Content and licensingview original scan buy a printed copy

Geology of the Tynemouth district (explanation of one-inch geological sheet 15, New Series)

By D. H. Land, B.Sc. with contributions by M. A. Calver, M.A., Ph.D. and R. K. Harrison, M.Sc.

Bibliographic reference: Land, D.H. 1974. Geology of the Tynemouth district (explanation of one-inch geological sheet 15, New Series). London: HMSO.

Natural Environment Research Council. Institute of Geological Sciences

Memoirs of the Geological Survey of Great Britain England and Wales

London Her Majesty's Stationery Office 1974. Crown copyright 1974. ISBN 0 11 880611 4*

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

(Front cover)

(Rear cover)

Preface

The Tynemouth district was originally geologically surveyed by H. H. Howell, the resulting map being published in 1866 at one inch, and in 1867 at six inches to one mile. G. A. Burnett and V. A. Eyles resurveyed the district in 1929–32, their six-inch maps being published between 1932 and 1937 and their one-inch map in 1953.

In the decade following nationalization of the coal mines, an intensive boring programme, the vigorous extension of mining and the widespread search for seams which could be quarried opencast, provided more geological data than the whole of the information that had been available to Burnett and Eyles. It was decided, therefore, to revise the map once more, and this was done by D. H. Land in 1959–62 under the supervision of Mr. W. Anderson. The six-inch maps (see list on p. ix) were published in 1963–4, and the one-inch in 1966 (Solid) and 1968 (Drift).

The geology of the Coal Measures lends itself in this account to portrayal by a series of maps illustrating individual cyclothems, with brief explanations, rather than by long verbal descriptions which would fail to do justice to the large amount of information available.

Dr. M. A. Calver, assisted by Miss Diane M. Gregory, has been responsible for Coal Measures palaeontology and fossil determinations, apart from the vertebrate fauna from Newsham, of which Dr. Sheila M. Andrews, Royal Scottish Museum, Edinburgh, revised the fish nomenclature and Drs. A. L. Panchen and Angela C. Girven, University of Newcastle upon Tyne, re-determined the amphibia. Permian fossils were named or revised by Mr. J. Pattison. Mr. R. K. Harrison was responsible for the petrology, based on petrography by himself, Mr. K. S. Siddiqui and myself. Mr. D. B. Smith advised the author on the Permian strata. The memoir has been edited by Mr. B. J. Taylor.

It is a pleasure to acknowledge the unstinting and ready help given by staff and employees of the National Coal Board, who invariably went out of their way to aid the author and his colleagues in their examination of borehole cores, mines, quarries, plans and records, and without whose cordial assistance this work could not have been accomplished.

Kingsley Dunham, Institute of Geological Sciences Director, Exhibition Road, London. SW7 2DE. 11th February 1974.

List of six-inch maps

The following six-inch to one-mile geological maps, all revised by D. H. Land, were published in the year stated:

• NZ27SE Burradon 1964
• NZ27NE Cramlington 1963
• NZ28SE Bedlington 1963
• NZ37SW Earsdon 1964
• NZ37SE Whitley Bay 1964
• NZ37NW Seaton Sluice 1964
• NZ38SW Blyth 1963

Manuscript copies of those portions which fall within the district, of the following six-inch maps, are available for public reference at the Institute of Geological Sciences at Leeds: NZ26NE, NZ28NE, NZ36NW, NZ36NE and NZ38NW.

Explanatory notes

• In this book, the word 'district' means the area of land included on the England and Wales one-inch geological sheet 15 (Tynemouth) plus the adjacent offshore areas which have been explored by boring and mining.
• Numbers in square brackets are National Grid references within 100-km square NZ.
• 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.
• The authorship of Carboniferous fossil species is given in the index.
• The maps of Coal Measures strata in (Figure 8) to (Figure 72) show lines ornamented and labelled as follows. Outcrop lines are labelled on the side on which the bed is present beneath younger strata. Values (in feet) against isopach lines are on the side of the line on which the strata are thicker. Limits of the area of development of a bed are ornamented on the side of the line on which the bed is present. Margins of washouts are ornamented on the side on which the coal is washed out. Lines of split are ornamented on the side on which the seam leaves diverge. Shafts and boreholes shown are those penetrating the strata mapped.

Chapter 1 Introduction

Area and physical features

This Memoir describes the geology of the district covered by the Tynemouth (15) Sheet of the one-inch geological new series map of England and Wales. Of the 216 sq miles in Sheet 15, only about a quarter is land (Figure 1), mostly in south-east Northumberland but including the northernmost tip of County Durham. Geological knowledge of the district is confined to the land area plus the few miles offshore within which boring and mining have been carried on (Figure 2). In the sequel the word 'district' means that part of the Tynemouth quadrangle of which we have geological knowledge.

Topographically the district has the low relief of a till plain further smoothed by post-glacial solifluction. The monotony of the landscape is mitigated by a few sandstone hills standing as islands in the drift, and by the incised river courses. A broad ridge extending east-south-east from near Killingworth to North Shields includes the highest point, only 293 ft above sea level. The coastline, though geologically interesting, is in no sense spectacular, low rocky headlands being separated by shallow sandy bays backed by dunes.

Population and industry

In the south the River Tyne enters the sea between Tynemouth on the north bank (population of the borough, which includes Cullercoats and North Shields, about 73 000) and South Shields on the south (population of the borough, only a small part of which is in this district, about [NZ 110 000]). The northern fringes of Wallsend extend into the district, and the south-west corner includes part of Newcastle upon Tyne. North of Tynemouth is Whitley Bay (population nearly 40 000) a seaside resort and dormitory town. Blyth (about 37 000) is the other large centre of population. Villages are scattered throughout the rest of the district, all of them originating either as colliery villages or as earlier settlements on sandstone 'islands', which provided well-drained sites with building stone to hand. New Hartley and Earsdon are examples of each category, respectively.

Coal mining is and has been for centuries an important industry, though it has contracted in recent years. In 1965, 20 mines (three only partly in the district) employed nearly 15 000 men. At the time of writing only five collieries, employing nearly 5000, are working; these are Bates (Blyth), Eccles and Fenwick (Backworth), Westoe (South Shields) and Bedlington A, producing about 2.5 million tons of coal a year. The last two are partly outside the district. Other industries, which are concentrated in the south and at Blyth, are brick-making, timber sawing, shipbuilding and repairing, electrical and mechanical engineering, iron founding, plastics manufacture, cotton weaving and fishing, besides the usual service industries. Despite the extent of urbanization, agriculture is still significant with the emphasis on milk and beef and crops such as oats. All along the coast, particularly in the southern half of the district, the holiday trade is an important activity.

Historical notes

At South Shields the Romans had a harbour protected by the fort of Arbeia on The Lawe [NZ 365 679], overlooking the mouth of the Tyne. The original Hadrianic fort was built of Magnesian Limestone about AD 122, and reconstructed in about AD 162 using reddened Coal Measures sandstone from the south-west part of South Shields. Under Severus, in the early 3rd century, the fort was entirely reconstructed as a supply base for his Scottish campaigns, this time using Coal Measures sandstone probably from Gateshead (Richmond 1952).

Local Coal Measures sandstones were used for almost all buildings in Northumberland from before the oldest still standing,. the late llth century Benedictine Priory church of Tynemouth, down to the 19th century when brick came into common use. Perhaps the most noteworthy building is Vanbrugh's Seaton Delaval Hall [NZ 3225 7655] described by Pevsner (1957, p. 51) as "a monument of Baroque grandeur and passionate power unmatched in England".

Coal mining (Nef 1932; Galloway 1882; Forster 1907, 1909, 1930; Smailes 1935) is recorded in this district from the year 1236 when the monks of Newminster Abbey, Morpeth, were granted mining rights near Blyth (Galloway 1882, p. 6). Since then mining has been continuous, although workings were only on a small scale, in near-crop bell-pits and drifts, during the first few centuries. From the earliest days, much of the production from the Northumberland and Durham Coalfield has gone to supply the London market. Annual shipments out of the Tyne to London and elsewhere were some 35 000 tons in the mid-16th century, rising to about 600 000 tons a year at the end of the next century. Corresponding figures for the ports in this district, namely Blyth, Hartley (later called Seaton Sluice), Cullercoats and North Shields are 500 and 33 000 tons (Nef 1932, p. 36). This great increase in coal production between 1550 and 1700 was a reflection of general economic advance in the whole country, which in this district was helped by an influx of capital and technical advances from the Midlands and the south. The most noteworthy name associated with this movement was Huntington Beaumont who gave his name to a coal seam, and introduced both the "art to boore with iron rodds" (Gray 1649) and also railways to transport coal to tidewater. The earliest borehole of which the record survives is the Killingworth West End Borehole [approx. NZ 280 710] drilled in 1694 to a depth of 214 ft ('Borings and Sinkings', No. 1233). This has the usual lithological terms such as white post, blue metal stone and grey thill, and can be readily correlated as passing through strata between the Burradon and Ryhope Little seams. Beaumont, whose family introduced railways to England, built the first Northumbrian 'waggonway' at Bebside, probably in 1609 (Lee 1943, pp. 22–5). The relatively gentle topography of this district and Tyneside generally, combined with the economic necessity for cheap and easy transport to tidewater, led to extensive waggonway development from Beaumont's time onwards. Mining to any depth below water table had to await Newcomen's pumping engine, first used in Northumberland in 1717 (Raistrick 1953). The 18th century was the great period for winning the High Main Seam in the area south of the Ninety Fathom Fault, but mines were still small (by modern standards) with only a small acreage won from any one shaft, as is picturesquely described by C. (1708). Modern mines with deep shafts, designed for a long life and working a wide take, were developed in the closing years of the 18th century and in the 19th, throughout the district. In the latter century the great rise in demand for steam coal led to large-scale exploitation of the area north of the Ninety Fathom Fault, an area which produces coal particularly suitable for this purpose.

Previous research

The first geological survey of the district was by H. H. Howell, his one-inch map being published in 1866 and the six-inch maps in 1867. A drift edition of the one-inch appeared in 1881. No memoir was written to accompany these maps, nor was one compiled following the 1929–32 revision by G. A. Burnett and V. A. Eyles.

Over a hundred works are cited in the references (pp. 158–64), but despite this long list, the present memoir is the first comprehensive description of the geology of the district. Generalized descriptions appeared in papers by Winch (1817), Wood and others (1863), Lebour (1878), Murton (1892), Woolacott (1913), Carruthers and others (1931) and Hickling and Robertson (1949), which all deal with a wider region.

The Coal Measures have attracted attention mostly for their fossils. Early workers include Atthey (1870, 1877), Hancock and Atthey (1868–71) and Howse (1890a, b) all interested primarily in the vertebrate fauna. Floras were studied by Kidston (1922) and Bolton (1926), bivalves by Hopkins in a series of papers (1928–35), ostracods by Pollard (1966, 1969), and amphibia by Panchen (1970, 1972). Coal seam correlation was detailed by Buddle (1831a, b) and only marginally improved by later authors. The coastal sections have been described by Absolom and Hopkins (1926) and Jones (1967). Restricted aspects of the Coal Measures appear in papers by Anderson and Dunham (1953) on reddened beds, Clarke and others (1961) on an offshore geophysical survey, Hickling (1950) on the coalfield prospects undersea, Hutton (1831) on the reddened strata beneath the Permian, Lebour and Smythe (1906) on a sandstone-filled washout, Magraw (1963) on Westoe Colliery, Richardson and Francis (1971) on fragmental clayrocks, and Sorby (1852) on cross-bedding.

Permian strata have been studied by Sedgwick (1829), Howse (1848, 1857), King (1850), Kirkby (1867), Lebour (1902), Haselhurst (1911), Woolacott (1912), Stoneley (1958) and Smith (1970a, b). Descriptions of the Tertiary dykes are furnished by Teall (1884a, 1888, 1889), Heslop and Smythe (1910), Smythe (1914), Holmes and Harwood (1929) and Randall (1953, 1954). Papers on the Quaternary include Howse (1864), Woolacott (1905), Smythe (1908, 1912), Merrick (1910), Bullerwell (1910) and Anson and Sharp (1960).

Geological sequence

In this district, the following divisions are present:

Geological history

Nothing is known of the pre-Carboniferous and lowest Carboniferous rocks in this district, except that from outcrops in the Lake District and Scottish Southern Uplands it may be surmised that the pre-Carboniferous basement consists of strongly folded Lower Palaeozoic strata.

In Carboniferous times the district lay in the Northumberland Trough and received over 7000 ft of deltaic sediments, all in rhythmic sequences, with mud-stone and sandstone predominant throughout, marine limestones prominent in the lower half and coals significant in the upper part. Gentle folding and uplift in the late-Carboniferous Hercynian orogeny was followed by erosion with weathering which reddened the surface strata. On this surface were deposited the Permian sediments; first the Lower Permian Yellow Sands as desert dunes and then the limestones and evaporites of the Upper Permian Zechstein Sea. While it may be presumed that a full sequence of Triassic, Jurassic and Cretaceous strata was also deposited over this district, erosion has removed all these rocks. During Tertiary times, tholeiitic dolerite dykes were intruded from the Mull igneous centre, and earth movements gave a gentle easterly tilt to the strata together with further faulting. The district no doubt underwent glaciation several times during the Pleistocene, but by far the greater bulk of known deposits belong to the last glacial episode, in late Weichselian times between 12 000 and 18 000 years ago. These are largely of boulder clay, but also include laminated clay, silt, sand and gravel, and solifluction deposits. Gravels deposited prior to this glaciation include erratics from previous glaciations. In Recent times thin near-coast peat has been overlain by blown sand which is still forming today, along with alluvium and beach deposits.

Chapter 2 Rocks older than Coal Measures

This district lies within the Northumberland Trough (see, for example, Taylor and others 1971, p. 38) and the Coal Measures which crop out here are conformably underlain by Millstone Grit and Carboniferous Limestone strata. The character of these strata can be judged from the Harton Borehole [NZ 396 656] on the coast nearly a mile south of the district (Ridd and others 1970) and from outcrops in districts to the north and west.

Millstone Grit (Namurian) strata comprise some 1300 ft of marine and non-marine mudstones and sandstones with seateartbs, thin coals and thin limestones, arranged in rhythmic sequences of relatively thin cyclothems. The base of the Millstone Grit is marked by the base of the Great Limestone, below which is the Carboniferous Limestone Series. The uppermost 2000 ft of this is characterized by a Yoredale-type rhythmic sequence (Taylor and others 1971, p. 37), in which thick marine limestones are a feature and sandstones are subordinate. Beneath this nearly another 1000 ft of mostly arenaceous strata were proved at Harton. The total thickness of Carboniferous strata, and on what they rest are not known.

Chapter 3 Coal Measures

Introduction

Within the district there are some 2800 ft of Coal Measures strata, resting conformably on the Millstone Grit and overlain unconformably by Permian rocks. During the past 25 years, the National Coal Board have drilled numerous boreholes, many of them cored, which have yielded more information than all previous drilling. This information, together with that derived from mine plans and surface and underground exposures, has been used to make fresh, detailed seam-by-seam correlation within the coalfield, as well as a palaeontologically based, general correlation of the sequence with the wider British and European successions.

Classification

The Coal Measures sequence in this district is shown graphically in (Figure 3) in relation to the standard British classification of Lower, Middle and Upper Coal Measures, and to the Westphalian stages and non-marine bivalve zones. This classification is based on data from the whole coalfield and on comparison with other fields, because many horizons in this district have yielded a fauna and flora too restricted to be a reliable guide. Very little is known, for example, of the bivalves of the Anthraconaia lenisulcata and Carbonicola communis zones, and virtually no fossils have been collected from strata above the Ryhope Marine Band. Apart from one meagre sandstone exposure, no details are known of the uppermost 900 ft of Coal Measures either from exposures or boreholes, and their outcrop is inferred on structural grounds. None of the marine bands has yielded the characteristic goniatites, and plants have been collected from only a few horizons. Despite all this, the subdivisions shown in (Figure 3) are regarded as well established, except that there is room for modifying the boundaries of the C. communis Zone.

In the first edition of the one-inch geological map (Howell 1866) the Coal Measures in this district were undivided, but in the second edition (Burnett and others 1953), resurveyed in 1927–32, they were divided into Lower, Middle and Upper Coal groups. The dividing lines were drawn at the Brockwell and High Main seams following Fowler (1936) in the Rothbury and Newbiggin (sheets 9 and 10) districts to the north, who divided his sequence at the homonymous seams, which are the Victoria and Ashington respectively of this district.

Sedimentology

In Westphalian times this district formed a small fragment of the Pennine depositional province (Calver 1969, p. 234) which was in turn part of the north-west European paralic belt. The depositional environment was deltaic with occasional marine incursions.

Cyclothems

The stratal sequence is rhythmic or cyclic with the pattern:

• 4. coal
• 3. seatearth
• 2. barren mudstones and sandstones
• 1. fossiliferous mudstone

As the most abrupt environmental change occurs by transgression at the top of the coal and base of the fossiliferous mudstone, this horizon is taken as marking the base of a cyclothem. Not only are cyclothems often incomplete, but they also show great lateral variation; moreover none can be traced far as an integral unit, because members split or die out. Though useful in analysing and describing the measures, the division of a given sequence into cyclothems is a subjective exercise. For these reasons, in detailing the stratigraphy of the Coal Measures, the strata between each pair of vertically adjacent, named coal seams or marine bands is considered as a unit.

Taking the Coal Measures succession as a whole, throughout the district, there is little vertical or horizontal variation within a limited range of oft-repeated facies, although in any one inter-seam interval, there is generally considerable variation, as may be seen by a cursory glance at any of the text-figures of vertical sections. If these sections were to be taken in isolation it is unlikely that they would be correlated. Detailed correlation was made by considering the whole suite of bore and shaft sections, placing particular reliance on the persistence of faunal bands and major coal seams and on the rhythmic characteristics of the succession. It is implicit in this work that the top and bottom of each seam or faunal band are regarded as time planes: at any rate, within the restricted limits of this district, diachronism is considered to be insignificant.

Although individual inter-seam units show much variation in thickness, groups of units display little overall variation, as Hickling (1950) showed. Isopachs for three such groups are given in (Figure 4) from which it will be seen that they demonstrate no general directional trend. Furthermore, if any two adjacent inter-seam units are compared, or a comparison is made between the thickness of a coal and the thickness or character of the underlying unit or of a sandstone within it, then no correlation is discernible. These facts imply that the lithology and thickness of each unit or each cyclothem was developed in response to slight differential subsidence of the deltaic region (of which this district is a part), that sedimentation kept pace with subsidence, and that the depositional surface at any moment had only a very slight gradient.

Mudstones and siltstones

The bulk of the sediments are mudstones and silty mudstones. These are micaceous, generally barren of fossils apart from plant fragments, and show every gradation from finest mudstone through silty mud-stone to fine sandstone. Ripple marks and small-scale cross-bedding are almost universal in siltstones and coarser rocks. A common rock is one composed of interlaminated mudstone and fine sandstone, the laminae generally varying in thickness between 0.01 and 1.0 in and being laterally variable and impersistent. Bioturbation and compaction effects such as load-casting, micro-faulting and minor slumping are common Ironstone nodules, generally flattened parallel with the bedding, are also common, particularly in the few feet above coal seams.

Sandstones

Sandstones are subarkosic, the dominant elastic being quartz, while quartzite, orthoclase, microcline (commonly perthite), acid plagioclase, muscovite and biotite are present in varying amounts. Rather poor sorting and angularity of grain are features. Common accessory minerals are zircon, garnet, rutile and tourmaline. The rocks are cemented by intergranular kaolinite, chlorite, fine-grained micas and quartz, or by secondary overgrowths leading to interlocking of the grains, and also in places by patchy calcite, baryte, or pyrite. This patchy cementation is commonest near faults and in coarser rocks ((Plate 7), fig. 5). Veinlets of carbonates and baryte with traces of iron, lead and zinc sulphides are common.

Geometrically the sandstones are either thin (generally less than 15 ft) and in widespread sheets ('sheet sandstones') or thick (30 to 150 ft) and of elongate, gently curving form in plan ('channel sandstones'). A single sandstone may be in both sheet and channel form in different areas. The sedimentology of these sandstones closely resembles that described by Potter (1962) in the Pennsylvanian of Illinois. Many of the sandstones below the Top Busty Seam are coarse grained even when in thin sheets, but at higher levels it is generally only the channel sandstones which are coarse. Often these channel sandstones occupy washouts which may cut down many feet into underlying strata. Sandstones in washouts generally contain mudstone, ironstone and coal pebbles—many of the last, known colloquially as 'scars' or 'scares', are coalified logs and branches. Practically all sandstones, whatever their grade, are cross-bedded on various scales. Neither cross-bedding nor other sedimentary structures such as ripples have been studied during the present work, except to record depositional current directions, which are essentially parallel with washout directions ((Figure 5)), being almost wholly between south-west and south-east. The main exception is the westerly-directed cross-bedding of the Seaton Sluice Sandstone within the east–west Bensham Seam washout. It is interesting to note that one of the earliest papers on cross-bedding and ripple marks, by Sorby (1852), was based partly on observations in this district. Subsequently Jones (1967) and Clarke (in Allonby and others 1964) have published observations.

Seatearths

Underlying everycoal seam is a seatearth, generally mudstone, characterized by the presence of rootlets and lack of bedding. There is no correlation between the thickness or character of a seatearth and that of the overlying coal. Seatearths are more persistent than their associated coals. In some localities and at some horizons, particularly in the lowest Coal Measures seatearth–sandstones or ganisters occur. At some levels, seatearths are noticeably brown or green in colour, in contrast to the prevalent grey; the reasons for these colours are not known. Ironstone nodules are almost ubiquitous in seatearths, and sphaerosiderite is not uncommon.

Coals

The coals of this district are bituminous and show an increase in rank both downwards and southwards from very weakly caking coals of National Coal Board class 802 to strongly caking carbonisation and gas coals of class 502. Calorific values are generally in the range 14 250 to 15 500 B.Th.U/lb (dry, ash-free basis). In the north, coals are suitable for steam raising and household use; in the south they can also be utilized for coking and gas-making (Jones 1945).

Most of the seams are split by seatearth or mudstone partings, and in places the top leaf of one seam may unite with the bottom leaf of the next higher seam.

Seams also show lateral thickness variations and may even die out altogether but there is no general pattern in these variations of partings and seam thicknesses, so each seam is discussed individually in the sequel.

Along with other strata, coal seams are subject to washouts, generally infilled by channel sandstones, and to thermal metamorphism adjacent to igneous dykes (Jones and Cooper 1970, pp. 59–63, pls. 4–7).

In addition to the usual bituminous coals, thin cannel coals occur at many horizons, particularly in the immediate roof of a normal seam. Cannels are rarely more than a few inches thick and are of limited areal extent; they are not associated with any underlying seatearth. They usually contain fish debris and 'Estheria', and appear to have formed from humic mud deposited in small lakes (Rayner 1971).

Reddened strata

The Coal Measures are reddened beneath the Permian unconformity to depths of the order of 70 ft. These reddened strata were first described by Sedgwick (1829) and Hutton (1831) who classed them as lower New Red Sandstone at the base of the Permian. They were first assigned to the Coal Measures by Howse (1857).

Anderson and Dunham (1953) ascribed the reddening to the oxidation in place of pyrite and chalybite and to the introduction of red iron oxide along joints and into the pore spaces of sandstones. These changes were accomplished before deposition of the basal Permian Yellow Sands. Smith and Francis (1967, pp. 18, 96) observed that in the uppermost few feet of Coal Measures strata, immediately beneath the Permian unconformity, reduction of the ferric oxides has produced a grey zone: this they associate with the euxinic environment of the Zechstein Sea, with its syngenetic pyrite, giving reducing conditions on and beneath the sea bed.

Apart from this reduced zone, strata at the top of the reddened zone are all coloured in varying degree, but when followed in depth the reddening becomes partial, patchy and selective. Data in this district on depths of reddening are sparse compared with the Durham district (Smith and Francis 1967, p. 18) where the depth of total reddening is 10 to 80 ft and partial reddening extends commonly to 100 ft and exceptionally to nearly 300 ft. In this district the deepest reddening observed was to 275 ft beneath the Permian in Offshore 9 Borehole.

Reddened strata are exposed below Tynemouth Castle and on Freestone Point to the south. On the foreshore [NZ 375 694] to the east of the castle the reddening effect is seen to advantage in a mudstone-pebble conglomerate in which the pebbles are reddish purple while the sandstone matrix, containing very little oxidizable iron, appears bleached by contrast (Plate 2B). Other exposures of reddened strata occur on the coast north of Cullercoats harbour [NZ 365 715] and north of the Collywell Fault at Seaton Sluice [NZ 339 766], as well as inland in the quarry [NZ 284 701] at Clousden Hill.

Seam correlation

The earliest published correlation of the seams of this coalfield is that by Buddle (1831a, b). Slight modifications followed in papers by Wood and others

(1863), Brown (1888), Murton (1892), Kirsopp (1907) and Hopkins (1927). Buddle's papers show that the succession was well understood even in his time. Despite this, seam nomenclature suffered considerably from homonyms and synonyms. Some of these arose simply from mis-correlation, but others were introduced on a commercial basis: the value of a newly named seam could be enhanced by association with a name of good repute or by avoiding a name of low repute (see e.g. Wood and others 1863, p. 160). The nationalization of the mines and the resumption of geological revision in the Tynemouth and Durham districts provided an opportunity to bring order into the nomenclature, and standard county names were agreed between the National Coal Board and the Geological Survey. The Northumberland names are set out in (Figure 3). In strata above the High Main (the highest widely worked coal) some seams which are too thin to be confidently correlated into County Durham have been given names of merely local significance: they are, in descending order; Clousden Hill, Killingworth, West Moor, Burradon, Rowlington and Moorland. From the High Main down to the Beaumont, the Northumberland and Durham names are compared below:

It should be noted that in Durham the Bentinck is regarded as a split off the Yard (Main) and is called Top Main; the Whitley is not recognized as such in Durham; and correlation of the Cheeveley with the Ruler is uncertain.

Below the Beaumont (Harvey) names are common to both counties.

General stratigraphy

Apart from the contained fossils, there is little to distinguish one part of the sequence (Figure 3) from another, except that coals over 3 ft thick are almost wholly confined to strata between the Harvey and High Main marine bands, and two groups of strata are dominated by thick widespread sandstones—those between the Quarterburn Marine Band and Victoria Seam and between Kirkby's and Ryhope marine bands.

As there are no structural complications, the numerous mines and boreholes provide a wealth of data on each seam and inter-seam unit, which is more cogently and succinctly illustrated graphically than verbally. For this reason, and also because they bring out the relations between various parameters, maps and sections are used extensively in the sequel. Zonal divisions are shown in (Figure 3).

Anthraconaia lenisulcata Zone

The basal Quarterburn Marine Band (Gastrioceras subcrenatum horizon, the Pot Clay Marine Band of the East Midlands) has not been proved, but the presumed horizon is taken about 50 ft below the thin Saltwick Seam.

Some 50 ft above the Saltwick is the Gubeon Seam (Figure 7) with the Gubeon Marine Band containing Lingula mytilloides and foraminifera in its roof, and 90 ft higher still is the Ganister Clay Seam. Strata in the lenisulcata Zone are largely sandstone.

Carbonicola communis Zone

The 40 ft of strata between the Ganister Clay and the Marshall Green seams (Figure 7) are thinly bedded sandstones and mudstones, with a median band containing Curvirimula and fish remains at approximately the same horizon as the Well Hill Marine Band of the Morpeth (14) district. The Marshall Green is up to 2.5 ft thick in the north, but only inches in the south. A coarse sandstone 25 to 50 ft thick follows ((Figure 8) and (Figure 9)) and is capped by a coal–seatearth followed by the Stobswood Marine Band with foraminifera and fish. This band is successively overlain ((Figure 9) and (Figure 10)) by mudstones with rare mussels at the base, sandstone up to 60 ft thick, coal–seatearth, and mudstones up to 20 ft thick with thin sandstones. These are followed by the Victoria Seam, which is 2 ft thick in the north, but only a few inches in the south. The Stobswood–Victoria interval is generally 50 to 70 ft.

t The Victoria and Brockwell seams are mostly between 50 and 80 ft apart ((Figure 11) and (Figure 12)). The Victoria roof carries fish debris, and a thin seam some 20 ft higher is overlain by a well-developed mussel band with Carbonicola pseudorobusta. There is a widespread sandstone below this band and a more restricted one above. The Brockwell (Figure 13), the lowest seam worked, is over 3 ft in the south-west, and carries a sparse roof fauna of Curvirimula and ostracods. Between 20 and 60 ft of mudstones with thin sandstones and an intermediate coal–seatearth, separate the Brockwell and Three-Quarter seams ((Figure 14) and (Figure 15)). The latter (Figure 16) is 1 to 3 ft thick.

A sandstone makes up most of the Three-Quarter to Bottom Busty interval which is generally 40 to 80 ft ((Figure 17) and (Figure 18)). This sandstone roofs the Three-Quarter in a central area; elsewhere the immediate roof is a fragmental clayrock, with rare Curvirimula and fish in overlying mudstone. The Bottom Busty (Figure 19) is banded and generally under a foot thick. Between the Bottom and Top Busty ((Figure 20) and (Figure 21)) are 20 to 40 ft of mudstone with plant remains, thin sandstones and a median coal–seatearth. The Top Busty (Figure 22) is banded in the south and under 2 ft thick over wide areas.

Anthraconaia modiolaris Zone (below the Harvey Marine Band)

The Top Busty to Tilley interval ((Figure 23), (Figure 24), (Figure 25)) is 10 to 90 ft, varying with the development of channel sandstones. Mudstones with plants form the Top Busty roof and below the Tilley are mudstones with a coal–seatearth in places. Though generally banded and thin, the Tilley (Figure 26) comprises over 2 ft of coal in some areas. Between the Tilley and Beaumont are 40 to 80 ft of strata ((Figure 27) and (Figure 28)) which include three coal–seatearths of which the middle one is impersistent. In the south-east Anthraconaia cf. williamsoni and Geisina arcuata occur in cannel above the highest coal. Sandstones up to 30 ft thick occur in different areas at several levels. The Beaumont (Figure 29) is 1.5 to 3 ft thick and widely banded. Except in the north where sandy strata intervene, the Beaumont is followed ((Figure 30) and (Figure 31)) immediately by a fragmental clayrock and this by an ostracod-mussel band, the Hopkins Band, characterized by Geisina arcuata (particularly abundant at the base) and Anthracosia regularis. Succeeding strata, generally between 35 and 65 ft thick, are mudstones with a widespread coalseatearth, thin sandstones and, in places, channel sandstones up to 65 ft thick.

Anthraconaia modiolaris Zone (including and above the Harvey Marine Band)

Marking the base of the Middle Coal Measures is the base of the Harvey Marine Band (the Anthracoceratites vanderbeckei Marine Band or Clay Cross Marine Band of the East Midlands) with a fauna in this district of Lingula mytilloides, fish remains and rare foraminifera. It is succeeded by a mussel-bed with Anthraconaia modiolaris, Anthracosia aquilina, A. ovum, A. phrygiana and A. subrecta. Overlying strata ((Figure 32) and (Figure 33)) up to the Plessey are 30 to 150 ft thick, being thickest in the south-west. At the base is a sandstone, which develops a thick channel facies in places, and this is followed by up to 50 ft of strata, locally sandstones, with the Cheeveley Seam near the base (Figure 34). The Cheeveley is over 2 ft thick in the north, dies out to the south-west and unites with the overlying Plessey towards the north-east. This latter seam (Figure 35) is 3 to 5 ft thick in the north but very thin in the south; it has been worked farther offshore (4.5 miles) than any other in the coalfield.

In the north and centre the Plessey to Hutton strata ((Figure 36) and (Figure 37)) are 15 to 50 ft thick and generally shaly. They include a prominent mussel band with (among other species) Anthraconaia salteri, A. curtata, Anthracosia aquilina, A. ovum and A. subrecta. In the south-east the strata are barren, sandy and thicker (25 to 70 ft). The Hutton Seam (Figure 38) is up to 6.5 ft thick in the south but elsewhere is less than a foot. Between the Hutton and the Northumberland Low Main ((Figure 39) and (Figure 40)) the strata are either thin (10 to 30 ft) and shaly, or thick (50 to 90 ft) and mainly channel sandstone. There are mussels in places above the Hutton, including Anthraconaia salteri, Anthracosia cf. beaniana, A. ovum, A. phrygiana and A. subrecta. The Northumberland Low Main (Figure 41) is 4 to 6 ft thick over most of the district, but banded and only 2 to 4 ft in the south-east.

Strata between the Northumberland Low Main and Durham Low Main seams ((Figure 42) and (Figure 43)) are generally 35 to 60 ft thick and divided by two coal–seatearths, the Whitley and Ellington. The Northumberland Low Main roof is cannelly, with fish and Naiadites sp.,and locally at Newsham yielded a varied amphibian and fish fauna. Above the Whitley Seam is the prominent Low Main Shell-bed with many species including Anthracosia beaniana, A. disjuncta and A. phrygiana. A sparse fauna, including Anthracosia lateralis comes from above the Ellington. Sandstones develop in places: in the north-east one cuts out the Northumberland Low Main over a wide area. The Durham Low Main (Figure 44) is banded but in most areas there are at least 2.5 ft of coal in the two main leaves.

A mussel band above the Durham Low Main yields Anthracosia aff. beaniana, A. disjuncta, A. phrygiana and other species. The mudstones containing this band ((Figure 45) and (Figure 46)) are overlain in places by the Table Rocks Sandstone, up to 50 ft thick, and elsewhere by silty mudstones with thin sandstones. These are succeeded by mudstones, above which is the Bensham Seam, which is generally between 30 and 60 ft above the Durham Low Main. Except in an east–west area through Tynemouth, the Bensham ((Figure 47), (Figure 48), (Figure 49)) is split into Top and Bottom seams, which in the northern half of the district are up to 30 ft apart. There are generally about 4 ft of coal in the Bensham seam(s).

Lower Anthracosia similis–Anthraconaia pulchra Zone

Between the Bensham and the Yard ((Figure 50) and (Figure 51)) are 50 to 100 ft of strata with a basal mussel band dominated by Anthraconaia pulchella. Three thin intermediate seams are present in different areas, together with sandstones, including the Seaton Sluice Sandstone, which have thick channel facies in places. The Yard Seam (Figure 52) is 2.5 to 3.5 ft thick and unbanded over almost the whole district.

Strata between the Yard and Bentinck ((Figure 53) and (Figure 54)) vary in thickness from about 2 ft at North Shields, where they consist of seatearth only, to 60 ft where channel sandstones are present. The Yard roof is virtually barren of fauna, with only a few mussel fragments and fish scales. Always less than 2 ft thick, the Bentinck over a wide area is represented only by seatearth.

Strata between the Bentinck Seam and the High Main Marine Band show complex lateral variations, with different pairs of vertically successive seams converging and diverging in different areas ((Figure 55) and (Figure 56)). Washouts are extensive. In central, north-eastern and south-eastern areas the Five-Quarter and Metal seams converge, as do the High Main and High Main Marine Band seams in the west-central area. Northwards both these pairs diverge and the Ashington Seam appears above the High Main, which in the north-west converges with the Metal, as do the Ashington and High Main Marine Band seams.

The Bentinck and Five-Quarter seams are generally 35 to 50 ft apart ((Figure 57) and (Figure 58)), the interval including a sandstone up to 30 ft thick. In the Bentinck roof is a mussel bed with a fauna including Anthraconaia cf. pumila [large form], Anthracosia aquilinoides, A. cf. planitumida and A. simulans. The Five-Quarter (Figure 59) is less than a foot thick in the south-west, but elsewhere there are about 2 ft of coal.

The Five-Quarter and Metal seams ((Figure 60) and (Figure 61)) are united over wide areas: elsewhere they are separated by up to 50 ft of strata which are mostly silty mudstones and fine sandstones. The Metal (Figure 62) is generally between 2 and 3.5 ft thick, but is banded over wide areas.

The Metal to High Main interval ((Figure 63) and (Figure 64)) varies from 0 to over 120 ft. Especially where it is thick, the lower part is generally sandstone; succeeding strata are mudstones, silty in part. In the south, the High Main (Figure 65) is a 6- to 8-ft low-ash coal, widely worked as the original basis for the large-scale exploitation of the coalfield. Beneath it are one or two leaves of inferior coal. In the north, the High Main is 1.5 to 4.5 ft thick and banded.

Around Blyth and in the south-west of the district a sandstone, the High Main Post, between 40 and 100 ft thick, forms most of the strata between the High Main and High Main Marine Band seams ((Figure 66) and (Figure 67)). In the south-east, the sandstone is thinner and mudstones above the High Main carry a fauna which includes Anthracosia lateralis. Westwards, in central areas, the strata are reduced to a few feet of seatearth. Towards the north, the Ashington Seam appears above the High Main and beneath a diminished High Main Post. In the north-west the strata are mostly pale grey mudstones. The Ashington Seam (Figure 68), though banded, reaches 3.5 ft in thickness in the north. Immediately beneath the High Main Marine Band is the thin coal seam of that name.

Between the High Main Marine Band and the Moorland Seam are some 80 to 100 ft of strata divided by two coal–seatearths ((Figure 69) and (Figure 70)). The marine band and these two coal horizons are each overlain by mudstones with mussels: the lower shell-bed (overlying the marine band) is generally known as the High Main Shell-bed and is present throughout the district, while the other two shell-beds and their coals fail in places. At the base, the High Main Marine Band, equivalent to the East Midlands Two Foot Marine Band, carries Lingula mytilloides and rare Myalina compressa. The thick overlying High Main Shell-bed is characterized by 'Estheria'in the lowest layers and by Anthraconaia cymbula, A. librata, Anthracosia acutella, A. atra and Anthracosphaerium radiatum. Similar assemblages are found in the two higher shell-beds. Sandstones occur, particularly below the Moorland Seam (Figure 72) which is generally banded and of poor quality, 2 to 3.5 ft thick in the north and dying out in the south. Some 20 to 70 ft above the Moorland, which carries no roof fauna apart from a few fish scales, is the Ryhope Little Seam (Figure 71). A widespread sandstone and in the north a thin coal occur below the Ryhope Little, which is 1 to 2.5 ft thick.

Strata between the Ryhope Little and Ryhope Five-Quarter seams (Figure 73) are about 30 ft thick (up to 60 ft in the south) and include a thin sandstone. In the roof of the former seam is the thin, impersistent Ryhope Little Marine Band with Lingula sp., correlated with the Clown Marine Band of the East Midlands. Succeeding mudstones yield Carbonita humilis and mussels, mainly Naiadites sp. The Ryhope Five-Quarter is a banded seam, up to 2 ft thick, with the top and bottom leaves up to 30 ft apart in the north and south-east. Anthracosia atra and A. cf. elliptica have been collected from the roof measures. Sandstones make up much of the 50 to 70 ft of strata between the Ryhope Five-Quarter Seam and Kirkby's Marine Band (Figure 73). These strata include two coal horizons (only one in the south-east), the lower of which is the Rowlington Seam of the North Seaton area.

Kirkby's Marine Band (Figure 74) correlated with the Haughton Marine Band of the East Midlands, is characterized by alternation of marine and non-marine phases. Marine fossils include Lingula spp. (L. cf. elongata in the lower part and L. mytilloides in the upper) and foraminifera; semi-marine phases are represented byPlanolites ophthalmoides and 'Estheria' and non-marine by Anthracosia atra and Naiadites spp.

Between Kirkby's and Ryhope marine bands (Figure 75) are 170 to 200 ft of mostly sandstone strata. About midway is the Hylton Marine Band, with the thin Burradon Seam 15 to 30 ft above it and another thin coal about 50 ft below. The impersistent Hylton Marine Band has a fauna of Lingula mytilloides and foraminifera and is correlated with the Sutton Marine Band of the East Midlands.

Upper Anthracosia similis–Anthraconaia pulchra Zone

The Ryhope Marine Band, correlated with the Mansfield Marine Band is the horizon of  'Anthracoceras' hindi, though the goniatite has not been specifically identified from this district. The band consists of a lower pectinoid-goniatite phase in black shale and an upper foraminiferal phase in grey mudstone.

Succeeding strata (Figure 76) are known from only a few boreholes; and no fossils have been collected, though mussels are recorded above most of the coal seams. Overlying the Ryhope Marine Band are 70 ft of mudstone, sandy at the top, capped by the 2.5-ft Usworth Seam. The succeeding 200 ft of measures up to the 15-in Killingworth Seam are relatively thin-bedded with at least nine coal horizons, and include mussel bands and thin sandstones. The Hebburn Fell Seam, in two leaves each about 2 ft thick, is 80 ft above the Usworth and the West Moor Seam, 2 to 2.5 ft thick and banded, lies 50 ft higher.

By analogy with the Sunderland (21) district there are some 370 ft of strata between the Killingworth Seam and the Down Hill Marine Band ('Anthracoceras' cambriense horizon or Top Marine Band of the East Midlands) which has not been proved in this district. These strata are unknown save for the 1.5-ft Clousden Hill Seam and overlying sandstone about midway.

Anthraconauta phillipsii Zone

On structural grounds, it is thought that about 500 ft of Upper Coal Measures strata, belonging to the Anthraconauta phillipsii Zone, are present in this district, but nothing is known of their stratigraphy.

Detailed stratigraphy

Strata below Marshall Green

Strata below the Marshall Green Seam (Figure 7) are known from only a few bore-holes. By comparison with the Throckley Borehole [NZ 1456 6761], west of Newcastle upon Tyne, the Cramlington Betsy Pit section probably extends down to about the base of the Coal Measures. Tentative correlations may also be made with the Saltwick and Gubeon coals of the eponymous localities farther west. Between the Gubeon and the overlying Ganister Clay Seam is a medium- to coarse-grained sandstone 60 to 80 ft thick. The Gubeon Seam carries a Lingula band in its roof, which in Offshore 6 Borehole contains foraminifera including Ammodiscus sp., Lingula mytilloides and fish remains. Above the Ganister Clay is a mussel band approximately on the horizon of the Well Hill Marine Band of the Morpeth (14) district. From an underground borehole at Backworth [NZ 3002 7257] Spirorbis sp., Carbonicola sp., Curvirimula sp. and Geisina arcuata were collected.

Marshall Green Seam to Stobswood Marine Band

Marshall Green Seam

(Figure 8). North of Seaton Delaval, the Marshall Green is known as the 'Victoria' or more particularly the 'Choppington Victoria'. It is between 12 and 30 in thick in the northern part of the district, but only a few inches thick in the south, except offshore of Tynemouth and at Westoe where it reaches 24 in. A mudstone parting is present around Newsham. Though a few borehole samples show ash contents of up to 16 per cent (air-dried coal), the quality is generally good, and the seam remains unworked throughout the district.

Strata above the Marshall Green

((Figure 8) and (Figure 9). At and offshore of Cambois and in places south of Blyth, the Marshall Green is overlain by up to 6 ft of unfossiliferous mudstone with ironstone nodules, rooty at the top and in places surmounted by a 1-in coal. This sequence is overlain by a sandstone, which over most of the district forms the immediate roof of the Marshall Green. The sandstone ranges irregularly between 25 and 50 ft thick. It is generally coarse, in places with quartz pebbles up to 0.75 in across, kaolinitic and feldspathic, and is cross-bedded in the lower and middle part. Towards the top the sandstone becomes rather finer grained and flaggy, and is overlain by a seatearth-coal horizon immediately beneath the Stobswood Marine Band.

In Cambois 55 Borehole, 2 miles E of the mouth of the River Wansbeck, the Marshall Green–Stobswood interval is abnormally thin, comprising only 19 ft of strata including 4 ft of sandstone. The thickest development, 66 ft of strata, all sandstone, is at Westoe Colliery, South Shields.

Stobswood Marine Band to Victoria Seam

The general sequence of strata from the Stobswood Marine Band to the Victoria Seam ((Figure 9) and (Figure 10)) is:

• Victoria Seam, up to 2 ft
• Sandstone and mudstone with roots, 4 to 22 ft
• Coal horizon (seam generally absent) on seatearth
• Sandstone, generally coarse, up to 70 ft
• Mudstone with Stobswood Marine Band at base, 2 to 25 ft

Stobswood Marine Band

The thin Stobswood Marine Band named from its occurrence in a borehole at Stobswood [NZ 2282 9457], 6 miles N of the district, has a fauna of fish debris and foraminifera, including Ammodiscus sp. In places, Planolites ophthalmoides occurs in grey mudstones immediately above the marine band. These mudstones are up to 30 ft thick, locally with scattered small mussels in the lowest 6 ft. They are succeeded by a thin-bedded and cross-bedded sandstone which is generally fine- to medium-grained, though coarse and kaolinitic in places. It is thickest in the north and south, but absent between North Blyth and Bedlington Station. In a few places, notably around Murton, there has been erosion at the base and the Stobswood Marine Band is cut out. Above the sandstone are between 4 and 22 ft of variably arenaceous and argillaceous strata with a coal–seatearth at the base, and the Victoria Seam seatearth at the top.

Victoria Seam

In the northern part of the district, north of Seaton Delaval, the Victoria Seam is locally called the 'Brockwell' or Thoppington Brockwell', the Marshall Green being known as the 'Victoria'. The Victoria Seam proper is not worked in this district; it is less than 20 in thick in the south, but from Newsham northwards it is a consistent seam 20 to 27 in thick with ash between 3.2 and 9.3 per cent (air-dried coal).

Victoria to Brockwell

The general succession between the Victoria and Brockwell seams ((Figure 11) and (Figure 12)) is:

• Brockwell Seam
• Seatearth
• Mudstones, silty mudstones and sandstone
• Mudstones with mussels, including Carbonicola pseudorobusta
• Median seam (absent in places) and seatearth
• Mudstone (absent in south)
• Lower thin seam (locally present)
• Mudstones and sandstones
• Thin mudstone with fish debris
• Victoria Seam

Strata between the Victoria and Brockwell (Figure 11) and (Figure 12) range between 36 and 111 ft in thickness, but are generally 50 to 80 ft thick, and reach a maximum in a belt running west of and parallel to the coast. They are divided near the middle by the median seam or its seatearth, overlain by a mussel band. In the southern part of the district these horizons fail, and the measures consist largely of fine-grained sandstones with some silty mudstone beds.

Except very locally at Cambois and South Blyth, the Victoria Seam is overlain by mudstone, with fish debris recorded in most boreholes, and Planolites ophthalmoides occasionally. Relatively thick sandstones occur towards the south and around Blyth, and in these areas the mussel band containing C. pseudorobusta is high in the Victoria–Brockwell interval. These sandstones are generally fine-grained and flaggy with many thin shaly partings, but around Blyth the lower parts are coarse and massive with a shale-pellet conglomerate. In the Backworth–Seaton area and between Bebside and North Blyth, a few feet below the median seam, the lower thin seam is present, and attains a thickness of 2 ft NE of Backworth. The median seam is generally only a few inches thick, but ranges from 0 to 18 in. The mussel band, present in northern and south-eastern parts of the district, has a distinctive fauna dominated by the large Carbonicola pseudorobusta. In Cambois 55 Borehole [NZ 3329 8520] the fauna is distributed through 27 ft of grey mudstone and includes Spirorbis sp., Carbonicola pseudorobusta, Curvirimula candela, C. subovata, Carbonita humilis, Geisina arcuata and fish scales. Other boreholes have yielded a similar fauna.

Succeeding the mussel band is a sandstone which is over 20 ft thick in areas shown in (Figure 11), but absent offshore from Cambois and around Seaton Sluice. It is generally fine- to medium-grained, being coarse and massive only near Blyth. Where the sandstone is thickest the mussel band is relatively close to the Victoria Seam. The highest strata form a variable succession of mudstones and silty mudstones with some thin coals or seatearths in places.

Brockwell Seam

(Figure 13). In the area where the underlying Victoria Seam is known as the 'Brockwell', (see p. 27), the Brockwell proper is called the 'Bandy'. Over the northern two-thirds of the district, the Brockwell is generally less than one foot thick. In a belt running south-south-west from Blyth it has a sandstone roof and suffers washout in places. At and offshore from the mouth of the Tyne the seam generally consists of a top leaf 12 to 19 in thick with thin coals below. In those areas where it is over 2 ft thick, it also has one or two dirt partings. The upper parting is generally less than 3 in thick, but the lower one (where present) ranges up to 9 in. The ash content of the clean air-dried coal in these areas is mostly between 6 and 12 per cent.

Brockwell to Three-Quarter

The Brockwell and Three-Quarter seams are from 15 to 73 ft apart ((Figure 14) and (Figure 15)), and the strata between them include an intermediate thin coal or seatearth which tends to be relatively near the Brockwell in the east, but nearer the Three-Quarter in the west.

Brockwell to intermediate seam

In the Blyth–Seghill area, the Brockwell roof is sandstone. Elsewhere the roof is mudstone, with a sparse fauna of mussels in scattered boreholes offshore from Cambois and near Newsham, Earsdon and Seaton Delaval. A borehole [NZ 3031 7631] at the last place yielded Spirorbis sp., Curvirimula subovata, Carbonita sp., Geisina arcuata and fish remains. Above these roof measures, sandy strata appear, either silty mudstone or sandstone which is over 20 ft thick in areas shown in (Figure 14). It is lithologically variable from finely to coarsely grained, from thinly to thickly bedded; in places it is flaggy, elsewhere cross-bedded. The sandy strata are generally overlain by a few feet of mudstone and this in turn by the seatearth of the intermediate seam.

Intermediate seam to Three-Quarter

The intermediate seam probably represents the New Seam of Stobswood Colliery [NZ 237 948] 6 miles NNW of the district. Only in two boreholes off Tynemouth is this seam over 11 in thick within this district and it is generally represented merely by seatearth. Overlying strata form a variable sequence of mudstones with one or two thin coal–seatearth horizons and sandstones in places. Mussels and fish debris are recorded from a few boreholes in the roof of the intermediate seam.

Three-Quarter Seam

(Figure 16). The Three-Quarter is notably consistent in quality and thickness: except very locally the coal is nowhere less than 12 or more than 36 in thick. In the central part of the district, between Newsham and Earsdon, it has a sandstone roof and may be partially washed out in places. In those areas where the seam is over 24 in thick, the ash content (air-dried coal) varies between 4.5 and 11.0 per cent.

Three-Quarter to Bottom Busty

The most noticeable bed within the Three-Quarter to Bottom Busty interval ((Figure 17) and (Figure 18)) is a thick sandstone extending over the whole district, except for three areas near North Seaton, Seghill and east of Tynemouth. This sandstone forms the roof of the Three-Quarter Seam over a wide central area; elsewhere the roof measures are mudstone. In a few localities a bed of fragmental clayrock, 2 to 6 in thick, is recorded in the immediate roof of the seam, while at and seawards from Cullercoats and North Seaton the roof mudstones are fossiliferous. From Bates 25 Borehole [NZ 3229 8401] Spirorbis sp., Carbonicola martini, Curvirimula subovata, Carbonita sp. and fish remains were collected. In places the succeeding mudstones include thin sandstone layers, and towards the top there is a thin coal–seatearth horizon. Overlying these strata, or in the central area immediately overlying the Three-Quarter Seam, is the sandstone mentioned above. It is between 50 and 70 ft thick over much of its extent, is cross-bedded in both thick and thin beds, and is fine- to coarse-grained. It is especially coarse towards the base, with quartz pebbles and conspicuous washes of pink garnet grains, and in places with coal and mudstone pebbles. However, the underlying Three-Quarter is not washed out. Between this thick sandstone and the Bottom Busty Seam are generally several feet of mudstone with thin sandstones, in places with a thin coal–seatearth near the base.

Bottom Busty Seam

(Figure 19). 'Busty' is a Durham name, but the seam, in most districts in two leaves, may be confidently correlated into Northumberland where it is invariably separated into Top and Bottom Busty. In this district, the Bottom Busty is a poor seam, more than 12 in thick only in the north, south-west and south-east; and where it is thickest, it is generally banded. In places the seam is absent, but (except in one locality east of Blyth) it seems likely that this is due not to washout, but to non-deposition, since the seatearth is present, and is overlain by mudstone.

Bottom Busty to Top Busty

In the interval between the Bottom and Top Busty seams ((Figure 20) and (Figure 21)) the strata range from mudstone to fine sandstone, both dark shale and coarse sandstone being absent. Individual beds are impersistent. The mudstones are rich in plant remains; animals are represented only by fish debris and fragmentary mussels in the immediate roof of the Bottom Busty at a few localities. The interval is generally 20 to 40 ft thick, reaching 70 ft in the north-west and falling to 1 ft off South Shields. A median coal, generally less than 10 in thick, is present over most of the district. Other coal–seatearths occur impersistently.

Sandstones are nearly all fiaggy with micaceous–carbonaceous film partings. In some areas sandstones form the dominant lithology, though rarely to the exclusion of mud-stone.

Top Busty Seam

(Figure 22). The Top Busty is generally of excellent quality, but is thin, being less than 2 ft thick over wide areas, and more than 3 ft only very locally. There are extensive washouts in the north-west and near Blyth. The most attractive reserves are in the south-east of the district.

Top Busty To Tilley

The Top Busty to Tilley interval ((Figure 23) and (Figure 24)) ranges in thickness from 9 to 92 ft. Over wide areas, especially where it is thick, this interval is dominated by a sandstone (Figure 25) which is kaolinitic, cross-bedded and fine- to coarse-grained, even pebbly in places.

The roof measures of the Top Busty over most of the district are mudstone, noticeably rich in plant remains and generally containing ironstone nodules, with scattered grains of sphaerosiderite in places. At only two localities have fish and fragmentary mussels been found above the seam. In some areas (Figure 23) there is a thin coal some feet above the Top Busty.

Above the thick sandstone and below the Tilley Seam are mudstones with plant debris and ironstone nodules, and locally (Figure 23) a thin coal which carries a meagre roof fauna of fragmentary Naiadites and fish debris.

Tilley Seam

((Figure 24) and (Figure 26)). The Tilley is generally banded, with up to four dirt partings; only near Cambois and Newsham is it a single seam. In those areas where there are more than 24 in of coal in the seam, the ash content is generally between 6 and 10 per cent. Workability of reserves will vary inversely with thickness of partings. The Tilley is sometimes called the 'Denton Low Main' and is correlated with the Widdrington Yard of the Rothbury and Newbiggin (9 and 10) districts to the north. At Bedlington and Preston it has been worked under the name 'Top Busty'.

Tilley to Beaumont

Through most of the district, the Tilley–Beaumont strata ((Figure 27) and (Figure 28)), generally between 40 and 80 ft thick, are divided into four cyclothems, recognized by the presence of three coal–seatearths, the middle one of which is relatively impersistent.

Sandstones are generally fine- to medium-grained, often flaggy, and rarely showing erosion at their bases. Thin bands and nodules of ironstone are common in the mud-stones and seatearths: the latter are usually coloured brown.

Where the Tilley roof is mudstone it contains numerous plant fragments. In only one borehole, Cambois 55, is a fauna recorded; it consists of Naiadites sp., Carbonita humilis and fish remains. In the north-west and south-east there is a sandstone 10 to

30 ft thick within the lowest cyclothem. A relatively thick sandstone (Figure 27) is developed in places in the uppermost cyclothem. Mussels and ostracods occur at the base of this cyclothem offshore from Tynemouth, with cannel coal in places: Anthraconaia cf. williamsoni, Geisina arcuata and fish scales are recorded from Offshore 6 Borehole.

Beaumont Seam

(Figure 29). The Beaumont (known as the Harvey in Durham and a few Northumberland mines) is the lowest seam that has been extensively worked. Large reserves remain where it is over 24 in thick, though irregularly developed partings over wide areas reduce its value. The ash content of the coal is generally between 5 and 10 per cent. Washouts trend generally south to south-west, which is in line with the southerly depositional dip of the sandstone overlying the Beaumont at outcrop on St Mary's Island [NZ 352 754].

Beaumont Seam to Harvey Marine Band

The Beaumont Seam to Harvey Marine Band strata ((Figure 30) and (Figure 31)) are characterized by a distinctive shell-bed, the Hopkins Band, at or near the base and the presence of several S–SW-trending 'channel' sandstones. The strata are generally between 35 and 65 ft thick, the total range being 26 to 71 ft.

Beaumont roof: Hopkins Band

Except in the extreme north where sandy strata up to 31 ft thick intervene between the Beaumont and the Hopkins Band, the Beaumont roof is a mudstone containing a mussel-ostracod fauna. This shell-bed was called the Hopkins Band by Carruthers (1930), after its original describer (Hopkins 1928), and has been detailed by Pollard (1966, 1969). At the base of the Hopkins Band, forming the immediate roof of the Beaumont, is a 'fragmental clayrock' (Richardson and Francis 1971) which has been found at localities scattered throughout the district. Offshore from South Shields this bed is 22 in thick in Westoe Colliery Underground Borehole 36 NE 62, and is 1 to 10 in thick in surrounding boreholes. Elsewhere it is generally less than an inch thick and has probably escaped observation in many boreholes.

The Hopkins Band proper, above the fragmental clayrock, is generally divisible into three distinct successive faunal phases, which are in stratigraphical order:

• 3. Grey mudstone with ironstone nodules and with Anthracosia, Naiadites and a few Spirorbis and Carbonita; the fauna becoming sparser upward with the shells commonly preserved in pyrite; passes down into
• 2. Grey mudstone with numerous Carbonicola, Naladites, Spirorbis and Carbonita.
• 1. Coquina of densely packed ostracod shells (mainly Geisina arcuata), Naiadites and Spirorbis; generally only a fraction of an inch thick.

In collections from this district the phases were not distinguished. Shankhouse Underground Borehole yielded Spirorbis sp., Anthraconaia aff. williamsoni, Anthracosia regularis, cf. Carbonicola venusta, Naiadites sp. nov. and Geisina arcuata; and from Offshore 5 Borehole came Spirorbis sp., Anthraconaia aff. modiolaris, Anthracosia regularis, cf. Carbonicola oslancis, Naiadites sp. intermediate between productus and quadratus, Carbonita humilis, Geisina arcuata and fish remains including Elonichthys sp.[scale].

Between 5 and 20 ft above the Hopkins Band, over most of the district, there is a coal–seatearth horizon (Figure 30) which in places has a mussel band in its roof. Ironstone nodules and plant fragments are common in the succeeding mudstones.

Higher strata are mostly mudstones and silty mudstones with thin sandstones; but in some areas (Figure 30) there are sandstones 20 to 65 ft thick, which in plan trend southwards curving to south-westwards, resting on erosion surfaces which extend down in places to below the Beaumont Seam. These sandstones are medium- to coarse-grained, generally cross-bedded and locally contain mudstone pebbles. Sandstone exposed at St Mary's Island—the lowest stratum to crop out in the district—shows trough cross-bedding with a depositional dip a few degrees east of south. The form of these sandstones, together with the erosion at the bases, suggest that they are channel sandstones in distributaries on the south-west flanks of a delta.

Underlying the Harvey Marine Band are seatearths with one or two thin coals. In places these seatearths are noticeably green in colour; in other places they are brown. Sphaerosiderite or small pyrite aggregates have been recorded in some boreholes.

Harvey Marine Band to Plessey Seam

Harvey Marine Band

The Harvey Marine Band, the base of which marks the base of the Middle Coal Measures, was named by Armstrong and Price (1954, p. 987) having been earlier recorded in this coalfield by Hopkins (1934, p. 186) from Bates Pit [NZ 3062 8228]. The marine band consists of very dark grey to black shale, finely micaceous and in places slightly silty, and is generally between 1 ft and 2 ft 9 in thick. Lingula mytilloides and fish remains, with foraminifera (including Glomospira sp.) in some localities, comprise the fauna, which is confined to the lower part of the black shale where this is thicker than 2 ft. Apart from those areas where the marine band is washed out (together with overlying strata) as shown in (Figure 32), there are several localities (also on (Figure 32)) where the band is absent and shale with mussels directly overlies the coal–seatearth at the top of the previous rhythm. This situation may be seen at Curry's Point [NZ 3510 7524], the only exposure of the horizon. Possibly in a strip from Tynemouth to Blyth the band was never deposited, for adjacent to this strip it is thin and in places no Lingula shells have been recorded from borehole cores, though their absence may be more apparent than real. Normally, however, Lingula shells are abundant, well preserved and up to 6.5 mm long.

Overlying the marine band ((Figure 32) and (Figure 33)) are mudstones with a thick mussel band carrying an abundant fauna and present all over the district except where washed out. The fauna from Curry's Point is: Spirorbis sp., Anthraconaia modiolaris, Anthracosia aquilina, A. ovum, A. aff. phrygiana, A. subrecta, Anthracosphaerium aff. turgidum, A. sp. nov. aff. affine, Naiadites quadratus and N. cf. triangularis. A similar fauna was collected in a cross-measure drift at West Sleekburn Colliery [NZ 281 848].

Succeeding these fossiliferous mudstones is a sandstone, present through most of the district (the 'main or lower' sandstone in (Figure 32)) and up to 150 ft thick in places. Where exposed [NZ 3500 7522] between 100 and 200 yd W of Curry's Point, it is represented by 3 ft of 'striped beds' (silty mudstone and fine sandstone alternations) overlying 3 ft of thinly bedded, fine-grained, micaceous sandstone with small-scale cross-bedding and large (up to 9 ft across) disc-shaped ferruginous segregations at the top. Elsewhere the sandstone is recorded as generally fine-grained, but in the areas where it is thick and occupying washouts it contains layers with mudstone and coal pebbles. It is overlain by a few feet of mudstones and the seatearth of the Cheeveley Seam.

The Cheeveley Seam

(Figure 34), present throughout the north and east of the district, lies high in the interval between the Harvey Marine Band and Plessey Seam, converging with the latter in the extreme north-east, where the two have been worked as a combined seam. Only in the north does the Cheeveley exceed 2 ft in thickness. Though more generally known as the Bottom Plessey or Low Yard, it was mined as the Cheeveley at Bullocks Hall Colliery [NZ 243 981] north of this district (Fowler 1936, p. 99) and this more distinctive name is used here. The seam is exposed [NZ 3493 7521] in the cliff south-east of the Saint Mary's Fault, where it is 15 in thick and is overlain by grey silty mudstone with plant debris.

Strata above the Cheeveley are mudstones and silty mudstones with a sandstone ((Figure 34) and 'upper sandstone' of (Figure 32)) in the area between Bebside and St Mary's Island. In the south-east a few mussels occur in the Cheeveley roof: Spirorbis sp., Anthracosia beaniana, A. cf. ovum, A. sp. intermediate between phrygiana and ovum and Naladites aff. quadratus were collected from Offshore 5 Borehole.

In the south-west of the district, about half-way between the Harvey Marine Band and the Plessey Seam, is a thin coal which is tentatively correlated with the Cheeveley Seam of the northern and eastern parts of the district. This thin coal is overlain by mudstones, silty mudstones and sandstone (the 'upper sandstone' in (Figure 32)).

Plessey Seam

The Plessey Seam (Figure 35) takes its name from a locality [NZ 240 790], also known as Plessay or Plessy, in the Morpeth (14) district to the west, where it was first mined at and near its outcrop. In the north it is one of the principal seams of the coalfield. Workings [NZ 3991 8433] from Mill Pit have the distinction of being the farthest offshore (4.5 miles from high-water mark) of any in the north-east coalfield. At some collieries, the Plessey was formerly called the Low Low Main.

South of Newsham, the Plessey thins, is split in places and is nowhere workable, but (apart from washouts) it may be traced as a thin coal throughout the district.

Plessey to Hutton

In northern and central areas, the Plessey to Hutton strata ((Figure 36) and (Figure 37)) are generally shaly and range in thickness from 13 to 51 ft. A rather poor mussel band appears in the mudstones immediately overlying the Plessey Seam and a prominent one higher up towards the Hutton. The higher is the one usually referred to as the 'Plessey Shell-bed' and is noted even in some of the old sinking records. A seatearth appears locally between the two mussel bands and in places there are thin sandstones at various levels.

The lower mussel band in the roof of the Plessey was examined in West Sleekburn Colliery near the shaft [NZ 281 848] and the following were collected: Spirorbis sp., Anthraconaia salteri, Anthracosia ovum, A. phrygiana, A. sp. between aquilina and ovum, A. sp. between ovum and phrygiana, Anthracosphaerium exiguum, Naiadites quadratus, N. cf. triangularis and palaeoniscid scales. The Plessey Shell-bed here, 12 ft higher up, yielded Anthraconaia salteri, Anthracosia cf. disjuncta, A. ovum, A. phrygiana, A. subrecta, A. spp. intermediate between aquilina/phrygiana and ovum/phrygiana, Anthracosphaerium exiguum, A. cf. affine and Carbonita humilis.

In the south-east, (roughly south-east of a line through Backworth and St Mary's Island) the strata are generally sandy and virtually devoid of mussels. Total thickness is in the range of 23 to 73 ft, with sandstone up to 45 ft thick in some areas comprising almost the whole interval. The mudstones commonly contain ironstone nodules and plant fragments; thin coal–seatearths are developed in places.

Strata belonging to the Plessey-Hutton interval, including the Hutton Seam itself, are rather poorly exposed on the coast north of the Hartley Steps Fault and again north of the Saint Mary's Fault. Crab Hill [NZ 3680 7105], the tidal rock east-south-east of Smuggler's Cave, is an outcrop of the sandstone below the Hutton and not, as indicated on the six-inch map, above that seam.

Hutton Seam

The Hutton Seam (Figure 38) is a thick workable (but banded) seam only in the south, reaching 6.5 ft at South Shields. In the north-east, it is washed out in three SW-trending strips which seem to unite into one broadly sinuous washout crossing the district and extending down to below the Plessey Seam. In the Durham coalfield this seam is one of the principal coals and has been widely worked, but in Northumberland, from Tynemouth northwards to Widdrington [NZ 250 950], 4 miles N of this district, it is only a few inches thick. In the Widdrington–Broomhill area in the north of the coalfield it again becomes of workable thickness, and has been mined and quarried as the 'Duke' or 'Broomhill Main'.

The Hutton is exposed at high-water mark south-west of Smuggler's Cave [NZ 3659 7104] where the section is coal 8 in on shaly coal 7 in, and on the shore between the Crag Point and Saint Mary's faults. In these places on the six-inch maps [NZ37SE and NZ37NW] a 'Bottom Hutton' and a 'Top Hutton' are shown, of which the 'Bottom Hutton' is now considered to be the Hutton, and the 'Top Hutton' a thin seam low down in the Hutton–Northumberland Low Main interval and present only in this coastal area.

Hutton to Northumberland Low Main

The measures between the Hutton and the Northumberland Low Main seams ((Figure 39) and (Figure 40)) are generally either thin (8 to 30 ft) and shaly or thick (50 to 90 ft) and dominated by channel sandstones.

In the north-western part of the district, the Hutton roof-mudstones contain a rather sparse fauna of fish and mussels, which is also found in a few localities in the south-east. Only around North Seaton and Sleekburn is this fauna at all prolific. A collection from West Sleekburn Colliery includes Anthraconaia salteri, Anthracosia phrygiana, A. spp. intermediate between ovum/aquilina, ovum/phrygiana and aquilina/disjuncta, Anthracosphaerium aff. radiatum, Naiadites quadratus and Carbonita humilis.

On the coast [NZ 3659 7108] a few yards south of Smuggler's Cave, the Hutton roof comprises 7 ft of dark grey, finely-micaceous mudstone with a few plant fragments and thin ironstone bands. A single specimen of the crustacean Anthrapalaemon dubius (Milne-Edwards) was collected here (Rhodes and Wilson 1957, fig. 1 and p. 1165). Above are 4 ft of pale grey seatearth–mudstone with ironstone nodules, then a 1-ft coal (called Top Hutton on the six-inch map) and a few feet of sandstone. Near the Ninety Fathom Fault this sandstone ((E37754); (Plate 7), fig. 5) is cemented by calcite containing radiating prismatic crystals of baryte.

In places (Figure 39) thick channel sandstones fill washouts in lower strata. The sandstones are generally fine- to medium-grained, micaceous, thin-bedded and cross-bedded; mudstone pebbles are common within washouts. In the north-east, the Northumberland Low Main is washed out (Figure 42); the sandstone above the seam is joined with the sandstone below, and the two are not distinguishable.

Sandstone appears along low-water mark at Whitley Bay [NZ 361 722] where about 30 ft of fine-grained cross-bedded rock are visible. Sections from the Hutton to the Low Main are exposed in the cliffs and foreshore between St Mary's Island and Crag Point, as detailed below. North-west of Saint Mary's Fault [NZ 3475 7535] the section is:

Between the Hartley Steps and Crag Point faults around [NZ 3450 7565] a similar section is exposed (Figure 40):

Northumberland Low Main Seam

(Figure 41). This seam is named 'Brass Thill' in County Durham; the Durham Low Main is the next higher major seam, generally called 'Five-Quarter' in Northumberland. Before Armstrong and Price (1954) indicated that the Durham seam was at a higher horizon, the two Low Main seams were thought to be one and the same. The county epithet is therefore necessary, but for brevity 'Northumberland' will be omitted in this section only. In the south of the district, at Wallsend, the Low Main has been called the 'Five-Quarter', and the overlying Durham Low Main or Northumberland Five-Quarter was known as the 'Six-Quarter'.

As its name implies, the Low Main is one of the most widely worked seams. Throughout most of the northern, west-central and eastern parts of the district it is between 4 and 6 ft thick and of excellent quality, with an ash content between 4 and 8 per cent (air-dried coal) and sulphur between 0.8 and 2.5 per cent. This quality seems to be maintained in the south-east though the seam is here banded. Large areas of coal remain intact south of Backworth and west of Tynemouth, where the seam is of reduced thickness (2 to 4 ft), with mudstone partings and an increased ash content.

An unusual feature of the Low Main is a linear, trough-like 'swelly' of thick coal flanked by thin coal. This feature is over 5 miles long, running from Newsham to beyond Backworth (Figure 41). It was described by Hurst (1860) who, with some reserve, ascribed it to penecontemporaneous deformation. Mining in the area has ceased, so the swelly is no longer accessible for study, but the following details from Hurst (1860) and mine plans show the nature of the phenomenon. As the swelly is approached from the west, at a distance of about half a mile, a parting appears in the lower part of the 4- to 6-ft Low Main. The lower leaf thins out completely before the swelly is reached, while the upper leaf thins to between 1.5 and 3 ft and in places is nipped out. This coal then thickens into the swelly itself, which is 130 to 200 yd wide, the seam gradually thickening from about 3 ft at each edge to 7 or 8 ft in the middle, and at the same time descending gradually from each edge a vertical distance of 20 ft near New Hartley increasing southwards to 60 ft at Backworth. According to Hurst, these variations in thickness and altitude are by 'easy graduations', and the thicker coal in the trough shows 'no other evidence than that of quiet deposition'. At its northern end, the swelly appears to die out, but the Low Main plans of this locality are deficient in information. The southern end has not been explored.

The origin of this 'swelly' is not obvious. While it is not so straight as Hurst (1860) thought, it is neverthless fairly straight and certainly has not the sinuosity of a river channel. Strata above and below are not affected, as Hurst pointed out, so that it originated during or immediately after coal formation. It may be significant that the direction is in line with that of contemporary depositional currents; and that the northern end lies within the area of the 'Newsham Cannel', which forms the immediate roof of the Low Main and is famous for its varied vertebrate fauna (see below).

The washout in the Low Main in the north-east is much more complex than can be indicated in (Figure 41). Followed eastwards towards the washout, the seam is first split by a median parting, then as the washout is approached, other partings appear and thicken, there are 'roof-nips' (narrow, linear, partial washouts trending roughly parallel with the main one), narrow complete washouts and abrupt changes in coal section (e.g. from 0 to 7 ft within a few yards).

Good exposures of the Low Main may be seen in the cliff at the bottom of Hartley Steps [NZ 3448 7566] and southwards, at high-water mark around Fanny Off Point [NZ 3465 7560] and along the top of the cliff to the south. In all these exposures, collapsed adits and burnt shale mark ancient workings.

Northumberland Low Main to Durham Low Main

Over much of the district, the measures between the two Low Main seams ((Figure 42) and (Figure 43)) include two coal horizons, the Whitley and Ellington seams, and up to four fossil horizons. The complete general succession is:

• Top Durham Low Main Seam
• Measures with mussels at base
• Bottom Durham Low Main Seam
• Measures with mussels at base
• Ellington Seam
• Measures with sandstone and with prominent mussel band at base
• Whitley Seam
• Measures with mussels towards base, and cannelly shale with fish remains at base
• Northumberland Low Main Seam

This succession varies in thickness from 5 to 85 ft, but over most of the district is between 35 to 60 ft thick.

Northumberland Low Main to Whitley Seam

The roof of the Northumberland Low Main is generally black shale, cannelly in many places with small pyrite tubes and nodules. A fauna of fish debris is common and in places there are mussels, especially Naiadites sp.

At Newsham this cannelly shale (Rayner 1971, p. 451) contains an interesting and varied fish and amphibian fauna described by Atthey (1870, 1877), Hancock and Atthey (papers between 1868 and 1871) and Kirkby and Atthey (1864), and listed by Howse (1890b, pp. 268–73). The fish collection needs re-study, but the nomenclature has been revised by Dr. Sheila M. Andrews as follows. Howse's names where different are given in square brackets, and some doubtful identifications are omitted.

• Acanthodopsis wardi Egerton
• Acrolepis hopkinsi McCoy [Gyrolepis rankinti (Agassiz)]
• Callopristodus pectinatus (Agassiz) [Ctenoptychius pectinatus (Agassiz)]
• Chirodus striatus (Hancock & Atthey) [Amphicentrum striatum Hancock & Atthey]
• Cladodus mirabilis Agassiz
• Ctenodus cristatus Agassiz
• Diplodus gibbosus Agassiz
• Elonichthys egertoni (Agassiz)
• Gyracanthus formosus Agassiz [G. tuberculatus Agassiz]
• Janassa linguaeformis Hancock & Atthey
• Megalichthys coccolepis J. Young
• Megalichthys hibberti Agassiz
• Platysomus forsteri Hancock & Atthey
• Platysomus parvulus Agassiz
• Platysomus rotundus Hancock & Atthey
• Pleuracanthus cylindricus (Agassiz) [Orthocanthus cylindricus Agassiz]
• Pleuracanthus laevissimus Agassiz
• Pleuroplax rankinei (Agassiz) [Pleurodus rankinei Agassiz]
• Rhabdoderma elegans Newberry [Coelacanthus lepturus Agassiz]
• Rhadinichthys hancocki (Atthey) [Palaeoniscus hancocki Atthey]
• Rhizodopsis sauroides Williamson
• Sagenodus inaequalis Owen [Ctenodus elegans Hancock & Atthey, C. ellipticus Hancock & Atthey, C. imbricatus Hancock & Atthey, C. obliquus Hancock & Atthey]
• Sphenacanthus hybodoides (Egerton) [Ctenacanthus hybodoides Egerton]
• Strepsodus sauroides Huxley
• Strepsodus (Archichthys) sulcidens (Hancock & Atthey) [Archichthys sulcidens Hancock & Atthey]

The amphibia have been studied by Drs. A. L. Panchen and Angela C. Girven who have supplied the following revised list:

• Batrachiderpeton lineatum Hancock & Atthey
• Eogyrinus attheyi Watson [Anthracosaurus russelli Huxley]
• Megalocephalus pachycephalus (Barkas) [Loxomma allmanni Huxley]
• Ophiderpeton nanum Hancock & Atthey Pteroplax cornutus Hancock & Atthey
• 'Urocordylus reticulatus' Hancock & Atthey (probably = Batrachiderpeton lineatum)

Hancock and Atthey (1869b) also described several species of fungus from Newsham which they assigned to Archagaricon spp.

Strata above the basal black shale are grey mudstones with ironstone nodules and plant fragments passing up into silty mudstones with a thin sandstone. This sandstone thickens to between 10 and 35 ft in two SW-trending areas near Blyth and Seaton Delaval. The Whitley Seam is absent in the south-west of the district and only a few inches thick elsewhere. These strata are intermittently exposed on the beach at Whitley Bay and well seen in the cliffs at Hartley [NZ 344 758] (see sections, p. 63).

Whitley to Ellington Seam

Throughout most of the district the roof mudstones of the Whitley Seam contain a prominent mussel band which is much better developed than that in the roof of the underlying Low Main. For this reason many authors (e.g. Trueman and Weir 1951, p. 116; Jones 1967) have named the mussel band above the Whitley Seam the 'Low Main Shellbed,' and thereby caused some confusion as to the exact horizon intended. This mussel band is well exposed along the foreshore at Whitley Bay (see section, p. 63) which is the type locality of Anthracosia beaniana King, the type species of Anthracosia. This species and A. phrygiana dominate the fauna which is listed in the section (below). The fossiliferous strata also include beds and nodules of shelly ironstone, the Whitley Ironstone, which was mined along Whitley Links in the 18th century. At Hartley [NZ 3448 7565] the same beds consist of 4 ft of mudstone with mussels and ironstone bands, and some dolomite with cone-in-cone structure. The fauna (listed below) is rather different as it includes Anthraconaia salteri, and Anthracosia beaniana has not been found.

Collecting at West Sleekburn Colliery from the roof of the Whitley Seam yielded a fauna similar to that from Whitley Bay: Anthracosia beaniana, A. aff. disjuncta, A. phrygiana, A. cf. ovum, A. sp. between aquilina and disjuncta, Anthracosphaerium exiguum?, Naiadites quadratus, N. sp. between productus and quadratus, Carbonita humilis and fish scales including Rhizodopsis sp.

Strata above the mussel band are silty mudstones followed by sandstone which is generally fine-grained, with small-scale cross-bedding. In the north-east, it is coarser and underlying strata are washed out.

Ellington to Durham Low Main Seam

The Ellington Seam is recognized only in the north where there are never more than 4 in of coal and generally only the seatearth. It is named from Ellington Colliery [NZ 284 917] in the district to the north, where it is over 2 ft thick in places. Strata up to the Durham Low Main are variably mudstones and sandstones, with sandstone prominent in southern parts of the district and a mussel band at the base in the north-west and at Hartley. From this band, Anthracosia lateralis, A. aff. phrygiana, A. sp. intermediate between ovum and lateralis, Naiadites aff. quadratus, Carbonita evelinae, C. humilis and C. scalpellus were collected at West Sleekburn Colliery.

Strata between the two Low Main seams are well exposed on the coast at Hartley [NZ 3435 7610] to [NZ 3455 7560] between the Crag Point and Hartley Steps faults, where the section is:

On the shore at Whitley Bay around [NZ 3600 7225] most of the strata are cut out by erosion at the base of the Table Rocks Sandstone which is younger than the Durham Low Main. The section is:

Durham Low Main Seam

(Figure 44). In Northumberland, the Durham Low Main is generally known as the 'Five-Quarter', except in the south (Rising Sun and Wallsend collieries in this district) where it is the 'Six-Quarter'. The Durham Low Main is banded almost throughout the district and generally has two leaves of thicker coal and several thin leaves. In some areas there are over 3 ft of mudstone, locally with mussels at the base, between the workable coals. At and north-east of Blyth and in the southern part of the district, the seam is rather thin, but elsewhere there are at least 2.5 ft of coal in the main leaves. Where it is exposed on the coast south of Crag Point [NZ 3433 7607] it is 2.5 ft thick with only a very thin parting.

Durham Low Main to Bensham

The Durham Low Main to Bensham interval ((Figure 45) and (Figure 46)) is generally 30 to 60 ft, the total range varying from 18 to 82 ft. The roof measures of the Durham Low Main Seam are mudstones with ironstone nodules, with fish debris at the base, and a mussel band above, from which Spirorbis sp., Anthracosia disjuncta, A. sp. between phrygiana and aquilina, A. sp. between phrygiana and nitida, and Naiadites quadratus were collected at West Sleekburn Colliery.

These mudstones are succeeded by the Table Rocks Sandstone (Figure 45) or by silty mudstones with thin sandstones. In some localities the silty mudstones include a coal–seatearth horizon with a poorly developed mussel band above, which in Offshore 6 Borehole yielded Spirorbis sp., Anthraconaia robertsoni, Naiadites sp., Carbonita humilis and fish fragments.

Table Rocks Sandstone

The Table Rocks Sandstone was named by Lebour and Smythe (1906) from its coastal exposure [NZ 364 720], where it lies in a washout channel which has cut down almost to the Northumberland Low Main. At the base of the sandstone at Table Rocks is a conglomerate of mudstone, ironstone and coal pebbles, and the underlying strata are much disturbed. Lebour and Smythe (1906) described the conglomerate and the disturbances in detail, and ascribed them respectively to unconformity and to thrusting after lithification; but from experience elsewhere in the coalfield, it is now clear that this is a case of washout with contemporaneous disturbance of the channel floor. The sandstone at Table Rocks is medium- to coarse-grained, thickly and thinly bedded and cross-bedded and is over 50 ft thick. The lower part is not well exposed, but the middle part is seen to be very massive, while the upper part is relatively thin-bedded and shows cross-bedding directions to the south-south-east and north-east. Large ovoid ironstone concretions, up to 15 ft across, weather into curious shapes (photo. L624).

Strata above the Table Rocks Sandstone up to the Bensham Seam are exposed in Brown's Bay [NZ 3645 7175] as follows:

Strata overlying the Durham Low Main are exposed [NZ 3433 7607] in the cliff south of the Crag Point Fault. where the section is:

The mudstone overlying the Durham Low Main here does not appear to contain any mussels, which is unusual in this district. The Table Rocks Sandstone at the top of this section re-appears on the northern, downthrow side of the Crag Point Fault (Plate 3A) in the lower part of the cliff, where its brown colour and southward directed cross-bedding contrasts with the brownish grey colour and westward directed cross-bedding of the Seaton Sluice Sandstone in the upper part of the cliff. The latter sandstone, belonging to the overlying Bensham to Yard measures (p. 72), here lies in a washout channel eroded to below the Bensham Seam. The same two sandstones in the same relationship are again exposed north of the Seaton Sluice Fault [NZ 3395 7680].

Bensham Seam

((Figure 47) to (Figure 49)). The Bensham Seam is one of the major worked seams of the coalfield, and is correlated with the Maudlin Seam of County Durham. In the northern part of the district it is split into a Top and Bottom Bensham by up to 30 ft of strata and these seams are worked separately under different names, as follows:

In an east-west area through Tynemouth, the Bensham is an undivided seam 4 to 5.5 ft thick. Away from this area a median parting comes in, gradually thickening northwards to about 3 ft along a line through Seghill and Holywell, beyond which the two leaves of the Bensham have to be worked separately, because within a short distance farther northwards the parting increases in thickness to over 10 ft. Both Top and Bottom Bensham are removed in wide ESE-trending washouts through Shank-house and Hartley. That there are two washouts, and not one which in places cuts down more or less deeply, is shown by the fact that over wide areas where the Bottom Bensham is washed out, the Top Bensham is developed normally. North of the washouts, the Bottom Bensham (Figure 48) reaches 3 ft in thickness in the west, while the Top Bensham attains 4 ft in places, but its value is reduced by a parting up to 11 in thick (Figure 49). The only exposure of the Bensham Seam is in Brown's Bay [NZ 3645 7175] where it may be seen in places at the base of the sandstone cliff on the south side of the bay, and at the top of the slope [NZ 3637 7176] at the head of the bay.

Bensham to Yard

Between the Bensham and Yard seams ((Figure 50) and (Figure 51)) the general succession is as tabulated below. The terms upper, middle and lower thin seams and upper sandstone are informal names used only in this account to facilitate description.

• Yard Seam
• Mudstones with upper sandstone, and at the base in the south a mussel band with 'Estheria'
• Upper thin seam, coal or seatearth (absent in the north-east)
• Mudstones and silty mudstones with mussels at the base in places
• Middle thin seam (coal or seatearth)
• Mudstones with Seaton Sluice Sandstone and with mussels at base in north-west Lower thin seam (in north-west only)
• Mudstone with mussel band at base
• Bensham Seam

The roof of the Bensham (or Top Bensham) contains a mussel band up to 20 ft thick in places characterized by Anthraconaia pulchella. In a collection from Offshore 5 Borehole this species was abundant and accompanied by Spirorbis sp., Anthraconaia aff. confusa, A. polita?, Anthracosia disfuncta, A. faba?, A. aff. lateralis, A. sp. cf. phrygiana, A. subrecta, Anthracosphaerium affine, A. exiguum, A. aff. propinquum and Naiadites productus. Locally there are no fossils; in other places the band is washed out. Succeeding strata are mudstones and siltstones with thin ironstone bands, and in the north-west the lower thin seam. This attains a thickness of 15 inches in one borehole and is overlain by mudstones with mussels.

Seaton Sluice Sandstone

The distribution of the Seaton Sluice Sandstone (new name) is shown in (Figure 50); it is well exposed at Brown's Point [NZ 366 717], Crag Point [NZ 343 763] and Seaton Sluice [NZ 338 769]. At Brown's Point, 40 ft of fine- to medium-grained, strongly cross-bedded sandstone, with cross-bedding directed between south and south-east, immediately overlies the Bensham Seam (photo. L 623). At Crag Point the sandstone, here forming the upper part of the cliff, is brownish grey and coarse-grained, and is cemented partly by baryte. The sandstone has westward-directed cross-bedding and a conglomeratic base with small quartz pebbles. Its erosive base cuts out the Bensham Seam and rests unconformably on the Table Rocks Sandstone (p. 67 and Plate 3A). The same sandstones are also well exposed at Seaton Sluice, where the base of the Seaton Sluice Sandstone may be traced from about one-third the way down the cliff, immediately north of the Seaton Sluice Fault, gradually descending to low-water mark on the north side of Rocky Island [NZ 3386 7696]. At the entrance to Hartley New Harbour [NZ 3393 7681] the lowest part of this sandstone contains quartz pebbles up to 0.5 in across, mud-stone pebbles up to 24 x 4 in, ironstone pebbles and large coal scars (photos. L643-L644). At the base is a layer of calcite pebbles, up to 2 in across, in which calcite appears to be a replacement, perhaps of siderite ((Plate 7), fig. 3). The sandstone was also quarried around [NZ 338 757] in the dene west of Hartley.

Strata above the Seaton Sluice Sandstone are mainly mudstones and silty mudstones with local thin sandstone partings and two coal–seatearth horizons, the middle and upper thin seams. The former apparently occurs only in the coastal area between Seaton and Tynemouth, although the detailed correlation of these strata is not certain.

In Collywell Bay [NZ 340 763], above the middle seam, which is here represented by 2.5 ft of carbonaceous shale, a 4-in cannel yields Anthraconaia pukhella, Anthracosia cf. caledonica, Naiadites productus, 'Estheria' and fish debris. Three feet higher is a 1-in clay bed composed of illite and chlorite, and containing authigenic baryte ((E37830); (Plate 7), fig. 4). At Whitley Bay on the south side of Brown's Point [NZ 3658 7162] at what is probably the same horizon as the Collywell Bay cannel (though the middle thin seam is not present), grey mudstone contains Anthraconaia pukhella, Anthracosia faba, A. simulans and Naiadites productus. In the south, the upper thin seam carries a roof fauna of indeterminate species of Anthracosia and Naiadites. This fauna or that above the middle seam may correlate with the Blackhall 'Estheria' Band (Magraw and others 1963, p. 164) of south-east Durham. The upper thin seam is 11 to 20 in thick around Newsham and New Hartley and in Collywell Bay; elsewhere it is much thinner or represented only by seatearth.

The upper sandstone distribution is shown on (Figure 50). In the north-east it is thick medium-grained, locally coarse and pebbly, and cross-bedded; and it here unites with the Seaton Sluice Sandstone. The fact that they are separate beds, however, is shown by the way they tongue out separately south-westwards. The upper sandstone is exposed on the foreshore at Cullercoats [NZ 3652 7152] where it is represented by 17 ft of fine-grained sandstone with silty mudstone partings. A small exposure adjacent to the Seaton Sluice Dyke [NZ 3395 7668] is of interest in showing metamorphism ((Plate 7), fig. 6).

Yard Seam

The Yard Seam (Figure 52), known as the 'Main' in Durham, is one of the most widely worked seams in the coalfield. It is remarkably consistent in its thickness and excellent quality. Splits and washouts are few and very local, and only in a few restricted localities is the seam either over 4 ft or under 2 ft thick. Throughout most of the district it is between 30 and 40 in and has been mined to crop (or beneath the sea to cover limit) everywhere except in the south-east. The coal crops out on the foreshore at Seaton Sluice, where it may be seen [NZ 3403 7669] coked against the Seaton Sluice Dyke at low-water mark, and again [NZ 3394 7638] coked against the Hartley North Dyke and in the cliff to the south. The Yard Seam is visible, when conditions permit, on the beach [NZ 3345 7725] north of Seaton Sluice (Hopkins 1931). It also crops out at Culler-coats in the cliff [NZ 3646 7154] and may be followed across the foreshore here, and also on the north side of Sharpness Point [NZ 3715 7000]. As on most foreshores, the coal at these localities has been quarried and the outcrop covered by sand and shingle, so that the seam is rarely visible.

Yard to Bentinck

Over much of the district the Yard to Bentinck interval ((Figure 53) and (Figure 54)) is between 20 and 55 ft, dwindling to only 1 ft at North Shields.

The Yard Seam roof is generally mudstone with ironstone nodules and plant fragments. Animal fossils are as a rule absent, but a few boreholes have yielded fish debris and rare Anthracosia spp. and Naiadites spp. Over much of the district these strata are succeeded by a sandstone which is fine- to medium-grained, partly cross-bedded and partly massive. The thicker parts of this sandstone are elongated north–south in accord with the general palaeocurrent direction. Above the sandstone are shaly strata with thin ironstone bands and nodules, and with a thin coal–seatearth 10 to 15 ft below the Bentinck in the extreme north-west.

Strata above the Yard Seam are exposed at Seaton Sluice, Cullercoats and Sharpness Point. On the foreshore [NZ 3392 7668], south of the Seaton Sluice Fault, 5 ft of grey mudstones with silty partings are succeeded by 10 ft of fine-grained, cross-bedded sandstone and this is followed by 14 ft of mudstones, with thin sandy partings in the middle and ironstone nodules in the upper part, beneath the poorly-exposed Bentinck Seam which is about 1 ft thick. Similar strata are exposed [NZ 3395 7636] in the cliff in Collywell Bay. At Cullercoats [NZ 365 715] the Yard roof comprises 2 ft of grey mudstone, followed by a 10-ft sandstone under the Bentinck seatearth and coal (2 ft thick). The sandstone is very shaly in the middle, and the upper and lower parts are well jointed with concentrically arranged, differential iron-enrichment within each joint block. On the east side of Sharpness Point [NZ 3718 6990] below the 1.5-ft Bentinck Seam and its seatearth are some 30 ft of fine-grained cross-bedded sandstone with silty micaceous partings in the upper part. Prominent joints, irregular in direction, but mainly north-east and south-east cut the rock into blocks within which concentric differential iron-enrichment is very noticeable, as at Cullercoats.

Bentinck Seam

The Bentinck Seam is not worked in this district, but has been worked at Ashington only a short distance to the north, where it received its name. It has also been called the Top Yard. In the south-eastern part of the district it is generally between 1 and 2 ft thick, but is less than a foot in the south-west. Over a considerable area north of Seaton Delaval (Figure 53) it is represented only by a seatearth, but in the north again exceeds a foot in places.

Relations of coal seams between the Bentinck Seam and the High Main Marine Band

Between the Bentinck Seam and the High Main Marine Band (Figure 3) there are five coal seams with somewhat complex relationships ((Figure 55) and (Figure 56)). In graphical order, the seams are:

• High Main Marine Band
• High Main Marine Band Seam
• Ashington Seam
• High Main Seam
• Metal Seam
• Five-Quarter Seam
• Bentinck Seam

In different areas, different pairs of these seams come together, either to coalesce to be separated by a parting so thin that they may be mined together. The Seam does not extend much farther south than Bedlington Station, and both it and the seams below are subject to extensive washouts.

Stratigraphical variation is particularly rapid in a north–south direction between Bebside and Bedlington Station: the Metal and Five-Quarter diverge northwards, as do the High Main and High Main Marine Band seams. The High Main and Metal converge in the same direction, while the Ashington Seam appears above the High Main and approaches the High Main Marine Band Seam. In the Morpeth (14) district to the west, the High Main, Metal and Five-Quarter all converge south of Bedlington, where in the Church Lane Borehole [NZ 2608 8112] for example, the three are represented by 18 ft of coal in 12 leaves within 31 ft of strata. These seams also come together east of Lynemouth in the Newbiggin (10) district to the north.

Local nomenclature is as complex as the stratigraphy. 'Metal' and 'Five-Quarter' are essentially north Durham names: in Northumberland these seams are generally known as 'Top Main' and 'Bottom Main' respectively. North of the River Wansbeck the Ashington Seam takes on the name 'High Main' and the High Main becomes known as 'Top Main' or 'New Main'. Local names are given in the table beneath (Figure 56).

Bentinck to Five-Quarter

Strata in the Bentinck to Five-Quarter interval ((Figure 57) and (Figure 58)) show relatively little variation in character or thickness. Though the total thickness ranges from 13 to 77 ft, over most of the district it is between 35 and 50 ft.

Overlying the Bentinck Seam are dark shales with fish debris, succeeded by mud-stones with a mussel band. The fauna in Offshore 6 Borehole comprises Spirorbis sp., Anthraconaia cf. pulchella, Anthracosia cf. lateralis, Naiadites aff. alatus, N. cf. productus, Carbonita sp. nov.,'Estheria' sp. and fish remains including Rhizodopsis sp. At most other localities, Naiadites spp. dominate the fauna. Above the fossiliferous strata come mudstones and silty mudstones with ironstone nodules and bands and with scattered plant fragments. In some localities this sequence is topped by a coal–seatearth followed by mudstone with mussels, which are neither so numerous nor widespread as those in the roof of the Bentinck. The upper part of the interval is made up of silty mudstones with, in places (Figure 57), a sandstone up to 30 ft thick, which shows ESE-trending linear developments. These mudstones and sandstones are overlain by the Five-Quarter seatearth.

On the coast, these strata are exposed in three places. At Seaton Sluice [NZ 3389 7665] the section is:

It is possible that the mussel band seen here is the sporadically developed upper one, not the main Bentinck roof mussel band. At Cullercoats on the foreshore [NZ 365 714] north of the North Pier, the Bentinck is overlain by a foot or two of dark mudstone with Anthracosia cf. aquilinoides, A. lateralis and Naiadites productus, and this is succeeded by about 75 ft of sandstones with mudstone partings. It is almost certain that the upper part of this sequence comprises sandstones belonging to the interval above the Five-Quarter which is here washed out. South of Sharpness Point are exposed about 10 ft of mudstones with silty partings and ironstone bands and nodules.

Five-Quarter Seam

The Five-Quarter (Figure 59) has been extensively worked in the central part of the district, where it is combined with the overlying Metal to form a 4-to 6-ft seam with one to three bands a few inches thick. Some areas of Five-Quarter between 2 and 3 ft thick, with ash contents 5 and 9 per cent, remain east and west of North Seaton and at Cowpen. Over a wide area offshore from Tynemouth, the seam is over 2 ft thick and as it is traced eastwards it both thickens and splits into an area where there is a workable section of 4 to 5 ft with less than 10 per cent ash. The only exposure of the seam is at Seaton Sluice [NZ 3387 7663] where it is 2 ft thick with a 9-in shaly coal 3 ft below. At Cullercoats and Tynemouth where the seam should cross the shore, it is washed out.

Five-Quarter to Metal

The Five-Quarter and Metal seams are united or nearly so over a wide central area and in the extreme north-east and south-east (Figure 60). North of Blyth and Bedlington Station intervening strata are mostly sandstone, generally fine-grained with small-scale cross-bedding and thin shaly partings. Under the southern part of Blyth, the Metal and Five-Quarter seams converge southward and become banded eastwards. In the Gordon Road Borehole [NZ 3169 8054] (Figure 61) for example, the two seams and intervening strata are represented by the following section:

Up to 50 ft of mudstone and silty mudstone separate the two seams in the southern part of the district. At a few localities Naiadites spp. are recorded in the Five-Quarter roof, and in places there are seatearth horizons. Sandstones are present around Shiremoor and Cullercoats, and also at Tynemouth where they form the foreshore on the north side of the castle and the infamous Black Middens reef on the south.

Metal Seam

Details of the Metal Seam are shown in (Figure 62). Although it is widely worked, reserves remain in parts of the north and south where there are between 2 and 3.5 ft of coal with about 10 per cent ash. In the south-east, though it is banded' there is at least one leaf 2 ft or more thick. The seam is poorly exposed at Seaton Sluice [NZ 3387 7663] where it seems to be about 4 ft thick, separated from the Five-Quarter by a few feet of mudstone.

Metal to High Main

The Metal to High Main sequence ((Figure 63) and (Figure 64)) ranges from a few inches of seatearth near Bedlington Station to 132 ft of strata at New Delaval, less than 2 miles to the south-east.

The lower part of the sequence, especially where it is thick, is generally sandstone (Figure 63) which is commonly fine-grained and massive where thick, but fiaggy with shaly partings where thin. Where underlying strata are washed out, the sandstone contains mudstone pebbles. At Seaton Sluice, the stack known as Charley's Garden [NZ 3396 7657] (Plate 2A) has been cut out of this sandstone by the sea attacking it along joints. Higher and lower beds with silty mudstone partings are exposed north and south of Charley's Garden, and show depositional cross-bedding directions between south-east and south-south-east. On the foreshore on the east side of Tynemouth Castle, sandstone with a mudstone–pebble conglomerate (Plate 2B) marks the washout of the Metal Seam. This conglomerate is particularly noticeable, because, lying only a few feet below the Permian unconformity, the mudstone pebbles are stained reddish purple while the sandstone matrix contains so little ferric iron that it appears bleached by contrast.

Above the sandstone, or where this is absent comprising the whole interval, are mudstones, silty in places, with plant fragments and ironstone nodules and bands. In one or two places, a few mussels are recorded in the roof of the Metal Seam, for example ?Anthracosphaerium propinquum in North Seaton 166 Borehole. Strata immediately beneath the High Main Seam are exposed in the north bank of Seaton Burn [NZ 3315 7484] where the shaly lowest leaves of the High Main rest on about 15 ft of pale grey mudstone, rooty at the top, with ironstone nodules, which in turn overlies at least 35 ft of fine-grained sandstone with shaly partings seen on the south bank about 200 yd to the east.

High Main Seam

The High Main Seam (Figure 65) is thickest and most widely worked in the south, where a large area of excellent quality coal, 6 to 8 ft thick in this and adjacent districts, formed the original basis of the large-scale exploitation of the Northumberland and Durham Coalfield.

In the extreme north-west, the High Main is an unhanded seam, but thence southwards to Shankhouse it is banded, though not so much as to make it unworkable. Where it is intact in the northern part of the district, there are between 1.5 and 4.5 ft of coal with ash content varying between 3 and 14 per cent; quality is generally better towards the north-west. In the unworked area around East Cramlington, there are generally 2 to 4 ft of coal with 4 to 11 per cent ash. The seam is washed out in a belt from Cambois to Seghill.

South-east of Seghill, poor quality 'Bottom Seams' occur below the High Main proper; in many old sections two are recognized, an upper 'Ground Coal' and a lower 'Bottom Coal', though the nomenclature is not entirely consistent. Near Seghill they have been called 'Crow Coal'. On the left bank of Seaton Burn near Silver Hill [NZ 3315 7484] they are exposed though the High Main itself is not seen. The section here is:

Samples of the High Main in the southern part of the district show that the ash content of the widely worked main leaf was between 4.8 and 7.1 per cent, but the bottom seams were never worth working. This is shown, for example, by the West Monkseaton Borehole [NZ 3384 7209] where the High Main section is:

Offshore from Tynemouth, the High Main becomes banded and deteriorates in both thickness and quality.

High Main Seam to High Main Marine Band

In the east-central and southern parts of the district (except the extreme south-east) a sandstone, the High Main Post, forms most of the strata between the High Main Seam and the High Main Marine Band Seam ((Figure 66) and (Figure 67)). This sandstone was formerly quarried near Billy Mill [NZ 334 695] and [NZ 336 692] where over 30 ft of thickly bedded, medium- to coarse-grained rock was visible. Good exposures may be seen in the banks of Seaton Burn [NZ 328 747] near Crow Hall, and also on the foreshore east of Blyth Harbour, from Shinny Gripe Lug [NZ 320 822] to Seaton Sea Rocks [NZ 330 806], where about 100 ft of fine- to medium-grained sandstone shows SSE-directed cross-bedding.

In the central part of the district, towards the western margin, the interval decreases and the sandstone thins and passes into argillaceous strata, until between Bebside and East Cramlington the High Main and the High Main Marine Band seams are separated by only a few feet of seatearth.

Ashington Seam

Northwards from Bebside and Cowpen, the interval increases and a coal, the Ashington Seam, appears in a median position beneath the High Main Post. In the north-west, strata above and below the Ashington are mostly pale grey mudstones with silty and ankeritic partings and sparse plant remains. Around West Sleekburn, the Ashington and High Main Marine Band seams converge.

The Ashington Seam is depicted in (Figure 68). It is not mined within this district but to the north it becomes an important coal, worked under the name 'High Main'.

In South Shields and offshore to the east and north-east, the High Main Post thins and the interval comprises a variable succession of mudstones, silty mudstones and sandstones with a mussel band above the High Main and a coal–seatearth horizon higher up. The mussel band has yielded Spirorbis sp., Anthracosia lateralis, Anthracosphaerium aff. radiatum, Naiadites aff.productus and Carbonita humilis in Offshore 5 Borehole; and Spirorbis sp., Anthraconaia cf. oblonga, Anthracosia sp. cf. lateralis, Anthracosphaerium?, Naiadites alatus, N. obliquus and Carbonita humilis from Offshore 6 Borehole.

Over the whole district, at the top of the interval is the High Main Marine Band Seam which is generally between 3 and 12 in thick, but varies between 0 and 18 in. The seam immediately underlies the marine horizon of the same name.

High Main Marine Band to Moorland Seam

Strata between the High Main Marine Band Seam and the Moorland Seam ((Figure 69) and (Figure 70)) are generally divisible into three cycles at two thin intermediate seams, referred to informally here as the upper and lower seams. The general succession is tabulated below:

The whole interval from the marine band to the Moorland varies in thickness from 70 to 122 ft, and is generally between 85 and 100 ft.

High Main Marine Band

The High Main Marine Band took its name (Anderson 1958) from the subjacent named coal, despite the fact that in places this is over 100 ft below. The band was first named (Anderson 1956) the 'High Main Lingula Band'.

Except in the Rowlington Dean Borehole [NZ 2824 8574], the High Main Marine Band Seam is immediately overlain by the marine band which consists of up to 23 in of black, finely micaceous shale. From North Seaton 166 Borehole [NZ 2950 8580], Lingula mytilloides, Myalina compressa, Geisina sp., Paraparchites sp. and fish remains were recorded, but in most localities only Lingula is found. The marine band is present in the north and south-west (Figure 69); elsewhere it is either absent or unrecognized. In the south-east it is certainly absent for here boreholes have been carefully searched. At Rowlington Dean Borehole the following section shows an unusual development of stratabelow the marine band:

Strata above the High Main Marine Band

(Figure 70). Overlying the marine band is mudstone containing the High Main Shell-bed, one of the most prolific mussel bands in the sequence, and recorded in many old borehole journals. In the West Sleekburn Borehole [NZ 2849 8497] the mussel band is 15 ft thick and contains Spirorbis sp., Anthraconaia cymbula, A. librata, Anthracosia atra, A. concinna, A. lateralis, A. aff. planitumida, A. simulans?, ?Anthracosphaerium radiatum, Naiadites alatus, N. obliquus, Carbonita humilis and palaeoniscid scales. In Offshore 6 Borehole the band is 9 ft thick and yields Spirorbis sp., Anthraconaia cymbula, A. librata, Anthracosia acutella, A. aquilina, A. concinna ?, A. lateralis, A. cf. subrecta, Anthracosphaerium radiatum, Naiadites alatus, N. aff. angustus, N. aff.productus, Carbonita humilis, C. sp. nov.,cf. Geisina sp., and fish remains including Rhabdoderma sp. and platysomid scales. Similar faunas occur in other boreholes throughout the district, with the addition of 'Estheria', particularly from low in the band. Above the mussel band, the strata become sandy and pass up locally into sandstone which exceeds a few feet in thickness only at Bebside. The lower seam is absent in part of the south of the district, elsewhere it is in places represented only by seatearth and is thickest (up to 15 in) between Blyth and Seaton Delaval.

Strata between lower and upper seams

Above the lower seam are mudstones, generally with a fauna represented by the following from Offshore 6 Borehole (between 600 and 611 ft): Spirorbis sp., Anthraconaia sp. between librata and cymbula, Anthracosia cf. acutella, A. cf. atra, A. aff. fulva, A. lateralis, cf. A. rubida, Anthracosphaerium aff. propinquum, Naiadites aff. alatus, N. cf. obliquus, Carbonita humilis, C. cf. scalpellus, 'Estheria' sp. and fish remains. Above these fossiliferous mudstones, the strata are generally silty mudstones with thin sandstone.

The upper seam is thinner and less persistent than the lower seam. It is washed out together with overlying mudstones south-south-west of Blyth.

Upper seam to Moorland Seam

Where not washed out, the mudstones at the base of these strata are notable for numerous, large 'Estheria', with Naiadites and fish remains. Except in the north, higher strata include a sandstone which from Blyth southwards is 50 to 65 ft thick, cross-bedded and coarse-grained. This sandstone is exposed in a number of places: on Blyth North Beach [NZ 319 822] where about 30 ft of massive medium-to coarse-grained sandstone shows cross-bedding directed north-westwards; on the north bank of the River Blyth [NZ 2891 8247] south of Mount Pleasant; at Lysdon Quarry [NZ 3083 7766] which is now almost overgrown; in old quarries [NZ 3165 7430] and [NZ 3187 7433] (now nearly filled in) and the nearby stream, on either side of Holywell Bridge; at Seghill [NZ 283 743] where the old village is built on sandstone which was also quarried at the west end of the village; in the railway cutting [NZ 3024 7065] at Holystone, where a few feet of rather shaly sandstone is seen; and at Prospect Hill [NZ 3120 7075] where the sandstone was formerly quarried. The highest strata beneath the Moorland Seam, where these are mudstones, are noticeably green in colour at some levels, and contain ironstone nodules and in places sphaerosiderite.

Moorland Seam

((Figure 71) and (Figure 72)). The Moorland Seam is named from Bedlington Moor Land, near the present Bedlington Station, where the coal was mined at least as early as the 18th century. Another area of ancient workings is Blackclose [NZ 277 860], in the north-west corner of the district, from which comes another name for this seam.

One of the earliest records of coal mining in England is near Blyth in 1236, where the Moorland Seam was worked along and near its outcrop westwards through Cowpen to Bebside. What appears to be the Moorland is visible in the roadside [NZ 2771 8198] on Bebside Bank, near collapsed adits. North of Seaton Delaval, the Moorland varies irregularly between 2 and 3.5 ft thick, is generally banded and has a rather high ash content. Its attraction appears to have lain in its shallow depth rather than in its quality. South from Seaton Delaval, the seam thins and dies out altogether in the Willington and Percy Main area. The Moorland is exposed in the south bank of Seaton Burn [NZ 3211 7449] at Holywell where a 12-in coal with a grey shale roof rests on 3 ft of seatearth becoming silty down and passing into sandstone.

Moorland to Ryhope Little

Strata between the Moorland and Ryhope Little seams ((Figure 71) and (Figure 72)) show considerable local variation, but no variations on a district scale are apparent. This may be partly due to the relatively restricted area available for study, for wide stretches of these beds have been eroded away. Because the area is restricted, no map is given showing facies limits and changes within the strata. Similarly for higher strata which are even more restricted in area, no maps have been drawn.

Around North Seaton, the Moorland to Ryhope Little interval varies between 40 and 70 ft, and includes an intermediate coal seam. The Moorland roof strata are silty and without any recorded fauna. They are succeeded by a sandstone up to 40 ft thick surmounted by the intermediate seam, which comprises up to 15 in of coal, generally in two leaves, or is marked merely by a seatearth. From the roof mudstones, fragmentary mussels and fish remains have been collected in a few boreholes. Succeeding strata up to the Ryhope Little are variable and include sandstone in places. The Ryhope Little is between 0 and 16 in thick, except at West Sleekburn Colliery where 51 in were recorded in the shaft.

West of Blyth, the Ryhope Little Seam has not been identified with certainty; seam intervals appear to vary considerably over short distances, but in general the picture is similar to that at North Seaton. The oval seam outcrop named Ryhope Little on the one-inch map at Bebside Bank [NZ 280 820] is now thought to be more probably the intermediate seam below. In the roadside cutting on Bebside Bank [NZ 277 820] two coals are seen, their outcrops marked by collapsed adits. The lower seam which is probably the Moorland, is about 2 ft thick, and is separated from the 1.5-ft higher one (probably the intermediate seam) by about 12 ft of sandstone.

Sandstone above the Moorland crops out on Blyth North Beach, forming the two reefs known as The Rockers [NZ 315 831] and Green Skeer [NZ 314 827], where it is medium-to coarse-grained with north-westerly directed cross-bedding, and contains ferruginous 'doggers' up to 12 x 65 ft in size.

In Newsham 2 Borehole [NZ 3022 7986] cannelly shale just above the Moorland Seam yielded Spirorbis sp., Anthraconaia sp. nov., Naiadites sp. and fish remains including Rhabdoderma sp. and Rhizodopsis sp. Dr. M. A. Calver comments "the Anthraconaia is a small elongate form not closely comparable with any described species but nearest to A. obscura" and adds that the occurrence of these small, elongate Anthraconaia appears to be linked with the canneloid lithology.

Between New Hartley and East Holywell, strata above the Moorland are penetrated by only a few old boreholes, and it is possible that near Seaton Delaval what has been mapped as the Ryhope Little may be the intermediate seam below. There are poor, intermittent exposures of silty shales and fine-grained thinly bedded sandstones in Seaton Burn [NZ 3143 7431] to [NZ 3094 7430] at Holywell.

South of Seghill and East Holywell, strata correlation is more firmly based. The Moorland–Ryhope Little interval is 20 to 45 ft and the intermediate seam dies out southwards being recognized in this area in only one or two boreholes where it is represented by a seatearth. The Moorland roof mudstones contain fish fragments and fragmentary Naiadites sp. A sandstone, up to 25 ft thick, is present and the Ryhope Little Seam is generally between 11 and 30 in thick. North-west of Backworth the seam consists of an upper leaf 6 to 10 in separated by a parting 2 to 5 in from a lower leaf 20 to 24 in thick.

Seaward from Tynemouth the interval is 25 to 55 ft. In the southern part of this area the strata are mostly sandstone, but the immediate roof of the Moorland is mud-stone with Naiadites sp. and fish remains (including in Offshore 6 Borehole, Diplodus sp.[tooth], Rhabdoderma sp. and Rhizodopsis sp.). In the northern part of this area a faunal band occurs about midway between the Moorland and Ryhope Little seams, and in Offshore 6 Borehole yielded a varied fauna of Spirorbis sp., Anthraconaia sp. (cymbula/librata group), Anthracosia atra, A. fulva ?, A. planitumida, A. sp. nov. cf. aquilinoides, Anthracosphaerium exiguum, Naiadites angustus, N. alatus, N. cf. productus, Carbonita cf. humilis, 'Estheria' sp. and scales of palaeoniscid and platysomid fish. The Ryhope Little Seam is between 15 and 28 in thick.

Ryhope Little to Ryhope Five-Quarter

In the roof of the Ryhope Little Seam is the thin, impersistent Ryhope Little Marine Band (Figure 73), recorded in this district only from Offshore 6 Borehole, where the fauna is limited to rare Lingula fragments which appear to have been winnowed and redeposited.

Erosion has reduced the extent of ground occupied by strata above the Ryhope Little Seam to several distinct areas (Figure 72), which will be dealt with separately.

In the North Seaton area the Ryhope Little to Ryhope Five-Quarter interval is 14 to 26 ft, and over most of the area it includes a sandstone up to 11 ft thick. Though the marine band has not been found in the roof of the Ryhope Little, mudstones a few feet above contain a restricted fauna in which ostracods are locally abundant; for example Naiadites cf. obliquus, Carbonita humilis, C. sp. and palaeoniscid scales were found in North Seaton 166 Borehole. The Ryhope Five-Quarter is in two distinct seams, separated by 10 to 24 ft of strata including mudstone with a few fragmentary mussels at the base and a thin sandstone above. The Bottom Ryhope Five-Quarter is 3 to 14 in thick, except in North Seaton Links Borehole where it is represented by seatearth only. The Top Ryhope Five-Quarter is very poorly developed, nowhere more than 12 in thick, and in many boreholes represented merely by seatearth.

Between Bebside and New Delaval the strata are similar to those at North Seaton, though the Ryhope Five-Quarter seams are slightly thicker.

In the south-west of the district, the strata between the Ryhope Little and Five-Quarter seams, while varying between 23 and 61 ft in thickness, are generally around 30 ft with a strip between Seghill and Rising Sun at over 40 ft. A 7- to 20-ft sandstone occurs throughout the area. At Havelock Quarry [NZ 2915 7290] the following section was seen:

The Ryhope Five-Quarter Seam in the south-western part of the district is between 9 and 24 in thick and, though generally banded, it is not separable into distinct Top and Bottom seams.

Strata in this interval have been proved in four boreholes in the south-east of the district where the thickness varies from 30 to 63 ft. In Offshore 6 Borehole, a few Lingula fragments were found in dark mudstone with pyrite in the immediate roof of the Ryhope Little. Up to 7 ft above the marine band, grey mudstone with plant debris and some thin ironstone bands yielded the following: Anthracosia atra, A. cf. acutella, A. planitumida, Anthracosphaerium cf. propinquum, Naiadites sp., Carbonita?, and (at the base) 'Estheria' sp. These basal fossiliferous mudstones are succeeded by fine- to coarse-grained, cross-bedded sandstone up to 55 ft thick, which is overlain by the Bottom Ryhope Five-Quarter, 7 to 19 in thick, and its seatearth. The Top Ryhope Five-Quarter, 13 to 28 in thick, is 20 to 30 ft higher, separated from the lower coal by a variable sequence of mudstone with seatearths, thin coals and sandstone and with rare mussels at the base.

Ryhope Five-Quarter Seam to Kirkby's Marine Band

At North Seaton, strata from the Top Ryhope Five-Quarter Seam to Kirkby's Marine Band (Figure 73) are about 70 ft thick and include two coal–seatearth horizons. The lower of these was named the Rowlington on six-inch geological map NZ28SE, from its outcrop in Rowlington Dean [NZ 2818 8593], where it is 6 in thick and is overlain by shale with ironstone nodules and underlain by seatearth and sandstone with shale partings. Overlying the Top Ryhope Five-Quarter are fossiliferous mudstones, from which Anthracosia atra, A. cf. elliptica, A. cf. fulva, Naiadites alatus, N. angustus, N. cf. obliquus, Carbonita sp. and fish remains were obtained in North Seaton 166 Borehole. The strata become sandier upwards, and the Rowlington Seam, some 12 to 20 ft above the Ryhope Five-Quarter, is underlain by sandstone. The Rowlington Seam is up to 13 in thick, and is separated by 14 to 28 ft of generally sandy strata from the overlying coal, which is up to 9 in thick. Higher strata, up to the coal beneath Kirkby's Marine Band are 25 to 30 ft thick, nearly all sandstone. At Hawks Cliff, on the coast [NZ 307 863] to [NZ 305 858] opposite Horsebridge Head, the top of this sequence is exposed, dipping north-westwards at about 1°:

South of Cowpen, up to 20 ft of strata are present above the Ryhope Five-Quarter and comprise mudstone with mussels at the base followed by sandstone. Another shallow outlier of these strata lies south of the Hartley Station Fault at New Hartley.

In the south-west of the district strata between the Ryhope Five-Quarter Seam and Kirkby's Marine Band are known only from boreholes, in some of which one, and in others two, intermediate seams are recorded. The thickness of the entire interval is 45 to 70 ft, increasing to between 90 and 115 ft in a north-south strip through Backworth and Rising Sun. At the base are mudstones with Anthracosia sp., followed upwards by silty mudstones and a sandstone which is up to 60 ft thick near Rising Sun. The intermediate seam or seams, which correlate in part with the Rowlington, are followed by mudstones, silty mudstones and sandstone. In West Moor Borehole [NZ 2690 7023], 700 yd W of the district, Naiadites obliquus, Carbonita humilis and an acanthodian spine were collected from just above the intermediate coal. The coal at the top of the sequence just below Kirkby's Marine Band is up to 12 in thick or represented merely by its seatearth.

In the south-east of the district, the Ryhope Five-Quarter Seam and Kirkby's Marine Band are about 50 ft apart with an intermediate seam, 1 to 19 in thick, rather high in the interval. Above the Ryhope Five-Quarter is a thin mudstone with traces of mussels, followed by 10 to 30 ft of sandstone. The roof of the intermediate seam is similarly mudstone with ironstone bands and poorly preserved Curvirimula sp. and 'Estheria' sp.

Kirkby's Marine Band to Ryhope Marine Band

Kirkby's Marine Band was named by Armstrong and Price (1954, p. 978) from its discovery by Kirkby (1860, p. 412) who recognized the alternation of marine and non-marine phases characteristic of the band in this coalfield. In most boreholes up to 1.5 ft of very dark, slightly silty mudstone with Lingula and foraminifera, are overlain first by up to 4 ft of grey mudstone with mussels including Anthracosia, Curvirimula and Naiadites, and then by several feet of strata with 'Estheria', Planolites ophthalmoides, foraminifera and Lingula at different levels. In an ideal sequence these forms represent successively more marine conditions (Calver 1968, pp. 9–13); and though in some localities there appears to have been a simple fluctuation to the marine acme and back, in other localities more complex fluctuations may be detected. This latter feature is exemplified by Offshore 5 Borehole (Figure 74) which shows one semi-marine and two non-marine intercalations within the marine band. In this borehole Lingula mytilloides is the dominant species. In the West Moor Borehole (near Killingworth, 700 yd W of this district) L. cf. elongata characterizes the lower leaf of the marine band and L. mytilloides the upper leaf, together with foraminifera including Glomospira sp. and Tolypammina sp. There is one exposure of Kirkby's Marine Band, in the shore section [NZ 3059 8621] at Hawks Cliff where the fauna does not appear to be very prolific: see section below.

Strata from Kirkby's Marine Band to the Ryhope Marine Band (Figure 75) are predominantly sandstones and are from 170 to 200 ft thick. Roughly midway in this sequence is the Hylton Marine Band, with the Burradon Seam 15 to 30 ft above, and another coal seam some 50 ft below. The sandstone between this coal seam and the Hylton Marine Band, named the North Seaton Sandstone by Fowler (1936, pp. 77–8), forms the upper part of Hawks Cliff at the northern margin of the district.

Strata exposed in the Hawks Cliff section [NZ 3056 8606] to [NZ 3083 8648] are as follows:

This section is the same as that described by Fowler (1936, p. 78) in which his "Blue shale with Carbonicola shells" represents Kirkby's Marine Band and its included mussel band. The Hawks Cliff strata are the highest exposed in the northern part of the district

In the south-western part of the district, the succession is known only from bore-holes which show little variation and are best illustrated by the West Moor Borehole (Figure 75) although this is 700 yd outside the district. Overlying the Kirkby's Marine Band mudstones is a sandstone 20 to 35 ft thick, fine- to medium-grained and thinly-bedded, which is exposed [NZ 2998 7224] in Backworth village. Above this sandstone is an unnamed coal between 3 and 14 in thick, (the same seam as is exposed in Hawks Cliff), succeeded again by 11 to 48 ft of thickly bedded North Seaton Sandstone, which was formerly quarried [NZ 2765 7296] south-east of Burradon House. At the top of the sandstone is a seatearth and coal succeeded by mudstones with marine fossils, the Hylton Marine Band, which at West Moor yielded foraminifera and Lingula mytilloides. This marine band is either absent or very poorly developed in places, for in the Scaffold Hill Borehole the horizon is represented by 5 in of dark grey unfossiliferous shale, and in some (uncored) boreholes neither seatearth nor shale are recorded. In Offshore 5 Borehole in the extreme south-east, however, it is better represented, being 4 ft thick with Lingula mytilloides, foraminifera (including Glomospira sp.), Planolites ophthalmoides and Hollinella sp. The band was named by Armstrong and Price (1954, p. 988) from Hylton [NZ 346 561] near Sunderland.

Overlying the Hylton Marine Band are 5 to 20 ft of mudstones with thin sandstones, capped by the Burradon Seam, a few inches thick, which was named on six-inch geological map NZ 27 SE from its former exposure in the now filled-in quarry [NZ 2743 7307] west of Burradon House and about 150 yd within the Morpeth (14) district.

The 70 to 80 ft of strata from the Burradon Seam up to the Ryhope Marine Band are almost wholly sandstone, of which the lower part is kaolinitic, massive and coarse-grained with some pebbly horizons and the upper part is generally finer grained and thinly bedded or flaggy. Above the sandstone are a few feet of shaly strata with a seatearth-coal horizon at the top. The sandstone is exposed at five places. In old quarries around Burradon House [NZ 2760 7305] over 30 ft of thickly bedded sandstone were formerly visible. Killingworth old village is built on an outcrop ridge of this sandstone which is exposed [NZ 2871 7089] in a quarry at the eastern end of the village. Scaffold Hill [NZ 302 696] is a drift-free eminence in which the sandstone has been quarried in a number of places. It is also visible in the railway cuttings and adjacent quarries at and near Benton Quarry Junction [NZ 2827 6879], where the cutting on the main line exposes 40 ft of medium- to coarse-grained sandstone with southward-directed cross-bedding. Longbenton old village is built on and of the same sandstone which forms a ridge extending at its eastern end [NZ 275 686] into the district.

Ryhope Marine Band to Killingworth Seam

From the Ryhope Marine Band up to the Killingworth Seam (Figure 76), between 270 and 300 ft of strata show a pattern of relatively thick coals and thin sandstones, like the strata below Kirkby's Marine Band.

The Ryhope Marine Band was named by Armstrong and Price (1954, p. 988) from its discovery in specimens from Ryhope by Tonks (1939), although it had been informally named by Burnett (1947) as the 'Ashington Marine Bed' from its presence in the Summer House Lane Borehole [NZ 2973 8766] near Ashington (in the Newbiggin (10) district).

This borehole shows the character of the marine band in the north of the district, north of the Stakeford Fault. Burnett (1947) records the following fossils (names revised) from 17 in of dark grey mudstone: Reticulatia craigmarkensis, R. cf. retiformis, Lingula sp., Productus carbonarius, small pyritized gastropods, Posidonia sulcata, Parallelodon ?, orthocone nautiloid, 'Anthracoceras' cf. hindi, Metacoceras aff. cornutum, goniatite Gen. et sp. nov. (Duncan in Currie and others 1937, p. 440 and pl. 4, figs. 9, 10), Hindeodella sp., Streptognathus sp. and fish debris. This fauna is representative of the productoid facies (see Calver 1968, p. 14) and is in contrast to the occurrences in the south of the district (below) where benthonic forms are less evident, and the pectinoid-goniatite facies is dominant. Immediately overlying this fossiliferous mudstone is a 5-in bed of ankerite-siltstone described by K. C. Dunham as follows: (E22779) "black ankerite-siltstone composed of ankerite (refractive index ω = 1.685 to 1.695) in crystals of 0.01 to 0.06 mm. Closely spaced streaks of carbonaceous material are present, and many remains of productids, gastropods and goniatites are preserved in coarse carbonate, in part ankerite, in part calcite. Globular masses of brown isotropic collophane occur, in places making bands in the rock. Very few quartz grains are present. The composition of the rock corresponds closely with the unique 'tank' of the Mansfield Marine Band in the East Midlands" (Dunham in Edwards and Stubblefield 1948, p. 251). No fauna was recorded by Burnett from the mudstones above the 'tank' though a foraminiferal phase may well have been present.

In the south, the Ryhope Marine Band has been proved in the extreme south-east (Offshore 9 Borehole) and in Benton railway cutting [NZ 2826 6888]. In Offshore 9 Borehole the section and fauna are:

The fossils are neither abundant nor well preserved, and the same may be said of those from Benton railway cutting where a similar facies occurs, though the upper foraminiferal phase was not detected. The Benton section, exposed on the east side of the cutting opposite the signal box is:

Mining levels indicate that strata to about 330 ft above the Ryhope Marine Band are present in the extreme north-west of the district, where they crop out beneath about 60 ft of drift, on the north side of the Stakeford Fault.

Strata above the Ryhope Marine Band in the south part of the district are best described from the West Moor Borehole (Figure 76) where the strata are similar to those proved in other boreholes in Northumberland and Durham. The relatively thick Hebburn Fell and Usworth coals, named from localities in the Sunderland (21) district to the south, maintain approximately constant intervals above the Ryhope Marine Band and may be correlated confidently. The West Moor and Killingworth seams were named on six-inch geological sheet NZ 27 SE.

Within this district, the only fossil collected from above the Ryhope Marine Band was a specimen of Naiadites cf. obliquus from the roof of the West Moor Seam, though other mussel bands have been noted during core examination.

Above the Ryhope Marine Band are about 70 ft of grey mudstone with scattered ironstone nodules and a few mussels at the top. Some 15 ft of sandy strata follow, capped by the Usworth Seam which is about 2.5 ft thick. The Hebburn Fell Seam is about 70 ft above the Usworth and the strata between comprise a thinly bedded sequence of mudstones, sandy mudstones and sandstones with two coal–seatearth horizons. Plant fragments and ironstone nodules are common, with Naiadites and fish debris above the coals. A sandstone beneath the Hebbum Fell Seam is the thickest stratum, amounting to 8 ft in West Moor Borehole. In Offshore 9 Borehole the measures below the Hebburn Fell are largely sandstone, which cuts out the Usworth Seam. In the West Moor and nearby boreholes, the Hebbum Fell is in two leaves, each about 2 ft thick and separated by 10 to 15 ft of mudstone with plants. The succeeding 40 to 50 ft of strata up to the West Moor Seam are similar in character to those between the Hebburn Fell and Usworth, and again contain two coal–seatearth horizons. The West Moor Seam is 2 to 2.5 ft thick, in two leaves, and is overlain by some 20 ft of mudstone with a mussel band at the base, and the seatearth of the next coal at the top. This seam is 3 ft thick, with an 8-in band, in Killingworth A Pit [NZ 2727 7054] where it is overlain by 3 ft of mudstone and this in turn by a 15-ft sandstone and 28 ft of mudstones with the 15-in Killingworth Seam at rockhead.

Strata above the Killingworth Seam

In the Forest Hall area [NZ 280 700] on the north side of the Ninety Fathom Fault there is room for 900 ft of strata above the Killingworth Seam to crop out. Apart from two old and doubtfully sited boreholes and exposures at Clousden Hill, these strata are quite unknown. They have been inserted on the map on structural grounds and the base of the Upper Coal Measures is inserted by analogy with the Sunderland (21) district, where the Down Hill Marine Band ('Anthracoceras' cambriense Marine Band), which marks this horizon, is 500 ft above the Hebburn Fell Seam.

A sandstone about 70 ft thick crops out at Clousden Hill [NZ 283 702] (known formerly as Closing Hill) where it was once quarried. In the south-west corner [NZ 2824 7017] of the northern quarry, is an exposure of 15 ft of fine-grained flaggy micaceous sandstone which is locally reddened (especially on the micaceous bedding planes) and contains reddened mudstone pebbles. At the bottom of the quarry, the 20-in Clousden Hill Seam, with a shale roof, was formerly visible (Hutton 1831, p. 72). The two boreholes referred to are Longbenton Moor Borehole, sunk in 1696 at a point "800 yds S. of West Post" and thought to be sited [NZ 2664 6984] about 500 yd N of Benton North Farm in the Morpeth (14) district, and Red House Close Borehole, dated 1749 and probably located [NZ 2769 6967] about 100 yd SW of Forest Hall Station. Their records show normal Coal Measures strata.

Chapter 4 Permian

Introduction

The Permian strata of this district (Figure 77) are seen at outcrop in only three small outliers. A fourth outlier at Forest Hall is inferred on structural grounds coupled with the presence of reddened Coal Measures in Clousden Hill quarries [NZ 2824 7017], though no Permian strata are or have been exposed or proved. The more extensive tract of Permian rocks cropping out beneath the sea has been proved in only a few boreholes.

Data on the Permian rocks are so fragmentary that the account which follows in this chapter is necessarily based on studies by Smith (1970a, b, 1971) on the outcrops to the south in County Durham. Previous workers on this system include Burton (1911), Haselhurst (1911), Howse (1848, 1857, 1890a, b), King (1850), Lebour (1902), Sedgwick (1829) and Woolacott (1912).

Sequence

The Permian sequence (Figure 78) in this district is as follows:

Lower Permian

Yellow Sands, or Basal Permian Sands

The Yellow Sands, or Basal Permian Sands, are formed of very poorly cemented, unfossiliferous, aeolian desert sand, disposed in the form of WSW–ENE seif dunes separated by areas with little or no sand, and hence showing considerable thickness variation. The upper part of the Yellow Sands was redistributed during the transgression of the Upper Permian Zechstein Sea, in which the Marl Slate and subsequent deposits were formed. At depth, the Yellow Sands are grey and pyritic, their yellow colour at outcrop being due to a limonite coating on the grains.

At Tynemouth Castle, the Yellow Sands are exposed in the north and east cliffs, (Plate 3B) where they are between 12 and 25 ft thick, and show southwards-directed cross-bedding.

In the cliffs forming the head of Cullercoats Bay, some 100 ft of Yellow Sands show large-scale dune-bedding directed between south and south-west. Caves up to 40 yd long have been excavated in the cliff by the sea along WNW joints. The Yellow Sands are also well exposed at Smuggler's Cave [NZ 3662 7111] and on the foreshore nearby. Within 20 yd of the Ninety Fathom Fault, which crosses the shore a few yards south of the cave, the Yellow Sands dip southwards at an angle increasing towards the fault to about 40°. Near the fault, anastomosing veinlets of fine-grained, interlocking, granular quartz, which has a cataclastic appearance in thin section ((Plate 7), fig. 1), traverse the rock in various directions, but predominantly on an azimuth of 110° (Plate 4B). This group of veins hades NNE at angles up to 40°. The other preferred vein direction is N–S and nearly vertical. Specimens of Yellow Sands from Smuggler's Cave ((E34398), (E34399), (E37745) and (E37827)) are described by R. K. Harrison as moderately compacted, pale ochre-yellow sandstone, consisting of well-rounded medium-grained sand, commonly of high sphericity, scattered in a matrix of finer sand to coarse silt. Clear igneous quartz predominates, with particles of subordinate cherty and other polygranular quartz, quartzite, quartzitic sandstone and silty mudstone. Feldspars are conspicuous and include orthoclase and microcline–microperthite. The fine matrix consists of microgranular kaolinite, micas and silty quartz. Calcite forms patchy cement, strongly replacive of the quartz.

There is a small outlier of Yellow Sands, with no higher strata preserved, at Seaton Sluice, on the downthrow side of the Collywell Fault. Some 10 ft are exposed [NZ 3391 7644] at the top of the cliff. Yellow Sands have also been proved in some boreholes offshore as indicated in (Figure 77).

Upper Permian

Marl Slate

The Marl Slate is a dark grey laminated bituminous dolomitic shale or shaly dolomite, between 1 and 5.5- ft thick, although 9 ft were recorded in Mill 11 Borehole. A rich fish fauna has been obtained from the Marl Slate, particularly at Cullercoats, where there are good exposures inside the South Pier [NZ 3653 7117] and at low-water mark on Beacon Rock [NZ 3661 7120] 80 yd E of the north end of the South Pier. Howse (1890b) lists the following fish from Cullercoats: Acentrophorus glaphyrus (Agassiz), Janassa bituminosa (Schlotheim), Palaeoniscus elegans (Sedgwick), P. freieslebeni (Blainville), P. macrophthalmus Agassiz, Platysomus striatus Agassiz, Pygopterus mandibularis Agassiz and Wodnika striatula Miinster. Stoneley (1958, p. 298) gives a floral list from the same locality: Paracalamites kutorgai (Geinitz), Annularia ? sp., Ullmannia frumentaria (Schlotheim) and unidentifiable wood. Bakevellia (Bakevellia) binneyi (Brown) is recorded by Kirkby (1867, p. 187) under the name Gervillia antiqua.

In Marden or Whitley quarries the Marl Slate was formerly seen to be 3.5 ft thick (Lebour 1902, p. 383) and has yielded Ullmannia frumentaria (Stoneley 1958, p. 298) and four species of fish (Howse 1848): Palaeoniscus elegans, P. freieslebeni, Platysomus striatus and Pygopterus mandibularis. At Tynemouth Castle, the Marl Slate, though well exposed in the north and east cliffs, is difficult to reach. On the north-west [NZ 3728 6946] it is about 2 ft thick, but eastwards it is disturbed, probably due to slumping (Smith 1970a, p. 19) and reaches a thickness of 5.5 ft at the north-east corner of the cliff [NZ 3746 6947]. It is possible that the unusual thickness in Mill 11 Borehole, in the north of the district, may be due to the same cause.

Lower Magnesian Limestone

In this district, the Lower Magnesian Limestone consists of 20 to 30 ft of evenly and thinly bedded dolomite, partly calcitic and sparsely fossiliferous. In detail, bedding planes are irregular and often stylolitic. In Marden Quarries the limestone weathers greyish white with faint diffuse brownish pink bands parallel with the bedding and at intervals of 0.5 to 2 in. The fauna from Marden (Howse 1848, 1890b; King 1850), indicated by M in the list at the end of the chapter, represents years of collecting when the quarries were working. On the foreshore at Cullercoats, the limestone weathers to a pale yellow colour and has not yielded any fossils.

Towards the end of Lower Magnesian Limestone time submarine slumping and sliding took place (Smith 1970a). Disturbed strata are exposed on the foreshore [NZ 3671 7116] at Cullercoats (Plate 4A) and were recorded by Haselhurst (1911, p. 17). At Tynemouth Castle, the Lower Magnesian Limestone is 8 to 10 ft thick, and includes a median sandstone containing dolomite and calcite pebbles and many large aeolian quartz grains ((Plate 7), fig. 2). At the north-west end of the cliff [NZ 3728 6946] this bed is 1.5 ft thick and is dolomitic at the top. At the north-east corner of the cliff [NZ 3746 6947] it is 4 ft thick and contains many small flaky dolomite pebbles in a 2-in bed near the top. Southwards, the bed thickens and the proportion and size of the dolomite pebbles increase rapidly. It is interpreted by Smith (1970a, p. 19) as a proximal turbidite, derived from some distance to the west, and incorporating Yellow Sands material and fragments of Shelly Lower Magnesian Limestone. These latter yielded to King (1850, p. xi) about a score of species (T in list at end of chapter) compared with a mere half dozen from the rest of the Lower Magnesian Limestone (C in list).

In two underground boreholes about 4 miles ENE of Blyth, namely Mill 10 [NZ 3879 8431] and Mill 11 [NZ 3824 8421], anomalous and thin sequences of Lower Magnesian Limestone have been proved, which may be explained as due to slumping (Smith 1970a, p. 20). In the western borehole (Mill 11) the Lower Magnesian Limestone consists of only 14 in of pale creamy grey, fine-grained dolomite. In the eastern borehole 4.5 ft of dolomite conglomerate are overlain by 2 ft of dark grey dolomite with a considerable proportion of aeolian quartz grains. The conglomerate consists of pebbles up to 2 in across, some rounded, some angular, of dark and light grey dolomite and dolomitic limestone in a matrix of dark grey, fine-grained dolomite with pyrite and aeolian sand grains.

Off Tynemouth, the Lower Magnesian Limestone has been penetrated in seven boreholes. In Offshore 16 Borehole it is probably 22.5 ft thick and in Offshore 14 Borehole is 24 ft; the other boreholes were not cored through this limestone. In Offshore 14 Borehole the upper part is massive, buff, dolomite while the lower part is thin bedded, grey in lighter and darker bands, more calcareous and shelly near the top. Fossils from this borehole are listed at the end of the chapter (0 in list).

Middle Magnesian Limestone

The Middle Magnesian Limestone of Durham and Northumberland comprises a carbonate facies, the Middle Magnesian Limestone itself, and an overlying sulphate facies, the Hartlepool Anhydrite. In County Durham, the best known feature of the limestone is the NNW-trending barrier reef which, assuming it extended north into this district, lay to the west of the present outcrops and has been entirely removed by erosion. The Middle Magnesian Limestone in this district is therefore represented by only a few feet of basinal facies dolomite (Smith 1970b, p. 76), marked at the top by a few inches of nodular (probably algal) dolomite, which is exposed [NZ 3561 7145] at the eastern end of Marden Quarry. The uppermost member of the Middle Magnesian Limestone formation is the Hartlepool Anhydrite, which has been almost entirely removed by solution in near-crop areas, but is probably present in force farther east. At the top of Mill 10 Borehole the basal 5.5 ft consisted of gypsum (pseudomorphing anhydrite) with thin dolomite partings. At Tynemouth Castle, the Hartlepool Anhydrite is represented by a solution residue of 2 to 9 in of grey and fawn, argillaceous and sandy dolomite. The bed is similar in appearance in Marden Quarries [NZ 3551 7134] where it is somewhat ferruginous.

Only the lowest 20 ft of the basal member of the Upper Magnesian Limestone, the Concretionary Limestone, are preserved on shore, where they are exposed at Cullercoats, Marden and Tynemouth. Whether any higher members are preserved offshore, is not known. In all outcrops and borehole provings, the Concretionary Limestone is collapse-brecciated, following solution of the underlying Hartlepool Anhydrite, and consists of a breccia of both angular and rounded fragments of grey and brown crystalline limestone, in a matrix of brown dolomitic limestone. At Marden, it is exposed on the south side of the quarries [NZ 3551 7134] where it is 20 ft thick, and in a small synclinal outlier at the eastern end of the quarries [NZ 3563 7147]. Some 10 ft of the limestone are visible at low tide at the eastern end of Saddle Rocks, Cullercoats [NZ 3675 7118] and [NZ 3676 7109], and Tynemouth Castle headland is capped by about 15 ft. No fossils have been recorded from the limestone in this district.

Fossils from the Lower Magnesian Limestone

In this list localities are indicated by letter: M Marden Quarries, listed by Howse (1848, 1890b) and King (1850). T Tynemouth Castle, collected by King (1850, p. xi) from blocks in the turbidite. C Tynemouth Castle, recent collecting. O Offshore 14 Borehole between 209 and 228 ft depth.

The names of forms recorded by Howse and King have been revised by Mr. J. Pattison in the light of modern taxonomy.

Chapter 5 Igneous rocks

Introduction

The igneous rocks of this district are intrusive tholeiitic dolerites, comprising the late-Carboniferous oversaturated Whin Sill and a suite of saturated (to slightly undersaturated) dykes of Tertiary age. The petrographical distinction between the quartz-dolerite of the sill (and associated dykes elsewhere), and the Tertiary dolerites ('tholefites) has long been known (Teall 1884a, b; Holmes and Harwood 1928, 1929). All, however, can be regarded as variants of a calcalkaline tholeiitic suite (Harrison 1968), though the periods of intrusion differed by some 240 million years (my). Differences in degree and type of sialic material assimilated may offer one explanation for the petrographical differences between the Whin Sill and the Tertiary dykes in the district, though differences in type and rate of emplacement of parental magma may have been more important factors. The homogeneity of the Whin Sill over large areas (compared with local petrographical variations in the Tertiary dykes of the district), indicates its origin from a vast parental oversaturated magma with only rare differentiation.

Whin Sill

The Whin Sill is a calc-alkaline quartz-dolerite sill-complex (Dunham 1948; Holmes and Harwood 1928; Teall 1884b), dated at 295 ± 6 my (Fitch and Miller 1967), which underlies the whole district and crops out between 14 and 22 miles to the west, where it is intruded in the upper part of the Carboniferous Limestone strata. In the coastal Harton Borehole [NZ 396 656], a mile south of the district, the Whin Sill is in three leaves (Ridd and others 1970), the highest being 200 ft thick at the top of the Carboniferous Limestone and the lowest 110 ft thick 1300 ft below. A 15-ft leaf occurs about midway between the others. Somewhat similar geometry was proved in a deep borehole [NZ 349 748] near St Mary's Island.

Tholeiitic dykes

Nine WNW-trending tholeiitic dolerite dykes cross the district (Figure 79). They are part of the dyke-swarm from the Tertiary volcano of Mull in western Scotland, some 200 miles away. Tea11 (1884a, 1888, 1889) was the first to describe these dykes, followed by Heslop and Smythe (1910), Smythe (1914) and Holmes and Harwood (1929).

Petrographically the tholeiitic dolerites are olivine-free or olivine-poor plagioclase-augite rocks, with the feldspar and pyroxene generally in ophitic relationship, and having an intersertal texture with a glassy mesostasis, which is usually devitrified or micro-crystalline.

Various types of tholeiitic dykes have been recognized by Bailey and others (1924) in Mull, and by Holmes and Harwood (1929) in Northumberland. The Tynemouth, Whitley, West Sleekburn and North Seaton dykes are of Brunton type ((Plate 6), figs. 1, 3 and 4) (Bailey and others 1924, pp. 285 and 372) in which the augite crystallizes in granular clots with plagioclase laths embedded and in places radially disposed. These crystalline groups are partly in contact and partly separated by mesostasis. The Hartley North and South and Seaton Sluice dykes ((Plate 6), fig. 5) are of Talaidh type (Bailey and others 1924, pp. 284 and 372) characterized by elongation of the augite crystals. A tholeiite intermediate between the Brunton and Talaidh types appears in the South Blyth Dyke, while the North Blyth Dyke is fairly even-grained with a tendency towards the Brunton type of texture.

Apart from the West Sleekburn Dyke which is 20 to 70 ft wide, continuous and nearly vertical, the dykes in this district are generally less than 15 ft wide, are laterally discontinuous at any given stratigraphical level, and are vertically discontinuous at any given point along their length. They thus appear (Figure 80) as a series of sections in echelon, connected by narrow cross feeders. The latter are rarely seen, but an example occurs south of Bebside [NZ 278 810] where a very narrow dyke extends north-north-eastwards, at the Bensham Seam level, halfway from one echelon to the next. Another example on a smaller scale is visible in the cliff [NZ 3396 7634] at Seaton Sluice in a 6-in subsidiary dyke 30 yd S of the main Hartley North Dyke. Traced up the cliff (photo. L 632) the dyke appears in several vertical segments, each offset a few inches from the one beneath, with each segment joined to the next by a thin irregular stringer of dolerite. The Hartley North Dyke itself terminates upward in the cliff [NZ 3395 7637] (Plate 5A). On the North Beach [NZ 3185 8221] an exposed section of the North Blyth Dyke, 4 ft wide and 60 ft long, disappears longitudinally beneath sandstone country rock. South of Blyth Harbour entrance [NZ 3246 8012] to [NZ 3275 8001] a subsidiary dyke of the South Blyth echelon traverses the Plessey workings. It is only a few inches wide and is 350 yd long from its western end, where it appeared in the roof of the seam, to its abrupt termination on the east.

Tynemouth Dyke

The Tynemouth Dyke has been described by Teall (1884a, p. 233, pl. 13; 1888, p. 203, pl. 12; 1889), Heslop and Smythe (1910, p. 12) and Holmes and Harwood (1929, p. 20). It is exposed on the foreshore [NZ 3750 6929] a few yards north of the west end of Tynemouth North Pier, where it is 12.5 ft wide and intruded into sandstone below the High Main. It is also seen over a width of 9 ft by the side of the road to the pier [NZ 3738 6931] where anorthite phenocrysts are prominent (Plate 5B). In the cutting [NZ 366 694] at the northern end of Tynemouth Station, Teall (1884a, p. 233) noted that the dyke is 11 or 12 ft wide and that the outcrop shows a lateral offset of 17 yd. The entire dyke-echelon has been proved intermittently underground from Offshore 5 Borehole [NZ 4152 6946] westwards almost to Killingworth [NZ 2914 7051].

Petrographically, the Tynemouth Dyke shows the Brunton texture ((Plate 4), fig. 1). Specimens (E34380), (E34381), (E37742) of least altered rock from the centre of the dyke on the foreshore exposure [NZ 3750 6929] and from the roadside exposure [NZ 3738 6931] ((E34375), (E34376)), exhibit clear, unaltered calcic plagioclase phenocrysts and glomeroporphyritic clusters (averaging 5 mm) in a dark grey groundmass. The composition of their cores, based on refractive index measurements (β = 1.580 ± .002), is about. Ab10 An„, and of the outermost zone is near Ab₄₀ An₆₀. A specimen ((E37756), (Plate 6), fig. 2) from Westoe Colliery [NZ 399 693] contains glomeroporphyritic aggregates of small (0.6 x 0.3 mm) stumpy anorthite crystals charged with inclusions of mesostasis and spinel (X-ray diffraction powder photograph X6357 by Mr B. R. Young). The hitherto unreported occurrence of spinel (as inclusions) in the Tynemouth Dyke, might well indicate (following Thomas 1922) that it formed together with the anorthite host, through the metamorphism of aluminous xenoliths by the tholeiite magma, presumably deep in the magma chamber. The groundmass varies a little in granularity, with the mainly unoriented labradorite laths averaging about 0.4 x 0.04 mm (0.3 x 0.03 mm in specimens (E34375), (E34376)). These laths are in ophitic arrangement with mainly granular (0.1 mm) anhedral augite. In places the labradorite laths radiate from an augite centre, and commonly show marked attenuation where they traverse the clinopyroxene. This appears to be due not to replacement, but to suppression of complete crystal growth with the contemporaneous crystallization of the pyroxene. Labradorite of later growth forms coarser anhedral plates with no twinning and undulatory extinction. Traces of probable olivine (replaced by chlorite) and of orthopyroxene mantled by augite occur very rarely in the groundmass. The mesostasis forms patches of dark greyish brown devitrified glass in which most of the opaque Fe-Ti minerals are set, together with fine meshes of feldspar needles (commonly curved or stellate), and granules of pyroxene.

Amygdales are common, mainly spheroidal, average about 1.0 mm diameter, and contain mesostasis, chlorite or carbonates (mainly dolomite). Feldspar laths have been re-orientated tangentially around the amygdales, owing to fluxioning by gas pressure. Amygdales vary inversely in proportion with respect to phenocrysts. Teall (1889) noted that vesicles only partially filled with glass, were later filled with chalcedony and calcite.

Modal analyses of the least-altered specimens gave (in volume per cent): phenocrysts 0.1–14.5; amygdales 2.4–8.3; mesostasis 15.4–29.8; groundmass: labradorite 33.6–42.2; clinopyroxene 24.3–33.3; chlorite 1.6–2.0. These show the very variable proportions of phenocrysts and amygdales.

Alteration of the dyke at Tynemouth [NZ 3750 6929] has occurred near its contacts with the Coal Measures sandstone country rock. Augite has been altered first to carbonate, owing to the reaction of volatiles (particularly carbon dioxide) with Mg and Ca to produce dolomite and calcite, releasing Fe to form goethite, and SiO₂ to chalcedony. Though slight chilling has occurred (ground-mass feldspars average 0.3 x 0.02 mm), the characteristic texture of the dyke is preserved indicating an autopneumatolytic alteration following crystallization. The lower pressures obtaining at the contacts doubtless facilitated the carbonatization process. Incipient alteration of the dyke is shown in a specimen (E37757) from Algernon Colliery [NZ 317 704] with much of the mesostasis and some clinopyroxene altered to carbonate and clay minerals. An advanced stage of alteration to 'white trap' is shown in an argillized specimen (E37758) from the same locality. In this, the phenocrysts have been altered to bluish white, opalescent disordered kaolinite and the groundmass to creamy disordered kaolinite with a little calcite and smectite (X-ray diffraction photographs X 6354–5 by Mr Young). Electron micrographs taken by Mrs A. E. Tresham of the pinacoid, prism and pyramid faces of a kaolinized pseudomorph after anorthite, show an overall alignment of the kaolinite platelets parallel to the pseudomorph faces, thus accounting for their preservation. The kaolinite forms a porous latticework of euhedral platelets bearing no crystallographic relation to that of the parent pseudomorph, within the overall parallel arrangement.

Whitley Dyke

The Whitley Dyke, which was discovered and tamed by Smythe (1914) from its exposure on the foreshore [NZ 3510 7384] at Whitley Bay, has been traced only intermittently across the district. Nowhere does it appear to be more than 2 ft wide. When the shore is clear of sand, which is unusual, it may be traced for about 130 yd cutting sandstone below the Plessey Seam. Near high-water mark the dyke is 18 in wide; traced eastwards it has a dextral dislocation of 4 ft and eastwards again gradually narrows out.

Petrographically, the rock closely resembles the Tynemouth Dyke in being a porphyritic and ophitic tholeiitic dolerite, and does not warrant detailed description ((Plate 7), fig. 1). Complete chemical analyses are given (p. 123) of fairly fresh and very altered dolerites (analyses 1 and 2 respectively) from a coal quarry [NZ 3405 7411] at Whitley Golf Links. A modal analysis of one section (E25392) gave (in volume per cent): amygdales 6.7 (carbonate 0.8, chlorite 5.9); mesostasis 24.6 (chloritized glass 14.9, iron ore 8.7, pyroxene 0.5, feldspar 0.5); groundmass 68.7 (augite 34.3, labradorite 32.9, chlorite 1.5).

At Whitley Bay, the dyke is mainly or completely carbonatized ((E34397), (E37740), (E37828), (E37829)), consisting of variably replaced labradorite laths (0.4 x 0.04 to 0.2 x 0.02 mm) set in a carbonated base, with spheroidal vesicles (0.5 mm) filled with carbonate and goethite. In the most replaced specimens ((E37828), (E37829)) nearly all constituents have been carbonated or argillized resulting in 'white trap'

Hartley South, Hartley North and Seaton Sluice dykes

The Hartley South, Hartley North and Seaton Sluice dykes may be considered as forming a multiple dyke-echelon, distinguished from the rest of the dykes in the district by being of Talaidh type. The name 'Hartley' was first used by Teall (1884a), though the Hartley North Dyke at its coastal exposure has also been called the Collywell Dyke, while Smythe (1914) applied the name 'Hartley' to a very minor branch of this intrusion. The dolerite from this multiple echelon is marginally altered to white trap, and it is not easy to find unaltered igneous rock even in the middle of these narrow dykes.

Hartley South Dyke

There is no outcrop of the Hartley South Dyke on the coast, but it is exposed intermittently over a length of 200 yd in the dene south-east of Seaton Delaval Mausoleum. The best exposure [NZ 3319 7616] shows the dyke in two branches, 20 ft apart, intruded in mudstones above the Five-Quarter Seam. Sharp but somewhat irregular dolerite–mudstone contacts are visible on the 10-ft wide southern branch, but the margins of the northern blanch are not visible. Between the two branches, the exposure shows a narrow stringer of dolerite ending upwards in the mudstone. Although rather altered, the dyke has been quarried on a small scale for road metal. Teall (1888, pl. 14) figured a specimen of the Hartley South Dyke from Shankhouse Colliery near [NZ 279 774].

Hartley North Dyke

In Collywell Bay, the Hartley North Dyke is exposed across the foreshore and in the cliff [NZ 3394 7637] where it terminates upward (Plate 5A). At the cliff base, the dyke is 7 ft wide; traced seawards its width varies irregularly between 5 and 9 ft, the dyke dividing into two branches over a few yards' length. Still farther east [NZ 3421 7631], north of Crag Point, the dyke is 4 to 5 ft wide, with a 1-ft leaf 3 ft to the south. A 6-in subsidiary dyke is seen in the cliff 30 yd S of the main dyke (p. 116 and Smythe 1914). Near its upward termination, the main dyke cuts through the Yard Seam as well as a 16-in seam about 6 ft below. Both these coals are coked to a distance of about 4 ft and visibly altered to about 3 yd from the dyke. Jones and Cooper (1970, pls. 4–7), have published photographs showing the progressive metamorphism of coal from this locality.

A typical specimen of dolerite from the base of the cliff (E37735) consists of a lattice of slender, marginally corroded labradorite laths (0.3 x 0.03 mm), coarser subpoikilitic plates of undulatory extinguishing labradorite, interstitial allotriomorphic augite, patchy turbid mesostasis and common spheroidal vesicles (0.3 mm) filled with carbonate (rare pyrite), rimmed with chlorite. A modal analysis gave (in volume per cent): plagioclase 35; augite 36; mesostasis 19; chlorite 7; iron oxide 1; carbonate 2; pyrite trace. Pale grey amygdaloidal dolerite ((E34384); (Plate 6), fig. 5) [NZ 3421 7631] from near Crag Point consists of a mesh of labradorite laths (0.5 x 0.06 mm), intersertal allotriomorphic augite forming radiating laths in places, patches of brown mesostasis and microphenocrysts of shadow-zoned plagioclase. The mesostasis is composed of chlorite, slender iron-oxide laths and feldspar microlites. Vesicles are filled with earlier dolomite and later calcite, with chalcedony or dark green to colourless alpha-cristobalite (X-ray powder photograph NEX 1169, by Mr. K. S. Siddiqui); they are mostly ringed with dark brown chlorite.

A specimen (E34394) at the contact with the coked Yard Seam shows a fluxioning of feldspar microlites in the dolerite in a turbid dusty chloritic and leucoxenic groundmass. The coke is charged with irregular inclusions of carbonate and radially-fibrous chlorite. The fluxioning and the inclusions are all attributed to the action of volatiles from the dyke and those driven off from the coal.

Seaton Sluice Dyke

The Seaton Sluice Dyke, about 6 ft wide, traverses the foreshore hading south at 20°. At low-water mark it is in contact with the Yard Seam, converted to coke. Near high-water mark, a few yards from the cliff, the dyke ends, but recommences about 50 ft to the south, and is exposed in the cliff. Underground workings in line with the exposed dyke have not encountered any dolerite.

Specimens ((E37733), (E37734), (E34390), (E34391), (E34392), (E34395)) of the Seaton Sluice Dyke are fine-grained dolerites showing all stages of alteration to 'white trap'. The least altered dolerite (E37733) from the cliff [NZ 3390 7667], consists of a mesh of labradorite needles (0.4 x 0.06 mm) with a turbid mesostasis and grains of allotriomorphic augite, chlorite, carbonate and opaque dust. Microphenocrysts of shadow-zoned plagioclase attain 1 mm length. Vesicles are common (1 mm) and filled with olive-green, radially fibrous chlorite or carbonate. The metamorphic effect of the intrusion on adjacent sandstone is shown in a specimen ((E34389), (Plate 7), fig. 6) from the foreshore at Seaton Sluice [NZ 3395 7668], in which leucoxene, chlorite, dolomite, calcite and pyrite have been introduced into the matrix of the feldspathic sandstone.

Netherton–South Blyth Dyke

The Netherton–South Blyth Dyke is known only from the colliery workings. It is generally narrow, but attains a width of 30 ft in places. Texturally it approaches the Talaidh type. A specimen (E37762) from the Plessey Seam level at Isabella Colliery [NZ 2987 8061] consists of a mesh of raggedly terminated slender (0.6 x 0.09 mm), corroded labradorite laths, intersertal allotriomorphic augite, coarser undulatory-extinguishing labradorite, patchy mesostasis and interstitial chlorite. There are scattered labradorite microphenocrysts (0.5 mm), and cubes of magnetite and skeletal ilmenite. The mesostasis is a feebly birefringent, cryptocrystalline, devitrified glass charged with laths of iron oxide and feldspar microlites. A modal analysis gave, (in volume per cent): plagioclase 43; augite 24; chlorite 1; carbonate (trace); ores 3; mesostasis (undifferentiated) 29.

Barrington–North Blyth Dyke

The Barrington–North Blyth Dyke is rarely over 10 ft wide. It is exposed only on Blyth North Beach [NZ 3185 8221] where it is 4 ft wide, intruded in the sandstone below the Moorland Seam, and reaching the surface over a strike length of 60 ft. The rock is of Brunton type, though two specimens: (E37925) from Bates Pit [NZ 3092 8243] and (E37834) from the beach exposure, do not show anorthite phenocrysts as in the Tynemouth Dyke. A mesh of labradorite laths (0.6 x 0.09 to 0.4 x 0.05 mm) contains allotriomorphic granular augite, and coarser plates of shadow-zoned poikilitic labradorite. Mesostasis is sparse, containing brown devitrified glass, turbid chlorite, iron oxide and a little quartz. Calcite-filled vesicles show glassy rims and patches of mesostasis. A modal analysis of one specimen (E37925) gave (in volume per cent): plagioclase 50; augite 25; mesostasis 15; chlorite, illite 4; opaques 5; carbonate 1.

West Sleekburn Dyke

The West Sleekburn Dyke, of Brunton type, is much the thickest and most continuous dyke in the district, being generally around 50 ft wide, but is nowhere exposed. It was briefly mentioned by Holmes and Harwood (1929, p. 14) and in more detail by Randall (1953, 1954) in connection with a mineralized cavity within the dyke [NZ 2846 8474] at West Sleekburn Colliery. These authors record the presence of serpentine pseudomorphs after olivine. A typical specimen of dark grey, medium-grained dolerite ((E37926); (Plate 6), fig. 4) contains glomeroporphyritic clusters of squat labradorite laths (averaging 1 mm long) with opaque inclusions, set in a mesh of ragged labradorite laths and very pale brown intersertal augite. There is a conspicuous interstitial mesostasis of dark brown devitrified glass charged with feldspar needles, carbonate and chlorite. In places this mesostasis is roughly spheroidal, suggesting late-stage vesicular development. A further specimen (E37732) from Bates Pit [NZ 3307 8318] is a little finer grained than the above and contains considerably more feldspar. Tabular labradorite forms rare glomeroporphyritic clots 5 mm across. This specimen consists (in volume per cent) of phenocrystic plagioclase 1; groundmass labradorite 56; augite 29; mesostasis 7; chlorite 3; opaque ores 3; carbonate 1.

North Seaton Dyke

The North Seaton Dyke is known only from colliery workings, and is described and named here for the first time, although it was recorded on the six-inch geological map Northumberland 70 NW (1932). Only one specimen (E15483) is now available, from the Northumberland Low Main Seam level in North Seaton Colliery [NZ 2784 8556]. The rock is a dark, slightly brownish grey (Munsell colour 2.5 YR 4¹0), finely crystalline tholeiitic dolerite of Brunton type, charged with small (0.5 mm) vesicles. Phenocrysts are restricted to sparse elongated feldspar needles (up to 2 mm length) ((Plate 6), fig. 3). Plagioclase laths (near Ab₄₀An₆₀ are slender, commonly bifurcate, curved and locally fluxioned, forming ophitic intergrowths with granular, anhedral pale green clinopyroxenes which include augite (2E = 98°) and pigeonite (small 2V). Labradorite laths are embedded in, and radiate from, granular pyroxene in Brunton-type texture.

Coarser, tabular shadow-zoned plagioclase has crystallized later than the labradorite laths and pyroxene. The dark glassy mesostasis is not abundant, but confined (with granules of iron oxide) to inter-feldspar patches. Chlorite is conspicuous mainly as grains, some of which show subhedral outlines possibly after olivine. Vesicles are mainly spheroidal and filled with parankerite, rimmed by chlorite.

A modal analysis gave (in volume per cent): labradorite 28; oligoclase 4; clinopyroxene 34; chlorite 1; mesostasis 30 (glass 7, chlorite 15, opaque Fe/Ti ores 8); vesicles 3 (chlorite 1, parankerite 2). This gives feldspar: feldspar + pyroxene = 48 per cent compared with an average of 47 per cent for the Brunton-type tholeiites (Holmes and Harwood 1929).

Chapter 6 Mineral veins

Almost every borehole core and natural section in the Coal Measures and Permian rocks shows narrow veins of calcite, ankerite or dolomite. These usually carry scattered small crystals of pyrite, galena or sphalerite; and baryte occurs in places.

Winch (1817, p. 5) observed galena veinlets in the Magnesian Limestone at Whitley, as did Haselhurst (1911, fig. 1) at Cullercoats. On the foreshore here [NZ 3668 7107], immediately south of the Ninety Fathom Fault, sandstone above the Hutton Seam is veined by calcite, baryte and pyrite, which partly replace the country rock ((E37754); (Plate 7), fig. 5). On St Mary's Island, the sandstone above the Beaumont Seam, which forms the island and its foreshore, is traversed by veins parallel to the Saint Mary's Fault. East of the lighthouse [NZ 3530 7539] they are of calcite. North-west of the lighthouse buildings [NZ 3519 7541] they are of calcite with pyrite and some sphalerite; traced eastwards they narrow out into iron-stained joints. Calcite veins traverse the foreshore at Seaton Sluice: the fault of that name carries patchy calcite [NZ 3341 7670], and veins striking north-west are seen [NZ 3403 7667] north-east of Charley's Garden, as well as to the west-north-west [NZ 3388 7661] where they carry pyrite also. The Seaton Sluice Sandstone at Crag Point is partly cemented by secondary baryte (Jones 1967, p. 187).

In many places, the tholeiite dykes show brecciation and veining along their central parts. Perhaps the clearest example is the Hartley North Dyke on the foreshore [NZ 3399 7636] in Collywell Bay, where calcite with some pyrite is followed by banded 'iris' agate ((E37970); (Plate 6), fig. 6). Randall (1953) described a cavity in the West Sleekburn Dyke [NZ 2846 8474] with pyrite, marcasite and ankerite. Marcasite has also been found at Rising Sun Colliery [NZ 3139 6764] where a cavity on a north–south fault was lined with 12 to 18 in of the mineral.

Chapter 7 Structure

The Carboniferous rocks of the district were faulted and gently folded in late-Carboniferous Hercynian movements, and tilted gently eastwards with further faulting in Tertiary times. (Figure 81) shows contours on the Harvey Marine Band at 50-ft intervals. The main structure (Figure 82) in the landward part of the district is the shallow Cambois–Seghill Syncline (Hickling 1950, p. 664), which is continued southward en échelon across the Ninety Fathom Fault by the Swallow Pit Syncline and the structural depression along the line of the Willington Fault. In the Sunderland (21) district to the south, this synclinal structure continues in the Jarrow–Hylton Syncline (Hickling 1950). In coastal areas, the curvature of the contours delineates the Whitley Anticline or Dome (Hickling 1950). This again is continued southwards en échelon by the anticline through North and South Shields and so into the Sunderland district, where the northern flank of the Harton Dome is indicated by the swing of the contours near the East Baltic Fault.

Most of the faults in the district (Figure 82) trend roughly east or south-east. The three largest, namely the Stakeford, Ninety Fathom and Saint Hilda faults, all hade at 45° and as they are approached on the downthrow side the dip towards the fault gradually increases to 45°, so that the strata meet the fault plane at right angles. On the upthrow side the strata are little disturbed.

Hercynian folding and faulting occurred together, for throws vary along faults with differential folding either side. Some prominent faults die out in quite a short distance, for example the Crimea Fault [NZ 318 785]. Most die out by splitting into several fractures with throws of a few feet. Faults of less than about 10 ft throw are not shown in (Figure 81) and (Figure 82), but they are plentiful in some areas.

Renewed earth movements in Tertiary times imparted a gentle easterly tilt to the strata, and re-activated some faults. Re-activation can be demonstrated only on the two faults (Collywell and Ninety Fathom) which affect Permian strata, but presumably it took place on others. Whether the dykes were intruded before or after the Tertiary movements is not obvious. The Hartley Dyke-echelon (Figure 79) appears to be associated with a belt of faulting, but in detail it is clear that the dykes are unaffected by the faults. Indeed in the whole district the only clear examples of dykes being influenced by faulting are where the West Sleekburn and North Blyth dykes run for some distance along the Isabella Fault (Figure 80) before resuming their normal trend. On the other hand, the South Blyth Dyke crosses the same fault without displacement.

Chapter 8 Quaternary

Introduction

Almost the whole of the land area of the district is covered by drift deposits, largely the product of a single late-Weichselian glaciation 12 000 to 18 000 years ago. Narrow strips of alluvium flank the streams, while sand dunes fringe the coast between the rocky headlands. The Quaternary deposits are described as in the following table:

• RECENT
• blown sand and beach deposits
• alluvium peat
• PLEISTOCENE
• late Weichselian glacial drift-complex
• pre-glacial gravels

Rock-head surface and buried valleys

Contours on rock-head, or base of drift, are shown in (Figure 83). From this it will be seen, by comparison with present-day surface contours, that the pre-glacial surface has a more pronounced topography, or higher relief index, than the present surface. The former is largely an erosional surface with valleys grading to below 100 ft below sea level; the latter is largely a till-plain constructional surface, further smoothed by solifluction, showing only gentle undulations. Its monotony is relieved by scattered hills of drift-free sandstone and by the incised post-glacial river gorges.

Drift-filled buried valleys were recognized by Woolacott (1905) who described and named the Sleekburn and Tyne valleys. Two more, the Cramlington and Brierdene valleys, are now recognized, while the many post-1905 borings enable a more detailed map of rock-head to be drawn (Figure 83). Anson and Sharp (1960) described rock-head in the coalfield from Blyth northward. They show a buried valley (no. 6 on their fig. 1) running south-south-east through Blyth, but this does not exist, the data they adduce belonging to the seaward end of the Cramlington Valley. The Sleekburn Valley represents the pre-glacial course of the combined Wansbeck and Blyth rivers, which joined near Hepscott [NZ 220 840], west of this district. (Figure 83) has been drawn assuming a continuously-graded long-profile down each buried valley, but some sections may have been over-deepened by glacial scour or sub-glacial meltwater erosion.

Pleistocene deposits

Pre-glacial gravels. In the lower parts of the buried valleys, beneath undoubted glacial drift, are gravels which may be alluvial gravels of pre-glacial rivers, but which are nowhere exposed. A bed of gravel was formerly visible on the coast opposite the half-tide shingle bank of Horsebridge Head and was described under this name by Bullerwell (1910). This gravel overlies Coal Measures sandstone, is overlain by boulder clay, and is in the southern lee of a pre-glacial sandstone cliff. It becomes coarser towards the cliff where it is composed almost wholly of local sandstone. Erratics, all well rounded, in the gravel include schist, Cheviot igneous rocks, Magnesian Limestone, Chalk flints, and rare Carboniferous Limestone. The deposit thins both southwards and westwards, and coastal recession has now entirely or almost entirely removed it. As Buller-well concludes, it is a beach deposit, deriving some of its material from an early glaciation.

Glacial drift-complex

The glacial drift of this district forms a single complex which may be generally divided as follows:

• 3. reddish brown boulder clay and other stony clays
• 2. gravels, sands, silts, laminated clays and boulder clays
• 1. grey and greyish brown boulder clay

In areas where the drift is less than 25 ft thick (see (Figure 84)) strata of item 2 are absent or reduced to a thin intermittent sand. The lower grey boulder clay or till can be correlated with the Lower Boulder Clay of Durham (Smith and Francis 1967), and this in turn correlated with the Drab Till of Holderness, which directly overlies the Dimlington Silts. These, being dated at 18 250–18 500 years old (Penny and others 1969), give an approximate date for the onset of glaciation. Similarly the presence of pollen zone I deposits with an age of about 12 000 years at Neasham [NZ 334 112], 35 miles S of the district (Blackburn 1952), gives an indication of the date of deglaciation.

Ice movements in this district are part of a regional pattern of movement from the north and west (Smith in Taylor and others 1971, pp. 83–9). Erratics in the boulder clays are mostly local Carboniferous rocks but also include igneous rocks from Cheviot and south-west Scotland and, south of Blyth, Lake District stones. Magnesian Limestone and Chalk flint erratics indicate derivation from outcrops in the North Sea. Glacial striations have been noted at Burradon [NZ 277 730] where an earlier E–ENE set is crossed by a later SE–SSE set (Smythe 1912, p. 89). On the coast at North Seaton [NZ 3051 8585], striae trend S5°E.

The lower grey or greyish brown boulder clay is present almost throughout the district. It is a tough, stony clay, up to 70 ft thick in places, and forms the bulk of the glacial drift deposits. Wisps and discontinuous beds of gravel, sand and laminated clay are common

While no generalized sequence can be given for the intermediate gravels, sands and clays, there is in most areas a tendency for the lower beds to be coarser than the upper. In the lower parts of the Tyne buried valley there are considerable thicknesses of sand and gravel. Laminated clays, up to 30 ft thick, occur in the Sleekburn and Tyne valleys.

The upper part of the glacial sequence is formed of reddish brown till or boulder clay and a variety of stony clays including ablation till, flow till, soliflucted material and the weathering products of these and of other glacial deposits. In general these upper clays have a relatively low load-bearing capacity. They tend to be sandier than the lower grey till, and their erratics, while of similar types, are fewer and smaller.

In some sections there is a clearly visible distinction between upper reddish clays and the lower grey clay. For example at Tynemouth near the Collingwood Monument [NZ 3700 6896] the two are separated by a bed of sand up to 3 ft thick, and at North Seaton [NZ 3050 8585] the division is marked by a striated glacial pavement of flat-lying erratics. In other sections, as in the cliffs south of Curry's Point, the distinction is vague.

Local details

The section at Tynemouth [NZ 3700 6896] has been briefly mentioned above. It continues for 300 yd eastwards and shows some 15 ft of reddish brown boulder clay, on fine sand up to 3 ft, on grey to greyish brown boulder clay, 30 to 40 ft thick, in which Carboniferous Limestone erratics are prominent. At Sharpness Point [NZ 3717 6995] the cliff is capped by 10 ft of brownish boulder clay. About the middle of Long Sands [NZ 366 706] there are nearly 50 ft of grey boulder clay with sand lenses. From the mouth of Brierdene Burn [NZ 3505 7395] to Curry's Point are cliffs of boulder clay up to 40 ft high; the upper part is reddish brown, while the lower part is brownish grey, with no clear line of separation; the topmost 2 to 3 ft are silty almost stoneless clay. Along Blyth North Beach [NZ 313 828] to [NZ 318 820] is a section, somewhat obscured by tip, showing 12 to 15 ft of dark brown, tough stony boulder clay overlain by 3 to 6 ft of red, somewhat sandy boulder clay with fewer and smaller stones. A section at North Seaton is referred to above.

Inland exposures are rare. There are small exposures of laminated clay in the banks of Sleek Burn [NZ 278 840] near the district margin, and intermittent exposures of reddish boulder clay lower down the stream. Opposite Mount Pleasant Farm on the south bank of the River Blyth [NZ 290 823], beneath 5 ft of alluvial clay and gravel are 4 ft of reddish brown stony boulder clay, on about 3 ft of grey boulder clay with large sandstone and limestone erratics. Old clay quarries near Seaton Delaval [NZ 2925 7585] and [NZ 2990 7510] formerly exposed up to 10 ft of reddish brown stony clay with some sandy pockets. North-west of West Field around [NZ 298 745] there are small sections of reddish brown sandy stony clay in the banks of Seaton Burn and its tributary stream.

Most borehole sections give little information about the drift except its thickness. For example, in the West Sleekburn Borehole [NZ 2849 8497] the section is: boulder clay 92 ft 5 in, sand 8 ft 5 in, boulder clay 16 ft 11 in; which is clearly an over-simplification, for the nearby West Sleekburn Colliery shaft section [NZ 2810 8480] reads as follows (the stoniness or otherwise of the clays is not mentioned):

A cored borehole half a mile farther south-west, the West Sleekburn Farm Borehole [NZ 2738 8427] (320 yd outside the district) gave this section:

Around Cambois, boreholes show boulder clay to be the main lithology with subordinate beds of sand and laminated clay. The uppermost 5 to 15 ft of the drift is a nearly stoneless, reddish brown clay.

Boreholes at Newsham show some subdivision of the thick drift in the Cramlington buried valley, as the following three examples show: Newsham No. 2 Borehole [NZ 3022 7986], sandy clay and stones 33 ft, on sandy clay and sand 4 ft, on boulder clay 14 ft; Newsham Park Farm Borehole [NZ 3032 7882], boulder clay 18 ft, laminated clay 2.5 ft, boulder clay 69 ft; Newsham South Farm Borehole [NZ 3127 7902], open hole 10 ft, red boulder clay 28 ft, grey boulder clay 19 ft. Farther south-west the buried valley in its deeper parts seems to be filled with boulder clay. The Cramlington Engine Pit [NZ 2874 7599] section is "blue stony clay 152 ft" (this is the thickest drift recorded in the district). A more varied sequence appears in the North Centre Bit Field Borehole [NZ 2925 7756]; stony clay 16.75 ft, sandy loam 2.75 ft, clay 0.5 ft, sand 2.75 ft, stony clay 27.75 ft, brown clay mixed with sand 18.5 ft, sand 1.75 ft, sandy clay 1.75 ft; total thickness 724 ft.

In the Brierdene buried valley an idea of the drift sequence may be gleaned from the East Holywell Fenwick Pit [NZ 3124 7300] section: soil 2 ft, red clay 18 ft, sand 5 ft, stony blue boulder clay 38 ft, brown clay 9 ft, gravel 6 ft, brown clay 15 ft, total 93 ft.

At Rising Sun in the south-west, No. 3 Shaft [NZ 2985 6851] was sunk through boulder clay 9 ft, sandy gravel 8.5 ft and blue clay 15.75 ft. Percy Main Shaft [NZ 3373 6710], about 100 yd S of the district shows sands and laminated clays beneath boulder clay: blue stony clay 78.5 ft, sand 2 ft, blue stony clay 73.5 ft, leafy clay 2.5 ft, sand 1.75 ft, sand and clay 2.25 ft, stony clay 2.25 ft, gravel 1 ft, sand 2 ft, leafy clay 9.5 ft, sand 4 ft, gravel 3.75 ft; total 183 ft. Boreholes on the left bank of the Tyne at the district margin show between 80 and 130 ft of drift with basal gravel 5 to 50 ft thick overlain by interbedded sands and laminated clays, boulder clay, more sand and laminated clay in a limited area, and an upper boulder clay and stony clays. Laminated clays are at least 35 ft thick in places. Beneath the central part of North Shields around [NZ 358 684] boreholes show two boulder clays separated by sand and gravel and underlain in places by gravel. Thicknesses vary widely and continuity of beds is doubtful. Under South Shields silty clays and laminated clays are important; towards the coast 'sand and boulders' make a third to a half of the drift section.

Recent deposits

Peat

Beneath the coastal dunes there are generally a few inches of peat which has been dated as Atlantic (pollen zone VITA) by Raistrick and Blackburn (1932). One or two inches of peat are visible beneath blown sand on North Seaton Links near [NZ 3045 8525], and up to 12 in of sandy peat similarly below the dunes at North Blyth [NZ 313 828] to [NZ 318 820].

Alluvium

Alluvium fringes the streams but the only extensive spread is on the south bank of the Blyth estuary. Here, opposite Mount Pleasant Farm [NZ 290 823], the alluvium consists of dark soil with sandstone and coal fragments 11 ft, on dull brown silty clay with small scattered rounded and angular sandstone fragments 2 ft, on brown sandstone gravel with rounded stones mostly below 4 in with a few up to 12 in across, 2 ft. A section at Blyth Gas Works [NZ 3145 8170] on the former tidal inlet showed made ground 16 ft, on silt and clay 4 ft, on sandstone.

Blown Sand

Blown Sand fringes the bays, in dunes up to 50 ft high. The inland edge of the dunes is generally indistinct, as the sand is blown inland to form a fringing veneer of sandy soil.

Beach deposits

Beach deposits call for little comment, being sand in the bays and shingle around and immediately south of the headlands. The general direction of long-shore drift is southwards. On the north side of the mouth of the Wansbeck a shingle storm beach, nearly a quarter of a mile long, has built up to about 15 ft above ordinary high tides. The beach from Cambois Colliery [NZ 305 847] southwards is largely made of colliery waste which was tipped on to the foreshore. In places, notably at Seaton Sluice, flint and glass slag pebbles are prominent in the beach; these are derived from ships' ballast and a former glass works. Also on the beaches at Seaton Sluice are patches of heavy mineral concentrates (Hawkes and Smythe 1931) rich in baryte and garnet, derived from local sandstones.

Made ground

Though made ground was not mapped in the revision of the district, it is important enough to deserve mention. It can be classed under four heads: (1) quarry infilling, (2) colliery tip, (3) ships' ballast and (4) domestic and industrial waste. Quarries for coal are refilled with the overburden stripped to reach the coal. The more extensive quarries are shown in (Figure 84). Smaller quarries for sandstone have generally been filled with domestic waste. Colliery tips form notable features on the flat landscape and are obvious both on the ground and on maps. Ships' ballast, chiefly flint gravels from the Thames estuary, formerly made prominent hills at Blyth and near the River Tyne, but those not built over have been largely removed for their gravel content. Sandy Island [NZ 336 768] at Seaton Sluice is a ballast hill. Much of Marine Park and the Tyne frontage at South Shields include extensive ballast heaps. Domestic and industrial waste and the debris of former buildings in towns form extensive spreads. An important industry from the 12th to the 19th century was salt manufacture by evaporation of sea water in 'pans' using low-grade coal (Pilbin 1935), a process which resulted in large amounts of ashes and salt waste being tipped around the works. In South Shields, for example, waste heaps up to 50 ft high over an area of 23 acres were mentioned as being on fire (by spontaneous combustion) in 1872–75 (Lyall 1877).

Drainage development

Development of the drainage of a district like this must be studied in a much wider regional context (e.g. Sisson 1960; Peel 1941); accordingly, only a few comments are included here. Topographically the district is of low relief: a till-plain smoothed by post-glacial solifluction. The main rivers, i.e. the Wansbeck, Blyth, Seaton and Tyne, all flow in post-glacial gorges. Other drainage is by minor consequent streams. The Wansbeck keeps close to the north bank of the buried valley so that the north side of the river carries little drift while the south side is almost entirely in thick drift. In general, the River Blyth flows east-northeast, but within a quarter of a mile of the coast, turns south for two miles parallel with the coast before joining the sea. This southerly turn appears to be a diversion of the mouth by blown sand. Around Gee's Hill [NZ 319 833] and Claywell Hill [NZ 317 821] the peninsula would be breached at high tide if the blown sand were removed.

Chapter 9 Economic geology

Coal

For the past seven centuries coal has been the chief mineral product of the district, and remains in this position today with a current output of the order of 2.5 million tons a year. While the most easily accessible areas of the thicker seams have been exhausted, considerable reserves of coal remain, largely in thin seams or offshore. Maps in Chapter 3 show the thickness and worked areas of each seam, and hence give some indication of reserves remaining. Coal quality is briefly mentioned in Chapter 3 (p. 13) and has been discussed by Jones (1945) and Edwards (1963). All collieries produce household and steam coal, with gas and coking coals in the south.

Other minerals

A brick works at Backworth uses locally mined mudstone. Laminated clays and superficial drift clays were formerly quarried for brick-making at many places throughout the district.

Sand and gravel occur as beach deposits, blown sand, glacial sands and gravels and outcrops of Permian Yellow Sands. No large-scale working is possible because the areas available are limited, the overburden is too great, or amenity and coast-defence considerations prohibit exploitation. Most of the old ballast hills have now been quarried away or built over. 'Burnt shale' in colliery tips still exists in quantity.

Sandstone for building was formerly widely quarried: reserves have hardly been touched. Limestone was quarried for lime-burning at Whitley, the Permian outlier here being almost entirely removed. Dolerite from the dykes was quarried for road metal on a very small scale near Seaton Sluice. Ironstone from the Whitley Ironstone was mined at Whitley Bay.

Mineral veins with pyrite, galena, sphalerite, calcite, ankerite and baryte occur throughout the district, but rarely exceed a fraction of an inch in width and so are of academic interest only.

Ground water

Barium salts are extracted from ground water at Backworth Colliery, and relatively high concentrations of calcium, barium and chloride are also recorded by Anderson (1945) in some ground waters at other mines.

Ground water is not abstracted for public supply, nor to any significant extent for industrial purposes, apart from mine dewatering. The ubiquitous presence of old workings and the disturbance to the natural regime they cause, the presence locally of undesirably high concentrations of iron, chlorides and sulphates and the limited natural recharge because of the impervious cover of boulder clay and built-up areas, all combine to make it unlikely that appreciable quantities of potable ground water will be obtainable.

Engineering geology

Ground conditions vary widely, and in the planning and construction of works and buildings, problems will arise from the presence of old mine workings and thick deposits of low strength glacial clays. Marine erosion is active along the coast (Tate 1894).

Appendix 1 Boreholes and shafts

This appendix shows the correlation adopted, by listing the depth to the nearest foot of the base of named coal seams and marine bands in the principal shafts and boreholes (Figure 85). These are listed in Institute of Geological Sciences registered number order. Each number is in two parts: the appropriate National Grid six-inch sheet number followed by an arbitrarily assigned serial number.

References to 'Borings and Sinkings' (1878–1910) are to the serial numbers of sections in that work.

Starting level is the altitude in feet above or below (—) Ordnance Datum of the zero of the section. In the case of boreholes and shafts from the surface this may not coincide with ground level.

Drift values are depths to the base of the drift, and may include made ground.

Where seams are split, the depths quoted are to the lower leaf. If an upper leaf forms a thick coal well separated from the lower, this is referred to in the notes.

Asterisked * values are approximate. Values (in parentheses) indicate that the named bed is absent, but its horizon is taken at that depth.−

The following abbreviations are used: