The geology of North-East Durham and South-East Northumberland

THE GEOLOGY OF NORTH-EAST DURHAM AND SOUTH-EAST NORTHUMBERLAND. By DAVID WOOLACOTT,

Read May 3rd,

D.Sc., F.G.S.

1912.

CONTENTS. PAGE I.-TABLE OF STRATA II.-THE COAL MEASURES II I.-IGNEOUS DYKES I V.-THE PERMIAN SERIES (a) The Yellow Sands . (b) The Marl Slate . (c) The Magnesian Limestone V.-THE HIATUS Vr.-THE GLACIAL A:;D POST-GLACIAL DEPOSITS.

87 88

91 92 93 9494101 101

This Paper was prepared for the use of the Members of the Association attending the Whitsun tide Excursion of 1912, and was issued as a Pamphlet. It is now reprinted with a few slight alterations.

I.-TABLE OF STRATA. Strata which occur in this district belong to the following T H Edivisions in descending order:-

RECENT A:;D GLACIAL.·

~

S U bm e r ged

forest (Whitburn Bay). Deposits of sand and gravel with marine shells (found up to the 150 ft. contour). Mounds of sand and gravel. Kaims, D e r osits of sand, leafy clay and re-asserted boulder clay. The stony boulder clay.

l

UPPER PERMIA:; OR THURINGIAN (Der Zechstein ).

Middlesbrough red beds with salt, gypsum anhydrite and thin fossi liferous magnesian limestonet 300 ft. The Magnesian Limestone up to 800 ft. The :\1arl Slate 3 ft.

(K upferschiefer) MlIllJLE PER~lIAN OR The Yellow Sands 0 to ISO ft. SAXO:
• The greatest thickness 0' these superficial depesits proved by borings In the Northumberland and Durham Coalfield is 233 ft. at Newton Hall, l'ramwellgate, ncar Durham. t Not seen in North-East Durham; only occurs in the South of Durham.

88

DAVID WOOLACOTT ON THE GEOLOGY OF

MIDDLE COAL MEASURES OR WESTPHALIAN

A series of coal seams, sandstones, shales, underclays, mussel-bands 1,500 ft.

FOur dykes occur in the district.*

IGNEOUS ROCKS.

j

The Tynemouth, Hartley and Collywell exposed on the coast of South-East Northumberland, and one-the Hebburn-is found in the collieries of North-East Durham (e.g., Whitburn).

II.-THE COAL MEASURES. The Coal Measures of Northumberland and Durham lie in the form of a syncline, and as the centre of the basin occurs in the neighbourhood of Sunderland, only the higher portions of these beds occur in the district under our notice. They belong entirely to the Middle Coal Measures (Westphalian), and contain the thickest and most productive seams. In South-Eastern Northumberland and in Durham, west of the Permian escarpment, they are buried beneath a variable thickness of superficial deposits, and are only exposed along the rivers and streams or where the thicker masses of sandstone rise to the surface. These latter outcrops generally have villages perched upon them. Along the coast of South-Eastern Northumberland, between Tynemouth and Seaton Sluice, they can be examined in an almost continuous section. t They are here seen to' consist of a series of yellowish, brownish, reddish, or greyish-coloured sandstones and grits, often occurring in wedge-shaped masses, dark grey and blackish bituminous shales.j coal seams, underclays, and musselbands. The mussel-bands are highly ferruginous,§ and other layers and nodules of clay ironstone occur. The seams exposed are the Low Main, Bensharn, Yard and Grey, but in the collieries lower seams-the Harvey (Beaumont) and the Brockwell-and a higher seam-the High main-are worked. Mr. S. R. Haselhurst has lately drawn up a correlation of the beds exposed in the Tynemouth to Seaton Sluice sections II as follows :SECTION EXPOSED FROM TYNEMOUTH TO SEATON SLUICE. HIGH MAIN Grey Shales. Red Sandstone. Yellow Shales with Micaceous Sandstone. GREY SEAM. Yellow Shales. ST. MARY'S Red and Brown Sandstones. IsLAND TO Yellow Shales. CRAG Sandstones. POINT.

}

BLACK MIDDENS TO

SPANiSH BATTERY.

* See note on page

92 regarding discovery of two new dykes. t A part of this section is shown in detail in Plate 27. Fig. I.

t A shale exposed just north of St. Mary's Island has cone-in-cone structure developed in it. § One of these exposed at Whitley was worked as ironstone seme years ago. II University oj Durham. Phil. Soc., vol. iv, Pt. 3, p. 162.

PROC. GEOL.

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PLATE

2 I.

[Photo by 5. R. Haselhurst. A.-PSEliDO-STROMATlSM PRODUCED BY THE SHEARING OF SANDY SHALES BENEATH A MASSIVE SANDSTONE IN THE COAL MEASURES, WHITLEY.

[Photo by D. Woolacott. B.-MAGNESIAN LIMESTONE, TROW ROCKS, SOUTH SHIELDS.

Disturbed beds lying along the Major thrust plane between the Lower Bedded Limestone and the Brecciated Beds of the Middle Division (see page II). To face page 88.

NORTH-EAST DURHAM AND SOUTH-EAST NORTHUMBERLAND YA RD SEAM.

Yellow Shales. Fire Clay. Brown Sand stone. BEN SHAM .

Black Shales and Sandstone. Red Sandstone. T able Rock Sandstone. Shales. Mu ssel-band. S ha le . Sand stone. Shale. Sandstone. Shale. Black a nd Red Shales.

Low

MAI N.

Black Shales. F ire-day.

89

SHARPNESS P T. , AND C ULLERCOATS.

}

TA BLE ROCK S SOUTHWARDS T OW .~RDS CULLERCOATS.

NORTH OF TABLE ROCKS.

SMlTGGLERS' CAVJ':, SO UTH of CU L L ER COA T S.

The Series has been highly faulted by a number of cast and west faults which, throwing both to the north and south, often repeat the beds. The chief of these faults are the Brierdene "Dyke," which, with a down throw to the north of some I 80 ft., shifts the outcrop of th e High Main seam about two miles and cuts the coast in Whitley Bay to the south of St. Mary's Island, and the Ninety Fathom" Dyke," which is exposed on the coast to the south of Cullercoats Bay. It here throws the Yellow Sands, Marl Slat e and Magnesi an Limestone against the Coal Measures in a most interesting section. This latter fault has a th row in the Coal Measures of some 600 to 1,000 ft., and is traceable from the coast to the south of Hexham, a distance of some twenty miles. Not only have these beds been faulted, but considerable horizontal movements have taken place in them, so that the softer beds (shales and sandy shales) have been considerably disturbed (fractured, tilted and folded), and certain of the beds have had secondary structures developed in th em , produced by the shearing of the mass. These simulate flow-structure and false-bedding, and have lately been carefully examined by Mr . S. R. Haselhurst, who has shown that the strata between Seaton Sluice and Tynernouth have had" pseudo-stromatism" extensively developed in them .* Professor Lebour and Dr. Smythe have sh own that one of the most mark ed of the se horizontal movem ent s occ urs at Whitley to the north of the Table R ock sandstone. H ere a series of shales and sandstones containing a mussel-band has been extensively disturbed by the movement. of a th ick compact sandstone bed over them, which has ploughed int o them, fault ing, folding and slickensiding them. t There is evidence to prove that th ese thrust-movements occurr ed after the post-Permian mo vemen t of the Ninety Fat hom Dyke, and they ap pear to be ... l} niv . Durham , P IJ il . S oc.. vel. iv , Pt . 3, page 167. t .. On a Case of Thrus t an d Unconformity in the Coa l Mea sures of Northumberlan d.' Qua rt. jau rn. Geol, S oc., v olv lxii (1906), P. 530.

