitic cobbles similar to those of Hawthorn Burn (p. 134). Because of the high degree of recrystallization, brecciation and small-scale faulting, these highest reef-beds can be traced north of Beacon Point for only about 250 yards. Southwards, though still highly recrystallized and brecciated, they can be traced for about half a mile until they pass beneath beach-level some 120 yd S. of Shot Rock. From the evidence of the exposures described above, the reef-limestone must here exceed 250 ft in thickness. A borehole [NZ 4405 4542], 80 yd E.N.E. of Beacon House, penetrated dolomitic reef-limestone to 202 ft without reaching the base.

About 15 ft of irregularly bedded, largely algal dolomite of reef-flat sub-facies is exposed in an old quarry [NZ 4371 4504], 450 yd S.W. of Beacon House. Small steep-sided domes, up to 4 ft diameter, break the roughly level bedding, and some thin beds and lenses contain algal pisolitic pellets similar to those described from Silksworth (Smith 1958, pl. vi). A limited fauna of small polyzoa, pedunculate brachiopods and small lamellibranchs occurs in irregular pockets between the domes. Fossils identified from here are Acanthocladia anceps and Bakevellia ceratophaga. About 15 ft of similar bedded reef-limestones are exposed in an old quarry [NZ 4390 4473], 300 yd W. of White Lea. Small gastropods (Omphalotrochus sp.) are additional to the fauna noted above, but algal pellets appear to be absent.

The most complete exposures of reef-limestone are in the sides of tunnels driven east and west from Easington Colliery shafts and of an inclined adit linking these to the surface (Figure 21). For most of its length the tunnel west of the shafts penetrates gently undulating, sparsely fossiliferous, bedded, soft cream dolomite belonging to the transitional beds at the base of Middle Magnesian Limestone. These are about 50 ft thick and show a gradual upwards enrichment in fossil content before passing into a cream friable and highly altered dolomite which forms the sides of the tunnel from 240 to 25 yd west of the West shaft. Least altered parts of this rock, which appears to be 30 to 50 ft thick, are composed of shelly reef-talus with an easterly dip of 5° to 10°. Shells, amongst which Horridonia horrida is especially common, are most numerous near the base and are progressively less abundant in higher parts. A full faunal list is given on pp. 169–70. The reef-talus is overlain, immediately west of the West shaft, by collapse-brecciated post-reef dolomite.

The coquina at the base of the reef is particularly well exposed at about 65 ft O.D: (a on (Figure 21)) in the inclined adit, where it is a poorly bedded, buff, friable dolomite containing an abundant and varied fauna of crinoids, polyzoa, brachiopods, gastropods and lamellibranchs. The dominant polyzoans are cryptostomatous, and the most common brachiopods are species of Horridonia, Stenoscisma and Spiriferids (see list, p. 169). Successively younger parts of the reef are exposed towards the mouth of the adit. Above the coquina there is a thinly bedded, bioclastic, dolomitic calcarenite (b on (Figure 21)) in which few shells are preserved intact, and this is succeeded (c on (Figure 21)) by vaguely-bedded friable dolomite similar to the coquina (a) with the exception that Productid and Spiriferid brachiopods are less common. At a still higher level (d on (Figure 21)) the tunnel passes through unbedded hard cream-brown dolomite with a fairly rich fauna dominated by retiform and straggling polyzoa, small brachiopods (especially species of Dielasma and Stenoscisma) and lamellibranchs (especially Pseudomonotis speluncaria). This fauna is closely comparable with that found in Fox Cover Quarry, New Hesledon, and in the lowest part of Hawthorn Quarry. From there to the surface the rock remains generally hard, and the fauna differs only in consisting of fewer and smaller individuals. The main feature of this section (e) of the adit is that the rock is divided into panels 5 to 30 ft long by sinuous, steeply dipping (usually about 80°), thin, laminated sheets of algal origin similar to those noted in the railway cutting east of Beacon House and in Hawthorn Quarry. In thin section (E29445) one of these sheets is seen to be a cal citic dolomite of silt-grade with a poikilitic calcite matrix and obscure traces of indeterminate organic structure. The dip of the laminated sheets is maintained at 80° to 85° until, about 27 yd from the adit mouth, it is reduced to about 45°. In the last 27 yd of the adit parts of the massive dolomite are collapse-brecciated and fragments of soft red and green marl are included.

Brecciated rocks are seen also in an old quarry [NZ 4355 4417] on the hillside immediately above the adit, where about 60 ft of limestone and dolomitic limestone dip eastwards at about 60°. Although this high original dip is characteristic of beds of the reef-front in this area, this rock cannot with certainty be recognized as part of the reef because advanced recrystallization and brecciation have obliterated all but major structures.

Easington

Dolomite of reef facies (faunal lists, pp. 170–1) lies between barren post-reef beds and lagoonal dolomite in the Mill Hill Bore, Easington. From the high proportion of alga-laminated material, the limited and generally stunted fauna and the presence of beds of bioelastic and oolitic dolomite, it is concluded that the reef-rock was formed during the last stages of reef formation near the edge of the lagoon. The section is:

Three old quarries are cut into reef-limestone on the east side of Townfield Hill, Easington Colliery, midway between the Cemetery and Paradise. The most northerly, Townfield Quarry [NZ 4343 4380], contains about 25 ft of hard, horizontal, irregularly-bedded alga-laminated dolomite similar to the uppermost part of the reef exposed in Hawthorn Quarry, with the exception that none of the domes exceeds 2 to 3 ft in diameter. Several lenses and pockets of pene-contemporaneously brecciated algal sheets and pisoliths were noted in the south-west corner and pockets containing many lamellibranchs and gastropods occur throughout the quarry. Fossils identified from here are: cryptostome polyzoa; Dielasma elongatum sufflatum, Orthothrix sp., Stenoscisma schlotheimi; Omphalotrochus taylorianus, O. thomsonianus, Strobeus geinitzianus (King); Bakevellia ceratophaga, Liebea squamosa, Parallelodon striatus [(Plate 6), fig. 7], Pseudomonotis speluncaria, Schizodus truncatus. Some 15 ft of similar dolomite in a small quarry [NZ 4356 4356] at the south end of the hill appear to be slightly higher in the reef-flat sequence than the beds in Townfield Quarry from which they differ in containing a higher proportion of crenulated alga-laminated material and fewer fossils. The latter include: cryptostome polyzoa including Fenestrellina retifonnis; Orthothrix excavata; Bakevellia anti qua, B. ceratophaga. In the third old quarry [NZ 4355 4373], midway between the other two, similar flat-lying sheets of sinuous laminated, fine-grained reef-dolomite is seen to pass over the reef-crest, becoming thicker and steepening to 70° at the quarry floor. Roughly bedded, brecciated and recrystallized dolomitic limestone dips eastwards at about 40° off the steeper reef-face. Rocks in this quarry have yielded: Batostomella crassa, Fenestrellina retiformis, Thamniscus dubius; D. elongatum sufflatum, Orthothrix excavata; Bakevellia cf. antiqua, Liebea squamosa; ostracods. Post-reef oolitic dolomite crops out at a slightly higher level, 250 yd S.W. of the middle quarry.

Horden to Castle Eden

The reef forms a ridge which can be traced southwards from Townfield Quarry almost to Castle Eden Burn, but it is exposed only at two localities. One [NZ 4315 4176] is on the top of the ridge on the site of the Saxon village of Yoden, now Peterlee, where a largely overgrown quarry contains irregularly laminated algal dolomite of reef-flat sub-facies. There is a wide variety of minor algal growth forms here and several examples of contemporaneous breccias (Plate 10B) composed of fragments of algal material which have been welded together by later algal growth. No shells were noted in this quarry. The other exposure [NZ 4354 4172], on the eastern slope of the ridge, resembles the section in the middle quarry of Townfield Hill, and comprises level thinly bedded, largely algal dolomite of reef-flat type passing abruptly into massive, steeply dipping dolomites of the reef-front. Parts of this rock are abundantly fossiliferous, and have yielded: 'Adhaerentina' permiana, 'Glomospira' sp.; Acanthocladia anceps, Batostomella crassa, ?Polyzoan ?Gen, et sp.nov.[see note on p. 181]; Dielasma elongatum; Naticopsis sp., Pleurotomaria?; Bakevellia antiqua, B. ceratophaga, Liebea squamosa, Pseudomonotis speluncaria; ostracods. A thin section (E29512) of a specimen from this quarry is a calcitic dolomite consisting mainly of dolomite grains (010 mm) together with very finely recrystallized areas replacing foraminifera, shell-fragments and pseudo-ooliths (? calcispheres). An old quarry [NZ 4347 4127], 620 yd E. of Little Eden, is now filled, but in 1947, Mr. G. D. Mockler saw 12 ft of mainly hard, compact, yellow, oolitic limestone with scattered shells. The adjacent farmhouse is built partly of dolomitic algal limestone similar to that in the quarry at Yoden. Cream dolomite with a sparse fauna corresponding to a position high in the reef sequence was temporarily exposed [NZ 4363 4054], 1050 yd S.E. of Little Eden.

Dolomites of reef facies overlie lagoonal beds (p. 126–7) in the valley of Castle Eden Burn, dipping eastwards from Seven Chambers [NZ 431 394], where they are high and inaccessible. Throughout the Seven Chambers sector the broadly undulate base of the reef dips gently eastwards and the rock is irregularly bedded in thick, massive units. In the cliffs at White Rock [NZ 4350 3963] 6 ft of thin- and medium-bedded dolomite separate a lower 15 ft and an upper 6 ft of thickly-bedded rock. All three units are composed of dense, cream-grey, finely crystalline dolomite containing much comminuted shell-debris and a sparse fauna of polyzoa, gastropods and lamellibranchs (especially Schizodus and Permophorus). At Ivy Rock [NZ 435 396] most of the cliff section is composed of cream porous reef-dolomite, containing a restricted fauna of lamellibranchs and gastropods in a crystalline matrix with much comminuted shell debris: a list of fossils collected at this locality is given by Trechmann (1913, pp. 215–6). The lowest 40 ft of the section are massive or very vaguely bedded, and locally brecciated, but the uppermost 10 ft are thickly and irregularly bedded, and where better exposed, some 100 yd E.N.E. of Ivy Rock, are seen to contain low irregular domes, up to 2 ft high and 9 ft in diameter, of the type previously described in the Easington Colliery area (p. 138). The domes can be traced eastwards for a short distance, but most of the cliff section as far as Craggy Bank [NZ 4376 3982] is formed by the lateral equivalent of the main part of the Ivy Rock section—cream, porous dolomite which becomes harder, more massive and, possibly, thicker. At Craggy Bank the fauna, which is dominated by small gastropods and lamellibranchs with subordinate polyzoa and small brachiopods, includes: Acanthocladia?, Fenestrellina retiformis, Thamniscus?; Orthothrix excavata, Stenoscisma sp. [juv.];Omphalotrochus sp., Pleurotomaria linkiana King, a turreted gastropod; Bakevellia sp. [juv.], Parallelodon striatus, Pseudomonotis speluncaria. The fauna becomes more varied eastwards and at a small exposure [NZ 4387 3985], 120 yd E.N.E. of Craggy Bank the reef-rock is composed largely of shells and shell-debris, and has yielded: coiled tubular foraminifera; Batostomella crassa, Fenestrellina retiformis, Synocladia virgulacea; Dielasma sp., Orthothrix spp.[including O. excavata but there is a great variety of forms, the broader ones approaching O. lewisiana];gastropods including ?Naticopsis minima; Bakevellia antiqua, Pseudomonotis speluncaria; ostracods. This, the most easterly exposure of reef facies in the Dene, probably lies close behind the reef-front. The highest parts of the reef are not exposed in the Dene, but are seen in a number of small diggings and an old quarry in a wood, 300 yd N.N.W. of Dene Leazes. Here, horizontal, thinly bedded alga-laminated dolomite lies about 200 ft higher than the lowest reef-rocks exposed at Seven Chambers, 350 yd to the north-west. Similar algal beds are exposed in a railway cutting [NZ 455 400], N.W. of Blackhall Colliery Station, where they are arranged in a series of flat-topped domes and are overlain by an interbedded sequence of algal and partly oolitic non-algal dolomites.

Hesleden

Dolomites of reef facies crop out extensively in the sides of the valley south of Hesleden and its eastward extension, Crimdon Beck. They are mostly well bedded and are probably largely or wholly younger than those exposed in Castle Eden Dene. The westernmost outcrops are cliffs [NZ 435 378] on both sides of the valley, 780 yd W. of Hesleden Station, where the section is:

The lowest member of the section is poorly exposed, but appears to be mainly of algal reef-dolomite with markedly undulate bedding. The overlying bed (p. 128) is of lagoonal facies. The uppermost member is of dolomite in which algal laminae are flat, slightly undulate or crinkled. 'Cryptozoon'-type algal domes up to 3 ft diameter are particularly well exposed (Plate 11B) in low cliffs [NZ 4350 3784] on the south side of the stream and form complexes at several levels. Thin beds of granular non-algal dolomite are present in some exposures.

This sequence can be traced downstream for a distance of about 1550 yd before passing below stream level, the maximum exposed thicknesses of the three units being 40 ft, 25 ft and 20 ft respectively. Over this distance, the uppermost unit changes progressively eastwards, as follows: the non-algal, granular dolomites interbedded with the laminated algal beds die out beyond a position 400 yd S.W. of Hesleden Station; the 'Cryptozoon'- type domes gradually diminish in size and complexity and eventually die out south of Hesleden; and the beds as a whole become more massive and homogeneous. In several places south and south-east of Hesleden these beds form prominent cliffs, and are finely laminated throughout, individual laminae being closely crenulated and exhibiting a wide variety of small-scale algal growth forms. It has not been established whether the laminated deposits are stromatolite-fixed granular sediments or are directly deposited by calcareous algae. They are regarded here as being of reef facies since lithification was clearly contemporaneous, although it is recognized that the reef-flat at the time of their deposition may have been only slightly submerged. No shelly fossils have been found in these beds.

The lowest member of the sequence is poorly exposed at several places near the base of the cliffs, but is well seen [NZ 4447 3773] on the north side of the stream, 400 yd E.S.E. of Hesleden Station. Here it is composed of thin- and medium-bedded cream granular dolomite, arranged in a series of compound domes which appear to originate from a single stratum at stream-level and rise to heights ranging up to about 20 ft. (Plate 10A). Fine alga-lamination is preserved in many of the least altered component 'beds'. Alga-laminated rocks are also interbedded with elastic shelly dolomite in depressions between the domes, which are spaced at roughly 25-foot intervals. The fauna is restricted to stunted lamellibranchs (especially Pseudomonotis speluncaria and Bakevellia spp.), small gastropods (including Naticopsis minima Brown [(Plate 6), fig. 8] and euryhaline brachiopods (especially Dielasma), and these forms also occur in small irregular pockets within the domes.

The top of the reef dips eastwards beneath interbedded algal and inorganic beds about 200 yd E.S.E. of the above exposure, and reappears in an anticline 1.5 miles downstream. The following generalized section was measured in a narrow gorge [NZ 4715 3705], 500 yd N. of Middlethorpe:

The section is directly comparable with that near Hesleden (p. 140), the middle member taking the place of the lagoonal shelly calcarenite. The domes in the lowest unit are most common in the lowest 10 to 12 ft; the uppermost 3 to 5 ft are more evenly bedded with fewer and flatter dome-structures, but with several rounded blocks of dense shelly dolomite which appear to be in or near the position of formation. The blocks forming the overlying conglomerate are of similar rock, but they seem to have been rolled and redeposited as a boulder bed at the reefshoulder. They consist of rounded cobbles and boulders up to about 1.5 ft in diameter, each of which has a stromatolitic envelope up to three-eighths of and inch thick. Interstices between the cobbles are partially filled with similar stromatolitic material, often contemporaneously brecciated, which in some cases encloses fossils and fossil debris including: 'Glomospira' pusilla; cryptostome polyzoa; Dielasma elongatum; Omphalotrochus sp.; Bakevellia antiqua, B. ceratophaga, Pseudomonotis speluncaria; Peripetoceras freieslebeni; ostracods. Traced south-eastwards for 100 yd within the gorge the conglomerate thins from 15 to 8 ft. It is thinner also towards the southwest where, at the foot of the railway embankment [NZ 4704 3705], it is no more than 2 ft thick. The lamination in the uppermost unit is finely crenulate throughout, but the beds themselves contain many minor domes similar to those near Hesleden. These domes are particularly well seen at a horizon about 18 ft from the top of the section and at the base where there is a complex of structures up to 5 ft high and 8 ft in diameter.

In Hesleden Dene No. 1 Bore [NZ 4672 3697] sunk in the valley floor west of the railway embankment, Trechmann (1942, p. 323) records drift on bedded dolomite to a depth of 58 ft and reef-limestones from 58 ft to the final depth of 230 ft. It is difficult to reconcile the sequences described above and on p. 140 either with the record given by Trechmann, or with samples collected from the cores by Mr. A. Fowler, but it seems probable that the fossiliferous bed (faunal list, p. 172) between 58 and 67 ft in the bore is the equivalent of the conglomerate in the section east of the railway embankment. Two other Hesleden Dene bores are mentioned by Trechmann (1954, pp. 203–4) and Fowler (1956, pp. 255–7). One [NZ 4660 3703], 160 yd W.N.W. of No. 1 Bore, penetrated cream granular bedded dolomite to a depth of about 190 ft, bedded and massive grey bioclastic calcarenite (faunal lists p. 173) with interbedded shaly siltstone bands to 231 ft, and granular and pisolitic beds to bottom of bore at 252.5 ft. The other [NZ 4654 3698], 200 yd W. of No. 1 Bore, cut grey bioclastic calcarenite between 232 and 272 ft and pisolitic beds from 272 ft to the bottom of the bore at 298 ft. A shelly assemblage (list, p. 172) remarkable for the paucity of polyzoan debris was collected by Mr. W. Anderson from between 246 ft and 257 ft. Correlation with adjacent surface exposures is again obscure, but it is probable that the place of true reef-limestone is taken in both bores by bioclastic carbonates of off-reef basinal facies. According to Trechmann (1942, pp. 313, 323) no reef-limestone was encountered at its expected position in the Thorpe Bulmer Bore, 1400 yd to the south-west.

Black Halls Rock

Bedded dolomites of reef facies are exposed for over 1500 yd in coastal cliff sections at Black Halls Rocks where the succession, resembling the upper part of the reef sequence in the Hesleden area, is as follows:

The reef dolomites are gently anticlinal, but the limits of outcrop are defined by normal faults which appear to be parallel with the original reef-front. The southern end [NZ 4763 3827] of the outcrop lies on the coast 780 yd E. of Black Halls, and is also seen in Cross Gill. In each case the junction with later conformable beds is steep (25° to 70°) and indicates the position of the reef-shoulder, which here trends about west to east. From Cross Gill the reef sequence rises gradually northward, the lowest horizons occurring in the core of the anticline on the foreshore at Black Halls Rocks. The northern limb of the anticline is less clearly seen, but reef rocks can be traced with difficulty through scattered poor exposures to the Blackball Fault which cuts the cliffs [NZ 4683 3939], 550 yd N. of Blackhall Rocks station. The lowest unit of this section is exposed only intermittently beneath the conglomerate and is best seen on the north-facing cliff [NZ 4731 3897], 560 yd E. 10° N. of Blackhall Rocks Station, where it is composed partly of contemporaneously brecciated and rolled fragments of small algal domes and stromatolitic debris (Plate 12).

The conglomerate crops out for about 400 yd in the core of the anticline and reaches a maximum thickness of 15 ft near the easternmost tip of Black Halls Rocks. North and south from there parts of the bed pass gradually into bedded alga-laminated dolomite containing rolled cobbles and similar dense masses which appear to be in their original position of formation. Most of the individual cobbles and boulders of the conglomerate are 6 to 12 in across. Their core consists of a dense mass of fine equigranular dolomite anhedra with abundant, extremely irregular, semi-concentric layers of more turbid finer dolomite crystals, set in a matrix of sparry calcite. Small shells and shell fragments form a minor constituent of most cobbles, especially in less dense outer zones composed of confused stromatolitic material. A hard, smooth finely crystalline stromatolitic envelope of very finely laminated dolomite encrusts each shell and cobble, and similar material forms sinuous sheets in the matrix. Some of these sheets are penecontemporaneously brecciated and have a second-generation stromatolitic overgrowth. Other interstitial material includes pisoliths (also probably organic), fine detritus and shelly material. Apart from stromatolites, fossils in these beds are: Acanthocladia anceps; Dielasma elongatum sufflatum; gastropods including Omphalotrochus sp.; Bakevellia antique, B. ceratophaga, Liebea squamosa, Pseudomonotis speluncaria, Schizodus truncatus; Peripetoceras freieslebeni. Faunal lists for the conglomerate bed are also given by Trechmann (1913, pp. 215–6; 1925, p. 136).

The upper member of the reef sequence is similar in most respects to its correlative in the Hesleden area (p. 140). The laminae form widespread crenulations of up to 3-in wave-length and 1.5-in amplitude, and these are particularly well preserved in a massive bed immediately overlying the conglomerate. Counts made at several localities within this bed give an average frequency of about 110 laminae per inch, and other beds of the algal sequence contain 90 to 120 laminae per inch. Most of the beds incorporate low domes somewhere along their exposure, but the most striking feature is the occurence at several horizons of broad flat-topped domes. In cliff sections most of the laminated beds are parallel and dip at low angles, but the even bedding is interrupted at intervals by steep down-folds in which some or all the beds in a group up to 4 ft thick dip sharply down to a common basal surface. Higher beds in such a group have a progressively shallower downfold, and the irregularities are usually evened out before the common base of the next generation of domes.

This structure is seen in three dimensions on the shore platforms, where the domes are roughly oval in plan (Figure 22). The longer axes of the domes tend to be aligned north-west to south-east, i.e. normal to the reef-front at this locality. In diameter they range from less than 1 yd to over 20 yd, those less than 4 yd in diameter having rounded tops. Domes are low and poorly defined in the upper 20 ft of the alga-laminated sequence which include intercalations of oolitic and non-organic granular dolomite at the northern and southern boundaries of the reef outcrop. Some of the alga-laminated beds are autobrecciated, and can be traced for several hundred yards by this characteristic. D.B.S.

Hart

Dolomites of reef facies are seen in two old quarries [NZ 448 340]; [NZ 449 340] near Whelly Hill House, 1.33 miles W.S.W. of Hart, and were cut in bores at the Naisberry Waterworks of the Hartlepools Water Company. The quarries contain 30 to 40 ft of thinly bedded alga-laminated dolomite interbedded with granular unlaminated, possibly inorganic, dolomite. Upper strata are fairly evenly bedded, but have broad undulations of the type seen in the uppermost 18 ft of the reef sequence at Black Halls Rocks. Some deeper, more pronounced downfolds on the north face of the east quarry [NZ 4500 3406] demarcate rounded domes up to 3 ft high, but because of widespread brecciation and alteration, the characteristic fine lamination is only locally preserved. There is less brecciation in the west quarry where finely crenulate alga-lamination simulating ripple marks is seen. Fine examples of small algal domes, rising through otherwise level-bedded dolomite to heights of up to 2 ft, occur in complex groups at a number of horizons near the base of the exposed sequence, and are especially prominent on a 12-ft face (Plate 11A) on the east side of the quarry [NZ 4486 3406]. D.B.S., G.D.G.

In the water boreholes at Naisberry finely laminated granular dolomite of algal origin, similar to that exposed near Whelly Hill House, occurs between depths of about 80 ft and 148 ft. The laminae are broadly undulate and in some parts finely crenulate, as at Black Halls Rocks and in Hesleden Dene. Below this, bedded granular shelly dolomite, thought to be of lagoonal facies, continues to about 1601 ft, and is underlain by thickly bedded cream and buff porous ?reef-dolomite, with a fauna dominated by fragmentary stunted gastropods and lamellibranchs, and including: ?Nodosaria kingii Paalzow, Nodosaria? [smooth form]; polyzoan fragments; Straparollus permianus, Naticopsis?, Omphalotrochus helicinus, O. cf. thomsonianus; Bakevellia antiqua, B. cf. ceratophaga, ?Parallelodon striatus, Permophorus sp., Schizodus sp.; ostracods. This bed is similar to the bedded reef exposed at Seven Chambers (p. 139). Between about 190 ft and 245 ft there is massive reef dolomite with a hard, finely crystalline matrix and a varied and abundant fauna: Acanthocladia anceps, Batostomella crassa, Fenestrellina retiformis, Thamniscus dubius; Dielasma elongatum, small valve of Strophalosiid; Dentalium aff. speyeri Geinitz; Naticopsis?, Omphalotrochus cf. helicinus, O. taylorianus, Pleurotomaria linkiana; Bakevellia antiqua, B. ceratophaga, Parallelodon striatus, Permophorus costatus, Pseudomonotis speluncaria, Schizodus schlotheimi (Geinitz). On some weathered surfaces of this rock, a confused fine concentric stromatolitic lamination can be seen. Between 245 ft and 248 ft oolitic and pisolitic dolomite, rich in gastropod and lamellibranch shells, each with a stromatolitic coating, marks a transition to underlying beds of lagoonal facies.

West Hartlepool

Several boreholes at the Hartlepools Water Company's works [NZ 507 333] penetrated dolomites of reef facies. In two of these Trechmann (1932, p. 170; 1942, pp. 321–2) describes the strata immediately below the base of the Upper Magnesian Limestone as reef-like rock with many concentric 'coatings' and as 'well-bedded… and much contorted': it is likely that these beds correlate with bedded, predominantly algal, reef-dolomites like those at Hesleden Dene, Black Halls Rocks and Hart. Bedded rocks below 286 ft in the 1940 bore (op. cit. p. 322) may be sub-reef. D.B.S.

Basinal facies

Under this heading, details are given of all Middle Magnesian Limestone deposits lying east of the reef-front, including transitional beds at the base of the division, bedded off-reef equivalents of the reef, and barren bedded dolomites (with interbedded evaporites) of post-reef age. The stratigraphical relationships of these sub-divisions are shown in (Figure 17) and (Figure 20).

Transitional beds and bedded off-reef deposits

Chourdon Point

Thickly bedded and massive, brown, bioclastic, dolomitic calcarenite crops out at the foot of the cliffs in a small bay [NZ 4416 4686] on the north side of Chourdon Point. The outcrop is about 25 yd long and 8 ft high, and has the form of a low dome. The dolomite is friable and highly porous except for an irregular 2.5-ft mass near the centre of the outcrop, which may have been detached from the reef-front, some 600 yd W.S.W. of Chourdon Point. The friable dolomite contains a varied and abundant fauna (see also Trechmann, 1954, pp. 201–2) indicative of the middle period of reef-growth. Fossils identified include: Fenestrellina retiformis; Crurithyris clannyana (King), Orthothrix excavata, Stenoscisma schlotheimi; Straparollus sp.non S. permianus (King); Bakevellia antiqua, Permophorus cf. costatus and Streblochondria pusilla.

Horden Dene, Easington Colliery

Middle Magnesian Limestone beds are exposed in Horden Dene from a locality [NZ 4424 4354], 250 yd E.S.E. of Easington Colliery station to the coast. Highly recrystallized, brown dolomitic limestone, thickly and irregularly bedded and extensively brecciated, is poorly exposed for about 120 yd in the bed of the stream. No diagnostic fossils have been found, but the lithological affinities of this rock are with off-reef beds as seen in other exposures, including one in an underground tunnel at Easington Colliery (p. 136) and outcrops in the Sunderland (21) district farther north.

Dene Holme, Horden

Middle Magnesian Limestone crops out on the south bank of Castle Eden Burn [NZ 454 404] from 150 to 300 yd W.S.W. of Dene Holme, where about 20 ft of granular and oolitic dolomite dips eastwards on the flank of a small anticline and overlie about 20 ft of irregularly bedded and massive cream shelly bioclastic dolomite. The latter contain many derived fragments of shelly reef-facies dolomite, carbonate sands, silts and oolite, as well as many polyzoa, brachiopods and lamellibranchs. The following fossils have been identified: algal filaments, some forming crusts about shells; Miocidaris keyserlingi; Acanthocladia anceps, Batostomella crassa, Fenestrellina retiformis; Dielasma elongatum, Orthothrix excavate, O. cf. lewisiana, Spiriferellina cristata multiplicata, Stenoscisma globulina; ?Loxonema fasciatum King, Omphalotrochus sp., Pleurotomaria sp.; Bakevellia antiqua, B. ceratophaga, Palaeolima? permiana (King), Parallelodon striatus, Pseudomonotis speluncaria, ?Streblochondria pusilla; ostracods. A faunal list for this locality is also given by Trechmann (1913, pp. 215–6). The fauna is notable for the paucity of cryptostome polyzoa, elsewhere almost ubiquitous in rocks associated with the reef phase. The core of the anticline is a low dome of massive cream dolomite lithologically similar to reef-facies rock.

Boreholes around Hartlepool

Basinal equivalents of the reef phase were penetrated in a number of boreholes around Hartlepool and in N.C.B. Offshore Nos. 1 and 2 bores. Trechmann (1913, pp. 187–8) found brachiopods and lamellibranchs below a depth of about 390 ft in cores of an 1888 boring [NZ 5163 3455] at the Warren Cement Works. The rock in which they were found is described as dark grey calcitic dolomite associated with varying quantities of gypsum and anhydrite. One mile E.S.E. of Warren Cement Works, the Hartlepool Lighthouse Bore [NZ 5320 3386] penetrated about 75 ft of beds in which a typical shelly reef fauna (lists, p. 176) occurred at three levels, separated by barren fine-grained dolomites (Magraw and others 1963, pp. 175, 199). The highest fossiliferous bed, lying between depths of 636 and 667 ft, appears to be equivalent to the main reef-building phase; it consists of grey, fine, bioclastic calcarenite, with scattered larger shell fragments, interbedded with cream or buff, finely crystalline or porcellanous dolomite, with scattered well preserved whole shells. The calcarenitic beds are similar to those in bore holes in Hesleden Dene (p. 142) and contain irregular streaks and fragments of dark grey siltstone and silty mudstone, and abundant foraminifera, crinoids, polyzoa, brachiopods, gastropods and lamellibranchs. Thin sections show that the matrix of the calcarenite consists largely of finely comminuted organic debris. The light-coloured fine-grained interbeds are largely colour-mottled in shades of buff. Both types of bed contain fairly abundant small-amplitude stylolites, and sporadic angular derived fragments of dolomite, mudstone and siltstone. Other beds of bioclastic dolomite containing derived rock fragments occur at depths of 710 and 744 ft, and are thought to be basinal equivalents of the early phases of reef-building, the lower horizon being taken as the base of the division. A succession like that of the 1888 Bore was cut in another bore [NZ 5003 3430] at Howbeck Pumping Station (Trechmann 1942, pp. 319–20). In both boreholes dips of 20° or over occur throughout the off-reef sequence. D.B.S.

The off-reef beds thin northwards and eastwards, and are interpreted to be only 37 ft thick in Offshore No. 1 Bore, 4 miles N. of Hartlepool (Magraw and others, 1963, pp. 175, 201). From between 1071 ft and 1074 ft in this bore the following were collected: 'Adhaerentina'permiana, 'Ammodiscus' ?, 'Glomospira'gordialis, uniserial chambered foraminifera [common; all Nodosaria or Lingulina form of chambers]; Horridonia ?[juv.], Neochonetes? davidsoni, Orthothrix excavata. ?Strophalosia morrisiana; Bakevellia cf. antiqua; ostracods. Neochonetes? davidsoni is common, and though some have radial ribs, most are smooth except for concentric growth lines. There is great variation in the length of the hinge line, and many of the shells are as long as they are wide. D.B.S., J.P.

Post-reef beds

Except at Black Halls Rocks and in Shippersea Bay, the outer edge of the reef lies behind the present shore, the coastal cliffs being composed of post-reef Middle Magnesian Limestone and Upper Magnesian Limestone, lying against the steep reef-face. A thin succession of post-reef Middle Magnesian Limestone also overlaps on to the reef in the Hesledon, Easington, Hesleden and Hartlepool areas.

Murton, Cold Hesledon and Hawthorn

The most westerly outcrops of post-reef Middle Magnesian Limestone are at the north end of South Hill, two-thirds of a mile N.N.W. of Cold Hesledon, where a few feet of bedded, granular, partly oolitic dolomite are seen in several small quarries and natural exposures. Fragments of similar dolomite are scattered on the ridge which culminates northwards in Fox Cover Quarry (p. 133), and there are good exposures in railway cuttings east of Hesledon East House, around Kinley Hill, and in adjacent coastal sections. The railway cutting [NZ 435 473], 450 yd E. of Hesledon East House, is in highly faulted and brecciated bedded dolomite extending for about 300 yd in an asymmetric anticline. Where least altered the dolomite is predominantly thin-bedded and granular with traces of ripple-marks and cross-bedding. Where brecciated, the rock is harder and more calcareous. Northwards-dipping beds at the northern end of the cutting may be Upper Magnesian Limestone. Thin-bedded, granular dolomite is also exposed in a second cutting [NZ 436 474], 200 yd farther north-east. A little to the south small exposures and rock fragments in the soil indicate that the top of Kinley Hill is formed largely of thinly bedded oolitic dolomite. This is also exposed in several small quarries nearby, where ooliths are locally almost obliterated by recrystallization. The main exposures are: natural outcrop [NZ 4336 4558], 270 yd E.N.E. of Kinley Hill (farm), 10 ft; shallow digging [NZ 4303 4670], 200 yd N.W. of Kinley Hill, 2 ft; old quarry [NZ 4302 4636], 220 yd S.S.W. of Kinley Hill, 8 ft; old quarry [NZ 4285 4609] 620 yd S.S.W. of Kinley Hill, 10 ft; old quarry [NZ 4313 4609] 540 yd S. of Kinley Hill, 15 ft; and old quarry [NZ 4327 4634] 300 yd S.S.E. of Kinley Hill, 8 ft. The rock exposed 200 yd N.W. of Kinley Hill contains a number of pisolitic beds. Thin sections (E29422), (E29451), (E29489), (E29490) of other rocks from this locality are described by Dr. Dearnley as oolitic calcitic dolomites of silt-grade, consisting of closely packed ooliths, with outer rims of fine-grained dolomite (0.01 to 0.02 mm) and cores of coarsely (0.25 mm) crystalline calcite and dolomite, set in a matrix of aggregated dolomite and calcite rhombs.

Oolitic dolomite also forms the uppermost 18 ft of beds exposed in a group of old quarries in a wood, 300 to 750 yd W.S.W. from Hawthorn Tower [NZ 4396 4613]. The oolitic rock is underlain by 15 to 18 ft of thin- and medium-bedded, granular or finely granular dolomite, with traces of cross-bedding at some horizons and with a 1-ft layer containing low domes up to 2 or 3 ft in diameter 6 ft above the base. These lower beds are the probable equivalent of interbedded algal and non-algal strata overlying the reef at Black Halls Rocks, Shippersea Bay and Hesleden Dene. This suggestion is supported by the section exposed nearby in Hawthorn Quarry [NZ 437 463], where the top of the reef-rock passes southwards at about the same level as the base of the section in the quarries in the wood. The post-reef beds in Hawthorn Quarry are about 50 ft thick; they are mainly inaccessible, but appear, from fallen fragments, to consist largely of granular dolomites similar to the upper beds exposed in the wood. The eastern slope of the reef in Hawthorn Quarry is truncated by a reverse fault, which brings down grey oolitic post-reef dolomite. About 12 ft of these beds are exposed at the main entrance [NZ 4383 4631] to the quarry.

At the coast, post-reef dolomites are exposed intermittently from the northern margin of the district to 470 yd S. of Beacon Point, where they overlie alga-laminated beds. Southwards for about 1050 yd from the northern margin of the district the coastal cliffs are composed of undulating, evenly bedded dolomite of broadly constant lithology, with a total thickness of 120 ft; traces of cross-bedding and some ooliths are seen in places. A prominent bed of soft, cream dolomite, 10 to 15 ft thick, can be traced southwards for several hundred yards from the northern margin and a well-defined lens of breccia lies near the base of the cliffs from 700 to 515 yd N.W. of Chourdon Point. About 125 yd farther south, bedded, saccharoidal sand-grade dolomite shows the first signs of brecciation which increases in intensity towards the south.

At Chourdon Point and immediately to the south, completely brecciated rock, hardened by dedolomitization and recementation, gives rise to bold cliffs in which fragments up to 8 ft across stand out in relief. Mechanical brecciation, due to a series of sub-parallel normal faults, has given rise to second-generation breccias at a number of places on the headland.

From Chourdon Point to Hawthorn Hive the breccias are interrupted only by a few patches of undisturbed, or slightly disturbed thin-bedded saccharoidal, sand-grade dolomite. Most of the breccias are formed of fragments of similar rock. The degree of brecciation varies from slight, where existing beds are broken up more or less in situ and fragments have moved only slightly relative to one another, to complete, where fragments of strata are incorporated from higher beds, some now removed by erosion. Some completely brecciated areas have ill-defined margins and occur near the middle of areas of lesser brecciation, but others form sharply defined 'gashes' bounded by steep slickensided surfaces cutting sharply across undisturbed bedding. Both types can be seen in the cliffs around Hawthorn Hive, where several breccias contain fragments of Upper Magnesian Limestone and red and green marls. The latter were probably deposited some hundreds of feet above their present position as part of the Upper Permian Marls. Carbonate rock in the brecciated zones, both in the fragments and the matrix, is generally more calcareous and harder than the unbrecciated parent rock.

From Hawthorn Hive southward past Beacon Point brecciation at first decreases: from about 480 to 320 yd north of the point the cliffs are formed by about 45 ft of thinly bedded, soft, finely granular dolomite, only slightly brecciated and apparently barren. Still farther south, however, extensive brecciation reappears and continues until the outcrop is terminated by faulting, 470 yd S. of Beacon Point. The succession in this ground is altogether about 130 ft thick. Where least altered the dolomites are thinly bedded, cream, and locally bear traces of original lamination and structures resembling cross-bedding. Elsewhere much of the sedimentary structure is obliterated by recrystallization. No undoubted algal structures have been seen.

Easington Colliery to Horden

Small old quarries [NZ 4298 4503]; [NZ 4322 4516] respectively 260 yd E. and 510 yd E. of Thorpe Lea West contain a few feet of massive, barren, grey, crystalline dolomitic limestone, the exact stratigraphical position of which is not clear but which are here assigned to post-reef beds on general lithological grounds. A little farther east 15 ft of hard thinly bedded, grey, fine-grained, saccharoidal dolomitic limestone are seen in an old quarry [NZ 4348 4552] 570 yd W.N.W. of Beacon House. Structures resembling small ripple-marks are preserved in those parts of the limestone which are not autobrecciated. Since this quarry is topographically on the same level as a group of quarries west-southwest of Hawthorn Tower (p. 147) the beds are presumed to lie on the upper surface of the bedded reef. An isolated exposure [NZ 4358 4446] in a colliery railway cutting, 370 yd W. of Low Grounds, Easington Colliery, contains 12 ft of brecciated grey-white massive crystalline dolomitic limestone of uncertain, but possibly post-reef, age. The other main inland exposure of post-reef beds comprises 18 ft of grey recrystallized cross-bedded oolitic dolomite at Couslaw Holes Quarry [NZ 433 436], 420 yd N.N.W. of Paradise, Easington Colliery. These beds lie slightly higher than the level of the reef-crest, 250 yd farther east (p. 139). Altered oolitic dolomitic limestone forms further small exposures [NZ 4271 4372]; [NZ 4302 4377], respectively 940 yd and 750 yd N.W. of Paradise.

At the coast, post-reef beds crop out for about 1.5 miles southwards from Shot Rock. Between Shot Rock (where they overlie interbedded algal and oolitic dolomite) and the Easington Fault, they are about 110 ft thick and are lithologically similar to the beds? north of Chourdon Point. There is fairly extensive autobrecciation at the northern end of the outcrop and immediately north of the Easington Fault. South of the Easington Fault, post-reef dolomites are almost continuously exposed in the cliff for about 1100 yd, and intermittently exposed between slipped masses of drift for a further 600 yd before passing beneath Upper Magnesian Limestone, 450 yd N. of the Horden Fault. Throughout this distance they are cream oolitic dolomites, 120 ft thick, in gently undulating partly collapsebrecciated beds. The oolite is largely recrystallized, and locally resembles the apparently non-oolitic beds at this horizon north of Shot Rock. Zones of complete collapse-brecciation occur at irregular intervals (Horden Point is an excellent example), and well-defined breccia-gashes with fragments of Concretionary Limestone and of red marl are seen 520 yd S. of Loom and 60 yd S. of Horden Point. No fossils have been seen in any of these post-reef cliff sections.

South of the Horden Fault the section is obscured by colliery spoil, but according to Trechmann (1925, pl. xiii) the beds are like those to the north. They reappear beyond the southern end of the colliery spoil at Whitesides Gill, 1000 yd S. of Horden Point, and continue southwards before eventually passing beneath Upper Magnesian Limestone beds about 700 yd N.W. of Dene Mouth. Their upper junction is obscured by recrystallization and their thickness is uncertain.

Blackhall Colliery to Hesleden

Late Middle Magnesian Limestone beds overlie the reef in Hesleden Dene and north and south of Black Halls Rocks, whilst beds thought to occupy an off-reef position are exposed in Castle Eden Burn and its tributary Hardwick Dene and have also been penetrated in a number of boreholes in the coastal and offshore areas.

In the dene south of Hesleden, post-reef dolomites succeed alga-laminated deposits of the reef-fiat. At Jack Rock [NZ 447 376] finely granular dolomite is interbedded with thin dolomites of algal origin in a 2.5-ft bed at the base, and an 8 ft algal bed is seen 22 ft higher. The intervening strata are predominantly of finely granular dolomite with locally preserved traces of small-scale cross-bedding, and with alga-laminated horizons at some exposures farther downstream. The following section, measured on the north bank [NZ 4545 3712], 470 yd W. of the church at Monk Hesleden, is representative:

The interbedded sequence exemplified above is probably altogether about 40 ft thick; it can be traced downstream through a series of discrete exposures to a position approximately south of Monk Hesleden Church, where it is succeeded by about 30 ft of thinly bedded, finely granular dolomites with small scale cross-bedding throughout. Some 12 ft of these beds are exposed [NZ 4580 3710] on the north side of the stream, 250 yd E. of the church, where they are overlain by 18 ft of thicker bedded dolomites which are inaccessible but are thought to be oolitic. Further exposures of these beds can be seen for another 300 yd downstream. Farther downstream beds of the Upper Magnesian Limestone form a broad shallow syncline, but the junction with the Middle division is nowhere exposed. Post-reef beds reappear some 750 yd farther east where a number of small outcrops occur on both sides of the valley for a distance of about 180 yd upstream from the railway embankment. The following section [NZ 4581 3692] was measured 340 yd W.N.W. of Middlethorpe:

The texture of the lowest bed is remarkable. It is predominantly composed of coarse ooliths, pseudo-ooliths and pisoliths, set in a fine-grained oolitic matrix. Scattered profusely through the rock are large (up to 15 mm) irregular, commonly grotesque pisoliths, elongated approximately parallel to the bedding. Many are hollow and now consist of a thin envelope only, whilst others contain aggregates of ooliths and oolitic debris. Some of the smaller pisoliths, too, are compound, and many of the ooliths have markedly eccentric shapes. It is in‑ ferred from nearby surface outcrops and the Hesleden Dene boreholes (Appendix 1, p. 142) that these beds occupy a position over, and slightly to the east of, the reef-crest.

Farther east, in Hardwick Dene, post-reef dolomites form the lower part of the sequence exposed near Hardwick Hall [NZ 450 392] and for about 1100 yd to the north. The lowest rocks form the cores of anticlines 600 and 750 yd N.N.E. of Hardwick Hall, and are of thin-bedded finely granular cream dolomites, over 75 ft thick. By analogy with other sections in the area they are the correlative, in part at least, of the uppermost, bedded part of the reef sequence, but because of advanced recrystallization most of their original structure has been obliterated and their exact stratigraphical position cannot now be established. They are overlain successively by about 25 ft of fiaggy, finely granular, cream dolomite, and about 35 ft of cross-bedded cream oolitic dolomite. At the base of the latter a pisolitic bed, well-exposed 300 yd N.N.E. of Hardwick Hall, bears a striking resemblance to the lowest member of the Middlethorpe section above, and almost certainly lies at the same horizon. Uppermost beds of the Middle Magnesian Limestone are again exposed [NZ 4516 4001] at the northern end of the Hardwick Dene as follows:

Few of the original structures in these beds have survived advanced alteration and their correlation with the upper members at the southern end of Hardwick Dene is tentative.

In a small old quarry [NZ 4623 3874], SC yd W. of Mickle Hill, there are 15 ft of cream cross-bedded oolitic dolomite; and at a natural exposure [NZ 4660 3814], 300 yd N. of Tweddle Black Halls, about 6 ft of irregularly bedded autobrecciated dolomitic limestone appear to be altered oolite. These are the only exposures in the ground between the coast and Hesleden Dene.

Along the coast at Black Halls Rocks, beds of reef facies crop out for 1500 yd in the core of an anticline (pp. 142–4). Post-reef strata comfortably overlap the reef-crest on the southern limb, and are well exposed southwards for about 80 yd from a locality [NZ 4783 3827], 780.yd E. of Black Halls. The lowest visible post-reef beds are composed of massive cream oolitic dolomite. The oolites are succeeded by 20 to 30 ft of soft, granular, partly autobrecciated dolomite, and then by about 25 ft of soft, oolitic dolomite. The uppermost beds are also exposed for about 65 yd in the core of a subsidiary anticline, the axis of which meets the coast 930 yd E. 18° S. of Black Halls. Exposures on the northern limb of the major anticline are discontinuous, but indicate the presence of a basal transition zone in which alga-laminated dolomite is interbedded with cream, oolitic dolomite.

These beds and the overlying oolite are extensively auto-brecciated, and terminate northwards at the Blackhall Fault which brings down Concretionary Limestone. D.B.S.

Hart, Hartlepool and offshore areas

Post-reef beds of Middle Magnesian Limestone age have been quarried at several places between Hart and West Hartlepool, but over most of this area they are buried beneath Upper Magnesian Limestone and are known only from boreholes. The largest exposures are in the west and south-west faces of an old quarry [NZ 476 345], 300 yd E. of Hart windmill, where about 40 ft of fine-, medium- and coarse-grained, saccharoidal, dolomitic limestone and calcitic dolomite are seen. They form undulating beds which are predominantly thick or massive except in the uppermost 13 ft, where thin-bedding predominates. Most of the rock is hard, dense and recrystallized, but secondary intergranular porosity is high in the lowest 15 ft of beds, and larger cavities occur throughout. The cavities are often grouped parallel to the bedding and are especially concentrated in a 12-ft bed in the middle of the section. There are local traces of lamination, and vague indications of low-angle cross-bedding suggest that at least parts of this rock were formerly oolitic. Similar hard compact massive rock, 7 ft thick, is exposed in a small quarry [NZ 4792 3407] at the north-western corner of Craggy Bank Wood, 870 yd E.S.E. of Hart windmill. Although unrecognizable in hand specimen, undoubted ooliths can be seen in thin section (E29922) of this rock, which is a fine-grained mass of dolomite grains, grouped in subspherical aggregates (about 0.10 mm in diameter), with a calcite matrix. Low-angle cross-bedding was noted in this quarry and in a number of small natural outcrops of similar rock nearby. Similar dolomitic limestone and calcitic dolomite are 15 ft thick in an old quarry [NZ 4725 3445], 70 yd S. of Hatt windmill, and 8 ft thick in an old digging [NZ 4743 3431], 280 yd S.E. of the windmill A shallow digging [NZ 4705 3359] on the south-west side of Naisberry crossroads is in 2.5 ft of well-bedded, compact, finely porous dolomite which has traces of low-angle cross-bedding and is probably equivalent to the beds exposed at Craggy Bank. No fossils were found in any of these quarries during the resurvey and this fact, coupled with the distinctive Ethology, strongly suggests inclusion of these beds with the Middle division of the Magnesian Limestone rather than Upper, as claimed by Trechmann (1913, p. 212 et seq.). D.B.S., G.D.G.

At Naisberry, two bores [NZ 4662 3362]; [NZ 4660 3364] penetrated about 50 ft of granular, saccharoidal, calcitic dolomite, overlying reef-limestone. In both byes small flat cavities occurred in the highest part of these beds, and it is possible that these represent shell-casts indicating the presence of a few feet of Upper Magnesian Limestone. Yellow dolomite, 33 ft thick, was proved in a similar stratigraphical position in a bore [NZ 5075 3339] at Hartlepool Waterworks, where the base of the Upper Magnesian Limestone was clearly defined (Trechmann 1932, p. 170).

Most of the remaining borings into post-reef beds of the Middle Magnesian Limestone are located east of the reef-front and penetrate barren dolomites of basin facies. These rocks, closely resembling their equivalents cropping out on the coast north of Black Halls Rocks, are widely brecciated. In a bore [NZ 5003 3430], near Howbeck Hospital, Hartlepool (Trechmann 1942, p. 319) they are represented by about 63 ft of bedded yellow dolomite, brecciated in the upper part. This thickness is anomalously small for this area, and is probably due to the removal of interbedded soluble rocks. Brecciated oolitic dolomite is reported from a short core taken in post-reef beds at 432 ft in the North Sands Bore [NZ 5027 3534], and 118.5 ft of rock described as yellow limestone, broken' and yellow limestone, very much broken' are recorded in the Hart Bore. According to Trechmann (1942, p. 313) most of the post-reef Middle Magnesian Limestone beds at the Thorpe Bulmer Bore are composed of brecciated dolomite, yellow above and grey below, but core recovery was poor and no thicknesses are available. Two beds 11 and 17 ft thick, and similarly described as 'broken', form part of a post-reef sequence of yellow and grey limestones at depths of 67.5 and 103.5 ft respectively below the base of the Upper Magnesian Limestone in an 1893 Bore approximately [NZ 511 319] at Burn Road, West Hartlepool. Other bores at Palliser Works [NZ 5061 3525], at the outskirts of Hartlepool, and at Villiers Street [NZ 5082 3233], Smalley's Pulp Works [NZ 5130 3186], Durham Paper Mills [NZ 5114 3187] and Nelson Street [NZ 5154 3197], all in West Hartlepool, penetrated a short distance into these beds, and all record yellow limestone or dolomite. The Nelson Street Bore was examined by Trechmann (1942, p. 325), who records 11 ft of porous dolomite, partly oolitic, below the Upper Magnesian Limestone. The position of the West Hartlepool bores relative to the reef-front is not known, but the presence of dolomite rather than anhydrite suggests that some, at least, of the bores are above the reef.

In the easternmost land areas and in the offshore area, thick deposits of anhydrite (the Hartlepool Anhydrite) have been proved above beds thought to be basinal equivalents of the reef. Anhydrite was first found under Hartlepool by a bore [NZ 5163 3455] sunk in 1888 at Warren Cement Works (Marley 1892, p. 94; Trechmann 1913, p. 187), and has since been confirmed by three 1923 borings at the Cement Works (Trechmann 1925, p. 140), and by the Hartlepool Lighthouse Bore (Magraw and others 1963, pp. 176–8. 199). The general sequences are shown in (Figure 23), in an attempt to reconstruct the relationships of. the Permian beds immediately north of Hartlepool Bay. In each bore a group of barren grey crystalline dolomites, containing abundant gypsum and anhydrite, occurs below the thick anhydrite, and in two cases the barren beds overlie fossiliferous dolomite. In Offshore No. 1 Bore and the Hartlepool Lighthouse Bore the dolomite immediately underlying the thick anhydrite has a nodular structure (Plate 13A) which appears to be of algal origin when seen in thin section (E29259). Although exact correlation is not yet possible, it is likely that, as in the Blackhall Colliery–Hesleden area, the barren beds are the equivalent of early post-reef beds, whilst the thick anhydrite passes laterally and with interdigitation into the later post-reef beds. The former presence of soluble interbeds in this latter group of strata was inferred by Trechmann (1913, p. 195) from the evidence of widespread collapse breccias and traces of sulphate. In the easternmost 1923 bore the anhydrite is overlain by 17.5 ft of 'limestone', and a sequence of interlaminated gypsum and fine-grained dolomite occurs at this horizon in the Lighthouse Bore. Although no confirmatory fossils were found in either bore it is thought (Magraw and others 1963, p. 177) that the beds immediately overlying the anhydrite are of Upper Magnesian Limestone age.

In Offshore Nos. 1 and 2 bores respectively anhydrite 429 and 500 ft thick is associated with a sequence of dolomites like that in the Hartlepool Lighthouse Bore. Full details of these three bores are given in Magraw and others (1963), and abridged records are given in the Appendix (pp. 294, 313). The top of the anhydrite in both offshore bores is defined by the smooth sharp base of the Upper Magnesian Limestone.

The lithology of the anhydrite is broadly constant in all the bores and in the workings of the Warren Cement Works Mine (Trechmann 1932, p. 168; Sherlock and Hollingworth 1938, P. 37). It is a hard, bluish grey translucent rock, finely to coarsely crystalline, in which fine-grained grey or brown dolomite forms an extensive, delicate mesh of fretted stringers. Locally these may compose up to 50 per cent of the mass, but they generally range between 5 and 30 per cent. Dolomite also forms beds up to 14 ft thick spaced at wide intervals in all the bores, but is especially prominent towards the base of the anhydrite in Offshore No. 2 Bore. In some beds the dolomite is very finely and evenly laminated, the laminae in some cases showing conspicuous contortion (Plate 13B). At the top and bottom of the Hartlepool Anhydrite the rock has been hydrated to gypsum up to 11 ft thick, and tabular selenite crystals, up to 0.5 in long, project into the anhydrite at many sulphate-carbonate interfaces. In the Warren Cement Works Mine, Trechmann (1932, p. 168) observed that much of the anhydrite was hydrated to gypsum at the north end of the workings, where it tended to thin out; and Hollingworth (in Sherlock and Hollingworth 1938, p. 37) reported that gypsum veins became more prominent towards the south end of the workings.

The macroscopic appearance of the rock in the mine and in boreholes indicates extensive replacement of dolomite by anhydrite, and this is confirmed by examination of thin sections. A typical section (E29256), from 844 ft in Offshore No. 1 Bore, is described by Dr. Dearnley as a dolomite-anhydrite rock consisting largely of anhydrite, with irregular lenses of small dolomite rhombs which are locally partly replaced by anhydrite. Large gypsum plates enclose anhydrite crystals, but also occur as replacements of dolomite. A thin gypsum vein cuts one dolomite band. The order of formation of the minerals appears to be first dolomite, then anhydrite and finally gypsum. Fluxion structures were noted by Dr. J. Phemister in anhydrite specimens (E17876), (E20804) from the Warren Cement Works Mine, and are clearly visible in weathered cores of anhydrite from Offshore No. 2 Bore. D.D.S.

Upper Magnesian Limestone

The Upper Magnesian Limestone is preserved only in the eastern part of the district (Plate 5). North of Black Halls Rocks the division is restricted to coastal areas where it forms four isolated shallow synclines. South from Black Halls. Rocks to the West Hartlepool Fault it crops out in a coastal belt 1 to 2 miles wide and over 4 miles long, but is exposed only at the north-western and south-eastern extremities. South of the West Hartlepool Fault these rocks are known only from boreholes.

This account follows the long-established practice of sub-dividing the Upper Magnesian Limestone of Durham into Concretionary Limestone below, and Hartlepool and Roker Dolomites above. This sub-division usefully takes account of two distinctive lithologies, but the junction betweenthem has never been precisely defined. A rough criterion is the presumed alga Tubulites permianus [(Plate 6), fig. 2], which has been only doubtfully recorded in the upper subdivision, but is very common in the lower. The remaining limited fauna of the Upper Magnesian Limestone (King 1850, table 1) is common to both groups and is dominated by euryhaline gastropods and lamellibranchs. Apart from foraminifera and ostracods only seven species are known, and of these only the lamellibranchs Liebea squamosa [(Plate 6), fig. 1] and Schizodus schlotheimi [(Plate 6), fig. 3] are at all common. The recognition by Mr. J. Pattison of a small, possibly punctate shell fragment (Dielasma?) from the Hartlepool and Roker Dolomites at Hartlepool is noteworthy, as brachiopods have hitherto not been recorded in Durham above the Middle Magnesian Limestone.

Writers from Kirkby (1861, p. 316) onwards have observed that all the forms in the Upper Magnesian Limestone are stunted and have attributed this to an inhospitable environment. The absence of polyzoa and brachiopoda (apart from the possible example noted above), both of which are generally intolerant of hypersaline water, supports this view. Plant remains are locally common throughout the Upper Magnesian Limestone.

At the close of Middle Magnesian Limestone times it is probable that the Zechstein Sea in this district had become almost filled and the Upper Magnesian Limestone was laid down on a surface of low relief. The buried reef protruded slightly above this surface and continued to exercise some local control over sedimentation: for instance, there are signs of overlap within the Upper Magnesian Limestone at Horden, Nesbitt Dene and West Hartlepool. It seems unlikely, however, that the reef acted as a western limit of deposition in a regressive sea as suggested by Woolacott (1912, p. 260; 1919b, p. 490) and Trechmann (1914, p. 260; 1925, p. 141), for it is overlain by Concretionary Limestone at Blackball Colliery and West Hartlepool (Trechmann 1913, p. 213; 1932, p. 170).

It is clear from (Figure 20) that the distribution of Upper Magnesian Limestone in the district is controlled by a combination of structure and the present erosional surface, accentuated as Woolacott (1919b, (Figure 1)) showed, by differential movement between the reef and the younger surrounding strata. This movement has lowered the base of the Upper Magnesian Limestone relative to the eastern face of the reef and brought the two into lateral juxtaposition. This is well seen at Shippersea Bay, where the base of the Concretionary Limestone has been lowered relative to the reef-crest by about 150 ft, of which about 20 ft can be accounted for by normal faulting. Some of the remainder may have been caused by differential compaction, but it is likely that most of the subsidence was effected by the solution of sulphate layers in the Middle Magnesian Limestone (p. 122). Collapse-breccias like those formed by solution in the Middle Magnesian Limestone are common also in the lower part of the Concretionary Limestone.

Gypsum occurs interstitially in granular beds and as irregular replacement patches, isolated porphyroblastic crystals and veins throughout the Upper Magnesian Limestone. It reaches a maximum in Offshore No. 1 Bore, where up to 50 per cent of a laminated dolomite in the Concretionary Limestone has been selectively replaced along the bedding. Generally, however, the gypsum is present in isolated blebs up to 3 in across, forming 3 to 5 per cent of the rock. At surface exposures the gypsum has been dissolved out leaving stellate cavities and in some instances contributing to the collapse of the surrounding beds.

The top of the Upper Magnesian Limestone is not exposed in the district, and the full thickness of the division is seen only in boreholes. Its maximum proved thickness is 416 ft in Offshore No. 2 Bore, but inland it is not known to exceed 200 ft and is usually less than 150 ft thick. At a boring in the southern part of West Hartlepool [NZ 5154 3197], a short distance north of the West Hartlepool Fault, the Upper Magnesian Limestone is about 190 ft thick, but only a short distance south of the fault the thickness is reduced to only about 80 ft. Since the main subdivisions are recognizable in the records of these bores, the sharp reduction is probably depositional, and may perhaps indicate penecontemporaneous movement along the fault. The reduced thickness south of the fault is maintained by the Upper Magnesian Limestone throughout the brinefield area around Middlesbrough and over wide areas of Yorkshire. D.B.S.

Concretionary Limestone

The Concretionary Limestone Group is intermittently exposed in coastal areas in the northern part of the district, but south of Hart it is known only from boreholes. It is composed mainly of thinly bedded granular dolomites of silt- to fine sand-grade, but the rock is locally recrystallized and in some such places contains many concretions. When freshly broken these rocks always smell strongly of petroleum (Trechmann 1931, p. 251) and both concretions and matrix yield a quantity of oily and carbonaceous matter on solution in acid" (Trechmann 1913, p. 198). Fine lamination is common in the lower beds, particularly at the base, where the Flexible Limestone, 1.5 to 12 ft thick, is represented by dense impure dolomite, cream or grey in surface outcrops, and grey, foetid, bituminous, and in places shaly at depth. Although this bed has yielded fish remains from Fulwell (in the Sunderland district) none has been found in the present district. Plant debris, however, is common; and poorly preserved lamellibranchs are recorded from a bed doubtfully referred to the Flexible Limestone at one locality (p. 158).

In coastal exposures the Concretionary Limestone falls into a lower group of beds containing abundant concretionary structures, and an upper group in which such structures are generally absent. The lower beds, 40 to 45 ft thick, are so laterally variable in lithology that exact correlation of adjacent sections is often difficult. The variation is due to irregular distribution of concretions, which locally combine to form massive hard grey crystalline limestone quite distinct from the normal thin-bedded cream soft granular dolomites into which they pass within a few feet either horizontally or vertically (Figure 24). The concretions lack the wide range of patterns found in the Sunderland area (Abbot 1903, pp. 51–2; Holtedahl 1921, pp. 195–206), and are generally subspherical, mutually interfering aggregates of radially crystalline calcite, 0.25 to 1.5 in across. The calcite crystals are brown or grey due to the presence of impurities, and commonly have scalenohedral terminations. Some interspaces between concretions are filled by yellow granular dolomite, others are empty. At many exposures where concretionary structures are rare or only incipient, the rock is composed largely of brown or grey crystalline calcite in which Tubulites permianus and species of Liebea and Schizodus are preserved together with traces of small scale cross-bedding, ripple-marks and thin slumped beds.

The upper subdivision of the Concretionary Limestone consists of cream soft granular dolomite which is essentially similar to non-concretionary parts of the lower beds. The fauna, also, is similar, but fossils are more abundant and T. permianus occurs in great numbers on many bedding planes. Trechmann (1913, p. 206) originally regarded these beds as part of the Concretionary Limestone, but he later (1931, p. 251) allocated them to the lower part of the Hartlepool and Roker Dolomites, and still later (1954, p. 205) gave them a separate status. Because of faunal and lithological similarities, however, Trechmann's original classification is preferred in this account.

In the coastal sections the total exposed thickness of the Concretionary Limestone is about 105 ft. Inland, in Castle Eden Dene and Nesbitt Dene, the absence of concretions and of T. permianus from outcrops of Upper Magnesian Limestone suggests that here the Concretionary Limestone may be partly or wholly overlapped. This evidence cannot be regarded as conclusive, however, in view of the range of lateral variation seen in coastal exposures. There is a further suggestion of overlap in boreholes at West Hartlepool Waterworks (Trechmann 1932, p. 170; 1942, p. 3) where no more than 35 ft of bedded non-concretionary dolomite separates Flexible Limestone from undoubted Hartlepool and Roker Dolomites. Under the southern part of West Hartlepool and also in the Amerston Hall, Bore, Embleton, the Concretionary Limestone is a hard grey impure foetid commonly bituminous dolomitic limestone, 19 to 65 ft thick. Small quantities of free mineral oil have been reported at this horizon from two of the bores under West Hartlepool. D.B.S.

Details

Easington Colliery

The northern of two outcrops near Easington Colliery is at the top of 80-ft coastal cliffs just inside the northern margin of the district, where 8 ft of hard, grey, thin-bedded, crystalline, dolomitic limestone overlies very soft highly weathered cream oolitic dolomite of the Middle Magnesian Limestone in a syncline 50 yd across. The southern outcrop also takes the form of a shallow syncline, occupying about 650 yd of cliff section from 60 yd N. of Loom [NZ 444 443] to the Easington Fault. For most of this distance exposures are relatively small and are separated by slipped masses of drift, by a thick mantle of weathered rock, or by colliery waste. It is not, therefore, possible to follow the base of the Concretionary Limestone with any accuracy, or to measure a composite section, though it can be estimated that the exposed thickness of the subdivision here is about 50 ft. At the northern end of this outcrop the lower part of the cliff is formed of Middle Magnesian Limestone, the top of which is marked by a discontinuous layer of small calcareous concretions of a type which, at Sunderland and Seaham Harbour, occurs immediately beneath bedded solution breccias. At Loom the bed immediately overlying the concretions is a 15-ft breccia composed of angular fragments of hard, grey crystalline limestone with poorly developed concretionary structures, in a matrix of soft, mealy dolomite. For practical purposes the base of the Upper Magnesian Limestone is here taken at the base of the breccia. The evidence, however, strongly suggests that this is an abnormal junction and that the removal of a soluble bed, probably anhydrite, from the top of the Middle Magnesian Limestone, has caused brecciation in the overlying Concretionary Limestone and brought it into juxtaposition with a bed formerly some distance below it. Brecciated beds are also seen at this level at the southern end of the outcrop, where they are 40 ft thick in places. Higher Concretionary Limestone beds exposed in a series of small isolated outcrops in the northern limb of the syncline consist of alternations of thin-bedded, cream granular dolomites and grey-brown crystalline dolomitic limestones. The latter in some cases contain poorly-defined botryoidal structures, and are commonly brecciated, wholly or in part, by the collapse of underlying beds. Poorly preserved lamellibranchs are present in slightly brecciated granular dolomite 83 yd N. of the Easington Fault, and in fragments of crystalline dolomitic limestone in the fault-breccia.

Horden to Black Halls Rocks

Immediately north of the Horden Fault Concretionary Limestone extends for about 210 yd along the coast from a locality [NZ 4465 4249] 540 yd S. of Horden Point to the mouth of Warren House Gill. Exposures are discontinuous and the contact with the underlying beds is nowhere seen. The beds are extensively brecciated, as between Loom and the Easington Fault, and their total thickness cannot be determined. Where unbrecciated they consist of thinly bedded, cream granular dolomite of silt- to fine sand-grade, with scattered traces of low-angle cross-bedding and with poorly-preserved moulds of Schizodus and Liebea. About 110 yd N. of Warren House Gill part of the rock is laminated, and tends to split into paper-thin sheets—often a characteristic of the flexible Limestone in the Sunderland area. Neither crystalline beds nor concretionary structures are found in any of these exposures, but the fauna and lithology resemble non-concretionary parts of the Concretionary Limestone north of Sunderland. The southern part of the outcrop, from Warren House Gill to the Horden Fault, is obscured by colliery waste. Concretionary Limestone, apparently overlapped by Hartlepool and Roker Dolomites, is thought to occupy a synclinal area beneath Horden, but is nowhere exposed.

Farther south Concretionary Limestone is exposed for about 950 yd along the coast north-west of the Blackhall Fault. The section [NZ 4631 4005], 720 yd E.N.E. of Blackhall Colliery Station is:

Traced southwards to an unnamed valley [NZ 4639 3993] the Concretionary Limestone, intermittently exposed, consists of partially or wholly fragmented finely granular or crystalline dolomite and dolomitic limestone in a matrix of cream, mealy dolomite. Some fragments contain moulds of Schizodus and Tubulites; others contain plant remains. Incipient globular concretionary structures occur at intervals. Further examples of collapse-brecciation are seen between this valley and Blue House Gill, where the lowest member of the gently dipping sequence is an 8ft bed of granular dolomite, and the highest [NZ 4655 3968] comprises a group of thin partly crystalline beds containing poorly preserved lamellibranchs (chiefly Schizodus and Liebea) and scattered fasciculate groups of a tubular fossil resembling Tubulites. The fauna and lithology of these beds indicate a position low in the Concretionary Limestone sequence; it is possible that the basal 8-ft dolomite is Middle Magnesian Limestone.

South of Blue House Gill as far as the Blackhall Fault higher beds are exposed. They comprise thin-bedded dolomitic limestones containing abundant concretionary structures. The following section [NZ 4682 3941] was measured 30 yd north of the position of the Blackhall Fault:

Inland, at Blackhall Colliery South Shaft, Trechmann (1913, p. 213) recorded 63 ft of Concretionary Limestone overlying the Middle Magnesian Limestone reef.

Crimdon to Hartlepool

The most complete section south of the Blackhall Fault extends for about 1090 yd in the cliffs midway between Black Halls Rocks and Crimdon Beck. The following composite section was measured in a syncline [NZ 477 382] at Limekiln Gill:

The two lowest units of the Upper. Magnesian Limestone in this section are similar in thickness and lithology to the Flexible Limestone, but differ from the latter in containing a Shelly fauna.

In the cliffs south of Limekiln Gill Middle Magnesian Limestone crops out in the core of an anticline. The Concretionary Limestone, dipping off the southern limb of this structure, is a repetition of the sequence measured at Limekiln Gill. The lowest 12 ft are non-concretionary and contain moulds of small lamellibranchs and of T. permianus. The overlying 31 ft of strata contain prominent concretionary structures which are particularly abundant in the more massive beds. These massive beds are usually about 1.5 to 3 ft thick, but laterally they give way abruptly along step-like interfaces to thin-bedded rocks containing only scattered concretions (Figure 24). Most beds contain internal moulds of lamellibranchs, often in abundance and sometimes uncompressed, while on some bedding planes there are large numbers of sub-parallel T. permianus. Partial collapse brecciation (Plate 13C) is widespread and breccia gashes incorporating fragments of red mudstone occur at intervals.

In the cliffs extending between 285 and 330 yd S.E. of Limekiln Gill the upper part of the above sequence appears to be represented by cream soft bedded dolomite, containing fossils only in the uppermost 6 ft. Farther south-east this is overlain by about 30 ft of similar thin-bedded and flaggy cream soft dolomite exposed in a shallow syncline 120 yd across. Moulds of lamellibranchs (chiefly S. schlotheimi) and of T. permianus are abundant. In the southern limb of the syncline, beds of this lithology are about 50 ft thick, the lowest 20 ft being the lateral equivalent of the soft dolomite exposed 285 to 330 yd S.E. of Limekiln Gill and the massive concretionary limestones into which they grade. Exposures are scarce between 450 and 820 yd S.E. of Limekiln Gill. At one locality [NZ 479 378] Middle Magnesian Limestone oolite forming the core of a small anticline is directly overlain by hard shelly thin-bedded dolomite locally forming the lowest member of the Concretionary Limestone. There is no brecciation either at the junction or in the conformable overlying beds. Brecciation is widespread, however, in most of the isolated exposures of finely granular (silt-grade) cream dolomite farther south, which contains small lamellibranchs and T. permianus, but in which concretionary structures are absent.

Concretionary Limestone, flexed in a gentle anticline, is continuously exposed from 820 yd to 1090 yd S.E. of Limekiln Gill. The northern limb is formed by about 21 ft of cream finely granular dolomite in flaggy and medium- to thick-bedded alternations containing moulds of lamellibranchs, and, in some beds, abundant sub-parallel T. permianus. Towards the crest of the flexure the dolomites become progressively harder and more calcareous, and midway along the exposure most beds pass laterally into hard crystalline concretionary limestone. Almost all the concretions are globular, radially crystalline, and 0.5 to 1.5 inches in diameter. Many are compound. Along the southern limb of the anticline only scattered concretionary structures are seen. The composite section at the southern end of the exposure is:

Analysis (Trechmann 1914, p. 236) shows the uppermost member of this section to be slightly impure dolomite with only 2.81 per cent excess calcite over the dolomite ratio. Trechmann described the rock as a "compact aggregate of very minute dolomite-grains". The lowest bed of the section passes northwards into non-concretionary dolomite. The base of the Concretionary Limestone is here about 15 to 20 ft below the lowest exposed bed so that the total thickness of the sub-division must locally be 105 to 110 ft.

Inland the Concretionary Limestone can now be seen only alongside Crimdon Beck, where it is exposed intermittently for 530 yd upstream and 60 yd downstream from the Blackhall Colliery–Hartlepool railway viaduct. All exposures are of cream soft bedded finely granular dolomite, containing moulds of L. squamosa and S. schlotheimi and large numbers of T. permianus. In a small outcrop in the stream bed, 440 yd W. of the viaduct, flaggy dolomite rests on cream oolitic dolomite, possibly at the top of the Middle Magnesian Limestone. In Nesbitt Dene, a mile or so to the west, the Concretionary Limestone appears to be locally overlapped by Hartlepool and Roker Dolomites. During 1960, a few feet of flaggy grey crystalline limestone and dolomitic limestone containing poorly-preserved lamellibranch moulds (chiefly Liebea) and T. permianus were exposed in shallow excavations [NZ 4876 3576], 250 yd W.N.W. of Springwell House.

Boreholes have proved Concretionary Limestone at Hartlepool, West Hartlepool and offshore. In a bore [NZ 5003 3430] at Howbeck Hospital, 1 mile S.E. of Springwell House, a section of the strata encountered beneath 140 ft of drift and Hartlepools and Roker Dolomite is:

Further details of this bore were given by Trechmann (1942, pp. 319–320) who assigned the hard platy rock at the top to the Hartlepool and Roker Dolomites.

In a bore at the Palliser Works [NZ 5061 3525], 1200 yd N.N.E. of the hospital, the Concretionary Limestone appears to be only about 10 ft thick. It is only 5 ft thick in a bore [NZ 5070 3343] at West Hartlepool Waterworks, where it consists of hard yellow platy dolomite, correlated by Trechmann (1932, p. 170) with the Flexible Limestone of Sunderland. From analysis of this dolomite Trechmann (1914, p. 238) calculated that there is 3.57 per cent of CaCO₃, in excess of that required to form pure dolomite: most of the 42.65 per cent insoluble residue is said to be silica. Farther south in Nelson Street No. 2 Bore [NZ 5154 3197], West Hartlepool, the Concretionary Limestone, including Flexible Limestone, is represented by 15.5 ft of hard grey dolomite at a depth of 241 ft (Trechmann 1942, p. 325). The same beds are 29 ft thick, 173 ft below the surface in a bore [NZ 5082 3233] at Villiers Street, West Hartlepool, where they are described by Fowler (1944, p. 201) as 'grey calcareous and micaceous dolomite interbanded with laminated dolomite, rich in bituminous streaks'. Quartz grains and muscovite flakes are seen in thin section to be widely distributed, and chest, fluorite, calcite and pyrite are also present. Bituminous material is concentrated chiefly in darker laminae, and is locally a major constituent of the rock. A specimen from 144 ft, rich in such laminae, was heated in a closed tube and yielded water and yellow oily material.

Because of its distinctive lithology the Concretionary Limestone can be recognized in drillers' records of the following old boreholes in the southern part of West Hartlepool:

The Flexible Limestone is represented by 2.5 ft of 'blue shaly limestone' in Burn Road No. 1 Bore, and by 3 ft of 'dark blue shale with small feeder of rock oil and sulphur water' in the Seaton Carew Bore.

In Offshore Nos. 1 and 2 bores the Concretionary Limestone is respectively 66 and 50 ft thick, including 3.75 ft and 6 ft of grey thin-bedded dolomite correlated with the Flexible Limestone. The sequence in Offshore No. 1 Bore is:

Because no fossils were found in this bore the top of the Concretionary Limestone is taken at a marked lithological break. In the interlaminated and interbedded sequences, the sulphate appears to replace dolomite along selected bedding planes, particularly those corresponding in horizon to the beds containing concretionary structures in coastal exposures. In Offshore No. 2 Bore the 44 ft of Concretionary Limestone above the Flexible Limestone consist of grey, massive dolomite, with no concretionary structures and only small amounts of secondary gypsum. D.B.S.

Hartlepool and Roker Dolomites

The Hartlepool and Roker Dolomites crop out in a syncline under the southern part of Horden, within an embayment of the Middle Magnesian Limestone reef at Thorpe Bulmer, and in the south-eastern part of the district. Inland, these beds are not known to exceed 150 ft in thickness, but they are 366 ft thick (with the topmost beds missing) in Offshore No. 2 Bore, 6 miles N. of Hartlepool. They are composed almost entirely of soft granular and oolitic cross-bedded ripple-marked dolomites which undergo no significant lateral variation in lithology.

Many of the ooliths in the oolitic beds are hollow; others have cores of crystalline calcite (Trechmann 1914, p. 250); whilst fluorite forms the cores of pisoliths in a boring at West Hartlepool (Trechmann 1941, p. 321). According to Woolacott (1919, p. 490) the ooliths were formed inorganically by the deposition of dolomite around gypsum nuclei. He quotes, as evidence, the gypsum still remaining in the oolith cores in borings around Billingham, 6 miles S.S.E. of West Hartlepool. Dunham (in discussion of Stewart 1963, p. 41), however, claims that the dolomite crystals forming the shells of the ooliths cut the concentric banding and that the original material was probably calcite. In the offshore area of the Durham district, oolitic dolomite with a gypsum cement contains many empty ooliths. Multiple ooliths and pisoliths are common, especially between 150 and 200 ft above the base of the sub-division.

The limited fauna (p. 153) of the Hartlepool and Roker Dolomites is unevenly distributed, some bedding-planes being crowded with moulds of shells whilst intervening beds are nearly barren. In the offshore area, where the highest beds are preserved, the Shelly fauna dies out about 200 ft above the presumed base of the sub-division. Plant remains, represented by obscure carbonaceous films, are present at all levels.

Details

At the coast the Hartlepools and Roker Dolomites form a series of isolated outcrops between slipped masses of drift extending for about 450 yd on the north side of Dene Mouth [NZ 457 408]. They consist of thin-bedded and flaggy cream finely granular (silt- to fine sand-grade) dolomites showing little vertical or lateral variation in lithology. Some highly porous beds may be altered fine oolites. Much of the bedding is slightly irregular, with local traces of shallow-angle cross-bedding and ripple marks. Thin discontinuous beds of dolomite mudstone occur also in places, and moulds of small gastropods and lamellibranchs (especially Liebea and Schizodus) are common at some horizons. The greatest thickness at any single exposure is about 20 ft, and the aggregate thickness is probably about 40 ft. Since Concretionary Limestone is not seen at this locality, the stratigraphical position of these rocks is determinable only by their fauna and lithology; these suggest a position low in the Hartlepool and Roker Dolomites.

Inland the Hartlepool and Roker Dolomites are exposed on the south side of Castle Eden Burn for about 250 yd upstream from the Horden–Blackhall Colliery road. Here they comprise about 50 ft of unevenly thin- and medium-bedded granular and oolitic dolomite; wedge-bedding is seen at some levels, and ooliths, many of them irregular or compound, are found chiefly in the upper parts of the sequence. About 20 ft of similar cream dolomite siltstone are exposed [NZ 4467 4039] on the opposite side of the Bum. Small-scale cross-bedding is widespread, but recognizable ooliths are rare. Since no diagnostic fossils were found among these rocks their correlation is based entirely on lithology and is thus tentative.

The following section is exposed [NZ 4516 4001] on the east side of Hardwick Dene, 900 yd N. of Hardwick Hall:

Much of the original texture of these beds has been obliterated by recrystallization. Trechmann (1913, p. 211) records Schizodus schlotheimi, 'Liebea septifer'and small gastropods from the uppermost 50 ft, and refers these beds to the Hartlepool and Roker Dolomites. Discontinuous exposures of these beds are also seen in a syncline between 780 and 600 yd N. of Hardwick Hall.

Two miles farther south, in Nesbitt Dene [NZ 460 370] beds thought to be Hartlepool and Roker Dolomites are represented by 50 to 60 ft of soft finely granular oolitic dolomite. Their base is nowhere visible, but it is inferred that the Concretionary Limestone is almost overlapped against the partially buried foreslope of the Middle Magnesian Limestone reef. The following section was measured in a small quarry [NZ 4619 3798], 1230 yd N.N.E. of Thorpe Bulmer:

Some 300 yd downstream these beds yielded the following: Tubulites permianus; L. squamosa and Schizodus schlotheimi: Trechmann (1942, p. 313) obtained 'Liebea hausmanni'and 'S. schlotheimi'from soft dolomite near the top of this sequence in the Thorpe Bulmer Bore. D.B.S.

At West Hartlepool the subdivision is now visible only in two old quarries [NZ 508 333], 800 yd N.N.W. of the station, and in a neighbouring railway cutting. The quarries contain a composite sequence of about 20 ft of cream granular and oolitic dolomite from which Trechmann (1913, p. 204) recorded 'Mytilus septifer', 'Pleurophorus costatus'and 'S. schlotheimi.'Current-bedding and thin lenses of sub-porcellanous dolomite occur throughout. Boreholes have proved beds of similar lithology to a depth of 34 ft below the floor of the more northerly of the two quarries (Trechmann 1913, p. 204; 1932, p. 170) and the beds in the railway cutting are also similar.

The old town of Hartlepool stands on a promontory of Hartlepool and Roker Dolomites, thinly covered with drift except on the seaward periphery where a sequence, 60 to 80 ft thick, is exposed in the cliffs and on wide wave-cut platforms. The beds are composed chiefly of granular and oolitic dolomite forming a series of low domes and shallow basins, with a low sheet-dip slightly north of east. The main bedding units are constant in thickness but cross-bedding, mostly small-scale, is widespread. Trechmann (1913, p. 204) measured 85 ft of beds at this locality and records 'Natica cf. leibnitziana', 'Turbo helicinus',small indeterminate gastropods, 'Mytilus septifer', 'Pleurophorus costatus'and 'Schizodus schlotheimi'from the lowest 35 ft. In addition Tubulites?, Omphalotrochus sp.and a fragment of Dielasma? (see p. 153) were collected during the resurvey from outcrops [NZ 5284 3340] on the beach, 320 yd S. of St. Hilda's Church, Hartlepool. An analysis (Trechmann 1914, p. 236) of an oolitic rock from Hartlepool Scars shows that it is an almost pure carbonate rock with 1.06 per cent CaCO₃ in excess of that required to satisfy pure dolomite. In the Hartlepools Lighthouse Bore, at the eastern end of the promontory, small specimens of Liebea and Schizodus were abundant in buff oolitic dolomite at 157.5 ft, proving that the Hartlepool and Roker Dolomites are here at least 200 ft thick. G.D.G., D.B.S.

The Hartlepool and Roker, Dolomites extend southwards beneath West Hartlepool and out to sea, where they have been proved in Offshore Nos. 1 and 2 bores. Under West Hartlepool they have been proved in the following bores: Howbeck Hospital No. 3 Bore [NZ 5003 3430] 107 ft (Trechmann 1942, p. 319); Hartlepool Corporation No. 9 Bore [NZ 5078 3249], 6 in; Villiers Street Bore [NZ 5082 3233], 118 ft; Smalley's Pulp Works No. 1 [NZ 5130 3186], 125 ft; Nelson Street No. 1 [NZ 5154 3197], 175 ft (Trechmann 1942, p. 324); Seaton Carew Bore 765 ft.; Casebourne Cement Works Bore 65.5 ft. Trechmann recorded small specimens of 'Liebea'and 'Pleurophorus'from the lower part of the Hartlepool and Roker Dolomites in the Nelson Street Bore, and Chondrites logaviensis Geinitz, Liebea squamosa and Schizodus schlotheimi were collected from these beds in Offshore No. 1 Bore.

The maximum proved thickness of the subdivision is 366 ft in Offshore No. 2 Bore (Magraw and others 1963, pp. 202–3), where it comprises:

Upper Permian Marls

The Upper Permian Marls are the deposits of the final silting up of the Zechstein Sea in Durham, and include portions of two evaporite cycles. The generalized sequence is:

These beds have been preserved only in the south-east of the district, around Embleton, where they crop out over an area of more than three square miles. Surface exposures are here obscured by drift and all the available information is from boreholes. These show that the subdivision thins westwards, and that most of the thinning is in the upper mudstones which are reduced from about 370 ft under the southern part of West Hartlepool to about 210 ft at Claxton. The top of the Upper Permian Marls is taken somewhat arbitrarily at the level where the intercalations of Bunter facies become predominant. This boundary is almost certainly diachronous; the scanty evidence from boreholes suggest that in addition to a gradual upwards increase in the proportion of sandstone, there is also a westerly increase, and this is taken to indicate that, as in Nottinghamshire (Sherlock 1926), there is lateral passage from mudstone to sandstone facies. Sulphates are absent at outcrop, presumably due to solution. D.B.S., G.D.G.

Details

At outcrop the Upper Permian Marls have been cored only in the Amerston Hall Bore, Embleton, where about 50 ft of dull brick-red sandy siltstone was proved. In uncored bores at Tinkler's Gill [NZ 4157 3054] and Middle Stotfold [NZ 4501 2987] these beds are respectively 75 ft and 206.5 ft thick. They have also been proved in a number of shallow bores in adjacent parts of the Stockton (33) district. The Upper Anhydrite and the Billingharn Main Anhydrite are not represented in the Amerston Hall Bore, and have not been recorded by the drillers of the uncored bores. Farther east, beneath Bunter Sandstone, the full thickness of the Upper Permian Marls is penetrated by three boreholes, of which the section in the Seaton Carew Bore (Bird 1888) may be taken as representative:

A similar section is recorded in the Caseboume's Cement Works Bore, West Hartlepool (Bird 1888), where the red mudstones are 390 ft thick, the Upper Anhydrite 18.5 ft, and the Billingham Main Anhydrite 62 ft thick overlying 15 ft 8 in of anhydrite mixed with limestone'. Since the maximum thickness of the Billingham Main Anhydrite at the type locality, 6 miles farther south, is 33 ft (Wood 1950) the Casebourne figure is exceptional, and may consist in part of anhydrite which has replaced Upper Magnesian Limestone. In another bore [NZ 4473 5276], 1 mile S. of Brierton, the lithology and thicknesses of the Dillingham Main Anhydrite and overlying marls and anhydrite are generally similar to those proved in the Seaton Carew Bore and in many boreholes (Marley 1892) around Billingham. In addition to these deep boreholes, the higher parts of the Upper Permian Marls were reached by a number of shallower holes, mainly in the Brierton and West Hartlepool areas.

North of the West Hartlepool Fault, the former presence of Upper Permian Marl is indicated by fragments of red and green silty marls which occur commonly in collapse-breccias within the Middle and Upper Magnesian Limestone in coastal areas north of Black Halls Rocks; and have been recorded as far north as Fulwell in the Sunderland (21) district Ming 1850, p. xvi). Farther east, beds tentatively interpreted as Upper Permian Marl have been reported (Clarke and others 1961, p. 207) from the undersea area off Tynemouth and these probably extend southwards and crop out on the sea bed in the eastern part of the present district. D.B.S., G.D.G.

Bunter Sandstone

Red sandstones of Bunter facies crop out, mainly beneath drift, over an area of about eight square miles between the West Hartlepool Fault and the southern margin of the district. Surface exposures in this area are found only on the foreshore at Seaton Carew and in the intertidal zone at Long Scar, 0.75 mile to the north-north-east. Farther west, borings show that these beds grade by alternation into the underlying Upper Permian Marls. The maximum recorded thickness of Bunter Sandstone in the district is 185 ft, in the Caseboume's Cement Works Bore, West Hartlepool. At Effingham, 6 miles farther south, the sandstone is about 700 ft thick, and structural evidence suggests that a comparable thickness is present immediately south of the Seaton Carew Fault.

The Bunter of the district is composed mainly of soft fine-grained thick-bedded, dull red sandstones, with subsidiary grey sandstones and red mudstones and siltstones. Current-bedding, ripple-marks, contemporaneoui (desiccation) breccias and ?sun cracks indicate shallow-water semi-continental deposition. Preferred orientations of fore-set current-bedding laminae indicate a south-westerly provenance which is in accord with the westerly increase in the proportion of sand noted in the transitional beds at the, base of the Bunter, and with the suggestion of a diachronous base falling westwards (p. 164). The siltstone and mudstone intercalations at outcrop contain wisps and irregular lenses and patches of pale grey-green colour: and at some localities there is extensive yellow and grey colouration which may be due to the former cover of peat—possibly an extension of the thick bed still preserved in a number of small patches at West Hartlepool. G.D.G., D.B.S.

Details

About 15 ft of thick-bedded and massive dull red soft fine-grained sandstone are exposed at low spring tides on Long Scar [NZ 520 310], where minor dome and basin structures are superimposed on a gentle anticline. The sandstone grains are predominantly sub-angular, and range from 0.125 to 0.250 mm except in thin coarser bands where they range up to 0–50 mm. Beds are inconstant in thickness, ranging from 6 in to 3 ft and are commonly current-bedded. The Long Scar rocks appear to lie about the middle of the Bunter Sandstone.

Little Scar [NZ 527 305] is the name given to a group of small outcrops on the foreshore at Seaton Carew. These beds lie near the base of the Bunter Sandstone and contain, in addition to red sandstone similar to that at Long Scar, beds of siltstone and mudstone. The siltstones and fine-grained sandstones are predominantly flaggy and thin-bedded, and are red, yellow and grey in colour; they exhibit abundant small-scale current-bedding and rare ripple-marks. The mudstones are darker coloured than the sandstone, contain thin grey-green bands, lenses and patches, and locally show signs of contortion and contemporaneous brecciation. Breccias of flakes and rolled fragments of mudstone in a fine sandstone matrix occur in several places. Current-bedding in the sandstones shows a marked preferred orientation indicating current-flow from the south and west, but ripple-marks are symmetrical and of the type normally ascribed to wave oscillation. In addition to forming individual beds, red mudstone also occurs infilling minor surface hollows in sandstones, and in some places contains desiccation cracks filled with sand.

Inland, Bunter Sandstone is proved in the following bores, all situated around the southern margin of West Hartlepool: Owton. Manor [NZ 4931 2956], 234 ft; C.W.S. Lard Works [NZ 5118 3158], 201 ft; Caseboune's Cement Works, 185 ft; and Seaton Carew, 93 ft. Due to the difficulty of recognizing the base of the Bunter facies, figures given are approximate. The Cement Works Bore, situated 1 mile N.W. of Little Scar, shows that red mudstone ('marl') is common in the lower parts of the Bunter sequence. G.D.G.

Keuper Marl

On structural grounds, it is inferred that more than 700 ft of strata are preserved above the base of the. Bunter near the coast immediately south of the Seaton Carew Fault. By comparison with the succession at Billingham, where the Bunter is only 700 ft thick, the uppermost beds are likely to be red Keuper Marl, though they are neither exposed nor proved by boring in the district. D.B.S.

Epigenetic minerals

Some of the many records of epigenetic minerals from the Permian rocks of Durham are summarized by Fowler (1943, 1957) who found that they tend to be concentrated in two parts of the succession. The lower comprises the Marl Slate and the immediately overlying beds, where the most common minerals are calcite, galena, chalcopyrite, pyrite, sphalerite and baryte; the higher lies near the top of the Lower Magnesian Limestone and is characterized by calcite, baryte and fluorite. Minerals also occur, however, throughout the remainder of the sequence: dolomite, baryte and pyrite are the most common, apart from gypsum and anhydrite, which are ubiquitous cavity-fillings in areas protected from solution.

Pyrite commonly replaces rock fragments, particularly mudstone, in the Basal Permian Breccias; and Phemister (in Fowler 1943, p. 43) records baryte and fluorite locally replacing country rock near the top of the Lower Magnesian Limestone. Most mineralization, however, is found in and along cavities, bedding-planes, joints and fissures; and this association is emphasized in the Ferryhill–Garmondsway area by a concentration of metallic ore-minerals close to the Butterknowle Fault.

A list of minerals recorded before and during resurvey is given, together with selected localities, in (Table 3).

The origin and age of the epigenetic mineralization is in dispute. Fowler (1943, p. 50; 1957, p. 265) considered it to be contemporaneous with mineralization seen in Coal Measures and followed Trotter (1944, p. 227) in assuming a Tertiary age. Dunham (1952, p. 4) agreed with this, though he believed the probable age of the workable deposits of fluorite in the north Pennines to be late Carboniferous or early Permian. Westoll (1943), however, claimed that in the Marl Slate some, at least, of the blende, galena, chalcopyrite and malachite is syngenetic; and that, as in the Kupferschiefer, these minerals show signs of diagenetic mobilization within the deposit and through overlying strata.

With the possible exception of baryte none of the epigenetic minerals in the Permian is present in commercial quantities, but these minerals are locally important in some dolomite quarries in the Lower Magnesian Limestone where they represent concentrations of impurities. D.B.S.

Permian fossils

In addition to the fossils listed in the stratigraphical account the following have been identified from underground exposures and boreholes.

Tunnels at Easington Colliery

See pp. 136–7 for stratigraphical details. There are at least three distinct types of fossil assemblages in these Easington Colliery collections. In the first type (localities 1 and 3) Stenoscisma is abundant and Horridonia, gastropods and larnellibranchs are fairly common. The lamellibranchs include such genera as Cardiomorpha, Solemya and Schizodus. Strophalosiids and cryptostome polyzoa are rare or absent. The second type of assemblage (localities 2 and 7) is dominated by Strophalosiids and includes abundant cryptostome 'polyzoa'. Horridonia and gastropods are rate or absent. Lamellibranchs are fairly common but are almost limited to Bakevellia, Pseudomonotis and Parallelodon. The third type (localities 5 and 6) is a sparser fauna dominated by Synocladia virgulacea which is rare or absent in the other two assemblages.

1. Horizontal tunnel, 70 yd W.S.W. of West Pit.Ht. above O.D. about 8 ft. National Grid Ref. [NZ 4367 4412]. Middle Magnesian Limestone, early reef-talus at foot of reef-slope. Algal filaments; 'Glomospira' pusilla; crinoid columnals; Acanthocladia anceps, Batostomella crassa, Fenestrellina retiformis, Protoretepora ehrenbergi (Geinitz), Thamniscus dubius; Cleiothyridina pectinifera, Crurithyris clannyana, Dielasma elongatum, Horridonia horrida [abundant] [(Plate 6), fig. 6], Orthothrix excavata, Pterospirifer alatus, Spiriferellina cristata multiplicata, Stenoscisma schlotheimi [abundant], Streptorhynchus pelargonatus. Strophalosiid [ventral valve with vermiform spines, asymmetrical pointed umbo: ?Craspedalosia or Dasyalosial; Straparollus permianus, Loxonema fasciatum, L. cf. retusum Dietz, L. sp.[with at least 12 whorls], ?Macrochilina symmetrica (King), Omphalotrochus sp.[including a fine-ribbed form intermediate between O. thomsonianus and O. taylorianus in number of whorls and spiral angle], Pleurotomaria linkiana, P. verneuili Geinitz, Strobeus geinitzianus; Bakevellia ceratophaga, Cardiomorpha modioliformis (King), Palaeolima? permiana, Parallelodon striatus, Permophorus costatus, Pseudomonotis speluncaria, Schizodus truncatus, Solemya biarmica, Streblochondria pusilla; ostracods. Polyzoa and Strophalosiid brachiopods are rare.
2. Horizontal tunnel, 55 yd W.S.W. of West Pit. Height above O.D. about 7.5 ft. National Grid Ref. [NZ 4368 4413]. Middle Magnesian Limestone, reef-talus at foot of reef-slope; slightly younger than at locality 1. Algal debris; Fenestrellina retiformis; Crurithyris clannyana, Dielasma elongatum, Orthothrix excavata, O. cf. lewisiana, Stenoscisma schlotheimi; indet. gastropod; Bakevellia antiqua, Parallelodon striatus, Pseudomonotis speluncaria. In contrast to that from locality 1, this fauna is dominated by cryptostome polyzoa and Strophalosiids.
3. Inclined adit, 400 yd W. of West Pit and 180 yd from adit mouth. Height above O.D. about 8 ft. National Grid Ref. [NZ 4341 4410]. Middle Magnesian Limestone, coquina at base of reef. 'Glomospira' pusilla; crinoid stems; Batostomella crassa; Dielasma elongatum, Horridonia horrida, Stenoscisma schlotheimi, Spiriferid fragments; Straparollus?, Macrochilina symmetrica, Naticopsis sp., Omphalotrochus spp.[including O. cf. taylorianus], Strobeus geinitzianus; Parallelodon striatus, Permophorus costatus, Pseudomonotis speluncaria, Schizodus sp.; Peripetoceras freieslebeni. This fauna is akin to that from locality 1 in the relative abundance of Stenoscisma and gastropods and the fact that Strophalosiids and, more remarkably, cryptostome polyzoa are unrecorded.
4. Inclined adit, as 3 but 150 yd from mouth. Height above O.D. about 115 ft. National Grid Ref. [NZ 4344 4411]. Middle Magnesian Limestone, massive reef-dolomite. Acanthocladia anceps, Fenestrellina retiformis; Dielasma elongatum, Stenoscisma schlothemi [abundant], Spiriferellina cristata multiplicata; Naticopis leibnitziana; Bakevellia?, ?Parallelodon striatus, Pseudomonotis speluncaria, Streblochondria pusilla.
5. Inclined adit, 125 yd from mouth. Height above O.D. about 135 ft. National Grid Ref. [NZ 4346 4412]. Middle Magnesian Limestone, massive reef-dolomite. Adhaerentina permiana, 'Glomospira' sp.; ?'Spongia' schubarthi Geinitz; Batostornella crassa, Fenestrellina retiformis, Synocladia virgulacea; Dielasma elongatum, Stenoscisma schlotheimi; Bakevellia antiqua, Pseudomonotis speluncaria; ostracods.
6. Inclined adit, 100 yd from mouth. Height above O.D. about 165 ft. National Grid Ref. [NZ 4348 4413]. Middle Magnesian Limestone, massive reef-dolomite. 'Glomospira' milioloides; ?'Spongia' schubarthi; Synocladia virgulacea; Orthothrix sp., coarsely spinose Strophalosiid, Stenoscisma sp.; Pseudomonotis speluncaria.
7. Inclined adit, 50 yd from mouth. Height above O.D. about 215 ft. National Grid Ref. [NZ 4353 4416]. Middle Magnesian Limestone, late-stage reef-dolomite. Batostomella crassa, Fenestrellina retiformis, ?Synocladia virgulacea; Dielasma elongatum, Orthothrix excavata, O. cf. lewisiana; Bakevellia? [juv]; ostracods.

Borehole at Mill Hill Reservoir, Easington

See pp. 113, 125, 137–8 for stratigraphical details Ht. above O.D. 509 ft. National Grid Ref. [NZ 4122 4248]

• (a) Dolomite, reef-top sub-facies. Depth 53 ft to 54 ft: Filamentous algal debris; Glomospira sp.; ?Naticopis alterodensis Dietz, N. leibnitziana, ?Omphaloptycha pupoidea Dietz, Strobeus?, small gastropod with an angular lower edge to the last whorl, indet. turreted gastropod; Bakevellia antiqua. Depth 56 ft 6 in to 63 ft 6 in: Filamentous algae, algal nodules [about 10.0 mm diameter]; Naticopsis?, Omphalotrochus sp.; Bakevellia cf. antiqua; ostracods. The shelly material occurs in pockets between sheets of algal filaments.
• (b) Massive reef dolomite. Depth 69 ft 9 in: Algal filaments; Omphalotrochus spp.; Bakevellia cf. antiqua, B. ceratophaga, Parallelodon striatus, ?Permophorus costatus. Depth 70 ft 6 in: Algal filaments; ?coiled foraminifer; indet. turreted gastropod; ostracod.
• (c) Soft bioclastic dolomite of reef facies. Depth 72 ft 6 in to 75 ft: Algal filaments [abundant]; 'Adhaerentina' permiana [abundant]; Fenestrellina retiformis, indet. cryptostome polyzoa; ?Craspedalosia lamellosa (Geinitz), Dielasma elongatum, Orthothrix excavata [abundant]; Omphalotrochus spp.including O. cf. helicinus and O. cf. taylorianus, smooth gastropods including Naticopsis sp.; B. antiqua, B. ceratophaga, Cardiomorpha modioliformis, Pseudomonotis speluncaria; ostracods. This fauna is dominated by 'Adhaerentina'and Strophalosiids. Gastropods and lamellibranchs are rare. The algal filaments are not in sheets as found higher in the borehole, but are (i) wound irregularly about the abundant shells and (ii) form series of nodules in single planes, the surfaces of which are covered with a brown crust. The nodules are up to 40.0 mm diameter. Depth 76 ft to 82 ft: Loxonema fasciatum, Omphalotrochus sp., indet. turreted gastropods; Bakevellia sp.[juv.], Permophorus? [large lamellibranchs with extended posterior and concentric ornament but no radial costae. They are more tumid than normal Permophorus costatus].
• (d) Soft granular dolomite, transitional between reef and lagoonal facies. Depth 82 ft 6 in to 83 ft 6 in: Spirorbis sp.; Strobeus?; lamellibranch fragment; rod-like structures, straight or curved with no regular internal structure seen [the dimensions are: diameter 8.0 to 13.0 mm and length 60.0 to 70.0 mm. They are possibly remains of worm burrows].
• (e) Lagoonal dolomite adjacent to reef. Depth 86 ft 6 in to 90 ft; Algal filaments; Loxonema fasciatum, ?Naticopis leibnitziana, Omphalotrochus spp.including O. helicinus, Strobeus geinitzianus, indet. turreted gastropod; Bakevellia antiqua, ?Permophorus costatus, Pseudomonotis speluncaria.
• (f) Soft granular lagoonal dolomite. Depth 90 ft to 120 ft: 'Ammodiscus' roessleri; Loxonema fasciatum, Omphalotrochus sp., Straparollus permianus, ?Strobeus geinitzianus; Bakevellia sp.; ostracods. Depth 164 ft to 171 ft 3 in: Coiled foraminifera including 'Glomospira' milioloides; Horridonia horrida; Astartella?; ostracods.
• (g) Fine-grained saccharoidal lagoonal dolomite. Depth 204 ft: 'Ammodiscus'?, 'Glomospira' pusilla; ?Productid spines; Bakevellia antiqua, Schizodus schlotheimi.
• (h) Fine-grained saccharoidal dolomite; transitional beds at base of Middle Magnesian Limestone. Depth 243 ft to 263 ft: Coiled foraminifera including 'Adhaerentina permiana', 'Ammodiscus' roessleri [abundant], Glomospira milioloides, G. pusilla, ?uniserial, chambered foraminifer; Astartella vallisneriana [abundant], Permophorus sp.; ostracods.
• (i) Lower Magnesian Limestone. Depth 280 ft: Coiled foraminifera; Cleiothyridina pectinifera. Depth 304 ft: Schizodus cf. schlotheimi; ostracods. Depth 313 ft: Coiled foraminifera; coarsely-ribbed lamellibranch. Depth 373 ft: 'Glomospira' cf. pusilla.

Hesleden Dene No. 1 Bore

Height above O.D. about 85 ft. National Grid Ref. [NZ 4672 3697]

• (a) Reef-dolomite
• Depth 176 ft to 180 ft: Algal debris; 'Adhaerentina' permiana, 'Glomospira' gordialis, 'G.' pusilla; cryptostome polyzoa including Thamniscus dubius; Strophalosiid [juv.]; Naticopsis leibnitziana, indet. turreted gastropod; Astartella sp., Bakevellia ceratophaga; nautiloid fragments; ostracods.
• Depth 187 ft to 190 ft: Batostomella crassa; Orthothrix excavata; ?Loxonema fasciatum, Omphalotrochus sp.; Bakevellia sp., Permophorus sp. [juv.] ostracods.
• Depth 228 ft to 230 ft: 'Glomospira' pusilla; Batostomella crassa; Dielasma?; Bakevellia antiqua, Parallelodon?

Hesleden Dene No. 2 Bore

Ht. above O.D. 92.6 ft. National Grid Ref. [NZ 4654 3698]

• (a) Middle Magnesian Limestone. Bedded off-reef calcarenite near foot of reef fore-slope.
• Depth 246 ft to 250 ft: 'Adhaerentina' permiana [abundant], 'Glomospira' gordialis, 'G.' cf. pusilla; ?Lingula credneri Orthothrix sp.and other Strophalosiids; Bakevellia cf. antiqua; ?ostracods; fish spine.
• Depth 251 ft to 257 ft: 'A.' permiana, ?Geinitzina jonesi (Brady), 'Glomospira' pusilla; ?sponge [very finely patterned mesh on a plane surface]; Horridonia horrida, Strophalosia morrisiana; Dentalium?, Straparollus permianus, ?Naticopsis minima, turreted gastropods including Strobeus geinitzianus; Bakevellia ceratophaga, Liebea sp., Perrnophorus costatus, Schizodus schlotheimi, S. truncatus, S. sp.[with the rounded beak of S. schlotheimi, but the umbo is at extreme anterior end of the shell], Solemya biarmica, ?Wilkingia elegans (King); ostracods.
• Depth about 270 ft: 'A.' permiana, 'Ammodiscus' roessleri, 'Glomospira' sp., ?uniserial, chambered foraminifer; ?trepostome polyzoa; ostracods.

Hesleden Dene No. 3 Bore

Ht. above O.D. 88.4 ft. National Grid Ref. [NZ 4660 3703]

• (a) Middle Magnesian Limestone. Bedded off-reef calcarenite near foot of reef fore-slope.
• Depth 193 ft to 194 ft: 'Adhaerentina' permiana, 'Glomospira' gordialis, 'G.' pusilla, uniserial, chambered foraminifera including ?Spandelinoides geinitzi (Reuss); crinoid columnals; Fenestrellina retiformis, Protoretepora ehrenbergi; Horridonia horrida, Orthothrix sp., Stenoscisma sp.; Omphalotrochus sp., Strobeus geinitzianus, ?S. leighi (Brown); ostracods.
• Depth 207 ft 6 in: 'G.' gordialis, 'G.' pusilla, uniserial, chambered foraminifera; Fenestrellina sp.; Dielasma sp., Strophalosiids including Orthothrix sp., Stenoscisma schlotheimi, ?small Spiriferid; Bakevellia cf. ceratophaga, Parallelodon striatus; ostracods; fish remains.
• Depth 209 ft to 212 ft: 'Adhaerentina' permiana, 'Glomospira' gordialis, G: pusilla, uniserial, chambered foraminifera; Batostomella crassa, cryptostome, polyzoa; Horridonia?, Orthothrix excavata [juv.]; Strobeus geinitzianus [abundant at 211 ft 6 in to 212 ft], indet. non-turreted gastropods; Astartella?, Bakevellia antiqua, B. ceratophaga, Permophorus costatus, Schizodus sp.; ostracods; lanassa bituminosa Schlotheim ((Plate 6), fig. 11).
• (b) Middle Magnesian Limestone. Hard crystalline oolitic dolomite.
• Depth 250 ft: 'Ammodiscus' roessleri, 'Glomospira' pusilla, uniserial, chambered foraminifera; Horridonia horrida; ostracods.

Fishburn No, 3 Bore

Ht. above O.D. 298 ft. National Grid Ref. [NZ 3718 3084]

• (a) Middle Magnesian Limestone, lagoonal dolomite.
• Depth 124 ft to 125 ft: ?Productid spines and Omphalotrochus?
• Depth 146 ft to 172 ft: 'Glomospira' sp.; Spirorbis?; crinoid stem; ?Productid spines; gastropods including Omphalotrochus?; Astartella?, Bakevellia antiqua, B. ceratophaga, Schizodus sp.; ostracods.
• Depth 197 ft to 216 ft 6 in: 'Adhaerentina' permiana, 'Ammodiscus'?, 'Glomospira' milioloides, 'G.' pusilla.; ?Fenestrellina retiformis; Horridonia horrida, H. horrida [juv.] or small Strophalosiid; ?B. antiqua, B. cf. ceratophaga, Permophorus costatus, Schizodus sp., Solemya?; ostracods.
• Depth 220 ft to 227 ft: Tubulites permianus (King) [see p. 131]; Astartella?, B. antiqua, B. ceratophaga, Permophorus sp., Solemya?, Schizodus schlotheimi, S. truncatus [juv.]; ostracods.
• (b) Lower Magnesian Limestone.
• Depth 285 ft: Strophalosia morrisiana.
• Depth 305 ft 6 in: 'Ammodiscus' roessleri, 'Glomospira' pusilla; B. antiqua; ostracods.
• Depth 320 ft: Rootlets; 'Adhaerentina' permiana, 'Ammodiscus' roessleri, 'Glomospira' pusilla,; ostracods.
• Depth 353 ft: Strophalosia morrisiana. Depth 386 ft: Lingula credneri; ?ostracod.

Fishburn No. 4 Bore

Ht. above O.D. 310 ft. National Grid Ref. [NZ 3858 3120]

• (a) Middle Magnesian Limestone, lagoonal dolomite.
• Depth 121 ft to 143 ft: Tubulites?; 'Adhaerentina' permiana, 'Ammodiscus' roessleri, 'Glomospira' cf. milioloides; Horridonia horrida; indet. turreted gastropod; Bakevellia antiqua, Permophorus sp. [juv.], Schizodus schlotheimi, Solemya? ostracods.
• (b) Lower Magnesian Limestone. Depth 300 ft to 307 ft: Rootlets.
• Depth 311 ft 6 in to 321 ft 6 in: Indet, plant remains; 'Glomospira' pusilla; Strophalosia morrisiana.
• Depth 330 ft to 359 ft: Plant fragments; 'Adhaerentina' permiana, 'Ammodiscus' roessleri, uniserial, chambered foraminifera including ?Geinitzina jonesi, 'Glomospira' pusilla; Acanthocladia anceps, Batostomella crassa, Fenestrellina retiformis, ?Hippothoa aff. voigtiana (King) [see note 1], Polyzoan ?Gen. et sp.nov.[see p. 181]; Crurithyris?, ?Dielasma elongatum, Horridonia horrida, Neochonetes? [see note 2], Pterospirifer cf. alatus (Schlotheim), Strophalosia morrisiana, Strophalosiid [juv.] [see note 3]; Bakevellia antiqua, Streblochondria pusilla; ostracods.
• Note 1. The ?Hippothoa differs from King's figured specimen (1850, pl. iii, fig. 13) in lacking a neck at the proximal end of each bead and in the regular increase in size of beads from the distal to the proximal end of the organism.
• Note 2. Several ventral valves are preserved. They are smooth except for concentric growth lines and spines in a row along the posterior margin and sparsely scattered on the rest of the valve. The cardinal extremities are upturned but the greater part of the valve is moderately convex. The dimensions of this valve are about 10.0 mm wide and 7.0 mm long. The dorsal valve was not clearly seen.
• Note 3. A flat, sub-triangular, ventral valve with numerous coarse spines which are neither vermiform nor adpressed.

Fishburn 'D' Bore

Ht. above O.D. 318 ft. National Grid Ref. [NZ 3567 3106]

• (a) Middle Magnesian Limestone, lagoonal dolomite.
• Depth 91 ft to 100 ft: Tubulites?; indet. gastropod; Bakevellia antiqua [stunted], B. cf. ceratophaga [stunted], Permophorus sp. [juy.]; ostracods.
• Depth 117 ft: Schizodus cf. truncatus.
• Depth 120 ft: 'Glomospira' pusilla, ?uniserial, chambered foraminifer; cryptostome polyzoa; Bakevellia sp.; ostracods.
• Depth 134 ft 6 in: 'Adhaerentina' permiana, 'Ammodiscus'?, 'Glomospira' milioloides; ?Strophalosia morrisiana [juv.]; B. antiqua, B. cf. ceratophaga; ostracods,
• Depth 140 ft to 152 ft: 'Adhaerentina' permiana, 'Glomospira' milioloides, 'G.' pusilla; Bakevellia sp., Schizodus? [juv.];ostracods.
• (b) Lower Magnesian Limestone.
• Depth 212 ft to 216 ft: 'Ammodiscus' roessleri, 'Glomospira' milioloides, 'G.' pusilla, uniserial, chambered foraminifer; Bakevellia cf. ceratophaga; ostracods.
• Depth 239 ft to 257 ft: Plant remains including Chondrites logaviensis; 'Adhaerentina' permiana, 'Ammodiscus'?, 'Glomospira' milioloides, 'G.' pusilla, ?Spandelinoides geinitzi; Acanthocladia anceps, Batostomella? [at 257 ft]; Strophalosia morrisiana; Bakevellia antiqua; ostracods.
• Depth 292 ft to 318 ft: Plant remains; 'Adhaerentina' permiana, 'Glomospira' milioloides, 'G.' pusilla; Batostomella columnaris (Schlotheim); Strophalosia morrisiana; Bakevellia cf. ceratophaga.
• Depth 326 ft: Plant remains [abundant]; 'Adhaerentina' permiana, 'Ammodiscus'?, 'Glomospira' pusilla; Batostomella crassa, cryptostome polyzoa; Crurithyris? [small valve].
• Depth 342 ft: Lingula credneri, Neochonetes? sp.  nov. [see note].
• There are several specimens of Neochonetes?. The ventral valve is wide and flat with a long hinge-line almost equal to the width of the shell. The surface has concentric growth lines and sparse and irregularly spaced coarse spines plus a single row of 74 coarse spines on each side of the umbo and parallel to the hinge-line. The beak does not overhang the hinge-line. There is a distinct area and delthyrium with a convex pseudodeltidium. The ventral valve is about 17.0 mm wide and 14.0 mm long. The dorsal valve is flat to slightly concave with coarse concentric growth lines becoming almost lamellose. No spines were seen on the dorsal valve.
• Assignment of these brachiopods to Neochonetes is doubtful because of the lack of any radial ornament and the presence of spine-bases on the ventral valve in addition to those adjacent to the posterior margin. Somewhat similar but smaller shells were found in the Lower Magnesian Limestone of Fishburn No. 4 Bore from between 330 ft and 359 ft.

Ten-O'-Clock Barn No. 1 Bore

Ht. above O.D. about 310 ft. National Grid Ref. [NZ 3992 2980]

• (a) Middle Magnesian Limestone, lagoonal beds.
• Depth 422 ft: Tubulites?; 'Ammodiscus' roessleri, 'Glomospira' sp.; ?Productid spine; Astartella?, Bakevellia antiqua; ostracods.
• Depth 458 ft 9 in to 462 ft: 'Adhaerentina' permiana, 'Ammodiscus' roessleri, 'Glomospira' cf. milioloides, 'G.' pusilla; Astartella vallisneriana, Bakevellia sp. Liebea squamosa, Palaeolima?, Schizodus schlotheimi; ostracods.
• Depth 465 ft 6 in to 470 ft 3 in: 'Adhaerentina' permiana, 'Ammodiscus' roessleri, 'G.' pusilla; cryptostome polyzoa including Thamniscus dubius; Horrjdonia horrida; indet. lamellibranch; ostracods.

Whin Houses Bore

Ht. above O.D. 307 ft. National Grid Ref. [NZ 3997 3058]

• (a) Middle Magnesian Limestone, lagoonal dolomites.
• Depth 224 ft to 226 ft 8 in: Tubulites?, strap-like plant remains; 'Glomospira' milioloides; Bakevellia sp.
• (b) Middle Magnesian Limestone, transitional beds.
• Depth 254 ft 6 in to 260 ft 9 in: 'Ammodiscus' roessleri, 'Glomospira pusilla; Neochonetes? davidsoni, Strophalosia morrisiana; ostracods.
• (c) Lower Magnesian Limestone.
• Depth 275 ft to 287 ft 6 in: 'A.' roesskri, 'Glomospira' milioloides and ?uniserial, chambered foraminifera.
• Depth 365 ft to 366 ft: G.' pusilia, uniserial, chambered foraminifera; cryptostome polyzoa; S. morrisiana; ostracod.
• Depth 403 ft to 405 ft: Plant remains; 'Adhaerentina' permiana, pusilla; Batostomella crassa, cryptostome polyzoa; indet. brachiopod; ostracods.
• Depth 414 ft: Strophalosia morrisiana.
• Depth 418 ft 6 in to 428 ft 6 in: 'A.' roessleri, 'G.' pusilla; Polyzoan, ?Gen. et sp.nov.[see note on p. 181], ?Penniretepora waltheri (Korn) [one stem with numerous short side branches. The finely ribbed reverse side only is visible]; ?Howseia latirostrata (Howse).
• The last named has a convex ventral valve, 10.0 mm wide and 9.0 mm long with a long hinge-line, an umbo which is tumid but does not overhang the hinge-line and spines including a row round the anterior margin.
• Depth 444 ft 6 in to 459 ft 6 in: 'G.' pusilla; crinoid columnals; Acanthocladia anceps; Crurithyris clannyana, Dielasma sp., Productoid? [juv.]; Bakevellia cf. antiqua; ostracods.

Hartlepool Lighthouse Bore

Ht. above O.D. 25.5 ft. National Grid Ref. [NZ 5319 3387]

• (a) Upper Magnesian Limestone, Hartlepool and Roker Dolomite.
• Depth 147 ft to 150 ft: Liebea squamosa, Permophorus sp., Schizodus schlotheimi; ostracods. The lamellibranchs are stunted to varying degrees.
• (b) Middle Magnesian Limestone. Bedded off-reef calcarenite.
• Depth 635 ft 9 in to 637 ft: 'Adhaerentina' permiana, 'Ammodiscus' roessleri, 'Glomospira' gordialis, 'G.' pusilla; crinoid columnals; Acanthocladia anceps, Batostomella crassa; Horridonia horrida, small valve of indet. Productid; ostracods.
• Depth 647 ft 3 in to 653 ft: ? 'Adhaerentina' permiana, 'Glomospira' 'G' pusilla, uniserial, chambered foraminifer, ?coiled foraminifer [very small: c.0.1 mm long]; crinoid columnals; cryptostome polyzoa; Horridonia?.
• Depth 655 ft 6 in to 658 ft 10 in: 'Ammodiscus' roessleri, 'Glomospira' gordialis, 'G.' pusilla, uniserial, chambered foraminifera including ?Nodosaria kingii, ?Spandelinoides geinitzi; crinoid columnals; Calophyllum profundum (Germar); Acanthocladia or Thamniscus sp., Batostomella crassa, Fenestrellina retiformis, Protoretepora ehrenbergi, ?Synocladia virgulacea; Crurithyris clannyana, Horridonia?, Spiriferid fragment, Stenoscisma?, Streptorhynchus pelargonatus; Strobeus geinitzianus; Bakevellia? [juv.].
• Depth 659 ft to 664 ft 3 in: Coiled foraminifera, uniserial, chambered foraminifera; Acanthocladia anceps, Fenestrellina retiformis, Thamniscus dubius; Crurithyris?, Orthothrix exavata, Spiriferellina cristata multiplicata, Stenoscisma sp., small indet. Strophalosikis; ostracods.
• Depth 664 ft 4 in to 667 ft 6 in: Crinoid columnals; ?echinoid spine; Acanthocladia or Thamniscus, Batostomella crassa; Horridonia horrida, Strophalosia morrisiana; indet. gastropod; ostracods; fish debris.
• (c) Middle Magnesian Limestone, transitional beds.
• Depth 707 ft 6 in to 717 ft 6 in: 'Glomospira' gordialis, 'G' pusilla, uniserial, chambered foraminifer; ?cryptostome polyzoa and ostracods,
• Depth 744 ft: 'Glomospira' pusilla; Batostomella crassa; cryptostome polyzoan fragments including Acanthocladia?; Productoid brachiopods, indet. Spiriferid.
• (d) Lower Magnesian Limestone, near base.
• Depth 841 ft: Coiled foraminifera including 'G.' pusilla; crinoid columnals Batostomella?. D.B.S.

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WOLANSKA, H. 1959. Agathammina pusilla (Geinitz) z Dolnego Cechsztynu Sudetow i Gor Swietokrzyskich. [A. pusilla (Geinitz) from the Lower Zechstein in the Sudeten and Holy Cross Mountains, with English summary]. Acta. palaeont. pol., 4, 27–59.

WOOD, F. W. 1950. Recent information concerning the evaporites and the pre-Permian floor of south-east Durham. Quart. J. Geol. Soc., 105, 327–46.

WOOLACOTT, D. 1912. The stratigraphy and tectonics of the Permian of Durham (northern area). Proc. Univ. Durham Phil. Soc., 4, 241–331.

WOOLACOTT, D. 1919a. Borings at Cotefield Close and Sheraton, Durham. Geol. Mag., 6, 163–70.

WOOLACOTT, D. 1919b. The Magnesian Limestone of Durham. Geol. Mag., 6, 452–65, 485–98.

Chapter 4 Intrusive igneous rocks

General account

Igneous intrusions in the Durham–West Hartlepool district take the form mainly of dykes and minor associated sills. They consist of quartzdolerites and tholeiites allied in type to the Whin Sill (Holmes and Harwood 1928). Unweathered rocks are dark grey and fine-grained, but at outcrop they develop a light to rusty brown limonitic skin. In thin section (p. 190), they are seen to consist essentially of plagioclase feldspar, pyroxene and iron ores with accessory orthoclase, quartz and pyrite, and secondary carbonates. Alteration is most pronounced at fine-grained margins, where primary minerals are replaced by carbonates and clay minerals giving rise to 'white trap'.

The principal dykes of the district are the Hett, Brandon and Ludworth dykes (Plate 14), and it is with the last-named that sills are mainly associated. Shales and mudstones adjacent to the intrusions are indurated and lose fissility, while some sandstones take up volatile material released from the coals. As noted by Edwards and Tomlinson (1958, p. 54), coal is altered for only a short distance on either side of the Hett Dyke, but more extensively adjacent to the Ludworth Dyke. In the Easington and Horden area, for instance, the latter is flanked by belts, 0.75 mile wide, of low volatile coals and associated effects can be detected for more than 1.5 miles to the north and south of it. To the east and west of this area, the zone of altered coal is much narrower.

Since the intrusions cut Middle Coal Measures, but are overlain by Upper Permian strata, they are clearly late Carboniferous or Lower Permian in age. The relationship of the intrusions to the structural features of the district is considered in Chapter V, and it will suffice here to note that the dykes have an east-north-easterly trend corresponding with that of some of the faults. According to Dunham (1948, p. 75), the dykes were intruded in tension fissures after the formation of the master joints and marginal faults and before the formation of the conjugate vein-fissures. E.A.F., D.B.S.

Details

Hett Dyke

Near the eastern margin of the Wolsingham (26) Sheet, the Hett Dyke is 12 ft wide trending N. 74° E in Harvey Coal workings. Followed eastwards into the Durham district, it is offset 50 yd to the north by a north–south fault, beyond which it can be traced towards Hett by a line of old quarries clearly marked by a partially-filled trench. At Hett the dyke was once worked from six shafts, and Teall (1884, p. 228) recorded its width at this locality to be 10 ft with a steep inclination towards the north. The position of the dyke in the Brockwell Seam, however, 700 to 750 ft below, is virtually vertically beneath the surface position. The dyke was also quarried [NZ 2875 3705] on the south side of the railway, but it is now exposed only in the bed of Tursdale Beck [NZ 2885 3707], 500 yd W. of Tursdale House, where it is at least 9 ft wide. For a distance of about 1.75 miles east of the beck, the surface position of the dyke is obscured by drift, but its continuity has been proved in the Busty, Harvey and Durham Low Main workings. The trend underground is about N. 73° E. near Tursdale Beck, and about N. 70° E. near Bowburn.

The dyke is next seen at outcrop 500 yd N.N.W. of Heugh Hall Row. Thereafter, it trends N. 66° E. in workings in the Busty Coal, 400 yd E. of Hill Top Farm, in the Bottom Hutton Coal, 1050 yd S.S.W. of Old Cassop, and in the Five-Quarter and Main coals, 500 yd S. and S.E. of Old Cassop. Middle Coal Measures crop out in Cassop Vale above the position of the dyke in the Bottom Hutton Coal and a small feature on the southern side of the Vale may mark the outcrop of the dyke. Above the underground positions of the dyke in the Busty, Main and Five-Quarter coals, however, the outcrop is formed by Permian rocks which shown no sign of having been intruded, though the line of the dyke can be followed at a locality [NZ 3365 3895] 550 yd S. of Old Cassop and elsewhere by subsidence fissures marking the limit of coal extraction beneath. This finally supplies the evidence which Holmes and Harwood (1928, p. 524) were unable to find in support of the generally held belief that the dyke continues in Coal. Measures beneath the Permian cover.

In the eastern area, the course of the dyke coincides with the plane of a small fault under Quarrington Hill near Hill Top Farm, and continues for about 1.5 miles to the east-north-east on the same line. The dyke is apparently absent east-north-east of a locality [NZ 3466 3942] 600 yd N.N.W. of Dene House Farm, but the fault continues in the Bottom Hutton Seam and thence through Thomley Colliery workings.

Brandon Dyke

The Brandon Dyke was formerly thought to die out before reaching the western margin of the district: in the Oakenshaw and Brandon collieries in the Wolsingham (26) district, it is about 6 ft wide, thickening eastwards to 9 ft, according to Holmes and Harwood (1928, p. 525). Approaching the western margin of the Durham–Hartlepools district, it has been proved as the northernmost of two thin dykes cut in the Durham Low Main Coal workings. The southern dyke is 12 ft wide at outcrop in the bed of the River Wear and is thought to continue eastwards into the district to an old quarry [NZ 2722 3954] 700 yd W.S.W. of High Houghall: it is probably an offshoot of the Brandon Dyke, though they are nowhere seen to join. The northern, main dyke was formerly exploited from two old quarries [NZ 2749 3965], now overgrown, in Saltwell Gill, 450 yd W. of High Houghall.

Farther east in the Hutton Seam workings, the Brandon Dyke has been proved [NZ 2799 3974], 150 yd N.E. of High Houghall, where it is 41 ft wide with 45 ft of cindered coal on the northern side and 210 ft of 'bad' coal beyond that. The mining plans suggest that strata on one side of the dyke are displaced with respect to those on the other side. The Brandon Dyke was proved in the Shincliffe Hutton workings between localities [NZ 2915 3995], 100 yd N.E. of West Grange,. and [NZ 3044 4012] 450 yd W. of Whitwell House. Near to Shincliffe Colliery shafts, the dyke is 4 ft wide and has been proved in the Busty and Durham Low Main workings where a small fault on the southern side of the dyke throws down 7 ft to the north. The dyke in this eastern part of its course trends about N. 83.5° E.

Unnamed dyke

An unnamed dyke lies 250 to 300 yd S. of the eastern part of the Brandon Dyke betwen a locality [NZ 2917 3968], 200 yd S.S.E. of West Grange, and another [NZ 3061 3988], 450 yd N.E. of Low Grange. About midway between these localities, it was proved to be 9 ft wide in the Hutton Seam. Its extent to the west is not known, but continuous workings in the Hutton Coal show that it does not extend farther east. In the Durham Low Main and Busty workings, this dyke trends N. 82° E.

Ludworth Dyke

The western limit of the Ludworth Dyke is not known, but the presence of sills in certain bores in the area south of High Grange suggests that it may extend at least 0.5 mile and perhaps as much as 1 mile to the west-south-west of Shincliffe station (see below). The dyke itself has been proved in the Shincliffe Durham Low Main Coal workings [NZ 2973 3920], and also in the Bowburn Harvey and Busty workings, being 33 ft wide in the Busty according to Holmes and Harwood (1928, p. 524).

Farther east the dyke forms the southern boundary of the Sherburn Hill Colliery workings and it is traversed by two drifts [NZ 3417 4034], 1300 yd W.S.W. of Ox Close. The principal drift, inclined southwards at 1 in 6 from the Main Coal, intersects the Durham Low Main Coal and underlying measures on the north side of the dyke, but again meets the Durham Low Main Seam on the southern side. The presence of a fault is inferred, though its throw and position in relation to the dyke are not clear. The width of the dyke in the drift is 90 ft, with a 6-in stringer 30 yd to the north. This is contrary to an account by Holmes and Harwood (1928, p. 524), who state that the dyke is here in two portions 10 ft apart, and 18 and 27 ft wide respectively. This report was presumably derived from a contemporary colliery horizontal section, which erroneously represented the dyke as a single intrusion bifurcating upwards so as to show the seams above the Busty and Harvey traversed by two dykes, progressively farther apart at higher levels.

The northern side of the dyke has been proved in a heading from the Five-Quarter Seam [NZ 3475 4054], 650 yd W.N.W. of Ox Close. In this area the trend is about N. 73° E. B.A.F.

The Ludworth Dyke was intersected in two parallel drivages in the Harvey Seam workings 900 yd S.S.W. of Ludworth Colliery shafts. It is 34 ft wide in one [NZ 3593 4085] and 32 ft wide in the other [NZ 3597 4087], and at both localities there is evidence of slight vertical displacement either along or near to the plane of intrusion. Another drivage [NZ 4065 4235], 1500 yd S.W. of Easington church, connects the Hutton workings of Shotton and Haswell collieries and proves the dyke to be 63 ft wide trending N. 72° E. along the plane of a fault, having a downthrow to the south of about 30 ft. The zone of cindered coal on the south side of the dyke is 86 ft wide. Farther east a drivage [NZ 4368 4356], 430 yd N.E. of Paradise, connecting the Durham Low Main workings between Easington and Horden collieries, proved the width of the dyke to be 49 ft along a trend of N. 73° E. and the throw of the fault to be about 50 ft. Still farther east two parallel drivages [NZ 444 446], in the Hutton Seam workings 3300 yd E. of Easington Colliery shafts, proved a width of 57 ft along the plane of a 40-ft fault. The trend is N. 69° E., and a minor off-shoot dyke is recorded 15 ft south of the main intrusion. The easternmost record of the dyke is in two parallel drivages [NZ 4756 4480]; [NZ 4765 4483] in the Durham Low Main Coal, 4200 yd E. of Easington Colliery shafts, where it trends N. 70° E. and is 17 and 25.25 ft wide respectively. The throw of the fault coincident with the dyke is still down to the south, but the amount is unknown. All the provings of the Ludworth Dyke suggest that it is essentially vertical throughout its length. D.B.S.

Intrusive sills

The intrusive sills of the district are all recorded from the south side of the Brandon and Ludworth dykes. In the district covered by the Wolsingham (26) Sheet, the 20-ft Brancepeth Sill (Holmes and Harwood 1928, p. 525) lies 52 ft above the Busty Seam and is probably a southern offshoot from the Brandon Dyke. A bore [NZ 2754 3875] about 650 yd S. of Butterby proved 17 ft 7 in of 'blue whin' at about 91 ft below the Bottom Hutton Coal. A bore [NZ 2888 3877] at High Butterby proved two sills, 1 ft 11 in and 7 ft 1 in thick, separated by 1.25 ft of seatearth-mudstone between46 and 56 ft below the Bottom Hutton; and another bore [NZ 2809 3777], 500 yd W. of High Croxdale, proved a 6.25-ft sill at 75 ft below the same coal. At Cassop Moor, cindered coal in the Busty seam extends for at least 825 yd from the Ludworth Dyke, a typical section at the limit of workings [NZ 3195 3937], 900 yd N.E. of Cassop Grange, being: cindered coal 19 in, on band 3 ft 1 in, ‘whin’ 22 in, cindered coal 24 in. It is inferred that the 'whin' is a sill which continues in the roof of the Bottom Busty Coal over a wide area. In the Cassop Grange Bore [NZ 3166 3879], 300 yd E.N.E. of Cassop Grange, and 1000 yd from the Ludworth Dyke, the Durham Low Main Coal is cindered and the roof is baked. In a bore [NZ 3048 3923], 460 yd N.W. of Whit-well South Farm, a dolerite sill, 21.75 ft thick, lies 62.25 ft below the Bottom Hutton Coal. In another bore [NZ 3205 3998], 575 yd E.S.E. of Whitwell East House and only 50 yd from the dyke, a 1-in sill of 'white trap' and a 15-in sill of dolerite were proved 34 ft and 13.5 ft respectively above the floor of the Main Coal; and other dolerite sills, 5 ft 10 in, 1 ft and 6 ft 1 in thick were met at 52 ft 1 in, 65 ft 3 in and 85 ft 8 in respectively below the Main Coal. A further dolerite was entered 87 ft 2 in below the Main Coal and this continued to the bottom of the bore, 8 ft 5 in below. E.A.F.

Petrography

Earlier petrographical accounts of some of the dykes and associated sills have been given by Bell (1875) and Teall (1884). Teall recognized their similarity to the Whin Sill and distinguished them from the Cleveland Dyke because of their greater basicity, higher specific gravity, greater degree of crystallinity and paucity of phenocrystic feldspar. Holmes and Harwood (1928, pp. 526–8) gave modal and chemical analyses of the Hett, Butterby and Ludworth dykes and concluded they were comagmatic with the Whin Sill.

Fresh specimens (E32391), (E32392), (E32393) obtained from the centre of theHett Dyke, from the centre of the southern of the two dykes proved on the western margin of the district, and from the lower of two sills in Butterby No. 2 Bore (p. 189) are very similar dark grey, evenly medium-grained rocks with sparse phenocrystic feldspars up to 3 mm long. Plagioclase laths in the groundmass average 0.3 by 0.05 mm and show some alignment in two principal directions, although in places their orientation is at random. Their maximum extinction angle in symmetrical section is near 36° and the refractive index (β) is 1.560 ± 0.003, indicating a labradorite composition near Ab₄₈An₅₂. Slightly coarser plagioclase crystals are zoned with outer zones near labradorite in composition. Accessory orthoclase is very sparse. Pyroxenes are abundant mainly as anhedral granules averaging 0.09 mm across, and scattered singly or in groups amongst the feldspar laths. Pale green augite is predominant, with refractive index β = 1.694, 2V (+) = 58 ± 2°. Though mainly anhedral, slightly coarser, twinned subhedral to euhedral crystals also occur. Enstenite is less abundant forming elongated prisms up to 0.4 by 0.1 mm, and commonly rimmed with granular augite. The orthopyroxene is weakly pleochroic with Z = pinkish brown, X = pale green, 2V (−) large; the negative sign indicating hypersthene. An intersertal pale brown mesostasis consists of a probably felsitic base with disseminated colourless to reddish brown microlites averaging 0.036 by 0.001 mm, specks of opaque iron oxide and globulites. Chlorite and carbonates also occur in the mesostasis. Titaniferous magnetite is prominent through the rock as subhedral to euhedral, or skeletal grains, averaging 0.08 mm, and is associated with finely granular pyrite. Quartz is a minor accessory mineral and part at least seems to be primary although, perhaps, of late formation. Small (0.5 mm diameter), rare spheroidal to irregular structures, possibly subvesicles, are infilled with quartz and carbonates, mainly dolomite (refractive index ω = 1.685).

Labradorite laths commonly penetrate augite granules as noted by Teall (1884, p. 229), indicating an earlier crystallization of the feldspar. This relationship is not always clear, however, and in places penetration is mutual and crystallization of the two components may have overlapped. The overgrowth by augite of hypersthene indicates the normal discontinuous reaction process. Magnetite tends to penetrate along cleavages in augite thus giving rise to skeletal crystals and indicating a later crystallization.

In general, the above description agrees with the earlier work, although Holmes and Harwood (1928, p. 502) noted glomeroporphyritic aggregates of plagioclase, with highly calcic cores approaching An₉₀ and with selvedges near An₅₀ to An₃₀. A chemical analysis of the Hett Dyke from Tudhoe, a little to the west of the district, given by Holmes and Harwood (1928, pp. 527–8) shows: SiO₂ 50.31; Al₂O₃ 13.50; Fe₂O₃ 3.86; FeO 8.29; MgO 4.98; CaO 9.63; Na₂O 2.39; K₂O 0.91; H₂O+110°C 0.99; 1–1.0–0.45; TiO₂ 2.16; P₂O₅ 0.27; MnO 0.12; CO, 2.24; S 0.11; BaO 0.04; SrO 0.02; Cl tr; Li₂O tr; total less O for S (0.04), 100.28.

A specimen (E27642) from the dyke exposed in the main drift in workings south of Sherbum Hill Colliery, was examined by Dr. K. C. Dunham who identified it as an altered dolerite. It consists predominantly of carbonate (mainly dolomite, with refractive index ω = 1.680, with lesser calcite, ω = 1.658) which almost entirely replaces the original rock. Clay minerals replace the feldspars of which only the characteristic lath-like outlines remain. Untwinned secondary feldspar is common. Accessory minerals include skeletal ilmenite and leucoxene in relatively large grains.

Of the Ludworth Dyke, one specimen (E23744) from a fault zone [NZ 444 446] at the Hutton Seam level, Easington Colliery, is a white, highly altered basalt or chilled dolerite (cf. 'white trap'). Plagioclase has been pseudomorphed by kaolinite, and pyroxene by carbonate, the ground-mass consisting of brown glass. Veinlets of opaque black glass are riddled with vesicles lined with dolomite. Altered dolerite (E29426) from a vertical dyke in a roadway in the Durham Low Main Seam, 960 ft below O.D., 1800 ft S. of South Shaft, Easington Colliery, consists, according to Dr. R. Dearnley, of pseudomorphed feldspar, pyroxene and leucoxenized ilmenite. The pseudomorphs after feldspar laths show ophitic texture, and comprise alkali feldspar, clay minerals, sericite, carbonates and quartz. Veins containing dolomite with a zeolite rimmed by pyrite, cut the dolerite. In an altered dolerite (E27642) from the main drift in the Low Main Seam workings [NZ 2973 3920], S. of Sherburn Hill Colliery, feldspar has beenreplaced by clay minerals and most of the rock consists of dolomite and calcite. Untwinned secondary feldspar occurs and there is accessory leucoxenized skeletal ilmenite.

In general, the fresh specimens examined show very close similarity to each other and differ significantly from the Whin Sill only in the development of intersertal and intergranular patches of mesostasis which indicate a tholeiitic trend. This may reflect a more rapid cooling history, since the intrusions described here are relatively thin. However, they are clearly consanguineous with the Whin Sill. Modal analyses (in volume per cent) of the three fresh specimens described are compared in (Table 5) below with quoted values (Holmes and Harwood 1928, p. 527) for the Hett Group. The analyses, by point count method, are of approximately 500 grain counts and the analytical error is about 1 per cent.

Comparison of the feldspar values shows close agreement and the difference between the pyroxene abundances is probably due to submicroscopic pyroxene inclusions in the mesostasis recorded. Comparison of the present modal analyses, however, with normative values given by the above authors (ibid., p. 527) shows close agreement in total pyroxene abundances. Some of the appreciable (5.56 per cent) normative orthoclase together with some of the quartz (9.77 per cent) may well occur in the cryptocrystalline mesostasis. R.K.H.

References

BELL, I. L. 1875. On some supposed changes basaltic veins have suffered during their passage through, and contact with, stratified rocks, and on the manner in which these rocks have been affected by the heated basalt. Proc. Roy. Soc., 163, 543–53.

DUNHAM, K. C. 1948. Geology of the Northern Pennine Orefield. Vol. I. Tyne to Stainmore. Mem. Geol. Surv.

EDWARDS, A. H. and TOMLINSON, T. S. 1958. A survey of low volatile coals in north-east and south-east Durham. Trans. Inst. Min. Eng., 117, 49–78.

HOLMES, A., and HARWOOD, H. F. 1928. The age and composition of the Whin Sill and the related dykes of the north of England. Mineral. Mag., 21, 493–542.

TEALL, J. J. H. 1884. Petrological notes on some north of England dykes. Quart. J. Geol. Soc., 40, 209–47.

Chapter 5 Structure

The structural history of the district falls into three phases, namely pre-Upper Carboniferous, Carboniferous–Permian and post-Permian. The only evidence relating to the first phase is provided by gravity surveys undertaken by Bott and Masson-Smith (1957) and Bott (1961) who postulate an abrupt thickening of Lower Carboniferous and, possibly, of Devonian sediments towards the south-south-east across a penecontemporaneous depositional hinge-belt. This belt bisects the district along an east-north-easterly line extending from Ferryhill through Horden, swinging from there first to the east and then to the south-east as it is traced beyond the coast-line: it is presumed to be continuous with the southern margin of the Alston Block as defined by Trotter and Hollingworth (1928) and Dunham (1948) in the ground farther west. This control over sedimentation may have continued into Namurian times, but the Coal Measures show no signs of its influence.

The second phase is generally accepted to be either late Carboniferous or early Permian in age. It produced most of the faulting and folding in the Carboniferous rocks, and was accompanied by the emplacement of minor intrusions of quartz-dolerite and tholeiite (Chapter 4). One of the principal fractures—the Butterknowle Fault—was initiated at this time along a line which coincides approximately with the earlier hinge-belt. These earth movements were followed by a period of erosion during which the whole of the local Upper Coal Measures and varying amounts of the Middle Coal Measures and earlier rocks were removed. The Permo-Triassic sediments were then deposited unconformably on the eroded surface of the remaining Carboniferous rocks.

The subsequent flexuring, faulting and eastward tilting of these later sediments is attributed to the third phase of earth movements, which is probably Tertiary in age. During this episode, there was renewed movement along some of the earlier fractures as evidenced by the greater displacement in the Coal Measures than in the Permian along many of the faults: the Butterknowle Fault is an example.

The Butterknowle Fault separates two areas of contrasted structural aspect. To the north folding is gentle, but to the south folds with closures of several hundreds of feet are aligned with their axes parallel to the Butterknowle Fault (Plate 14).

Structure of the Carboniferous rocks

North of the Butterknowle Fault

The north, but along its southern margin it strike throughout most of the northern swings almost due east-west, parallel to area is between 25° and 35° west of the Butterknowle Fault. In the western part of the area are several broad folds with north-north-westerly axes and with closures of up to 200 ft though they are commonly less than 100 ft; there are also a number of minor folds with axes lying either east-west or east-north-east. In the eastern part of the area, where the easterly dip increases to between 100 and 300 ft per mile, the amplitude of the minor folding is generally less than 40 ft, and these structures do not show on (Plate 14).

Three main trends of faulting are recognized: north-easterly, north-northwesterly, and easterly.

The north-easterly faults trend between 45° and 55° east of north and are almost straight. Throws appear to remain constant at between 5 and 30 ft along most of their length and few exceed 50 ft. The north-north-westerly faults trend between 25° and 40° west of north. Individual faults are generally of shorter linear extent than those of the northeasterly group, though the few which are of comparable length have larger displacements. Thus, the Sherburn Fault has a maximum throw of over 200 ft, and the Durham Main Fault and others in the same area over 100 ft. Throws of more than 100 ft are also known in the faults bounding the Castle Eden Disturbance, the Wingate Trough, and along an undersea fault 3 miles east of Hawthorn Hive. The easterly faults, which trend between 80° and 100° east of north, include many minor faults arranged in line or en échelon. In the eastern part of the area, they also include larger structures such as the Easington, Horden and Blackhall faults, which have local displacements of over 100 ft.

Pairs of faults form troughs in each of the three groups, but those in the north-easterly group are small and shallow. The largest and deepest troughs are in the north-north-westerly group: they include the Wingate Trough, which is symmetrical and is 180 ft deep in the Harvey Seam, and the monoclinal Castle Eden Disturbance which has a western limb up to 200 ft higher than the eastern. Troughs are most numerous in the easterly group, but most of them are shallow.

A few small faults do not fit into any of the three major groups. The most notable are those associated with the dolerite dykes, which trend between 66° and 80° east of north. Apart from trend, these faults are very similar to those in the north-easterly group.

Butterknowle Fault and area to the south

The Butterknowle Fault can be traced in mine workings for eight miles between the western margin of the district and Hurworth Reservoir. On the southern, downthrow, side the measures dip towards the plane of the fault generally at angles up to 45°. Clarke (1962, p. 213) cited maximum dips of about 1 in 1.6 in parts of the Dean and Chapter Colliery take and 1 in 2.1 in parts of the Thrislington Colliery take, but he notes in addition that the dips can be irregular in magnitude close to the fault plane and that dips of 80° to the north occur adjacent to the fault near Thrislington Shafts. However, he observed that there is generally a slight diminution of dip within a few yards of the fault plane. In an examination of the workings from Dean and Chapter Colliery during the resurvey, no sign of compressional fracture was seen and all the minor faults associated with, and parallel to, the main structure are normal and highly inclined.

Where intersected in a cross-measures drift [NZ 2822 3373], about 50 ft W. of the main road east of Skibbereen, the Butterknowle Fault hades at 45° and has a throw of about 700 ft. Farther east, about 0.75 mile N.E. of Trimdon, the throw of the fault in the Coal Measures diminishes to about 300 ft, and the steeply dipping measures on the southern side of the fault form the northern limb of the Trimdon Anticline. The axis of this anticline in the Harvey Seam lies between 1000 and 1200 yd south of the fault and the axial plane seems to dip south, parallel to the plane of the fault. This parallelism suggests that the fault and anticline are linked in origin. The anticline gives way southwards to a syncline, on the southern limb of which the Millstone Grit Series abuts against Permian rocks at the margin of the coalfield. The trend of the synclinal axis is roughly parallel to that of the anticline, but this parallelism does not extend to the axial plane which, in the syncline, has no clearly defined inclination. Moreover, in the anticline it is the northern limb which dips most steeply and in the syncline it is the southern limb: thus the two folds are of opposite asymmetry. Culminations and depressions lie along the axes of both folds (Plate 14).

The most numerous faults in the worked coalfield south of the Butterknowle Fault are those trending approximately north-north-west; they have throws of up to about 80 ft. Some of these faults lie along and adjacent to the Ferryhill Gap and two of them form a trough 60 ft deep, from which small southeasterly faults diverge. In the Garmondsway area the northern limb of the Trim-don Anticline is broken by short faults of north-north-westerly trend. The northern limb is also traversed by two easterly faults: one—the Garmondsway Fault—has a southerly downthrow of 130 ft; the other fault, which has a northerly throw of 100 ft, is near the anticlinal crest. The ground to the south is traversed by two groups of generally minor faults: one group trends north-north-westerly; the trend of the other group varies from west-south-west to east-south-east and is parallel or sub-parallel to the Butterknowle Fault. One of the latter group, the Butterwick Fault, has a throw to the south of over 100 ft: it is thought to continue eastwards, first diminishing in throw around Ten-o'-Clock Barn and then becoming identified as the West Hartlepool Fault, which in the Embleton area is inferred from bores to have a throw of at least 500 ft in the Carboniferous. In this area the fault appears to be coincident with the axis of the main syncline.

Structure of the Permian rocks

North of the Butterknowle Fault

Contours drawn on the base of the Permian rocks are shown on (Plate 15). Since the Permian rocks thicken downdip to the east, the dip of the higher beds is slightly less than the lower, but the average is about 110 to 150 ft per mile. North of the Easington Fault, the average dip of the Coal Measures exceeds that of the unconformity so that successively higher beds crop against the base of the Permian. South of the fault, the unconformity dips slightly more steeply than the Coal Measures and this, together with the difference in strike between Carboniferous and Permian strata, results in a closure of the coalfield towards the east.

Almost all faults of more than about 10 ft displacement in the Coal Measures are reflected in the overlying Permian rocks cropping out along the coast; either as clean, relatively simple breaks having a hade of about 20°, or as nearly vertical shatter belts up to 20 or 30 ft wide. In both cases the displacement in the Permian strata generally appears to be considerably less than in the underlying coal workings. Thus, the Easington Fault at the coast throws about 190 ft in the Coal Measures, but only 30 to 50 ft in the Permian; similarly, the southern branch of the Blackhall Fault throws about 30 ft in the Coal Measures as compared with 3 ft in the Permian, though the relative displacements of its northern branch are 40 ft and 35 ft.

One of the few sizeable faults proved in the Coal Measures, but having no apparent extension into the Permian, is associated with the Ludworth Dyke. It has a throw of 40 to 50 ft in colliery workings, but no displacement can be traced in the incompletely exposed overlying Permian beds.

Along the sides of the escarpment spurs, the dip at the base of the Permian is low, but it increases near the heads of several of the re-entrants, and this is particularly apparent at the eastern ends of the Pittington Hill, Sherburn Hill and Quarrington Hill spurs.

In addition to the major structures shown in (Plate 15), most exposures of Permian beds contain low-amplitude rolls and flexures of non-tectonic origin. In many places, these appear to have been caused by local variations in sedimentation such as those caused by deposition over high points on the underlying Carboniferous or over dunes in the Basal Sands. Elsewhere, however, particularly east of the Middle Magnesian Limestone reef, such structures are thought to be due mainly to differential compaction and to differential subsidence caused by the solution of sulphates interbedded with carbonates. This process is also thought to account for a complex brecciated belt containing many minor strike faults which runs parallel with the reef-front and which is seen in many coastal exposures.

Butterknowle Fault and area to the south

The throw of the Butterknowle Fault appears to be much less in Permian strata than in Carboniferous: comparative figures near Skibbereen, for instance, are 350 ft (by extra polation) and 700 ft respectively.

Near High Hill House [NZ 2727 3292], 550 yd N.W. of the windmill, a fault with less than 25 ft throw in the Permian can be seen. The fault plane dips to the north, and on its northern side, the Permian is dragged down against Coal Measures, and dips at 50° to the north. However, within a yard or two the dip is reduced to between 8° and 20°, though in the adjacent quarries fissure-bounded blocks of strata dip in various directions. Although a throw of 35 ft is recorded in the Brockwell Seam workings underground, the same fault only throws a few feet in the Harvey Seam below this locality.

At Ferryhill, the anticlinal axis in the Permian is roughly parallel to the axis in the Coal Measures, but lies generally about 150 to 200 yd to the north of that in the Brockwell Seam. The folding in the Permian is commonly disturbed by the anomalous attitude of fissured blocks as seen, for example, in a quarry [NZ 2857 3278] at the northern end of the Ferryhill road cutting. A short distance to the south, where the axis crosses the cutting, three minor anticlines can be seen in a horizontal distance of 200 yd. East of the Ferryhill Gap, the structure of the anticlinal area is proved by bores to be more complicated. Contours on the base of the Permian suggest that instead of a single anticline, as in the Coal Measures, the Permian rocks contain several minor folds, the axes of which are commonly short (Plate 15). However, it is not clear to what extent the present detailed form of the unconformity is affected by pre-Upper Permian erosion (see below).

The broad linear correspondence between the anticlines in the Carboniferous and the Permian rocks is not apparent in the synclinal structures. Basal Permian contours show that a 'lows' opens to the south-east 0.5 mile N.W. of Rushyford, a similar 'lows' falls southwards from Mainsforth, and a third falls south-eastwards 0.5 mile S. of Fishburn Colliery. These 'lows' appear, at first sight, to represent the positions of valleys on the pre-Upper Permian peneplain, but this cannot easily be reconciled with other factors. For instance, the two western ‘lows’ lie over the Coal Measures synclinal axis, and the Fishburn 'low' falls southeastwards in close parallel to the same axis. Moreover, Basal Permian breccias resting in and on the margins of the hollows show no apparent preferential distribution along the bottoms of the 'lows', and commonly contain a significant proportion of Carboniferous Limestone debris which must have been derived from the south, i.e. against the present slope of the unconformity. These factors suggest that the depressions are at least partly tectonic in origin.

Beyond Hurworth Reservoir, the eastern extension of the Butterknowle Fault and the structures to the south of it have been inferred from the evidence of boreholes and a gravity survey. In some of the bores which do not reach the base of the Permian, its position can be estimated from the stratigraphy. The most doubtful area is a belt between Sheraton Grange [NZ 434 337] and West Pasture [NZ 467 289] where bores are widely spaced and the gravity information is open to several interpretations. At the western end of this belt, the West Hartlepool Fault at Embleton is considered to have a throw of about 500 ft in the Coal Measures and about 300 ft in the Permian. Between Dalton Piercy and West Hartlepool the throw can be estimated only in the Permian, where it seems to be about 600 ft. But there is virtually no indication of this fault on the gravity traverses, and its position is inferred mainly from the bore data. The Seaton Carew Fault is located mainly by the gravity survey and by two bores south of Low Stotfold which indicate displacement of at least 80 ft and by other bores which suggest that it is much greater-probably of the same order as that of the West Hartlepool Fault-and the Permo-Triassic outcrops are calculated on this basis. A fault linking these main faults is based almost entirely on gravity information. There is no information on the structure immediately south of the Seaton Carew Fault, but in the neighbouring parts of the Stockton (33) District to the south, the Permo-Triassic beds dip steadily eastwards and Keuper Marl is present in the coastal area 2 to 3 miles south of Seaton Sands. It is assumed that the strike swings westwards near the Seaton Carew Fault and the outcrop of the Keuper Marl has been calculated on this assumption.

Age of the structures

Most of the faults were initiated in late Carboniferous or early Permian times and the greater part of their displacement probably dates from this period. The folds of the western part of the district are probably also of this age, as may be the Mainsforth Syncline which has a pronounced north-north-westerly trend even after contours are corrected to the sub-Permian surface. However, many of the folds have an east-west trend when the inclination of the sub-Permian surface is subtracted.

The dykes are generally believed to have been intruded during a phase of this orogeny when compression was relaxed. It is here suggested that this phase may have been followed by one of compression in a different direction and that this resulted in the folding in the southern part of the district and in the formation of the Butterknowle Fault along earlier lines of weakness.

At a later period, probably in Tertiary times, the Permian was tilted and there was renewed movement along the Butterknowle Fault with accommodation structures in the adjacent folds. At least one of the cross-faults in the Ferryhill Gap throws both Coal Measures and Permian rocks an equal amount of 60 ft and it thus seems possible that some of the faulting in the district was initiated by these earth-movements. E.A.F., D.B.S.

References

BOTT, M. H. P. 1961. A gravity survey off the coast of north-east England. Proc. Yorks. Geol. Soc., 33, 1–20.

BOTT, M. H. P. and MASSON-SMITH, D. 1957. The geological interpretation of a gravity survey of the Alston Block and the Durham Coalfield. Quart. J. Geol. Soc., 113, 93–117.

CLARICE, A. M. 1962. Some structural, hydrological and safety aspects of recent developments in south-east Durham. Mining Engineer, 27, 209–31.

DUNHAM, K. C. 1948. Geology of the northern Pennine orefield. Vol. I. Tyne to Stainmore. Mem. Geol. Surv.

TROTTER, F. M., and HOLLINGWORTH, S. E. 1928. The Alston Block. Geol. Mag., 65, 433–48.

Chapter 6 Pleistocene and Recent

Introduction

Most of the district is covered by drift which is generally thin in the central part of the area, but which exceptionally reaches a thickness of about 300 ft along buried valleys. The oldest deposits, which are preserved in fissures along the coast, consist of breccias and clays, partly pre-glacial and partly early glacial in age. They are followed by more extensive deposits formed during the Pleistocene glacial periods. These consist mainly of boulder clay, laminated clays, sands and gravels. Certain other stony clays may also have been deposited during these cold periods, but their mode of origin is uncertain. Laminated clays, terrace of warp deposits and associated raised storm beach and river terraces found in the south-eastern part of the district are probably late-glacial or early post-glacial. Widespread alluvium and some other river terrace deposits are thought to be mainly Recent in age.

Some of the earliest studies of the glacial geology and buried valleys in Durham were by Howse (1864) and Wood and Boyd (1864). Bore and shaft records published during the latter part of the nineteenth century form the basis of work by Woolacott (1905, 1906, 1909) on the buried valleys. General accounts of the glacial deposits have been given by Woolacott (1921), Raistrick (1931, 1934) and Hickling and Robertson (1949), while descriptions of the drift of the coastal area of east Durham have appeared in a series of papers published by Trechmann between 1912 and 1952. The district forms part of a much wider area dealt with by Carruthers (1939, 1953) in his accounts and interpretations of glacial drifts. E.A.F., D.B.S.

Buried valleys

The buried valleys of the district (Figure 25) form part of three major systems; the River Wear system in the west, an eastern coastal system, and a River Tees system in the south. The watershed between the first two lies a mile or two east of the Permian escarpment, though some of the tributaries of the Wear system do not breach the escarpment.

The buried valley of the River Wear begins near Witton Park in the Wolsingham (26) district, 2 to 3 miles upstream from Bishop Auckland. Between Bishop Auckland and Finchale Priory, 3 miles N.N.E. of Durham, its average gradient is approximately equal to that of the modern valley and with certain exceptions its course is also similar. The longitudinal profiles of the buried valley and its tributaries show certain peculiarities, however. For instance, those of the River Deemess and Old Durham Beck seem to be hanging tributaries to the main Wear buried valley, which they join near Houghall and near Old Durham respectively. There is also a sudden fall in gradient from −80 to −140 ft O.D. at the bottom of the main valley between Finchale Priory and Chester le Street, in the Sunderland (21) district. Similar irregularities in the Tyne Valley west of Newcastle upon Tyne have been explained (Hickling and Robertson 1949, p. 28) as due to 'glacial super-deepening' by the erosion of the valley bottom by the Tyne Glacier because the ice-flow was impeded by high ground at Gateshead and Low Fell. However, it is difficult to accept this explanation in Central Durham since there is no apparent reason for such deepening in this area. It is suggested instead that a more likely agent of erosion was sub-glacial melt-water and this accords with the presence of much gravel and sand believed to be sub-glacial in origin (p. 244) at or near the changes in profile; some small buried valleys seem to be glacial drainage channels which have been wholly or partially filled (p. 237). The Ferryhill Gap also follows a buried valley for at least Dart of its course.

The buried valleys in the eastern area are less well proved by borings and shaft sinkings than those to the west, but their courses are commonly indicated by the distribution of solid outcrops and their intersection with the coastline is well exposed in cliffs. They rise close to the present watershed at about 400 to 500 ft O.D. and fall eastward at 50 to 100 ft per mile. Several of the smaller valleys seen in coastal sections lie well above present sea-level and are completely filled, but some of the deeper buried valleys, such as those at Hawthorn and Castle Eden, are only partly drift-filled and late-glacial or post-glacial valleys have been excavated along their courses. The bottoms of the deeper buried valleys at Hawthorn, Easington Colliery, Castle Eden, Limekiln Gill (Blackhall Colliery) and Crimdon cross the coast considerably below present beach level and probably continue for some distance out to sea. In cliff sections their sides are seen to slope at angles ranging from 8° to over 70°, but are generally 10° to 20°—considerably shallower than those of the present day valleys. D.B.S.

An important member of the River Tees system of buried valleys trends east-south-east through Hurworth Burn and Brierton. Apart from this, only the upper pat ts of a few buried tributary valleys of the Tees system lie within the district. One of these is proved by bores at Rushyford, a second continues southwards from the Ferryhill Gap through the ground near Nunstainton

East, and a third rises near Fishburn and falls to the east or south-east through the ground near Ten-o'-Clock Barn and Middle Swainston. In Ten o'-Clock Barn No. 1 Bore, the drift is 300 ft thick with rockhead at about O.D. Farther east, a buried valley west of West Hartlepool was thought by Radge (1939, p. 184) to represent a former course of the River Tees. This view is not supported by more recent information which suggests a col within the valley near High Tunstall.

Pleistocene deposits

For consideration of the Pleistocene deposits the district is divided into four areas, namely western, central, southern and eastern (Figure 26). The western area corresponds with the River Wear Basin west and north of the Permian escarpment; the central area corresponds with the Permian plateau and is mainly over 400 ft above O.D.; the southern area lies in the northern part of the Tees Basin, south of the Ferryhill–Fishburn ridge; and the eastern area comprises a strip following the coast and extending inland for a distance of 2 to 8 miles.

The character and relationships of the glacial deposits differ from one area to another and this has led to certain difficulties of interpretation and correlation. In the western area, for instance, there is no evidence of more than one glaciation, whereas in the eastern area there appears to be clear indication of three such episodes. In the following account, therefore, factual descriptions of the Pleistocene, area by area, are followed by sections in which conclusions are drawn concerning the sequence of glacial events and correlation and chronology. A further section attempts to reconstruct the main features of deglaciation in the Wear Valley around Durham. D.B. S. , E.A.F.

Eastern area: general account

The Pleistocene succession in the eastern area is as follows:

The inter-relationships of these deposits are shown diagrammatically in (Figure 27).

The fissure deposits are preserved in numerous vertical or steeply inclined breccia-filled clefts in the Magnesian Limestone in the coastal area from Crimdon Beck northwards. Almost all extend vertically for the height of the solid rock in the cliffs (up to 80 ft) and Trechmann (1915, 1920) noted that some could be traced across parts of the foreshore now covered with re-sorted colliery waste. Most of the fissures are from 3 to 25 ft wide and are linear, but some are approximately circular in plan. Both varieties are found among beds partially or wholly brecciated by solution-collapse. Linear fissures also lie along fault-planes and are common in the brecciated zone (p. 122) parallel with and immediately east of the reef-front. Walls of the fissures commonly bear near-vertical slickensides and many of the breccia fragments are striated and polished.

The breccias are composed mainly of fragments of Magnesian Limestone, the fragments nearest the sides of the fissures generally being of wall rock, while those towards the centre are derived from higher beds, many of which (including Upper Permian Marls) have since been removed by erosion. Some fissures also contain clays, with wood and other plant material, mammalian bones and freshwater shells of early Pleistocene age (Trechmann, op. cit.; Lesne 1920; Reid 1920). One fissure [NZ 4776 3813], 90 yd S. of Limekiln Gill, contains a number of erratic stones (Trechmann 1915, p. 57) and another [NZ 4478 4217], 180 yd S. of Warren House Gill, has yielded stones of Scandinavian origin (Trechmann 1920, p. 181).

The oldest glacial deposit of the district—the Scandinavian Drift (Trechmann 1915, p. 53)—occupies the floor of a buried valley at the mouth of Warren House Gill (p. 210). It consists of tough gritty grey clay containing abundant pebbles derived from Norway, but devoid of erratics from Scotland or Northern England. Shell fragments are abundant and include (Trechmann 1915, p. 65) many Arctic forms now extinct in British seas. The deposit has not been recorded anywhere else in the district and although a boulder of larvikite formerly seen in a temporary exposure in Castle Eden Dene (Trechmann 1915, p. 54; Woolacott 1921, p. 64) suggests that pockets of Scandinavian Drift may be preserved beneath younger drift in other buried valleys, it is generally supposed that the Scandinavian ice did not extend much farther west than the present coastline. The shelly Scandinavian clay at Warren House Gill is overlain by a silty deposit, which Trechmann (1920, p. 174) claimed to be 'loess', redistributed in the upper part by water.

The Lower Gravels occupy isolated depressions in the eroded surface of the Permian rocks in the eastern area. At the coast and in the adjacent deep denes most of these depressions are only a few yards across and the deposits are generally less than 5 ft thick; they may represent infillings of closed hollows. By contrast a discontinuous sheet of gravel up to 8 ft thick extends above rockhead for several hundred yards in Castle Eden Dene. Moreover, up to 20 ft of interbedded sands, gravels and clays filling buried valleys, may belong to this subdivision. The Lower Gravels are characterized by a high proportion (commonly 50 to 60 per cent) of pebbles derived from the local Magnesian Limestone; the remaining pebbles comprise a varied suite of Carboniferous limestones and sandstones, red, green and purple lavas, granites, gneisses, schists, flints, quartz, quarzites and dolerites.

The Lower Boulder Clay is a stiff, dark grey or grey-brown gritty clay which weathers brown or buff. As in other areas it contains many pebbles, cobbles and boulders of local Magnesian Limestone, Carboniferous sediments, Ordovician lavas from the Lake District, granites and Silurian greywackes from the Scottish Southern Uplands and blocks of dolerite of Whin Sill type. It also contains some Cheviot porphyries as well as boulders of Shap Granite, which are restricted to the southern part of the area.

Where complete sections through the Lower Boulder Clay are known only from bore and shaft sinkings, the deposit is undivided, but in the coastal cliffs between Chourdon Point and Hart Station four subdivisions are widely recognizable even where the total thickness of Lower Boulder Clay is as little as 7 ft. They are:

The junctions are not everywhere sharp and in some places the subdivisions are not easily discerned at close quarters. Seen from a distance, however, slightly different weathering tints and 'stepped' profiles caused by differential resistance to erosion are locally apparent. The lowest subdivision appears to be the most resistant to erosion and is also the most variable in thickness and the most persistent. Scattered rounded and sub-rounded stones are mainly less than 2 in across, and are more numerous in the lower two subdivisions than in the highest. The two grey-brown clays which cannot be separately distinguished where the median red bed is absent, are somewhat more plastic than the lowest clay, but are otherwise similar in texture and stone content. The red bed is remarkably persistent throughout the cliffs, though seldom more than 2 to 6 in thick: it is generally stoneless but appears locally (as in the cliffs 1500 yd S.E. of Black Halls Rocks) to pass into a sandy or gravelly layer. Small chalky shell fragments are common in all three stony clays but are most numerous in the lowest, from which Trechmann (1952, p. 172) recorded Cyprina islandica (Linné), Tellina balthica (Linné) and Saxicava sp.at an exposure in Castle Eden Dene.

Lower Boulder Clay is absent from a number of places around Hawthorn, Easington Colliery, Peterlee, Horden and Hart, where drift is thin and higher members of the sequence rest directly on rockhead. Throughout the eastern area the Lower Boulder Clay commonly grades by interdigitation to the overlying Middle Sands. Elsewhere, as from 550 to 600 yd N. of Horden Point for example, the top of the boulder clay is sharp and apparently conformable to the overlying sands, and in yet other places (e.g. 600 yd N.N.E. of Horden station) the overlying sands rest on a smooth (?eroded) surface which truncates vague colour-banding in the upper part of the clay. More pronounced erosion is indicated by deep channelling in the top of the Lower Boulder Clay in the floor of buried valleys at Hawthorn Hive [NZ 440 460], 'Waterfall' [NZ 445 435], Easington Colliery and Done Mouth [NZ 457 407], where Lower Boulder Clay has been largely or wholly removed and the hollow so formed filled with later gravels.

The Middle Sands consist of two divisions. The lower is composed of fine bright red sand interbedded in many places with subordinate beds of red silt and clay, with beds of red and grey stony clay, and with localized beds of coarser sand and gravel. The deposit is unevenly distributed and appears to lie mainly in buried valleys and wide depressions in the surface of the Lower Boulder Clay. Between such areas it is thin or absent. In the fine red sand bedding is generally even and horizontal, and cross-bedding and ripple-marks are comparatively rare. Stones are mainly restricted to scattered thin lenses of fine gravel and are absent towards the top of the subdivision where the sand contains little or no mica. Interbedded red clays and silts form extensive thin even layers and contain neither stones nor clearly defined sedimentary structures. They are present at all levels in the deposit. In contrast, the beds of stony clay resembling boulder clay occur mainly in the zone of interdigitation at the base of the Middle Sands. Coarse gravel is also concentrated in the lowest part of the deposit where it commonly fills the bottoms of buried valleys and in some places rests directly on rockhead. In the few places where it can be seen the top of the lower division of the Middle Sands makes sharp contact with the overlying deposits and is locally channelled.

The upper division is composed mainly of gravel, although sand with a few stones is common in the lower part; it also contains laminated clay in the area south of West Hartlepool. It is more extensive than the lower division, being commonly 5 to 20 ft thick and absent only on a few rockhead 'highs', such as the west–east ridge south of Hart. The gravel is widely calcreted, especially in the uppermost 2 or 3 ft, and in some exposures sand of this division is strongly cemented by calcium carbonate. At Shippersea Bay (p. 208) calcreted gravel containing abundant marine shells appears to have become incorporated by re-working into this division. This is the Easington Raised Beach of Woolacott (1920, 1922) and Trechmann (1931).

Where the lower division of the Middle Sands is absent (pp. 207–9) the sands and gravels of the upper division rest with a sharp contact on the eroded surface of Lower Boulder Clay, but no re-working of the latter is evident. At Warren House Gill, where the lower division is relatively thick (p. 211), the lowest member of the upper division is a thin bed of stony clay closely resembling boulder clay, and at some exposures such stony clay is interbedded with sand and gravel in this division. In other places (p. 213) such an interbedded sequence appears to represent the whole of the Middle Sands and it is difficult to separate the two divisions. In places the top of the Middle Sands is sharp and apparently not eroded, but elsewhere it grades by alteration into the overlying Upper Boulder Clay. Where a junction is sharp (p. 213), bedding in the uppermost gravel appears to be undisturbed, although numerous pebbles are shattered and fragments slightly displaced relative to each other. Where the upper junction is gradational (p. 213) the interbedded sequence is generally 2 to 3 ft thick, though exceptionally as much as 10 ft. In such sequences the top of the Middle Sands is taken at the base of the lowest thick bed of boulder clay. Stones in the upper division of the Middle Sands comprise a suite similar to that of lower parts of the Upper Boulder Clay, and contain a proportion of purple lavas probably derived from the Cheviot Hills and of fragments of Magnesian Limestone. Small chalky fragments of indeterminate shells are present in most exposures and the deposit has also yielded mollusca and vertebrate bones (p. 216).

Along the coast the Upper Boulder Clay reaches a maximum thickness of 40 ft in well-exposed cliff sections. It is 20 to 30 ft thick over large areas inland but is absent, probably due to late- or post-Glacial marine erosion, in a belt passing north-north-eastwards through West Hartlepool. Where unweathered, it is a dark brown to purplish brown stiff gritty clay texturally similar to the Lower Boulder Clay, but where it is weathered it is reddish brown and is thus readily distinguished from the brown lower deposit. The colour difference is also reflected in the derived soils and this, together with a scarp-like feature which commonly occurs at the margin of the Upper Boulder Clay, serves to delineate the two deposits at outcrop. The upper clay differs from the lower also in having a higher proportion of fragments of Upper Magnesian Limestone and a lower proportion of Lower Magnesian Limestone. Purple porphyritic erratics similar to the Lower Old Red Sandstone lavas of the Cheviot Hills are present in both clays, but Trechmann (1915, pl. viii) and Raistrick (1931, fig. 33) showed that they are restricted to a coastal area which corresponds approximately with the distribution of the Upper Boulder Clay. The base of the Upper Boulder Clay is sharp at some places and gradational by interdigitation at others (p. 213). Where it is gradational the lowest part of the deposit commonly contains streaks, lenses and thin beds of sand and stoneless clay (p. 211), but these are generally absent where the base is sharp. Higher parts of the deposit are less variable and lenses of sand and stoneless or laminated clay are rare. At some exposures (p. 213) the lower part of the deposit is darker brown than the upper part, but this colour difference appears to be local. The characteristic reddish weathering generally extends to only a few feet below the present surface. The top of the Upper Boulder Clay is defined only where it is overlain by Morainic Drift, mainly near the western margin of the eastern area. The few exposures show the clay there to be deeply channelled and locally eroded away completely. It would seem, however, that the deposit is persistent beneath most of the Morainic Drift.

The Morainic Drift is a heterogeneous deposit which occurs chiefly in a triangular tract between Easington, Elwick and Hart. This tract falls naturally into a western belt of north-north-westerly ridges (Figure 28) comprising the Easington–Elwick Moraine (Francis and others 1963, p. 106) and an irregular eastern area in which the Morainic Drift is hummocky and is interpreted as kame and kettle moraine.

Several patches of gravel lie on Upper Boulder Clay in the coastal area north of Crimdon Beck. They are of uncertain origin, but because of their stratigraphical position they are here grouped tentatively with the Morainic Drift, and designated Upper Gravels.

The laminated clays, which lie at the surface in much of the lower Tees valley, extend northwards into the present district in a triangular area around Claxton. They are not exposed and are not shown separately on the one-inch map. Where seen in ground covered by parts of the neighbouring Stockton (33) Sheet, the clays range from chocolate brown to red and grey in colour, and are generally silty. Sand is concentrated into scattered ripple lenses and load or slump pouches along certain bedding planes. Small pale grey calcareous concretions, commonly grotesque, occur widely at the base of the soil developed on these clays.

The so-called 'Prismatic Clay', the highest division of the Pleistocene sequence in the eastern area, is a heterogeneous deposit which generally consists mainly of clay or silt with scattered erratic stones, but in many places has much of the character of, and grades down into, the underlying deposit. It derives its name from its characteristic columnar jointing which closely resembles that produced by desiccation of Recent stream alluvium. The deposit is widespread in the eastern area and most common on the Upper Boulder Clay. Where overlying gravel the 'Prismatic Clay' is very sandy and fills pipes extending down into the gravel.

Eastern area: details

The eastern area differs from other parts of the district in that the inter-relationships (Figure 27) of the glacial deposits are well seen in the deep dens and coastal cliffs; sections are commonly continuous for some hundreds of yards and show much lateral variation. A typical section towards the northernmost end of exposures in the coastal cliffs is seen [NZ 4428 4646] 70 yd S. of Chourdon Point, as follows:

This sequence can be traced southwestwards to the head of Hawthorn Hive, where a deep buried valley, filled with Middle Sands, cuts through theLower Boulder Clay and into the underlying dolomite. The section [NZ 4410 4508] here is:

South of the buried valley the Lower Boulder Clay, the Middle Sands and the Upper Boulder Clay are all slightly thicker than at Chourdon Point, and are continuously exposed to Beacon Point and beyond. At a locality [NZ 4435 4547], 20 yd N. of Beacon Point, the section consists of:

Southwards from Beacon Point the Lower Boulder Clay thins progressively against rockhead around the head of Shippersea Bay [NZ 4425 4528], where 13 ft of sand and gravel regarded by Woolacott (1920, 1922) and Trechmann (1931) as a raised beach deposit (the 'Easington Raised Beach') rests on a bevelled platform of Magnesian Limestone at about 90 ft A.O.D. The lowest 2 to 3 ft of the deposit consist of poorly cemented coarse sand and fine gravel; higher parts consist mainly of coarser gravel which is firmly cemented in the uppermost 8 ft. Woolacott (1922, p. 66) stated that the gravel was overlain 'by a few inches of soft sand containing shell fragments', but this section is not now visible. Pebbles in the gravels are well rounded, and many in the lower 6 to 8 ft are bored by Saxicava and other marine organisms. Woolacott (1922, p. 65) also recorded such borings in the surface of the underlying limestone, though none was seen during the resurvey. The gravels contain a high proportion of local limestone together with a suite of rocks of Scottish, Cheviot and Lake District origin similar to that in the Lower Boulder Clay. Trechmann (1952, p. 171) also recorded two Scandinavian pebbles.

Shells and shell fragments (listed by Woolacott 1920, p. 65) are abundant in the lower beds of the deposit, but are less common in the higher, calcreted beds and towards the north end of the exposure. Woolacott claims that these shells indicate a climate similar to that of the present day. This accords with the view expressed by Mr. D. F. W. Baden-Powell (in litt.) that the fauna indicates an interglacial rather than an interstadial climate, and that although the Purpura shells are very worn, none has the characteristics of ancient forms such as P. carinata Brown. Radiocarbon age determination, carried out by Dr. Meyer Rubin (U.S. Geological Survey, Washington D.C.) shows that shells (sample No. W-1426) from the beach are more than 38,000 years old. The C¹⁴/C¹² and O¹⁶/O¹⁸ ratios of carbonate from one of the shells was determined by mass spectrometry by Dr. Irving Friedman in the Denver laboratory of the U.S. Geological Survey, who found them to be typical of a marine organism. His results show that this shell from the sample dated has not been appreciably contaminated nor its C¹⁴ content altered by contact with groundwater.

The lateral extent of the beach is in doubt because critical sections are inaccessible. Northwards, the gravel thins to 3 to 4 ft against rising rockhead, but it is not clear whether it passes into or is older or younger than the calcreted gravel of the Upper Division of the Middle Sands, which rests on rockhead for about 80 yd north of the main exposure and can then be traced on to Lower Boulder Clay. Southwards the gravel can be traced for about 60 yd on rockhead before passing on to Lower Boulder Clay. Beyond this locality, however, no shells have been found and the gravel which overlies the boulder clay appears to be continuous with the upper part of the Middle Sands. This gravel is overlain by about 25 ft of red-brown Upper Boulder Clay which appears to be in situ and to be continuous with stony clay which overlies the beach gravel at the main exposure. Clay from this has worked down for about 2 ft into the top of the gravel, the bedding of which is undisturbed, although many of the pebbles are broken and their parts slightly displaced relative to each other. The field evidence thus suggests that the raised beach deposit is post-Lower Boulder Clay and pre-Upper Boulder Clay, and that it now forms part of the Upper Division of the Middle Sands.

The Lower Boulder Clay reappears on the south side of Shippersea Bay but farther south, from 830 to 310 yd N. of Shot Rock, the Upper Division of the Middle Sands again oversteps it and rests directly on Magnesian Limestone. Rock-head is highly irregular from 230 to 60 yd N. of Shot Rock, and has a profile like the present marine platform at the base of the cliff. A typical section [NZ 4432 4480] 80 yd N. of Shot Rock, is:

The gravel at the base of this section is composed predominantly of local Magnesian Limestone cobbles and boulders and is thought to be a beach deposit like that at Shippersea Bay. After reappearing 210 yd S. of Shot Rock, Lower Boulder Clay maintains a thickness of 2 to 10 ft for about 1100 yd before thinning out under a buried gravel-filled valley at 'Waterfall' (Horden Dene). For most of this distance the Lower Boulder Clay is immediately overlain by the Lower Division of the Middle Sands. A representative cliff section [NZ 4439 4431], 40 yd S. of Loom, is:

One of the more significant inland sections in the northern part of the eastern area is seen in low cliffs [NZ 4264 4584] on the north side of North Dene, Hawthorn:

A little farther south patches of Upper Gravels overlie Upper Boulder Clay at Spring Bank [NZ 435 428] and Paradise [NZ 434 432]. The Upper Gravels are also recorded in a borehole [NZ 4310 4230], 150 yd S.W. of Horden Hall, which penetrated soil I ft, sandy clay 5 ft, gravel 2 ft, Upper Boulder Clay 21 ft, Middle Sands 3 ft, Lower Boulder Clay 21 ft.

A buried valley seen in the cliff at 'Waterfall' is about 75 yd across and 12 to 20 ft deep. It cuts through the Lower Boulder Clay into the underlying limestone and is filled with sands and gravels of the Lower Division of the Middle Sands, here about 25 ft thick. Southwards to the mouth of Warren House Gill the Lower Boulder Clay ranges in thickness from 2 to 15 ft, the Middle Sands from 10 to 70 ft and the Upper Boulder Clay from 5 to 20 ft. The following section was measured in the coastal cliffs [NZ 4450 4341] 150 yd S. of Waterfall:

North of Horden Point sands of the Lower Division of the Middle Sands are mainly brown, but they become increasingly redder southwards and are almost entirely red from 350 yd S. of the Point. Between 50 and 200 yd S. of the Point a buried valley is cut through the Lower Boulder Clay into the Magnesian Limestone and is filled with cross-bedded gravels of the Lower Division. Trechmann (1915, p. 68) recorded a few small fragments of shells and hornblende-and biotite-schist from these gravels. The gravels pass upwards into evenly bedded red and brown sand and silt, which are overlain successively by flat-lying gravel of the Upper Division and by about 20 ft of Upper. Boulder Clay. A section representative of the sequence between the buried valley and Warren House Gill is exposed [NZ 4465 4250], 540 yd S. of Horden Point, as follows:

At Warren House Gill the Lower Boulder Clay is underlain by a buried valley in the lowest part of which Trechmann (1915, p. 53) recorded a deposit which he termed Scandinavian Drift. His section is now largely obscured by colliery waste but about 4 ft of tough plastic gritty grey clay containing small pebbles and numerous fragments of thick-shelled arctic lamellibranchs and gastropods can still be seen [NZ 4470 4234] at beach level on the north side of the present valley. Trechmann recorded (op cit., p. 61) that the width of the outcrop was slightly less than a quarter of a mile and he observed a maximum thickness of '12 or 14 ft in the cliff section'. He analysed (op cit., pp. 64–5) 500 pebbles and found 7.9 per cent to be of larvikite and 1.3 per cent of nordmarkite, and that a large proportion of-the rocks are characteristic: of the Oslo area of Southern Norway. A number of large boulders of larvikite, rhombporphyry and nordmarkite are scattered on the foreshore opposite Warren House Gill, but the clay now exposed yields only pebbles 1 to 2 inches in diameter. Shells in the clay are described by Trechmann as 'thoroughly Arctic' in character, and as constituting a fauna closely comparable with that of the Bridlington Crag of the Yorkshire coast. Trechmann (1920, pp. 173–8) recorded that the boulder clay is overlain by a lenticular brown silty deposit banked against the southern slope of the buried valley. The lower 6 ft of this deposit is unbedded, and was interpreted by Trechmann as loess. It is overlain by a similar but layered deposit containing thin beds of sand and fine gravel and interpreted as loess redistributed by water.

The sequence overlying the Scandinavian Drift is well exposed in a gully [NZ 4464 4224] on the south side of Warren House Gill:

Colliery waste obscures much of the drift section between Warren House Gill and Whitesides Gill, but the sequence to the south of the latter is similar to that in the gully (above) and both divisions of the Middle Sands are continuously represented. However,between about 900 and 420 yd. north of Dene Holme the Lower Division thins progressively southwards and for at least 50 yd the gravel of the Upper Division rests unconformably on a few inches of irregularly bedded clays and sands, and these in turn upon an irregular (?eroded) surface of Lower Boulder Clay. A section [NZ 4553 4086], 390 yd N. of Dene Holme, is:

In the above section it is possible that the top of the Lower Boulder Clay should be taken 3 in higher, at the top of the 2-in bed of dark brown stony clay which, like the 9-in bed below, has a leached or weathered appearance reminiscent of the lower part of a clay soil profile. The lower part of the Lower Boulder Clay is exposed 15 yd N. of the above section, where the lowest few inches of the deposit are weakly laminated; the base is smooth and rests on a varied deposit up to 2 ft thiCk which occupies a rockhead hollow and consists mainly of gravel with wisps and lenses of orange and red sand and dark brown stony clay. Quartz, Carboniferous Limestone, coal and dolerite are amongst the pebbles in the gravel.

Farther south the unconformity rises again and in the cliffs [NZ 4573 4057], 200 yd E.N.E. of Dene Holme, separates 4 ft of partly calcreted fme gravel from 8 ft or more of interbedded fine red sand and sandy silt containing thin beds of yellow-brown gravel and one thin bed of grey clay. The base of the Middle Sands is not seen here, but is exposed [NZ 4590 4039] in cliffs 380 yd E.S.E. of Dene Holme:

In the cliffs between this locality and Black Halls Rocks indifferent exposures of drift indicate a sequence generally similar to that farther north. The Lower Division of the Middle Sands, however, has not been traced south of a locality about 400 yd S.E. of Dene Mouth.

A short distance farther south Trechmann (1915, 1920) described a number of fissures (now obscured by colliery waste) in the Magnesian Limestone on the foreshore near Blackhall. Colliery. In describing the contents of two of the fissures [approx. 463 400] he distinguished (1920, p. 184) an earlier clay containing much partly pyritized plant material from a later clay containing fresh-water shells, large masses of peaty material and trunks of oak, elder and pine. In an exhaustive treatment of plant material from the earlier clay, Reid (1920, p. 106; in Trechmann 1920, p. 184) distinguished 114 species of plants, from which she inferred derivation from a woodland habitat on limestone some distance from the sea. She considered that the flora is post-Reuverian, pre-Tiglian in age, and thus earliest Pleistocene according to present classification. Reid stated (1920, pp. 108, 111) that the flora of the later clay indicates that it is of Cromerian or slightly later age and that it was deposited in an essentially aquatic habitat in a climate generally similar to that of today. Nine species of insects were identified by Lesne (1920) in material from the fissures supplied by Mrs. Reid. Lesne stated (pp. 487–8) that three of these species are now extinct in western Europe, four are closely related to forms living today, and that two are common insects which could have been introduced into the sample during or after collection. Hesuggested that the insects he identified as Trechus and Argutor may be the direct ancestors of forms now living in parts of western Europe and that both these genera 'sont des formes hygrophiles qui recherchent les stations fraiches ou froides.'

Farther down the coast, in cliffs [NZ 4732 3858], 670 yd E.S.E. of Blackhall Rocks Station, the following section can be seen:

Stones in the 'Prismatic Clay' include shelly Carboniferous limestones, sandstones and shales with a few stones, including quartz, of non-local origin. The uppermost layer and overlying soil contain Neolithic chipped flints. The lower part of the sequence is repeated in cliffs [NZ 4763 3825], 1150 yd E.S.E. of Blackhall Rocks Station, where the multi-layered nature of the Lower Boulder Clay is well seen. The section is inaccessible and thicknesses are estimated:

About 100 yd to the south-south-east, at the motith of Lime Kiln Gill [NZ 4769 3818], a depression in rockhead, 85 yd wide at beach level, contains over 15 ft of cross-bedded partly calcreted shelly gravel (Lower Gravels) overlain by Lower Boulder Clay. The gravel thins sharply against the steep southern side of the depression, but thins out gradually against the shallower northern slope up which it extends as a 1- to 3-ft bed to about 30 ft above beach-level. Trechmann (1915, p. 68) noted that pebbles of Lake District rocks are common in the gravel which he later (1920, p. 191) interpreted as being the deposit of a sub-glacial stream.

On the southern side of the depression, in cliffs [NZ 4771 3814], 1300 yd S.E. of Blackhall Rocks Station, the following section is seen:

The lowest member of this section overlies about 20 ft of poorly exposed dark brown stony clay, with red clay beds near the top. These rest, in turn, on the Lower Gravels filling the buried valley at Lime Kiln Gill. The contact between the Lower Boulder Clay and the gravels is not exposed at this locality, but on the northern side of the depression it is clear and sharp and is marked by locally-preserved traces of orange-coloured silt or clay.

A short distance inland, several patches of Upper Gravels have been mapped [NZ 462 392], [NZ 471 388] and [NZ 472 380], 700 yd W.N.W., 350 yd E.S.E. and 1000 yd S.S.E. of Blackhall Rocks Station. Several of these contain small exposures of clean coarse ill-sorted gravel in which no shells have been found.

To the north-west of Blackhall the Lower Division of the Middle Sands has been exposed in many temporary excavations in and around the new town of Peterlee where the deposit is bright red and contains thin beds and lenses of red and brown laminated clay. Red sand of this division is also exposed at many places in the lower reaches of the deeper valleys, particularly Castle Eden and Crimdon dens. A borehole [NZ 4323 3952], 730 yd N.W. of Dene Leazes, Castle Eden, proved:

Middle Sands are exposed farther south in the north bank of Heads Hope Dene [NZ 4219 3723], 540 yd W. of Eden Vale, Castle Eden, where, beneath 2 ft of soil and weathered red-brown pebbly clay, they consist of the following: irregularly bedded brown clay 6 in, red sandy silt 5 in, on brown laminated clay thinly interbedded with yellow sandy silt 1 ft 2.5 in. The lowest member of the sequence overlies dark brown Lower Boulder Clay exposed in a separate section nearby. Middle Sands are also seen on the north bank of Crimdon Beck [NZ 4498 3613], 1060 yd W.N.W. of Thorpe Bulmer, near Hart, where they are represented by 8 ft of clayey and sandy gravel poorly calcreted near the base. Here, four subdivisions can be recognized in the Lower Boulder Clay: dark brown stony clay with thin layers of brown-red sand near the base 4 in, on dark grey-brown stiff stony clay 1 ft, dark grey-brown (locally dark reddish) stiff stony clay with uneven laminae of brown sand 1 ft 8 in, dark reddish brown stony clay with poorly defined bedding visible on weathered surfaces 1 ft. This section is in a slipped block and the beds dip eastwards at 10 to 30°. Middle Sands also crop out farther downstream in Crimdon Beck and its tributary, Thorpe Bulmer Beck, where they occupy a deep buried valley. Farther to the south-east, between Hart Station and Springwell House, 2.5 ft of interbedded sand and stony clay resting conformably on thin Lower Boulder Clay were seen in temporary exposures. In one of these [NZ 4869 3575], 240 yd N.N.W. of Springwell House, the following section was measured:

Sections in adjacent excavations show that the Lower Boulder Clay is 2 to 6 ft thick.

In Fifty Rigs Plantation Bore [NZ 4337 3492], 780 yd W.S.W. of Sheraton, deposits, thought to be those of a buried valley or glacial lake, underlie 18 ft of stony clay as follows:

The borehole lies a short distance to the west of the Easington–Elwick Moraine, the most northerly exposure of which is in a small quarry [NZ 4421 3257] near Shotton Hall, where 15 ft of gravel are seen. The topography between Easington and Hutton Henry is morainic, but there are no exposures; it is inferred from the nature of the soils, however, that the deposit consists mainly of gravelly clay north of Shotton and of sand and gravel between Shotton and Hutton Henry. Exposures of morainic drift between Hutton Henry and Sheraton consist of sand and gravel. The most southerly is an old quarry [NZ 4470 3538] at the south end of Sedgewick Hill, Sheraton, where 6 ft of brown and red-brown gravel are now exposed and where Trechmann (1915, p. 74) recorded worn fragments of Cyprina islandica (Linné), Turritella sp.and Mactra sp., and noted Cheviot 'porphyrites' among the erratics.

Between Sedgewick Hill and Sheraton a deep cutting has proved that a prominent hill mapped as morainic drift is in fact formed of a mantle of Upper Boulder Clay resting discordantly on a thick lens of laminated clay and sand. A generalized section is:

Bedding in the laminated clay at the northern end of the cutting is horizontal, and is truncated by the overlying boulder clay. This also truncates a number of faults in the laminated clay, presumed to have been caused by the pressures exerted by overriding Upper Boulder Clay ice. One of these, a reversed fault, demonstrates that such pressure acted from a north-easterly direction. The lateral passage from clay to sand is accomplished in a distance of about 40 yd. The sand dips to the north at about 5° to 10°.

South of Sheraton the moraine appears to be formed mainly by gravelly clay or clayey gravel, capping the prominent Farden, Whangdon and Beacon hills; it is exposed only in a small quarry [NZ 4421 3257] on the east side of Beacon Hill where 20 ft of gravel with a clay matrix are visible. It is possible, however, that some of these hills are of similar origin to that between Sedgewick Hill and Sheraton.

East of the Easington–Elwick Moraine morainic drift gives rise to a hummocky (?constructional) topography best seen in the area between Castle Eden and Hart. It rests on a rolling surface of Upper Boulder Clay and consists of coarse ill-sorted gravel, of which 8 ft are exposed [NZ 4473 3531] 1100 yd E. of Sedgewick Hill. The gravel, which has been worked at several localities near Thorpe Bulmer [NZ 450 350], gives rise to very stony soils. Several small enclosed hollows, some peat-filled, occur within this hummocky area, and others are also found around Castle Eden and Shotton where the deposit consists mainly of fine red sand. BetweenHart and Elwick the morainic drift is less hummocky than north of Hart and appears to be mainly clayey. South of Elwick, however, the main constituent is gravel which forms a number of low mounds [NZ 450 310] around Dove Cote. Where exposed, 120 yd E. of Elwick church, it is a heterogeneous deposit consisting mainly of ill-sorted sand and gravel with streaks and lenses of reddish brown stony clay inclined at angles up to 40°. Pebbles here are similar in type to those in the Lower and Upper boulder clays, although farther north Trechmann (1952, p. 172) recorded 'much Cheviot andesite' in a small conical hill south of Hesleden. Small chalky shell fragments are common in less clayey parts of the morainic drift.

Steep primary slopes, here interpreted as ice-contact faces, are found mainly around Hutton Henry, Nesbitt and Sheraton (Figure 28), where they range up to 40 ft in height. In the area of the Easington–Elwick Moraine they are on the eastern side of the ridges, excellent examples being on the flank of Sedgewick Hill, Sheraton, and on a number of gravel mounds north and south-east of Fleet Shot Farm. In the hummocky area between Sheraton and Nesbitt, where drainage is partly internal, the ice-contact slopes are more variable in direction and are generally less than 20 ft high. Meltwater channels are uncommon here, but about 0.5 mile east of Sheraton an excellent example trends north–south for about 300 yds. The walls of this channel and adjacent ice-contact slopes consist of unconsolidated sand and gravel lying at or near the angle of rest; they appear to have undergone little modification by subsequent erosion.

West of the moraine, exposures of Lower Boulder Clay are uncommon, but the following layered sequence at the top of the Lower Boulder Clay is seen beneath 5 ft of alluvial sand and gravel in the east bank of Bedlam Gill [NZ 4191 3137], 1700 yd N. of Embleton:

To the south and east Middle Sands, the Lower Division of which is bright red and about 15 ft thick, overlie Lower Boulder Clay in deep valleys [NZ 420 290] immediately east and north of Embleton church. Farther east the sand is mainly brown and it contains thin beds of red and brown laminated or stony clay where exposed in valleys [NZ 450 290] near Lower Stotf old and along Dalton Beck. A typical section is found in the west bank of Dalton Beck [NZ 4696 3030], 850 yd N.W. of Brierton:

About 1000 yd upstream, at Dalton Piercy Crag [NZ 4653 3142], the upper subdivision of the Middle Sands is represented by calcreted gravel from which mollusca and vertebrate bones have been obtained. The mollusca include Helix nemoralis Linnd and Oxychilus?: the vertebrates are identified by Mr. C. J. Wood as Bufo vulgaris Laurent, Rana temporaria Linné, and Arvicola sp.The gravel at this outcrop contains a number of deep natural cavities and it is possible that the bones were introduced into these after the deposit had formed. Farther east an old sand pit [NZ 479 301], 400 yd E. of Brierton, contains 23 ft of sand from which Trechmann (1939, p. 99) obtained a humerus of Coelodonta antiquitatis (Blumenbach). This deposit is believed to belong to the Upper Division of the Middle Sands. About 0.5 mile to north-east these sands are overlain by Upper Boulder Clay in a pit [NZ 484 306], 1000 yd N.E. of Brierton. The section is as follows:

Middle Sands are well exposed in the south-west bank of Claxton Beck [NZ 4629 2875], 1980 yd S.W. of Brierton, where beneath 1 ft 8 in of superficial red-brown gravelly clay they consist of the, following:

A section on the east bank of the stream, 70 yd E.S.E. of this locality, is in sand which is the equivalent of the lowest member of the above sequence and which overlies dark grey Lower Boulder Clay. Red-brown Upper Boulder Clay is present in situ about 20 ft above the top of the measured section. D.D.S.

The terrace of warp (p. 246) on which most of West Hartlepool has been built is cut mainly in solid rock and Lower Boulder Clay, the Upper Boulder Clay having been removed by marine erosion. It is broken 700 yd S.S.W. of the railway station by a gravel mound [NZ 509 321] which is believed to be post-Upper Boulder Clay in age. At Hartlepool Docks [NZ 520 340] boulder clay exposed in a temporary excavation contained stones which Trechmann (1915, p. 77, footnote 3) believed to be indicative of a westerly or north-westerly provenance. Since the field relations of the clay suggest that it is older than the Upper Boulder Clay capping the nearby promontory of Hartlepool, it is probably Lower Boulder Clay, though Trechmann's description of it is not fully consistent with this interpretation. Alternatively, though less likely, it may represent an isolated and possibly unique patch of an earlier drift.

Farther south a group of closely spaced boreholes have proved thick sequences of drift. In most of these the Middle Sands are only 2 to 20 ft thick and are represented by laminated clay which grades downwards by alternation to Lower Boulder Clay. Most of the bores lie just beyond the southern margin of the district, but one [NZ 5100 2845], 1410 yd S.S.W. of Seaton Carew station, penetrated the following succession:

Central area: general account

In the central area the earliest and most extensive drift deposit is Lower Boulder Clay which ranges in thickness up to 120 ft, but is generally much less. It is overlain in places by small isolated patches of sand and gravel, and in other places (especially in the ground bordering the eastern area) by laminated clays which are locally as much as 160 ft thick.

The Lower Boulder Clay is similar to and continuous with the deposit of the same name in the western area, though it includes stones derived locally from the Magnesian Limestone in addition to those named (p. 225) in that area. The sands and gravels are closely associated with meltwater channels. Deposits of sand in the eastern part of the area are extensions of the Middle Sands farther east (p. 204), but the sand and gravels elsewhere in the area cannot be correlated certainly with similar deposits in other areas.

The laminated clays fill or partially fill broad depressions in the surface of the Lower Boulder Clay at Edder Acres and Wingate (Figure 29). The clays are dark brown and contain numerous films and laminae of fine brown sand which, near Edder Acres, increase in thickness and number as they are traced eastwards. Pebbles are rare. The outcrop of the laminated clays is bounded to the east by the Upper Boulder Clay and Morainic Deposits of the eastern area (p. 205). In most places the nature of the contact is uncertain, but there are some indications that the laminated clays are locally overlain by both Upper Boulder Clay and Morainic Deposits. D.B.S.

Central area: details

Haswell to Fishburn

The characteristic drift deposit of the plateau is brown boulder clay, which exceeds 25 ft only in buried valleys and where banked against slopes. The lower parts of the deposit, exposed mainly near the crest of the scarp, are lighter brown and more gritty than higher parts, and a slightly higher proportion of the pebbles are derived locally from the Magnesian Limestone. The deposit gives rise to brown stony clay-loam soils which, in most places, are readily distinguishable from reddish soils formed on the Upper Boulder Clay of the eastern area (p. 205).

The boulder clay rests on an undulating rock surface and fills a number of buried valleys. Most of these have been located by bores and shafts and an additional V-shaped valley up to 12 ft deep has been traced for about 150 yd in ground cleared for quarrying operations [NZ 330 360], 750 yd N. of Coxhoe East House, Coxhoe. The maximum recorded thickness of clay is 120 ft in Ludworth Colliery Shaft, and 69 ft were penetrated in Deaf Hill Shaft. In surface exposures the clay rarely exceeds 15 ft and the following may be taken as representative: Crime Rigg [NZ 342 418], 1 to 5 ft; east lip of Tuthill Quarry [NZ 390 420], Haswell, 3 to 12 ft; Shotton Quarry [NZ 399 418], 4 to 8 ft; Wingate Quarries [NZ 370 370], up to 8 ft; old quarry [NZ 368 360] at West Moor Lime Works, Trimdon Grange, up to 12 ft; West Comforth Quarry [NZ 319 346], 3 to 10 ft. D.B.S., E.A.F.

Where drift is less than 25 ft thick, it is generally composed solely of boulder clay, but thicker sections, known almost entirely from bores and shafts, commonly contain one or more beds of sand and gravel. In Shotton Colliery Engine Pit [NZ 3974 4124], 2.5 ft of gravel lie at the base of the drift, and in Hetton Colliery Blossom Pit [NZ 3596 4702] 21 ft of sand and gravel rest on rockhead. These examples are exceptional, however, for most beds of sand and gravel are underlain by 10 to 25 ft of boulder clay.

Outcrops of sand and gravel in the western part of the central area are restricted mainly to the ground north of Haswell where they form low rolling mounds flanking a meltwater channel [NZ 370 440] to [NZ 370 450] at South Hetton. The best section available at the time of writing is in excavations [NZ 377 447], 350 yd N.N.W. of Fallowfield, South Hetton, where foreset beds in up to 20 ft of very poorly sorted, irregularly bedded gravel dip mainly westwards. Workings in up to 30 ft of rather more sandy gravel, 250 yd N.W. of Fallowfield, are no longer visible. About 8 ft of poorly sorted gravel are seen in an old quarry [NZ 3759 4508] at the south-western end of Cockhill Plantation, South Hetton, and 1.75 miles farther east, 3 ft of clayey gravel rest on Magnesian Limestone in a small quarry [NZ 4035 4511] at the top of Coop Hill. The only other good sections are in disused sand pits [NZ 401 421] at Thorpe Moor Farm, 0.75 mile N.N.E. of Shotton Colliery; here up to 12 ft of well-sorted fine and medium gravel appear to pass below dark brown boulder clay at the margins of the pits.

South of Haswell, sand and gravel are present mainly in small widely separated patches, generally resting on boulder clay, but also forming narrow outcrops immediately west of the edge of the Upper Boulder Clay of the eastern area. The two largest patches are between 200 and 800 yd N.W. of Kelloe church, and near Kelloe Law [NZ 365 375], where gravel occupies several acres of arable land dominated by a prominent gravel hill known as The Banks.

Sand and gravel at the eastern margin of the central area are in most cases an extension of the Middle Sands farther east (p. 204). Principal exposures are in an old pit [NZ 3979 3476], 400 yd W.N.W. of White Hurworth, where 11 ft of sand and fine gravel are seen; and in silage pits [NZ 4044 3459] at the east side of Stob Hill, 650 yd W.N.W. of Hurworth Burn station, where 2 ft of brown stony clay and soil overlie 1.5 ft of brown clayey sand, 1 ft of white (?leached) sand and 2 ft of brown clayey gravel.

Edder Acres

A triangular tract of thick drift occupies ground below the 450-ft contour between Wheatley Hill, Shotton Colliery and Wellfield. The drift comprises Lower Boulder Clay which appears to be continuous with that of the remainder of the central zone, overlain by thick deposits of lacustrine laminated clay, sand and gravel. The greatest known thickness is in a shaft [NZ 4073 3855] at Wellfield, where the section comprises 'blue clay' and 'leafy clay' [laminated clay] 98.5 ft, loamy sand 54.5 ft, on 26 ft of boulder clay, which rests on rockhead. In general the laminated clay is found only below 435 ft 0.D., though the sands and gravels locally extend to slightly above this level.

Because of the cover of later deposits, the boulder clay is seen only in deep excavations such as those at Shotton brickworks [NZ 398 403], in the bottom of deeply entrenched valleys such as Calf-pasture and Edder Acres dens, and in shafts and boreholes. Records of boreholes and inferences based on field exposures suggest that this clay ranges from about 10 to 30 ft in thickness.

It is overlain in almost the whole of the Edder Acres area by laminated clay, best exposed in workings at Shotton brickworks. At the west end [NZ 3975 4016] of the workings, 1200 yd S.S.E. of Shotton Colliery station, the section is:

There is local discordance at the base of the higher stony clay and in places the laminae of the underlying bed are overturned in an east-south-easterly direction. Pebbles in the higher clay are similar to, though less abundant than, those in the boulder clay at the base of the section. Mr. P. Beaumont (in litt.) suggests that the deposit may be a mud flow. The higher clay is apparently not present at the eastern end [NZ 3999 4023] of the workings where 42 ft of laminated clays contain much more sand than at the western end and include a 14.5-ft bed in which sand and clay are evenly interbedded. Sand laminae in this bed contain current-ripples and foreset-bedding, indicative of movement towards the west, i.e. in the direction of decreasing sand content.

Because of undulations in the surface of the Lower Boulder Clay the laminated clays range widely in thickness, reaching a recordedmaximum of 98.5 ft in Wellfield Shaft (p. 220). They are indifferently exposed in the valley between Swan Castle and Edder Acres and have been proved in boreholes near Edder Acres Farm. The deposit was formerly worked for brick-making 500 to 800 yd N.E. and 700 to 900 yd S.S.E. of the present brickworks. Further west, filled-in brick clay workings [NZ 368 400] and [NZ 382 398], north of Thornley and Wheatley Hill, occupy a similar stratigraphical position with respect to the boulder clay and lie at about the same topographical level. South of Edder Acres the laminated clays were formerly worked for brick- and tile-making around Wellfield [NZ 408 384]. At Shotton, temporary excavations [NZ 411 397] along a new road revealed 8 ft of laminated clay which appeared to pass eastwards beneath morainic drift and Upper Boulder Clay, and a similar relationship is inferred from poor exposures in the flanks of Castle Eden Dene and its tributaries a short distance south and west of Shotton.

Sand and gravel, most of which lies topographically higher than and appears to overlie the laminated clay, forms low mounds 900 yd N.N.E., 850 yd N.W., 750 yd E. and 700 yd S.E. of Edder Acres Farm.

Wingate

Drift around Wingate occupies a buried valley, and is considerably thicker than in most of the central zone. The greatest recorded thickness is 191 ft 8 in in Hutton Henry Marley Pit [NZ 4141 3692]; it is 130 ft in the Perseverance Pit, 330 yd farther south and only 62 ft in Wingate Colliery Lord Pit [NZ 3967 3718] towards the northern edge of the tract.

The lowest deposit is the dark grey-brown Lower Boulder Clay. The record of the Lord Pit makes no distinction between boulder clay and the overlying deposit, but 28 ft 8 in of clay—presumed to be boulder clay—is reported overlying rockhead in the Marley Pit. It is now exposed only in a railway cutting [NZ 4120 3715], 930 yd N.E. of Wingate station, where it is overlain by 3 ft of sand; it was formerly seen in a disused brick-pit [NZ 403 371], 600 yd N.N.W. of Wingate station (Trechmann 1952, p. 176).

The deposit at the surface over most of the Wingate tract is laminated clay, which was formerly worked extensively, but is now exposed only in temporary sections. It is generally found only below about 435 ft O.D. and may be continuous with the laminated clay around Edder Acres. At brick pits 600 yd N.N.W. of Wingate station Trechmann (loc. cit.) recorded 15 ft of laminated clay lying on 1 ft of sand, and collected numerous freshwater lamellibranchs from a 2 ft bed towards the base. Laminated clay from this pit is illustrated by Carruthers (1953, fig. 2b; pl. i). During the resurvey 11.5 ft of red-brown sandy laminated clay was noted in a small temporary exposure [NZ 4094 3684], 500 yd N.E. of Wingate station. Similar clay was seen in a number of shallow excavations around the ruins of Hutton Henry Colliery, and in the banks of Heads Hope Dens [NZ 4219 3722], 480 yd S. of Castle Eden station, where it was 3.5 ft thick. Laminated clay is not separately distinguished in the records of the three colliery shafts but 84 ft of clay immediately below the surface at the Marley Pit is presumed to be laminated from the evidence of the nearby excavations.

In the eastern part of the Wingate tract, sand and gravel up to 25 ft thick form several acres of moundy ground between Wellfield House and the railway line, and are exposed in a number of old workings around Beech House [NZ 4084 3719]. Gravel also forms moundy ground 800 to 1200 yd E. of Wellfield House, and occupies a smaller area 500 yd E.N.E. of Wingate Station. Most of the sand and gravel appears to lie above the top of the laminated clay, but there is some overlap of levels and lower parts of the gravel may pass locally into upper parts of the laminated clay. As in the Edder Acres tract, the laminated clays are poorly exposed in the flanks of valleys (Heads Hope Dene and its tributaries) entering the eastern area, but here too, they seem, from their general field relationships, to be at least partly overlain by Upper Boulder Clay and Morainic Drift. The localities at which laminated clays have been proved are shown on (Figure 29), which also shows the presumed maximum extent of the lake in which they were deposited and the position of the channels which drained it. D.B.S.

Southern area: general account

A tripartite subdivision of the drift can be recognized in the southern area as follows: Upper Stony Clay 0 to about 30 ft, Middle Sands and Gravels 0 to about 50 ft, on Lower Boulder Clay 0 to about 54 ft. The Lower Boulder Clay closely resembles that of the western and central areas, but contains boulders of Shap Granite as well as other stones of local and distant origin. The sands and gravels form isolated mounds overlying the Lower Boulder Clay and also occur intermittently between the two clay deposits. The Upper Stony Clay is of uncertain origin and is only poorly exposed over a limited area. B.A.F., G.D.G., D.D.S.

Southern area: details

Chilton to Rushyford

In the tract southwest of Kay's Hill, drift is thin and consists mainly of Lower Boulder Clay. It is exposed only in the sides of a swallow hole [NZ 2952 2912], 225 yd E.S.E. of Standalone, where it appears to be rather more than 14 ft thick. A buried valley trends south-eastwards under the alluvium of the Rushyford Beck at Rushyford, where the surface seems to be composed of very stony boulder clay, and where an old clay pit was worked [NZ 2807 2887], 200 yd W.N.W. of the inn. A small isolated patch of sand and gravel caps a low hill about 1150 yd W.N.W. of the inn.

Between Kay's Hill and Nunstainton East the gently undulating ground seems to be entirely composed of Lower Boulder Clay which is 54 ft thick in a bore [NZ 3104 2932], 650 yd N.W. of Nunstainton East.

Two patches of sand and gravel rest on the boulder clay and cap low hills about 350 yd S.W. and 450 yd S.S.W. of Nunstainton East. Sand is exposed to a thickness of 25 ft in an old sand pit [NZ 3122 2941], 550 yd N.W. of the same farm and crops out round the western margin of the hill to the north-north-west. At the eastern end of the pit brown Upper Stony Clay rests on the westwards-sloping surface of the sand and forms the upper part of the bill. The sand can be traced round the southern flank of the hill where it has been worked in old pits about 100 yd N.W., 75 yd W. and 125 yd S.E. of Nunstainton East. The outcrop of sand can be followed into the western side of a valley about 250 yd E. of the farm, but on the eastern side the sand seems to wedge out and Upper Stony Clay is presumed to rest on Lower Boulder Clay. On the northern flank of the hill, the sand also seems to wedge out. Upper Stony Clay overlies sand in a railway cutting about 680 yd N.E. of Nunstainton East, and also forms the surface of two hills on either side of the railway. North-eastwards from there, over rough ground known locally as Linger and Die, it rests directly on Lower Boulder Clay. Sand and gravel form the surface of the south-eastern part of the hill around Stony Hall and apparently rest on Lower Boulder Clay in a railway cutting 400 yd farther north. Their relationship to the Upper Stony Clay, however, is obscure. A bore [NZ 3261 2952], about 60 yd S.S.E. of Stony Hall, penetrated a thick sequence of sand and clay overlying presumed Lower Boulder Clay as follows: