Geology of the country around Bellingham Memoir for 1:50 000 geological sheet 13

By D.V. Frost and D.W. Holliday

Bibliographical reference: Frost, D.V. and Holliday, D.W. 1980. Geology of the country around Bellingham. Mem. Geol. Surv. G.B., Sheet 13, 112 pp.

• Authors: D.V. Frost and D.W. Holliday
• Contributors:
• Palaeontology; Pattison, K.J. Gueinn and J.E. Robinson
• Petrography; N.G. Berridge and S. Siddiqui
• Photography; K.E. Thornton

Institute of Geological Sciences Natural Environment Research Council

London Her Majesty's Stationery Office 1980. Printed in England for Her Majesty's Stationery Office by Staples Printers St Albans Limited at The Priory Press, St Albans, Herts © Crown copyright 1980. ISBN 0 11 884137 8

• Authors:
• D.V. Frost, BSc, PhD Institute of Geological Sciences, Leeds LS15 8TQ.
• D.W. Holliday, MA, PhD Institute of Geological Sciences, Keyworth, Nottingham NG12 5GG.
• Contributors:
• N.G. Berridge, BSc, PhD; J. Pattison, MSc and K. S. Siddiqui, MSc Institute of Geological Sciences, Leeds.
• J.E. Robinson, BSc, PhD University College, London.
• K.J. Gueinn, BSc, PhD Palaeoservices, Watford.

Other publications dealing with this and adjoining districts

Books

• British Regional Geology, Northern England, 4th Edition, 1971
• One-inch Sheet Memoirs, Geology of the country around Bewcastle, 1970
• Economic Memoir, Geology of the Northern Pennine Orefield, Vol. 1, Tyne to Stainmore, 1948

Geological maps

• 'Ten Mile' Map of Great Britain (1: 625 000), Sheet 1, Scotland and Northern England, 3rd Edition, 1979 Overprinted with sheet lines of One-inch and 1: 50 000 Geological Series
• Quaternary Map of the United Kingdom, north sheet, 1977
• One-inch to one mile (1: 63 360) and 1: 50 000 sheets
• Kielder Castle (7) Solid and Drift editions 1950
• Elsdon (8) Solid and Drift editions 1951
• Rothbury (9) Solid Edition 1934 (reprinted 1966 with National Grid)
• Bewcastle (12) Drift Edition 1934 (reprinted 1965 with National Grid) Solid and Drift editions 1969
• Bellingham (13) Solid and Drift editions 1980
• Morpeth (14) Solid and Drift editions 1955
• Brampton (18) Solid and Drift editions 1931. Solid edition reprinted and enlarged to 1: 50 000 scale in 1976
• Hexham (19) Solid edition 1956, reprinted and enlarged to 1:50 000 scale in 1975
• Newcastle upon Tyne (20) Out of print. New edition in preparation (Old Series 105 SW, 1870 revised 1892)
• Special Geological Sheets (1:25 000)
• Bewcastle Sheet NY 57 Solid and Drift editions

Preface

This memoir describes the geology of the district covered by the Bellingham, New Series Sheet 13 of the One-Inch Geological Map of England and Wales. The district was originally surveyed between the years 1875 and 1878 on the six-inch to one mile scale by H. Miller Jnr. and D. Burns under the superintendence of the District Surveyor H. H. Howell with H. W. Bristowe as Senior Director. Parts of the district show evidence of an earlier six-inch survey and some field maps used by Miller and Burns already contained printed geological boundaries. This earlier surveyor was probably G. A. Lebour who worked for the Geological Survey from 1867 to 1874 and later published papers on the district when he became Professor of Geology at Armstrong College, Newcastle upon Tyne.

The geological map was published as Old Series sheet 106 SE at the one-inch scale in 1881 (Solid edition), and the Drift edition came out in 1883. No explanatory memoir for the sheet was published despite the existence of an excellent manuscript account by Miller.

Small marginal areas in the east and west were resurveyed by G. A. Burnett in 1932–5 in connection with the adjoining Sheet 14 (Morpeth) and by J. B. W. Day, D. H. Land and D. A. C. Mills in 1954–8 in relation to Sheet 12 (Bewcastle). The present revision survey has been carried out by Drs D. V. Frost and D. W. Holliday during the years 1968 to 1975 with Mr B. J. Taylor as District Geologist. For two years of that period Dr Holliday was absent, seconded to the Geological Survey Department of Jamaica. The list of six-inch maps with the names of the Surveyors is given on p. ix. The mineral deposits of the Settlingstones and Fallowfield areas were investigated by Sir Kingsley Dunham during the period 1939 to 1945. The revised 1:50 000 sheet was published in 1980 in both Solid and Drift editions.

Drs Frost and Holliday shared the writing of this memoir. In Chapter 6 on Dinantian and Namurian palaeontology, the section on macrofossils was written by Mr J. Pattison (collection of fossils mainly by Messrs Pattison and Monograptus J. Reynolds), that on ostracods by Dr J. E. Robinson and that on miospores by Dr K. J. Gueinn. Dr N. G. Berridge, assisted by Mr K. S. Siddiqui, supplied mineralogical and petrographical data for several chapters. The memoir was compiled by Dr D. V. Frost and edited by Mr B. J. Taylor.

Grateful acknowledgement is made to numerous organisations and individuals, in particular the Forestry Commission, for permission of access both for surveying and borehole drilling; to Mr W. Johnson, the Chief Forester and his staff at the Stonehaugh Office; to Mr H. A. Baker of the University of Leeds for details of his magnetometer survey in the Bingfield area; to Tilcon Ltd and McLaren and Company Ltd for details of production from their respective quarries; to the National Coal Board for help with reference to old mine plans and opencast records; and to Mr B. Arthur, County Surveyor, Northumberland County Council, for his co-operation in siting boreholes and providing information on shallow proving holes and temporary sections.

G. Monograptus Brown, Director, Institute of Geological Sciences, Exhibition Road, London. SW7 2 DE. 4 April 1980

Six-inch maps

The following is a list of six-inch geological maps included in the area of 1:50000 Geological Sheet 13 with the date of survey for each map. The surveying officers are: G. A. Burnett, J. B. W. Day, D. V. Frost, D. W. Holliday, D. H. Land and D. A. C. Mills. Copies of the maps are deposited for public reference in the libraries of the London and Leeds Offices of the Institute of Geological Sciences. Uncoloured dyeline copies of those marked by an asterisk are available for purchase. Xerox copies of the remaining partially surveyed sheets are also available.

Explanatory notes

• In this memoir the word 'district' means the area of land included on the England and Wales 1:50000 geological sheet 13 (Bellingham).
• Numbers in square brackets are National Grid references within 100 km squares NY.
• Numbers preceded by the letter E refer to the Sliced Rock Collection of the Institute of Geological Sciences.
• Numbers preceded by the letter L refer to the Geological Survey Photograph Collection of the Institute.
• Numbers preceded by the letters NEXD refer to X-ray diffractograms in the Institute of Geological Sciences North of England registered collection.
• The authorship of the fossil species is given in the index.
• The term 'striped beds' is used throughout this memoir to describe interbanded and interlaminated sandstones, siltstones and silty micaceous mudstones.

Geology of the country around Bellingham—summary

The Bellingham district includes much of the Roman Wall country, the Northumbrian lakes, North Tynedale and Redesdale-all areas of outstanding, unspoilt beauty. They are underlain by Carboniferous rocks, 1600 m thick which were laid down around 300 million years ago. In the south and east, 'Yoredale' limestones, sandstones and shales with the intrusive dolerite of the Whin Sill form scarp and dip-slope features, but in the forested areas to the north and west thick boulder clay of Pleistocene age mantles most of the solid rock and forms its own distinctive drumlin topography.

This memoir is the first comprehensive published account of the geology of the district. After an introductory chapter, the stratigraphy of the Carboniferous rocks is described in detail, with comprehensive correlation diagrams of sections and boreholes together with complementary palaeontological identifications.

Accounts of the igneous rocks and structure of the region are followed by chapters on the Pleistocene and economic geology. Appendices list boreholes, shafts, measured sections and geological photographs and conclude with a comprehensive bibliography.

Geological sequence

Chapter 1 Introduction

Area and physical features

This memoir describes the geology of that part of southwest Northumberland covered by the Bellingham Sheet (13) of the 1:50000 geological map of England and Wales (Figure 1). The ground rises from below 200ft OD in the North Tyne valley in the south-east to about 1150ft OD in the north-west. Most of the district is within the River North Tyne catchment (Figure 2), but small areas in the south and south-west drain to the South Tyne, in the east to the Wansbeck and Pont, and in the west to the Irthing. With the exception of the Irthing drainage which flows into the Solway Firth, all the rivers discharge to the North Sea. Much of the western part of the district is in the Northumberland National Park (Philipson, 1969), and includes the impressive scenery of the Northumberland Lakes, the Whin Sill escarpment and North Tynedale (Plate 1), which can all be appreciated from the Pennine Way.

The district is predominantly agricultural and sparsely populated. Arable crops are important in the more sheltered low ground of the valley bottoms, but much of the higher ground forms rough pasture. The high fells and moorland provide grazing for sheep but this is now reduced in importance following extensive re-afforestation (Figure 2) and (Plate 16), which has improved the drainage of the high ground. Coal was formerly widely worked on a small scale, but the Robin Rock Drift is now the only active mine. Galena, witherite and baryte were mined around Settlingstones and Fallowfield, but the witherite mine at Settlingstones, the last venture of a once flourishing industry, closed during the period of resurvey. Five 'whinstone' (dolerite) quarries are working at present (1977) within the district. Small quantities of sandstone for building are wrought at Prudhamstone Quarry, and crushed sandstone is employed by the Forestry Comission to surface forest roads. Ironstone formerly was worked extensively around Ridsdale and Bellingham. Limestone, sand and gravel, and glacial and Carboniferous clays also have been worked in the past.

There are many features of historical interest in the district, but it is for the Roman archaeology, both here and in the area to the south, that it is best known. Some of the best preserved stretches of Hadrian's Wall, set in magnificent scenery (Plate 1), follow the crest of the Whin Sill escarpment from Crag Lough to Sewingshields Crags. The district contains three major Roman forts, Housesteads, Carrawbrough and Chesters, together with numerous smaller sites. In addition, a number of pre-Roman camps and standing stones are to be seen, and a wooden cross at the side of the B6318 road at the top of Brunton Bank marks the site of King Oswald of Northumbria's victory over the Welsh in AD 633. Old enclosures, cultivation terraces and ironstone smelting hearths show continuous settlement in post-Roman times. The district is rich in the remains of old castles and fortresses of the Middle Ages, many of which were built as defences against the Scots.

Previous research

Reference to the geology of the district can be found in many early works but the first systematic study was the primary six-inch geological survey by Hugh Miller Jnr., and D. Burns between 1875 and 1878. The solid edition of their one-inch map was published in 1881 followed by the drift edition in 1883. This map was not accompanied by a detailed geological succession nor were any major lithological subdivisions of the Carboniferous shown. A descriptive memoir written by Miller was not published. Small areas on the eastern and western edges of the district were resurveyed by G. A. Burnett (1932–35) and J. B. W. Day, D. H. Land and D. A. C. Mills (1954–58) respectively.

This memoir is the first comprehensive description of the geology of the district (Figure 3), though a number of generalised descriptions have appeared in works which deal with wider regions (e.g. Lebour, 1889; Garwood, 1910; Smith, 1912; Hickling and others, 1931; Taylor and others, 1971). In addition, important contributions to knowledge of the Carboniferous rocks of the district include those by Tate (1867a), Lebour (1873, 1875a, b), Johnson (1959), Fowler (1966) and Frost (1969). Igneous rocks have been studied by Tate (1867a, b, 1870). Topley and Lebour (1877), Teall (1884a, b), Heslop and Smythe (1910), Weyman (1910), Holmes and Harwood (1928, 1929), Smythe (1930), Randall (1959a, b), and Ineson (1972). Mineral deposits have been described by Wilson and others (1922), Smith (1923) and Dunham (1948); and the drift deposits and glacial retreat phenomena by Dwerryhouse (1902) and Smythe (1908, 1912).

Memoirs describing adjacent areas include those by Miller (1887), Clough (1889), Trotter and Hollingworth (1932), Fowler (1936) and Day (1970).

Geological sequence

The numerous classifications proposed previously for the Carboniferous rocks of the Bellingham and adjacent districts are summarised in (Figure 4) and were reviewed by Day (1970). Because of the cyclothemic nature of these rocks and their vertical and lateral variation, the major lithological divisions traditionally recognised in Northumberland were defined in relation to marker beds, generally of supposed or established palaeontological significance, rather than on strict lithological grounds. This method, though not in accord with modern views of lithostratigraphical subdivision, has proved in the main to be of practical value in northern England. The term 'group' as used here and by earlier workers does not necessarily imply correspondence with a lithological group as recognised by current international usage.

During the resurvey it has proved possible to follow the classification proposed by Day (1970) for the adjacent Bewcastle district with only one boundary adjustment. The base of the Liddesdale Group was defined by Lumsden and others (1967) at the base of the Dinwoodie Beds of the Langholm district, a horizon believed to correlate with the Naworth Bryozoa Band of Brampton (Trotter and Hollingworth, 1932) and Bewcastle (Day, 1970). However, the faunal grounds for taking this horizon as the base of the Dibunophyllum Zone (Lumsden and others, 1967; Day, 1970) are now known to be invalid (George and others, 1976, pp. 41–45) and the band is known only from boreholes in a limited area and cannot be traced on the ground. The Redesdale Limestone occurs a little way below the horizon of the band (Figure 4) and (Figure 16) and forms the lowest stratum that can be mapped reliably over the whole Bellingham district. The base of this limestone, therefore is taken here as the local base of the Liddesdale Group (Figure 4). The Redesdale Limestone was also taken as a group boundary in the adjacent ground to the north (Fowler, 1966). Only in the south-west of the district is the limestone difficult to trace and here the overlying Fourlaws (= Naworth) Limestone is more readily mapped (cf. Trotter and Hollingworth, 1932).

Geological history

No pre-Carboniferous rocks have been proved within the district, though it may be surmised from outcrops in the Lake District and Southern Uplands that the sub-Carboniferous basement consists of strongly folded Lower Palaeozoic strata. Many syntheses of Lower Palaeozoic history suggest that northern Britain was formed by the collision of two crustal plates brought together as a result of the closure of a proto-Atlantic (Iapetus) Ocean. It has been inferred that the continental (or Iapetus) suture is along the line of the present Solway Firth and extending across Northumberland (Phillips and others, 1976; Moseley, 1978). In this view, the suture is likely to occur just beyond the northern margin of the Bellingham district.

In Carboniferous times the district lay in the Northumberland Trough, a sedimentary basin bordered by the Southern Uplands to the north and the Cumbrian and Alston blocks to the south (Figure 5). The northern margin of the trough probably corresponds closely to the Lower Palaeozoic Iapetus suture. During Lower Carboniferous and early Namurian times about 2600 m of shallow marine and deltaic deposits, derived from the north and east (Robson, 1956; Frost, 1969; Leeder, 1974) were laid down in the district. Evidence from the adjacent Bewcastle and Langholm districts suggests that the basin edges were sources of sediment supply only during the earliest part of Carboniferous sedimentation (Leeder, 1974). A restricted marine fauna is found throughout much of the Border Group but most of the limestone beds are impure and thin. This is in contrast to the Liddesdale Group and lowest part of the Stainmore Group where abundant marine faunas occur but are largely restricted to thick persistent limestones and accompanying calcareous mudstones. A marked thickening of the Upper Border Group northwards, apparently across the Antonstown Fault, suggests some tectonic activity contemporaneous with sedimentation. In Lower Carboniferous times there was considerable volcanic activity in areas to the north and north-west, mainly in Scotland, but no representatives of this vulcanism have been detected in the Bellingham district.

Evidence from adjacent districts suggests that later Namurian and Westphalian rocks were laid down in the district but all trace of these has now been removed. Much of this erosion probably took place in the late Carboniferous and early Permian, when the rocks were folded and faulted and the Whin Sill suite of quartz-dolerite sills and dykes were intruded. The nature and extent of any Permian, Mesozoic and Tertiary sediments and earth movements in the district must be largely matters for speculation based on evidence from elsewhere. A period of tholeiite dyke intrusion in early Tertiary times can be demonstrated and a period of late Tertiary uplift inferred. It is probable that the present drainage system was initiated following this uplift.

In this district there is evidence for only one (Devensian) glacial advance and retreat during which the boulder clay, glacial sand and gravel and morainic drift were deposited. At the close of this period the larger rivers in the main followed their previous courses, but the drainage was considerably modified in detail during the glaciation and some river capture occurred. During post-glacial time the rivers have deposited large volumes of alluvium and terrace deposits, mainly sand and gravel. In the same period the climate has favoured the growth of peat, notably on the upland moors, especially in the west and north-west of the district, but also in ill-drained hollows in lower-lying areas. Some of these hollows were for a period occupied by lakes, the present lakes being remnants of a once larger system. Screes and landslips date from the close of the glaciation to the present time. The most recent deposits are waste-tips from mines and quarries.

Chapter 2 Middle Border Group

The Middle Border Group was defined by Day (1970, p. 82) in the Bewcastle district as extending upwards from the base of the Whitberry Band (Chonetes cumbriensis Band of Garwood, 1931) to the base of the Clattering Band (Figure 4). It is approximately equivalent in age to the Fell Sandstone Group of Miller (1887). Unfortunately neither the Whitberry, nor Clattering bands were recognised in the north-east of the Bewcastle district and similar problems of identification exist in the Bellingham district. A deep borehole at Stonehaugh, drilled during the resurvey of the district, encountered strata which has been assigned to the Middle and Upper Border groups; the Middle Border Group is not considered to crop out in the district (Figure 6).

Day (1970, p. 105) in the Bewcastle district, correlated the Clattering Band with the Kingbridge Limestone. Macropalaeontological evidence from the Stonehaugh Borehole suggests that this limestone is represented by 7.52 m of calcareous beds at a depth of 396.95 m (p. 46). However, palynological evidence from the same borehole indicates that the boundary between the TC and the Pu miospore zones (Figure 26) occurs at about 281 m. The strata between 281 m and the base of the borehole at 601 m contained miospores typical of the Pu Zone which is considered to be sub-D₁ in age, belonging to the Holkerian (S₂), Arundian and possibly Chadian stages (George and others, 1976). Unpublished work by Williams (Neves and others, 1973, fig. 15) in the Brampton district showed that the highest recorded miospores then considered to belong to the Pu Zone, occurred immediately beneath the Kingbridge Limestone. The upper boundary of the Middle Border Group cannot therefore be accurately defined and is tentatively drawn at a depth of 396.95 m in the Stonehaugh Borehole.

The rocks of the Middle Border Group are therefore at least 200 m thick and consist of a series of alternating mudstones and siltstones, commonly calcareous and rarely shelly, together with thin, impure, dark grey limestones, seatearths and thin coals. These lithologies usually occur grouped together in measures between 3 and 13 m thick which are separated by massive, fine-grained, pale grey sandstones some 15 m thick often with gradational margins. In the lowest 115 m of the Stonehaugh Borehole the limestones are commonly algal and the mudstones and seatearths are stained red in colour with the latter containing calcareous and reddened ferruginous nodules. This sequence is also unusual in that seatearths form about 25 per cent of total lithologies.

Chapter 3 Upper Border Group

Introduction

The Upper Border Group was defined by Lumsden and others (1967, p. 105) in the Langholm district of southern Scotland and applied by Day (1970, p. 105) to the Bewcastle district as extending upwards from the base of the Clattering Band to the base of the Naworth Bryozoa Band. Recognition of these limits and the practical difficulty of tracing them on the ground has posed many problems in the Bewcastle and Bellingham districts. In the Stonehaugh Borehole the base of the Upper Border Group is fixed at a depth of 396.95 m on a combination of lithological and palaeontological evidence outlined in the previous chapter. The top is drawn at the base of the Redesdale Limestone, which can be traced over much of the district without difficulty and which lies only some 10 m below the Naworth Bryozoa Band. The succession in the Bellingham district is shown graphically in (Figure 7), (Figure 8), (Figure 9), (Figure 10), (Figure 11), (Figure 12) and (Figure 13).

Limestones with names well established in the literature (Trotter and Hollingworth, 1932; Lumsden and others, 1967; Day, 1970) such as Cumcrook, Lanercost, Millerhill, Appletree and Leahill have been recognised within the district and new names like the Low Carriteth and Birtley limestones introduced for beds higher in the Group. The Thirlwall Coal in the south-west of the district is correlated with the Furnace Coal of the Redesdale and Bellingham areas and the Bellingham or Carriteth Coal is probably the equivalent of the Solport, Waverley and Plashetts coals. The Low Carriteth Limestone is therefore a probable correlative of the Plashetts Dun Limestone (Figure 7), (Figure 8) and (Figure 9).

The uppermost 305 m of the Upper Border Group were proved in the Ridsdale Borehole and are sporadically exposed over a large area of outcrop mostly in the northwest of the district. The lowest 200 m or so do not occur at outcrop but were proved in Stonehaugh Borehole.

The Upper Border Group as originally defined is 582 m thick in the Archerbeck Borehole (Langholm district), and is 646 m thick in the lower reaches of the River Irthing if the assumed correlation is correct. It is thicker still in the North Tyne catchment between the Antonstown and Harrett's Linn faults, where Day (1970, p. 108) calculated a thickness of 1800 m. In the Bellingham district the average thickness is about 600 m, but the group thickens northwards across the Antonstown Fault where at least 600 m of strata belonging to the upper part of the group crop out. These beds appear to be equivalents of the Lewisburn Beds of the Kielder district (Clough, 1889; Fowler, 1966).

Re-interpretation of the Harton Borehole (Ridd and others, 1970) on the north Durham coast is shown in (Figure 9), and confirms the lateral persistence of the group eastwards to the coast. The lowest 60 m of strata proved in the Harton Borehole are quartzitic sandstones and were compared by Ridd and others (1970, p. 95) with the Fell Sandstones (Middle Border Group), but are now considered to correlate with the Spy Rigg Sandstone.

The original definition of the Upper Border Group was intended to exclude all rocks of D₁ age, and the base of the overlying Liddesdale Group in both the Bewcastle and Langholm districts was thought to coincide with the incoming of D, species such as Lithostrotion junceum. However, this species has now been recognised in the Low Carriteth Limestone, some 100 m below the top of the Upper Border Group in the Bellingham district, and George and others (1976) on micropalaeontological evidence have assigned the whole of the Upper Border Group to the lower part of the Asbian (D₁) stage.

Lithology

The Upper Border Group rocks show considerable lateral variation, but despite this, the main limestones and some of the higher sandstones can be traced from the River Irthing right across the district.

Limestones are impure with variable amounts of sandy and argillaceous matter and show ferruginous weathering. Commonly they pass laterally into and are interbedded with calcareous sandstones, siltstones and mudstones, locally with abundant bioclastic debris. The limestones are mainly biomicrites with abundant bryozoan and crinoid debris and a lime-mud matrix. They are locally burrowed, poorly laminated and sporadically bioturbated (Plate 2.1) and (Plate 2.2). Some fine-grained ferruginous micrites, up to 0.3 m thick, are laminated and silty, usually lacking in fauna, and resemble 'cementstones' (Belt and others, 1967): these may be lagoonal or lacustrine in origin. Other fine-grained limestones associated with calcareous mudstones are nodular and only locally developed; these appear to have resulted from diagenetic redistribution and local concentration of calcium carbonate within the mudstone. They are analogous to the nodular cementstones of Belt and others (1967). Algal limestones, common in the Lower and Middle Border groups, are absent in the Upper Group. Marine faunas, though generally rich in individuals, are limited in the number of species.

Mudstones and siltstones are commonly finely laminated and locally bioturbated. Carbonaceous matter including plant debris is present in varying quantities, and it is not unusual for plant material to be found mixed with marine fossils. Ironstone nodules are locally abundant. Some beds have numerous calcareous sandstone and sandy limestone laminae and burrow in-fills. Coarser, micaceous, siltstone is commonly interbanded and interlaminated with silty mudstone and fine-grained sandstone (striped beds).

Sandstones are mainly fine-grained, less commonly medium-grained; coarse-grained pebbly sandstones are relatively rare. At outcrop, they range from flaggy to massive, commonly exhibiting both large- and small-scale trough cross-stratification. Planar lamination has also been observed, as have siltstone laminae, carbonaceous, micaceous and silty mudstone partings and cross-laminae. Marine fossils occur in some sandstones and others show signs of burrowing. Some sandstones have disconformable bases and rest on scoured surfaces; others have gradational bases.

All the above lithologies locally contain rootlets and form seatearths some of which are in places capped by coals up to 2 m thick. Most of the coals contain bands and partings of mudstone, siltstone, or locally limestone, and only rarely are the seams thick and uniformly developed. Thin lenticular coals, without seatearths, are probably not derived from in-situ growth but from transported vegetation or by erosion and redistribution of a pre-existing seam.

Sedimentary environments

The lithologies described above can be grouped into three main facies associations.

Facies association 1

Facies association 1 comprises largely marine strata showing much lateral and vertical variation in lithology, and in which no consistent upwards coarsening or fining trends have been detected. Locally cyclothemic sequences occur in which marine beds grade up into seatearth commonly overlain by coal. Such cycles show affinities to the coarsening-upwards cycles characteristic of facies association 2. Many of the beds are impersistent, though the major named limestones can be traced throughout much of the district despite their changing lithology. Signs of burrowing and bioturbation are common in the clastic rocks (Plate 2.1) and (Plate 2.2) which range from mudstone to medium-grained sandstone. Sedimentary structures seen in the sandstones include planar bedding, large- and small-scale trough cross-stratification. The association is commonly capped by seatearth with a thin coal or is terminated at an erosion surface beneath the sandstone member of the third association (Figure 10)F. The marine beds were deposited in a very shallow sea and perhaps also on tidal-flats, of greatly fluctuating water energy, close to a source of clastic sediment. From time to time sediment locally built up above sea level allowing plant colonisation and peat formation in coastal marshes.

Facies association 2

Facies association 2 consists of sequences coarsening-upwards from shelly mudstone to sandstone (Figure 10)G&I. The thinnest examples are only a few metres thick (Figure 10)G, but the thicker examples, generally with a well developed limestone in the basal marine portion, are 15 to 20 m thick and are similar to the Yoredale cyclothems that make up the overlying Liddesdale Group (Figure 10)I. In the thicker cycles the upper sandstone member, fine- to medium-grained with large-scale trough cross-stratification, is laterally persistent. A seatearth, generally with overlying coal, is found at the top of the sandstone member. These features suggest that the association was formed by the outgrowth of a deltaic complex into a marine environment (cf. Leeder, 1974, p. 142; Elliott, 1975).

Facies association 3

Facies association 3 comprises fining-upwards sequences from erosive-based sandstones to siltstones and mudstones (Figure 10). The sandstone member, fine- to coarse-grained, rests on the basal scoured surface and shows a broadly fining-upwards trend. The overlying siltstone-mudstone member is generally devoid of marine fossils but commonly contains seatearths and coals; limestones where present are mainly of the 'cementstone' type. These characters suggest that the association can be referred to a coastal plain fluviatile environment (cf. Leeder, 1974, p. 150). The cycles with marine fossils in the upper part may be of interdistributary bay or tidal-flat origin.

At a few localities, sequences of beds were found with basal erosion surfaces that initially fined-upwards from sandstone to mudstone but higher, with no break in deposition, coarsened upwards back to sandstone capped by seatearth and coal (Figure 10)D&E. No analogues have been found in the literature.

Sedimentary history

Below the level of the Bellingham Coal, the Upper Border Group is chiefly composed of marine beds (facies association 1) and fining-upwards cycles (facies association 3). The latter are particularly numerous north of the Antonstown Fault. Thus, much of the group records repeated alternations of shallow marine and fluviatile coastal plain environments. Coarsening-upwards sequences (facies association 2), indicative of delta progradation, occur more rarely. However, above the Bellingham Coal coarsening-upwards deltaic units (15 to 20 m thick) become the dominant facies, occurring together with sporadic fining-upwards cycles. The persistence and argillaceous nature of the marine members and the overall thickness of the cycles suggest that the sea, though shallow, was somewhat deeper than that in which underlying measures were deposited. These deltaic cycles mark an important change of sedimentation from that of the lower part of the group and form a transition to the Yoredale facies of the overlying Liddesdale Group.

Details

South of the Antonstown Fault

Strata below the Millerhill limestones do not crop out but were proved in the Stonehaugh Borehole where the base of the Upper Border Group is taken at 396.95 m. The measures comprise a series of generally calcareous mudstones, mostly thin impure limestones, seatearths and coals, alternating with thick sandstones.

A limestone some 8 m thick with mudstone partings occurs about 129 m above the Kingbridge Limestone and is correlated with the Cumcrook Limestone of the Bewcastle district (= Hogg Limestone of the Archerbeck Borehole). The limestone is grey to pale grey, impure and sporadically shelly at the top, with a fauna including abundant bryozoa and Punctospirifer scabricosta. Some 87 m of measures separate the limestone from a series of limestones which are correlated with the Lanercost limestones (= Carlyle Beds) of districts to the west. The limestones are sandy with silty and mudstone laminae and are sporadically shelly. The fauna from these measures includes Lingula lumsdeni, Pleuropugnoides pleurodon, Leiopteria hendersoni, Modiolus spp., Phestia attenuata and myalinids.

An overlying coal, 49 cm thick, may be the equivalent of the Hogg Coals of the Bewcastle district. A sandstone some 20 m thick, containing a mudstone band 3 m thick near its middle, separates the coal from largely calcareous measures proved in the top 80 m of Stonehaugh Borehole.

These calcareous measures contain the Millerhill limestones. The Lower Millerhill Limestone is represented by only 1.29 m of calcareous sandstone and siltstone containing bioclastic debris, with a shelly mudstone parting. The Upper Millerhill Limestone is 2.49 m thick and comprises grey muddy bioclastic limestone which passes down into sandstone at its base. This limestone is partially exposed in an old quarry [NY 7391 7454] northeast of Grindon Green, where 0.76 m of massive bioclastic limestone are seen. The highest part of the Upper Millerhill Limestone is the lowest bed exposed in Rowantree Cleugh [NY 7134 8190]. In the Ridsdale Borehole [NY 8946 8288] the Millerhill Limestones are represented by several thin limestone bands none of which exceed 0.60 m in thickness. They are separated by calcareous shelly mudstones containing ostracods and plant debris. Beds from below the Lower Millerhill Limestone [NY 6976 7723] to above the Upper Millerhill Limestone [NY 7027 7738] crop out in Thross Burn (Figure 11), column 3 and nearby, in discontinuous exposures, in Coal Burn [NY 6946 7787] to [NY 6975 7829].

The measures between the Upper Millerhill Limestone and the Spy Hole Limestone can be seen at a number of localities near the western margin of the district. A fairly complete section in Chirdon Burn, from the Upper Millerhill Limestone (Chirdon No. 1 Limestone) [NY 6963 8023] to the Spy Hole Limestone (Chirdon No. 2 Limestone) [NY 701 1 8023] has been measured ((Figure 11), col. 7a and Day, 1970, p. 280). The only complete sections are those in Rowantree Cleugh [NY 7139 8184] and the Stonehaugh and Ridsdale boreholes (Figure 9) and (Figure 11). They comprise sandstones, some shelly and calcareous, with calcareous mudstones and a thin coal.

The Spy Hole Limestone has a variable lithology ranging from argillaceous limestone to sandy limestone and calcareous shelly sandstone. It is exposed in Smaley Cleugh [NY 7017 8125] and again in the quarry at Rowantree Cleugh [NY 7142 8184]. In Stonehaugh Borehole the limestone is some 9 m thick but is represented in Ridsdale Borehole by several limestone beds separated by fossiliferous mudstones together totalling some 10 m. One such limestone band 1.30 m thick is exposed [NY 8064 7703] in Warks Burn.

The strata overlying the Spy Hole Limestone are visible in discontinuous exposures in Rowantree Cleugh and include some shelly sandstones and a coal 35 cm thick, which has been worked hereabouts [NY 7146 8180] and is probably a correlative of the Throssburn Foot Coal (Day, 1970, p. 300) seen in the River Irthing in the Bewcastle district. A coal at this horizon has also been worked near Stonehaugh [NY 7924 7656] and [NY 8149 7700]. Overlying these beds in the River Irthing, and underlying the Wiley Sike Limestone, are strata including a number of thick sandstones which locally coalesce into one thick bed, the Spy Rigg Sandstone. Sporadic outcrops of sandstones in this part of the sequence occur locally south-east and south-west of Blackaburn [NY 8009 7767]; [NY 7711 7680]; [NY 7496 7611]. A fairly complete section is exposed in Rowantree Cleugh [NY 7146 8180] to [NY 7186 8125] (Figure 11), col. 8. Beds seen in the south bank of Chirdon Burn [NY 7071 8026] to [NY 7087 8025] are thought to repeat part of this sequence.

A sandstone considered equivalent to the Spy Rigg Sandstone is well exposed around the forestry village of Stonehaugh. It forms a waterfall over 7 m high [NY 7904 7600] in Middle Burn and provides precipitous sides to Warks Burn [NY 7938 7647] which has cut a gorge 20 m deep through the sandstone north of the village. At Devil's Leap, in the River North Tyne, a sandstone some 27 m thick with a central carbonaceous mudstone band of about 3 m is thought to represent the Spy Rigg Sandstone in this eastern part of the district.

The Wiley Sike and Forster's Hill limestones overlie the Spy Rigg Sandstone in the Bewcastle district and are correlated with limestones in the Bellingham district (Figure 11). However, there is some evidence (Day, 1970, p. 302) to suggest that the Wiley Sike Limestone does not persist to the eastern edge of the Bewcastle district. If this should be confirmed then the Wiley Sike Limestone of the present account would be in fact the Forster's Hill Limestone of Bewcastle. The limestone given the latter name in the Bellingham district, would then correlate with the unnamed sandy limestone between the Forster's Hill and Appletree limestones of the Irthing sections (Figure 11).

Corals and brachiopods, including Semiplanus sp.nov.(of Ramsbottom in Day, 1970), are particularly abundant in exposures of the Wiley Sike Limestone (1 to 2 m seen) in a tributary of Thross Burn [NY 7051 7786] to [NY 7061 7776]. The sandy top 0.5 m of the same limestone crops out in Forth Cleugh [NY 7474 7613] (Figure 11), col. 5 and numerous loose blocks with Semiplanus sp.nov.occur downstream. About 3 m of sandy limestone with mudstone partings, believed to be the same limestone, can be seen in Dodd Sike [NY 7059 7885] and were proved in the nearby Clintburn Moor Borehole [NY 7099 7948] (Figure 11), col. 6.

The Wiley Sike and Forster's Hill limestones are separated by about 4 m of mudstone in the Irthing Valley (Day, 1970, p. 299) but when traced northwards along the western margin of the Bellingham district this interval thickens to about 35 m due to the incoming of sandstones. In Forth and Linshields cleughs [NY 7474 7613] to [NY 7441 7657] there is only one major sandstone (Figure 11), col. 5. However, in the Clintburn Moor Borehole [NY 7099 7948] (Figure 11), col. 6 and in nearby discontinuous exposures in Dodd Sike [NY 7064 7889] to [NY 7116 7738] several sandstones were proved between these limestones. Two sandstones and interbedded mudstones and siltstones, seen in a section in Chirdon Burn [NY 7086 8028] (Figure 11), col. 7b are thought to be just below the Forster's Hill Limestone. This limestone, about 1 m thick and locally rich in ostracods, is seen in Linshields Cleugh [NY 7441 7657]. In the Clintburn Moor Borehole [NY 7099 7948] the limestone, 0.33 m thick, is very sandy, and loose blocks of similar lithology occur in Dodd Sike [NY 7116 7938]. A thin limestone in Chirdon Burn [NY 7088 8028] (Figure 11), col. 7b, reported by the Primary Survey, is believed to be the Forster's Hill Limestone.

A limestone exposed near Grindon Green [NY 7297 7350] and in old quarries [NY 7227 7382] and [NY 7187 7367] to the west of the farm is thought to be close to the Forster's Hill Limestone horizon. It exhibits lithologies ranging from massive crinoidal limestone to coarsely bioclastic, ferruginous and calcareous, cross-bedded 'sandstone'. A limestone only 0.30 m thick at this stratigraphical level is exposed in Warks Burn [NY 7958 7641]; in Stonehaughshields Water Borehole [NY 7978 7629] largely calcareous measures, 6.60 m thick at a depth of 58.91 m are considered to be at a similar horizon.

In the River North Tyne near Lee Hall [NY 8618 7946] and [NY 8685 7991] an impure limestone is exposed, varying between 0.50 and 0.90 m in thickness and consisting of dark grey-blue, massive, ferruginous and sandy limestone, which is considered to be at the Wiley Sike/Forster's Hill horizon. Beds of similar lithology and horizon, 0.74 m thick at a depth of 191.11 m and 0.25 m thick at a depth of 191.57 m separated by 0.20 m of mudstone, were proved in the Ridsdale Borehole.

Strata above the Forster's Hill Limestone are exposed in Linshields Cleugh [NY 7441 7657] to [NY 7439 7687] and Chirdon Burn [NY 7088 8028] to [NY 7132 8036] and proved in the Clintburn Moor Borehole [NY 7099 7948] (Figure 11), cols. 5, 6 and 7b. Beds at much the same horizons and extending up to the Appletree Limestone are seen in Greenlee Cleugh [NY 7217 7588] to [NY 7200 7613] (Figure 11), col. 2; (Figure 10), col H, Warks Burn [NY 7335 7525] to [NY 7281 7514], West Cleugh [NY 7384 7617] to [NY 7363 7611] (Figure 11), col. 5, Chirdon Burn and Crummels Sike near Allery Bank [NY 7450 8122] to [NY 7489 8126] (Figure 11), col. 9 and High Carriteth Burn [NY 7849 8300] to [NY 7855 8304] (Figure 11), col. 10. The beds are laterally variable, though the lower part generally contains at least one major sandstone, while the higher beds are more argillaceous and contain a number of coal seams. The most notable exposures of the lower sandstones are in Chirdon Burn at Cat Linns [NY 7015 8035] and Jerry's Linn [NY 7450 8122]. Coals in the higher beds have been worked, notably in Linshields Cleugh [NY 7446 7667] and Crummels Sike [NY 7486 8128].

Beds below the Appletree Limestone are also exposed in Coal Cleugh [NY 7320 7264] near Grindon Green, in Middle Burn near Stonehaugh [NY 7909 7546] to [NY 7910 7589] and in Warks Burn [NY 7988 7658]. They include a shelly crinoidal limestone up to 2.60 m thick, sandstones and thin coals. In the past these coals have been worked locally near Stonehaugh [NY 7910 7545]; [NY 7990 7642]. Harelaw Crags [NY 7635 7708] and a nearby quarry provide exposures of massive strongly jointed sandstone up to 6 m thick in this part of the sequence. A coal beneath this sandstone was worked from Harelaw Pit [NY 7605 7678] and from numerous old levels in the neighbourhood.

The Appletree Limestone is a ferruginous weathering, sandy, crinoidal limestone or calcareous shelly sandstone which commonly shows trough cross-stratification. It comprises one or more beds not exceeding 4 m in overall thickness. Poor exposures are seen near Grindon Green [NY 7265 7308] and in Middle Burn [NY 7634 7344] and [NY 7910 7541].

It becomes increasingly sandy northwards: in High Carriteth Burn [NY 7855 8304] there are only sporadic shelly lenses in sandstone. The limestone is also exposed at several localities in Greenlee Cleugh [NY 7206 7610]; [NY 7218 7574] and in Warks Burn [NY 7290 7524] to [NY 7278 7514], Peppie Sike [NY 7300 7530] to [NY 7288 7571] and Crummels Sike [NY 7489 8120]. It has been recognised in the Robin Rock Drift, Stonehaughshields and Ridsdale boreholes (Appendix 1), as thin impure limestone bands associated with calcareous and carbonaceous mudstones, some of which are rich in ostracods, plant fragments and shell debris.

The strata between the Appletree and Leahill limestones show considerable lateral variation (Figure 11). Calcareous sandstones and siltstones with some thin limestones are common, but locally there are thick non-calcareous sandstones. One coal seam appears to be fairly persistent and has been worked near Allery Bank [NY 7536 8223]. These beds have been proved in the Wells Cleugh Borehole [NY 7354 7893] (Figure 11), col. 4 and the principal surface exposures are in Greenlee Cleugh [NY 7220 7570] to [NY 7223 7565] (Figure 11), col. 2, High Carriteth Burn [NY 7855 8304] to [NY 7862 8306] (Figure 11), col. 10 and at several localities in Chirdon Burn, between Allery Bank and Bower [NY 7536 8223]; [NY 7542 8249]; [NY 7546 8267] to [NY 7536 8260] (Figure 11), col. 9. Farther south they are exposed in Middle Burn [NY 7910 7537] to [NY 7920 7528], Warks Burn [NY 8385 7688], and in Hindleysteel Quarry [NY 7500 7290] (Plate 2.1) and (Plate 2.2).

The Leahill Limestone fine-grained and argillaceous, is about 3 m thick in the south-west of the district, and thins northeastwards becoming sandier and splitting up into several bands (Figure 12).

Near Hindleysteel Farm, a forestry quarry [NY 7497 7285] exposes 0.30 m of impure ferruginous and dolomitised limestone, rich in corals (including Lithostrotion martini), brachiopods and gastropods. Exposures at Coalcleugh [NY 7300 7290] show limestone with mudstone partings containing a similar fauna to that at Hindleysteel. Some 0.30 m of limestone are exposed in Middle Burn [NY 7922 7526], 3.50 m in Warks Burn [NY 8414 7664] and 1.22 m in Heugh Deans [NY 8696 7992]. Other important exposures are in Greenlee Cleugh [NY 7223 7565], Warks Burn [NY 7240 7517]; [NY 7158 7527], Clintburn [NY 7274 7931] to [NY 7282 7980] and Chirdon Burn between Allery Bank and Bower [NY 7502 8177]; [NY 7509 8175]; [NY 7504 8184]; [NY 7526 8222]; [NY 7540 8249]; [NY 7535 8260]; [NY 7555 8282];[NY 7557 8289] (Figure 12), col. 2. In High Carriteth Burn [NY 7839 8277] to [NY 7849 8300]; [NY 7862 8306]; [NY 7865 8323] (Figure 12), col. 4 the Leahill Limestone consists of calcareous sandstone with sporadic sandy limestone laminae. The limestone has also been proved in Robin Rock Drift, and Stonehaughshields and Ridsdale boreholes.

The measures between the Leahill Limestone and the Bellingham or Carriteth Coal show considerable lateral variation (Figure 12). West of Haining Head these beds seem to be largely sandstone [NY 718 757]; [NY 7164 7528] underlain by 1.5 m of sandy limestone [NY 7191 7537]; [NY 7221 7549]. In Clint Burn [NY 7277 7970] to [NY 7283 7981] and in the Wells Cleugh Borehole [NY 7354 7893] the beds are dominantly shelly calcareous mudstones and argillaceous limestones with local thin coals (Figure 12), col. 1. An ostracodrich mudstone in the borehole, 0.36 m thick and 3.12 m above the Leahill Limestone, may be the equivalent of the Gavelock Ostracod Band of the Bewcastle district. The sections in these beds in Chirdon Burn near Allery Bank and Bower [NY 7509 8174]; [NY 7514 8209]; [NY 7540 8251]; [NY 7532 8262] are in general sandier, and a persistent sandy limestone can be recognised (Figure 12), col. 2 which probably correlates with the similar limestone near Haining Head. In Clint and Chirdon burns these marine beds appear to grade up into the overlying sandstone which commonly is shelly towards the base and locally contains sandy limestone lenses. In High Carriteth Burn [NY 7827 8255] to [NY 7839 8277] (Figure 12), col. 4 and at Cairnglastenhope [NY 7558 8098] this trend continues: sandstones, locally shelly, with limestone lenses, become more abundant and the marine strata become less distinct from the overlying sandstone. The Whitchester Limestone a coarse-grained bioclastic sandy limestone, up to 5 m thick, appears to be an example of a shelly lens within this sandstone. The limestone can be traced from the quarry [NY 7761 8311] to Whitchester Farm [NY 7737 8304]; farther west [NY 7711 8314] only local thin shelly lenses can be found at the same level in the sandstone. Between Haining Head and Bower this sandstone is a persistent marker which together with the overlying seatearth does not exceed 10 m in thickness. It is well exposed at many localities, e.g. Warks Burn [NY 7221 7547] to [NY 7241 7519], Clint Burn [NY 7263 7973] to [NY 7293 7995], Chirdon Burn [NY 7494 8161]; [NY 7524 8224]; [NY 7537 8254] and Coal Cleugh [NY 7635 8212] to [NY 7620 8260]. Farther north, towards the Antonstown Fault, the sandstone thickens considerably (Figure 12). On Roughside Moor [NY 7357 8392] to [NY 7380 8267] and in Eals Cleugh [NY 7485 8346] it is at least 12 m thick and overlain by about 15 m of poorly exposed mudstones, siltstones and sandstones commonly interlaminated with mudstones and with numerous seatearths, the top 3.20 m of which were proved in the nearby Eals Cleugh Borehole [NY 7442 8404]. In the Low Carriteth Borehole [NY 8003 8385] 12.65 m of similar beds with seatearths in the top 2.25 m, were proved on top of the sandstone (Figure 12), col. 5. Assuming a similar thickness in the nearby Hesleyside Colliery Borehole [site uncertain], where these beds were not separated in the log, the underlying sandstone has a thickness hereabouts of about 30 m. Borings at Bellingham and Ridsdale (Figure 12), cols. 8 and 9 prove that this thick sandstone persists eastwards in areas close to the Antonstown Fault.

To the south and east of the district sandstone again dominates this part of the sequence. The Warks Burn has cut a narrow gorge through this sandstone at Ramshaw Mill [NY 845 768].

To the north-east, in the North Tyne valley at Heugh Clints [NY 8704 8003], sandstone forms impressive crags overlooking the river. Massive cross-laminated sandstone, some 9 m thick, is exposed at the top of an old river cliff [NY 8845 8576] in the Rede valley near The Crag.

The overlying Bellingham or Carriteth Coal forms a useful stratigraphical marker because it has been worked in many parts of the district and numerous old adits, bell-pits and spoil heaps attest to its presence. In the area between Bellingham and Low Carriteth a typical section worked at Hesleyside Colliery [NY 8020 8402] was as follows: 48 cm of top coal overlying 71 cm of fireclay on 41 cm of coal. Another dirt parting, 20 cm thick, separates the main seam from 25 cm of coal at the base of the section. The seam deteriorates to the north-east and south-west by splitting and thinning. The 25 cm of coal and dirt exposed in Middle Burn [NY 7933 7520] and 15 cm of coal exposed near Bridge House [NY 8227 7971] are correlated with this seam. At Clintburn the coal is said to have been 30 cm thick, and near Allery Bank 20 cm of coal can be seen [NY 7523 8225]. It is 1.14 m thick in the Eals Cleugh Borehole [NY 7442 8404] and 1.37 m in the Low Carriteth Borehole [NY 8003 8385], and in both boreholes contains numerous mudstone partings. The only other coal of comparable thickness in the North Tyne valley is the Plashetts Coal of the ground north of the Antonstown Fault and it appears probable that the two seams are indeed the same (Figure 7) and (Figure 8). A section quoted by Fowler (1966, p. 89) for the Plashetts Coal worked in Falstone Colliery north-west of the Bellingham district showed the main seam to be 114 cm thick on dirt 10 cm and floor coal 13 cm.

The measures between the Bellingham Coal and the Low Carriteth Limestone range from 9 m of largely calcareous beds in the south-west of the district to 34 m of predominantly arenaceous rocks in the north and north-east. In the Robin Rock Drift Borehole [NY 724 708], the 7.49 m of limestone, locally fossiliferous and interbedded with calcareous mudstone proved at a depth of 39.65 m are considered to reach as far east as the Warks Burn area [NY 850 766], then to be largely replaced by sandstones with mudstones, seatearths and thin coals in the Bellingham and Ridsdale areas (Figure 9).

In the Eals Cleugh [NY 7442 8404] and Low Carriteth [NY 8003 8385] boreholes, the Bellingham Coal is overlain by about 12 m of mudstones with thin limestones and bands and laminae of calcareous sandstone (Figure 12). Ostracods are abundant at some levels in the mudstones and brachiopods have also been observed. In both boreholes a thin limestone rests directly on the coal and higher in the sequence there are two limestones separated by only 1 cm of coal. Mudstones, 5 to 6 m thick, with calcareous sandstone bands, seen in March Burn near Oxcleugh [NY 7936 8136] to [NY 7942 8125] are thought to occur in this part of the sequence. At Allery Bank [NY 7523 8225] and Clintburn [NY 7262 7973] to [NY 7252 7970] the equivalent beds show little evidence of a marine origin, being composed of sandstone, siltstone and mudstone forming sharp-based fining-upwards cycles. In the Eals Cleugh and Low Carriteth boreholes the mudstones with limestones pass up into the lowest of four persistent sandstones (see p. 17) which is seen at crop at several localities, e.g. Howlerhirst Crags [NY 7871 8258] to [NY 7873 8341] and Whetstone Sike [NY 7510 8144]. Arenaceous measures below the Low Carriteth Limestone are also exposed in Houxty Burn [NY 8225 7957], Low Carriteth Burn [NY 8005 8383] and Hesleyside Burn [NY 8160 8342].

The Low Carriteth Limestone is between 1.5 and 2 m thick, slightly ochreous at crop but markedly purer than any of the underlying limestones of the Upper Border Group. It contains sporadic corals including Lithostrotion junceum and L. martini together with gigantoproductoids.

The limestone is partially exposed in Low Carriteth Burn [NY 8007 8377] showing a grey-blue, crinoidal, bioclastic rock with Lithostrotion junceum. Further exposures occur in Coal Cleugh [NY 7896 7409], Gofton Burn [NY 8555 7600], Holywell Burn [NY 8746 7937] and Houxty Burn [NY 8210 7952]. A limestone formerly seen at Green Gears [NY 7776 8383] is thought to be this bed, as are poorly exposed limestones cropping out in Coal Cleugh [NY 7623 8280] and Whetstone Sike [NY 7533 8125] and [NY 7549 8118].

Accepting the equivalence of the Bellingham and Plashetts coals, then a correlation of the Low Carriteth Limestone with the Plashetts Dun Limestone logically follows as both lie some 20 to 24 m above the coals (Figure 8). Fowler (1966, p. 89) describes the Plashetts Dun as a greyish, ochreous limestone between 1.5 and 1.8 m thick with crinoids and corals. In Black Burn [NY 775 908], Robinson (in Westoll and others, 1955, p. 3) recorded Dibunophyllum sp.and a crushed specimen of Palaeosmilia cf. murchisoni from the Plashetts Dun Limestone and further collecting during the present resurvey has yielded Dibunophyllum bourtonense and Lithostrotion sp.? portlocki group.

The measures between the Low Carriteth Limestone and the Birtley Limestone are from 10 to 25 m thick (Figure 9), (Figure 10), (Figure 11) and (Figure 12). In the south and west of the district most of the sequence is mudstone, but when traced north-eastwards a more typically Yoredale cyclothem is approached, with fossiliferous mudstones at the base passing up into sandstone locally topped by a coal. The fossiliferous mudstones are exposed in Coal Cleugh [NY 7896 7406], Low Carriteth Burn [NY 8008 8373] and Hesleyside Burn [NY 8154 8332] and were proved in Eals Cleugh and Ridsdale boreholes.

The mudstones pass upwards into sandstones near the top of the cycle; these are well exposed in Coal Cleugh [NY 790 740], on Carriteth Moor at Bell Crags [NY 792 820], Watch Crags [NY 786 821], South Mesling Crags [NY 789 825], Mesling Crags [NY 792 826] and Shitlington Crags [NY 830 809]. The overlying coal and mudstone have been proved in the Wells Cleugh [NY 7354 7893] and Eals Cleugh [NY 7442 8404] boreholes and in Low Carriteth Burn [NY 8006 8338]. Steeply dipping argillaceous limestones and mudstones close to the Whitchester Moor Fault in March Burn [NY 7945 8124], are thought to belong to this part of the sequence. A 2 cm coal is exposed [NY 7898 7392] in Coal Cleugh at the top of the sequence.

The Birtley Limestone is impersistent and of variable lithology, composed of up to two distinct argillaceous limestone beds separated by some 3 m of measures. The maximum thickness of an individual bed of limestone is 1.22 m in the Bellingham Borehole. The Birtley Limestone is defined in Holywell Burn [NY 8750 7934] where 0.30 m of impure limestone are exposed.

The measures between the Birtley Limestone and the Furnace Coal are up to 30 m thick, chiefly sandstones with subordinate mudstones and thin coals including the Wark Seam (see Appendix 2, 87 NE 3 and 4) and rarely limestones. They are sporadically exposed in Coal Cleugh [NY 7897 7391] to [NY 7867 7360], Warks Burn [NY 8565 7650] and Gofton Burn [NY 8579 7607] and are recognised in the Bellingham and Ridsdale boreholes and the Seventy-Fathom Pit at Ridsdale (Figure 12). Sandstones are well exposed in Low Carriteth Burn [NY 8011 8300], Whitchester Crags [NY 7685 8250] and Pundershaw Burn [NY 7840 7985].

The Furnace Coal, up to 63 cm thick, has been sporadically worked in the Ridsdale and Bellingham areas where, as its name implies, the coal was used in the coke ovens and blast furnaces associated with the old ironstone industry (p. 87). In places the coal is split into several thin seams interbedded with mudstones, thin limestones, seatearths and Banister-like sandstones. The Furnace Coal is considered to be a split off the much thicker and more economically important Thirlwall Coal of the Brampton and Gilsland areas (Figure 9); (Day, 1970, p. 130).

In the south-west of the Bellingham district the Thirlwall Coal was worked at Wallshield Colliery [NY 7148 7018] and from the nearby Rushey Hill Shaft [NY 7177 7030] where the seam was 86 and 101 cm thick respectively. It was mined on a larger scale from Ventners Hall Colliery [NY 7242 7066] until 1959, and a new drift has recently been opened some 600 m to the east at the New Robin Rock Mine [NY 7298 7089]. The seam in this area dips south at about 10°, is about 1 m thick and commonly has a mudstone or seatearth roof. It was proved to be 94 cm thick in High Tipalt Borehole. The outcrop of the coal can be traced intermittently eastwards by means of old shafts and workings. A 12 cm coal in Gofton Burn [NY 8582 7608] and old workings noted on Buteland Fell [NY 8915 8215] are considered to be at the Thirlwall horizon.

The Furnace Coal was proved to be 40 cm thick in Seventy-Fathoms Pit, Ridsdale and 20 cm of coal considered to be the Furnace seam is exposed in a small stream [NY 8992 8614] near Woodburn Station. This seam, 40 cm thick, was formerly seen and locally worked in Shaw Cleugh Kiln Pit [NY 9118 8639]. In the Ferneyrigg Borehole the Furnace Coal is 50 cm thick.

A coal once worked over a large area at shallow depths near Brieredge [NY 8080 8310] and reported to vary in thickness between 50 and 63 cm is also correlated with the Furnace Coal. This seam is associated in places with shelly mudstones and thin limestones, as for instance at Wells Cleugh Borehole [NY 7354 7893], Green Moor [NY 7418 7837] and [NY 7467 7803], March Burn [NY 7978 8095] and the Upper Hall Pit [NY 8430 8366] Bellingham.

The Furnace and Upper Hall coals are some 7 to 12 m apart separated by variable measures which commonly include thin impure limestones, fossiliferous mudstones and thin sandstones.

Two limestones exposed in Hareshaw Burn [NY 8418 8366] are 30 and 40 cm thick and separated by 20 cm of mudstone. The upper 30 cm limestone is rich in bryozoans and brachiopods including: Fenestella spp., Buxtonia sp., Pleuropugnoides pleurodon and Punctospirifer redesdalensis. A limestone 85 cm thick at this horizon is also exposed in Hesleyside Burn [NY 8125 8302].

The Upper Hall Coal was first found in the Upper Hall Pit [NY 8430 8366] sunk in 1846 by the Hareshaw Iron Works Company of Bellingham where the seam proved to be 38 cm thick (Figure 12). It is 30 cm in the Seventy-Fathoms Pit, Ridsdale, but only 15 cm in the Ferneyrigg and Ridsdale boreholes. It is not exposed in the north-eastern part of the district although many old workings indicate the proximity of outcrop, e.g. near Broomhope [NY 8800 8397].

A water borehole at Linacres Farm [NY 8142 7849] proved two coals 30 and 38 cm thick separated by 1.83 m of sandstone. These coals are considered to be near correlatives of the Upper Hall Coal, as is a 30 cm coal in a small exposure near Coal Cleugh [NY 7957 7389].

The measures between the Upper Hall Coal and the Redesdale Ironstone Shale are largely arenaceous and average some 27 m in thickness. Boreholes such as Ridsdale and Ferneyrigg show the sandstones to contain thin coals associated with seatearths (Figure 12). Bell Crags [NY 7725 7292] and Little Bell Crags [NY 7775 7292] provide excellent exposures in these measures showing massive, cross-bedded, fine-grained pale grey to brown sandstones which form pronounced features in the forested area south-west of Stonehaugh. Little Bell Crags, which have been quarried by the Forestry Commission for roadstone, are directly underlain by a thin impure limestone. Sandstone caps much of the high ground on Whitchester, Cairnglastenhope and Green Moors, forming numerous crags and is also seen in a number of Forestry Commission quarries, e.g. [NY 7275 7755]; [NY 7335 7776]; [NY 7440 7965]; [NY 7538 8035]; [NY 7810 8158]; [NY 7723 8213]; [NY 7700 8275].

In the Bellingham area these measures contain two named and locally worked ironstones-the upper Isabella Band (3 cm) and the lower Thomas Band (16 cm). A nearly continuous section of these measures is provided by exposures in Hareshaw Burn [NY 8419 8370] to [NY 8430 8403].

In the north-east of the district, a sandstone beneath the Redesdale Ironstone Shale forms a continuous feature stretching from Birtley to near Ridsdale including exposures of some 10 m of massive cross-bedded fine-grained sandstone at Millknock Quarry [NY 8800 7940] and at Lowshieldgreen Crags [NY 8980 8100]. This sandstone is also exposed on Buteland Fell at Allery Crags [NY 8862 8200] and at Calf Close Crags [NY 8800 8420] near Broomhope.

The Redesdale Ironstone Shale is well known in the geological literature for its profusion of well-preserved fossils, particularly bryozoans, brachiopods, bivalves and crinoids (Lebour, 1873; Smith, 1910; Delepine, 1940; Hemingway, 1972). It is now poorly exposed, the two best localities being near The Steel [NY 8948 8340],

Ridsdale (on private ground) and in Hareshaw Burn [NY 8425 8445] to [NY 8420 8460] near Bellingham. The 'shales' are some 9 m thick, with subsidiary concretionary siderite nodules forming up to 10 per cent of the total sequence. These, varying in size up to 35 cm, occur as scattered discontinuous concretions, locally coalescing to form irregular bands. They are commonly associated with pyrite which together with calcite forms cavity infills.

The shales' are very fossiliferous, the fossils being concentrated into layers sometimes preserved in ironstone. The most distinctive horizon is the 'Shell Band', which occurs near the middle of the 'shales'. It was recognised by the miners and used by them to subdivide the beds into upper and lower 'plate' or 'shale'. The Shell Band is up to 25 cm thick and commonly forms a shelly limestone poor in siderite and so rejected as valueless by the miners. It now remains in large piles such as those in Sir William Armstrong's quarries near The Steel [NY 8955 8303] or scattered throughout the innumerable waste tips around Ridsdale and Bellingham [NY 886 842] and [NY 843 841].

Delepine (1940) described Beyrichoceratoides redesdalense (Hind) from the Redesdale Ironstone Shale at Ridsdale, and Wilson (1952) correlated this horizon, by virtue of a similar faunal association including goniatites, with the Cove Marine Band of southern Scotland. Trotter and Hollingworth (1932) emphasised the lithological similarities between the Redesdale Ironstone Shale and the Naworth Bryozoa Band. Although an important faunal horizon, field evidence shows that the Redesdale Ironstone Shale supports large nodules and a rich fauna only in a very limited area around Ridsdale and Bellingham. It is a facies fauna which, given a suitably muddy environment, could have existed at many levels in this part of the sequence. A locality near Woodpark [NY 8471 8015] also exposes fossiliferous mudstones with ironstone nodules which lie stratigraphically below the Woodpark Limestone. This limestone was considered to lie some 366 m below the Redesdale Limestone by Fowler (1966, p. 103), but Mr Pattison reports (p. 48) that the fauna is more typical of the highest beds of the Upper Border Group and the overlying Lower Liddesdale Group. These mudstones have been correlated therefore with the Redesdale Ironstone Shale.

The measures between the Redesdale Ironstone Shale and the Redesdale Limestone are up to 10 m thick and composed largely of sandstone. This sandstone, which is separated from the Redesdale Limestone by only a few centimetres of carbonaceous and micaceous shale, commonly shows slump structures and has been extensively burrowed. It forms a discontinuous feature in the south-west of the district and is exposed at Todd Crags [NY 7670 7184] near Greenlee. In the north-east it is exposed in Hareshaw Burn [NY 8420 8460] and at several localities near Ridsdale [NY 8885 8421], [NY 8948 8342] and [NY 8067 8395].

North of the Antonstown Fault

Because of the great lateral variation shown by the beds north of the Antonstown Fault and the lack of reliable marker beds, it is not possible to give a single general description. Local successions can be built up within fault-blocks but correlation between these is only tentative (Figure 13) and relies considerably on the known or assumed position of the Plashetts Coal.

Yarrow Moor In the area north of the Elf Kirk Fault and to the west of the Smalesburn and Falstone faults, a succession has been built up largely from boreholes sited just beyond the northern margin of the district for the Kielder Dam, and supplemented by local outcrop data (Figure 13), col. 5. The main marker bed in this succession is the Shilburnhaugh Coal which has been worked extensively hereabouts (Fowler, 1966; Land in Day, 1970, pp. 151–152). However, other seams have also been worked. A 61 cm thick coal, formerly thought to be the Shilburnhaugh, was worked near Shilling Pot [NY 7150 8713] and proved in a nearby borehole [NY 7146 8725]. This may well be the same as the 40 cm thick coal, 12 to 15 m above the Shilburnhaugh Coal seen in an adit mouth [NY 7925 8676] near Hollin Crags. Overlying sandstones can be seen in Hollin Crags [NY 704 867] and nearby scarps. Two thin limestones are exposed in a neighbouring stream [NY 7963 8640]; [NY 7061 8634].

The Yarrow Moor sequence cannot be related directly to any widely recognised market bed. On the limited evidence available, the Shilburnhaugh Coal may be correlated with the Thorneyburn and Bearsmouth coals, and is thus of the order of 135 m below the Plashetts Coal. New data from the Kielder Dam boreholes (south-west corner of the Elsdon district) show that the structure is more complicated than previously thought (Land in Day, 1970, fig. 27) and that the stratigraphical relations between the named horizons are less certain.

Bluesteel Sike The narrow strip of country between the Elf Kirk and Merlin faults is heavily drift covered and a few discontinuous exposures are to be seen in Bluesteel Sike, upstream of [NY 713 853]. The stratigraphical position of these beds is unknown; if the direction of downthrow of the faults has been correctly determined then they are likely to be high in the Upper Border Group, probably above the Plashetts Coal.

Broomley Burn The ground between the Merlin and Whickhope Linn faults is also largely covered in drift. Part of the sequence was proved in the Broomley Burn Borehole [NY 7952 8496] (Figure 13), col. 2 supplemented by exposures on the south side of Broomley Burn. A coal seam formerly worked here [NY 702 849] was thought by the Primary Survey to be the Plashetts Coal and said to be 1.7 m thick, but the resurvey shows that it is probably the thinner coal 14 m above the Plashetts. Exposures [NY 7016 8489] and [NY 7046 8490] show thicknesses of 25 and 80 cm respectively.

Smales Burn and Smalesmouth Moor In the area bounded on the south by the Kyloe Fault, on the north-west by the Smalesburn Fault and on the north-east by the Falstone Fault, exposures in Smales Burn and on Smalesmouth Moor can be fitted together to build up a local succession (Figure 13), col. 3. However, only in limited parts of this succession are there any available details from the measures between the sandstones, and the stratigraphical thickness between component sections is commonly unknown due to faulting and can only be estimated.

The oldest part of the succession, an alternation of sandstones and siltstones and mudstones with thin coals (Figure 13), col. 3a; (Figure 10), col. E is known from discontinuous exposures near Archy's Linn [NY 7158 8341] to [NY 7099 8304], in part repeated downstream by faulting [NY 7160 8342] to [NY 7170 8348]. These beds are faulted against overlying strata comprising a 2.5-m thick limestone associated with mudstone (Figure 13), col. 3b depicted as directly overlying the Archy's Linn sequence or at even higher levels. The limestone is a fine-grained biomicrite in four posts separated by thin mudstone partings [NY 7169 8354]; [NY 7174 8351]; [NY 7182 8356]; [NY 7186 8363]. Locally the top part is coarse-grained and sandy. The strata overlying this sandstone are very poorly exposed in Cross Cleugh [NY 7181 8356] to [NY 7190 8337].

Farther downstream, across the northernmost branch of the Whickhope Linn Fault, another incomplete sequence of beds can be deduced from outcrops in the stream [NY 7203 8497] to [NY 7190 8372] and from the overlying sandstone crags on Smalesmouth Moor [NY 724 845] (Figure 13), col. 3c. As the fault downthrows northwards this sequence is thought to overlie those mentioned above (Figure 13), col. 3b. The middle part of the succession is the most completely exposed [NY 7189 8373] to [NY 7193 8400], only the sandstones in the overlying and underlying beds being seen as a general rule. A number of thin coal seams, up to 30 cm thick were formerly visible and some of these have been locally worked.

Near Smalesmouth, more than 100 m of beds occur in the burn [NY 7302 8600] to [NY 7256 8541], but exposure is discontinuous and dips variable and relatively steep (up to 25°), so that no complete or reliable stratigraphical section can be constructed. Most of the crops are of sandstone, one of which, up to 6 m thick, is particularly well exposed [NY 7289 8576]; [NY 7287 8562]. A number of thin limestones can be seen and some thin coals were formerly worked. Particularly extensive workings to a coal about 50 cm thick [NY 7296 8569] can be seen near Smalesmouth Farm. From the limited data available these poorly exposed beds do not repeat any of the sequences seen farther upstream. They appear to underlie the sandstone crops of Smalesmouth Moor and it seems likely that they occur stratigraphically between the sections shown in columns 3b and 3c of (Figure 13).

The relative stratigraphical position of all the beds exposed in the Smalesburn area is uncertain. (Figure 13) has been constructed assuming that the main crag-forming sandstones of Smalesmouth Moor are the same as those of other areas.

King Horn The only exposures in the ground between the Kyloe and Antonstown faults are in the three low sandstone features of King Horn [NY 716 826]. The stratigraphical position of these sandstones is not known but they are likely to be older than any rocks seen in Smalesburn.

Donkleywood The country between the Kingsley Crag and Rough Cleugh faults is largely covered by drift and the exposures are too scattered for any composite section to be constructed. A sandstone, about 15 m thick, forms a dip slope and prominent scarps to the north-west of Donkleywood. It is seen in a number of quarries [NY 7406 8677]; [NY 7421 8663] and in Eckies Cleugh [NY 7415 8645] where 4 m of the underlying mudstones, siltstones and silty sandstones are also exposed. Overlying the arenaceous measures are some sandstones dipping at about 35° in Rough Cleugh [NY 7496 8664] to [NY 7504 8658] and mudstones with thin coals and limestones seen in Ryeclose Burn [NY 7533 8675] to [NY 7541 8703]. Mapping to the north in the Elsdon district suggests that the beds near Donkleywood are less than 100 m below the Plashetts Coal.

Thorneyburn and Stokoe Crags Much of the area bounded by the Rough Cleugh, Falstone, Antonstown and Boughthill faults is underlain by 30 to 40 m of massive fine- to medium-grained sandstones, separated by siltstones and mudstones (Figure 13), col. 6. These sandstones form the prominent Stokoe Crags [NY 751 854] and Stokoe High Crags [NY 751848] and are also well exposed near Greystead [NY 7651 8531] to [NY 7702 8543], Low Thorneyburn [NY 7652 8670] and Rushen [NY 782 865].

A sequence of beds, 165 m thick, beneath these sandstones, has been established in Thorney Burn [NY 7620 8727] to [NY 7646 8657] (Figure 13), col. 6, where the strata are commonly steeply dipping (locally vertical) and repeated by sub-isoclinal folds. For the most part these comprise sandstones, mainly 3 to 4 m thick, separated by siltstones and mudstones with thin limestones and coals (see also (Figure 10), cols. A and F). A sandstone 20 m thick forms a spectacular gorge and waterfall near Hill House [NY 7614 8702] and may be the massive sandstone seen at Crag House [NY 7583 8660]. The Thorneyburn Coal (Figure 13), col. 6, more than a metre of carbonaceous mudstone with coal seams, was once worked extensively hereabouts and is exposed in the stream [NY 7638 8675]; [NY 7631 8668] and nearby in Rough Cleugh [NY 7591 8630]. The coal, 46 to 53 cm thick, formerly worked below Stokoe High Crags [NY 748 844] may be the same seam. The Thorneyburn Limestone [NY 7638 8658] to [NY 7642 8677] (Figure 13), col. 6, 70 cm thick, is fine-grained and bioclastic; it weathers rusty-brown and is in one post. It is underlain by calcareous sandstones and siltstones and thin sandy and silty limestones. The limestone and underlying beds are reminiscent of the Leahill Limestone and associated strata seen around Allery Bank (p. 14). Another limestone, a few metres above, crops out in Thorney Burn [NY 7645 8652]. On the other side of the River North Tyne, a prominent post of limestone, 65 cm thick, in a roadside waterfall [NY 7563 8583] under the lowest sandstone of Stokoe Crags, may be the same limestone or possibly the Thorneyburn Limestone. Steeply dipping beds, adjacent to the Rough Cleugh Fault, in Rough Cleugh [NY 7508 8656] probably repeat part of the Thorneyburn succession.

Beds above the massive sandstones of Stokoe Crags were proved in a water borehole at Greystead Rectory [NY 77118586] and include a limestone said to be 2.13 m thick (Figure 13), col. 6. Mapping in the adjacent parts of the Elsdon district suggest that the beds around Thorneyburn and Stokoe Crags are below the Plashetts Coal. The highest beds in the Greystead Rectory Borehole are probably 50 to 60 m below this coal.

Lanehead East of the Boughthill Fault, the strata underlying the Plashetts Dun Limestone are exposed in Lancy's Cleugh, largely beyond the northern margin of the district (Figure 13), col. 7. The limestone, 1.55 m thick and ochrous, is particularly well exposed [NY 7997 8737] but the Plashetts Coal is much obscured in a steep bank [NY 7982 8732], and only 32 cm of coal were seen. The seam may well be thicker here, however; it was formerly worked from numerous bell-pits near Birchhope where the crop of the coal enters the Bellingham district [NY 808 870]. Another coal, 28 cm thick, occurs about 15 m lower in the sequence [NY 7967 8720]. Below this coal, mudstones and thin limestones occur down to the bridge at Greenhaugh [NY 7960 8719]. Downstream of the bridge the section to [NY 7940 8691] is less complete but three major sandstones can be seen here and in the hillside to the south [NY 7955 8683]; [NY 7947 8664]. The lowest of these sandstones and underlying strata were proved in the nearby Lanehead Borehole [NY 7954 8614] (Figure 13), col. 7. Part of the borehole sequence is repeated in exposures of sandstones, siltstones and mudstones in Tarset Burn [NY 7872 8627] to [NY 7880 8634] (Figure 10), col. D. Three coal seams, one up to 30 cm thick, are seen here also, though none was recorded in the borehole. The Bearsmouth Coal, said to be 60 cm thick, has been worked extensively from bell-pits near Lanehead [NY 7905 8551] to [NY 7999 8578] (Figure 13), col. 8.

Hareshaw Common and Callerhues Crags Some 300 m of measures beneath the Plashetts Coal crop out in the moorland area north of Charlton. They are sporadically exposed in Charlton and Linthole burns (Figure 13), col. 8 and sandstones form numerous scarps and crags such as Long Crags and High Crag. Farther east, strata above the Plashetts Coal are poorly exposed, but some of the youngest beds form Callerhues Crags and are calculated to lie some 50 m below the Redesdale Limestone.

Some of the oldest strata north of the Antonstown Fault are exposed in Linthole Burn [NY 8141 8494]. They comprise some 20 m of dark grey mudstones containing ostracods and fish, together with thin gastropod-rich limestones and calcareous siltstones up to 0.70 m. Thin flaggy sandstones also occur. These beds are probably equivalent in age to the Jock's Pool Limestone of the Bewcastle district (Figure 13), col. 8. They are overlain by massive sandstones up to 6 m thick, the highest of which forms a waterfall and feature in Closehill Wood [NY 8138 8519].

The remaining part of the sequence in the Hareshaw Common area is dominated by thick and laterally persistent sandstones which are represented at outcrop by numerous scarps and crags. The lowest sandstone splits up into three leaves which are well exposed at Long Crags [NY 8150 8565]. The Bearsmouth Coal overlies the sandstones of Long Crags and was worked from an adit [NY 8975 8610] near Fieldhead where the section previously recorded was an upper coal 25 cm, overlying 'band' 3 to 46 cm, on coal 10 cm, on 'band' 20 cm, on coal 46 to 51 cm. Old shafts and pits enable the crop of the coal to be traced for a further 2 km to the south-east before it is terminated by the Antonstown Fault.

The coal is overlain by mudstones associated with three thin impure limestones exposed in Charlton Burn [NY 8072 8620] and also proved in a nearby borehole (Hareshaw No. 1042) drilled in 1846. These measures are overlain in turn by the next thick sandstone sequence which forms features at Shiel Crags [NY 8074 8639] and Rough Crags [NY 8169 8596]. This sandstone is considered to underlie much of the boulder clay covered area [NY 833 857] between Linden Hill and The Shanks and is not exposed again until Hareshaw Burn where it forms cliffs 30 m high and the waterfall of Hareshaw Linn [NY 8418 8541]. The sandstone forming the waterfall is flaggy with the basal bed rich in coal fragments and the topmost beds commonly calcareous, ferruginous and well cemented.

The highest persistent sandstone in the Hareshaw Common area is well exposed in High Crag [NY 8132 8636] which is formed by some 10 m of fine-grained sandstone with a ferruginous and calcareous cement, the topmost 2 m being particularly well cemented. The sandstone thins westwards but to the east splits into several leaves and is thought to be represented by sandstone features [NY 8455 8510] between School Crag and Blakelaw. In this area, old trial holes and a disused level for coal indicate the lateral persistence of a thin seam for over one kilometre. This coal is calculated to lie some 20 m below the horizon of the Plashetts Coal which is estimated to crop out beneath School Crag [NY 8470 8570].

The sandstone of Little Callerhues Crag [NY 8500 8585] closely overlies that of School Crag (Figure 13), col. 8 but the highest beds crop out at Callerhues Crags which are a landmark on the high moorland between Bellingham and West Woodburn. Comprising massive pinkish grey weathering sandstone they give rise to a prominent scarp over 1 km in length, up to 20 m high at an altitude of over 300 m.

Chapter 4 Liddesdale Group

General account

The Liddesdale Group was defined in the Langholm and Bewcastle districts (Lumsden and others, 1967; Day, 1970) as extending from the base of the Naworth Bryozoa Band to the base of the Catsbit (=Great) Limestone (Figure 4). As previously explained (p. 3), in the Bellingham district the base of the group has been drawn some 10 m lower, at the base of the Redesdale Limestone. The Liddesdale Group is therefore equivalent to the combined Lower and Middle Limestone groups of some earlier classifications. The base of the Low Tipalt Limestone, or Lower Bankhouses and Lower Crook Burn limestones of Johnson (1959), Middle Camphill Limestone of White (1954) and Frost (1969), conveniently divides the group into lower and upper divisions, the base of the upper division marking the incoming of Brigantian or Upper Dibunophyllum Zone (D₂) fossils.

Rocks of the group crop out in a broad south-west to north-east arcuate belt across the middle of the district, but the complete succession has not been proved at any one locality. (Figure 14) and (Figure 15) show generalised successions for the lower and upper divisions and indicate their likely correlation with sequences to north and south. (Figure 16) and (Figure 17) (Lower Liddesdale Group) and (Figure 18), (Figure 19) and (Figure 20) (Upper Liddesdale Group) show graphically the sequence compiled from boreholes and exposed sections. The lower group is not as well exposed as the upper, and contains fewer thick mappable limestones.

The Lower Liddesdale Group is 260 m thick in the south and west, increasing to 300 m in the north-east. This thickening is limited to the upper part of the sequence, above the Gunnerton Fell Limestone, and largely results from the presence of thick lenticular sandstones. These thicknesses compare with 274 m in the Archerbeck Borehole near Langholm (Lumsden and Wilson, 1961) and slightly under 200 m in the Harton Borehole (Ridd and others, 1970) on the north Durham coast.

The Upper Liddesdale Group is 375 to 400 m thick through most of the district, but in the extreme south, around Settlingstones and Fourstones, there is a rapid southerly thickening of the beds to around 550 m. As described in more detail below (Figure 18), (Figure 19) and (Figure 20), this is not a uniform thickening but is more marked at certain horizons. Some parts of the sequence thicken towards the north. Apart from this belt of thicker strata in the south of the district, the Upper Liddesdale Group is not greatly thicker than the equivalent beds on the Alston Block (Figure 15). Thus the area of greatest relative subsidence was in an east-west-trending belt restricted to the extreme southern margin of the Northumberland Trough (Holliday and others, 1975, pp. 326–327).

Classification and previous research

The base of the Liddesdale (Lower Limestone) Group (Figure 4) was previously taken at the lowest limestone with Lower Dibunophyllum Zone (D₁) fossils that was adequately exposed and traceable by features in any particular area, e.g. the Naworth (south-west Northumberland), Redesdale (mid-Northumberland) and Dun (north-east Northumberland) limestones. It was widely believed that these horizons were equivalent (Miller, 1887; Smith, 1910; Trotter and Hollingworth, 1932) because of faunal and lithological similarities. Robinson (in Westoll and others, 1955) discovered D, faunas below the Redesdale Limestone of north Tynedale in the Piper's Cross and Plashetts Dun limestones, and so Fowler (1966) and Day (1970) concluded that the Naworth and Redesdale limestones were not equivalent. Frost (1969) supported the correlation of the Naworth Limestone with a horizon close to that of the Redesdale or Fourlaws limestone, on the grounds that it was possible to map one bed close to the outcrop of the other. Ramsbottom (in discussion of Frost, 1969) objected to the correlation on the grounds that the Redesdale Limestone was not the lowest horizon with D_I fossils in mid-Northumberland.

The resurvey has indicated that the Piper's Cross, Belling and Wood Park limestones, occurring in faulted outcrops in the North Tyne area, are all equivalent to the Redesdale Limestone. The Plashetts Dun Limestone, some 140 m below the Piper's Cross in Black Burn (Fowler, 1966, p. 91), is probably the equivalent of the Low Carriteth Limestone, 113 m below the Redesdale Limestone in the North Tyne area (Figure 7). Both the Plashetts Dun and the Low Carriteth Limestone are the lowest beds in mid-Northumberland in which Lithostrotion junceum has been recorded.

The resurvey has also re-established that the Redesdale and Naworth limestones, if not precise equivalents, are stratigraphically fairly close. Their exact equivalence, originally suggested by Miller (1887) and endorsed by Trotter and Hollingworth (1932) had much lithological evidence in its favour. The Greenlee Borehole [NY 7727 7149] shows how similar the sequences below the two limestones are, the richly fossiliferous mudstones associated with ironstones underlying the Naworth Limestone being comparable with the Redesdale Ironstone Shales. However, as noted by Miller, the overlying Fourlaws Limestone has then to be equated with a thin unfossiliferous limestone which he denoted by the letter 'n'. The most satisfactory correlation is therefore between the Naworth Limestone, of the Brampton district with the Fourlaws Limestone of the North Tyne area (Figure 16).

The palaeontological basis for the previous classifications also has been called into question, the base of D₁ (Asbian Stage) now being taken at the base of the Upper Border Group on micropalaeontological evidence (George and others, 1976).

Apart from small adjustments (Trotter and Hollingworth, 1932; Johnson, 1959; Holliday and others, 1975), the correlation of the Upper Liddesdale Group has been established for many years in terms of some of the bed names originally used on the Alston Block by Forster (1809) (Figure 14) and (Figure 15). The Upper Liddesdale Group corresponds exactly with the D₂ Zone (Johnson, 1959; Day, 1970; Burgess and Mitchell, 1976) or the Brigantian stage of George and others (1976). Rocks of this age in the south of the district were described by Johnson (1959), the present survey differing only in matters of detail. In particular it seems the west to east lithological changes and splitting of limestones are less common than had been thought by Johnson. Details of the beds above the Three-Yard Limestone were published by Lebour (1875a, b). Descriptions of the Upper Liddesdale Group in the eastern part of the district have not hitherto been published, though these strata formed the subject of an unpublished thesis by White (1954). Again, the present survey differs for the most part only in detail. For details of the Group in adjacent areas see Day (1970), Fowler (1936, 1966), Frost (1969), Johnson (1959), Miller (1887), Smith (1912) and Trotter and Hollingworth (1932).

Lithology

Individual limestones of the Liddesdale Group rarely exceed 6 m in thickness. On analysis they give CaO over 50 per cent, MgO normally below 1 per cent, CO₂ plus FeO 46 per cent, and insoluble residues averaging about 3 per cent (Frost, 1969, p.283). They are fine-grained to coarse-grained biomicrites and biosparites containing crinoidal, shell, bryozoan and algal debris.

Microfossils are fairly common, including ostracods and foraminifera. The Lower Demesne Limestone is locally pseudobrecciated, and others have undergone partial recrystallisation and dolomitisation. Both the Redhouse Burn and Three-Yard limestones have been affected by iron contamination of their calcite. The source of iron contamination is probably integral to the primary composition; each limestone contains at least accessory proportions of iron oxide and sulphide and in some cases microcrystalline pyrite is conspicuously abundant. Similarly the requisite magnesium for the comparatively minor amounts of secondary dolomite-ankerite could have been derived from selectively concentrated metastable magnesian calcite present in certain fossil skeletons, notably those of some algae. The Four Fathom Limestone is locally silicified. Chert nodules are a distinctive feature of the Bankhouses Limestone. Mudstone partings characterise some beds such as the Redesdale, Bankhouses, Oxford and Three Yard limestones.

Local variations of thickness and lithology occur in the limestones of the Lower Liddesdale Group but conditions were apparently remarkably uniform in the Upper Liddesdale Group, each marine transgression spreading over the whole of the district accompanied by its associated and commonly distinctive faunal assemblage. The limestones are thickest in the south-west, and, particularly in the Lower Liddesdale Group, thin to the north-east of the district where they may be represented in places by shelly sandstones. The Melmerby Scar Limestone of the Alston Block is the lateral equivalent of a group of limestones in the Lower Limestone Group with intercalations of clastic sediments (Figure 14).

The terrigenous clastic sediments of the group commonly form coarsening-upwards cycles, more than 15 m thick, from mudstone to sandstone which, together with the underlying limestones, are known as Yoredale cyclothems (Dunham, 1948, 1950; Moore, 1958; Johnson, 1959). These cycles are characteristic of the Liddesdale Group in general and the Upper Liddesdale Group in particular. The mudstones immediately overlying the limestones are generally calcareous and shelly, but upwards they become silty and less calcareous, with ironstone nodules and finely comminuted plant debris. This upward change in lithology is reflected in an upward change in both macro- and microfauna (Chapter 6). The mudstones pass up, by inter-lamination and interbanding of siltstone and sandstone, into coarsening-upwards sandstones which are fine-grained and silty at base, with numerous mudstone and silt-stone laminae. At crop they are flaggy, either planar-bedded or with small scale cross-stratification. Higher in the cycle the beds are less silty and more massive, better sorted, and locally medium-grained, with large scale trough cross-stratification.

By contrast, some sandstones grade upwards from coarse to fine grain, have sharp erosive bases, and cut out considerable thicknesses of older beds 'in washouts'. These sandstones are locally feldspathic, contain large tree trunks and pebbles derived from the eroded underlying strata and are commonly trough cross-stratified. Sandstones of this kind are especially abundant in the north-east of the district in the upper part of the Lower Liddesdale Group and the lower part of the Upper Liddesdale Group. The large scale cross-bedded units, which generally indicate sediment transport from the north, locally show signs of penecontemporaneous deformation. The sandstones contain small heavy mineral suites with zircon, tourmaline, rutile and garnet particularly common (Frost, 1969; Hemingway and Tamar-Agha, 1975). In the Lower Liddesdale Group, sandstones form an increasing proportion of each cyclothem when traced from the south-west to the northeast of the district, but there is no such trend in the Upper Liddesdale Group.

The top of many cyclothems is marked by a thin coal or carbonaceous mudstone resting on a seatearth or ganister. The coals (Smith, 1912) have been worked locally and spasmodically from small drifts or bell-pits, but only the Fourlaws Coal is sufficiently thick to have warranted extraction on a large scale and over a longer period of time. Overlying the Yoredale cyclothems and preceding the next major limestone there are commonly a number of relatively thin coarsening- and fining-upwards cycles (minor cycles) locally with marine beds and coals (Johnson, 1959), e.g. (Figure 20), col. 4.

The coarsening-upwards Yoredale cyclothems indicate repeated marine transgressions into the area, followed by delta progradation during the periods of regression. The erosive-based fining-upwards sandstones are thought to be the infillings of delta distributary channels (Moore, 1958; Leeder, 1974; Elliott, 1975). Where persistent coal seams and/or thin marine bands cap the cycles it would seem that the delta was temporarily abandoned and the overlying minor cycles indicate various styles of post-abandonment sedimentation prior to the next major marine transgression (Elliott, 1974, 1975).

Details

Lower Liddesdale Group

Measures from the Redesdale Limestone to the base of the Fourlaws Limestone are some 50 m thick, containing several minor cycles with thin coals, for example, the Chapelburn Coal, and thin limestones such as the Naworth Bryozoa Band (Figure 16).

The Redesdale Limestone is usually well exposed but it is difficult to trace in the south-west of the district for about 6 km between Greenlee and Tipalt burns. From 7.77 m thick at Ferneyrigg Borehole in the north-east of the district, the limestone thins westwards to about 4 m near Ridsdale and to less than 3 m around Bellingham. At Greenlee Borehole towards the south-west of the district, a bed 1.30 m thick is correlated with the Redesdale Limestone. This bed forms a small feature [NY 7245 7060] near Ventners Hall Old Colliery and sporadic exposures show about a metre of ferruginous weathering argillaceous limestone. In Tipalt Burn [NY 7113 6960] near Wall Shield this limestone contains corals and gigantoproductoids. Frost (1969, p. 284) showed that the Redesdale Limestone thinned northwards from the Bellingham district, and he recorded a thickness of 2.40 m at Leehouse Linn [NY 9650 9298] near Elsdon. The limestone has not been recognised in the neighbouring Rothbury (9) district.

There are numerous exposures of the Redesdale Limestone in the district and in the type area near Ridsdale (Lebour, 1873), the limestone and underlying Redesdale Ironstone Shales have been extensively quarried (Plate 3) and (Plate 4). A typical section measured in the quarries [NY 8949 8342] near The Steel is as follows:

Nearby, Ridsdale Borehole [NY 8946 8287] proved the overall thickness of the limestone to be at least 3.8 m. Some 3 km to the south-west, in old quarries [NY 8820 8160] near Buteland, the lower massive part of the limestone is 2.6 m thick and the upper 2 m interbanded with calcareous mudstone. Limestone 'posts' in this upper portion are particularly rich in Lithostrotion junceum, mostly badly preserved and with corallites parallel to the bedding planes.

The Redesdale Limestone is some 3.3 m thick in Dinley Burn [NY 8800 7695] near Wark and at least 3.15 m thick in a small stream [NY 8481 7995] near Woodpark. The old quarries at Woodpark are now largely overgrown and valley bulging has disturbed the beds in the stream making thickness measurements liable to error. Lithostrotion junceum colonies are particularly common.

In Hareshaw Burn [NY 8419 8460], 1.5 km N of Bellingham, the Redesdale Limestone is only 2.3 m thick. Sporadic exposures [NY 8152 7834] and [NY 8142 7829] near Low Stead Farm and in the neighbouring Blacka Burn, 5 km S of Bellingham, show up to 2 m of limestone again rich in Lithostrotion.

The measures between the Redesdale and Fourlaws limestones are not continuously exposed in any stream section but were proved in both the Ferneyrigg and Greenlee boreholes (Figure 16). The mudstones overlying the Redesdale Limestone are best seen at Steel Quarries [NY 8948 8347], in Hareshaw Burn [NY 8417 8461] and near Woodpark [NY 8486 7986]. From the last locality they yielded: Fenestella cf. oblongata, Penniretepora recticarinata, Polypora verrucosa, Sulcoretepora cf. raricosta, Leptagonia caledonica, Rugosochonetes hardrensis, Tornquistia spp., Pernopecten concentricus, Streblopteria? redesdalensis.

Sandstones underlying the Fourlaws Limestone are well exposed in Hareshaw Burn [NY 8410 8480] and in old quarries at Park House [NY 8803 7684] near Wark. They are also well seen in the Woodburn Quarries [NY 9020 8580] where they are divided by a small local unconformity into a lower massive sandstone and an upper thinly bedded and alternating sandstone/mudstone sequence. A nearby quarry [NY 8990 8585] shows an erosive base to the lower sandstone associated with a sandstone breccia and containing mudstone and carbonaceous fragments.

In the south-west of the district, Bowmer Crags [NY 7365 7064] and Slippery Stones [NY 7260 7050] provide good exposures of brown, fine- to medium-grained cross-bedded sandstone.

The Fourlaws Limestone was originally named from Fourlaws Edge [NY 9123 8355] near Ridsdale but it is better known for the fauna described by Smith (1910) from the nearby Waterfalls Quarry [NY 9096 8145]. The limestone is not well exposed compared with the underlying Redesdale Limestone. In Ferneyrigg Borehole the Fourlaws Limestone is 5.05 m thick and composed of massive, dark grey crinoidal limestone. Some 2.40 m of limestone with thin shale partings, up to 10 cm thick, are exposed in a quarry [NY 9154 8477] near Ridsdale. Brownish ferruginous weathering, possibly due to partial dolomitisation, is a common characteristic of the limestone in this area. The limestone is finely crinoidal and as at Waterfalls Quarry the fossils are usually concentrated into small pockets with a preponderance of gastropods, bivalves and cephalopods over the more usual coral/brachiopod assemblage. In this north-eastern part of the district the limestone is generally poorly fossiliferous.

Some 3.12 m of massive limestone with shaly partings are exposed in quarries [NY 8970 7878] near Rubbingstob Hill and about 2 m at Catreen Farm quarries [NY 8860 7794]. Some 3.65 m of well bedded, massive, finely crinoidal limestone are present on the east bank of the River North Tyne near Chipchase Castle. The castle foundations stand on the Fourlaws Limestone.

The Fourlaws Limestone can be traced from the North Tyne valley westwards and is seen to be up to 4.88 m thick in streams such as Mollerstone Sike [NY 780 720] and Greenlee Burn. It is also exposed in Forestry Commission quarries at Green Carts [NY 7720 7160] and Sweet Rigg [NY 7620 7103]. The fauna from Green Carts quarry included: Lithostrotion junceum, L. martini, L. portlocki, Dielasma sacculum, Gigantoproductus sp.(cf. Productus (1 of Smith, 1910), Leptagonia caledonica. Greenlee Borehole [NY 7726 7149] nearby proved 7.64 m of grey fossiliferous massive bioclastic limestone with a mudstone band 0.63 m thick 1.45 m from the top.

The most westerly exposures of the Fourlaws Limestone are seen north of Edges Green. In a large swallow hole [NY 7166 6935] up to 2.4 m of limestone with Lithostrotion junceum and gigantoproductoids are present. Limestone exposed in Pont Gallon Burn [NY 7232 6939] is similar in lithology and fauna to that at Greenlee.

A limestone at this horizon is referred to in the Brampton and Bewcastle districts by Trotter and Hollingworth (1932) and Day (1970) as the Naworth Limestone.

In the central part of the district near Low Stead, and separated by faults from the main outcrop, is a limestone [NY 8150 7822] some 1.8 m thick which is considered to be equivalent to the Fourlaws. A bed of similar thickness at this horizon is poorly exposed in Hareshaw Burn [NY 8410 8489].

The measures between the Fourlaws Limestone and the Fourlaws Coal, 33 m thick in the Ferneyrigg Borehole, are corn-posed largely of sandstone, but with fossiliferous mudstones immediately overlying the Fourlaws Limestone. Sarelaw Crag [NY 9114 8528] near Ridsdale, composed of 9 m of massive fine-grained sandstone, is typical of the arenaceous measures. At Hawkside [NY 7880 7280] the sandstone forms a scarp feature which shows sporadic exposures of fine-grained sandstone; it forms a waterfall [NY 7665 7087] in Greenlee Burn, where the sandstone is pale grey and fine-grained with a ganisteroid top containing stigmarian rootlets.

The Fourlaws Coal, one of the few economically important seams of the district, has been worked over much of the eastern area and can be traced as far west as Haughton Common some 9 km from the western margin of the district. It is a variable seam, made up of several leaves separated by dirt partings. The thickest single leaf which has been worked was 81 cm, recorded at Cowden Colliery [NY 9113 7907]. The coal averages 69 cm between Simonburn and Ridsdale and is fairly uniform in thickness. At Goatstones [NY 8405 7458], 3 km W of Simonburn, the coal deteriorates into three leaves, none exceeding 36 cm, in a composite section totalling 1.40 m. Farther west [NY 8001 7305] an impure coal, 28 cm thick, was recorded in Sell Burn and in Greenlee Burn a ganisteroid seatearth is immediately overlain by a thin unfossiliferous limestone at the Fourlaws Coal horizon.

Coal was last mined near Gunnerton at Sutty Row Colliery [NY 9053 7756] which closed during the resurvey for economic and geological reasons. The workings were particularly wet—a feature of many of the small mines in this area. Other collieries to work the Fourlaws Coal in past years were situated at Hareshaw Head [NY 8454 8835] just beyond the northern margin of the district and at Elsdon some 13 km NE of Bellingham. The quality of the coal is poor because of abundant mineralised cleats which produce a high ash content.

The wide geographical extent of the Fourlaws Coal shows that the Northumberland Trough had built up to sea level and remained sufficiently stable to maintain a land flora for many years.

The strata between the Fourlaws Coal and the Lower Gunnerton Fell Limestone are some 50 m thick and extremely variable in character. In the south-western part of the district the measures are largely arenaceous with rare thin coals. Northeastwards from the Simonburn area, they exhibit minor cyclicity with lithologies following a fairly regular ascending order of limestone, mudstone, sandstone and coal, typical of Yoredale cyclothems but much reduced in thickness, usually to less than 10 m.

The variability of these measures was illustrated by Frost (1969, fig. 3) who collectively named the thin limestones as the Stiddlehill Calcareous Bands from details obtained from Borings and Sinkings records (1878–1910). Two Institute boreholes drilled near Simonburn and Ferneyrigg proved further details in this part of the succession and emphasised the difficulties of detailed comparisons and correlation over even this limited area (Figure 16).

The measures contain up to five limestones which are usually less than 1 m thick, dark grey in colour, bioclastic and crinoidal. Squashed colonial corals and gigantoproductoids are fairly common. The mudstones show ferruginous staining and contain small ironstone nodules. They are commonly fossiliferous and include ostracods, as well as the usual muddy-water assemblages such as: Fenestella spp., Composita ambigua, Lingula mytilloides, Productus redesdalensis and Phestia attenuata. The sandstones are fine-grained and monazite is a common constituent of the heavy mineral suites (Frost, 1969, p. 286). Much of the sequence is composed of seatearths or seatearth-like mudstones containing calcareous nodules, and ganisters or ganisteroid sandstones showing bioturbation.

These measures are similar to those of the upper part of the Upper Border Group-a factor emphasised by the numerous thin coals (up to 23 cm) and carbonaceous mudstones which top many of the minor cycles. Several coals have been worked locally like the Shanks Kiln Coal named after the Shanks Kiln Pit [NY 9253 8530] near Ridsdale. Exposure of these measures is poor, but thin coals and sandstones can be seen in Shaw Cleugh [NY 9125 8600] near East Woodburn and one of the highest limestones crops out [NY 9103 8270] near Fourlaws Farm, Ridsdale.

The Gunnerton Fell Limestone was originally named by White (1954) in the Coal Burn [NY 9055 7646] where it lies within poorly exposed measures, some 60 m thick, overlying the Fourlaws Coal. Frost (1969, p. 10) correlated two limestones in close proximity in this burn with the Lower Penchford Limestone of the country to the north and with the two limestones sporadically exposed beneath sandstone crags of Hepple Heugh 1.5 km E of Ridsdale. However, the Ferneyrigg Borehole has shown that in the Ridsdale area many of the limestone horizons are represented by fossiliferous mudstones or by shelly bands in sandstone, making bed for bed correlation uncertain. The recent survey also indicates that the lower limestone of the two which crop out beneath Hepple Heugh may be one of the Stiddlehill Calcareous Bands.

Because of this doubt the Lower Gunnerton Fell Limestone is defined at Simonburn, some 3 km W of Gunnerton where the Simonburn Borehole enabled the Fourlaws Coal sequence to be linked with that of the overlying measures which are well exposed in the Simon Burn. The Lower Gunnerton Fell Limestone, 1.5 m thick in the Simonburn Borehole, is grey in colour, massively bedded and contains numerous colonies of Lithostrotion junceum. The topmost 0.30 m are exposed [NY 8748 7380] in Simon Burn.

The measures between the Lower Gunnerton Fell and the Ladies Wood limestones vary between 25 and 40 m in thickness. They include the thin bioclastic limestones which were assigned the letters '1' and 'm' by the primary surveyors in the Roman Wall area, the Upper Gunnerton Fell Limestone (Figure 17) and probably the Lower Penchford Limestone of Frost (1969, p. 286). They have been proved in Cairney Croft Borehole some 4 km SW of the district and can be traced by sporadic exposure through the Roman Wall [NY 7700 7024] and Simonburn areas to the North Tyne valley and thence north-eastwards to the Ferneyrigg Borehole where the limestones are considered to be represented by fossiliferous mudstones or by fossil concentrations in a sandstone. The sandstones are normally less than 10 m thick but in the area east of Ridsdale thicker lenses like those forming Hepple Heugh and Aid Crag locally expand the sequence.

These measures span the transition between the minor cyclicity of the underlying rocks and the regular cyclothems of the higher beds of the Liddesdale Group. The best continuous section is exposed in Simon Burn (Figure 17):

The Ladies Wood Limestone is almost invariably underlain by a thin coal or carbonaceous mudstone and its relation to the underlying beds is well shown in Crook Burn [NY 8935 7213].

The Ladies Wood Limestone (White, 1954; Frost, 1969) varies between 3 and 5 m in thickness and is massive, grey-blue, finely crinoidal and bioclastic In the Ferneyrigg Borehole a calcareous mudstone parting is present 1.09 m from the top of the limestone, and in Coal Burn near Gunnerton a section [NY 9058 7594] shows 0.46 m of limestone overlying 1.80 m of mudstone which separates it from the main part of the limestone. Fossils include Lithostrotion junceum and gigantoproductoids, and at this horizon also is the lowest common occurrence of algal nodules referred to the form genus Osagia.

The Ladies Wood Limestone is one of the lowest horizons in the Northumberland Trough which can be mapped and recognised throughout the district. It is correlated to the south and west near Brampton with the Denton Mill Limestone and to the northeast in the Alnwick and Berwick areas with the Dun Limestone (Figure 14) and (Figure 17). It was assigned the letter 'k' by the primary surveyors and was called the Middle Penchford Limestone in the Otterburn district (Frost, 1969). The resurvey of the Bellingham district supports the conclusion that the Ladies Wood Limestone is the lateral equivalent of the lowest beds of the Melmerby Scar Limestone of the Alston Block, which are separated by an increasing thickness of clastic sediments when traced north-eastwards.

The measures between the Ladies Wood and Lower Demesne limestones range from about 30 m in the south and west of the district to some 55 m in the north-east. The differences are largely accounted for by the thicknesses of arenaceous rocks in these measures which form such features as Swallow Crags [NY 7350 6885], Townshield Bank [NY 8170 7300], the waterfall of Carkey Linn [NY 8670 7323], Simonburn, and the impressive scarp, over 30 m in height, of the Great Wanney Crags [NY 932 834]. Some of the sandstones are feldspathic and show an erosive base: e.g. the Great Wanney Crags sandstone in the Ferneyrigg Borehole (at 190.27 m) contained sandstone fragments and ironstone nodules together with coal fragments.

The mudstones overlying the Ladies Wood Limestone are exposed below Carkey Linn [NY 8672 7331] and in Coal Burn [NY 9059 7589] near Gunnerton. They are fossiliferous, the fauna including Fenestella spp Penniretepora spp Gigantoproductus sp. latissimus group, Globosochonetes parseptus, Tornquistia cf. scotica, Aciculopecten interstitialis, Pernopecten concentricus.

The Upper and Lower Demesne limestones (White, 1954; Frost, 1969), consist of several variable beds of limestone separated by mudstones, thin sandstones and coals totalling some 10 m of measures (Figure 17). They are syrionymous with limestones 'i' and 'j' of the primary survey and probably the Lower and Middle Wishaw Limestones of the Otterburn district (Frost, 1969, p. 289).

The limestones probably represent the highest beds of the Melmerby Scar Limestone of the Alston Block which split and separate in a north-easterly direction (Figure 14). The Woodend Limestone of the Berwick area is suggested as a correlative of the Demense limestones (Frost, 1969, pl. 10).

Gunnerton Burn [NY 908 756] provides the best exposures of the Demesne limestones in the following section (Figure 17):

The limestones are not very fossiliferous but contain Osagia nodules and the following species which help to differentiate the beds from those lower in the succession: Diphyphyllum sp., Lithostrotion maccoyanum and Gigantoproductus sp.intermediate between the maximus and giganteus groups.

A sporadic but unusual feature of the Lower Demesne Limestone is a pseudobrecciated texture which is considered to have been formed by penecontemporaneous and partial alteration of the limestone to dolomite. This feature is well displayed in outcrops in the Roman Wall area [NY 8234 7264] and [NY 8414 7333], near Tecket Farm [NY 8663 7297] in Simon Burn and in Cuddy's Cleugh [NY 9433 8657] near East Woodburn.

The Upper Demesne Limestone is usually thinner and more variable than the Lower Demesne Limestone and therefore cannot be mapped continuously throughout the district. It is exposed in Simon Burn [NY 8658 7283] where two limestone bands 84 cm and 91 cm thick are separated by 122 cm of grey mudstone. The limestone has not been detected in the Ray Fell area in the northeast of the district: it is probably penecontemporaneously eroded here.

Fossils from the measures between the Lower and Upper Demesne limestones collected from the Ferneyrigg Borehole include: Lithostrotion junceum, Pleuropugnoides pleurodon, Productus redesdalensis, Rugosochonetes celticus, Schizophoria sp., Nuculopsis gibbosa, Sanguinolites clavatus and Bollandoceras?

The measures between the Upper Demesne and the Lower Camphill limestones vary from about 10 m in the south-west of the district to nearly 30 m in the north-east. This thickening is due to an increasing proportion of arenaceous strata which forms features [NY 9240 7818] near Colt Crag Reservoir. Nearby [NY 9257 7820] a thin coal was previously recorded, 15 to 20 cm thick some 17 m above the Upper Demesne Limestone. This coal was proved to be 22 cm thick in the Ferneyrigg Borehole. In the Gunnerton Burn section a thin impure limestone is exposed within a sandstone estimated to be below this coal horizon.

The Lower Camphill Limestone (White, 1954; Frost, 1969) is a relatively thin but persistent limestone which reaches a maximum thickness of 2 m at the Barrasford Sanatorium Borehole [NY 9225 7646]. Elsewhere it varies from 1.54 m (Colt Crag Farm Borehole) [NY 932 785] to 0.30 m on Ray Fell where it is directly overlain by sandstone and is assumed to be partialy 'washed out'. The limestone is best exposed in Simon Burn [NY 8637 7274] (Figure 17) and near Cawburn Rigg [NY 7390 6858] where it is usually dark grey but with ferruginous staining, and composed of finely crystalline, crinoidal, bioclastic limestone. At the top and bottom the limestone is argillaceous and thinly bedded. In Ferneyrigg Borehole 1.78 m of shelly mudstones separate the Lower Camphill Limestone from an underlying argillaceous limestone, 0.25 m thick. Near Cawburn Rigg [NY 7320 6816], a limestone band, 0.61 m thick, lies some 2.74 m above the Lower Camp hill Limestone.

The Lower Camphill Limestone was named in the Gunnerton area and is sporadically exposed in the Roman Wall area where the primary surveyors denoted the bed by the letter 'h'. It is the highest limestone in the D₁ Zone but fossils are not common.

The measures between the Lower Camphill and the Low Tipalt limestones are largely arenaceous. Throughout the district they give rise to such impressive crags as King's Crags [NY 7960 7110], Stooprigg [NY 8433 7256], and Long Crags [NY 9215 7750]. They also form the sandstone gorge and waterfall at Tecket Linn [NY 8630 7268] near Simonburn.

The sandstones are medium- to coarse-grained, locally pebbly and massively bedded with cross-bedding indicating an origin predominantly from the north-east. Heavy mineral suites show a dominance of purple zircons over the colourless variety (Frost, 1969, p. 289).

Some 5 m of silty mudstones with thin sandstone bands underlying the Low Tipalt Limestone are exposed in Crook Burn [NY 8388 7235].

Upper Liddesdale Group

The Low Tipalt and Bankhouses limestones are neither as well exposed nor form such prominent features as might be expected of such thick and persistent limestones. This is probably because they are argillaceous and each contains several thick mudstone partings. They were both referred to by the letter 'g' by the primary surveyors in the Roman Wall area where it is difficult to map them as separate limestones. The Low Tipalt Limestone is mainly dark grey and 3 to 6.5 m thick; the Bankhouses Limestone is lithologically similar and is about 8 m thick. In both limestones bioclastic debris, including corals and brachiopods, is abundant locally with Osagia (‘Girvanella') haloes and Saccamminopsis sp. A 2-cm coal was proved 8 cm above the Low Tipalt Limestone in the Ferneyrigg Borehole [NY 9579 8364]. The most important exposures of the limestones are in Crook Burn [between 8390 7229] and [NY 8466 7208] (Figure 18), col. 5 and in quarries [NY 9120 7567] and [NY 9183 7691] near Gunnerton.

Up to 6 m of strata, mainly sandstone, separate the limestones in the eastern part of the district (Figure 18), cols. 7 and 9 but in the south and south-west only rarely can they be separated in the field. In the extreme north-eastern part of the district the Bankhouses Limestone does not seem to be present. A sharp-based coarse-grained sandstone is less than 0.5 m above the Bankhouses Limestone in the Ferneyrigg Borehole [NY 9579 8364] and it seems probable that the limestone is locally 'washed-out' in this area. This sandstone (Camphill Sandstone of the Gunnerton area), 15 to 20 m thick, forms prominent scarps and features in the eastern part of the district such as Gunnerton Quarry [NY 9166 7640], Long Crag [NY 9270 7753] to [NY 9323 7800], Lunga Crags [NY 9502 8260] to [NY 9562 8320] (Plate 5) and Ray Crags [NY 9693 8634] to [NY 9730 8690]. In the south and south-west, though a sandstone is present in this part of the sequence, for example at Banno Crags [NY 8280 7215], it is generally thinner and finer grained (Figure 18), cols. 2 and 5.

Coal 54 cm thick and mudstone occur above the sandstone in the Ferneyrigg Borehole [NY 9579 8364]; a thin coal, probably at the same level, was also proved in the Cawburn Rigg Borehole [NY 7397 6811] (Figure 18), cols. 2 and 9. This coal is overlain by up to 5 m of sandstone and mudstone which are overlain by a 1 to 1.5 m thick unnamed muddy limestone which has been proved in borings across the district. Overlying strata, 10 to 16 m thick, up to the Greengate Well Limestone are only rarely seen at crop. Mainly sandstones were proved in the Cawburn Rigg and Ferneyrigg boreholes with mudstones and siltstones and thin coals, which may be persistent.

The Greengate Well Limestone up to 4 m thick, has locally been dug for lime but most workings are now largely grassed-over. The limestone is grey to dark grey and locally contains Osagia haloes near the top. The best exposures are in Crook Burn [NY 8578 7217] where the limestone was referred to by Miller as Limestone 'f', at Sweethope [NY 9547 8222] and near the old school near Gunnerton [NY 9102 7472] to [NY 9079 7434]. The limestone is locally known as the School Limestone after this latter locality (White, 1954; Frost, 1969). The 15 to 20 m thick coarsening-upwards clastic sequence above the limestone is particularly well exposed in the north bank of the River North Tyne near Barrasford [NY 9100 7316] to [NY 9136 7308] (Figure 18), col. 6 and was also proved in the Cawburn Rigg Borehole [NY 7397 6811] (Figure 18), col. 2. The sandstone member is again seen in notable exposures near Sweethope [NY 9555 8214]; [NY 9503 8310] and in Ray Burn [NY 9627 8449]. Locally there are some thin coals near the top of this sandstone and one, fairly persistent, directly underlies the Oxford Limestone.

The Oxford Limestone, 5 to 6 m thick, is seen in many natural and quarry exposures, and commonly forming a marked feature, it is readily traceable across the district. It is a grey to dark grey limestone with numerous red weathering Osagia haloes and although Osagia occurs in other limestones, they are rarely so obvious or in such abundance. The Oxford Limestone is particularly rich in corals and brachiopods. There are numerous exposures, noteworthy ones being near Broomlee Lough [NY 7903 6990] and [NY 7960 7041 ], north of Sewingshields [NY 8100 7108], near Tepper Moor [NY 8567 7189], in Barrasford Quarry [NY 917 747] (where the limestone is partly converted to marble adjacent to the Whin Sill), near Gunnerton [NY 916 752], Hetchester [NY 9514 8027], Sweethope [NY 9538 8139], Ferneyrigg [NY 9590 8389], Ray Burn [NY 9636 8453] and Ray Demesne [NY 9689 8549].

The coarsening-upwards sequence, 12 to 20 m thick (Figure 18), overlying the Oxford Limestone, is nowhere completely exposed or proved within the district. The argillaceous beds are commonly fossiliferous; they were formerly worked for tile manufacture near North Heugh [NY 9539 8026]. Important exposures include those at Cawburn Rigg [NY 7402 6806], Sweethope Dean [NY 9592 8192]; [NY 9587 8205] and Ferneyrigg [NY 9566 8345]. The sandstone member commonly forms a marked feature with sporadic exposures, the most notable being those west of Broomlee Lough [NY 7762 6920], in the north bank of the River North Tyne near Barrasford, where trough cross-stratification is well shown [NY 9157 7302] to [NY 9194 7313], in Swin Burn [NY 9338 7537], Dry Burn [NY 9455 7717], near Thockrington [NY 9519 7922], Sweethope Dean [NY 9604 8198] and near Larkhall [NY 965 845] to [NY 967 847]. Locally, as in Sweethope Dean [NY 9621 8200], the sandstone is overlain by a few metres of argillaceous beds with thin coals.

The Barrasford Limestone (described as the Tynebottom Limestone by Trotter and Hollingworth (1932) and Johnson (1959)) is a grey to dark grey limestone up to 4 m thick, locally forming a prominent feature in which some relatively extensive quarries were formerly opened. Exposures are poor in the Roman Wall area, but 2 m of limestone are seen north-east of Tepper Moor [NY 8657 7182]. At the type locality in the River North Tyne (Holliday and others, 1975, p. 329) the limestone is well exposed [NY 9198 7313], and further exposures occur to the north-east in Swin Burn [NY 9202 7346], near Great Swinburne [NY 9387 7544] and [NY 9425 7580], Swinburne Quarry [NY 951 765], North Heugh [NY 9570 7999] to [NY 9573 8023]; [NY 9570 8051] to [NY 9573 8068]; [NY 9583 8122] to [NY 9593 8134], Sweethope Dean [NY 9627 8197], and [NY 9593 8198] where the limestone and associated beds are locally steeply dipping and caught up in a fault-plane, and at Berry Hills [NY 9659 8339].

Between the Barrasford and Colwell limestones the strata show more lateral variation than is usual in the Liddesdale Group. The persistent Dalla Bank Limestone and the impersistent Haughton Limestone occur within these strata. Over much of the district these beds are 20 to 25 m thick, but a boring at Settlingstones Mine (Figure 18), col. 4 suggests that 35 to 40 m of strata are present in the extreme south of the district. Southerly thickening of beds is known to occur higher in the Liddesdale Group (Figure 18), (Figure 19) and (Figure 20), but this is the lowest level at which such thickening can be demonstrated within the present district. However, comparison with the Tipalt Burn sequence in the Brampton district (Figure 18), col. 1 suggests that this is also a feature of the lower part of the Upper Liddesdale Group.

The beds immediately above the Barrasford Limestone are poorly exposed. The Haughton Limestone, up to 1.25 m thick, and underlying coal and sandstone are seen in the River North Tyne near Haughton Castle (type locality) [NY 9186 7305] and again in Swin Burn [NY 9286 7408]. At these localities it is in one post with a yellow weathering (?dolomitic) central portion. The limestone is not known for certain to the west; it may be present in the Steel Rigg Borehole [NY 7492 6775] but was not recorded in the boring at Settlingstones, though a thin coal may indicate an adjacent horizon (Figure 18), col. 4. It has been traced north-eastwards from Barrasford towards Colwell but does not appear to be present in the neighbourhood of Swinburne Quarry [NY 951 765], on the evidence from boreholes and nearby quarry and natural exposures (Figure 18), col. 8. Whether this is a further case of a 'washout' is not known. Apart from a limestone crop, formerly seen in Ray Burn [NY 9723 8526], there is no evidence that the Haughton Limestone occurs in the north-eastern part of the district. The sandstone which overlies the limestone forms prominent features in the eastern half of the district and is exposed in the River North Tyne [NY 9214 7306], Swin Burn [NY 9290 7392], south of Swinburne Castle [NY 9380 7479], Swinburne Quarry [NY 9521 7646] to [NY 7515 7686] and North Heugh [NY 9604 8081].

The Dalla Bank Limestone (Holliday and others, 1975, p. 329) is generally about 1 m thick (Figure 18) but locally around Barrasford, as at the type locality in Swin Burn [NY 9234 7347], it is at least 2.5 m thick. It is poorly exposed on the shore of Broomlee Lough [NY 7950 6984]. To the north-east of Barrasford the limestone is exposed in a road cutting [NY 9434 7550] on the A68. Generally it is not well exposed though a number of crops were formerly visible, e.g. in Thockrington Burn [NY 9632 7909]. The limestone forms a broad dip-slope on top of the Whin Sill with local exposures [NY 9648 8243] near Hawick; it is seen in the River Wansbeck (Crook Dean) [NY 9703 8319]; [NY 9713 8327], and in Ray Burn [NY 9748 8531] and was formerly visible in the railway cutting at Blackhalls [NY 9766 8582].

The clastic beds overlying the limestone are exposed near Barrasford in the River North Tyne [NY 9221 7296], and in Swin Burn [NY 9236 7346]. Scattered exposures occur in Crook Dean [NY 9696 8295] to [NY 9746 8364] and in Ray Burn [NY 9748 8531] to [NY 9761 8532]; [NY 9786 8524] to [NY 9795 8526]. At most localities there are thin coal seams in the highest beds (Figure 18).

The Colwell Limestone (described as the 'Single Post' Limestone by Trotter and Hollingworth (1932) and Johnson (1959)), is a dark grey evenly-bedded limestone, up to 5 m thick, which locally forms a feature and has been quarried in many areas. It was mapped by the primary survey and assigned the letter 'c'. It has been proved underground in Settlingstones Mine (Figure 19), col. 3 and is seen in many surface exposures, e.g. north of Housesteads [NY 7825 6920], Broomlee Lough [NY 7950 6975], Sewingshields [NY 8065 7045], a quarry at Green Carts [NY 8875 7170], near Barrasford in the River North Tyne [NY 9220 7293], in Swin Burn [NY 9238 7345]; [NY 9277 7354], in Coal Burn [NY 9365 7434] to [NY 9392 7436], the type locality at Colwell (Holliday and others, 1975, p. 329) [NY 9511 7562]; also [NY 9555 7628]; [NY 9583 7746], Thockrington [NY 9635 7899], Plashetts (Bavington) [NY 9667 8190], Crook Dean [NY 9700 8316]; [NY 9748 8362] and Ray Burn [NY 9750 8530]; [NY 9796 8526]. A faulted inlier of the limestone was proved in shallow borings at Colwell Five Road Ends [NY 9515 7447].

When traced from the south-west to the north-east across the district the beds between the Colwell and Eelwell limestones show considerable variation in lithology and thickness (Figure 19), but interpretation of this variation is hindered by the inadequacies of the borehole and shaft records. All the shaft sections (Figure 19), cols. 2, 3, 4 and 6 are old and generalised; some shafts have more than one version (four in the case of the Frederick Shaft) of the strata proved, which vary considerably in detail. Certain modern records such as the New Onstead and Great Bavington boreholes (Figure 19) cols. 10 and 11 are highly generalised and are interpretations of drillers' logs of uncored boreholes. However, it is thought that the relative positions and identifications of the major limestones shown in (Figure 19) are largely correct. There are four persistent limestones; an unnamed bed, the Lower and Upper Bath-House Wood limestones (which join to form one limestone near the southern margin), and the Shotto Wood Limestone. More local thin sandy limestones and calcareous beds are also known at various levels, e.g. between the Shotto Wood and Eelwell limestones near Hallington [NY 9869 7608] and between the Upper Bath-House Wood and Shotto Wood limestones near Errington [NY 9565 7212] (Figure 19), col. 8. Probably of similar lithology are the relatively thick limestones recorded in the shaft sections in the south of the district (Figure 19), cols. 3, 4 and 6, which do not correlate with any of the persistent limestones. The beds between the Colwell and Eelwell limestones thin from about 110 m in the north-east to around 85 m near Barrasford and then sharply thicken to about 160 m near the southern margin of the district (Figure 19). The thickening in the south is almost entirely in the beds above the Shotto Wood Limestone, from about 15 m to about 90 m. There is a marked thickening of the beds between the two leaves of the Bath-House Wood Limestone towards the northeast, about 4 m at Barrasford increasing to about 25 m in the north-east. The beds between the Lower Bath-House Wood and Colwell limestones range from 30 to 45 m thick but no overall trend is apparent.

The most complete section in the beds above the Colwell Limestone is in the River North Tyne at Barrasford [NY 9221 7290] to [NY 9235 7278] (Figure 19), col. 7. The sandstone seen here, with a thin coal on top, forms a strong feature and is locally well exposed in the Roman Wall area at Dove Crags [NY 7950 6970]. Though probably persistent to the north-east it is less well exposed, being best seen in a quarry near Cornhills [NY 9665 8398]. A persistent unnamed limestone, rarely more than 1 m thick some 19 m above the Colwell Limestone is grey in colour and finely bioclastic. It broadly corresponds to the 'Cockleshell' Limestone of earlier workers (Trotter and Hollingworth, 1932; Johnson, 1959) but a number of exposures formerly ascribed to that limestone are now thought to be of the Bath-House Wood Limestone. The 'Cockleshell' Limestone is seen in the River North Tyne near Barrasford [NY 9235 7278] and locally to the north-east, e.g. against the Colwell Fault in Hallington Burn [NY 9809 7501], near Colwell [NY 9626 7696] and near Crookdene [NY 9726 8296]. The overlying sandstones, siltstones and mudstones are exposed near Barrasford in the River North Tyne [NY 9235 7278] to [NY 9238 7259] and in Swin Burn [NY 9276 7347]. To the north-east the sandstone is locally exposed, e.g. near Crookdene [NY 9759 8315] and nearby in the River Wansbeck [NY 9849 8402].

The Bath–House Wood Limestone (Limestone 'a' of the primary survey, and described as the 'Scar' Limestone by Trotter and Hollingworth (1932) and Johnson (1959)), is a grey to dark grey bioclastic limestone. In the south-western corner of the district it is locally divided into two leaves by thin beds of sandstone and mudstone (Figure 19), col. 5, though only locally can the two be mapped separately. Only one limestone at this level was recorded in Settlingstones Mine (Figure 19), cols. 3 and 4 and in the north-east part of the Brampton district (Figure 19), cols. 1 and 2 (Trotter and Hollingworth, 1932; Johnson, 1959). The limestone is exposed near Sewingshields [NY 8094 7013] and [NY 8072 7005], and its two leaves locally form separate features near Walwick Fell [NY 876 709] though there are no exposures of the intervening strata. In the River North Tyne at Barrasford about 4 m of beds, locally including a thin coal are exposed [NY 9236 7278] to [NY 9241 7254]. These beds thicken in the ground to the north (Figure 19).

The Lower Bath–House Wood Limestone, type locality in the River North Tyne near Barrasford [NY 9239 7258] (Holliday and others, 1975, p. 329), is seen also in Swin Burn [NY 9276 7346], Hallington Burn [NY 9806 7508], near Homilton [NY 9717 7888], in Ferneyrigg Burn [NY 9689 8376] and in the River Wansbeck [NY 9849 8402]. The limestone ranges up to 3 m in thickness, is not as well exposed as the Upper Bath–House Wood Limestone, forms a smaller feature and was rarely dug for lime.

The Upper Bath–House Wood Limestone, up to 4 m thick, is exposed at the type locality in the River North Tyne near Barrasford [NY 9241 7252] (Holliday and others, 1975, p. 329), as well as at Middle Farm [NY 9426 7321 ], Hallington [NY 9841 7565], New Onstead [NY 9752 7987]; [NY 9762 8030], near Crookdene [NY 9795 8209] to [NY 9787 8234]; [NY 9782 8258]; [NY 9809 8286] and at Shield [NY 9902 8403]. Numerous swallow holes into the limestone can be seen on either side of the Great Bavington to Plashetts road to the west of Bavington Crags [NY 9776 8067] to [NY 9791 8122].

There is no complete surface section north-east of Barrasford, in which the beds between the leaves of the Bath–House Wood Limestone are exposed. In the burn near Hallington [NY 9810 7510] to [NY 9810 7588] there is a good section in the beds below the Upper Bath–House Wood Limestone, where the coal seam proved in the Homilton Borehole [NY 9773 7852] (Figure 19), col. 9, is seen to be up to 30 cm thick. The sandstone under the limestone here is massive and unusually thick (at least 7 m), and locally rests directly on the coal seam. The mudstones and siltstones above the Upper Bath–House Wood Limestone are poorly exposed in the district, but the overlying sandstone forms a good feature in the Roman Wall area and can be traced as far east as Hallington Mill.

Notable exposures include those in the River North Tyne [NY 9247 7222], near Errington [NY 9566 7204] (Figure 19), col. 8 and sporadically in Erring Burn [NY 9688 7315] to [NY 9846 7441]. It appears to be thin and is only locally recognisable along the eastern edge of the district, but in the north-east, 3 m of sandstone were seen just beyond the district margin at Kirkwhelpington [NY 9976 8421]. In the Erring Burn area a thin coal is seen, locally up to 30 cm thick, which occurs on top of this sandstone (Figure 19), col. 8, [NY 9567 7199]; [NY 9713 7328]; [NY 9753 7337], and which may have been worked from a nearby old adit [NY 9813 7401].

The Shotto Wood Limestone (Holliday and others, 1975, p. 329) has not previously been recognised as a separate bed in the succession, exposures of the limestone formerly having been referred to the Bath–House Wood ('Scar') Limestone, possibly because the limestone was not recorded in the Cockmount Hill Shaft (Figure 19), col. 2. However, comparison with the Frederick Shaft at Settlingstones (Figure 19), col. 3 suggests that the limestone near the bottom of the Cockmount Hill Shaft could be the Shotto Wood Limestone rather than the Bath–House Wood ('Scar') Limestone as generally has been assumed (Trotter and Hollingworth, 1932, fig. 7; Johnson, 1959, fig. 8; Holliday and others, 1975, pl. 23). Over much of the district the Shotto Wood Limestone is about 1 m thick but this increases to about 3 m in the south and south-west. The limestone although thin, is locally exposed in both the southwestern and north-eastern parts of the district where it forms wide outcrops on top of the dip-slope of the Whin Sill, e.g. near Housesteads [NY 7818 6833] and [NY 7828 6842], and in the Great Bavington area between Clay Walls and Northside [NY 9858 7942] to [NY 9895 8276]. Other exposures are in Settlingstones Burn [NY 8509 6890] to [NY 8522 6885], Cowey Sike [NY 8390 6887] to [NY 8418 6882], the type locality in the River North Tyne [NY 9248 7216], near Errington [NY 9669 7185], in Linn Burn [NY 9758 7331], in the River Wansbeck at Kirkwhelpington [NY 9957 8432]; [NY 9985 8492] and in East Whitehill Quarry, Knowesgate [NY 9961 8559].

The beds above the Shotto Wood Limestone, up to the Eelwell Limestone, are completely exposed, but cut by a small fault, just beyond the margin of the district in the River Wansbeck at Kirkwhelpington [NY 9959 8438] (Figure 19), col 12. The lower part of the sequence is also exposed in the River North Tyne [NY 9249 7211], where a thin coal occurs a few metres above the limestone (Figure 19), col. 7. This coal thickens westwards to 46 cm and was formerly worked from a shaft at Tower Tie on Walwick Fell [NY 8914 7102]. A fairly persistent sandstone, up to 20 m thick, underlies the Eelwell Limestone in the southern part of the district. Notable crops include those near Housesteads [NY 7842 6830] and Sewingshields [NY 8110 6987] where the sandstone was quarried for use in the construction of the Roman Wall on Walwick Fell [NY 8828 7073], and in the River North Tyne [NY 9251 7213] to [NY 9258 7190]. The extremely thick sequence at this level in the southern margin of the district is known only from the old records of the Settlingstones Mine, the beds being mantled by very thick drift.

The Eelwell Limestone is a massive grey bioclastic limestone, devoid of mudstone partings, which can be traced across the southern part of the district and along its eastern edge. Over much of this area the limestone is 5 to 6 m thick but this increases in the extreme south to about 10 m (Figure 20). It has been extensively quarried along the length of the crop, and is well exposed around Moss Kennels [NY 8060 6935], near Walwick [NY 8878 7033]; [NY 8931 7069]; [NY 8963 7079]; [NY 9017 7096]; [NY 9083 7116], around Bingfield [NY 9724 7254]; [NY 9802 7307]; [NY 9870 7400], and just beyond the eastern margin of the district near Hallington [NY 9870 7695] and Kirkwhelpington [NY 9958 8439].

Thin sections of the Eelwell Limestone (E43780 to (E43787) show it to be rich in algal remains throughout, and it appears to vary between a packed biomicrite and a biomicrosparite for the most part, but it becomes a biosparite towards the top. Samples from 1.5 and 2.5 m above the base show appreciable dolomitisation (c. 30 per cent at 2.5 m) which seems to be primarily related to anastomose multiple microgranular veining, possibly related to and grading into stylolite planes. X-ray diffraction analysis suggests traces of siderite and ankerite in the basal metre of the limestone.

The strata between the Eelwell and Three Yard limestones have been proved in a number of old borehole and shaft sections but continuous surface sections are not common (Figure 20). Two persistent limestones, the Redhouse Burn Lower and Middle limestones, occur in these beds and a third limestone, the Redhouse Burn Upper Limestone, is persistent in the eastern part of the district and in adjacent parts of the Morpeth district. There is a thickening of these beds from 50 to 55 m in the east to about 80 m in the extreme south of the district, the increase taking place in the beds between the Eelwell and Redhouse Burn Lower Limestone (11 m in the east increasing to 45 to 50 m in the south). The strata between the Redhouse Burn Lower and Middle limestones thicken northwards from 1.5 m at Greenhead in the Brampton district (Trotter and Hollingworth, 1932) to about 7 m in Grindon Hill Shaft and about 20 m in the east of the Bellingham district. The overlying strata, to the base of the Three Yard Limestone, maintain a consistent thickness of 20 to 25 m across the district.

A thick sandstone above the Eelwell Limestone in the south of the district, proved in the Joicey and Grindon shafts (Figure 20), cols. 2 and 3 forms a pronounced feature with large exposures between Bradley Hall and Grindon at Deafley Rigg [NY 7887 6818] and [NY 8098 6937]. A coal seam in the beds above, also seen in the shafts, was said to be 46 to 61 cm thick in old workings near Moss Kennels [NY 8012 6869]. Farther east there is little evidence for the presence of a thick sandstone between Chollerton and Bingfield, mudstones and siltstones with thin sandstones occurring at this level in Redhouse Burn [NY 9714 7209] to [NY 9730 7195], but a thick sandstone has been proved at crop and in boreholes to the north-north-east just beyond the margin of the district (Figure 20), cols. 6 and 7.

The Redhouse Burn Lower Limestone is dark grey in colour and finely bioclastic. About 0.5 m thick in the south of the district, it thickens to about 1.5 m in the east (Figure 20). It is exposed in Knag Burn [NY 8006 6863], in the River North Tyne near Dunkirk [NY 9297 7091] and near Errington Red House in the type locality [NY 9736 7196], also [NY 9720 7165] (Holliday and others, 1975, p. 330). Near these latter localities, at Bingfield, the limestone forms a good feature and has a relatively broad crop in which it is locally exposed e.g. [NY 9816 7288]. To the north, it can be seen at a number of localities just beyond the eastern edge of the district, e.g. near Fairspring [NY 9987 7463], in Sharney Sike, Hallington [NY 9935 7674] and in Vicarage Burn, West Harle [NY 9973 8183].

Thin sections of the Redhouse Burn Lower Limestone (E43788) to (E43792) from Redhouse Burn [NY 9736 7196] indicate a bioclastite with a sandy base and mixed fossil content; crinoid, algal and foraminiferal remains dominate the fossil assemblage in various samples. In view of the degree of metasomatism shown it seems risky to rely on textural evidence to give a supposed genetic classification of lithologies but ostensibly this limestone is predominantly a biosparite. Stained sections and X-ray diffraction analysis together indicate that almost the whole fabric of the rock has been altered metasomatically. On average at least 5 per cent of the matrix has been replaced by a range of minerals in the dolomite-ankerite series and siderite is also present in some samples. Most of the remaining calcite has been infiltrated by iron metasomatism to varying degrees. Ferricyanide staining tests show that in general the matrix is most strongly affected, and that the least affected parts include brachiopod and crinoid remains; the latter often show selective iron enrichment at their margins or in preferred sites in the fabric of plates and columnals confirming that iron enrichment has been a secondary phenomenon. The dolomitic minerals occur in two chief modes: as scattered well crystallised rhombs or sparry clots and as microgranular aggregates associated mainly with stylolites and related vein phenomena. The beds between the Lower and Middle limestones occur in discontinuous exposures in the stream sections noted above. In the east the complete sequence has been proved in boreholes just beyond the eastern margin of the district at Steel Rigg [NY 9962 7916] and Bavington Hill Head [NY 9951 7962]. The cores of the latter borehole were examined by J. B. W. Day, who noted several bands of marine shells in the argillaceous beds and thin bands (5 cm thick) of sandy limestone on top of the two sandstone beds (Figure 20), col. 7.

The Redhouse Burn Middle Limestone thins from 1 to 1.5 m in the south-west to as little as 0.35 m in the Bavington area just beyond the eastern margin of the district. It is lithologically similar to the Redhouse Burn Lower Limestone, but is commonly silty at the base. It is exposed in Knag Burn [NY 8007 6859], in the River North Tyne near Dunkirk [NY 9275 7078] to [NY 9296 7085], at Keepwick [NY 9510 7122] and in the type locality (Holliday and others, 1975, p. 330) in Redhouse Burn [NY 9748 7194]. It is also exposed at a number of localities in the extreme west of the adjacent Morpeth district, e.g. near Fairspring [NY 9989 7467] and in Sharney Sike, Hallington [NY 9952 7688].

Thin sections (E43793) to (E43795) show the limestone to have a silty base and like neighbouring limestones appears to be predominantly a mixed biosparite. It is however distinguished by a particularly high intensity and degree of iron enrichment in the calcite; only local scattered fossil fragments remaining unaffected. In addition, stylolitic planes are particularly abundant and in one sample from near the top, some of the microsparite matrix is probably secondary material of analogous solution recrystallisation origin. Staining and X-ray diffraction results show that this secondary granular material consists of a similar range of carbonates to those occurring in the Redhouse Burn Lower Limestone.

Beds above the Redhouse Burn Middle Limestone, up to the Three Yard Limestone, are not completely exposed anywhere within the district and are fully known only from borehole records (Figure 20). A number of sandstones form features and are exposed around New Beggarbog and Moss Kennels [NY 8025 6863] and [NY 8203 6930].

To the east of the River North Tyne, the Redhouse Burn Upper Limestone, usually about 0.5 m but locally up to lm thick, occurs in the sequence. Formerly seen in the railway cutting at Cocklaw Mills [NY 9304 7082], it was noted during the resurvey near Keepwick [NY 9516 7114]; [NY 9544 7091], and in the type locality (Holliday and others, 1975, p. 330) in Redhouse Burn [NY 9761 7192]. Here the limestone (E43796), (E43797) is again superficially similar to those described above but appears to be sandy throughout. A sample from near the base resembles an analogous specimen from the Redhouse Burn Middle Limestone in that most of its calcite is strongly ferroan although other iron-bearing carbonates are less abundant. A sample from 0.55 m above the base contrastingly contains significant proportions (perhaps 10 per cent in all) of dolomite-ankerite minerals and this is correlatable with the presence of stylolitic structures and patches of microgranular destructive replacement microsparite' in parts of the rock matrix. Conversely the calcite in this sample is apparently only weakly ferroan compared with other specimens of the three Redhouse Burn limestones.

Between Cocklaw and Bingfield a Baggy sandstone, locally 6 m thick [NY 9451 7092], underlies the Three Yard Limestone. Between Carr Edge [NY 883 694] and Walwick [NY 908 708] much of the interval between the Eelwell and Three Yard limestones is composed of massive, cross-stratified, fine- to coarse-grained sandstone [NY 885 697]; [NY 9059 7088]. The Redhouse Burn limestones do not appear to be present here and are thought to be 'washed out' by a large, distributary-channel sandstone under the Three Yard Limestone. A number of thin coals have been proved close under the limestone (Figure 20).

The Three Yard Limestone is grey to dark grey, up to 5 m thick, commonly crinoidal and with numerous mudstone partings. It contains a band rich in the alga Calcifolium okense about 1 m above the base (Holliday and others, 1975, p. 325). The limestone is not well exposed within the district except around Bingfield where it forms a prominent feature [NY 9777 7209]; [NY 9863 7257] to [NY 9913 7362]. Other major exposures include those near Grindon Shaft [NY 8377 6780], in Cocklaw Dean [NY 9453 7088], near Keepwick [NY 9512 7071]; [NY 9536 7074] and in Steel Rigg Quarry [NY 9965 7917] just beyond the eastern margin of the district.

Thin sections of the limestone (E43798) to (E43800) [NY 9778 7208] are primarily of biomicrite with a significant proportion of intraclasts at the base; algae are prominent among bioclastic remains. Mineralogically this limestone shows extensive but very weak iron contamination of the calcite and contains larger proportions of siderite than dolomite-ankerite. The siderite occurs as disseminated rhombs and has been subjected to partial alteration to limonite (E43800).

Strata between the Three Yard and Four Fathom limestone thicken from around 35 m in the east to around 50 m in the south (Figure 20). These beds largely comprise a single unit broadly coarsening-upwards from mudstone to sandstone with a variable set of sandstones, siltstones and mudstones with thin coal seams at the top. A coal seam, said to be 61 cm thick, was reported in the shales above the limestone between Bradley Hall and New Beggarbog [NY 7945 6800]. The overlying sandstone also forms crags hereabouts at Little Shield [NY 7922 6791] and is well exposed in the River North Tyne [NY 9125 6984] to [NY 9090 6951] and in Cocklaw Dean [NY 9454 7074] to [NY 9457 7056]. The junction between this sandstone and the underlying argillaceous sequence is exposed at several localities between Swallow Burn and the A68 road [NY 953 706]; [NY 9562 7070]; [NY 9589 7073]; [NY 9629 7085]; [NY 9712 7097].

The Four Fathom Limestone is a grey, wavy-bedded, bioclastic limestone up to 10 m thick. It is locally cherty and commonly contains numerous Saccammznopsis fusulinaformis. It commonly forms a pronounced feature and is locally well exposed, e.g. near East Crindledikes [NY 7889 6760], Grindon Hill [NY 8245 6855], Frankham Cottages, Fourstones [NY 8804 6839], in the River North Tyne near Walwick Grange Farm [NY 9090 6948], near Cocklaw Quarry [NY 9368 7054] to [NY 9460 7056]; [NY 9463 7036] and near Bingfield [NY 9889 7217] to [NY 9953 7331].

The beds between the Four Fathom and Great limestones are about 45 to 50 m thick (Figure 20). The argillaceous beds above the Four Fathom are very poorly exposed within the district but the overlying sandstone forms a crag-bearing feature over much of its crop and has been extensively quarried. The most notable of these workings is Prudhamstone Quarry [NY 8838 6868] to [NY 8860 6895] (Plate 6) where about 9 m of medium- to coarse-grained sandstone in four posts can be seen. Each post is generally massive with an irregular erosive base but passes laterally and vertically into flaggy, laminated and cross-laminated, locally contorted, beds. Northerly origins are indicated for the depositing currents. The sandstone is exposed in the River North Tyne at Walwick Grange Farm [NY 9081 6939] and at Redhouse Crag [NY 9707 7064] to [NY 9760 7074] and Beukley [NY 9813 7099]. The strata overlying the sandstone are well exposed in Prudhamstone Quarry (Figure 20), col. 4 and were proved in a borehole at Brunton Quarry, approximate site [NY 9285 6995] and in borings on the western margin of the Morpeth district (Figure 20), col. 6. These beds include some thin coals and a number of marine beds, the highest being the most persistent and comprising sandy limestone and shelly sandstone. It is probably the equivalent of the Iron Post Limestone of the Alston Block to the south. A thin ironstone containing bivalves, Lingula, fish scales and spines, and ostracods, said to occur in the neighbourhood of Brunton and Cocklaw quarries and which was worked around 1858, is probably just above this limestone. A massive sandstone up to 4 m thick is present at the top of these beds, notably at Prudhamstone Quarry, in the River North Tyne at Walwick Grange Farm [NY 9078 6919] and locally to the east near Cocklaw Quarry [NY 9405 7044] and Beukley [NY 9765 7055]. From Brunton Quarry [NY 9282 6992] eastwards, a thin coal is present beneath the Great Limestone. The coal thickens to around 35 cm just beyond the eastern margin of the district.

Chapter 5 Stainmore Group

Burgess and Holliday (1979, p. 43) defined the Stainmore Group in the Brough district as the beds from the base of the Great Limestone up to the base of the Swinstone Top Marine Band. The group is thus coeval with the Namurian epoch and correlates with the Millstone Grit Series as understood in the mid and south Pennines, and with the Upper Limestone Group and part of the 'Durham' Millstone Grit of Durham and Northumberland (Figure 4). In this district, only the lowest 210 m or so of the Stainmore Group crop out in the south-eastern part of the district. The strata range from the Great Limestone at the base to approximately 40 m above the Oakwood Limestone (Figure 21). These beds are considered to be of Pendelian (E₁) age (p. 51) Uohnson and others, 1962; Hull, 1968). The sequence present is broadly comparable with that proved elsewhere in the Northumberland Trough, but is nearly twice as thick as the equivalent section on the Alston Block to the south. It is probable that there is a southerly thickening of these beds in the district, similar to that observed in the Upper Liddesdale Group, but this cannot be proved because of the narrow outcrop and the limited amount of borehole data.

Despite the limited exposure of these beds, they have received considerable attention from previous workers. The basic stratigraphy was understood by the middle of the 19th century, largely as a result of knowledge gained from coal and lead mining. Work in the present century has been concerned with the refinement of detail and in correlation beyond the district, particularly with the Alston Block. Previous accounts giving details of the Namurian rocks of this and adjacent districts include those by Lebour (1875a, b; 1885), Trotter and Hollingworth (1927, 1932), Hedley and Waite (1929), Dunham (1948) and Johnson (1959).

The Stainmore Group rocks show regular rhythmic repetitions of lithology similar to those described above from Lower Carboniferous strata, and indicate a continuation of deltaic and shallow marine sedimentation from the Upper Liddesdale Group. However, only the beds from the Great to Little limestones form a typical Yoredale cyclothem, the characters of the beds above the Little Limestone suggesting that a change of delta type occurred at that level. A similar change in sedimentation is found at the same level in the Brough-under-Stainmore district (Burgess and Holliday, 1979).

Stratigraphy

Great Limestone to Little Limestone

The Great Limestone is by far the thickest (up to 15 m) and purest limestone within the district and has been extensively quarried along the length of its crop. Three major divisions of the limestone have been recognised throughout the district and also in adjacent areas.

Individual beds of limestone and mudstone can also be traced for several kilometres (Figure 22), such continuity being a well established feature of the Great Limestone elsewhere (Fairbairn, 1978; in press). The lowest division of the limestone, up to 2 m thick, is commonly dolomitic and locally contains abundant Chaetetes depressus (see Johnson, 1958). The middle division, 5 to 6 m thick, of 'Main Posts' is composed of grey, wavy-bedded, fine-grained limestone with few macrofossils. The Brunton Band (Johnson, 1958), a biostrome characterised by abundant Calcifolium okense, occurs in this division. The main partings between the limestone posts are laterally continuous and in a few cases contain thin (up to 2 cm thick) mudstone partings. The top of this division is made up of a single post 1 to 2 m thick with numerous impersistent partings. The upper division of 'Tumbler Beds', about 7.5 m thick, is characterised by numerous persistent mudstone partings; one such about 0.5 m thick is readily identified in the major exposures.

Throughout the district the limestone shows a strong degree of folding (Lebour, 1875b, pl. xxxii, fig. 2). These folds, known locally as 'rolls', are concentric and restricted to the limestone, dying out both above and below. The trends of the folds range from due north to north-east. They appear to belong to the 'Normal type' of Shiells (1964, p. 474) which formed at right angles to the regional stress. Within the district other limestones only rarely show similar deformation though in north-east Northumberland comparable folding is found in most of the major limestones (Shiells, 1964).

The strata between the Great and Little limestones, about 65 m thick, (Figure 23) have been described by Lebour (1875a, b), Hedley and Waite (1929) and Johnson (1959). The beds comprise a complex cyclothem similar to those in the Upper Liddesdale Group and can be divided into two major divisions (Johnson, 1959). The lower part forms a coarsening upwards clastic sequence suggesting deposition by a high-constructive lobate delta (Elliott, 1974). The upper division begins at the Snope Burn Band (Trotter and Hollingworth, 1927; Hedley and Waite, 1929; Johnson, 1959), a sandy marine horizon, which marks a period of delta abandonment (cf. Elliott, 1974). The overlying beds, which are vertically and laterally variable, include the once extensively worked Little Limestone Coal and are the result of post-abandonment sedimentation in a variety of environments. A similar two-fold division of the Great Limestone cyclothem is characteristic of the Weardale, Teesdale and Stainmore areas (Elliott, 1974, 1975).

Little Limestone and overlying beds

The Little Limestone, 4.0 to 7.5 m thick, is argillaceous in part and commonly contains mudstone partings. It has been only sparsely worked.

The overlying beds up to the Oakwood Limestone (Figure 24), approximately 85 m thick, previously described by Lebour (1875a) and Hedley and Waite (1929), form a Yoredale-type cyclothem in that calcareous and argillaceous beds are most common near the base, thick sandstones occur in the middle and the highest beds contain numerous seatearths and coals (including the locally worked Oakwood Coal). In detail, however, this interval comprises three cycles within which minor impersistent rhythms can be recognised. The sandstones were correlated by Hedley and Waite (1929), following Trotter and Hollingworth (1927), with the sequence on the Alston Block. They believed that only two major sandstones, Pattinson's and Firestone sills, were present, but another sandstone, the White Sill, occurs between the two previously named (Dunham, 1948, p. 31). It is probable that the sandstones of the three cycles recognised in the Bellingham district correlate with the three sandstones of the Alston Block (Figure 21), but it is thought that any use of Alston Block nomenclature in the district is premature in the light of stratigraphical uncertainty in the area to the south (Dunham, 1948) and the lack of detailed work in the intervening ground.

The Oakwood Limestone up to 1 m thick, is believed to correlate with the Crag Limestone of the Alston Block (Dunham, 1948, p. 44) (Figure 21) and the overlying grits and sandstones appear to be equivalents of the Grit and Slate sills.

Details

The Great Limestone is seen in numerous quarries and natural sections. The most extensive and complete sections are in Fourstones Quarries [NY 886 686] to [NY 889 688], Brunton Quarry [NY 928 700] and Cocklaw Quarry [NY 938 703] (Figure 22), though the first two named are used as rubbish tips. Brunton Quarry [NY 9290 7005] is the type locality of the Chaetetes and Brunton bands (Johnson, 1958) (Plate 7). The former band is also exposed near Fourstones at the top of Prudhamstone Quarry [NY 8844 6871]. Calcareous mudstones overlying the limestone are well displayed in Fourstones (10.5 m thick) and Cocklaw (8 m thick) quarries. The overlying sandstone, the Black Pasture Sill of Hedley and Waite (1929), forms a prominent feature to the south of Brunton and Cocklaw quarries. Black Pasture Quarry [NY 931 699] (Plate 8) exposes about 15 m of sandstone with shelly lenticular patches containing Schellwienella crenistria. The sandstone is also exposed in the River North Tyne [NY 909 689] near Walwick Grange Farm.

Beds between the Black Pasture Sill and the Little Limestone are known largely from old borings, (Lebour, 1875a; Hedley and Waite, 1929). The marine beds, including the Snope Burn Band, are composed mostly of shelly calcareous sandstone with minor sandy limestone. The Little Limestone Coal is persistent throughout the area and was said to range locally up to 1.7 m thick in the Fallowfield Mine workings (Figure 23); an average thickness is about 60 cm. Locally coals occur at other levels, one immediately beneath the Little Limestone being the most persistent. Another coal, about 2 m lower down and up to 60 cm thick, was proved in NCB Opencast Executive borings at Ponthead [NY 979 694] which demonstrate the lateral variation in the beds associated with these coals. Overlying the Little Limestone Coal is the only well exposed bed in this part of the sequence, a sandstone variable in both grain size and thickness. Between the River North Tyne [NY 914 685] and Greenfield Farm [NY 955 694] the sandstone is coarse and gritty and is well exposed at Brady's Crag [NY 9385 6997].

The Little Limestone is a persistent bed proved in many boreholes (Figure 24) but rarely seen at outcrop, quarries near Beamwham [NY 8090 6776], Fallowfield Dene Cottages [NY 9402 6795] and Greenfield Farm [NY 9592 6925] being most notable. In boreholes and sections to the south of the district, the overlying mudstones and siltstones are highly fossiliferous and contain numerous bands and laminae of ironstone and calcareous sandstone and sandy limestone (Hedley and Waite, 1929; Johnson, 1959). A sandstone up to 6 m thick which passes locally into more silty beds, overlies these shales and is well developed notably near Fourstones [NY 8920 6820] and near Errington Hill Head [NY 9685 6955]. Some boreholes indicate that a calcareous bed overlies this sandstone.

The overlying shales are poorly exposed but the succeeding thick sandstone is seen in numerous crag, stream and quarry outcrops eastwards from Wall to the edge of the district and again in the lower parts of Warden Hill [NY 900 682] east of Fourstones.

Strata overlying this sandstone are known largely from boreholes and sections south of the district. Beds below the Oakwood Coal and Limestone are poorly exposed in Fallowfield Dene downstream of [NY 9416 6788] The Oakwood Limestone is seen south of the district boundary [NY 9364 6737]. Overlying sandstones form strong features capping Warden Hill [NY 904 679].

Chapter 6 Dinantian and Namurian palaeontology

Macropalaeontology

The Carboniferous rocks in the Bellingham district are irregularly cyclic, mostly shallow water and largely of a clastic facies, and this affects their faunas in two important ways. First, the rapid vertical and lateral changes in lithology are accompanied by complementary variations in the fossils. The limestones commonly contain brachiopods and, less commonly, corals; the marine shales include more bivalves and fewer corals; and brackish water sediments contain inarticulate brachiopod-bivalve-ostracod assemblages with few species. Second, the conditions of deposition were generally unfavourable to the stratigraphically most useful faunas found in Carboniferous rocks elsewhere in Britain, such as those corals and brachiopods which flourished in the shallow, clear-water seas of 'standard' limestone facies and the goniatites and thin-shelled bivalves characteristic of the deep-water basins. Consequently the correlation of the local sequence with established successions elsewhere has been founded on somewhat meagre evidence. Nevertheless, the district does contain some classic fossil localities, the best known of which are exposures of the Redesdale Ironstone Shale.

The earliest classifications of the Carboniferous rocks in Northumberland were based on lithology (Lebour, 1876; Miller, 1887). Not until the early years of this century was there a detailed description of the local faunal succession. This was by Smith (1910) who recognised several 'palaeontological horizons' and correlated them with coral/brachiopod zones established by Vaughan (1905) in the Bristol area (Figure 25). Garwood (1913) proposed a separate coral/brachiopod zonal scheme in what is now south Cumbria and in 1931 he extended it to the Lower and Middle Border groups in north Cumbria, which are stratigraphically lower than any rocks cropping out in this district. Meanwhile, Bisat (1924) and others had established a number of goniatite zones in the Namurian and Viséan rocks of basinal facies in Lancashire, Yorkshire and the north Midlands. Both these and the coral/brachiopod zones, especially the latter, were correlated with the Carboniferous rocks of Northumberland and adjacent areas by several authors (Trotter and Hollingworth, 1932; Hill, 1938; Westoll and others, 1955; Johnson, 1959; Fowler, 1966; Lumsden and others, 1967; Day, 1970). The result of their work was broad agreement on the correlation in the upper part of the Dinantian succession. This is shown in columns 4, 6 and 7 of (Figure 25), except that most authors, although disagreeing about its exact position, placed the base of D_i at or near the top of what is now called the Upper Border Group. Except in north Cumbria (Garwood, 1931; Day, 1970), faunal evidence for the age of the rocks below the Upper Border Group was generally lacking.

In recent years the classification of the Carboniferous of Northumberland has received fresh impetus from the establishment of stages for the Dinantian in the British Isles by George and others (1976) and from advances in micropalaeontology. Microfossil groups such as miospores (Neves and others, 1972, 1973), ostracods and foraminifera are especially valuable locally because they are more widespread and common than any diagnostic macrofossils. The distribution of the first two groups in the Bellingham district is discussed below by Drs K. J. Gueinn and J. E. Robinson respectively. Micropalaeontological studies have resulted in some revision of the pre-existing classifications, the most notable change being the assignment, on foraminiferal evidence, of the whole of the Upper Border Group to the Asbian Stage (D₁) (George and others, 1976, p. 41).

During the resurvey about 6000 fossils and microfossil samples were collected from some 250 exposures and fourteen boreholes. The stratigraphical distribution of selected fossils is shown in (Figure 26), (Figure 27), (Figure 28) and (Figure 29). Complete records of macrofossils collected, with locality and horizon details, can be examined in the Palaeontological Department of the Institute.

Stonehaugh Borehole (Upper, Middle and? Lower Border groups)

The Stonehaugh Borehole proved nearly 600 m of strata (Figure 26), most of which does not crop out in the district. The highest 60 m in the borehole yielded a fauna generally similar to that from beds between the Upper Millerhill and Leahill limestones which are exposed locally. It includes Fenestella and other bryozoa, Buxtonia sp.nov.(of Ramsbottom in Day, 1970) Echinoconchus spp., Linoprotonia spp., Pleuropugnoides pleurodon, Semiplanus sp.nov.(of Ramsbottom in Day, 1970), Aviculopecten spp., Leiopteria hendersoni, Modiolus spp., Naiadites crassus, Streblopteria? redesdalensis and abundant ostracods. Marine fossils were also common in the beds between the depths 60 and 420 m but the fauna was much more limited. The limestones yielded Fenestella, P. pleurodon and Punctospirifer sp.and the fossiliferous shales contained inarticulate brachiopods, Leiopteria hendersoni, Modiolus spp., myalinids, Naiadites crassus, Phestia attenuata, Sanguinolites spp., and ostracods. Very few fossils were recorded in the largely terrigenous strata below 420 m although there are algal limestones at 492 and 566 m.

Ccrrelation with the well documented faunal successions to the west in the Bewcastle district (Ramsbottom in Day, 1970) and the Archerbeck Borehole (Wilson, 1961) is hindered by the scarcity of diagnostic fossils. No corals were recorded in the borehole, nor any foraminifera below a depth of 50 m. The absence of good marine faunas in the Stonehaugh Borehole at horizons which to the west do contain them is in accordance with the known eastward diminution of marine characteristics in the faunas of the Northumberland Trough (George, 1969; Ramsbottom, 1973).

The interpretation of the succession in the borehole shown in (Figure 26) (except that in the last column) is based on the distribution of certain species which are common in the Northumberland Trough and which appear to be of some stratigraphical significance within its confines. Against this interpretation, however, is the palynological evidence set out by Dr Gueinn on p. 56. He places the Pu/TC miospore zones boundary in the borehole at a depth of 280 m and in the Bewcastle district at 100 m or more below the base of the Upper Border Group. Miospore evidence would thus put the base of the Upper Border Group in the borehole no less than 200 m higher than that shown in (Figure 26) on the faunal evidence. It would also suggest that the borehole ended well down in the Lower Border Group so that one of the algal limestones below 420 m might be the equivalent of the Hillend Algal Band in the Cambeck Beds (Day, 1970, p. 67).

The following points can be made in support of the interpretation shown in (Figure 26):

1. The trepostomatous bryozoan Dyscritella nana in both the Bewcastle and Langholm districts was found to be restricted to beds about the Middle and Upper Border groups boundary. In the borehole the range of the species, apart from some doubtful, fragmentary specimens at 210 m, is 396 to 417 m.
2. The limestones between these last two depths have yielded a fauna including D. nana, Composita ambigua, Linoprotonia corrugata and abundant Punctospirifer sp.which is comparable with that of the Desoglin and Kingbridge limestones, respectively just below and above the base of the Upper Border Group in the Bewcastle and Brampton districts.
3. Graham (1970, pp. 172–173) noted that below the Upper Liddesdale Group in the Archerbeck Borehole the distinctive brachiopod Lingula lumsdeni is restricted to the Carlyle Beds somewhere between 150 and 250 m above the bottom of the Upper Border Group. In the Stonehaugh Borehole its range is from 116 to 189 m and it is abundant at about 175 m.
4. A comparison of the general distribution of macrofossils in the borehole with those of the Langholm district (Wilson in Lumsden and others, 1967), e.g. of Punctospirifer and Pteronites angustatus, favours a Middle/Upper Border Group boundary at about 400 m.
5. The only limestone in the borehole to yield abundant radially growing algal genera such as Garwoodia and Ortonella is the one at 566 m. The forms it contains are similar to those in the Middle Border Group limestones (including the Dunblar R igg Limestone) in the Middle Shield Borehole of the Bewcastle district.
6. None of the several marker bands in the Lower Border Group Cambeck Beds of the Bewcastle district, nor the Whitberry Band at the top of that formation, has been recognised in the borehole.

Upper Border Group (except the Stonehaugh Borehole)

The Asbian age of the Upper Border Group has been discussed above. The only macrofossils collected during the resurvey which directly support this assignment are Lithostrotion junceum from the Low Carriteth Limestone and Dibunophyllum bourtonense and Gigantoproductus sp.cf. latissimus group from the equivalent Plashetts Dun Limestone. However, from the latter, Westoll and others (1955) have also reported other characteristic Asbian forms: Dibunophyllum sp.and Palaeosmilia cf. murchisoni. Additional direct macrofaunal evidence for the age of the group is provided by the goniatite Beyrichoceratoides redesdalensis from the Redesdale Ironstone Shale indicating a position low in the B, Zone (George and others, 1976, p. 45).

The limestones from the Upper Millerhill up to and including the Leahill contain faunas in which the most common species are Lithostrotion martini, Echinoconchus spp., Pleuropugnoides pleurodon, Productus garwoodi, Punctospirifer sp., Spirifer sp. striatus group, and the two brachiopods assigned by Ramsbottom (in Day, 1970, p. 171) to Buxtonia sp.nov.and Semiplanus sp.nov.These faunas are similar to those from the same limestones exposed along the River Irthing (Day, 1970, pp. 128–129, 299–302) and of the Lewisburn Beds between the Barney's Cut Sandstone and the Old Bridge Limestone in the Kielder district (Fowler, 1966). The Wiley Sike Limestone has abundant colonies of fasciculate Lithostrotion some of which have been referred to L. pauciradiale. They differ from the forms of that species common in the lower part of the Upper Liddesdale Group, however, in that the septa are shorter and have no tendency to dilate in the tabularium. The Leahill Limestone has a particularly rich fauna and yielded a number of molluscan species including Schizodus fragilis, a large form of Naticopsis and some coiled nautiloids.

The marine shales of the Group are characterised by an abundance of the bivalves Aviculopecten murchisoni, A. subconoideus, Leiopteria hendersoni, Phestia attenuata, Pteronites angustatus and Sanguinolites spp., especially S. striatus. Some forms appear to be of local stratigraphical significance and assist correlations across the Antonstown Fault. For example, south of the fault, Aviculopecten, Phestia attenuata and abundant Pteronites angustatus occur in a distinctive faunal sequence in the 5 m of marine shale above the Carriteth (or Bellingham) Coal in both the Low Carriteth and Eals Cleugh boreholes. North of the fault the same fauna was recorded by Fowler (1966, p. 89) above the Plashetts Coal. In both areas these were respectively the highest beds in which Pteronites angustatus was found. An abundance of the same species near the top of its local range was also recorded by Wilson (1961) above the Waverley Coal in the Archerbeck Borehole.

A little higher in the succession, the Low Carriteth and Plashetts Dun limestones mark, in their own areas, the first appearance of characteristic Asbian forms as noted above, and the shales overlying both limestones have yielded the lowest local records of Tornquistia. The bivalve species Leiopteria hendersoni and Aviculopecten murchisoni may also be of some correlative value. The former, common in the shales of the lower part of the group, does not range above the Low Carriteth Limestone in the district. The distinctive spinose Aviculopecten murchisoni is a characteristic constituent of the shales above the Leahill Limestone although it is not restricted to this horizon.

A few metres below the top of the group is the Redesdale Ironstone Shale, which has yielded many type, figured and cited specimens. Lebour (1876) recorded 102 species from these beds and later authors who have described fossils from them include Hind, 1896–1905 (several bivalve species); Lee, 1912 (trepostomatous bryozoa); North, 1920 (Punctospirifer redesdalensis); Muir-Wood, 1928 (productoids); Wright, 1950–1954 (Aphelocrinus dunlopi and Talanteocrinus redesdalensis); Wilson, 1959 (Wilkingia elliptica) and Brand, 1972 (Leptagonia caledonica). The characteristic fauna of the Redesdale Ironstone Shale, in which the commonest species are Fenestella spp., Stenodiscus redesdalensis, Composita ambigua, Leptagonia caledonica, Pugilis scoticus, Punctospirifer redesdalensis, Actinopteria persulcata, Nuculopsis gibbosa, Phestia attenuata and Streblopteria? redesdalensis appears to be of only limited geographical extent: in the present district it does not extend beyond the north-central areas.

Lower Liddesdale Group

The base of the group in this district is drawn at the base of the Redesdale Limestone which, locally, is the lowest bed containing abundant Lithostrotion junceum and the form of Gigantoproductus referred to 'Productus α' by Smith (1910).

The equivalent Piper's Cross Limestone has the same attributes in the upper North Tyne Valley succession. The marine beds in the sequence from the Redesdale Limestone to the Upper Gunnerton Fell Limestone contain a fauna characterised by the presence of the above-mentioned species and Lithostrotian martini, Fenestella cf. oblongata, Penniretepora recticarinata, abundant stick bryozoa, Buxtonia sp.(of Muir-Wood, 1928, pl. 12, figs. 20, 21), Fluctuaria undata, Leptagonia caledonica, Productus redesdalensis, Pugilis scoticus, Pernopecten concentricus and Streblopteria? redesdalensis. Some of these species are also common in the Redesdale Ironstone Shale. This fauna can be recognised locally in the Wood Park Limestone which has previously been considered to be much lower in the succession (Fowler, 1966, p. 103), but is now correlated with the Redesdale Limestone. Elsewhere, elements of the same fauna can be seen in the Naworth Limestone and associated shales of the Brampton district, the Dinwoodie Beds of the Archerbeck Borehole and probably also in the Macgregor Marine Bands of south-east Scotland (Wilson, 1974) although the last also contain some species which in the Bellingham district, do not range as high as the Redesdale Ironstone Shale. All of these strata mark, in their respective areas, the first appearance of varied marine faunas with high Viséan forms. In the past, they have all, either directly or indirectly, been referred to as the lowest beds of D (i.e. Asbian) age. Although the base of the Asbian Stage is now taken to be much lower it seems likely that the arrival of the faunas under discussion was, at least approximately, contemporaneous. Furthermore, the event, most probably a marine transgression, which introduced them to a large area of northern England and southern Scotland, can be expected to have also caused a marked change within the faunas of the Asbian succession in areas to the south. Evidence for an intra-Asbian transgression has already been noted by Ramsbottom (1977, p. 284).

The palaeontology of the Lower Liddesdale Group in the eastern part of the district has been well documented by Frost (1969). In contrast with the Upper Border Group, typical Asbian macrofossils are fairly common. They include Axophyllum vaughani, Dibunophyllum bourtonense, Palaeosmilia murchisoni, Gigantoproductus spp.of the maximus group and Lonsdaleia duplicata melmerbiensis. In Britain south of mid-Yorkshire, Lonsdaleia is found only in Brigantian rocks but in northern England the genus appeared during the Asbian, first in its fasciculate form L. duplicata s.l. and later, but before the end of the Asbian, as the cerioid L. floriformis s.l.

Some characteristic Brigantian fossils such as Diphyphyllum spp.and Lithostrotion maccoyanum were found in the Upper Demesne Limestone near the top of the group. L. maccoyanum was also collected from the Lower Gunnerton Fell Limestone. The transitional nature of late Asbian faunas in northern England has been noted previously by Hudson (1938, p. 312) and Burgess and Mitchell (1976, p. 622).

Algal nodules and encrustations, Lithostrotion junceum, L. portlocki and gigantoproductoids of the G. latissimus and G. maximus groups are common in the limestones throughout the Group. Frost (1969, p. 291) observed that the average number of septa in the corallites of L. junceum is greater in the lower than in the higher limestones of the group and this change was also seen in the specimens collected during the resurvey.

The marine shales associated with the limestones are commonly very fossiliferous, the most abundant forms being Lithostrotion junceum, Fenestella spp., Penniretepora recticarinata, Buxtonia spp., Productus redesdalensis, Rugosochonetes hardrensis group, Aviculopecten interstitialis, Leiopteria spp., Limipecten dissimilis and Sanguinolites spp.The especially rich fauna collected from the limestone and marine shale sequence (= the Lower and Upper Demesne Limestones) between 129 and 142 m in Ferneyrigg Borehole includes Pustula aff. rugata and abundant Productus redesdalensis. Its general composition is comparable with that in the lower part of the Archerbeck Beds between the depths of 1972 ft and 2032 ft 9 inches (601.07 and 619.58 m) in the Archerbeck Borehole (Wilson, 1961, pp. 56–57).

As in the Upper Border Group, brackish water phases are marked by more limited faunas including inarticulate brachiopods, modioliform bivalves, Naiadites crassus and ostracods. A band between the Redesdale Limestone and the Chapelburn Coal in the Greenlee Borehole yielded only ostracods and abundant shells of the non-marine bivalve Naiadites obesus. Authors who have described fossils from the Lower Limestone Group of the district include Brady, 1876 (foraminifera); Smith, 1910 (Productus α);Lee, 1912 (trepostomatous bryozoa); Smith, 1913 (Aulophyllum fungites redesdalense); Weir, 1931 and Longstaff, 1933 (gastropods); and Shiells, 1969 (Kochiproductus cororius).

Upper Liddesdale Group

The Upper Liddesdale Group is equated with the Brigantian stage and the D₂ Zone. The group's stratigraphical palaeontology in the southern part of the district has been described by Johnson (1959). He supported the view, put forward by previous authors including Trotter and Hollingworth (1932), that the base of the D₂ Zone should be drawn at the bottom of what is now called the Low Tipalt Limestone on the grounds that it contains the local equivalent of Garwood's Girvanella Nodular Bed' (1913) and also the characteristic D₂ fossils Lithostrotion maccoyanum and Orionastraea aff. phillipsi. During the resurvey L. maccoyanum was found lower in the local succession and, as pointed out above, the entry of Brigantian faunas, here and elsewhere in northern England, is gradual through several cyclothems. Nevertheless, the Low Tipalt and the overlying Bankhouses Limestone are the lowest in which several Brigantian forms, including Diphyphyllum lateseptatum, Lithostrotion maccoyanum, Dictyoclostus spp.and Gigantoproductus sp. giganteus group, are common. The drawing of the Asbian/Brigantian boundary at about this horizon is supported by the palynological evidence (see p. 60).

Typical Brigantian macrofossils found in the limestones of the group during the resurvey include Aulophyllum fungites pachyendothecum, Dibunophyllum bipartitum, Alitaria panderi, Avonia youngiana, Productus productus and Pugilis senilis. The Bankhouses Limestone yielded a form of Orionastraea with some affinities to O. edmondsi and distinct from that described from the same limestone by Johnson (1959). The Greengate Well and Oxford limestones contain abundant Lithostrotion pauciradiale, characteristic of early Brigantian limestone faunas in northern England. The Oxford is the most prolific of the limestones in the Upper Liddesdale Group of the district and commonly yields a rich 'reefy' fauna with numerous small productoids and gastropods as well as algal nodules.

Several species, most obviously the fasciculate Lithostrotion, disappear in the higher limestones of the Group. A comparison of the horizons at which first Lithostrotion pauciradiale and later L. junceum become rare and then absent in this district with the equivalent levels in the Alston Block succession supports the correlation of the Eelwell and Redhouse Burn limestones with the (Alston Block) Scar and Five Yard limestones respectively. The local distribution of these species is shown in (Figure 27) as are the ranges of the species of the algal genus Calcifolium used by Holliday and others (1975) in support of the same correlations. Evidence relevant to these correlations which might be expected from the gigantoproductoids has not been forthcoming locally. Gigantoproductus spp.of the giganteus group do not appear to be as plentiful in the Brigantian limestones of the district as they are in equivalent horizons on the Alston Block, and forms comparable with the Fourlaws Limestone 'Productus α' continue into the Upper Liddesdale Group. However, the presence of gigantoproductoids, at least closely related to the G. giganteus s.s. of the Alston Block Scar Limestone, in the Eelwell Limestone of north Northumberland is further supported for the correlations proposed by Holliday and others (1975).

The doubtfully foraminiferal genus Saccamminopsis which occurs in large numbers in several Brigantian limestones of the Askrigg and Alston blocks (Hallet, 1970) has been found only in the Four Fathom and Bankhouses limestones during the resurvey. The 2 to 5 mm wide S. fusulinaformis was collected from the former but the Bankhouses Limestone yielded a smaller species with a diameter of about 1 mm. A similar small form of Saccamminopsis has been recorded in the late-Asbian Robinson Limestone of the Brough district (Pattison in Burgess and Holliday, 1979).

Few fossils have been collected from the shales of the group in the course of the resurvey and most of these are from boreholes. The commonest forms are Rugosochonetes spp.of the celticus group.

Stainmore Group

The position of the Dinantian/Namurian boundary in northern England is based largely on evidence presented by Johnson and others (1962). They recorded Cravenoceras leion, which is the diagnostic goniatite of the basal Namurian marine band, in shales above the Great Limestone at Greenleighton, a few kilometres north-east of the Bellingham district. As a result of this and other goniatite finds the bottom of the Namurian is known to lie between the Four Fathom and Great limestones, and for mapping purposes is taken at the base of the latter.

Few Namurian fossils have been collected during the resurvey and only from the Great and Little limestones and the shales above the former. The presence of three biostromes in the Great Limestone was noted by Johnson (1958). Two of these can be seen at Brunton Bank Quarry in the south-east corner of the district. The Chaetetes Band in the bottom 1.5 m of the limestone there, has a rich macrofauna including abundant Chaetetes depressus, Diphyphyllum lateseptatum and Lonsdaleia floriformis laticlavia. The Brunton Band is about 4.5 to 8.5 m higher and contains the alga Calcifolium okense. The third biostrome described by Johnson, the Frosterley Band which is a coral/brachiopod bed with abundant Dibunophyllum bipartitum near the top of the limestone, is not found in the district. However, individual specimens of D. bipartitum are scattered in the equivalent part of the limestone at Brunton Bank Quarry.

The shales above the Great Limestone at Fourstones contain a largely brachiopod fauna in which Rugosochonetes cf. celticus and Spirifer cf. bisulcatus are common. The Little Limestone at Newtown Quarry, Fallowfield, has yielded a number of brachiopod species including Quasiavonia aculeata and the shales above that limestone in the Dilston Water Borehole a few kilometres south of the district, were found to contain Productus spp.and the bivalve Streblopteria ornata, a species which is abundant in the lower Namurian strata of central Scotland.

Ostracod faunas (J. E. Robinson)

History of ostracod studies

In the late 19th century numerous ostracods from the Bellingham district were described by Jones and Kirkby (1886a, b) and Jones and others (1884). Many of these specimens, from localities collectively called 'Warksburn' or 'Ridsdale', were obtained during the primary survey. The interest then was primarily in new and undescribed genera and species, with the aim of adding to the total count of Carboniferous fauna, rather than an assessment of the stratigraphical usefulness of ostracods for correlation. Indeed, it was not until the years 1951–53 that such possibilities were examined, when the present author sought to employ ostracod faunas in an analysis of Upper Border Group stratigraphy of the Falstone and Kielder area in the upper reaches of the North Tyne valley. It emerged from that work that three ostracod associations could be recognised in the Upper Border Group:

1. A rich and varied lower fauna from the Lewisburn, Plashetts and Whickhope B urn areas.
2. A middle fauna closely associated with marine limestones and shales (the Old Bridge Limestone and Plashetts Dun Limestone horizons).
3. An upper fauna in which the elements of the lower returned, but with recognisable species differences allowing its distinction.

Subsequent work, including that undertaken for this memoir, has broadened the extent of similar Upper Border Group faunas, and added a further time extension in the inclusion of the Liddesdale Group. From a wider consideration of the successions of the north of England and Scotland, it emerges that the continuous Yoredale-type facies of the North Tyne succession clearly affords one of the best standards for faunal sequences of the Asbian, Brigantian and Pendleian stages.

Ostracod occurrence and possible palaeoecological conclusions

Throughout the succession, ostracods are found in a wide variety of mudstone lithologies representing several environmental facies, the most important of which can be termed carbonaceous, ironstone, and marine. Of these, the first two are characterised by high numbers of specimens, often visible to the naked eye as bedding plane spreads, but with only a limited number of species. For the 'carbonaceous facies' common species are 'Carbonita' fabulina, Cavellina attenuata, Cavellina extuberata, Glyptolichvinella spiralis and species of Shishaella [Paraparchites auct.]. This facies offers the greatest abundance of ostracods to the field collector, usually in a roof shale to a coal seam, or from shaly lenses within seatearths. Commonest in the Upper Border Group, this facies fauna occurs also in the Liddesdale and Stainmore groups with but little change in composition. In living ostracod ecology, in addition to favourable salinity, temperature and substrate, the presence of vegetation either as living algae or waterlogged detritus accumulations is regarded as of prime importance, providing both shelter and nourishment for thriving populations. Similar conditions are envisaged for the 'carbonaceous facies' fauna. The slow evolution rate apparent for the species involved, make the facies fauna of limited stratigraphical use.

For the ironstone facies, common species are Acutiangulata aequalis, Cavellina cf. subovata, Sansabella amplectans and Shishaella [Paraparchites] sp.Generally there are fewer species than in the carbonaceous facies, but the number of individuals can be high. The close association of the fauna with clay-ironstone nodules or ferruginous limestone bands, seems adequate evidence for a primary iron-rich pool environment. Once again, this facies fauna is of little value in correlation.

Marine facies faunas are recovered from mudstones closely associated with limestones or from those bearing typical marine macrofauna such as camarotoechoids, productoids or spiriferoids. Characteristic ostracod genera include Amphissites, Bairdia, Beyrichiopsis, Cavellina, Glyptopleura, Healdia, Kirkbya, Knoxiella and Scrobicula. Such diversity of assemblage is characteristic of modern shallow-water, offshore environments. There may be several different ostracod faunas at any one horizon sampled along strike; a situation paralleled in modern nearshore ecology.

Marine faunas from the Upper Border Group are more varied than those from the Liddesdale Group. This may result from the greater abundance of vegetation detritus during Upper Border Group sedimentation, a factor favouring ostracod diversity, whereas the strongly rhythmic Liddesdale sedimentation was less generally favourable. Several Upper Border Group genera do not continue into the Lower Liddesdale Group. More important, however, is the high rate of evolution of marine species through time. In this facies it is possible to chart the vertical range of species of genera such as Bairdia or Kirkbya and so distinguish Upper from Lower Liddesdale strata (Figure 28).

In the marine facies ostracods are seldom visible upon bedding planes or broken surfaces, so that collecting is based upon the recognition of lithologies which have proved successful from previous experience. Even so, samples may be poor in fauna, with success as low as 30 to 40 per cent. Tough, indurated and unweathered material may also present problems in preparation, and is one reason for disappointing results from borehole cores. Best results come from partly weathered material from surface outcrop.

The ostracod faunas of the Bellingham district record the following sequence of events. During Upper Border Group sedimentation the area was one of diverse palaeogeography, with lagoonal and brackish-water swamps expanding from time to time (the carbonaceous and ironstone facies), and at other times inundated by marine transgressions of variable strength and extent. In the Lower Liddesdale Group, the rhythm of transgressions became more pronounced and widespread in their effect. This pattern was continued in the Upper Liddesdale Group. Above the Great Limestone, the cyclothems became more arenaceous and the ostracod faunas are accordingly poorer.

Faunal sequence

Upper Border Group

The Middle Border Group and the lower part of the Upper Border Group do not crop out within the district. These beds were proved in the Stonehaugh Borehole but samples obtained from the lower cores were too indurated to provide useful faunas.

North of the Antonstown Fault three ostracod faunal assemblages have been recognised in the Upper Border Group. The highest of these has also been recognised widely in the area to the south but more work is required to determine fully the extent of the others. The lowest assemblage was obtained from Smales Burn and (outside the district) from the Lewis and Whickhope burns. Typical species include Amphissites whickhopensis, Beyrichiopsis fimbriata, B. subdentata Cavellina attenuata, C. longula, C. cf. parallela, Glyptopleura berniciana, Kloedenellitina berniciana, Knoxiella robusta, Monoceratina antiqua and Sulcella affiliata. The fauna is characterised by the abundance and variety of cavellinids, followed by lesser numbers of beyrichiopsids, glyptopleurids and knoxiellids.

A change in ostracod fauna is associated with the increasingly marine character of the succession commencing with the Alpha Limestone of Lewisburn, continuing with the Old Bridge Limestone, and completed with the Plashetts Dun Limestone of Falstone. Typical assemblages include Bairdia submucronata, Cavellina cf. glandella, Glyptopleura sp., Healdia cornigera early variants, Jonesina fastigiata, Rectobairdia cf. lecta, Scrobicula indistincta and Seminolites porosus.

In another review of fauna of this age (Robinson, 1978), Jonesina fastigiata was chosen as nominate zone fossil for the lower Asbian Stage (=Upper Border Group).

The upper part of the Upper Border Group shows a return to the mixed facies environments which had characterised the lower part of the Group. There are more frequent coals and ironstones, and fewer limestones. A consequence is the return of genera and faunal associations already described for the earlier period, but with morphological features which suggest evolution of new species, and whereby the younger fauna can be distinguished. As examples of these differences, Beyrichiopsis fimbriata (Plate 9)18a & 18c shows stronger flank costae than earlier variants of the species; Sulcella affiliata and several species of Cavellina show the development of a pointed posterior prominence to their valve outline. These differences have not yet been fully examined to substantiate the idea of new species, but the differences are clearly recognisable. These forms apart, the higher beds also include as new species Beyrichiopsis simplex and Libumella cribrosa.

Good faunas of this age are available from the outcrops north and south of Middleburn [NY 792 750], from the strike section in Warks Burn between Warksburn Bridge and Longlee, commencing [NY 857 764], and from the stream draining John Side, Tarret Burn [NY 807 885], just beyond the northern margin of the district.

Lower Liddesdale Group

A substantial change in ostracod fauna occurs just below the base of the Redesdale Limestone, which marks the base of the Group. To some extent this change is a reflection of the change from Upper Border Group irregular rhythms to the Yoredale-type facies above the Redesdale, and the virtual disappearance of the carbonaceous and ironstone assemblages which provided much of the faunal character to the Border Group. Nevertheless, if only the marine assemblages are considered, there are noticeable genus and species substitutions. Genera which disappear include Acutiangulata, Beyrichiopsis, Glyptopleura, Kloedenellitina and Knoxiella. New genera include Bairdiolites, Birdsalella, Knoxina and Shivaella. Other genera which show the development of new species include, Amphissites, Bairdia, Kirkbya, Libumella, Monoceratina, Scrobicula, Silenites and Sulcella (Sohn, 1960, 1961). There is a considerable increase in the number of bairdiids in any assemblage, ranging from small, neat, early Bairdiolites species through the elongate Bairdia lecta (Plate 9)14, to the large Pustulobairdia confragosa (Plate 9)11. This last species could serve as a key to the recognition of Lower Liddesdale strata, along with Coryellina ventricornis which shows an acme in its occurrence at this level. In the Kielder and Elsdon districts a similar faunal change takes place near the level of the Piper's Cross Limestone, supporting the correlation of that limestone with the Redesdale Limestone.

Within the Lower Liddesdale Group of the Bellingham district, there is a marked increase in ostracod fauna towards the top of the group, at about the horizon of the Ladies Wood and Demesne limestones. At this level appear Bairdia orientalis, Healdia penchfordensis (Plate 9)10, Knoxina spinosa, Phlyctiscapha berniciana and Rectobairdia hopeshieldensis. This is essentially the fauna of the Penchford Limestones of the Elsdon district, but also has correlation potential for comparisons with the Dun and Woodend limestones of north Northumberland and the upper part of the Melmerby Scar Limestone of the River Gelt section of the Brampton district. In view of the varied lithologies from these localities, this faunal similarity suggests a strong case for the use of ostracods in faunal stratigraphy. However, it should be noted that a particular fauna is seldom confined to one horizon, but links together successive Yoredale units (e.g. Ladies Wood–Lower and Upper Demesne limestones).

Representative faunas can best be collected from the Broomhope valley [NY 895 834], Simonburn Bridge [NY 873 737] and Gunnerton [NY 906 754].

Upper Liddesdale Group

With the onset of more typical Yoredale patterns of sedimentation, corresponding changes occur in the ostracod faunas of the marine facies. The younger faunas include Berdanella, Birdsalella, Bolbozoella, Coryellites, Cribroconcha (Plate 9)6 and Incisurella. Incoming new species are, Amphissites cf. centronotus, Cribroconcha insculpta, Cribroconcha perplexa (Plate 9)6, Kirkbya quadrata (Plate 9)8, Sansabella cf. bella and Sulcella cristata.

The Upper Liddesdale Group can be subdivided on the basis of gradual faunal change and the arrival of new ostracod species. The Bankhouses, Oxford and Barrasford limestones have similar faunas which can be separated from those of the Bath-House Wood, Eelwell, Three Yard and Four Fathom limestones. These latter limestones together contain ostracod assemblages characterising the P₂ goniatite Zone, a fauna marked by the acme of Bairdiolites elevatus, Cribroconcha perplexa, Kindlella bituberculata, Kirkbya quadrata (Plate 9)8, Shleesha oblonga and Sulcella cristata.

If the Lower Liddesdale Group is characterised by an abundance of Bairdia species, the Upper Group by contrast shows the dominance of healdiids (Coyellites, Cribroconcha, Healdia and Incisurella). Best exposures are to be found in Crook Burn [NY 858 722], Teppermoor [NY 856 717] and Moss Kennels [NY 893 691].

Stainniore Group

Many genera present in the Liddesdale Group continue into the Stainmore Group, but at a species level there are significant changes. New genera include Asturiella (Bless in Van Arneton, 1970) and Knightina. New species and the acme for previously recorded species include Asturiella cicatricosa (Plate 9)4, Bairdia beedei, Cavellina benniei (Plate 9)2, Coryellina reticosa, Cribroconcha inflata (Pate 9)1, Editia hieroglyphics and Incisurella concinna. This fauna is characteristic of the Great Limestone of south and central Northumberland. Similar faunal changes have been recognised in the Midland Valley of Scotland, West Cumberland, the Pennines, North Midlands and North Wales successions.

Typical faunas of the Great Limestone and basal Stainmore Group can be collected from the quarries at Fourstones [NY 887 688], Brunton Bank [NY 929 700] and Cocklaw [NY 938 703].

Miospore assemblages (K. J. Gueinn)

Miospore assemblages have been recovered from 80 surface and borehole samples from the Bellingham district. Based on a composite section, the ranges of selected miospore species have been plotted in (Figure 29). The distribution of these closely follows that observed by Neves and others (1972, 1973) in the Lower Carboniferous of the Midland Valley of Scotland. Thus it has been possible to apply the scheme of miospore zonation proposed by them to the Bellingham district and to make correlations on a regional scale.

In addition to the samples referred to above, miospores have been recovered from a further 65 samples obtained from scattered localities within the Bellingham district, the exact stratigraphical horizon of which were uncertain. By comparison with the distribution of miospore species observed in the composite succession, local correlations have been suggested.

Lycospora pusilla (PU) zone

Floras assignable to the Pu Zone were collected from below 286 m in the Stonehaugh Borehole. Spores of the genus Lycospora occurred in large numbers throughout, thereby precluding an assignment even of the oldest strata in the borehole to the Schopfites claviger–Auroraspora macra (CM) Zone. The samples were relatively impoverished in the number of species which they contained compared with those from the succeeding Perotrilites tessellatus–Schulzospora campyloptera (TC) Zone. Few species were recorded which did not also occur in the TC Zone and in general the assemblages from this interval were characterised by the absence of species which are generally present in the TC Zone of other areas of northern England and Scotland. However, the infrequent occurrence of species not recorded above the Pu Zone in the neighbouring Bewcastle district, i. e. Schopfites claviger, Crassispora trychera and Astulatisporites multicapitis tend to confirm a Pu Zone assignment for this interval, and furthermore their infrequency of occurrence suggests a position near to the upper limit of their ranges and therefore to the upper part of the Pu Zone.

Perotrilites tessellatus–Schulzospora campyloptera (TC) zone

The base of the zone is taken at a depth of 280.42 m in the Stonehaugh Borehole and is here marked by the first appearance of the genus Schulzospora. Above this level the genus is a consistent member of the microflora, occurring in 15 of 19 samples assigned to the TC Zone. A progressive increase in the variety of the microflora occurs upwards from the base of the zone with many characteristic zonal species appearing (Figure 29). These include Verrucosisporites baccatus (Plate 10)6, Perotrilites tessellatus (Plate 10)21 and Waltzispora planiangulata (Plate 10)1.

The Stonehaugh Borehole provides a continuous sequence across the boundary between the Pu and TC zones and represents the only such sequence so far described from northern England and Scotland, apart from Marshall Meadows Borehole in north-east Northumberland (Neves and others, 1973).

In a study of the distribution of miospore species in the Bewcastle district, the oldest assemblages recorded from the Middle Border Group were from the base of the section measured in the River Black Lyne, north of the Dappleymore Fault (Day, 1970, p. 297) approximately 65 m below the top of the group. These contain many species characteristic of the TC Zone, which have not been recorded in the youngest assemblages assigned to the Pu Zone from approximately 30 m above the base of the Middle Border Group in Whitberry Burn, i.e. Schulzospora spp., Crassispora aculeata (Plate 10)8, Perotrilites tessellatus, Verrucosisporites baccatus, Densosporites intermedius, Umbonatisporites variabilis and Waltzispora planiangulata.

According to Day (1970, p. 82) the Middle Border Group is some 300 m thick in this area. The oldest TC Zone flora and the youngest Pu Zone flora are separated therefore by approximately 200 m of strata. The horizon taken as the base of the TC Zone in the Stonehaugh Borehole must therefore lie within this interval.

Neves and Williams in Day (1970, pp. 172–175) recorded assemblages from Upper Border Group strata exposed in the River Irthing. These were from coals and shales near the base of the Crammell Linn Sandstone and from a coal and its roof shale between the Lower and Upper Millerhill limestones. These assemblages are comparable to those recorded from the upper part of the Stonehaugh Borehole.

The stratigraphically lowest surface samples examined from the Stonehaugh area (SAL 2000, 2562, 4228 and 4229) (Figure 29), about 18 m above the Spy Hole Limestone, are characterised by the association of Tripartites distinctus (Plate 10)11 and (Plate 10)12 and Acanthotriletes acritarchus (Plate 10)7. In the interval between the Appletree and Low Carriteth limestones the following species appear (Figure 29): Remysporites magnificus, Diatomozonotriletes fragilis, Ahrensisporites duplicatus (Plate 10)13, Kraeuselisporites echinatus, ?Apiculatisporis porosus (Plate 10)3, Potoniespores delicatus (Plate 10)9, and Cribrosporites cribellatus (Plate 10)22. The association of T. distinctus and A. acritarchus was also observed from the Chirdon Burn section (sample SAL 4151) a few metres above the Appletree Limestone. Williams (1971) recorded similar TC Zone assemblages from below the Thirlwall Coal and in the Archerbeck Borehole from a horizon about 10 m below the Burns Beds. This distinct association in the south-western part of the Northumbrian Trough appears to be a potentially valuable means of correlation.

Only a few samples from outcrops north of the Antonstown Fault have been examined. Microfloras containing T. distinctus, indicative of a high TC Zone age, have been found below the Plashetts Coal and near to the Thorneyburn Limestone. At the latter horizon ?A. porosus and P. delicatus were also noted. Only meagre floras were obtained from the Lewisburn section (Figure 13), col. 1 (Fowler, 1966), but the occurrence of P. delicatus, 8 to 9 m above the Barney's Cut Sandstone, T. distinctus and D. fragilis, 4 m below the Alpha Limestone, and C. cribellatus, 9 m above the Old Bridge Limestone, suggests that most of the beds exposed there are also of high TC Zone age.

Raistrickia nigra–Triquitrites marginatus (NM) Zone

Three palynological associations can be recognised in the strata assigned to this zone.

The oldest one was recorded from sample SAL 4214, 2 m above the Low Carriteth Limestone. Appearing at the base of their ranges at this level were Monilospora mutabilis (Plate 10)20, Densosporites cf. velatus and Murospora parthenopia (Plate 10)15. Raistrickia nigra (Plate 10)4 and Dictyotriletes pactilis first appear in sample SAL 4220 from the Warks Burn section at a horizon approximately equivalent to the Furnace Coal. Triquitrites marginatus, the other zonal index species of the NM Zone, first appears above the Furnace Coal in sample SAL 1991. Monograptus mutabilis and D. cf. velatus have a very limited range from the Low Carriteth Limestone to the Fourlaws Limestone.

Assemblages suggestive of a horizon close to the base of the NM Zone have been recorded by Collins (personal communications in Neves and others 1972) from near the Plashetts Dun Limestone in the Elsdon district. This supports the correlation of this limestone with the Low Carriteth Limestone of the Bellingham district and the correlation of the Piper's Cross Limestone with the Redesdale Limestone (p. 22).

Assemblages containing the distinctive association of Monograptus mutabilis and D. cf. velatus together with the index species of the NM Zone are also known from the East Lothian region where they have been recorded from strata associated with the Cove Upper and Lower limestones (Clayton, 1972) and from the Spilmersford Borehole at depths of 120.4 and 123.4 m (Neves and Ioannides, 1974, p. 84) from marine strata named the Tynehome Beds by Davies (1974). This lends support to the correlation proposed by Wilson (1952) of the Upper and Lower Cove marine bands with the Redesdale Limestone and Ironstone Shale respectively. Wilson (1974, p. 46–47) preferred to regard the Redesdale Limestone and Ironstone Shale as general correlatives of the MacGregor marine bands, which include the Cove marine bands.

In the interval between the Fourlaws Limestone and Fourlaws Coal several relatively short ranging species die out, i.e. T. distinctus, A. duplicatus, D. fragilis, P. delicatus and Monograptus parthenopia (Figure 29).

The second palynological association occurs between the Fourlaws Coal and the Upper Gunnerton Fell Limestone and is recognised mainly on negative features, i.e. the absence of the species just mentioned and the diagnostic species of the succeeding association.

The base of the third association is marked by the first appearance of Murospora margodentata (Plate 10)19 at the level of the Upper Gunnerton Fell Limestone (SAL 1983). The incoming of this species below the VF Zone is a feature which has been recognised both in the Archerbeck Borehole (Williams, 1971) and the Midland Valley of Scotland (Neves and others, 1973).

Tripartites vetustus–Rotaspora fracta (VF) Zone

The oldest assemblage assigned to this zone is from sample (SAL 1985), from a shale parting in the Bankhouses Limestone. This marks the base of the range of T. vetustus (Plate 10)10, T. nonguerickei, Crassispora maculosa and Diatomozonotriletes cervicornutus (Plate 10)17. Monograptus margodentata ranges up from the preceding zone and is present in the youngest sample (SAL 2069), a short distance below the Greengate Well Limestone. This overlap of the range of Monograptus margodentata with species of the VF Zone has also been recorded in the Midland Valley of Scotland (Neves and others, 1973).

Marshall and Williams (1971) described the distribution of miospore species across the Viséan–Namurian boundary in the Roman Wall area in the south of the Bellingham district. They recorded species considered by Neves and others (1973) to first occur within the VF Zone, e.g. Crassispora maculosa and Grandispora spinosa from a shale at the level of the Bankhouses Limestone. T. vetustus and T. nonguerickei were recorded from slightly higher in the sequence. These results are in agreement with those of the present study.

They recorded the first occurrence of Cingulizonates cf. capistratus from near the Redhouse Burn Lower Limestone. This species is common in the Bellispores nitidus–Reticulatisporites carnosus (NC) Zone. However, since only one sample was examined between the Scar (Bath-House Wood) Limestone and the Four Fathom Limestone, the boundary between the VF and NC Zones in the Bellingham district cannot be placed precisely at present.

Chapter 7 Intrusive igneous rocks

General account

The Carboniferous rocks of the district are intruded by two groups of basic igneous rocks. The most important of these is the Whin Sill quartz-dolerite sill-complex and associated east-north-east trending dykes of late Carboniferous or early Permian age. There are also a number of east-southeast trending tholeiite dykes of Tertiary age. The term 'tholeiite' is used here solely in the petrographical sense of a dolerite or basalt with glassy mesostatis; the usage is conventional in this region.

Whin Sill and related dykes

Quartz-dolerite sills belonging to the Whin Sill suite (Holmes and Harwood, 1928; Fitch and Miller, 1967), intruded into Upper Liddesdale Group strata, form a crescent-shaped crop across the southern and eastern parts of the district. Dykes of similar chemical and mineralogical composition, broadly trending towards the east-north-east or north-east, are associated with the sills. Work outside the district has established that the Whin Sill is of late Carboniferous or early Permian age (Holmes and Harwood, 1928). This conclusion is supported by isotopic age determinations using the potassium-argon method, including samples from the present district, which suggest that the age of the sill-complex is around 295 million years (Ma) (Fitch and Miller, 1967; Wadge and others, 1972).

Early workers in the district regarded the Whin Sill as eruptive lava contemporaneous with the adjacent sediments (Hutton, 1832; Phillips, 1836), and they did not accept the clear evidence for an intrusive origin demonstrated by Sedgwick (1827) in Teesdale. An intrusive origin for the Whin Sill of this and adjacent districts was recognised by Tate (1867a, b, 1870) and became widely accepted following the work of the primary survey (Topley and Lebour, 1877). Details of many important exposures are given in these papers and also those by Weyman (1910), Johnson (1959) and Randall (1959a). Over large areas the stratigraphical horizon at which the sill is intruded does not vary greatly, though there are many local small changes. Elsewhere there are sudden shifts in horizon and the contacts are highly discordant. Johnson (1959, p.92) considered that these transgressive steps are probably coincident with faults but Randall (1959a, p. 390) observed true transgressions as well as faulted contacts. It is probable that some of the faulting occurred penecontemporaneously with intrusion. In the south of the district the sill has a lenticular form, and in the east, dolerite has been intruded at more than one level. The maximum proved thickness in the district is 67.67 m at Carr Edge West Shaft. It is probable that the Whin Sill was fed by the associated dykes but the relationship between the two can nowhere be demonstrated.

General petrological and chemical accounts of the Whin Sill suite include those by Teall (1884b), Holmes and Harwood (1928) and Smythe (1930). The latest review is by Dunham (1970) who also (1972) contributed to a study of pyroxenes in the dolerite. Typically the Whin Sill dolerite is composed of plagioclase feldspar (48%), clinopyroxene (29%), iron-titanium oxides (7%), with small amounts (totalling 11%) of orthopyroxene, pseudomorphs after olivine, chlorite, amphibole, carbonates, sulphides and apatite. In addition most rocks carry some phenocrysts (5%) of plagioclase, clino- and orthopyroxene and pseudomorphs after olivine. There are also interstitial areas with quartz and alkali feldspar. The maximum grain size is about 2 mm. Both sills and dykes become fine-grained towards their margins where the rock is generally a black tachylite. In parts of the district the dolerite is cut by thin hydrothermal veins (quartz-calcite-pyrite) dating from the final stages of the sill's emplacement. In boreholes at Swinburne Quarry, tongues of fine-grained basalt with chilled margins are associated with these veins and also intrude the dolerite (see also Smythe, 1930, p. 102). Amygdales are particularly common between Barrasford and Swinburne quarries. For the most part these are filled or partly filled by quartz and calcite, but Randall (1959b) has described examples carrying the zeolite mineral pectolite, and also stevensite, a montmorillonite group mineral.

Adjacent to hydrothermal veins the dolerite is sometimes altered to a white clay-carbonate rock, 'white whin'. Rock of this type at Settlingstones Mine has been studied by Ineson (1972). Locally the contact rocks of the sill, adjacent to highly carbonaceous country rocks, have undergone a similar alteration.

Pockets of deeply altered Whin Sill are present in several quarries in the North Tyne valley. The zone of alteration is usually underlain by fractured or faulted dolerite. Thin sections of the altered dolerite show that the ferromagnesian minerals have been changed into clays and also show evidence of shearing. Hornung and Hatton (1974) have described highly altered dolerite from various localities in northern England which they consider to have resulted from in situ tropical or sub-tropical weathering in Tertiary times.

The country rocks adjacent to the sills and dykes have been variously subjected to thermal metamorphism (Hutchings, 1898; Robinson, 1970). Sandstones are converted to quartzite; argillaceous rocks become spotted and are converted to smooth porcellanous whetstones; and limestones locally become saccharoidal, notably those with the lowest carbon content (Randall, 1959a; Robinson, 1971). Many new minerals have been formed in the impure limestones, e.g. idocrase, grossularite.

Details

Whin Sill

Some of the finest scenery of the district occurs along the Whin Sill outcrop between Steel Rigg [NY 759 677] and Sewingshields Crags [NY 808 703] (Plate 1). The scarp face of the Whin Sill at these places and Highshield Crags [NY 7440 6785], Peel Crags [NY 7560 6765], Hotbank Crags [NY 7770 6855], Cuddy Crags and Housesteads Crags [NY 7840 6870] often exceeds 30 m in height. In this area the sill is intruded into the Shotto Wood Limestone with which it forms, for several kilometres, a composite dip-slope along which the vegetation on the two differing rock types contrasts sharply in both colour and variety. In Sewingshields Crags [NY 8030 7015] the excellent columnar jointing causes the rock to weather out into isolated trapezoid pinnacles at the top of the crags.

The sill changes horizon to the Bath-House Wood Limestone at Busy Gap [NY 795 695] near Housesteads Fort. Johnson (1959, p. 92) considered that such transgressive steps probably coincided with faults, but the present survey was unable to confirm this.

Randall (1959a, p.390) discussed the same problem in the Barrasford area and observed the presence of both faulted contacts and true transgressions. In the absence of visible connection between sills he considered them as a series of individual units intruded at different levels. He concluded that faulting does control the shape of some of the outcrops but that there is no evidence to indicate whether faulting is pre-intrusion, the Whin magma having stepped along existing fault planes, or whether it is post-intrusion, so that the sill is actually faulted. It is possible however that some if not all the faulting occurred penecontemporaneously with the intrusion.

A raft, 2 m thick, of baked Bath-House Wood Limestone is exposed towards the base of the scarp [NY 8114 7041] near Sewingshields Castle. The Bath-House Wood Limestone rests directly on the Whin and with it forms a composite dip-slope for 2 km along strike. A transgression is assumed to occur in the drift-filled hollow west of Shield on the Wall [NY 823 705], for on Brown Moor the sill rests directly on a sandstone higher in the Bath-House Wood cyclothem.

The Whin Sill is exposed in Settlingstones Burn [NY 8510 6887] overlain by the Shotto Wood Limestone (here partly saccharoidal) and by associated spotted whetstones. A thickness of 47 m of dolerite was proved in the nearby workings of Settlingstones Mine and a similar thickness at the same horizon in the Stonecroft Pumping Shaft [NY 8544 6891]. At Greyside Shaft [NY 8587 6906] the Whin Sill, 55 m thick, is intruded just below the Bath-House Wood Limestone. This horizon is maintained towards the north-east in the Carr Edge West Shaft [NY 8802 7006], where the Whin Sill is 67.67 m thick.

Limestone contact rocks in the neighbourhood of Greyside Cottages appear to show the inhibiting effect of a high carbonaceous content on metamorphism that was commented on by Randall (1959a). A carbonaceous biomicrite (E47906) [NY 8521 6885] shows comparatively little alteration compared with the distinctly granoblastic texture, with pyrite and phyllosilicate mineralisation, shown by a less carbonaceous limestone (E47908) from the same area [NY 8514 6885]. A mudstone occurring between these two localities [NY 8517 6884] is metamorphosed to a conspicuously spotted hornfels (E47907). The spots are euhedral pseudomorphs after probable porphyroblastic interpenetration twins of cordierite (but see also p. 66) and traces of its characteristic sectorial twin pattern are still preserved in the mainly six-sided pseudomorph sections. The remainder of the rock consists of abundant formerly bioclastic fossil pseudomorphs set in a microcrystalline groundmass made turbid by abundant opaque granules. Thin-section examination and X-ray diffraction analysis (NEXD1046) indicate that the cordierite porphyroblasts and fossil remains have been replaced by kaolinite, smectite, calcite and ankerite intergrowths with minor opaque accessories; the carbonate minerals are more abundant in the fossil remains. The predominant mineral in the microcrystalline matrix is plagioclase with some smectite and kaolinite, but the X-ray data gives no indication of the opaque mineral which is therefore inferred to be 'amorphous' carbon. The apparent total absence of quartz from this rock is unusual and worth special mention.

On Teppermoor Hill [NY 876 714] dolerite forms a strong scarp feature and broad dip-slope, but diminishes in thickness to the east near Black Carts [NY 8870 7137]. The thin sills associated with the Bath-House Wood Limestone near Barrasford may be the featheredge of this sill. 'White Whin', 0.32 m thick, underlies the Lower Bath-House Wood Limestone [NY 9238 7260] and 1.10 m of dolerite underlies the Upper Bath-House Wood Limestone [NY 9239 7254] in the River North Tyne. This latter sill can be traced some distance northwards. Possibly related sills are intruded into the Colwell Limestone in Swin Burn [NY 9276 7359] and were formerly seen north of Chollerton [NY 9330 7283] in the sandstone below the Eelwell Limestone.

Another sill, lensing out to the west, is seen near Sharpley [NY 8765 7229]. It is at least 25 m thick at Keepershield Quarry [NY 894 728] and transgresses from a horizon near the Barrasford Limestone to below the Oxford Limestone.

In the northern part of Keepershield Quarry [NY 8940 7230] the base of the Whin Sill has been proved to rest on a fine, greenish grey, baked sandstone above the Oxford Limestone. A trial borehole of 10 m or so, drilled from the same level in the quarry floor in the southern part of the excavation, failed to bottom the sill suggesting an abrupt downward change of horizon or a thickening of the sill. Shatter-zones up to 5 m wide were observed in this quarry along near-vertical faults with 5° to 20° hade. The dolerite in these zones has been altered to a soft yellowish brown clay to a depth of at least 20 m from surface. Hornung and Hatton (1974) attribute this kind of alteration of the Whin Sill to late Tertiary tropical or sub-tropical weathering, and such a process would be most active where numerous fracture planes provide easy access for water. A glacial drainage channel closely follows one fault-zone, which is a natural line of weakness.

The crop of the Whin Sill crosses the River North Tyne at Kinglish Crags [NY 9076 7311] where it may be intruded below the Greengate Well Limestone. Nearby, the sill was said to be only 3 m thick in exposures on the line of the dismantled railway [NY 909 740].

A sample of the thin sill exposed near Chollerton [NY 9239 7254] is a coarse basalt with abundant devitrified glassy mesotasis. The composition of the oscillatory zoned plagioclase is typical of normal 'Whin', there are three varieties of optically distinct pyroxene present and some calcite-phyllosilicate pseudomorphs after olivine. The most abundant pyroxene is common augite but some crystals are in structural continuity with cores of pigeonite and the augite also locally forms rims to occasional prismatic crystals of hypersthene. The predominant opaque accessory mineral is magnetite. A sample (E47914) of the metasomatised thin 'White Whin' sill collected nearby [NY 9235 7253] has a similar texture and probably had a similar original composition although all the ferromagnesian minerals, the mesostasis and part of the plagioclase have been replaced by carbonate and chlorite. Most of the opaque oxide is leucoxenised although some fresh runic patches remain unaltered.

To the north, in the workings of Barrasford Quarry [NY 914 746] about 30 m of dolerite are exposed, overlain by the Oxford Limestone which is locally saccharoidal, containing grossularite garnet and idocrase (vesuvianite) (Smythe, 1950; Randall, 1959a), though generally fossils are still recognisable. Spotted whetstones on top of the limestones were also noted. The Whin Sill transgresses to levels above the Oxford Limestone towards the north-east. At Toddle Crags [NY 9135 7500] the sill, some 15 m thick, has cut across the Oxford Limestone which can be seen as a series of isolated mostly horizontal rafts which step down from the top to the bottom of the sill when traced from the south-west to the north-east respectively (Weyman, 1910; Randall, 1959a). Many of the features in the quarry described by Randall have been removed. In this area Randall (1959b) has described a variety of amygdale-like structures. One type is filled with quartz and calcite and others, related by Randall to late stage enrichment of Ca and Mg in the residual phases of the Whin Sill magma, contain stevensite, pectolite, chlorite, calcite and pyrite.

The dolerite at Barrasford Quarry [NY 914 746] is normally a fairly fresh variety lacking any significant smectite. It contains typical zoned plagioclase and two optically distinct pyroxenes, augite and pigeonite, the latter being subordinate and distinctly prismatic in habit. Accessory interstitial quartz is accompanied by hornblende and in this respect the Barrasford material differs from that worked at Kirkwhelpington Quarry [NY 99 85] where biotite occupies an analogous position in the fabric. At Kirkwhelpington the pigeonite is less distinctly prismatic. In both quarries the otherwise fresh normal dolerite shows late stage hydrothermal partial replacement of pyroxene by chlorite and calcite.

At Barrasford Quarry (see also Randall, 1959a) samples were taken of the contact rocks where, against the Oxford Limestone [NY 9164 7463], the Whin Sill is chilled, metasomatised and locally autobrecciated. The texture is that of a microporphritic basalt with microphenocrysts of plagioclase and subordinate ferromagnesian minerals set in a cryptocrystalline groundmass. The adjacent limestone is altered to calc-silicate hornfels and marble, generally coarser in grain size than the unaltered rock. Locally the chilled 'Whin' is in immediate contact with altered sediments, apparently without having undergone alteration other than chilling e.g. (E47176), but thin section and X-ray diffraction analysis (NEXD1155) indicate that although the macro-texture is that of a porphyritic basalt, all components except perhaps the accessory opaque oxides are replaced by secondary minerals. The most abundant of these is smectite but the labradorite microphenocrysts are replaced by a felsic aggregate, probably of sodic plagioclase, and there is also relatively coarsely crystalline colourless clinopyroxene present; minor components include biotite, chlorite, magnetite and traces of quartz. The plagioclase alteration becomes less intense a few millimetres from the contact. In the same specimen a discontinuous 3 mm thick band of yellowish, altered, chilled basalt partially separates the hornfels from the 'normal' basalt described above. In thin section this band differs from the dark grey rock in its lack of opaque oxide grains and in containing a higher proportion of clinopyroxene. Optical and X-ray diffraction (NEXD 1156) characteristics confirm that this is diopside and it occurs in both porphyroblastic and microcrystalline form. X-ray results again confirm the presence of smectite and plagioclase (although primary labradorite is not preserved) but in contrast indicate the absence of significant proportions of chlorite, biotite and magnetite. A second specimen collected at the same locality (E47175) shows brecciation of the altered chilled basalt but very similar mineral assemblages to those described above accompanied by some epidote and potassic feldspar. Individual angular fragments show alteration to assemblages dominated by diopside or smectite and the two types are often closely associated, even on a microscopic scale.

The implication of these relationships is that the intrusion was pulsatory; the first pulse chilled and was metasomatised to a diopsidic product, then a later phase gave a smectite-rich product and was either associated with or succeeded by a phase of partial brecciation and hydrothermal cementation of the breccia.

The limestone wall rock of this same locality (E47176) must also have been metasomatised, for despite the preservation of the outline of large crinoid fragments the hornfelsed rock is rich in granular subhedral garnet, aggregates of olive-green chlorite (probably mainly secondary to garnet) and euhedral prismatic idocrase; calcite and quartz are comparatively minor constitutents, considering the context. The garnet and idocrase occur in two generations and the earlier larger porphyroblasts of the former are zoned. All the garnet is anisotropic, indicating that a composition in the ugrandite series is to be expected. Local accessory bundles of slender fibre-like crystals occurring in a crinoid columnal pseudomorph are tentatively identified as fibrolitic sillimanite. Other specimens collected at this same locality [NY 9164 7463] include marmorised but apparently uncontaminated bioclastic limestone (E47177) and hornfelses possibly derived from more pelitic sediments. One of these (E47178) is almost cryptocrystalline but X-ray (NEXD838), (NEXD839), (NEXD840) and optical tests suggest that it consists of a quartz-free intergrowth of smectite and albite-oligoclase with accessory leucoxene; another specimen (E47179) contains abundant quartz and chlorite in a cryptocrystalline groundmass (NEXD841), (NEXD842), (NEXD843), 'spots' of euhedral poikiloblastic feldspar up to 0.07 mm in length and stellate aggregates of white mica from 0.04 to 0.08 mm in diameter. A specimen of contact-altered limestone from 220 m to the northwest (E47174) only shows simple marmorisation with a general coarsening of former micrite to a grain size of about 0.04 mm and partial destruction of internal fossil structures. As described by Randall (1959b) the recrystallisation is associated with a clarification of calcite crystals and a concentration of impurities at intergranular boundaries.

Samples were also collected from xenolithic rafts within the Whin Sill at Barrasford Quarry [NY 9119 7453]. A former bioclastic limestone (E47911) has been converted into an ugrandite-chloritequartz-idocrase-microcline-plagioclase marble. The abundant euhedral, locally birefringent garnet shows partial replacement by both calcite and chlorite. Despite the strong metamorphism the ghost outlines of former crinoid remains are still distinguishable. A former possibly more argillaceous limestone (E47912) shows even better preservation of fossils locally, but for the most part it has been converted into a microcrystalline aggregate of smectite and plagioclase with poikiloblasts of calcite. The preservation of the fossils has occurred by selective replacement of the original carbonate by individual new mineral components—some are preserved in calcite, some in smectite, some in feldspar. In view of the high fossil content of this rock there is obviously a possibility that its new composition is the product of intensive metasomatism rather than a primary high silicate content although highly fossiliferous shales are part of the local sedimentary sequence.

The Whin Sill is well exposed to the north-east of Barrasford Quarries where it is closely related to the Oxford Limestone which can be seen both above and below the sill. At one point [NY 9220 7550] both the limestone and the overlying mudstone occur within offshoots of the sill. At Reaver Crag [NY 929 757] the sill changes horizon upwards towards the north-west to a position below the massive sandstone overlying the Oxford Limestone. Apart from a 0.6 m band of Whin Sill exposed within this sandstone in a stream section [NY 9338 7537] near Swinburne Castle, the sill lies between this sandstone and the overlying Barrasford Limestone in the country immediately to the north-east.

At the time of survey (1971) the main face of Swinburne Quarry [NY 9498 7678] showed some 30 m of dolerite with numerous—vertical quartz-calcite-pyrite filled joints and, towards the top, quartz vesicles, up to 8 cm in diameter, similar to those mentioned previously near Barrasford. Sandstone and limestone rafts are also present in Swinburne Quarry.

A band of Whin Sill near the top of the working face of the quarry, varying from a few centimetres to a metre thick, was altered to a yellowish brown clayey rock with numerous slip-planes and polished surfaces. Thin sections (E50511) of the altered dolerite show the ferromagnesian minerals to have been changed into yellowish brown clays. The feldspar has resisted alteration and the original porphyritic texture is retained. Some clay grains show signs of shearing. A pattern of veinlets is filled with secondary chalcedony and iron oxides. The specific gravity of the fresh dolerite is 2.91, while that of the altered rock is 2.61. As in Keepershield Quarry the altered dolerite coincides with a fault which determines the course of a glacial drainage channel.

Two of a series of prospecting boreholes in the Whin Sill at Swinburne Quarry intersected cognate basaltic minor intrusions, each up to several centimetres in thickness, showing marked chilling against the dolerite. One of these boreholes illustrates that the basaltic intrusion was multiple, with at least two basalt phases being present, separated by a cooling interval since the last one is chilled against its predecessor (Plate 11.1).

A thin section (E41887) shows that the dolerite of the host Whin Sill is largely carbonated and both of the later intrusive episodes are characterised by carbonate-rich end-stage hydrothermal phases of crystallisation. The two basalts are both microporphyritic, essentially similar in appearance both to each other and to the chilled marginal facies of the Whin Sill itself. The microporphyritic plagioclase laths are more or less fresh and show some oscillatory normal zoning from cores of about An₇₀. Scattered large pseudomorphs of calcite after pyroxene, and talc after olivine, may have been cognate xenocrysts rather than phenocrysts (see below). The matrix appears to have been glassy at the chilled margins and holo-crystalline elsewhere but carbonation of all but the plagioclase and opaque oxide minerals would have obliterated any mesotasis that was present. The earlier of the two basalts appears to have been slightly richer in opaque oxides and to have suffered less carbonation than the later. Both are associated with multiple vein mineralisation in which the crystalline phases include calcite, quartz, euhedral biotite, fibrous amphibole and pyrite; in the earlier basalt this same assemblage, excluding the sulphide, also occurs in tenuous 'pegmatoid' patches modifying the basaltic fabric.

Similar basaltic minor intrusions, very probably continuations of one or other of those described above but lacking multiple structure, occur elsewhere in the same borehole and a section of the deepest example (E41889) clearly illustrates the stoping action of the basalt on adjacent dolerite to give both xenoliths and xenocrysts; it also shows the intimate spatial and, by implication, chronological interrelationship of the basalt and the carbonate-rich vein mineralisation (Plate 11.2). Analogous basalt-dolerite structural, textural and mineralogical relationships are present in a second borehole 150 m distant. Here the effects of hydrothermal carbonating alteration are less marked in both basalt and host rock. The 'Whin' dolerite (E41890) shows only minor chloritisation and carbonation of pyroxene and retains much intersertal devitrified glass; it also contains distinct olivine pseudomorphs and is rich in lamellar accessory opaque oxide. The intruding basalt contains phenocrysts of mainly fresh augite and talcose pseudomorphs after olivine, and although the groundmass pyroxene is carbonated it retains its primary granular form. The associated carbonate-quartz-biotite-amphibole veins lack pyrite and although the basalt is xenolithic it appears to lack xenocrysts; the vein mineralisation affects the dolerite wall-rock and here, there is an associated minor proportion of pyrite present. The intrusion into the Whin Sill is sufficiently thick at this locality to show coarsening at its centre where it approaches a typical Whin Sill texture (E41891). In this coarsest facies it is possible to distinguish some unaltered prismatic clinopyroxenes in the groundmass and these show a larger axial angle, and therefore presumably calcium content, than the microphenocrysts in the same rock. This accords with a trend towards calcium enrichment in the later stages of crystallisation culminating in the calcite-rich veining and secondary carbonation associated with the end-stage hydrothermal liquors.

Swinburne Quarry was also the site of well developed smectite mineralisation of the Whin Sill (Siddiqui, 1976). The smectite, which replaces olivine and augite, is relatively rich in magnesium and iron, and poor in aluminium.

Northwards, the Whin Sill, 10 to 15 m thick, forms crags near Thockrington [NY 955 785]; [NY 956 790]. Locally hereabouts [NY 9524 7841], there appears to be another thin sill in the underlying beds. The main part of the Whin Sill, 5 to 10 m thick but probably thickening eastwards, is seen again in Sweethope Crags [NY 961 811] but lenses out to the north-east near Plashetts [NY 9651 8160]. A sill reappears at the same horizon to the north in Hawick Crags [NY 964 821] and at Hawick [NY 964 8261 but is not seen again in the ground to the north.

In the eastern and north-eastern parts of the district and adjacent areas in the Morpeth district, there are two other sills at higher stratigraphical levels. The lower of these underlies the Upper Bath-House Wood Limestone, is 1.29 m thick in the Homilton Borehole [NY 9773 7852] and was formerly seen around New Onstead [NY 9748 7982]; [NY 9756 8024]. 'White whin' 0.61 m thick, was proved below the Upper Bath-House Wood Limestone in an old shaft at Kirkwhelpington [NY 9955 8423] in the Morpeth district and is probably part of the same sill.

The upper sill appears suddenly to the north of the Hallington Reservoir Fault [NY 9781 7713] which also carries the Bavington Dyke. At its southern extremity the sill is believed to overlie the Shotto Wood Limestone but about 500 m to the north it transgresses to a level just below this limestone and continues at this horizon along the remainder of its crop. Numerous exposures, prominent crags and broad dip-slopes, all made by the dolerite, occur between Homilton [NY 978 7841 and Clay Walls [NY 979 798].

At Divethill Quarry [NY 9805 7920] the dolerite is 11 to 12 m thick, and the underlying baked mudstones and Upper Bath-House Wood Limestone are cut by irregular stringers of basalt and are locally much disturbed by the intrusion of the sill (Figure 30). Specimens taken from the country rock (limestone and calcareous sediments) show a rather different style of contact alteration from that found at Barrasford Quarry. Bioclastic limestones (E47916) to (E47918) again show a general coarsening recrystallisation with the partial preservation of fossil forms but here there is also disseminated chlorite and scattered porphyroblastic pyrite mineralisation. The chlorite tends to occur as small spherulites, and the somewhat irregular distribution of these spherulites in cumulose concentrations suggests that they are metasomatic in origin, although primary compositional variation in a laminated limestone-calcareous siltstone specimen (E47919) illustrates that primary composition also influenced their development. It seems probable that the ore minerals are derived from the sediments by metamorphic redistribution; one sample (E47920) is rich in finely and fairly evenly disseminated pyrite 'droplets' and another (E47919) contains laminae and lenses of both pyrite and hematite aligned parallel to the bedding. Quartz is a minor but consistent component of this mineralisation and it frequently occurs as poikiloblasts showing apparent radial twinning, not unlike the sectorial twinning of cordierite in appearance. This same poikiloblastic radial-twinned habit was also noted in the garnetiferous limestone wall-rock at Barrasford Quarry already described (E47176). X-ray analysis (NEXD1155) confirmed the identity of quartz and the absence of cordierite and osumilite.

At Clay Walls [NY 984 795] saccharoidal limestone can be seen in old workings and nearby [NY 9859 7941] baked mudstones, thickening eastwards, occur between the sill and the overlying limestone, suggesting that the sill dips more steeply eastwards than the enclosing sedimentary rocks. Northwards between Great Bavington [NY 979 801] and Northside [NY 986 825] there are almost continuous crags of dolerite. Saccharoidal limestone immediately overlies the Whin Sill and together they form the dip-slope with the dolerite projecting through the limestone in several places [NY 986 804]; [NY 985 810]; [NY 9835 7985]. Dolerite 15.54 m thick was proved in a borehole at Great Bavington [NY 9845 8029]. North of Northside the Whin Sill is much obscured by drift, but is exposed beyond the eastern margin of the district at Three Farms [NY 989 835] and in the River Wansbeck at Kirkwhelpington [NY 997 843] (Weyman, 1913). The crop of the sill is displaced 2 km westwards back into the district by the Sweethope Fault. About 12 m of dolerite are visible in West Whelpington Quarry [NY 976 838] and in sporadic crops to the north-east, most notably in East Whitehill Quarry [NY 996 856], where 10 m of dolerite is overlain by fossiliferous mudstone and the Shotto Wood Limestone.

Carboniferous basic (Whin) dykes

The St Oswald's Chapel Dyke (Holmes and Harwood, 1928, pp. 520–521) was proved underground in the Little Limestone Coal workings from Acomb Drift, near High Barns [NY 9195 6805]. A north-easterly trending fault and dyke can be traced on the ground from near Fallowfield [NY 9251 6862] to the eponymous locality [NY 9369 6958] though nowhere in this belt is the dyke well exposed. However, to the north-east near Brady's Crag [NY 9395 6981] the dyke, 10 m wide, is seen in and near a farm road. It is exposed in a track adjacent to Cocklaw Dean [NY 9462 7042], and again nearby [NY 9513 7073], 14 m thick, where the baked country rocks are also well seen. There is no surface evidence of the dyke for some distance to the north-east, but a magnetometer survey (Figure 31) and (Figure 32) by Mr H. A. Baker of the Department of Mining and Mineral Sciences, University of Leeds, has shown that the dyke continues at depth but does not reach the present surface. Dolerite is again seen in Linn Burn [NY 9798 7310] near Bingfield, and Mr Baker's work suggests that the dyke is at rockhead for some distance in this area. The lateral displacement of its crop by the Todridge Fault is well shown. Exposures of dolerite in the south bank of Erring Burn [NY 9702 7322]; [NY 9713 7328] were formerly regarded as belonging to a thin sill; the contacts with the country rock are largely obscured but seem to be at low angles. However, Mr Baker's survey shows that these crops belong to an east-north-easterly trending dyke, the Erring Burn Dyke which is probably an en échelon continuation of the St Oswald's Chapel Dyke.

The St Oswald's Chapel Dyke (E47909), (E47910) has a general texture and composition akin to those of the Whin Sill. The normally zoned plagioclase has a composition ranging from about An₇₅ to An₅₈, the mesostasis is in part devitrified glass and in part a quartz-feldspar-carbonate assemblage, accessory olivine is replaced mainly by talc, and the abundant accessory opaque oxide is generally fresh. Distinctive features include the presence of only one optically distinguishable pyroxene, an augite, and the partial alteration of this pyroxene to fairly well crystallised plates and aggregates of olive-brown highly birefringent smectite.

The Erring Burn Dyke (E47172), (E47173) is petrographically similar to the St Oswald's Chapel Dyke in its general texture and most elements of its primary mineralogy, including feldspar composition and the nature of its accessory opaque minerals and mesotasis. It differs in containing minor amounts of ragged prismatic hypersthene and, locally (E47172), large xenocrysts of calcic labradorite. The main deuteric alteration product is ankerite, instead of the smectite found in the St Oswald's Chapel Dyke. The differences between the two dykes are within the range of variation found in the Whin Sill and do not necessarily indicate that they are of different origin.

The east-north-easterly trending Bavington Dyke, which locally follows the Hallington Reservoir Fault, is exposed near Colwell [NY 9597 7652] and again beyond the margin of the district near Hallington High Farm [NY 9914 7754]. Its westernmost exposure is northwest of Colwell near Woodford Bridge, where a dyke [NY 9408 7605] under 1 m in width was mapped by the primary survey in the stream bed in contact with the sandstone overlying the Oxford Limestone. The dyke coincides with a fault. A poorly exposed dyke is present on the northern bank of Lisles Burn [NY 9322 8637] near Linnheads. Miller, in the primary survey, reported a width of 1 m but noted that it was not laterally persistent. This dyke may be a western extension of the Causey Park Dyke of the Rothbury district to the north-east.

Tertiary dykes

The distribution and petrology of the Tertiary tholeiite dykes of the north of England have been described by Teall (1884a) and Holmes and Harwood (1929). They have an east-south-easterly trend and are considered to be part of the dyke-swarm from the Mull volcanic centre in Scotland. No absolute age determinations have been made on rocks from this district, but the consanguineous Cleveland Dyke has been dated as 58.4 ± 1.1 Ma by Evans and others (1973).

Petrographically the Tertiary dykes differ most obviously from those of Carboniferous age in the nature of their mesostasis, which is glassy or cryptocrystalline throughout, and in general containing more distinctly defined amygdales. Neither hypersthene nor pigeonite have been recognised in the specimens collected but analcime is present in the amygdules of many. A visual assessment, unsupported by modal analysis, suggests that the Tertiary basalts and dolerites have a higher pyroxene to plagioclase ratio but a lower magnetite content than their Carboniferous counterparts.

Holmes and Harwood (1929) recognised several different types of tholeiite, three of which are represented in this district. In the Brunton type, the pyroxene crystallises in granular clots with plagioclase laths embedded and in part radially disposed. These crystalline groups are partly in contact and partly separated by the mesostasis. The Talaidh type is similar but characterised by elongation of the augite crystals. The third type, the Acklington type, is slightly more acid with feldspars exceeding pyroxenes in amount, and with no tendency to clustering of the crystals.

The dykes are laterally discontinuous at any given level, and thus appear at the present surface as a series of short, en échelon sections.

Details

In the north of the district, from Greenhaugh to Kirkwhelpington, there are a number of short dykes aligned en échelon. About 13 km to the south, the Bingfield and Warks Burn dykes, though widely separated, are almost exactly in line. The Crookdene Dyke lies between these two groups.

The Greenhaugh Dyke cutting Upper Border Group rocks in Greenhaugh Burn [NY 7942 8691], is no longer exposed. During the present resurvey the hitherto undiscovered Longheughshields Dyke was mapped in a small burn [NY 8171 8476] east of Charlton, where it is some 1.60 m wide and trends north-west to south-east. The Hareshaw Burn Dyke was reported by Miller in the primary survey crossing Hareshaw Burn [NY 8437 8411] near the old ironstone workings. The dyke was 2.1 to 2.7 m wide and coincidental with a small fault. Fragments of dolerite are still visible in the eastern bank of the burn. The 1 m-wide Chesterhope Burn Dyke was recorded by Miller in the burn [NY 8974 8510] near High Chesterhope trending E 13° S. Its structural location is unusual in that it occurs along the axial plane of a small syncline.

Near the eastern margin of the district five dyke sections crop out. The Cross Hollows Dyke can be seen in the banks of Ray Burn [NY 9723 8522] cutting strata below the Dalla Bank Limestone. The Ray Mill Dyke [NY 9783 8517] was not seen during the resurvey, but Burnett, when surveying the Morpeth district, noted two parallel dykes each 0.6 m wide at this locality, and also mapped the Herpath Wood Dyke 2.75 m wide nearby [NY 9811 8536]. The Horncastle Wood Dyke 2.0 m wide, was seen during the resurvey [NY 9813 8511] but the reported crop of the Castle Dean Dyke [NY 9827 8506] was not found. Holmes and Harwood (1929) describe the Cross Hollows Dyke as an Acklington type dolerite, the Ray Mill and Horncastle Wood dykes as Brunton type and the Castle Dean as Talaidh type.

The Crookdene Dyke (Heslop and Smythe, 1910), of Talaidh type (Holmes and Harwood, 1929), cuts beds between the Dalla Bank and Colwell limestones at the eponymous locality [NY 9702 8319] where it is a more or less vertical body of rock intruded into a small fault. In the river exposures the dyke is 0.55 to 0.60 m wide with the northern part altered to a rock resembling 'white whin'. The dyke appears to thin upwards to about 0.10 m. The igneous rock encountered at a depth of 67.36 to 74.68 m in the Ridsdale Borehole [NY 8946 8288] may be part of this dyke. Thin sections from the Crookdene Dyke (E46361) to (E46364) showed it to consist dominantly of pale coloured augite and simply or slightly oscillatory zoned labradorite with accessory opaque oxides and sparsely irregularly distributed pseudomorphs after olivine. A varying proportion of dusty intersertal glass and amygdales containing chlorite, smectites, calcite, ankerite and locally analcime are also present. The habit of the clinopyroxene varies from granular to prismatic or sub-ophitic, and the plagioclase prisms are typically slender and often 'crossed' in the manner characteristic of tholeiites. Where the dyke has undergone carbonate metasomatism (E46364) the original fabric of the rock is preserved by the relatively unaltered plagioclase and 'earthy' (?leucoxene) pseudomorphs of opaque oxide, although the remainder of the primary and deuteric minerals are replaced by aggregates of calcite with minor amounts of ankerite and siderite and local poikiloblasts of pyrite. A sample of limestone (E46365) taken from the contact of the dyke [NY 9702 8319] is a packed biomicrite showing a general coarsening of the calcite fabric causing little more than a 'blurring' of the normal fossil-matrix interrelationships although internal skeletal structures are generally destroyed.

Warks Burn Dyke of Brunton type, is well exposed in the burn south of Horneystead [NY 8135 7707]. It is some 1.70 m wide, occupying a small fault with downthrow to the south, and can be traced intermittently for some 600 m trending E 23° S. Miller recorded probably the same dyke some 3 m farther east in Gofton Burn [NY 8442 7609] within sandstone. In Warks Burn it is strongly but irregularly jointed showing chilled margins and a marked central area some 0.10 m wide of poorly resistant rock which is weathered and in places mineralised. This median zone of the dyke is composed of coarse nodular calcite associated with leucoxene and it is probably a screen between two units of a multiple intrusion. At this locality it is clear that the alteration of otherwise fresh dolerite and basalt is concentrated at the margins of the intrusions (E41042) to (E41050). The range of textures and mineralogical assemblages in the unaltered parts of the dyke is very similar to that found in the Crookdene Dyke. Minor additional variations include the development of a coarse truly ophitic texture in one unit of the multiple intrusion (E41043), the local presence of plagioclase xenocrysts and the occurrence of a fibrous zeolite in some amygdules. The carbonate metasomatism has been even more extreme at the margins of this dyke to give a typical 'white trap' lithology (E41044) in which the plagioclase is replaced by kaolinite and the remainder of the rock by calcite. It is noteworthy that in this particular dyke the replacive carbonate is essentially all calcite whereas the carbonate of the amygdules is ankerite and siderite.

The Bingfield Dyke (Holmes and Harwood,1928, pp. 520–521; 1929, p. 17), which is the type example of the Brunton type of tholeiite, is intruded along the Barrasford Fault, and can be seen at two localities in Redhouse Burn near Bingfield [NY 9729 7194]; [NY 9774 7183]. The full thickness of the dyke, 0.76 to 0.91 m, was formerly visible here. The magnetic survey by Mr H. A. Baker shows the anomaly due to this dyke cutting that caused by the St Oswald's Chapel (Whin) Dyke (Figure 31). Mr Baker's results suggest that the dyke does not reach rockhead much beyond the present known exposures.

Samples taken from the Bingfield Dyke [NY 9763 7183] and also others from the Horncastle Wood [NY 9812 8511] and Cross Hollows [NY 9823 8523] dykes, are fresh basalts essentially similar in lithology to the Crookdene Dyke. The greenish to brownish phyllosilicate minerals occurring in amygdales appear to be mainly chloritic although traces of smectite are present in the Bingfield and Horncastle Wood (E43819) samples (NEXD1168), (NEXD1168), (NEXD1170). The Cross Hollows Dyke (E43820) appears to lack olivine pseudomorphs and it is the only one of the three containing plagioclase xenocrysts and analcime in its amygdales. The Bingfield sample (E47915) is distinctive in that its glassy mesotasis is altered or partly altered to a greenish substance. Some of the greenish to brownish amygdalar and intersertal material in this and other samples is virtually isotropic and it could therefore include a proportion of palagonite; X-ray results (NEXD 1167) only indicate traces of smectite with no peaks corresponding to the chlorite or serpentine groups. The augite in the Bingfield sample has a 2V of approximately 48° and the plagioclase has a core composition of approximately An₇₅; these figures are probably fairly representative of the Tertiary suite in this area.

Chapter 8 Structure

General account

The Lower Carboniferous strata of Northumberland and north-east Cumbria were deposited in a continuously downwarping basin, the Northumberland Trough, elongated approximately east–west and bounded to the north-west, north and south by the Southern Uplands and Cheviot massifs and Alston Block respectively (George, 1958, fig. 23, p. 298). The Carboniferous rocks dip gently away from the Cheviot Block to the north-east, east and south. This block acted as a buttress when the Carboniferous rocks were subjected to the stresses of the Hercynian Orogeny and was responsible for the style of folding and faulting around the margin of the resistant Cheviot Granite and associated Old Red Sandstone lavas.

The structural pattern of the Bellingham district is closely comparable with those of the Otterburn district (Frost, 1969), north-east Northumberland (Westoll and others, 1955; Shields, 1964) and the north-eastern area of the Bewcastle district where Day (1970) recognised three deformational episodes affecting Carboniferous and later rocks. The Bellingham district lies some 20 km south of the Cheviot Block and is south-west of the Bolton–Swindon and Cragend–Chartners fault-system (Shiells, 1964, fig. 18). The structures in this district therefore occupy the next major shear zone to the south, but the folding and faulting is less intense than farther north, presumably due to the increasing distance from the plate margins (see p. 4) and the diminishing effect of the Lower Palaeozoic basement in the more central areas of the Northumberland Trough (Frost, 1969, p. 281).

The Bellingham district can be divided into two structural areas separated by the Sweethope Fault (Figure 33). South of this fault the strata dip gently to the south and east at about 10° with only minor dislocation; north of the fault the rocks are in places steeply dipping and commonly faulted and folded. The chief feature of this structurally complex area is a down-faulted block lying between the Antonstown and Sweethope faults. These have vertical displacements to the south and north respectively of up to 250 m, and are some 5 km apart and roughly parallel. A plexus of smaller scale faults and folds of various trends occurs in the intervening area, e.g. the Bellingham Anticline. The hade of the Sweethope Fault can be calculated in the Fernyrigg area to be 50°. In many places the fault comprises several closely spaced fracture-planes of similar trend.

The existence of faults at surface is usually determined on stratigraphical evidence or by extrapolation and interpretation from adjacent areas because such structures are commonly represented by negative features like peat or boulder clay filled valleys. Even in stream sections the critical part is often not exposed but separation of strata is necessary because of opposing dip directions or juxtaposition of differing lithologies.

The faults of the district have two preferred trends, a dominant east-north-east trend and a secondary east-southeast direction (Figure 34). They may be interpreted as conjugate shears resulting from an east–west compression. There is, however, a marked, parallelism in both sets, between the trends of the faults and those of the folds (Figure 34), the former theoretically produced by tension, the latter by compression. For example, between Bellingham and Ridsdale the Bellingham Anticline has an axial plane parallel to the Antonstown Fault on the north and the Sweethope Fault to the south. Some fold axes are displaced by faults, confirming at least two stages of movement. Frost (1969, fig. 2) showed that in the area to the north, the dominant joint direction lay at 60° to 70° from the dominant fault direction-a trend continued in the Bellingham district.

The sequence of events at the close of Carboniferous times which can explain such structures is as follows:

1. Hercynian, north-south compression producing the Bellingham–Ridsdale anticline as well as numerous other small folds.
2. Release of north-south compression resulting in a period of tension. This was followed by shear faults which trend slightly north and south of east (Figure 34) and are best explained by a resultant east-west compression. The set trending between 55° and 75° became dominant due to the configuration of the Cheviot Block in the elongate Northumberland Trough. The 'rift' between the Antonstown and Sweethope faults belongs to this phase. Evidence that these faults are important regional structures is provided by their linear continuity with major faults outside the district. In addition, the Antonstown Fault was considered to have acted as a hinge-line affecting rates of sedimentation at an early stage in the geological history of the area (Figure 7).
3. The district was intruded by the Whin Sill complex and its associated dykes, the latter following old lines of weakness. (Figure 34) shows that the dominant trend of dyke intrusion is northeastwards. A conjugate set of later Tertiary dykes, with an east-south-east trend, e.g. the Bingfield Dyke, cuts across and displaces the north-east trending dykes.

Further evidence of minor folding, faulting, dyke intrusion and also mineralisation is shown in the south-east of the Bellingham district between Settlingstones and Stagshaw. Such features show an increase in structural activity in the Northumberland Trough as the southern margin is approached at the Stublick Fault system which lies a few kilometres south of Hexham.

The deformational history of the Bellingham district is obviously long and complex. Most of the movements were of Hercynian age, perhaps following old Caledonoid lines of weakness in the basement, but much of the evidence now seen results from the last adjustments made to stress by reactivation of faults probably in Tertiary times.

Details

In the north-western part of the district the Antonstown Fault is not seen at surface but its position can usually be fixed with some precision owing to the juxtaposition of rocks with diverging strike directions or of widely differing stratigraphical horizon. In its course across the adjacent Bewcastle district the fault has a northerly downthrow to within a kilometre of the Bellingham district, across which the throw is generally down south, varying considerably in amount with the faulting and folding on either side. West of its junction with the Falstone Fault, the Antonstown Fault throws down south.

The position of the Antonstown Fault is mapped in Hareshaw Burn [NY 8412 8493] where beds overlying the Fourlaws Limestone and dipping 20° to the north meet Upper Border Group beds dipping south at 30°, giving a vertical displacement of some 300 m. Farther east, the fault position is marked by the termination of sandstones crags [NY 8472 8497] and [NY 8508 8510] which show sudden increases in dip of up to 50° at their margins.

A dyke associated with the Antonstown Fault has been mapped in the north-eastern part of the district near Linnheads [NY 9322 8637]. Extrapolation of the fault eastwards from the Bellingham district suggests that it continues into the Causey Park Dyke and associated fault of the Rothbury district.

The Antonstown Fault was recorded during the primary survey in the railway cutting [NY 8980 8592] (now overgrown), near Woodburn Station. A small branch fault in the nearby Woodburn Quarries [NY 8991 8585] affects the sandstone above the Redesdale Limestone. This sandstone is crossed by a shatter belt some 5 m wide which contains planes of fracture dipping at 65°.

In the north-eastern corner of the district, in Cuddy Cleugh [NY 9434 8663] an almost flat-laying, falls-producing sandstone, marks a dislocation of some 100 m where it abuts against the more steeply dipping (27°) Lower Demesne Limestone.

A southward increase in dip from 20° to 85° over a distance of 247 m provides good evidence for the major east-west Sweethope Fault in Blacka Burn [NY 8151 7812] near Low Stead. Farther east, beneath Black Crags [NY 8275 7830] at Hetherington, a heavily veined dolomitised limestone correlated with the Fourlaws Limestone (Lower Liddesdale Group) crops out adjacent to beds some 230 m lower in the succession (Upper Border Group). This fault can be traced to the eastern margin of the district and was detected in Rushy Burn [NY 9328 8249], near Lunga Crags [NY 956 832], and in the Wansbeck Valley east of West Whelpington Quarry [NY 9740 8364] to [NY 9799 8379]; [NY 9849 8403] to [NY 9859 8410]. Just beyond the eastern margin of the district the fault splits into several branches.

Farther east, large scale faulting near Mitford, in the Morpeth district, may be the continuation of the Sweethope Fault system.

Disturbed and broken strata proved between 427.71 and 429.46 m in the Ferneyrigg Borehole [NY 9579 8364] have been taken as the Sweethope Fault Zone. Lateral as well as vertical movements probably occurred along the Sweethope faults with the formation of new minor folds along and at right-angles to their length as at Devil's Leap [NY 8680 7995] near Wark, as well as steep dips in areas such as at Billerley [NY 8365 7950].

The Bowmer Crags Fault [NY 7365 7053] is the largest dislocation of many small faults which can be mapped in the south-western part of the district, where clearly defined features made by both sandstone and limestone show many breaks of continuity. The sandstone scarp of Bowmer Crags swings southwards into the fault line with trends NW–SE. It has been proved underground in the Thirlwall Seam where the downthrow is some 5 m to the southwest. The fault plane is nearly vertical.

The Rough Cleugh Fault [NY 7507 8658] is marked by vertical and steeply dipping beds near Donkleywood. It is thought to run parallel to the monoclinal structure that can be seen in Thorney Burn [NY 7645 8682] to [NY 7631 8668] and nearby [NY 7591 8630]. Only minor normal faulting, aligned with this flexure, has been detected; vertical strike-slip faults with 2 or 3 m displacement, trend normally to the fold. The south-easterly trending Slatyford Fault can be seen in Thorney Burn at Hillhouse Clints [NY 7620 8728].

Steeply dipping beds seen in Smales Burn [NY 7170 8348] are taken to indicate a branch of the Whickhope Linn Fault and highly dipping beds in a tributary stream near Archy's Linn [NY 7130 8307] are thought to be close to a branch of the Kyloe Fault.

A number of faults can be seen in the Chirdon Burn valley. An east-south-easterly fault downthrowing north crosses the stream upstream of Cat Linns [NY 7087 8027]. Disturbed, brecciated and veined sandstones adjacent to the Allery Bank Fault are exposed near the footbridge [NY 7492 8154]. A fault, normal to the latter, runs parallel to the burn opposite Allery Bank; a landslip revealed sharp downturning of the beds on the upthrown side [NY 7501 8169]. Downstream of Allery Bank, beds close to the Leahill Limestone are repeated by gentle folding and by a number of minor faults [NY 7538 8246]; [NY 7532 8260]; [NY 7555 8285].

The Snabdaugh Moor Fault can be traced from the termination of sandstone crags [NY 7711 8348]; [NY 7782 8399] and the marked downturning of strata [NY 7699 8319]; [NY 7828 8424]. In High Carriteth Burn [NY 78518300] an east-south-easterly fault, downthrowing south, brings the Leahill Limestone against beds below the Appletree Limestone. The Whitchester Moor Fault can be seen in March Burn [NY 7945 8124] where steeply dipping beds and disturbed mudstones crop out.

Faults, generally with small throws, can be seen in Clintburn [NY 7275 7964]; [NY 7272 7931], in Greenlee Cleugh [NY 7230 7559] and Warks Burn [NY 7233 7521]; [NY 7239 7519]; [NY 7227 7514]; [NY 7287 7524]; [NY 7302 7520].

The Tecket Fault, trending at 140°, crosses Crook Burn [NY 8598 7253] south of the old quarries in the Bankhouses Limestone. On the east bank of the burn, an old level indicates former mineral workings along the fracture. Small faults of a similar trend are common upstream, and calcite mineralisation in joints in the Upper Bankhouses Limestone is exposed near the weir [NY 8573 7217]. Nearby, a fault [NY 8550 7218] and associated vein up to 30 cm wide are reported to carry considerable high grade baryte.

The Broomhope Fault is exposed in the old ironstone and limestone quarries [NY 8890 8414] near Ridsdale where the fault-plane, which coincides with the crest of the Ridsdale Anticline, shows considerable calcite veining.

Examples of small faults with a north-south alignment are exposed in Hesleyside Burn [NY 8159 8337], and in a small stream near Woodpark [NY 8478 8009]; and a disturbed zone of sandstone with high angles of dip, between two parallel faults some 45 m apart, occurs at Harelaw Crags [NY 7630 7707].

Faults with a south-east trend are exposed in Warks Burn [NY 8605 7646] and [NY 8577 7643] near Wark. A fault of similar trend truncates the western end of Aid Crag [NY 9180 8366] near Ridsdale, which shows an upturn in dip to 20°. The eastern end of the crag is traversed by several faults trending between 100° and 140° with vertical slickensides on the fault-planes.

A fault with a south-west trend is exposed in a small stream [NY 9032 8230] near Swine Hill Roman Camp, Ridsdale. The fault-plane, along a ganisteroid sandstone, dips at 62°.

Minor folds in beds associated with the Colwell Fault are exposed in Hallington Burn [NY 9804 7501 and in Mootlaw Burn [NY 9903 7491]. Steeply dipping beds on the line of the Barrasford Fault crop out in Swin Burn [NY 9238 7347].

Several faults are coincident with dykes although the vertical displacement is usually small. For example, the fault associated with the dyke crossing Hareshaw Burn [NY 8437 8411] has a down-throw north of some 5 m. Other examples can be seen in Warks Burn [NY 8120 7714], Swin Burn [NY 9390 7603], and the River Wansbeck [NY 9702 8319].

Most normal faults are considered to have been formed in strata during a period of tension. In the Bellingham district there are, however, many examples of compression faults and associated thrust structures. Those which are exposed are only on a small scale but nevertheless indicate that compressional stress was an important element in the structural development of the district.

The best example is seen in Warks Burn [NY 8200 7687] and corn-prises a thrust-plane trending west-north-west, dipping at 60° and overthrust from the south, producing considerable shearing of individual sandstone beds within an alternating sequence of Upper Border Group lithologies (Figure 35)a. Farther upstream at Biggy Haugh [NY 7905 7636] beds on either side of a thrust fault have been upturned but not fractured except along the fault plane which trends NE–SW and dips at 70° (Figure 35)c and (Plate 12). Similar compression structures are exposed in Moss Kennels Quarry [NY 8060 6933] on the Roman Wall, in Middle Burn [NY 7936 7521] near Stonehaugh and in the banks of the River North Tyne [NY 8643 7642] near Wark (Figure 35)b.

'Rolls' or folds of small amplitude, dying out both upwards and downwards are particularly well displayed in the Great and Eelwell limestones. The trends of such folds generally range from north to north-east. Low angle thrusts are associated with rolls in the Eelwell Limestone in Moss Kennels Quarry [NY 8060 6933]. The origin of such rolls is debatable, but compressive forces, be they gravitational or tectonic, were active penecontemporaneously with the deposition and consolidation of the thicker limestones of the Carboniferous in this district.

Chapter 9 Pleistocene and Recent

Much of the district is covered by superficial or 'drift' deposits of Pleistocene and Recent age (Quaternary) (Figure 36) which rest on the older 'solid' rocks beneath. The unconformity between the solid and drift deposits marks a long period of earth history concerning which only scanty evidence is to be found within the district. Late Namurian and Westphalian strata, similar to those in adjacent districts, were probably laid down, but the thickness and nature of any Permian, Mesozoic and Tertiary sediments that may have existed must remain speculative. Following the Tertiary earth movements and dyke injection, the Northumbrian region entered a phase dominated by erosion in which the main elements of the present topography emerged. Apart from a relatively short period of mainly glacial deposition, this erosive phase continues to the present day.

Descriptions of the glacial deposits are included in a number of papers concerned with the glaciation of the wider Northumberland and Durham region (Dwerryhouse, 1902; Smythe, 1912; Raistrick, 1931; Taylor and others, 1971). The escarpments of the district were studied by Miller (1880) and aspects of the river development discussed by Miller (1883), Peel (1941) and Day (1970). The sand and gravel deposits of the southern part of the region, and their economic potential, have been considered by Lovell (in press). Peat deposits and the post-glacial vegetation history have been studied by a number of workers (e.g. Raistrick and Blackburn, 1932; Blackburn, 1953; Pearson, 1960; Chapman, 1964a, b). Details of Quaternary deposits in adjacent districts can be found in Miller (1887), Clough (1889), Smythe (1908), Trotter (1929), Trotter and Hollingworth (1932), Fowler (1936) and Day (1970).

In common with many other parts of the north of England the glacial deposits of the district comprise a single till-complex overlain by retreat-stage sands and gravels, all of Devensian age (Francis, 1970; Evans and Arthurton, 1973). This late date is reflected in the freshness of the landforms produced during the glaciation and deglaciation of the district. During the glacial maximum the whole of the district was submerged by ice flowing predominantly from the west and north-west and carrying, in addition to local Carboniferous and Whin Sill erratics, rock fragments from the Lake District and southern Scotland. During glaciation, and more especially during the deglaciation phase, numerous meltwater channels were formed. As a result of glacial interference there was local modification of the pre-glacial drainage pattern and some adjustments to river-catchment boundaries. As the ice melted back, lakes, some of which persist to the present day, formed in ice-eroded and drift-dammed basins. In post-glacial times these basins became sites of peat deposition, followed by more widespread development of blanket-peat in the higher parts of the district. Streams and rivers, in some cases cutting new channels, laid down terrace and alluvial spreads of gravel, sand and silt. The various terrace features indicate successive lowerings of base level related to migration of nick-points or changes in sea level. Locally the older terraces are overlain by peat. Other deposits formed since the glaciation include landslips, screes, head and tufa.

Boulder clay

The most widespread superficial deposit within the district is boulder clay or till which locally exceeds 55 m in thickness (Figure 36). Typically, boulder clay comprises unsorted, rounded and scratched rock fragments up to boulder-size set in a pale grey clay to sand matrix; in some parts of the district the deposit is gravelly and the finer grades are correspondingly reduced. Local variations reflect differences in source material. Lenses of sand and gravel, silt and laminated clay are common, particularly in the lower lying areas. In many areas the boulder clay forms well defined landforms such as drumlins and glacial flutings.

When fresh, boulder clay is generally stiff and compact but on exposure, particularly during periods of rain, it quickly degrades and becomes liable to flow. Natural exposures are therefore not common and in most cases have undergone extensive landslipping and down-slope creep, particularly noticeable in stream-side scars. The top of the boulder clay is generally weathered to a depth of 2 to 3 m and is brownish yellow in colour, sticky and poorly consolidated.

Pebbles in the boulder clay are dominantly Lower Carboniferous limestones and sandstones; locally Whin Sill dolerites are abundant especially to the south and east of its outcrop. These rock types are largely of local origin. Far-travelled erratics are much less common but are of importance as ice-provenance indicators. The distribution of Lake District and Scottish erratics in the district was described by Dwerryhouse (1902), Smythe (1912), and Raistrick (1931). These authors concluded that an ice-stream, travelling eastward, invaded the south-west of the district, carrying Permo-Triassic erratics from the Carlisle Basin, as well as rocks from the Lake District and Scotland. In the west the till deposited by this ice is predominantly red in colour owing to finely ground Permo-Triassic rock. Traced eastwards the red colour gives way to grey with an increasing amount of incorporated local debris. The northern limit of Lake District erratics follows a line from Houxty Burn to Prestwick Burn and to Sweethope (approximately grid line 80 N). A second ice-stream, travelling south-eastwards down the North Tyne valley, entered the north-west of the district carrying both Scottish and North Tyne erratics and deposited a grey boulder clay. The two ice-streams merged in the central part of the district and together moved to the east and east-north-east.

Ice-movements deduced from the form and elongation of the drumlins and glacial flutings in the district, together with the occasional striae (Figure 36), are in broad agreement with these conclusions.

Much of the boulder clay has the characters of a sub-glacial lodgement till. Locally, particularly in the low ground around Barrasford and Humshaugh and in the Erring Burn valley, where till overlies and is intimately interbedded and admixed with outwash deposits, an englacial and supraglacial origin seems likely (cf. Boulton, 1972). In such areas with complex drift sequences, till cannot always be separated from glacial sand and gravel in the field and all are mapped together as boulder clay.

Details

In the north-western part of the district the boulder clay is exposed in many active landslip scars, notably those in the valley of Chirdon Burn e.g. [NY 749 822]; [NY 752 826]. In the low ground near the River North Tyne 20.42 m of grey boulder clay with sporadic gravelly lenses was proved in a water borehole at Greystead Rectory [NY 7711 8586]. It is 0 to 15 m thick beyond the edge of the district at the Kielder Dam Site [NY 708 880]. On the higher ground there are some large drift-free areas, notably to the south and east of Smales Burn and Chirdon Burn. Over much of the adjacent ground the drift is probably relatively thin, but locally it may be thick, as for example in the Broomley Burn Borehole [NY 7052 8496], where 17 m of grey boulder clay was proved. In the area between Wark and the north-west corner of the district, the boulder clay commonly forms south-easterly aligned linear landforms, some partly rock-cored, showing all gradations from drumlins to glacial flutings. The flutings have an amplitude of around 15 m and are up to 2.5 km in length. In many instances the hollows between the drift ridges have been deepened by the action of sub-glacial meltwaters, and some are wholly or partially occupied by post-glacial streams. The best examples of glacial flutings are those on Watergate Moor; they are similar to those described by Gravenor and Meneley (1958) in northern Alberta, Canada. Similar features have been aptly called washboard moraines. Holt Hill [NY 806 804] is a drumlin which tails off south-eastwards into an elongate ridge trending at 120°.

Water boreholes in the central part of the district, west of Wark, proved up to 51 m of boulder clay which is moulded into large drumlins in a swarm generally aligned north-west to south-east. The banks of the Warks Burn have slipped in many places, revealing boulder clay, the best sections occurring between Stonehaugh and Whygate. One scar [NY 7843 7599], some 6 m high, exposed predominantly brown clay with many small rock fragments both angular and rounded, together with sporadic large boulders mostly of limestone but including sandstone, siltstone and granitic erratics. Farther upstream [NY 7740 7582], a lens up to 0.80 m thick of sand and fine pebbles is present within the boulder clay.

There are numerous rock outcrops in the north-eastern part of the district, many forming impressive crags, but they are usually surrounded by boulder clay even at elevations of 300 m. Little is known of this boulder clay as exposures and boreholes are rare. It appears to blanket the minor irregularities of the bedrock and rarely exceeds 10 m in thickness except for sporadic drumlins trending east or east-north-east. Ferneyrigg Borehole [NY 9579 8364], proved a drift-filled hollow nearly 7 m deep adjacent to a shallow quarry in the Oxford Limestone with less than 1 m of overburden.

In the country bordering the River North Tyne, between Gunnerton and Hamshaugh, the boulder clay contains large amounts of sand and gravel, particularly in its upper part. A temporary exposure in a road-cutting through a drumlin near Keepershield [NY 9014 7261] gave the following section:

On the other side of the cutting, where the ground rises sharply to the south-west, several boreholes and temporary exposures showed a simple sequence of grey boulder clay which was progressively more weathered and brown towards the top. These observations suggest that a thin lens of outwash gravels on the surface of the lodgement till has been overlain by weathered till flowing from the higher ground to the south-west. The unbedded nature of the top part of the gravel suggests that this also has been subject to flowage. Temporary exposures in a housing development at Humshaugh [NY 919 711] showed up to 1.5 m of yellowish brown structureless sand and gravelly clay, similar to that seen at Keepershield. These and other observations at numerous degraded exposures suggest that in this area the main grey boulder clay (lodgement till) is overlain and passes laterally into a complex of yellowish brown sandy and gravelly (?flow) till with pockets and lenses of outwash sand and gravel, some large enough to have been worked locally. To the east, in the Erring Burn valley, laminated clays proved in old brickpits [NY 9618 7307] are associated with these deposits. Part of the area covered by these deposits is flat or gently undulating but much of the ground comprises broad ridges and locally drumlins aligned parallel with the inferred south-easterly direction of ice movement.

The drift in the south of the district where drainage is directly into the River South Tyne, is mainly grey boulder clay, locally very thick, particularly between Grindon Hill and Fourstones, ranging up to 55 m at Settlingstones. According to Dwerryhouse (1902, p. 597) the boulder clay is gravelly in the ground close to the River South Tyne, which locally enters the district at Fourstones. Over the high ground underlain by Namurian rocks in the southeastern part of the district, grey boulder clay up to 14 m thick, with thin sand partings, has been proved.

Morainic drift

Morainic drift is distinguished from boulder clay on morphological and lithological grounds. It forms ridges, irregular mounds and knolls which comprise angular blocks, mainly of sandstone, with little matrix. In the two largest deposits in the district, morainic drift locally passes laterally into water-laid glacial sand and gravel deposits, which could not be mapped separately.

Details

An arcuate spread of morainic drift [NY 735 735] at an elevation of about 260 m occurs near Hindley Steel, in the south-west of the district. It is poorly exposed, some 2 km in length, 300 m wide and up to 10 m high, containing gravels largely of local origin but with a proportion of erratic material including red Triassic sandstones, greywackes and granites derived from the north and west. A small section near its south-eastern edge [NY 7385 7345] showed about 1 m of sand and gravel interbedded with two purplish pink clay bands, all dipping at 15° to the south-west.

Farther north, in the Rede valley near Hole [NY 8670 8465], a north-south discontinuous and irregular ridge of sand and gravel has summits at an elevation of some 150 m. It consists of reddish brown clayey sand with pebbles, mostly of sandstone, and with bedding dipping north-eastwards. The ridge is parallel with the valley, some 30 m above the present river level and its base rises gently northwards with the valley. The deposit may be a detached remnant of the more extensive Lisles Burn Moraine (see below).

Extensive hummocky spreads of sands and gravels cover the sides of the Lisles Burn at similar elevations to those in the Rede valley, and are deeply dissected by the Risey and Lisles burns. A drumlin shaped mound [NY 9144 8664] (Plate 13) in the bottom of the Lisles valley is capped by sand and gravel. The deposits have been worked from an old pit [NY 9251 8608] near Whetstone House. Although the pit is largely overgrown, angular sandstone fragments up to 0.3 m in length are common in the top part, and appear to overlie brown sand which contains small pebbles of sandstone and ironstone together with coal fragments. Miller during the primary survey recorded the juxtaposition of coarse angular morainic deposits and well rounded water-rolled gravel in the stream near Threeburn Mouths [NY 9441 8635]. The deposits therefore have a complex history, initially formed near the margin of melting ice and then partly resorted by meltwater streams.

At Smales [NY 719 845] and below Stokoe Crags [NY 757 858] rounded mounds have been mapped as morainic drift though no exposures of the deposit were seen. A low narrow ridge dominantly composed of loose angular sandstone, occurs 450 m north of Donkleywood [NY 744 868].

An isolated ridge [NY 8060 8525] 300 m x 30 m and 6 m high near Charlton on the north bank of the River North Tyne shows numerous sandstone blocks in the soil but provides no further evidence as to its content. The north-west to south-east alignment is parallel with the bordering Whiteypot Sike and to the overall trend of drumlins in that area.

Gravels referred to as the Simonburn Kames by Miller in his manuscript have not been separately identified during the resurvey in the Simonburn area. Several fields to the north and south of the village support brown sandy loams and sandy clay soils containing numerous pebbles. Gravel of unspecified thickness was passed through in a sinking for the pump at Simonburn Rectory [NY 8705 7362] and was encountered in drains near Burn House [NY 869 738]. Pebbles were also common in the top 1.80 m of the Simonburn Borehole [NY 8735 7372].

Glacial drainage channels

Numerous channels cut by glacial meltwater occur in the district (Figure 36). Many of these are followed by the present drainage but a large number have been abandoned and are now dry. They are typically steep-sided and flat-bottomed, and cut into both solid and drift deposits. Channel length ranges from a few tens of metres to 2 km; width ranges from 10 to 150 m and depth from 2 to 20 m. Some channels begin and end abruptly and others do not follow the general slope of the ground. Longitudinal profiles of many channels, particularly those that cut across cols, are humped. These observations suggest that most of the channels are the result of the subglacial flow of meltwater, in places under hydrostatic head, rather than the previously held view that they were cut by meltwater flow marginal to a wasting ice-sheet or as spillways of ice or drift-dammed lakes (Dwerryhouse, 1902; Smythe, 1912; Trotter, 1929; Raistrick, 1931). However, in those areas where lakes formed in very late glacial times, notably in the southwestern part of the district, a number of channels acted as lake outflows. In the Northumbrian Lakes area, such channels still drain the present-day lakes. It is uncertain in most cases whether such channels were primarily cut by the outflow of the lakes or were cut subglacially and later modified.

In the western and central parts of the district the sub-glacial drainage largely appears to have been parallel with the inferred direction of ice movement. Thus meltwater from the present Irthing catchment basin flowed under hydrostatic head over the watershed into the present Tyne valley, where it joined meltwater coming down the North Tyne valley. In the north-east, meltwater was carried across the Rede valley and over the watershed into the Wansbeck catchment. In the south and south-east some meltwater crossed into the South Tyne valley, but much of the sub-glacial drainage was carried eastwards into the present-day catchment of the rivers Blyth and Pont.

Details

Some of the best examples of channels occur on the dip slope of the Whin Sill in the Roman Wall area. They cut into solid dolerite to varying depths and are usually about 20 m wide. Mostly they trend north-south directly down-dip. The bottom of the channel is invariably masked by boulder clay and in some cases contains small peat deposits. The base of a channel in Highshield Crags [NY 7617 6774] lies some 10 m above the level of the water in the adjacent Crag Lough.

Other examples of drainage channels cut into solid rock are provided in the Bellingham area [NY 826 849] where a series of meandering channels have dissected sandstones in the Upper Border Group and which once drained south-eastwards into the North Tyne valley. They are now represented by flat-bottomed marshy areas bordered by sandstone outcrops.

Glacial drainage channels in other parts of the district are invariably associated with drift covered areas and cut only through the boulder clay. They are well displayed on the left bank of the River North Tyne [NY 873 772] near Wark. Here they trend generally southwards parallel to the valley sides, curving gently round bordering drumlins and eventually breaking through to the main terraced area of the river. Good examples of channels in drift are also seen near Simonburn [NY 8884 7300] and [NY 8653 7335] and northwest of Charlton [NY 8010 8693].

In the west of the district channels are commonly floored by peat [NY 7130 6880], in some cases linking one peat bog to another at a lower level [NY 7105 7194]. In the south of the district near Sewingshields, a channel [NY 8225 7050] has served as the main outlet for the large peat deposit known as Fozy Moss.

Glacial sand and gravel

Sand and gravel of probable supraglacial origin, associated with boulder clay and morainic drift, has already been mentioned. In the south-eastern part of the district, in the area between Gunnerton, Hallington, Bingfield and Humshaugh, some larger spreads of sand and gravel, commonly, though not always, forming mounds and ridges, have been mapped (Figure 36). As noted previously, the separation in the field of these deposits from boulder clay is not always clear cut. The thickest deposits are probably about 10 m thick but in the main they form only thin skins on the underlying boulder clay. Small scale old diggings are numerous but largely grassed-over and exposures are rare. These show that the sand and gravel, which is locally cemented by calcium carbonate, is evenly-bedded with local cut-and-fill structures and more rarely cross-bedded. Some of the thinner deposits have interbeds of laminated clay and silt. Locally these deposits are overlain by a thin yellowish brown sandy and silty clay with sporadic stones, suggestive of flow till. These features suggest a supraglacial origin for the sand and gravel (cf. Boulton, 1972). Evidence from limited degraded outcrops and from fox and rabbit diggings suggests that gravel is not always present in these deposits.

Details

Gravel pits near Liddell Hall [NY 960 756] reveal up to 5 m of sand and gravel, locally overlain by up to 0.5 m of brown till (Plate 14). In parts of these workings sand is dominant, with gravel absent or present in only small quantities. Shallow borings and excavations along the A68 also proved only limited amounts of gravel, and the sand was found to be poorly sorted in places. Beds of laminated clay and silt, more than 1 m thick, were proved. At Barrasford, 9 m of sand and gravel were proved in a well at Ellwood House [NY 9138 7348] and 2 m of bedded sand and gravel cut by small faults were seen in a temporary exposure [NY 9161 7338].

Head

There are two varieties of head within the district, namely scarp-slope and valley-fill deposits. They consist of a hetrogeneous matrix varying from clay to pebbly sand containing a variable proportion of angular and subangular rock fragments up to a metre or so in size derived from up-slope outcrops usually of sandstone or Whin.

Scarp-slope head deposits have an irregular hummocky appearance and merge up-slope into boulder screes. Down-slope the matrix becomes more clayey and there are fewer cobbles and boulders.

Valley-fill head deposits have a similar lithology to scarp slope head particularly along their margins, being ill-sorted and structureless, but when traced towards the middle of the valley, the enclosed rock fragments become progressively more rounded and distinctly stratified the deposit becomes lithologically indistinguishable from river gravel.

Head deposits are generally considered to have formed during late Pleistocene times before an extensive vegetation cover had been established and during periods of plentiful water supply from melting ice. The deposits predate most river terraces and alluvium, peat and landslips.

Details

Good examples of scarp-slope head deposits occur beneath the numerous scarps of the district, particularly the crags with the following names: Wallshield [NY 7145 7060], Horneystead [NY 8080 7760], Ravensheugh [NY 8315 7491], Little Callerhues [NY 8495 8586], The Crag [NY 8845 8585], Allery [NY 8881 8200] and Great Wanney [NY 9300 8330]. The scarp face of the Whin Sill in the Roman Wall area is also mantled by a combination of head and scree deposits merging imperceptibly into one another and which is particularly well seen at Sewingshields Crags [NY 8030 7017]. Valley-fill head deposits are more difficult to differentiate from terrace or alluvial deposits or boulder clay infills particularly where exposure is limited. Examples of such deposits are present near Long Crags [NY 8121 8582], near The Hole [NY 8710 8450] and near Low Learn [NY 8796 8629] where about 1 m of sandy clay with sandstone boulders and cobbles is exposed.

River development

The drainage of the district has evolved over a long period (Sissons, 1960). Although the main outlines of the drainage pattern can be related to the regional structure (e.g. Merrick, 1915) much of the detail of its origin and early history must remain speculative. This section is concerned solely with the effects of the glaciation on the preglacial drainage pattern and on the development of the present drainage and related deposits in post-glacial times.

As noted previously, during the period of ice cover the drainage was largely subglacial and was influenced more by the direction of ice movement than by the elevation of rockhead. At the same time large amounts of glacially transported debris were deposited and locally rock-basins were deepened by ice-erosion. Thus, it is to be expected that only the major features of the preglacial and post-glacial drainage would coincide. Major rivers such as the North and South Tyne and the Rede are in similar positions to those occupied by preglacial rivers, although locally it can be inferred from borehole records that the preglacial rivers flowed up to a kilometre away from their present courses in channels now filled with drift deposits. Similarly most of the major tributary valleys appear to have formed in preglacial times though commonly totally new courses were cut in post-glacial times or existing subglacial channels deepened. There are a number of examples of major diversion of tributary streams from their preglacial courses. The best example is that of Blacka Burn which flows eastwards towards Low Stead and then turns to the north [NY 813 779], flowing through a rock-gorge to join Houxty Burn at Esp Mill. Borings hereabouts suggest that the preglacial Blacka Burn did not change direction but continued to flow eastwards towards Wark. Thick drift in a boring near High Tipalt [NY 697 685] suggested to Day (1970, pp. 259–260) that in preglacial times the headwaters of the present River Irthing flowed in a now buried valley from the Bewcastle district across the south-western corner of this district to join the River South Tyne near Haltwhistle. Another buried valley, an ancestor in part of Settlingstones Burn, was proved by mine workings at Settlingstones (Dunham, 1948, fig. 30). A possibly related buried valley has been proved by commercial borings to the east-north-east near Torney's Fell.

The drainage pattern of the minor streams, including the headwaters of the Rivers Wansbeck and Pont, is largely post-glacial in origin but locally follows channels originally cut by subglacial meltwater. This is particularly true in the country west of grid-easting 87 and north of northing 75, where the drainage pattern is closely controlled by the strongly lineated drift morphology (Figure 36), except in drift-free areas. However, even in the remainder of the district, where the drift is generally thinner and the geomorphology is closely related to geological structure, there is considerable glacial and post-glacial modification of drainage by glacial deepening of shale-floored basins and the random dumping of glacial debris. Lakes were formed locally and new channels cut or existing subglacial channels deepened. The stream diversions so produced are numerous and have resulted in local captures of catchment. These account for the complex and irregular watershed, in the south-west of the district, between the streams which flow eastwards to the River North Tyne and those which flow to the south into Tipalt Burn and Caw Burn and thence into the River South Tyne. Post-glacial capture of parts of the North Tyne drainage by the River Wansbeck in the Sweethope Loughs area, can be ascribed to similar causes. Most of the lakes, which formed in late-glacial times (Pearson, 1960), were later drained due to the downcutting of the outflow channels. The former lake sites are hollows filled by peat and alluvium (clay, silt and sand). The present natural lakes are the shrunken remnants of much larger bodies of water.

In post-glacial times spreads of alluvium have been laid down by the streams and rivers. Previous river levels are marked by deposits lying on terraces cut at heights above that of the present river. These terraces are commonly regarded as indicating successive lowerings of base levels (Peel, 1941) though Miller (1883) interpreted them as the natural products of continuously downcutting rivers. Peel (1941) studied the longitudinal profile of the North Tyne and concluded that there is a major nick-point just below Bellingham at a height of about 350ft (107 m) above sea level. Upstream of this point the river is graded to a level 140 to 150ft (about 45 m) above the present base level. The alluvium of the present floodplain, up to 7 m thick, is mainly composed of sand with lenses of gravel, except at the base where coarse gravels are commonly found. The terrace deposits, chiefly sand and gravel, are rarely more than 2 m thick. A narrow strip of gravel, believed to have been river-deposited but lacking a terrace-form, occurs near Ridley Stokoe [NY 7501 8576]. Near Humshaugh [NY 927 711 sandy deposits having a moundy form have been mapped as river terrace deposits, but might more correctly have been classed as glacial sand and gravel. Nearby in the Erring Burn Valley [NY 9557 7246]; [NY 959 725] flat-topped mounds of sand and gravel have been similarly arbitrarily divided.

Peat

Peat, largely consisting of Sphagnum and Eriophorum, is widespread in the western part of the district (Plate 15), and covers restricted areas in the east: Detailed studies of sites within or just outside the district have been made by Raistrick and Blackburn (1932), Blackburn (1947, 1953), Pearson (1960) and Chapman (1964a,b) (see also Day, 1970, pp. 262–263). On morphological grounds the peat can be divided into hill peat and basin peat, but these are not distinguished on the map. In the basins, fen peats were the first to form (pollen zones IV, V and VI), overlying the deposits of shallow lakes, and overlain by brushwood and then Sphagnum–Eriophorum peats (pollen zones VI to VIIa). These changes do not appear to have been synchronous in every basin (Pearson, 1960; Chapman, 1964a). Later, in pollen zone VIIb, Sphagnum–Eriophorum peat, commonly with a birch layer at the base, spread over a wide area beyond the basin margins. At Coom Rigg Moss [NY 693 794], on the border between the Bewcastle and Bellingham districts, Chapman (1964a) has demonstrated that several basins have been united by the formation of blanket bog to form one single peat covered area. Basin peats locally exceed 10 m in thickness (Pearson, 1960). Hill peats rarely exceed 2 m in thickness. The minimum mapped thickness is about 0.5 m; beyond the mapped limit thin deposits of peat, grading down to peaty soil, are widespread over the higher ground in the north and west of the district.

Near Clintburn [NY 732 813] woody peat, up to 2 m thick, forms terrace-like flats about 3 m above the level of the stream. Preliminary palynological investigation by Dr R. Harland suggests that these deposits are Sub-Atlantic (pollen zone VIII) in age. Similar terrace peats in the Bewcastle (12) district (Day, 1970, p. 263) are older (Pollen zones V to VIIa).

Landslip and scree

Numerous landslips have occurred in the district. For the most part these are where steep slopes of boulder clay have been undercut by stream action. Slips of this kind, particularly common in the valleys of the Chirdon, Warks, and Hareshaw burns, range in age from earliest post-glacial times to the present day. Inactive slips, no longer subject to stream attack, are commonly truncated by river terrace deposits and were formed at times when the river level was higher than now. Some of the largest active landslips, e.g. those near Allery Bank [NY 748 820]; [NY 752 826] occur on the outer banks of stream meanders. Slipped masses of glacial sand and gravel occur near Chollerton [NY 939 719] on the banks of Erring Burn.

Screes, now largely grassed over, occur in front of some of the larger whinstone and sandstone crags.

Calcareous tufa

Small areas of calcareous tufa occur in the district. They commonly mark the position of spring lines or cover limestone crops in streams. A large area of tufa has been deposited, and subsequently partly eroded, by springs believed to emanate from the Bankhouses Limestone [NY 9611 8526] near Ray Demesne. No areas of tufa are extensive enough to be shown on the maps.

Made ground

Railway embankments and quarry- and mine-waste form the bulk of the made ground. Tips from the Redesdale Ironstone workings are particularly extensive. Other large tips include those near Settlingstones, Stonecroft and Fallowfield mines and at Barrasford, Prudhamstone and Fourstones quarries. Fourstones, Brunton Bank and Black Pasture quarries are used as domestic refuse tips.

Chapter 10 Economic products and water supply

The Bellingham district is sparsely populated and far removed from large conurbations and the centres of trade and industry. The local population have therefore sought and utilised natural resources and were until recently self-sufficient as regards the majority of their needs. There are vast reserves of roadstone (dolerite), building stone (sandstone) and aggregates, and large potential water supplies. At the time of writing, Kielder Reservoir dam is under construction near Falstone, just beyond the north-west corner of the district. It will impound the largest man-made reservoir in Europe. Until it closed a few years ago Settlingstones Mine was the world's leading producer of witherite. Redesdale Ironstone had a reputation for yielding excellent iron, but operating costs were high and the industry did not survive beyond about 1860.

Metalliferous and associated minerals

The northern part of the Haydon Bridge mining field (Dunham, 1948, pp. 319–328) lies within the Bellingham district. In two distinct areas rocks of the Upper Liddesdale and Stainmore groups are cut by mineral veins which occur along faults, commonly with a north-easterly trend. At Fallowfield, the more easterly area, there is only one major vein but to the west around Settlingstones, there are several veins en échelon. These were extensively investigated in the past and there have been important workings at Settlingstones, Stonecroft and Fallowfield. Galena, the principal object of the early workings, together with sphalerite, normally forms only a small part of the vein material. The gangue is mainly either witherite or baryte (Dunham, 1948), both of which have a wide range of uses (Cummings and Bichan, 1970; Collins, 1972) and are now of commercial value and seem certain to be the subject of further interest in this area.

The age of this mineralisation and that of the Northern Pennines as a whole is still uncertain. The veins post-date the Whin Sill and are largely confined to Carboniferous rocks. This may indicate that the main phase of deposition occurred in the Westphalian–Zechstein interval, though redistribution of certain minerals may well have continued at times since that period (Dunham, 1974).

North of the major mineral occurrences only minor showings of galena and other vein minerals have been noted (Smith, 1923). Whether these have a common origin with the deposits of the main orefield is not known.

Details

The mining geology of the Settlingstones, Stonecroft and Fallowfield areas has been described by Wilson and others (1922) and Smith (1923) and more fully by Dunham (1948). Only a summary of the extensive details provided by these authors is given here. See also Anon (1968), Cummings and Bichan (1970) and Collins (1972).

Settlingstones

The early workings at Settlingstones, near to the crop of the vein in the burn, were for galena, with baryte and ankerite as the main gangue minerals. As the workings progressed towards the southwest, the vein was displaced by a cross-course beyond which the mineralisation changed to witherite with only small amounts of other minerals. From 1873 to the closure of the mine in 1969, witherite was the sole mineral produced. The witherite orebody had a width of 2.5 to 3 m, exceptionally reaching 9 m, in a productive zone 1300 m in length, which was terminated by a crosscourse near Grindon Hill Shaft. The richest mineralisation was generally found where the Whin Sill formed one or both of the vein-walls.

Closure was due to exhaustion of witherite ore, but considerable amounts of baryte are said to have been proved in the most southerly workings beyond the termination of the witherite. There is scope for further exploration in the Settlingstones area and it is probable that considerable reserves of barium minerals await proving. There is much unexplored ground to the south and east of Settlingstones, and the formerly productive St Andrew and Bewick veins to the south of the district have not been investigated at the level of the Whin Sill. The Grindon Hill Fault to the west of Settlingstones has a trend subparallel to the known veins but has not been investigated.

Stonecroft

A complex of veins to the north-west of Settlingstones, centred on Stonecroft, was worked between 1853 and 1896. Galena was again the main objective with baryte as the major gangue mineral and lesser amounts of sphalerite and ankerite. As at Settlingstones, the ore-shoots were in the Whin Sill. Some large tailing dumps remain. Most of the available ore seems to have been extracted but there are indications that the veins may continue to the south of their proven limits.

Fallowfield

The workings at Fallowfield have a long history of lead mining terminating in 1914. From 1846 to the close, witherite was the major product. The main workings were around Fallowfield Dene but small trials were made to both the south-west and north-east with little success. The vein, up to 12 m wide, occurs in a fault with a substantial downthrow, of up to 73 m, to the south-east. Strata encountered in the mine range from the Namurian Oakwood Limestone down to the Four-Fathom Limestone near the top of the Liddesdale Group. The deepest workings were around 110 m below surface, barely reaching the Great Limestone on the hanging-wall. It appears likely that workable ground remains in this mine but the capital costs of gaining access and working the ore are likely to be high. The Whin Sill, so productive at Settlingstones and Stonecroft, is at too great a depth to attract exploration in the foreseeable future.

Minor occurrences

A number of other occurrences of galena have been tried, but in no case was an economic deposit located.

Loose pieces of mineralised limestone are all that remains of old lead workings [NY 8779 7244] near Sharpley. The vein was worked in the last century by Sir Lancelot Allgood of Nunwick and although the ore was said to be good there was insufficient quantity to warrant continuing exploitation. A nearby vein [NY 8644 7280] at Tecket was similarly uneconomic to work.

Farther upstream, in the Crook Burn, several other small veins were tried [NY 8600 7252] and [NY 8574 7216] with little success. At one locality [NY 8550 7220] referred to as Teppermoor Old Lead Mines, a north-easterly vein was reported to be up to 30 cm wide containing high grade baryte.

An adit in the banks of the North Tyne near Barrasford [NY 9124 7322] was driven north-west through strata below the Oxford Limestone probably to intersect a small fault inferred to occur there. No signs of mineralisation are to be seen now but it is possible that the fault-plane with some vein material was formerly visible.

A number of narrow veins (up to 2 cm wide) carrying calcite, quartz and pyrite cut the Whin Sill in Swinburne Quarry [NY 949 766] but are not known in the neighbouring country rocks. At Quarry House Mine [NY 9645 8082] a vein, up to 60 cm thick, with similar mineralogy, together with galena, was investigated by surface workings and three shafts were sunk through the Whin Sill into the underlying rocks of the Upper Liddesdale Group (Smith, 1923, p. 17). These workings up to 55 m deep, appear to have reached the Barrasford Limestone. Trials for lead where the Sweethope Fault cuts the Whin Sill, near Kirkwhelpington [NY 9955 8423] beyond the eastern margin of the district are mentioned by Smith (1923, pp. 16–17).

In the banks of the River Wansbeck near Crookdene [NY 9708 8320], an adit was driven, through beds below the Colwell Limestone, apparently to intersect a small fault carrying the Crookdene Dyke. No mineralisation can now be seen where the fault and dyke cross the river. However, coal is known hereabouts and the adit may have been driven for this.

Road metal

The most important source of road metal in the district is the dolerite of the Whin Sill. It is worked from five quarries at Keepershield [NY 894 723], Barrasford [NY 913 744], Swinburne [NY 949 768], Divethill [NY 981 792] and Kirkwhelpington [NY 976 838] Reserves are enormous and though the major part of these are in the National Park they should provide a valuable source of aggregate for many years to come.

The Forestry Commission have opened up several sandstone and limestone quarries in Wark Forest to provide material for foundations of their own road network. This base is then often surfaced with the dust and remnants from the crushing and grading plants provided by the nearby commercial Whin quarries.

Details

Dolerite

Kirkwhelpington Quarry (Tilcon) [NY 976 838] although small, is typical of the whin quarries in the Bellingham district. It was opened in 1938 and for the first eleven years generated its own electricity so that stone production was limited. Grid power was supplied in 1949 with a resulting increase in output. It produces both graded whin and granular sub-base together with dust. There are no local or unusual difficulties in quarrying, the operation following the standard drilling and blasting and the use of front-end loaders to the primary crushers. The dolerite has a crushing strength of 52 500 p.s.i. and present production is around 100 000 tonnes per annum to local and Tyneside markets.

Divethill Quarry (McLaren & Co. Ltd.) [NY 981 792] was first opened in 1935 and has recently modernised to increase output. It employs nine local men who produce dolerite for readymix concrete, roadmaking, house building and constructional and civil engineering works over much of Northumberland.

At the time of the resurvey, Keepershield Quarry [NY 894 723] was the only whin quarry where, after the initial blasting of the face, the blocks were broken by hand to a finer grade before proceeding to the crushing process.

No production details were available for the two largest whin quarries in the district at Barrasford and Swinburne.

Sandstone and limestone

Sandstone at Little Bell Crags [NY 778 730] and on Cairnglastenhope Moor [NY 7439 7965] have been extensively quarried in the past few years by the Forestry Commission. On a smaller scale, limestone has been quarried at Green Carts [NY 772 716] and on Sweet Rigg [NY 762 710] in the Naworth Limestone and from Rowantree Cleugh [NY 7141 8184] in the sandy Spy Hole Limestone.

The only locality where limestone is now commercially worked for roadstone is at Barrasford Quarry where small amounts are obtained from the Oxford Limestone, here overlying the Whin Sill. Brunton [NY 928 700], Cocklaw [NY 937 703], and Fourstones [NY 889 688] quarries formerly produced large tonnages from the Great Limestone, a proportion of which was burnt for lime.

Coal

Coal has been worked throughout the district, mostly on a small scale won from bell-pits, short adits or levels, and more rarely from small collieries which did not excavate to depths of more than 100 m. There are numerous seams throughout the Carboniferous succession but they are normally less than 1 m in thickness. Earliest workings were probably Roman and coal was certainly dug in the 13th century for household use, but the main period of activity was in the 19th century. At the time of the resurvey only one small, privately owned colliery was in operation. Typical difficulties of coal mining in this district are the thinness and variability of poor quality seams, low in rank and with numerous bands and partings, and hence a high ash content. These factors, coupled with faulted strata and large quantities of groundwater, suggest that no large-scale commercial workings of these coals can be envisaged in the foreseeable future.

The most successfully worked seams have been the Thirlwall Coal in the west, the Plashetts or Bellingham Coal in the northern and central areas, the Fourlaws, Gunnerton or Cowden Coal in the north-east and the Little Limestone Coal in the south-east. There are suitable sites for further small-scale workings by both deep mining as well as by opencast methods.

Details

Upper Border Group and Lower Liddesdale Group coals

Thirlwall Coal

Wallshield Colliery [NY 7147 7017] extracted coal from an area of 600 m x 300 m. At least four drifts were driven and two shafts sunk, one 12 m deep to work the coal which was up to 86 cm thick and dipped to the south at about 1 in 6. The most easterly limit of workings was reached in 1933 but the colliery did not close until 1954. The roof of the seam was referred to as a 'bastard seggar' which was unstable and made working the coal particularly dangerous. In adjacent workings to the north-east from Rushey Hill Colliery [NY 7178 7030] the seam reached a metre in thickness. Water was drained away from these workings at a rate of 35 gallons per minute (3l/s). The pit closed at the same time as Wallshield Colliery.

Smith (1912, p. 145) states that the Thirlwall Coal is excellent for household, steam and coking purposes, but that it leaves a heavy dark red ash on combustion.

Robin Rock Drift (Ventners Hall Colliery) [NY 7242 7066] Little remains at surface to indicate the past importance and extent of underground workings of this colliery. The coal was worked out from an area 2 km x 1 km before being closed by the N.C.B. in 1959. Tips and pit head gear have been levelled and removed. In the west, the seam shared the difficult roof conditions with those experienced in the neighbouring Wallshield and Rushey Hill collieries but the dip was more gentle at 1 in 10. The coal was brought up the main drift by conveyor. Another drift known as the Back Drift [NY 7292 7083] was still open during the resurvey and exposed a 10 cm thick coal in a section along its walls. This level has also now been filled, and a new adit driven close by [NY 7289 7085] under licence from the N.C.B. This New Robin Rock Drift has extended the workings north-eastwards and found conditions drier than those in the old colliery. The seam averages 90 cm in thickness.

The Thirlwall Coal has been worked on a much smaller scale from several drifts [NY 7375 7140] to the east of Robin Rock but appears to deteriorate towards Greenlee. In the north-east part of the district, two seams named the Upper Hall and Furnace coals are considered to be close stratigraphical equivalents to the Thirlwall Coal.

Upper Hall Pit [NY 8430 8366] was sunk at Hareshaw Ironworks, Bellingham and proved the Upper Hall Coal, 38 cm thick separated by 4.5 m of measures from the underlying Furnace Coal of similar thickness. They were worked locally for use in the iron works but were of poor quality; no underground plans exist.

Other workings considered to be at this stratigraphical level are visible near Ridsdale [NY 880 840], Linacres Farm [NY 8157 7857], Wark Colliery [NY 8558 7651], and Brieredge Farm. At Brieredge, the coal 51 to 64 cm thick, was worked at crop and from two shafts [NY 8080 8320] and [NY 8064 8276] 10.67 m and 5.49 m deep respectively.

Coal, 46 cm thick, was worked from a shaft [NY 8303 7873] at Kings House (now Manor Farm). This seam is probably at the Furnace horizon.

Old levels at Broadgate [NY 8925 8630] worked a thin coal below the Furnace Seam.

Plashetts or Bellingham Coal

This coal was worked between 1910 and 1927 at Hesleyside Colliery [NY 8014 8400] near Low Carriteth. The workings were mostly on a small scale, despite a borehole [81)11 8365] made in 1910 in an attempt to prove further reserves. The total thickness of the seam and dirt bands exceeded 2 m, but the best workable fractions were only 50 cm and 40 cm thick separated by a 70 cm band of seatearth. Low Carriteth Borehole [NY 8003 8385] was drilled during the resurvey near the colliery and proved the two main leaves of the seam to be 35 cm and 29 cm thick with a seatearth parting of 57 cm. The lower 29 cm leaf contained many pyrite nodules. The borehole also proved artesian water at shallow depth comparable in composition with that which drains from the old workings of the colliery.

Extensive workings, considered to be in the Plashetts Coal, can be seen scarring the moorland near Birchhope [NY 810 870] on the northern margin of the district. Correspondence of the slope of the land and the dip have enabled large areas to be worked from near-surface bell-pits known locally as 'fairy pits' or 'Kelties'.

The area of old workings [NY 746 836] in the vicinity of Roughside suggests that the Bellingham Coal was profitably extracted here in the past. Eals Cleugh Borehole [NY 7442 8404] proved the seam to be 1.14 m thick with only thin mudstone partings; and this area is probably a good prospect for future small-scale mining operations.

Old workings, levels and tips [NY 8325 8064] beneath Shitlington and Billerley crags are thought to be in the Plashetts or Bellingham Coal, where the seam was recorded as some 60 cm thick. The same coal is poorly exposed [NY 8230 7975] below Bridge House in the Houxty Burn and contains ostracods and a thin limestone in its roof. It was reported to be of good quality, 46 cm thick south of Billerley Farm [NY 8380 7932].

Fourlaws, Gunnerton or Cowden Coal

Goatstones Colliery [NY 8453 7473] worked an area of coal, known locally as the Cowden Seam, some 700 m x 200 m beneath Goatstones Farm near Simonburn. An adit was driven from the eastern side of the workings and two air shafts of 11.6 m and 7 m depth were sunk to the north side. The seam comprised upper and lower leaves 43 cm and 35 cm respectively separated by 60 cm of dirt. The upper leaf was also split by a 7 cm dirt parting through its middle. The dip was 1 in 7 underground, disturbed by several small faults of up to 7 m vertical displacement. Poor roof conditions were encountered in the north-west sector where the roof was shale, but this passed southwards into a ganister which provided better support.

Farther downstream, near Allgood Farm, the coal was worked at crop and in numerous old levels [NY 8535 7443].

The Simonburn Borehole [NY 8735 7372], drilled during the resurvey, proved the continuance of the seam into the North Tyne valley where two leaves 30 cm and 14 cm thick were separated by coal and dirt up to 94 cm. Future workings in this area would need to be pumped dry.

Sutty Row Colliery [NY 9054 7755], near Gunnerton, closed during the resurvey of the district in 1975. The average thickness of the Fourlaws coal in the workings was 60 cm and it dipped south-eastwards at 1 in 15. The workings were restricted towards the outcrop by numerous old bell-pits and limited down-dip by groundwater in quantities too great for economic pumping. Extension of the 'take' along strike was not allowed under the existing N.C.B. mining licence. The oldest mine-workings date from 1896 and were reached from Birtley Colliery Old Pit (Downcast Shaft), [NY 9014 7772] some 31 m deep. The so-called New Pit (or Upcast Shaft) [NY 9030 7770] was some 36 m deep. More recent workings were reached by a 1 in 3 drift [NY 9054 7755].

Gunnerton Pit worked the Fourlaws or Gunnerton Coal until 1920 from a shaft [NY 8979 7662] 38.4 m deep sunk in 1876. The seam had an average thickness of 60 cm and a dip to the south-southeast of 1 in 14.

Cowden Colliery was founded on a shaft [NY 9113 7907] 35.68 m deep. No underground information is known but workings up-dip must have been limited by the numerous bell-pits and shallow diggings present near the outcrop.

Fourlaws Hill Top Colliery near Ridsdale was worked until 1906. The general section of strata showed the seam to be 70 to 81 cm thick with a sandstone floor and roof. Some 65 cm of coal with a dirt parting are still exposed at the mouth of a level [NY 9095 8307] on the site of the old colliery.

In the 1950's several new levels [NY 9110 8347] and [NY 9107 8362] were driven at intervals along the outcrop at Fourlaws Edge and provided sufficient coal for the local farmers. One old shaft called Shipley's Old Pit [NY 911 834] on Fourlaws Edge was worked between 1846 and 1852 in conjunction with the Aid Crag Pits, Ridsdale.

Aid Crag Pits The Ridsdale Ironstone company sunk several shafts and drilled exploratory boreholes in the vicinity of Aid Grag, the exact location of some are uncertain.

The Fourlaws Coal was worked from, among others, rurnace Pit [NY 919 839], Folly Pit [NY 9169 8399], Aid Pit or Engine Pit [NY 9201 8401]. A railway track was built to transport the coal, as well as sandstone, from near Aid Crag to Ridsdale. The coal was variable but usually comprised two leaves 60 and 20 cm thick separated by some 30 cm of dirt.

Other collieries were opened and further boreholes drilled in the Stiddlehill Common area. Stiddlehill Colliery [NY 9197 8491], also known as Ridsdale Colliery, was sunk in 1871 but abandoned in 1879 largely because of flooding in the workings. A shaft known as New Pit [NY 9140 8530] was sunk in 1909 but had a limited life working the seam up-dip. Another shaft also known as Stiddleh ill Colliery, New Pit [NY 9198 8493] was sunk on higher ground by Mr Mundle under the ownership of Mr Barker only to encounter faulted strata as well as inferior coal, and the colliery finally closed in 1932.

Shanks Kiln Pit [NY 9254 8530] was sunk in 1892 but unfortunately the thin seams overlying the Fourlaws Coal were mistaken for the main seam and the workings abandoned as uneconomic.

Extensive tips provide evidence of old workings [NY 9082 8608] in the Fourlaws Coal near East Woodburn. The primary survey however recorded only a 30-cm thick coal which was then exposed in the adjacent railway cutting.

The Fourlaws Coal has also been worked in the faulted ground between Ridsdale and Bellingham, e.g. near Redesmouth [NY 884 827] and north-east of Blakelaw [NY 8495 8473]. Old levels to the south near Black Law [NY 8050 7357] and [NY 8004 7303] were driven to the Fourlaws.

Miscellaneous workings

Hilda Drift (1941) worked a thin representative probably of the Chapelburn Coal on the banks of the Pont Gallon Burn [NY 7285 6981].

Harelaw Pit [NY 7605 7678], north-west of Stonehaugh, worked a seam 38 to 46 cm thick above the Forster's Hill Limestone. A seam at a similar horizon was won from shafts [NY 7988 7645] near Stonehaugh village. Nearby, in Sandy Sike, there are old workings [NY 7923 7657] in a coal 41 cm thick at a horizon between the Millerhill and Forster's Hill limestones.

There are many old trials and workings for coal in the Warksburn valley, where thin seams of the Upper Border Group crop out. They can be seen at the following localities [NY 8415 7662], [NY 8150 7700] and [NY 8180 7630].

Bearsmouth Colliery (1883) [NY 8076 8610] north-west of Charlton, consisted of an adit driven eastwards to a seam comprising: top leaf 25 cm, coal and dirt 43 cm on lower leaf 48 cm. It was also worked along the crop both to the east and west.

Upper Liddesdale Group coals

A few thin coals of no economic significance occur in the Upper Liddesdale Group including, in the north-eastern part of the district, a thin representative of the Shilbottle Coal. In the past these coals have been worked only locally on a very small scale. A coal 33 cm thick was reported to have been worked from a level [NY 8060 7055] north of Sewingshields. This coal lies closely above the Barrasford Limestone and another of similar thickness was also reported beneath the limestone.

Stainxiore Group (Namurian) coals

The Little Limestone Coal, though no longer mined, was extensively worked in the past. The main mines were Fourstones and Stagshaw collieries and coal was also worked for a time in the Fallowfield galena and witherite mine. The most northerly workings of Acomb Colliery extended into the distrct. Numerous other surface workings and shafts occur near the crop of the coal. Because of the unknown extent of the oldest workings, the quantity and distribution of remaining reserves in the district must be conjectural. However, the average thickness of the coal (60 cm) is not sufficient to suggest any immediate economic interest.

The Oakwood Coal has not been worked within the district though it was won from Acomb Colliery beyond the southern edge.

Building stone

Most of the farms and houses in the district are built of local stone and only recently have cheaper alternatives been allowed in some council and forestry developments. Sandstone has been quarried since Roman times; excavations near Sewingshields [NY 8100 6985] in the sandstone beneath the Eelwell Limestone were probably made for building Hadrian's Wall. This sandstone is characterised by convolute cross-bedding and dressed stone in this section of the Wall commonly displays such features.

Among large sandstone workings in more recent times, Woodburn Quarries [NY 899 858] and [NY 902 858] provided stone for East and West Woodburn, quarries at the Reenes [NY 826 843] and Longhaughshields [NY 820 850] for Bellingham and Millknock Quarry [NY 880 794] for Birtley. Only two quarries, Black Pasture [NY 931 699] and Prudhamstone [NY 884 687] were sufficiently large to send stone outside the district. The latter quarry is still active on a small scale.

Limestone is little used as a building stone but small quarries may have been opened for local walling stone.

Whinstone, largely in the form of rounded glacial erratics, has been incorporated into field walls and barn foundations.

Thin sandstone beds interlaminated with mudstones overlying the Redesdale Limestone at Birtley [NY 8810 7855] were once worked for roofing 'slate' but the industry was only a local concern judging from the small size of the shallow diggings.

Lime

In the past most large farms supported their own limestone quarries and kilns in which the stone was burnt and then spread on the fields to neutralise the acid and replenish the leached soils of the district. There is good evidence to support the view that the width of Hadrian's Wall was reduced when the construction teams reached areas where limestone cropped out and lime was used as a cementing agent. Improved communications and transportation made local kilns uneconomic but limestone was burnt as recently as the 1950's in the Redesdale Limestone quarries at Buteland [NY 880 816].

Brick clay

A pit near Chesterhope Cottage, the exact site of which is uncertain, was sunk through some 3 m of boulder clay overlying some 11 m of measures down to a seatearth 1 m thick. This clay was used in the nearby brickworks [NY 8985 8517] together with a mixture of boulder clay and shale. An excavation [NY 8989 8507] open during the time of the first survey has now been filled and levelled.

Clay from an old pit [NY 8418 7370] 1 km S of Goatstones was probably used for lining the kiln at the nearby limestone quarry [NY 8380 7385].

Glacial laminated clays were formerly worked for brick-making in the Erringburn Valley [NY 9618 7305].

A timber works near High Pithouse, 4 km south of Ridsdale, stands on the site of a tile works. Boulder clay was presumably the main raw material although the outcrop of the Fourlaws Coal is close by and its fireclay was probably also used.

There were tile works on Wark Common [NY 835 781], at Brieredge [NY 807 828] near Bellingham and [NY 9115 7950] and [NY 8950 7710] east of Wark. The Wark Common works used boulder clay as a basic raw material, the others extracted mudstones and fireclays associated with the nearby coal outcrops.

Mudstones above the Oxford Limestone were formerly worked for tile manufacture near North Heugh [NY 9540 8025], as were the mudstones above the Great Limestone in workings adjacent to Fourstones Quarry [NY 8930 6875].

Ironstone

Ridsdale and Bellingham were thriving centres of ironstone mining in the 19th century. The ironstones are nodular ores composed of concretionary siderite occurring in mudstones 9 m or so thick some 3 to 12 m below the Redesdale Limestone. Although many mudstones in the district contain nodules it was only at this restricted horizon and in this local area that the nodules were big enough and sufficiently concentrated to warrant economic extraction. The largest nodule was reported to weigh 23 kg. The mudstones were originally dug at outcrop and then mined using pillar and stall techniques beneath increasing overburden (Lebour, 1873; Hemingway, 1972). Adit mouths are still visible near Ridsdale [NY 9019 8409] and Bellingham [NY 8438 8401]. In 1871 some 21000 tons were extracted from underground workings in the Ridsdale area.

The Hareshaw Iron Company was established at Bellingham with an investment of some £150000. In the 1860's there were three blast furnaces and several coke ovens in operation. Pits were sunk for coal and a dam built across Hareshaw Burn to supply water to power waterwheels to drive the blast furnace bellows.

The ironstones were however relatively low in iron content, the coal seams were thin and transport costs to Hexham and beyond high. The company operated only for a few years and by the time the Hexham–Morpeth railway reached Bellingham, better Jurassic ores from Yorkshire and new techniques with larger installations at Consett and elsewhere made the venture uneconomic (Bell, 1864). The iron smelted at Hareshaw had the distinction however of being used in the construction of the High Level Bridge over the River Tyne at Newcastle.

Sand and gravel

In the terraces of the rivers North Tyne and Rede there are extensive deposits of sand and gravel; only in the south of the district have these deposits been evaluated (Lovell, in press). Many thousands of tons were extracted from the North Tyne between Hesleyside and Dunterley during the first half of this century.

Minor diggings for sand and gravel are found in many parts of the district. Around Humshaugh and Chollerton most workings were in the gravelly upper portion of the boulder clay. Elsewhere, between Bingfield and Colwell, glacial sands and gravels overlying the boulder clay have been worked. The most substantial working, that at Liddell Hall near Colwell [NY 960 756] (Plate 14), periodically supplies small quantities.

Morainic sands and gravels near The Hole [NY 868 844] and in Lisles Burn [NY 925 861] have been worked locally from small pits.

Peat

Peat covers large areas in the north and west of the district (Plate 15), and has accumulated to depths of over 10 m in some of the larger basins such as Fozy Moss [NY 825 712]. Most peats are largely unexploited because of their inaccessibility, being dug only locally and intermittently for domestic use on remote farms, particularly in bad seasons or times of depression (e.g. on Huntlaw Moss [NY 7615 7575] and [NY 775 762]). Now much of this north-western area has been opened up by forestry roads and there are many localities from which peat might be dug for agricultural or horticultural purposes. It is noticeable that coniferous trees grow very slowly in the basin peat areas. In the past, because of the ill-drained nature of the ground, such areas were left unplanted. The two interests of forestry and peat exploitation could therefore coexist (Plate 16).

Water supply

Except for small areas in the south, east and west, the district lies within the catchment of the River North Tyne. It has an average annual rainfall ranging from over 45in (114 cm) in the north-west to below 35in (89 cm) in the south and east. There are several impounding reservoirs (e.g. Colt Crag and Hallington) which together with the public and private water supply, are controlled by the Northumbrian Water Authority. A few centres of population such as Bellingham, W ark and Humshaugh have mains water, but many outlying settlements and isolated farms obtain supplies from wells and springs.

Carboniferous rocks may be regarded as multi-layer aquifers in which the individual sandstones and limestones form unit aquifers separated by impervious mudstones. Beneath cover, groundwater in each unit is confined under pressure so that the final restwater level in a borehole is related to the individual pressures within each unit aquifer penetrated. Under these conditions movements of groundwater from unit to unit within the borehole is almost certain to occur.

It is a characteristic of this type of aquifer that true equilibrium between yield and pumping water level may not be attained under test conditions and the apparent maximum yield of a bore during test may exceed its maximum continuous yield when working (Day, 1970, p. 268).

Most boreholes in the district that have been drilled for water are less than 80 m deep, about 15 cm in diameter and yield up to 1.26 l/s (1000 gallons per hour). A weekly consumption for an average farm of say 15 000 to 22 000 litres (20000 to 30000 gallons) ensures that restwater levels recover quickly after pumping. The water is usually of good organic purity but somewhat hard and may contain appreciable amounts of iron which appears as a finely divided iron oxide precipitate.

A borehole at Stonehaughshields [NY 7978 7629] was drilled in Upper Border Group strata to provide water for the forestry village of Stonehaugh. It was 74 m deep with 25 cm perforated casing, and on test yielded 2.52 l/s (2000 gallons per hour) with a depression of water level of 15 m from which recovery was slow.

A borehole at Barrasford Sanatorium of similar depth but only 18 cm in diameter, and drilled in beds of the Liddesdale Group, yielded an artesian flow varying from 2.52 to 6.82 l/s (2000 to 5400 gallons per hour). Water was struck in fissures in the Low Tipalt Limestone and additional flow was obtained from the underlying sandstone. The water contained a brown suspension of iron oxide and calcium carbonate; it was hard (total hardness 323 mg/1 as CaCO₃) and with a rather high percentage (0.022) of free ammonia which probably came from the reduction of nitrates by iron compounds.

The Institute of Geological Sciences boreholes (Report Series Nos. 75/7 and 76/10) drilled in 1974–75 for strati-graphical information tended to confirm the groundwater potential in this district. Eight boreholes out of a total of eleven drilled were artesian and the flow was apparently not affected by the drought of the summer of 1976. Comprehensive yield tests have not however been carried out.

Analyses by Dr W. Monograptus Edmunds of water samples taken from the artesian boreholes together with those from springs and old colliery workings included for comparison are shown in (Figure 37).

Most of the samples are of calcium and magnesium bicarbonate type but the two deep boreholes, Stonehaugh and Ferneyrigg, yielded cation-exchanged water of sodium bicarbonate type. The high fluoride content in the Stonehaugh Borehole sample may be correlated with the very low calcium. Strontium and barium values are rather high in water from Greenlee Borehole possibly indicating mineralisation in the Naworth Limestone.

Although some are rather hard, all these waters have excellent potability. The particularly low nitrate levels are noteworthy.

Appendix 1 List of boreholes and shafts

This appendix lists, by six-inch maps, the main borehole and shaft records for the district. For each record the permanent record number, location and the stratigraphical range is given, together with the starting level (where known), the total depth, the thickness of drift and the 'Borings and Sinkings' number (where relevant). Copies of the complete records may be obtained from the Institute at a fixed tariff. Abbreviations are as follows:

S–Stainmore Group, ULd–Upper Liddesdale Group, LLd–Lower Liddesdale Group, UBo v Upper Border Group, MBo–Middle Border Group, BH–Borehole, Lst–Limestone.

Appendix 2 List of measured sections

This appendix lists, by six-inch maps, the main measured section records for the district. For each record the permanent record number and the stratigraphical range is given. Copies of the complete records may be obtained from the North of England office of the Institute at a fixed tariff. Each entry in the list shows first the permanent record number and location of the section and then its stratigraphical range.

(NY77NW/3) Greenlee Cleugh Leahill Limestone [NY 7226 7565] to below Appletree Limestone [NY 7200 7612]

(NY77NW/4a), (NY77NW/4b), (NY77NW/4c), (NY77NW/4d), (NY77NW/4e), (NY77NW/4f), (NY77NW/4g), (NY77NW/4h), Warks Burn Sections [NY 7241 7513]; [NY 7281 7514]; [NY 7299 7521]; [NY 7301 7521]; [NY 7302 7521]; [NY 7314 7522]; [NY 7323 7523]; [NY 7326 7526] in strata from Leahill Limestone to below Appletree Limestone

(NY77NW/5a), (NY77NW/5b) Haining Moor Sections [NY 7295 7617]; [NY 7312 7618] to [NY 7315 7616] in beds below Leahill Limestone

(NY77NW/6) Green Moor Section [NY 7272 7835] in strata above Low Carriteth Limestone

(NY77NW/7) Clintburn Sections [NY 7293 8000] to [NY 7281 7977]; [NY 7253 7974]; [NY 7275 7965]; [NY 7276 7963]; [NY 7275 7971] in beds above and below Leahill Limestone

(NY77 NE/3) Middle Burn and Warks Burn Section in Upper Border Group from Leahill Limestone to above Millerhill Limestone [NY 7936 7509] to [NY 7926 7651]

(NY77SE/2) Coal Cleugh Section in Upper Border Group from above Leahill Limestone [NY 7919 7480] to Redesdale Limestone [NY 7781 7239]

(NY77SE/3) Middle Burn Section in Upper Border Group [NY 7933 7494] above Leahill Limestone

(NY77SE/4) Greenlee Burn Section in the Lower Liddesdale Group; Ladies Wood Limestone (K) [NY 7800 7070] to Redesdale Limestone [NY 7621 7132]

(NY78NW/123) Eckies Cleugh Section [NY 7414 8645] in Upper Border Group

(NY78NW/124) Yarrow Moor Section in adit mouth [NY 7025 8677]: Beds associated with second coal above Shilburnhaugh Coal

(NY78NW/125) Smales Burn Section [NY 7296 8577] to [NY 7303 8579] in Upper Border Group

(NY78NE/16) Lancy's Cleugh Sections [NY 8000 8737] to [NY 7944 8701] in beds below Plashetts Dun Limestone

(NY78NE/17) Tarset Burn Sections [NY 7880 8634] to [NY 7873 8626] in beds just above Bearsmouth Coal

(NY78NE/18) Thorneyburn Sections [NY 7635 8661]; [NY 7631 8668]; [NY 7637 8673]; [NY 7642 8678]; [NY 7639 8678] to [NY 7635 8686]; [NY 7627 8693] to [NY 7623 8696]; [NY 7620 8697]; [NY 7619 8698] to [NY 7614 8700]; [NY 7619 8726]; [NY 7620 8723]; [NY 7720 8689] in beds below Thorneyburn (?Leahill) Limestone

((NY78NE/19a)–(NY78NE/19b) Herdlee Close Burn Sections [NY 7530 8697]; [NY 7530 8682] in Upper Border Group

(NY78NE/20) Ryeclose Burn Section [NY 7532 8675] in Upper Border Group

(NY78NE/21) Rough Cleugh Section [NY 7508 8655] in Upper Border Group

(NY78NE/22) Roadside waterfall Section [NY 7582 8583] in beds above Thorneyburn Limestone

(NY78SW/4a), (NY78SW/4b), (NY78SW/4c), (NY78SW/4d), (NY78SW/4e), (NY78SW/4f), (NY78SW/4g), (NY78SW/4h), (NY78SW/4i), (NY78SW/4j), (NY78SW/4k), (NY78SW/4l), (NY78SW/4m) Smales Burn Sections [NY 7193 8400]; [NY 7202 8495]; [NY 7172 8446]; [NY 7192 8424]; [NY 7106 8307]; [NY 7120 8311]; [NY 7128 8315]; [NY 7142 8339]; [NY 7147 8337] to [NY 7153 8339]; [NY 7175 8350]; [NY 7178 8353]; [NY 7191 8374]; [NY 7192 8386] in Upper Border Group

(NY78SW/5) Crummels Sike Section in Appletree Limestone and underlying beds [NY 7488 8125]

(NY78SW/6 Chirdon Burn Section [NY 7498 8172] in beds above Leahill Limestone

(NY78SW/7a), (NY78SW/7b), (NY78SW/7c) Chirdon Burn Sections [NY 7133 8036]; [NY 7078 8023]; [NY 7086 8030] in Upper Border Group

(NY78SW/8) Rowantree Cleugh Section [NY 7187 8125] to [NY 7139 8184] in Spy Hole Limestone and overlying strata; immediately overlies strata proved in Rowantree Cleugh Borehole (NY78SW/3)

(NY78SW/9) Broomley Burn Section [NY 7016 8490] in Upper Border Group; overlies strata proved in Broomley Burn Borehole (NY78SW/2)

(NY78SE/1a), (NY78SE/1b), (NY78SE/1c), (NY78SE/1d), (NY78SE/1e), (NY78SE/1f), (NY78SE/1g) Chirdon Burn and Cairnglastenhope Sections [NY 7509 8175]; [NY 7514 8207]; [NY 7523 8225]; [NY 7542 8223]; [NY 7553 8101] to [NY 7560 8097]; [NY 7543 8250]; [NY 7531 8263] to [NY 7543 8260] in Leahill Limestone and associated beds.

(NY78SE/2a), (NY78SE/2b) Oxcleugh and March Burn Sections [NY 7935 8137] to [NY 7939 8129]; [NY 7945 8124] in Upper Border Group

(NY78SE/3a), (NY78SE/3b), (NY78SE/3c), (NY78SE/3d), (NY78SE/3e), High Carriteth Burn and Whitchester Sections [NY 7877 8316]; [NY 7864 8322]; [NY 7825 8249] to [NY 7840 8280]; [NY 7761 8311]; [NY 7864 8306] to [NY 7852 8300] in Leahill Limestone and associated beds

(NY86NE/15) Prudhamstone Quarry Sections [NY 8843 6870] in beds below Great Limestone

(NY86NE/34) Fourstones Quarry Section [NY 8864 6869] in Great Limestone

(NY86NE/35) Fourstones Quarry Section [NY 8883 6883] in Great Limestone

(NY86NE/36) Park Shield Section [NY 8973 6928] in beds below Four Fathom Limestone

(NY86NE/37a)-c Settlingstones Burn Sections [NY 8521 6885]; [NY 8517 6885]; [NY 8515 6885] in Shotto Wood Limestone and associated beds

(NY87NW/5)–(NY87NW/9) Warks Burn Sections [NY 8450 7675] to [NY 8041 7702] in Upper Border Group strata between Furnace Coal and Leahill–Spy Hole Limestone

(NY87NW/10) Gofton Burn Section [NY 8494 7612] in Upper Border Group above Low Carriteth Limestone

(NY87NW/11) Blacka Burn Section [NY 8151 7812] from Lower Liddesdale Group to Upper Border Group [NY 8188 7927]–Upper Gunnerton Fell Limestone to below Redesdale Limestone

(NY87NW/12) Houxty Burn Section [NY 8188 7927] to [NY 8292 7981] in Upper Border Group strata mostly below the Low Carriteth Limestone

(NY87NW/13) Woodpark Section [NY 8480 7995] to [NY 8470 8015] (on 88 SW); Upper Border Group and Lower Liddesdale Group above and below the ?Redesdale Limestone

(NY87NE/3) & (NY87NE/4 Warks Burn–River North Tyne Upper Border Group. Sections [NY 8610 7648] and [NY 8574 7643] between the ?Leahill Limestone and the Furnace Coal

(NY87NE/5) Gofton Burn Upper Border Group. Composite sections [NY 8580 7608] near Furnace Coal/Birtley Limestone

(NY87SW/1) Crook Burn Liddesdale Group; Bankhouses Limestone to below Low Tipalt Limestone [NY 8396 7225]

(NY87SE/9) Crook Burn Section in the Upper Liddesdale Group; Oxford Limestone [NY 857 719] to Bankhouses Limestone [NY 8597 7247]

(NY87SE/10) Simonburn Section in Lower Liddesdale Group; Low Tipalt Limestone [NY 8630 7263] to Lower Gunnerton Fell Limestone [NY 8748 7380]

(NY88NW/7) Hareshaw Burn Section of Upper Border Group [NY 8416 8543] to [NY 8408 8500]

(NY88NW/8) Charlton Burn Sections of Upper Border Group [NY 8076 8700] to [NY 8075 8595]

(NY88NW/9) Linthole Burn Sections of Upper Border Group [NY 8133 8568] to [NY 8140 8500]

(NY88SW/8) Hareshaw Burn Section in Lower Liddesdale Group (Fourlaws Limestone) to Upper Border Group (Furnace Coal) [NY 8411 8492] to [NY 8412 8361]

(NY88SW/9) Low Carriteth Burn Section in Upper Border Group above the Low Carriteth Limestone (8005 8380] to [NY 8012 8300]

(NY88SW/10) Longhaughshields Burn Section in Upper Border Group [NY 8180 8484] to [NY 8158 8478]

(NY88SW/11) Hesleyside Burn Section in Upper Border Group from Brieredge Coal [NY 8100 8286] to Low Carriteth Limestone [NY 8160 8337] (NY87NW/13) [NY 8680 7994]

(NY88SE/4) River North Tyne–Wood Park Upper Border Group [NY 8697 8008] Appletree Limestone

(NY88SE/5) Blakies Banks Upper Border Group [NY 8772 8078] to [NY 8735 8070]

(NY96NW/35a), (NY96NW/35b), (NY96NW/35c), (NY96NW/35d) Red Burn (Fallowfield) Sections [NY 9406 6789]; [NY 9420 6800]; [NY 9381 6765]; [NY 9378 6751] in beds below Oakwood Coal

(NY96NW/36) Mewsley Burn Section [NY 9077 6952] in beds below Four Fathom Limestone

(NY97NE/13) Hallington Section [NY 9810 7512] in beds below Upper Bath-House Wood Limestone

(NY97NE/16) Hallington Section [NY 9869 7607] in beds above Shotto Wood Limestone

(NY97NE/17) Hallington Section [NY 9814 7587] in beds below Upper Bath-House Wood Limestone

(NY97NE/18) Divet Hill Quarry Section [NY 9803 7921] in Upper Bath-House Wood Limestone and associated beds

(NY97NE/19) Thockrington Section [NY 9633 7913] in beds below Colwell Limestone

(NY97SW/3) Brunton Quarry Section [NY 9295 7005] in Great Limestone

(NY97SW/5a), (NY97SW/5b), (NY97SW/5c), (NY97SW/5d), (NY97SW/5e), (NY97SW/5f), (NY97SW/5g), (NY97SW/5h), (NY97SW/5i), (NY97SW/5j), (NY97SW/5k), (NY97SW/5l), (NY97SW/5m), (NY97SW/5n) River North Tyne and Swin Burn Sections [NY 9248 7204]; [NY 9256 7247]; [NY 9249 7213]; [NY 9241 7253]; [NY 9239 7260]; [NY 9246 7279]; [NY 9188 7305]; [NY 9249 7255]; [NY 9222 7298]; [NY 9218 7303]; [NY 9237 7346]; [NY 9276 7346]; [NY 9286 7408]; [NY 9137 7307] to [NY 9100 7316] in beds from above Shotto Wood Limestone to above Greengate Well Limestone

(NY97SE/44) Errington Section [NY 9568 7185] to [NY 9566 7211] in Shotto Wood Limestone and underlying beds

(NE98 NE/5a), (NE98 NE/5b), (NE98 NE/5c) Ray Burn Sections [NY 9796 8526]; [NY 9762 8531]; [NY 9748 8531] in beds between Colwell and Dalla Bank limestones

(NY98SE/14a), (NY98SE/14b) Crookdean Sections [NY 9711 8325]; [NY 9716 8331] in beds associated with Colwell Limestone

(NY98SE/15a), (NY98SE/15b), (NY98SE/15c), (NY98SE/15d), Kirkwhelpington Sections [NY 9959 8436]; [NY 9958 8438]; [NY 9967 8420]; [NY 9987 8420] in Whin Sill and beds from the Eelwell Limestone to below the Shotto Wood Limestone

Appendix 3 List of Geological Survey photographs

Copies of these photographs are deposited in the libraries of the Institute of Geological Sciences at Exhibition Road, London SW7 2DE, and Ring Road Halton, Leeds LS15 8TQ. They all belong to Series L and may be supplied as black and white prints or lantern slides, and as colour prints or 2 x 2 in colour transparencies, all at a fixed tariff.

Upper Border Group

Lower Liddesdale Group

Upper Liddesdale Group

Stainmore Group

Whin Sill

Drift

Economic

Scenery

The following form part of an older collection of black and white photographs taken in the late 1940's and now contained in Book 1 of 'Old Newcastle Office Photographs'. They all belong to Series NL and may be supplied as black and white prints or lantern slides.

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Fossil index

• Acanthotriletes acritarchus Neville
• Acanthotriletes socraticus Neves & Ioannides
• Actinopteria persulcata (McCoy)
• Acutiangulata
• Acutiangulata aequalis (Jones & Kirkby)
• Ahrensisporites duplicatus Neville
• Algal nodules
• Alitaria panderi (Muir-Wood)
• Amphissites
• Amphissites centronotus (Ulrich & Bassler)
• Amphissites cf. centronotus
• Amphissites wickhopensis Robinson
• Anaplanisporites denticulatus Sullivan
• Aphelocrinus dunlopi (Wright)
• Apiculatisporis? porosus Williams
• Apiculiretusispora multiseta (Luber) Butterworth & Spinner
• Archaeozonotriletes variabilis (Naumova) Allen
• Asturiella
• Asturiella cicatricosa Robinson
• Aulophyllum fungites pachyendothecum (Thomson)
• Aulophyllum fungites redesdalense Smith
• Auroraspora balteola Sullivan
• Auroraspora solisortus Hoffmeister, Staplin & Malloy
• Aviculopecten interstitialis (Phillips)
• Aviculopecten murchisoni (McCoy)
• Aviculopecten subconoideus Etheridgejun.
• Aviculopecten spp.
• Avonia youngiana (Davidson)
• Axophyllum vaughani (Salée)
• Baculatisporites fusticulus Sullivan
• Bairdia
• Bairdia beedei Ulrich & Bassler
• Bairdia cf. beedei
• Bairdia lecta Bushmina
• Bairdia orientalis Bushmina
• Bairdia submucronata Jones & Kirkby
• Bairdia sp.
• Bairdiolites
• Bairdiolites elevatus Robinson
• Berdanella
• Beyrichiopsis
• Beyrichiopsis fimbriata Jones & Kirkby
• Beyrichiopsis plicata (Jones & Kirkby)
• Beyrichiopsis simplex Jones & Kirkby
• Beyrichiopsis subdentata Jones & Kirkby
• Beyrichoceratoides redesdalense (Hind)
• Birdsalella
• Bolbozoella
• Bolbozoella nodosa Robinson
• Bollandoceras?
• Buxtonia sp. nov.
• Buxtonia spp.
• Calcifolium
• Calcifolium okense Schwetzov & Birina
• Camptotriletes cristatus Sullivan & Marshall
• 'Carbonita' fabulina (Jones & Kirkby)
• Cavellina
• Cavellina attenuata (Jones & Kirkby)
• Cavellina benniei (Jones, Kirkby & Brady)
• Cavellina extuberata (Jones & Kirkby)
• Cavellina cf. glandella (Whitfield)
• Cavellina longula Cooper
• Cavellina cf. parallela Croneis & Gutke
• Cavellina cf. subovata Coryell
• Cavellina valida (Jones, Kirkby & Brady)
• Chaetetes depressus (Fleming)
• Cingulizonates cf. capistratus (Hoffmeister, Staplin & Malloy) Staplin & Jansonius
• Colatisporites decorus (Bharadwaj & Venkatachala) Williams
• Composita ambigua (J. Sowerby)
• Corbulispora candellata (Waltz) Bharadwaij & Venkatachala
• Coryellina reticosa (Jones & Kirkby)
• Coryellina ventricornis (Jones & Kirkby)
• Coryellites
• Crassispora aculeata Neville Pl.
• Crassispora maculosa (Knox) Sullivan
• Crassispora trychera Neves & Ioannides
• Cravenoceras leion Bisat
• Cribroconcha
• Cribroconcha inflata Robinson
• Cribroconcha insculpta Robinson
• Cribroconcha perplexa Robinson
• Cribrosporites cribellatus Sullivan
• Cristatisporites bellus Bharadwaj & Venkatachala
• Densosporites intermedius Butterworth & Williams
• Densosporites cf. velatus Felix & Burbridge
• Diatomozonotriletes cervicornutus (Staplin) Playford
• Diatomozonotriletes fragilis Clayton
• Diatomozonotriletes magnus Beju
• Diatomozonotriletes cf. rarus Playford
• Diatomozonotriletes saetosa (Hacquebard & Barss) Hughes & Playford
• Dibunophyllum bipartitum (McCoy)
• Dibunophyllum bourtonense Garwood & Goodyear
• Dibunophyllum sp.
• Dictyoclostus spp.
• Dictyotriletes cf. cheveriensis Playford
• Dictyotriletes pactilis Sullivan & Marshall
• Dictyotriletes plumosus Butterworth & Spinner
• Dielasma sacculum (J. de C. Sowerby)
• Diphyphyllum lateseptatum McCoy
• Diphyphyllum sp.
• Diploporaria marginalis (Young & Young)
• Discernisporites micromarzifestus(Hacquebard) Sabry & Neves
• Dyscritella nana Lee
• Echinoconchus spp.
• Editia hieroglyphica Robinson
• Eriophorum
• Fenestella
• Fenestella cf. matheri Condra & Elias
• Fenestella oblongata Koenig
• Fenestella cf. oblongata
• Fenestella spp.
• Fluctuaria undata (Defrance)
• Garwoodia
• Gigantoproductoids
• Gigantoproductus giganteus (J. Sowerby)
• Gigantoproductus sp. latissimus (J. Sowerby) Group
• Gigantoproductus spp. maximus (McCoy) group
• Gigantoproductus sp. (cf. Productus α of Smith 1910)
• Globosochonetes parseptus Brunton
• Glyptolichvinella spiralis (Jones & Kirkby)
• Glyptopleura
• Glyptopleura berniciana Robinson
• Glyptopleura sp.
• Grandispora echinata Hacquebard
• Grandispora spinosa Hoffmeister, Staplin & Malloy
• Healdia
• Healdia cornigera (Jones & Kirkby)
• Healdia penchfordensis Robinson
• Hollinella radiata (Jones & Kirkby)
• Incisurella
• Incisurella concinna (Jones & Kirkby)
• lonesina fastigiata (Jones & Kirkby)
• Kindlella bituberculata (McCoy)
• Kirkbya
• Kirkbya quadrata Robinson
• Kloedenellitina
• Kloedenellitina berniciana Robinson
• Knightina
• Knightina votadiniae Robinson
• Knoxiella
• Knoxiella robusta Robinson
• Knoxina
• Knoxina spinosa (Jones & Kirkby)
• Knoxisporites stephanephorus Love
• Knoxisporites triradiatus Hoffmeister, Staplin & Malloy
• Kochiproductus coronus Shiells
• Kraeuselisporites echinatus Owens, Mishell & Marshall
• Leiopteria hendersoni (Etheridge jun. )
• Leiopteria spp.
• Leptagonia caledonica Brand
• Libumella
• Libumella cribrosa Robinson
• Libumella reticulata Robinson
• Limipecten dissimilis (Fleming)
• Lingula sp.
• Lingula lyntsdeni Graham
• Lingula mytilloides J. Sowerby
• Linoprotonia corrugata (McCoy)
• Linoprotonia spp.
• Lithostrotion junceum (Fleming)
• Lithostrotion maccoyanum Edwards & Haime
• Lithostrotion martini Edwards & Haime
• Lithostrotion pauciradiale (McCoy)
• Lithostrotion portlocki (Bronn)
• Lithostrotion sp.of the portlocki group
• Lonsdaleia sp.
• Lonsdaleia duplicata melmerbiensis Smith
• Lonsdaleia duplicata (Martin) s.l.
• Lonsdaleia floriformis laticlavia Smith
• Lonsdaleia floriformis (Martin) s.l.
• Lophotriletes plicatus Butterworth & Spinner
• Lophozonotriletes muricatus Hibbert & Lacey
• Lycospora
• Lycospora pusilla (Ibrahim) Somers
• Microcheilinella subcorbuloides (Jones & Kirkby)
• Modiolus spp.
• Monilospora mutabilis (Staplin) Clayton
• Monoceratina
• Monoceratina anliqua (Jones & Kirkby)
• Monoceratina youngiana (Jones & Kirkby)
• Murospora cf. aurita (Waltz) Playford
• Murospora intorta (Waltz) Playford
• Murospora margodentata Beju
• Murospora parthenopia Neves & Ioannides
• Murospora sublobata (Waltz) Playford
• myalinids
• Naiadites crassus (Fleming)
• Naiadites obsesusEtheridgejun.
• Naticopsis
• Nothamusium radiatum Hind
• Nothamusium transversum Hind
• Nuculopsis gibbosa (Fleming)
• Orbisporis convolutes Butterworth & Spinner
• Orionastraea
• Orionastraea edmondsi Hudson
• Orionastraea aff. phillipsi (McCoy)
• Ortonella
• Osagia ('Girvanella')haloes and nodules
• Ostracods
• Palaeolima simplex (Phillips)
• Palaeosmilia murchisoni Edwards & Haime
• Palaeosmilia cf. murchisoni
• Penniretepora recticarinata (Young)
• Penniretepora spp.
• Pernopecten? concentricus (Hind)
• Perotrilites tessellates (Staplin) Neville
• Phestia attenuata (Fleming)
• Phlyctiscapha berniciana Robinson
• Pleuropugnoides pleurodon (Phillips)
• Polypora verrucosa McCoy
• Potoniespores delicatus Playford
• 'Productus'a Smith
• Productus garwoodi Muir-Wood
• Productus productus (J. Sowerby)
• Productus redesdalensis Muir-Wood
• Productus spp.
• Pteronites angustatus McCoy
• Ptylopora pluma McCoy
• Pugilis scoticus (J. Sowerby)
• Pugilis senilis (Muir-Wood)
• Punctatisporites irrasus Hacquebard
• Punctospirifer redesdalensis North
• Punctospirifer scabricosta North
• Punctospirifer sp.
• Pustula aff. rugata (Phillips)
• Pustulatisporites multicapitis Bertelsen
• Pustulobairdia confragosa (Samoilova & Smirnova)
• Quasiavonia aculeata (J. Sowerby)
• Raistrickia nigra Love
• Rectobairdia dorsennata Robinson
• Rectobairdia hopeshieldensis Robinson
• Rectobairdia cf. lecta Tschigova
• Remysporites magnificus (Horst) Butterworth & Williams
• Rhipidomella michelini (Lévéille)
• Rotaspora fracta Schemel
• Rugosochonetes celticus (Muir-Wood)
• Rugosochonetes. spp.of the celticus group
• Rugosochonetes hardrensis (Phillips)
• Rugosochonetes hardrensis group
• Rugospora corporata Neves & Owens
• Rugospora polyptycha Neves & Ioannides
• Saccamminopsis fusulinaformis (McCoy)
• Saccamminopsis sp.
• Sansabella amplectans Roundy
• Sansabella cf. bella Scott
• Sanguinolites clavatus (Etheridge jun.)
• Sanguinolites spp.
• Schellwienella crenistria (Phillips)
• Schizodus fragilis (McCoy)
• Schizophoria sp.
• Schopfites daviger Sullivan
• Schulzospora campyloptera (Waltz) Hoffmeister, Staplin & Malloy
• Schulzospora rara Kosanke
• Schulzospora spp.
• Scrobicula
• Scrobicula indistincta Robinson
• Scrobicula scrabrida Robinson
• Scrobicula scrobiculata (Jones, Kirkby & Brady)
• Seminolites porosus Robinson
• Semiplanus sp. nov.
• Shishaella [Paraparchites] sp.
• Shivaella
• Shleesha oblonga (Jones & Kirkby)
• Silenites
• Spelaeotriletes pretiosus (Playford) Neves & Belt
• Spinozonotriletes uncatus Hacquebard
• Spirifer cf. bisulcatus J. de C. Sowerby
• Spirifer striatus (Martin)
• Spiriferellina octoplicata (J. de C. Sowerby)
• Stenodiscus redesdalensis (Lee)
• Stenozonotriletes mirabilisNeville
• Stick bryozoa
• Streblopteria ornata (Etheridge jun.)
• Streblopteria redesdalensis (Hind)
• Sulcella
• Sulcella affiliata (Jones & Kirkby)
• Sulcella cristata Robinson
• Sulcoretepora cf. raricosta (McCoy)
• Syringothyris cf. exoleta North
• Talanterocrinus redesdalensis Wright
• Tholisporites? biannulatus Neves
• Tholisporites decoratus Bharadwaj & Venkatachala
• Tornquistia
• Tornquistia cf. scotica Brand
• Tornquistia spp.
• Trace-fossils
• Trepostomatous bryozoa
• Tricidarisporites arcuatus Neville
• Tricidarisporites dumosus (Staplin) Sullivan & Marshall
• Tricidarisporites fasciculatus (Love) Sullivan & Marshall
• Tricidarisporites serratus (Playford) Sullivan & Marshall
• Tripartites distinctus Williams
• Tripartites nonguerickei (Horst) Potonié & Kremp
• Tripartites vetustus Schemel
• Triquitrites marginatus Hoffmeister, Staplin & Malloy
• Umbonatisporites variabilis Hibbert & Lacey
• Vallatisporites ciliaris (Luber) Sullivan
• Verrucosisporites baccatus Staplin
• Verrucosisporites eximius Playford
• Waltzispora planiangulata Sullivan
• Waltzispora polita (Hoffmeister, Staplin & Malloy) Smith & Butterworth
• Waltzispora sagitala Playford
• Wilkingia elliptica (Phillips)

Figures, plates and tables

Figures

(Figure 1) Location of the Bellingham district.

(Figure 2) Drainage of the district and adjacent areas.

(Figure 3) Distribution of the principal geological formations.

(Figure 4) Carboniferous classification.

(Figure 5) Thickness variations and interrelationships of Lower Carboniferous formations across Northumberland.

(Figure 6) Middle Border Group: section of Stonehaugh Borehole.

(Figure 7) Upper Border Group: comparative vertical sections south (Bellingham) and north (Falstone) of the Antonstown Fault.

(Figure 8) Correlation of strata between the Bellingham Coal and Redesdale Limestone with strata between the Plashetts Coal and Piper's Cross Limestone.

(Figure 9) Upper Border Group: boreholes and sections.

(Figure 10) Sections illustrating cyclothems in the Upper Border Group.

(Figure 11) Upper Border Group: sections of strata below the Leahill Limestone.

(Figure 12) Upper Border Group: sections of strata between the Leahill and Redesdale limestones.

(Figure 13) Upper Border Group: sections of strata below the Plashetts Dun Limestone, north of the Antonstown Fault.

(Figure 14) Correlation of Lower Liddesdale Group limestones with limestones in the Berwick area and on the Alston Block.

(Figure 15) Correlation of Upper Liddesdale Group limestones with limestones in north-east Northumberland and on the Alston Block.

(Figure 16) Lower Liddesdale Group sections between the Redesdale and Lower Gunnerton Fell limestones.

(Figure 17) Lower Liddesdale Group sections between the Lower Gunnerton Fell and Low Tipalt limestones.

(Figure 18) Upper Liddesdale Group sections between the Low Tipalt and Colwell limestones.

(Figure 19) Upper Liddesdale Group sections between the Colwell and Eelwell limestones.

(Figure 20) Upper Liddesdale Group sections between the Eelwell and Great limestones.

(Figure 21) Stainmore Group generalised section compared with Allenheads boreholes (Alston Block) and Throckley Borehole (Northumberland Trough).

(Figure 22) Great Limestone sections showing bedding planes and mudstone beds.

(Figure 23) Stainmore Group sections between the Great and Little limestones.

(Figure 24) Stainmore Group sections above the Little Limestone.

(Figure 25) Summary table of Carboniferous stratigraphical classifications.

(Figure 26) Stonehaugh Borehole: fossils and stratigraphical divisions. A black circle indicates that the fossil occurs in abundance. AAA indicates an algal limestone.

(Figure 27) Stratigraphical distribution of selected Carboniferous fossils. The symbols X and cf. indicate respectively that the fossil is recorded, or doubtfully recorded in the rocks of a particular cyclothem. A square enclosing the X indicates that the fossil is common.

(Figure 28) Range chart of Carboniferous ostracods.

(Figure 29) Range chart of Carboniferous miospores.

(Figure 30) Field-sketch of quarry face, Divethill Quarry (1972).

(Figure 31) Total magnetic field anomaly map of the Bingfield–Errington area: survey by H. A. Baker.

(Figure 32) Magnetic anomaly profiles across the dykes in the Bingfield-Errington area: survey by H. A. Baker.

(Figure 33) Structure of the Bellingham district shown by contours on the base of the Redesdale Limestone.

(Figure 34) Rose diagrams to illustrate the structural trends of: a) Faults and folds. Each 0.5 km of fault or 0.1 km of fold axis is represented by a unit length to the nearest 10° of arc from the centre of the rose. Faults are represented by shaded areas, fold axes by unshaded areas. b) Joints and dykes. Every 91 m of dyke is represented by a unit length to the nearest 10° of arc from the centre of the rose. Dykes are represented by shaded areas, joints by unshaded areas. Number of joints measured = 300.

(Figure 35) Compression faults. a) Warks Burn near Mortley. b) River North Tyne near Wark. c) Biggy Haugh, Stonehaugh.

(Figure 36) Map of drift deposits and related features.

(Figure 37) Groundwater analyses.

(Figure 38) Locations of boreholes, shafts and measured sections.

Plates

(Front cover)

(Plate 1) North-facing scarp face of the Whin Sill at Crag Lough. (L01513)

(Plate 2.1) Trace-fossil in sandstone at Hindleysteel Quarry. Teichichnus- like structures on the underside of a calcareous sandstone. (L01522)

(Plate 2.2) Trace-fossil in sandstone at Hindleysteel Quarry. Hypichnial casts including Phycodes-like forms on the underside of a calcareous sandstone. (L01523)

(Plate 3) Ridsdale Ironstone workings: a quarry near Broomhope from which the Redesdale Limestone and the Redesdale Ironstone Shale were extracted. (L01572)

(Plate 4) Old workings in the Redesdale Ironstone Shale showing the ironstone nodules, Steel, Ridsdale. (L01526)

(Plate 5) Lunga Crags. Sandstone showing contorted cross-bedding. (L01537)

(Plate 6) Strata above the Four Fathom Limestone, Prudhamstone Quarry. (L01550)

(Plate 7) Chaetetes band near the base of the Great Limestone, Brunton Quarry. (L01551)

(Plate 8) Sandstone overlying the Great Limestone, Black Pasture Quarry. (L01553)

(Plate 9) Carboniferous ostracods. The specimens with numbers prefixed by OS are in the collections of the British Museum (Natural History) and those prefixed by MPK are at the Institute of Geological Sciences, Leeds… Stainmore Group: 1) Cribroconcha inflata Robinson 1978: right aspect; Great Limestone; Cocklaw Quarry, Brunton Bank, [NY 9362 7020]. (OS 7414) x 50. 2) Cavellina benniei (Jones, Kirkby & Brady 1884): left aspect; horizon and locality as fig. 1. (OS 7339) x 50. 3) Incisurella concinna Jones & Kirkby 1885): right aspect; horizon and locality as fig. 1. (OS 7431) x 50. 4) Asturiella cicatricosa Robinson 1978: right aspect; Great Limestone; Greenleighton Quarry, Rothley, [NZ 0345 9183]. (OS 7435) x 50 Upper Liddesdale Group: 5) Sulcella cristata Robinson 1978: left aspect; Four Fathom Limestone; Brackies Burn, Chesterholme, [NY 7715 6643]. (OS7358) x50. 6) Cribroconcha perplexa Robinson 1959: right aspect; Eelwell Limestone; Moss Kennels Quarry, [NY 8015 6893]. (MPK2537) x 50. 7) Healdia cornigera Uones & Kirkby 1867): right aspect; shale in Oxford Limestone; north of Teppermoor, [NY 8569 7185]. (OS 7439) x 50. 8) Kirkbya quadrata Robinson 1959: left aspect; shale in Sandbanks (Four Fathom) Limestone; Beadnell foreshore, [NU 2381 2882]. (MPK 2538) x 50. 9) Bairdiolites elevatus Robinson 1959: right aspect; shale in Acre Limestone; Bowsden, Lowick, [NU 9288 4200]. (OS 6857) x 50 Lower Liddesdale Group: 10) Healdia penchfordensis Robinson in press: right aspect; shale in Middle Penchford Limestone; Grasslees Burn, [NY 9378 9775]. (MPK 2539) x 50. 11) Pustulobairdia confragosa (Samoilova & Smirnova 1960): right aspect; shale above Penchford Limestone; Durtrees Burn, Shittleheugh; [NY 8648 9515]. (OS 7471) x 30. 12) Cavellina valida Uones, Kirkby & Brady 1884): left aspect; shale above Upper Gunnerton Fell Limestone; Simonburn Bridge, [NY 8733 7360]. (OS 7341) x 40. 13) Phlyctiscapha berniciana Robinson in press: right aspect; shale above Middle Penchford Limestone; Grasslees Burn, [NY 9378 9775]. (MPK2540) x 40. 14) Bairdia Lecia Bushmina 1970: right aspect; horizon and locality as fig. 12. (MPK2541) x 40… Upper Border Group: 15) Cavellina attenuata (Jones & Kirkby 1886): left aspect; shale in Upper Border Group about the horizon of the Appletree and Leahill limestones; Warksburn, [NY 8215 7692]. (MPK 2542) x 40. 16) Glyptopleura berniciana Robinson 1978: left aspect; horizon and locality as fig. 15. (OS7614) x 40. 17) Jonesina fastigiata (Jones & Kirkby 1867): left aspect, female; horizon and locality as fig. 15. (OS 7369) x40. 18a), 18b), 18c) Beyrichiopsis fimbriata Jones & Kirkby 1886: horizon and locality as fig. 15. Left aspect, female; (OS 7354), dorsal aspect, female; (OS 7355) and right aspect, male; (OS 7356) respectively. All x40

(Plate 10) Carboniferous miospores. All magnifications x 500. 1) Waltzispora planiangulata Sullivan, MPK 1762, SAL4220/4, Upper Border Group, Warks Burn [NY 8560 7654]. 2) Waltzispora polita (Hoffmeister, Staplin & Malloy) Smith & Butterworth, MPK 1763, SAL 2022/1, Upper Border Group, Warks Burn [NY 8605 7646]. 3) ?Apiculatisporis porosus Williams, MPK 1764, SAL 1989/1, Lower Liddesdale Group, near Newtonrigg [NY 8375 7540]. 4) Raistrickia nigra Love, MPK 1765, SAL 2084/2, Upper Border Group, Dinley Burn [NY 8768 7644]. 5) Dictyotriletes plumosus Butterworth & Spinner, MPK 1766, SAL2020/1, Upper Border Group, Warks Burn [NY 8605 7646]. 6) Verrucosisporites baccatus Staplin, MPK 1767, SAL 2020/1, Upper Border Group, Warks Burn [NY 8605 7646]. 7) Acanthotriletes acritarchus Neville, MPK 1768, SAL 2002/1, Upper Border Group, tributary of Middleburn [NY 7625 7320]. 8) Crassispora aculeata Neville, MPK 1769, SAL 2001/1, Upper Border Group, Middleburn [NY 7706 7400]. 9) Potoniespores delicatus Playford, M PK 1770, SAL 4220/4, Upper Border Group, Warks Burn [NY 8560 7654]. 10) Tripartites vetustus Schemel, MPK 177 1, SAL 1985/1, Upper Liddesdale Group, near Stooprigg [NY 8396 7225]. 11) Tripartites distinctus Williams, MPK 1772, SAL 2028/2, Lower Liddesdale Group, Birky Gill [NY 9027 9049]. 12) T. dzstinrtus Williams, MPK 1773, SAL 1989/1, Lower Liddesdale Group, near Newtonrigg [NY 8375 7540]. 13) Ahrensisporites duplicatus Neville, MPK 1774, SAL 2001/1, Upper Border Group, Middleburn [NY 7706 7400]. 14) Knoxisporites stephanephorus Love, MPK 1775, SAL 1994/1, Lower Liddesdale Group, Simonburn [NY 8729 7357]. 15) Murospora parthenopia Neves & Ioannides, MPK 1776, SAL 199 1/1, Upper Border Group, near Newtonrigg [NY 8360 7556]. 16) Diatomozonotriletes saetosa (Hacquebard & Barss) Hughes & Play ford, MPK 1777, SAL 1985/1, Upper Liddesdale Group, near Stooprigg [NY 8396 7225]. 17) D. cervicomulus (Staplin) Playford, MPK 1778, SAL 1985/1, Upper Liddesdale Group, near Stooprigg [NY 8396 7225]. 18) D. magnus Clayton, MPK 1779, SAL 1991 /1, Upper Border Group. near Newtonrigg [NY 8360 7556]. 19) Murospora margodmtata Beju, MPK 1780, SAL 2091/2, Lower Liddesdale Group, near Goatstones [NY 8332 7358]. 20) Monilospora mutabilis (Staplin) Clayton, MPK 178 1, SAL 1991/1, Upper Border Group, near Newtonrigg [NY 8360 7556]. 21) Perotrilites tessellatus (Staplin) Neville, MPK 1782, SAL 2084/1, Upper Border Group, Dinley Burn [NY 8768 7644]. 22) Cribrosporites cribellatus Sullivan, MPK 1783, SAL 2085/1, Lower Liddesda le Group, near Birtley [NY 8818 7720]. 23) Schulzospora rara Kosanke, YIPK 1784, SAL 1990/1, Upper Border Group, near Newtonrigg [NY 8371 7544].

(Plate 11.1) Cognate intrusion in the Whin Sill, Swinburne Quarry. Partially carbonated Whin dolerite (upper right) intruded by two generations of marginally chilled partially carbonated basalt. The earlier basalt (centre) contains an associated diffuse hydrothermal segregation aligned subparallel to its contact. The later basalt (top and near bottom) is branched and shows stoped off xenoliths of both the Whin and the earlier basalt. It too shows hydrothermal associates but in this case they occur in sharply defined veins, one of which is orientated parallel to the wall of its associated intrusion. (E41887). x 6, ordinary light [NY 9501 7688]. Depth 13.62 m.

(Plate 11.2) Cognate intrusion in the Whin Sill, Swinburne Quarry. Partially carbonated Whin dolerite, finer grained than in (Plate 11.1), cut by veins of hydrothermal mineralisation (bottom) and partially carbonated chilled basalt. The basalt vein shows stoping along one contact and an intimate spatial relationship with the carbonate mineral vein on the other. The centre of the basalt vein contains diffuse hydrothermal carbonate-rich segregations. (E41889), x 6, ordinary light. [NY 950 1 7688], depth 24.19 m.

(Plate 12) Compression fault in thinly bedded sandstone, siltstone and mudstone; Upper Border Group, Biggy Haugh, Warks Burn. (L01519)

(Plate 13) Drumlin capped by sand and gravel, Lisles Burn Valley. (L01565)

(Plate 14) Glacial sand and gravel cut by a small fault, Liddell Hall. (L01563)

(Plate 15) Recently drained area showing peat and boulder clay, Scotchcoultard Waste. (L01570)

(Plate 16) Alluvial flats in an area of mature forest, Warks Burn, near Stonehaugh. (L01517)

(Back cover )

Tables

(Geological sequence ) Geological sequence of the Bellingham district

Tables

Geological sequence