PROe. GEOL. Assoc., VOL. XXIV,

PART 2, 1913.J

7

9°

DAVID WOOLACOTT ON THE GEOLOGY OF

phenomena produced in the Coal Measures at the same time and by the same forces as the horizontal movements which will be shown to have occurred so extensively in the Permian. South of the Tyne the Coal Measures are no longer exposed on the coast; they sink beneath the Permian deposits. To the west of the Permian escarpment they rise to the surface, but are generally covered by a thick layer of superficial deposits. They lie beneath the east of Durham in a synclinal form, whose centre lies beneath Sunderland district; the dips within the area towards the centre of the basin being very low. This syncline is a distinct accentuation of the Coal Measure basin of Northumberland and Durham-a basin within a basin-hence the highest Coal Measures of the two northern counties possibly occur beneath the Magnesian Limestone in the east of Durham. The Hutton Seam is some 1,400 ft. beneath the base of the Permian at Sunderland, some 458 ft. at Marsden Colliery, four miles to the north, and 833 ft. at Horden Colliery, twelve miles to the south; this gives a small measure of the extensive denudation that must have occurred before the deposition of the Permian on the Coal Measures. * Several of the faults in the Coal Measures proved in the colliery workings do not cut the Permian strata above them, while some have a considerably smaller throw in the higher than the lower series. The Ninety Fathom "Dyke" is of the latter class. The major period of faulting was pre-Permian, although vertical movements of considerable displacement have occurred since Permian times. One of the most interesting features of the Coal Measures of this area are the beds-often highly ferruginous-containing remains of fresh or brackish water lamellibranchs. These bands, often entirely composed of Carbonicula aquilina, have been called mussel or anthracosia bands, t and are useful for purposes of correlation, but sufficient attention has not yet been paid to them. There appear to be six or seven such beds, those above the High Main and Low Main seams being most persistent. Besides these bands other layers with fossil mollusca occur. One of these strata that outcrops on the north bank of the Wear opposite Claxheugh, east of the fault that crosses the river, consists of a dark grey fissile shale containing three or These layers contain a varied four bands of clay ironstone. fauna with remains of insects Eloblattina mantidoides (related to the present-day cockroach) and Lithomylacris kirkbyi," entromostraca Beyrichia arenata and Cythere fabulina,' lamellibranchs Carbonicula (Aneylus) vinti (Hind), Anthracoptera,· and plants.] * The unconformity is of much greater magnitude in the south of Durham, as there the Permian rests on Millstone Grit and Carboniferous Limestone. t The shells are now generally composed of calcite, and the interior of clay ironstone Mr. R. C. Burton has shown that the shell material has often been replaced by kaolinite. :\: J. W. Kirkby. Geol, Mag., vol. iv, 1867, pp. 388-39°.

NORTH-EAST DURHAM AND SOUTH-EAST NORTHUMBERLAND.

91

A marine band with Lingula 7Ilytiloides was passed through in the Ryhope Colliery sinking. Numerous remains of plantsStigmaria, Lepidodendron, Sigillaria, Neuropteris, etc.-occur in the Coal Measures, and the late T. Atthey collected many fish and amphibian remains from the shale above the Low Main seam. These are now in the Hancock Museum, at Newcastle. The upper beds of the Coal Measures-as at Tynemouth Cliff-are generally stained red. These layers were looked upon by Murchison as belonging to the Roth-todt-liegende, but that they are Coal Measures reddened by iron carried from the Yellow Sands above is now generally accepted.

nL-IGNEOUS DYKES. Miss M. K. Heslop, who has made the latest study of the dykes of Northumberland and Durham, has supplied the following notes, in which the work of Dr. Teall is incorporated;" on the four dykes occurring in this district. All the intrusions follow a north-west and south-east course and belong to a group which is bounded by the Acklington Dyke on the north, and the Cleveland Dyke-which is usually regarded as having been intruded in Tertiary times-on the south. They all possess an intermittent porphyritic and amygdaloidal character. The Tynemouth Dyke comes to the surface in the cliff near Tynemouth Pier, where until lately it could be seen as a yellowish decomposed rock, cutting vertically through the Coal Measure sandstone, and "passing up into the Yellow Sands above."! The exposure facing the sea is now covered by the buildings for a searchlight, but the dyke may still be seen a little to the west facing the River Tyne, Fresh hand-specimens are at a dull grey colour, and porphyritic felspars, calcite amygdaloids and even the ground mass felspar-laths may be distinguished with the unaided eye. Under the microscope a 101Y power shows the phenocrysts to consist of groups of intergrown twinned felspars-allied to anorthite-which are deeply zoned whenever they come in contact with the ground mass. The amygdaloids show circular sections and often include a portion of the glassy residue. The ground mass of the rock is made up of ophitically-intergrown groups of felspar and augite, the former being in long narrow lath-shaped sections, while the latter occur in plates or grains. There is a considerable amount of dark glass which is rendered almost opaque by the • "Petrographical notes on the North of England Dykes," Quart. [ourn, Geol; Soc., vol xl pp. 209-246. t G. A. L. Lebour... Geology of"orthumberland and Durham," p. 87.

DAVID WOOLACOTT ON THE GEOLOGY OF

presence of much granular iron oxide and skeleton crystals of augite thickly studded with these grains. The ground mass felspars are chiefly labradorite, although other plagioclase felspars occur. The augites rarely if ever show good outlines, but the larger plates are not infrequently twinned. There would seem to be some analcime in the glassy base. A dyke to the south of this which is found in Hebburn and in Whitburn Collieries is remarkably like the Tynemouth Dyke in colour, texture, and the presence of amygdaloids, but porphyritic felspars are rare or absent. oil< Some four miles north of the Tynemouth Dyke two other dykes occur, running parallel to each other and to the southern intrusion. One is seen in Collywell Bay, where the actual head of the dyke is exposed in the cliff section, the other-the Hartleyoccurs a quarter mile further north. t The Collywell Dyke possesses the general structure of the Tynemouth rock, but the ground mass felspars are gathered into bundles around which the augite curves and twists in interminable strands so that separate crystals cannot be detected. It gives rise to many beautiful forms strongly recalling the acanthus leaf in general appearance. It is doubtless a viscosity effect, as it becomes more prominent towards the summit of the intrusion. The Hartley and Collywell Dykes are markedly amygdaloidal, but do not seem to be porphyritic. In the latter intrusion, however, there are nodules of intergrown felspars similar in all respects to the phenocrysts of the Tynemouth Dyke, but occurring in comparatively large masses instead of singly. Only the outer parts of the inclusions show zoning. No porphyritic crystals or nodules of felspar have been seen in the Hartley Dyke.

IV.-THE PERMIAN SERIES. The Permian of north-eastern Englandj presents a facies quite distinct from that of the north-west. It is much more easily correlated with the German Permian than with that of the Vale of Eden. A land barrier existed between these two areas of deposition in England during Permian times, the Pen nine anticline having been already formed. The Lower Permian of the Continent is probably not represented in north-eastern England, but the Middle and Upper divisions present similar • A dyke (possibly tbe same as the Hebburn) which Is worked for road metal at Coaley Hill, a few miles to the west of Newcastle, has converted a coal seam into a cinder coal with a prismatic structure. + Dr. J. A. Smythe has lately discovered two thin dykes on the coast of south-east Northumberland, one about thirty yards south of the CclIywell Dyke and another a few yards to the south of the Brierdene Burn. Both dykes are less than one foot In thickness. :l: For sections across the Permian series, see plate 27. figs 2 and 3.

NORTH-EAST DURHAM AND SOUTH-EAST NORTHUMBERLAND.

93

facies in Durham and in Germany. Both were deposited in a more or less inland sea undergoing desiccation. CORRELATION WITH THE PERMIAN SERIES ON THE CONTINENT.* Upper Permian The Magnesian LimeDer Zechstein. (Thuringian) stone group'[ up to 1,100 ft.

Middle Permian (Saxonian).

Kupferschiefer.

Marl Slate 3 ft.

Weissliegendes. Rothliegendes. metres.

The Yellow Sands up to ISO ft.

500-2,000

Lower Permian (Artinskian).

Group of sandstones, conglomerates, shales, marls, limestones, and dolomites.

The Yellow Sands?

(a) THE YELLOW SANDS. This representative of, or of a portion of, the Rothliegendes and Weissliegendes (Middle Permian) of the Continent rests on the denuded edges of the Coal Measures, and underlies nearly the whole of the calcareous facies of the Permian of the district. It is a very irregular deposit, filling up the hollows of the floor on which it rests. Its thickness varies from ° to IS0 ft. and it thins out irregularly but continuously towards the south and south-west. In Northumberland it occurs in three or four distinct outliers, in two of which-on Tynemouth Cliff and in Cullercoats Bay-its relation to the Coal Measures beneath and to the Marl Slate and Magnesian Limestone above can be seen. In Durham it is exposed in Frenchman's Bay, and can be traced more or less continuously along the base of the Permian escarpment. The chief characteristics of this deposit are: (I) It is generally false-bedded, but the grains are more regularly arranged near the top of the deposit. (2) It is seldom bedded in distinct layers. (3) The grains composing it are generally quartz, but there is an admixture of felspar, mica, garnet, zircon, rutile, and tourmaline. t (4) The larger fragments composing it are rounded, but the smaller grains are angular. These are not sorted, but large and small grains are intermingled with one another. (5) It is yellow along the outcrop, but it is a bluish, greenish, or greyish colour in pit sinkings. It is very irregularly cemented by carbonate of lime, '" For a fuller discussion of the Permian of the area, reference should be made to a

paper sbortly to be publisbed by tbe Autbor on .. Tbe Stratigraphy and Tectonics of tbe Permian of Durham (northern area)," Univ. of Durham. Phii. Soc" vol. tv, pt. s. t Iucluding tbe Magnesian Limestone proper and red beds with salt, gypsum and the fossiliterous Magnesian Limestones of South Durham.

: Mr. R. C. Burton bas made an extensive study of the minerals of higher specific gravity in these sands.

94

DAVID WOOLACOTT ON THE GEOLOGY OF

being in some places hard and compact, at others soft and friable. (6) Itis a water-bearing horizon. (7)No fossils have ever been found in it. These sands appear to have been derived from an area lying to west and north-west, in which some metamorphic rocks were exposed. It was at first an ::eolian deposit of sand dunes on the edge of the encroaching Permian sea, and later washed up and deposited under water.

(b)

THE MARL SLATE.

This thinly laminated, arenaceous, argillaceous, calcareous bed is traceable above the Yellow Sands throughout the area. It may be looked upon as a passage bed from the arenaceous beds beneath to the calcareous above. Its thickness is from three to five feet, and for so thin a deposit, is a remarkably persistent layer. It is generally yellow along the outcrop, but is greyish and blackish when unweathered. It is usually overlaid by Magnesian Limestone, but on Tynemouth Cliff there is a calcareous sandstone and conglomerate some six feet in thickness between it and the limestone, and in Cullercoats Bay some thin beds of sand are intercalated above it among the lower beds of the limestone. At its base silica and alumina form the greater part, while near the top 80 per cent. is composed of the carbonates of lime and magnesia. The most remarkable feature of this bed is the large number of fish remains. Many of the specimens are contorted, as if the fish had been suddenly poisoned by an increase in the saltness of the sea. They can generally be obtained from most exposures. Pakeoniscus and Platysomus are the most common genera. Besides these, remains of reptilia (Proterosaurus), cephalopoda (Nautilus freieslebeni), lamellibranchiata (Myalina hausmanni), brachiopoda (Lingula credneri and Discina nitida) and plant-remains occur.

(c)

THE MAGNESIAN LIMESTONE.

This deposit of bedded and un bedded limestones reaches a thickness of 878 ft. (as proved by boring)* in the south-east of Durham, but in the north-east it is considerably thinner (500 to 600 ft.), It is often yellow in colour, but brown, grey, and white varieties occur. The calcium carbonate varies from 99 to 38 per cent., and the magnesium carbonate from less than I to about So per cent. It is never a true dolomite, while it someThe amount of times approximates to a pure limestone. silica, alumina, and oxide of iron varies from less than I in the purer limestones up to 30 per cent. in the more marly varieties. t • If the beds were dipping, this may be greater than their true thickness. t Some shaly partings in the Lower Limestone contain nearly 80 per cent. of these substances. See also note, page 99.

PROC. GEOL.

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PLATE

22.

[rllOto by O. C. Wilmol. SECTION AT HETTON DOWNS QUARRY.

Rocks of the Permian escarpment south of the "Year: Yellow Sands (I), Marl Slate (2), and Lower Bedded Limestone (3).

To face page 94.

NORTH-EAST DURHAM AND SOUTH-EAST NORTHUMBERLAND.

95

It sometimes contains grains of sand, and thin arenaceous beds occur locally. Besides quartz, particles of garnet, zircon, and other minerals have been found. * Thick beds of soft yellow marl occur at many parts of the deposit, and some of the more sandy varieties of the limestone are associated with these. It can be divided into the following divisions :(a) Upper: (I) Yellow bedded limestone of Roker . . . . 100 ft. (2) The concretionary limestone of Fulwell and Marsden, a series of concretionary and non-concretionary limestones and marls . . • • . • . 250 ft. (3) The Flexible Limestone 10 ft. (6) Middle: Bedded yellow, (I) Unbedded (as a rule) highly \ fossiliferous limestone of non - fossiliferClaxheugh, Tunstall, etc. ous limestones forms a ridge of high replaced of the northern ground and reachesathickend of Marsden ness of 300 ft. Often brec- on the Bay and coast ciated and entirely changed from Hendon in character - rendered east by toSeahamHarmore calcareous, crystalbour. Often line and cellular, and foshighly brecsils obliterated. t ciated ISO ft. (c) Lower: Bedded brown limestones of Frenchman's Bay, Houghton, etc. Upper beds often disturbed. 40 to zoo ft.

I

The chief peculiari ties of the Magnesian Limestone of this area are (I) the distribution of its fossils (2) the great north and south ridge of unbedded fossiliferous rock reaching a thickness of 300 ft., but thinning rapidly to the east and being replaced by a bedded unfossiliferous limestone (3) the great thickness of brecciated beds that occur at various horizons (4), the unique concretionary structures that have been developed on one horizon, and (5) the cellular structures. (I) Palaonlolog)! of the Magnesian Limesfone.-The fauna of this limestone is very restricted (about 140 species), and is most peculiarly distributed. The marked feature is the small number of individuals in the Lower, their very great profusion in the Middle or Fossiliferous division, and the sudden decrease both in the number of species and individuals in the Upper-only a few genera remaining. The table on page 96 shows the principal palseoniological features of the Marl Slate and Magnesian Limestone. (2) The Fossiliferous Limes/one.-This division of the limestones forms the ridge of high ground which runs from • Mr. C. T. Trechmann has studied a limestone residue from these beds at Hartlepool, and found in it: (I) Quartz grains, some with idiomorphic outlines, others

irregular and full of inclusions (chiefly iron pyrites). (0) Iron pyrites in aggregates and in separate crystals. (3) Highly refractive grains resembling zircons. (4) A dichroic mineral, possibly tourmaline.

t In the south of the district, •. g.. Tunstall Lodge, Murton, Haswell, etc., this limestone passes westwards into a hedded yellow rock with a limited fauna.

TABLE OF THE PRINCIPAL PAL-EONTOLOGICAL DIVISION OF THE MARL SLATE AND MAGNESIAN LIMESTONE OF NORTHUMBERLAND AND DURHAM. DIV1SIONS.

F1SH AND PLANTS.

ZONES.

COMMONEST SPEC1ES.

ui

Myalina hau smanni, Pleurophorus costatus, Axinus dubius,

UPPER YELLOW.

'" 'u

G ENERAL FEATURES.

'"c,

CONCRE1"IONARY LIMESTONE.

FLEXInLE LIMESTONE.

-e'" ~

r

"5

Acentroph orus, Acrolepis and Ullm annia, etc. (Fulwell).

'" ~

0

Z

Acentrorrh orus and Aerolepis Marsden).

'0

ui

"''''" ~"'"

,,~ o u :::: N ::: . ....

MIDDLE FOSSILIFEROUS LIMESTONE.

r:llo-.....Cl

~ c,

o

E

Platysomus .

v~

..:: ..c::g~ ..... ~

~U ~

-l 'O'" MARL SLATE.

VI

B "" " "".

-0°

-l :l - -~ ~ ....: LOWER LIMESTONE.

Myalina hausmanni, Pl europhorns costa tus , AxilJUS dub ius, Turbo permianus.

u

Pla.tysomus, Palesoniscus, Lepidotosaurus, Pr oterosaurus, Ullmanoia, etc.

:l

0'"

... "

~:g

'"c0

N

En tromostraca Foraminifera (Byer 's Quarry, Marsden).

Fossils in these beds ar e not numerous. Few genera, few individuals. Nobrachiopods, bryozoa, ceph alopods, corals, en crinites ha ve ever been found in the beds above the Fossiliferous Limestone.

t:l

> <:

a

~

o > o o ~ r-

o

P rodu ctu s horrid us, Spirifer alatus, Strophal osia goldfussi, Te rebratula elonga ta, F enestella retiformis .

Very rich in individuals. About 120 species; Brachiopods and bry ozoa specially numerous. Several species are restricted,

Pr oductus horr idus, Spi rifer alatus, Fenestella ret iformis.

Fossils simi lar to Fossiliferous Limestone, but on ~ thirty species . Indivi uals scarce.

....... 00

ID C1'

z

.,

0:

t'J

o t'J o ro o

.<::

A few species of marine invertebrates in Marl Slate.

0<

o

"l

NORTH-EAST DURHAM AN D SOUTH-E AST NORTHUMBERLAND .

97

Boldon Hills by Claxheu gh, Humbledon Hill, Tunstalls Hills to the coast at H awthorn, and then by Harden Colliery and Blackhall sink ing. This bed is often a soft yellow hiahly magnesian limestone," but sometim es it is white and more calcareou s. t It also occurs as a hard, crystalline, cellular, highly calcareous non -fossiliferous rock, which has bee n produc ed from the softer yellow rock by the leachin g out of the magnesium carbonate, and segregation of the calcium carbon ate. Fr om th is mass the fossils have been obliterated. It has also in places been highly brecciat ed . It appears to have originally formed a bank of shells- many of them drifted-in the Middle Permian sea. This bed thins out suddenly to the east, bein g replaced by non-fossiliferous rock.] and on the west it passes into a bedded yellow limestone with a limit ed fauna.§ It marks a portion of the Permian sea that was fresher than th e surrounding waters, and thus was abl e to support life in greater abundance. Only about 120 species occur, but it is exceedingly rich in individuals. It is the fossiliferous division of the P ermian par ex cellence, there being a sudden restriction in the number of species, and in the number of individuals in the beds both above and beneath it. Most of the fossils are casts ; occasio nally, however, well-preserved speci mens are found with the ir internal parts shown. The commonest gene ra are :Penestella retijormis (Sch!.). Synodadia virgulacea (Gein). Productus horridus (Sow). S trophalosia gold/ ussi (Mun st). Camarophoria schlotheimi Sp irijer alatus (Sch!.). (v Buch). T erebratula elonKata (Sch!.). lJ-fonoHs spelun caria (Schl.). Area tumida (Sow). N autilus freieslebeni (Gein). (3) Th e Brecciated B eds.-The Brecciat ed Beds are confi ned to the Middle and lower part of th e Concr etion ary divisions of the limestone. They, however, occur at various horizons. Within the area which we are considering, they have been caused by movement s in the limestone produ ced by more or less horizontally d irected forces. JI This thru sting has brought about a decrease in the lateral exten sion of the Pe rmia n, and the layers with least compressive stren gth have been shattered. The Lower limest one resisted the pressures, and th e consequence was, that the surface between it and the yielding Middle limestones, becam e a plane of shearing along which the latter beds moved. Oth er minor shear * Magnesian carbonate', 40 to 45 per cent. t An oolitic variety containing for a min ifera occurs along the coast to the soutb of H awthorn Dene. t Seen al ong the coa st at Rybope . § Seen In old quarry at T unst all L od ge an d in Ha sw ell Quarry; II It Is p ossible th at cert ain of the breccias in th e P er mi an of Dur h am may h ave been prod uced by tb e Int ern al sol uti on of bed s, or by otber cau ses, b ut the evidence for the prod uction of tbe chie f br ecc iated b eds in thi s distr ict by thrusting see ms to the a utho r to be co mplete.

98

DAVID WOOLACOTT ON THE GEOLOGY OF

planes occur at various horizons. Associated with this extensive development of crush brecciation and these more or less horizontal shear (or thrust) planes are several other dynamically produced features :-( J) Disturbed and displaced masses of Lower Limestone, (2) slickensided and grooved, horizontal and vertical surfaces, (3) cleaved limestones, (4) folded and buckled layers, (5) some beds have been squeezed out, others thickened, (6) breccias have been forced up into the beds above and below them (intruded breccias), and (7) phacoidal, lenticular, strain-slip and other structures have been produced by shearing. The main thrusting was probably directed from between west and northwest to east and south-east. The phenomena caused by these horizontal movements can be examined along the coast between Ryhope and Sunderland, at Claxheugh, on Boldon Hills, etc., but perhaps best of all at Marsden. (See photographs, Platc c I (n) and Plate 23, and also sections, figs. I and 2, Plate 28). Experiments made on the compressive strength of the rocks affected by the thrust at Marsden indicated that the forces acting reached a maximum of some 300 tons per square North of the Tyne the phenomena both in the foot. Coal Measures and Permian are much the same as those in the strata of Durham. There the Ninety Fathom "Dyke" appears to have acted as a buffer or minor horst, and hence these horizontal forces must have operated after the post-Permian shifting of this fault. This thrusting was most probably connected with a general movement of the North of England strata against the horst of the Lake District massif, which may have been subsidiary effects of the Miocene uplift, that produced such marked changes in the physiography of Britain. Some faulting within the district can be proved to have occurred subsequent to these horizontal movements. (4) The Concretionary Limeslone.-The division above the Flexible limestone is characterised by an extraordinary development of concretionary structures. It lies in the form of a syncline beneath Sunderland, and composes the hills of Cleadon, Fulwell, and Bildon; reaching a maximum thickness in the northern part of the arca--Cleadon and Marsden-of some 300 ft. Some other parts of the limestone are concretionary, but these structures are always more or less incipient, and never approach the complexity of those in this division. The latter consists of several interbedded deposits. The most characteristic of these beds are the cellular and globular concretionary limestones-the "greystones" of the Marsden and Fulwell quarrymen and the "Honeycomb or Main Limestone" of Fulwell are of this character. Associated with these arc bedded non-concretionary (or incipient concretionary) limestones (compact, brown, light and dark grey, sometimes bluish) which comprise the "bluestones" of Marsden and the" whitestones " of Fulwell, There are also irregular beds

PROC. GEOL.

Assoc.,

VOL.

XXIV.

PLATE 23.

[Photo by Godfrey Bingley. A.-CELLULAR CONCRETlO;'>lARY LiMESTONE: UPPER LIMESTONF, FOLWELL QUARRIES.

[Photo by Dr. Lishman. B.-SPHERICAL CONCRETIONARY LIMESTONE: Top OF UPPER CONCRETIONARY LIMESTONE, PARSON'S ROCK, RaKER.

To face page 98.

NORTH-EAST DURHAM AND SOUTH-EAST NORTHUMBERLAND.

99

of soft, pulverulent, yellow" marl.'?" The least magnesian of these divisions arc the compact" bluestones," and the most magnesian are the" marls," the" greystones " being intermediate in composition. The amount of magnesia originally present in the limestone before the concretionary structures began to be developed would certainly seem to have been the determining factor in the setting up of these structures, and the presence of siliceous and argillaceous impurities appears to have had a deterrent effect. The compact highly calcareous "bluestones" are not concretionary, neither are the impure marls, but the" greystones " (beds now intermediate in composition and in spite of much removal of magnesium carbonate from them almost certainly of an intermediate type before the concretions began to form in them) have had a complicated series of concretionary structures developed in them. Dr. George Abhott has classified these and has shown that there appears to have been a gradual development of some particular types. He has also made a collection of photographs of them. The concretions are segregations subsequent to deposition of calcium carbonate from the beds in which they occur. It is noteworthy that where a spherical concretion is embedded in a matrix, the cement is always more highly magnesian than the concretion, and that where the magnesium carbonate has been leached out from other divisions of the limestone along fissures, etc., concretionary action has been set up in these strata. t For field purposes the varied structures may be divided into spherical and cellular. In the development of the spherical-cannon ball, botryoidal and stellate-concretions fossils have occasionally acted as nuclei, but this is by no means always the case. It seems certain that the bedding planes were developed before either of the types started to form, as they often act as dividing lines. It is, however, exceedingly difficult to understand in the case of the cellular types-honeycomb, coralloid, etc.-the origin of the other lines anastomosing through the rock, which have apparently acted as guiding lines for the development of the concretionary growths. (5) Cdlular Structures.:-:The Magnesian Limestone of Durham is a peculiarly cellular rock. It has been supposed by some geologists that these structures proved that the rock had been dolomitised subsequent to deposition, but it is noteworthy that the most cellular parts of the limestone are not the most magnesian; indeed, most of the cellular types appear to have been produced by the removal from the rock (by solution or by mechanical action) of the magnesium carbonate, or in some :+' Some of the so-called" marls" In the Magnesian Limestone do not contain much more aluminous impurities than parts of tbe limestone itself. The word is thus often a misnomer. They are always soft, yellow, higbly magnesian beds. See the analysis of Great Marl Bed on p. roo. t On the coast just north of Byers Quarry, Marsden, a brecciated mass appears to have had a concretionary structure impressed on it after the smashing up occurred.

100

DAVID WOOLACOTT ON THE GEOLOGY OF

ANALYSES· OF

SO:\IE

TYPES OF THE LIMESTONE.

CO:'\CRETIO~ARY

:\IAG~ESIAN LIMESTONE SERIES, DURHAM.

Bluestone from Byer's uarry , arsden,

.a

CaCO s MgCO s SiO Fe/>s & AI.O s Water

97.84+ 1.3 ·5 ,26 .2

Grey spherical concreMarl from tions, embedded in Great Marl soft, yellow marl. FulBed, well Quarries. Fulwell Quarries. Concretions. Marl.

55.4 8 4 0.9 2

95.58 2.36

} 3·04 .56

1.4 .66

Cellular concretionary greystone. I I Main or Honeycomb llmestone;' Fulwell Quarries.

56.53 38.54 3.6

96.55 1.46 1.06

I.33

·93

cases of both it and the calcium carbonate. The cellular structures may be classified as follows : (I) Concretionary cellular produced by the segregation of the calcium carbonate round points and along lines, and the removal of the earthy magnesian residue. (See photograph, Plate 23.A).

(2) Cellular or negative-breccia caused by the solution of the original pieces of the magnesian limestone breccia from the more calcareous cementing matrix. (3) Solution-cavities produced by the leaching out of the magnesium carbonate from a magnesian limestone and the consequent formation of a calcareous, crystalline, highly-cellular rock. (4) Geodes are a cellular structure which are possibly connected in formation with the last type. They may be looked upon as being negative concretions, but the original constituents of the geodes are not clear. They are generally lined with crystals of calcite or dolomite, and are characteristic of the Lower Limestone which has been called the "Geodic Limestone." (5) Fractured-cellular. This type is peculiar to the brecciated zone. At the time of thrusting, the rock has been fractured into rhomboidal masses, and these fractures have been cemented by calcareous matter and the contiguous rock rendered more calcareous. The yellow magnesian limestone has been subsequently removed. • From analyses by Mes srs. Kirkby and Browell and other analysts. t Some analyses of this stone give a higher percentage of calcium carbonate than this,

NORTH-EAST DURHAM AND SOUTH-EAST NORTHUMBERLAND.

101

V.-THE HIATUS. It would seem safe to assert that representatives of many of the major divisions of the Mesozoic strata, so well developed in North-Eastern Yorkshire, were deposited over the district we are discussing, probably ending with a deposit in upper Cretaceous times. The shore line of the Secondary sea lay during part of that time to the north and west of the area, but the era of sedimentation passed away at the end of the Cretaceous Period and a prolonged epoch of denudation began. The two northeastern counties along with most of the rest of Britain were being upraised in the early Tertiary age, culminating in the Miocene uplift. Britain now formed part of the European continent, there being a more or less continuous land connection between England and the mainland. North-Eastern England was being sculptured into its pre-Glacial contour. The principal upland valleys were formed, the escarpments of more durable rock produced, and the broader features of the present physiography determined. Within our area the low but well-marked and continuous escarpment of the Permian was developed, and the ridges of Coal Measure sandstone formed. The pre-Glacial valleys of the Northumberland and Durham coalfield along which the bed rock lies beneath sea-level (reaching r69 ft. below O.D. at Dunston, near Gateshead), and which are buried in Glacial, re-assorted Glacial, and post-Glacial material, prove that the district was considerably more elevated before the Great Ice Age than it is now. * The constructional shore-line of the pre-Glacial" Sleek burn," "Tyne" and "Tees" must have lain far to the east of the present coast-line; indeed, during part of the epoch they were only tributaries of a major stream running over the present North Sea area. The" Wcar" was then a tributary of the "Tyne," the buried valley of this river running from Durham City down the Team valley to the confluence with the Tyne valley, a little to the west of Gateshead-the present main line of the North Eastern Railway follows this old course.

Vr.-THE GLACIAL AND POST-GLACIAL DEPOSITS. There are two distinct types of deposit that are usually regarded as Glacial in the districrt-i-f r ) the true stony boulder-clay, a real moraine profondeand (2) deposits of more or less boulderless clay, leafy clay, sandy clay, gravel and sand-s-in the deposition of which water, whether running or tranquil (dammed up by • Woolacott, "Pre-Glacial Valleys of Northumberland and Durham Coalfield." Quart.}our». Goal. Soc" vol. lxi, Feb. 1905, p. 6~; .. Physical Features of Northumberland and Durham," Geog.journ., vol. xxx, July 1907, p. 36. t These deposits reach a tot at proved thickness of 233 ft.

102

DAVID

woo LACOTT

ON THE GEOLOGY OF

ice or other barriers to form lakes), seems to have played an important part. * Striated surfaces, and boulders belonging to several "foreign" localities have been found within the area. The Scandinavian ice seems never to have invaded the district, although some boulders of Norwegian rocks which have been found in South Durham (near the end of Castle Eden Dene) and Yorkshire lead us to think that it must have ultimately nearly reached it, and this sheet may have been the barrier producing the lakes in which the peculiar leafy clays, etc., of the Tyne valley were deposited. In the true boulder-clay fragments of rock have been found from the Scottish Highlands, South of Scotland, northern part of the Lake District, the Cheviots, and the north and west of Northumberland, and in the other type of deposit chalk and flint also occur. The two last-named rocks may have been carried by the Scandinavian ice from an outcrop in the North Sea and then floated up the Glacial lakes occupying the Tyne valley on detached masses of icc. The Lake District ice was the first to retreat from the area and from the land to the west. Dr. Smythe has shown that a Glacial lake occupied the country to the north-west of Newcastle held up by ice coming down the east coast from the South of Scotland and Cheviot area at the latter part of the Glacial period, and he has mapped a series of dry valleys, "slacks" or "swires," cut by the overflows from this lake, e.g., N ewbiggin Dene, west of Kenton. t In North-East Durham two well-developed Kaims occur. One of these constitutes the main mass of Warden Law and the surrounding hillocks, and consists of some 200 ft. of gravel and sand; the other, which is being worked at the present time for sand, forms the winding hill of Grindon. Round Fulwell and Cleadon Hills there is a deposit of sand and gravel reaching IS0 ft. above sea-level, resting on stony boulder-clay, and containing marine shells. Taking into account all the evidence, I regard this as a true raised beach.j Another explanation would be that it marks the height to which the waters of an ice-dammed lake were held up by the North Sea icesheet at the end of the Glacial period. In either case the whole of the eastern part of the Tyne valley and surrounding district must have been submerged. A deposit of peat, containing roots and stems of trees and nuts, that is exposed from time to time in Whitburn Bay seems to be a growth of vegetable material in situ, and is thus a submerged • For a description of these deposits see Mr. E. Merrick,

II

Superficial Deposits

around Newcastle." Proceedings Univ, Of Durham Phil. Soc., vol, iii, pt. 3 (I90B-g), p. '41. t "Glacial Phenomena between Tyne and Wansbeck." Trans, Nat. llist. Soc. ' Northumberland, Durham ana Newcastle, vel, iii, pt. I (New Series) '908, p. 79.

1: In a water-worn cave at upper margin of these deposits, remains of the Wild Boar, Badger, Red Deer, Great Auk. and Man were found. Remains were also found In a cave In the Magnesian Limestone near Ryhope Colliery.

NORTH-EAST DURHAM AND SOUTH-EAST NORTHUMBERLAND.

103

forest.* Deposits of peat also occur at Forest Hall near Newcastle, at Curry's Point, and elsewhere. Horizontally-bedded sand dunes occur to the north of Whitley Bay, and those of a cross-bedded hillocky type are developed along the Blyth sands. Since the Glacial period the present river courses have been developed. The Wansbeck and the Blyth have been eroded at the sides of the pre-Glacial "Sleekburn," the Tyne flows more or less along its former course, while the Wear has carved an entirely new course, mainly through rock from Durham to the sea at Sunderland, producing the gorge-like nature of this river near its mouth. t REFERE~CES.

Geological Survey Maps I in. scale. Drift and Solid. South-East Northumberland, Sheet lOS, N.E. North-East Durham. Sheet lOS, S.E. GENERAL.

1886. 18g7.

IgIO.

LEBOUR, G. A. L.-" Geology of Northumberland and Durham." WOOLACOTT, D.-" Geology of North-East Durham" (a popular work). Sunderland. LEBOUR, G. A. L.-" Geology" in Victoria History of County Durham. GARWOOD, E. J.-" Geology of Parish of Tynemouth, History of Northumberland," vol. viii. -------.-"Geology of Northumberland and Durham," "Geology in the Field." Geologists' Association. COAL

MEASUR~:S.

BUDDLE, JOIlN.-" Synopsis of the Scams of Coal in the Newcastle District." Trans. Nat. Hist. Sac. Nor/humber/and, vol, i, p, 2r5. 186r. KrRKBv, I. W.-" On the Remains of Insects from the Coal Measures of Durham." Ceol. Mag., vol. iv, pp. 388'39°. 1887. BROWN, M. WALTO~. "A further attempt for the Correlation of the Coal Seams of the Carboniferous formation of the North of England." North of England Inst, ot Mining Eng., vol. xxxvii, pp·3- 2 I • Ig06. LEBOVR, G. A. L., and SMYTHE, J. A.-" On a Case of Thrust and Unconformity at Whitley." Quart. :!ourn. {;tol. Soc., vol. lxii, pp·53O-55!. KIRSOPP, J.-" :o.fap and Vertical Sections of the Northumberland and Durham Coalfield." IgI r. Bu RTO:-l', R. C.-'· On the Formation of Kaolinite in Coal Measure Shale." Proc, Univ. Durham Phil. Soc., vel, iv, pt. I, p. 24. • Antlers of elYV,,' elaphu: (Red Deer) ha ve been found in this deposit, and In Silt of Jarrow Slack. t The lurning of the river out of Its old coarse was prob.ably owing to the boulderclay having been thicker on tbe west (Ihe d!recllon from ~hlCh the ice came) than ?n the east side of ilS old filled-up valley, but It may have Originally started to denude us course on the edge of the retreating ice-sheet.

1°4 1912.

DAVID WOOLACOIT ON THE GEOLOGY OF

HASELHURST, S. R.-" A Case of Megascopic Pseudo-Stromat ism in the Coal Measure s of Northumberland," Proc, Unio, Durham P hil. Soc., vol. iv, pt. 3, p. 162.

IGNEOUS DYKES. TEALL, J . J . H .-" Petrologic al Notes on the North of England Dykes." Qua,·t. Y ourn. Geol, Soc., vol. xl, pp. 209-46. 19 10• HE SLOP, MIss M. K ., and SMYTHE,J. A.-" On a Dyke at Cr ookdene, No rthumbe rland and its Relation to the Coll ywell, Tynemouth, and Morpeth Dyke s." Quart, y ou,.n. Geoi, Soc., vol. lxvi, pp.I -18. PERMIAN.

1835. 18 4 8 . 1849. 18 57. 1863. 1 864.

1866.

1883. 1889· 18g1. 1902.

I g07· 1909. Ig1 I.

H UTTON, W.-" N otes on the New Red Sandstone of the Cou nty of Durham below the Magnesian Limestone." Tran s. Nat. Hist; Soc. Northumberland, etc., vol. i, pp. 60-74. SEDGWICK, A.-" Intern a l Structure of the Magnesian Limestone." Trans, Geol. Soc., Second Series, vol. iii, p. 37. HOWSE, R.-" Catalogue of the Permian Fossils of Northumberland and Durham." K ING, W.-" Monograph of the Permian Fossils." Pal. Soc., 1849. HOWSE, R.-" N ote s on the Perm ian System of Durham and Northumberland." A nn. and J1fag. N at . Hist., J an. 1857, p. 6. DAGLlSH , J., AND FORSTER, G. B.-li O n the Magnesian Lime stone of Durham." Tra ns. N . of E ng. Inst; Min. Eng., vol. xiii, p. 205. KIRKBY, J. W._u On So me Rem ain s of Fi sh and Plants from the Upper Lime stone." Quart. y ourn. Geol. Soc., vol. xx, pp. 345-358. BROWELL, E. J. , AND K IRKBY, J. W.-" On the Chemical Com position of the Magnesian Limestone an d the Associate d Beds of Du rham ." Na t. H ist, Tram. No rth umberla nd and Dur ham, vol. i, pt . II, P P· 2 0 9- 213· LEBOUR, G . A. L.-" On the Breccia Ga shes of the Durham Coast." Tr ans. N . E ng. Ins t, M in. E ng., vol. xxii i, p. 165. HOWSE, R.- " Gui de t o Collection of Local Fossils in N at. Hist. Mu seum , New castle. " GARWOOD, E. J .-"On the Or igin and Mode of Form at ion of the Concretions in t he Mag-nesian Lim est ones of Durham." Geol . Mag., New Series, vol. viii, pp. 433-440. LEBOU R, G. A. L.-" The Marl Slate and Yell ow Sands of NorthTrans. In st: Min . Eng., vol. xxiv, umb erland a nd Du rh am." pp. 370 -391. WOOLACOTT, D._" E xplan ation of the Claxheugh Secti on. " Nat. Hist, Trans. N ort humberland, etc., vol. xiv, pt . 2, p. 2II . ABBOTT, G.-" Cell ular Magnesian Limestone." Quart. yourn . Geoi. Soc., vol . lix, p. 51. - - - - --.- " Con creti on s in S.E. N aturali st." WOOLACOTT, D.-" On a cas e of Thrust an d Crush Bre cciation in the Magnesian Limestone , Co unty Durham" (Marsden Section). Proc. Univ . Durham . Phil. Soc., Memoir NO.1. H ASELHURST, S. R .- " S ome Phen omena in the Permian of Northumberland a nd their relat ionship to sections in D urh am and Cumberland." Univ. Du rham Phil. Soc., vol. iv, pp. 15-24.

NORTH-EAST DURHAM AND SOUTH-EAST NORTHUMBERLAND.

IgII.

105

WOOLACOTT, D.-" The Stratigraphy and Tectonics of the Permian of Durham (northern area)." Abstract in Quart. Jount. Geol, Soc., vol. lxvii, p. 312. WOOLACOTT. D. "The stratigraphy and tectonics of the Permian of Durham (northern area). Uniu. of Durham Phil. Soc., vol. iv., pt. 5.

Ig12.

GLACIAL AND RECENT. WOOD, N., and BOYD, E. F.-" On a ' Wash' or Drift through a portion of the Coalfield of Durham." Trans. N. Eng. Inst. Min. Eng., vol. xiii, p. 6g. 1864. HOWSE, R.-" On the Glaciation of the Counties of Durham and Northumberland." Trans. N. Eng. Inst. Min. Eng., vol. xiii, p. 16g. Ig05-1909. WOOLACOTT, D.-Two papers on "Pre-Glacial Wash of the Northumberland and Durham Coalfield." Proc. Umv. Durham Phil. Soc., vol. i i, pt. 5. P: 205, and vol. iii, pt. 3, p. 153. Ig05. .-" The Superficial Deposits and Pre-Glacial Valleys of the Northumberland and Durham Coalfield." Quart. yourn. Ceol. Soc., vol. lxi, p. 8g. Ig07. - - - - - - - . - " The Origin and Influence of the Physical Features of Northumberland and Durham." Geogr. Journ., vol. xxx, P·3 6. Ig08. SMYTHE, J. A.-" Glacial Phenomena between Tyne and Wansbeck." Trans. Nat. Hist..Soc. Northumberland, etc., vol. iii, pt. 1 (New Series). p. 7g. Igog. MER HICK, E.-" Superficial Deposits around Newcastle." Proc. Uniu. Durham Phil. Sor., vol, iii, pt. 3, p. 141. Ig12. SMYTHE, J. A.-" The Glacial Geology of Northumberland." Nat. Hist. Soc. Northumberland, etc., vol. iv (New Series), p. 86. 1864.

DESCRIPTIONS OF THE PLATES 27, 28. PLATE 27. FIG. I.-SECTION FROM TYNEMOUTH TO ClJLLERCOATS BAY. Vertical Scale, 120ft. to I in.

Horizontal Scale, Ii miles to 1ft.

D.S. Coal Measures with evidences of thrusting at the base of Tynemouth Cliff and south (and to the north) of Cullercoats Bay. The thrust and unconformity in the Coal Measures at Whitley, described by Lebour and Smythe, lies a little to the north of this section (Qua,·t. yourn. Geoi. ,s'oc., vol. lxii, 1906, pp. 550-551). The two Permian outliers of Tynemouth Cliff and Cullercoats Bay are shown. I. Brecciated Middle Limestone. 2. Thrust plane with disturbed beds beneath. 3. Lower Limestone (with arenaceous limestone on Tynernouth Cliff). 4. Marl Slate. 5. Yellow Sands. U. Unconformity between the Coal Measures and Permian. F. Ninety Fathom" Dyke." FI. Fault south of Tynemouth. D. Tynemouth Basaltic Dyke. The exposure is covered more or less along its whole length by boulder clay. PROC. GEOL. Assoc., VOL. XXIV, PART 2, 1913.J 8

106

DA VID WOOLACOTT O N

F IG. 2.-SECTION ACROSS

P ERM IAN

TH~:

GEO LOG Y O F

OUTCRO P FROM

DOWN HI LL

TO R OKER.

C.M . Coal Meas ures. 1. Yellow Sa nd s. 2. Marl S late . 3. H ig hly disturbed Lower Limestone. The sect ion of this rock endeavours to give a gen era l impr ession of th e exposur es seen along flank s of Boldon H ills-a t base of Down H ill and near Hylton Ca stle . Thi s di sturba nce is on the same horizon as the sheared and tilted beds ab ove the thrust plane in Frenchman' s Ba y . 4. Fo ssiliferous Un bedd ed Middle Limestone, often brecciated . 4A. Breccia (probably a brecciated pa rt of Fossilifero us Limeston e with fossils-if an y were originally present-oblite rated) . 5. Bedded yell ow Middle Limestone, which are high ly bre cciated along t he ban ks of the \Vear west of Sunderla nd Bridge, correspondi ng to brecc ia shown above X . T he bre cciated beds have been noted by K irk by to occur bene ath Upper Limestone in Ful well Q ua rries. X . F ish bed of Fulwell, not exp osed along surface, but worked in to at base of Concretiona ry Li mestone. This bed corre spon ds in position with Flexible Li mestone seen abo ve Brecciated Beds a long River Wear beneath Sunderland Bridge. 6. Upper Con cretiona ry Li mest one with the most varied development of conc retionary struct ures and occas ional fish rema ins. F olded and sometimes bre cciat ed . 7. Upper Yellow Lime ston e of Roker. F. Fa ult s. The section is partly obscured by boulder clay , B C, which is only shown above the Coal Measures. F IG. 3. -SEC1lON ACRO SS THE PERM IAN O UT CROP FR OM H IGH D OWNS QUARRY, BETTON, T O S UNDE RLAN D, SHOWING THE S EQ UENCE IN THE NORTH OF D llHF. AM.

C.l\L Coal Meas ure s. 1. Yell ow Sands. 2. Marl Sla te. 3. Lo wer Regularly-bedded Limestone seen in High Downs Quarry, B ett on (see photograph, Plate 22) a nd (the to p beds) in T unstall H op e, a valley to south-west of Tun stall H ills. This bed probably thick ens eastward. 4- and 5· Middle Magnesian Lime stone s. (4) Are un bedded , ge nerally highly fossiliferous rocks , thinning rapidly on eastern ma rg in and replaced by bedded yell ow rocks, often highl y brecciated (5 ) . On the south-eastern flank s of T unstall H ill (ne ar Ry hope Colliery) the re is a bed of marly mi caceous san d bet ween + and S. 6 and 7. The Upper Limestones. The lower (6) is th e Con cretionar y Limestone of Mowbra y Pa rk (Bildon Hill), Sunderl and, a nd the upper the bedded yellow limestones of the foreshore, Sunderland , and of Roker. 8. K aim-like mas s of sand and gra vel. Other superficial dep osits a re omit ted . T he boulder clay, etc., is most thi ckly dist ributed over s. Disturbances in the Limestone (Faults, etc) a re omit ted as they do not alter the genera l sequence,

NORTH-EAST DURHAM AND SOUTH-EAST NORTHUMBERLAND. PLATE

107

28.

FIG. I.-SECTION FROM THE SOUTH OF MARSDEN BAY TO THE TROW ROCKS, SOUTH SHIELDS.

Yellow Sands and Marl Slate. There are two or three limited exposures of these beds in Frenchman's Bay. 2. Lower bedded Limestones. 3 Disturbed beds produced by shearing of the upper beds of the Lower Limestone along Major Thrust Plane. 4. Brecciated Beds of Middle Limestone-Breccia and Negative-Breccia. Portions of original bedding are preserved at intervals. The top of these beds in cliff opposite the Velvet Beds is very irregular. They ha ve been forced up into the regularly bedded rocks above. S. The brecciated, folded. fissured and cleaved area is one of the most interesting exposed in the district, as the evidence for thrusting is perhaps most clearly seen in this section. This part of section is drawn in great detail in the memoir on " A Case of Thrust and Crush-Brecciation in the Magnesian Limestone, County Durham," and the southern part of it is shown in the section below, Fig. 2. 6. A concretionary limestone with fossils. 1.

FIG.

2.-SECTION AT SOUTH END OF MARSDEN BAY, SHOWING HIGHLY-DISTURBED AREA PRODUCED BY THRUSTING. MOVEMENTS APPEAR TO HAVE TAKE:'-l PLACE TOWARDS THIS AREA FROM Two OPPOSITE DIRECTIONS, VIZ.: ro-' TO 15° N. OF vV., AND 10° TO ISO S. OF E.

It is the most intensely shattered area exposed in a continuous section,and shows some of the chief phenomena produced by the thrusting. M L, Middle bedded yellow Limestones; FL., Flexible Limestone, which is traceable beyond the fault F, at base of cliff. Rocks above belong to the lower Upper and were originally very irregularly bedded, consisting of yellow and brown Limestones with thick irregular beds of light grey compact limestone (V). C (same as 6 in Plate 28, fig. I) is a concretionary greystone of the Upper Limestone containing invertebrate fossils. There is, except at F and between U and R, little vertical displacement in the section. Near the Grotto the Flexible Limestone is intensely shattered. At P the ends of some wedge-shaped beds appear to have been bent back on themselves, and there is much slipping and minor thrusting in beds at Q. At R a vertical cleavage structure can be seen to pass into a brecciated rock. Above Rr the beds ale folded and buckled, the softer beds are squeezed out and the whole mass brecciated against an irregula! plane seen running obliquely up above S. This part appears to have stood white the rocks all either side have been pressed in towards it. At T the breccia is intensely folded, and at U the gradual passage from bedded to shattered rocks is well shown. The grey crystalline rock is highly cleaved at V, and a portion of it is apparently thrust into beds above at X. Breccia and strain-slip planes are developed at Y. W is a typical vertical breccia-fissure, and Z is a V-sbaped Breccia-gash. The fault F is later than the thrusting. The cleavage in the area runs 10° to IS° E. of North. A detailed section of tbe exposnre to the north of this area is given in my memoir on the Ma rsden district.