The geology of the South Wales coal-field ..

Geological Survey of Great Britain · 1899 · Historical

The country around Bridgend, which is described in this the Sixth Part of "the Memoir on the Geology of the South Wales Coal Field

Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.

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Uemoirs Of The Geological Survey.

England And Wales.

The Geology Of The

South Wales Coal-Field.

Paet Vi.

The Country Around

Bridgend.

BEING AN ACCOUNT OF THE REGION COMPRISED IN SHEETS 261, 262 OF THE MAP.

By

Aubrey Strahan, M.A., F.R.S., F.G.S.,

And

T. C. CANTRILL, B.Sc.

(With parts by H. B. WOODWARD, F.R.S., F.G.S., and R. H. TIDDEMAN,

M.A., F.G.S.)

PUBLISHED BY ORDER OF THE LORDS COMMISSIONERS OF HIS MAJESTY'S TREASURY.

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2O1, 262.

Memoirs Of The Geological Survey.

England And Wales.

The Geology Of The

South Wales Coal-Field.

Pakt Vi.

The Country Around

Bridgend.

BEING AN ACCOUNT OF THE REGION COMPRISED IN SHEETS 261, 262 OF THE MAP.

By

Aubrey Strahan, M.A., F.R.S., F.G.S.,

And

T. C. CANTRILL, B.Sa,

(With parts by H. B. WOODWARD, F.R.S., F.G.S., and R, H. TIDDEMAN,

M.A., F.G.S.)

PUBLTSHBD BY ORDER OF THE LORDS COMMISSIONERS OF HIS MAJESTY'S TREASURY.

London:

FEINTED FOR HIS MAJESTY'S STATIONERY OFFICE, BY WYMAN & SONS, LIMITED, FETTER LANE, E.C,

And to be purchased from

E. STANFORD, 12, 13, and 14, LONG ACRR, LONDON ;

JOHN MENZIES&Co., ROSE STREET, EDINBURGH;

HODGES, FIGGIS & Co., GRAFTON STREET, DUBLIN;

From any Agent for the sale of Ordnance Survey Maps ; or through any

Bookseller from the Ordnance Survey Office, Southampton.

Price, Is. 6<L

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P K E F A C E.

The country around Bridgend, which is described in this the Sixth Part of "the Memoir on the Geology of the South Wales Coal Field, is illustrated in Sheet 261-2 of the New Series Oneinch Map. The area is occupied for the most part by Lower Lias, and by the Rhaetic and Keuper subdivisions of the Trias, but it includes a small part of the South Crop of the Coal Field and numerous inliers of Carboniferous Limestone which project through the Secondary strata.

The original survey was made by Sir H. T. De la Beche, Sir W. E. Logan, D. H. Williams, W. T. Aveline, and T. E. James on the Old Series One-inch Maps 20. 36, and 37, which were published about the year 1845. The separation of the Rhaetic strata and a revision of the area south of the Coalfield were begun by H. W. Bristow in 1864, and completed by Mr. H. B. Woodward in 1871. The revised edition was published in 1873.

The re-survey was made on the six-inch scale under the superintendence of Mr. Strahan and was published in 1901. The western half of the map was surveyed by Mr. Tiddeman, the eastern half by Mr. Oantrill, with the exception of the northeastern margin which was surveyed by Mr. Strahan. The present volume includes the description of the eastern half by Mr. Cantrill and of the western half by Mr. Strahan, based on the notes left by Mr. Tiddeman on his retirement from the staff. Mr. Woodward supplies an account of the Liassic and Rhaetic tracts which were examined by him for the purposes of the General Memoir on the Lias of England and Wales. The principal changes made in the map as the result of the re-survey consist in the extension of the Lias of Cowbridge over a district formerly thought to be occupied by Old Red Sandstone, the discovery of further inliers of Carboniferous Limestone in the Lias near Wick, and the distinction of the literal from the normal type of Lias throughout the whole area.

The Old Red Sandstone includes, in its upper part, some quartzitic and pebbly grits ; the whole, so far as exposed, appears to correspond in character to the Brownstone subdivision, but in the absence of fossils it cannot be definitely referred to either Upper or Lower Old Red Sandstone.

The Carboniferous Limestone maintains the same general character as in the Cardiff district. Thick but impersistent limestones appear locally in the Lower Limestone Shales.

The Millstone Grit is covered for the most part by Secondary Rocks. It consists of shales with subordinate sandstones, and belongs therefore to the type which characterises the South Crop rather than to that of the north side of the Coal Field.

The small tract of Coal Measures which falls within the margin of the map contains representatives of the lower seams,

7665. 750.— Wt. 18408. 12/04. Wy. & S. 2044r. A

(iv)

which, however, have been only partly proved and worked to a very limited extent.

The Old Red Sandstone and Carboniferous Hocks were thrown into great east and west folds and subjected to denudation on an enormous scale before the Secondary Bocks were laid down upon them, so that those later strata rest unconformably upon all the earlier formations. The detailed mapping moreover has rendered it possible to recognise many of the features of the pre-Triassic landscape, and to trace step by step the submergence cf the old land-surface beneath the Keuper and Rhaetic waters, and its final disappearance in the Liassic sea. The Carboniferous Limestone, then as now, stood out in bold escarpments and formed an island, the margin of which has been traced with much precision.

Some later (post-Liassic) movements have been worked out in detail. They follow generally the lines of the older disturbances, though they rarely agree with them precisely in position.

The map includes a part of what appears to have been the southern margin of the South Wales glacial system. In its north-eastern part large tracts are overspread by a gravelly drift derived from the north and north-east and partly from the immediate neighbourhood. At Pencoed this local drift overlies a stiff boulder-clay containing boulders from a distant source. These erratics, which were first noticed by the late John Storrie, have been microscopically examined by Messrs. Howard and Small, with the result of showing that they can be matched in West Pembrokeshire.

In Chapter XI will be found an account of the economic products of the district. The most important of them was the haematite yielded by the Carboniferous Limestone where that rock was or had been overlain by Keuper. The mines are now all abandoned. In the same chapter the principal sources of water-supply are enumerated.

The map is issued in two editions. On the edition for Solid Geology the glacial deposits are omitted, while on the edition for Superficial Geology, those deposits are shown by colour, as well as the Solid Geology, where not concealed by them.

J. J. H. Teall,

Director. Geolo'jtcal tinrrei/ Office,

.jy, JcniLi/ii titiwt, London, 4th November, 1904.

(v)

Table Of Contents.

Page. PREFACE BY THE DIRECTOR iii

CHAPTER I. — INTRODUCTION AND TABLE or STRATA 1

Chapter Ii. — Old Red Sandstone 4

CHAPTER III.— CARBONIFEROUS LIMESTONE SERIES. (1) Eastern part;

(2) Western part 6

Chapter Iv. — Upper Carboniferous Rocks : — Millstone Grit.

Coal Measures 16

CHAPTER V. — TRIAS : — Introduction. Keuper : — Eastern park Western

part 20

CHAPTER VI.— TRIAS (cont.) Rhcetic Beds .'—Introduction. Eastern part.

Western part 35

CHAPTER VII. — LIAS: — Introduction. Eastern part. Western part.

Coast Section, Sutton to Aberthaw - - - - - 58

Chapter Viii. — Faults And Disturbances 89

CHAPTER IX.— GLACIAL DEPOSITS -.—Introduction. Eastern part.

Western part 95

Chapter X. — Post-Glacial Deposits 103

CHAPTER XI. — ECONOMIC PRODUCTS : — Building Stone and Road Metal.

Lime, Cement and Silica. Galena. Hcematite. WATER SUPPLY - 106

(vi)

List Of Illustrations.

Plate. Gliff at Southerndown showing Lower Lias resting unconformably upon Carboniferous Limestone. From a photograph by R. H. TIDDEMAN Frontispiece.

Fig. 1. Map of pre-Triassic Folds. By T. C,- GANTRILL 8

i; 2. Map showing Triassic Geography. By A. STEAHAN - - -24

„ 3. Section of cutting south of St. Mary Church Road Station. By

T. 0. Oantrill 43

„ 4. Section at south end of Cowbridge cutting. By T. C. GANTRILL 46

,, 5. Section of the cliffs at Sutton, Southerndown and Dunraven.

By H. B. WOODWARD 63

„ 6. Fault in Lower Lias, east of Dunraven Castle, Glamorganshire.

By H. B. WOODWARD 87

„ 7. Section across Llanbleiddian Hill. By T. G, GANTRILL - - 91

„ 8. Section from the Coast near Sutton to near Laleston. By A.

Strahan 92

„ 9. Transverse section, Mwyndy Mine. By S. VIVIAN - - - 108 „ 10. Transverse section, Mwyndy Mine. By S. VIVIAN - - - 108 „ 11. Transverse section, Trecastle Mine. By S. VIVIAN - - - 109

Geology

Of The Country Around

Chapter I.

Introduction And Table Of Strata. By A. Strahan.

This map includes the western half of the tract of Secondary rocks which constitutes the Vale of Glamorgan, and extends northwards to the south crop of the coalfield. The Triassic and Liassic strata rest unconformably upon highly tilted Carboniferous and Old Red rocks. Without doubt they once overspread the whole vale, but denudation has bared the more prominent features of the surface on which they were laid down. Among the pre-Triassic features thus revealed may be mentioned the escarpment of Carboniferous Limestone which runs from Bonvilston to Cowbridge on the south side of the Cowbridge-Cardiff anticline ; the corresponding escarpment which forms the northern limb of the same anticline ; some tracts of Old Red Sandstone between these two ; the limestone which appears at the surface in several domes on the line of this anticline westwards ; and lastly, the rocks forming the southern margin of the coalfield, which there is reason to think formed approximately the limit of the area originally overspread by the Secondary rocks referred to.

The waste undergone by these old physical features is evidenced by the vast amount of debris which they have contributed to all the Secondary strata, and, no doubt, accounts for the fact that none of them rise to any great height. The limestone reaches its greatest elevation above the sea at Lillypot, 447 feet, at St. Jlilary Down, 440 feet, and at Tair Onen, 424 feet. Elsewhere in the south escarpment it falls short of 400 feet. The northern escarpment reaches 400 feet south of Llanharry, but in most other parts falls short of 300 feet. The domes further west slightly exceed 300 feet in places, but never reach 400 feet. The Trias and Lias generally form a gently undulating tract occasionally reaching 300 feet above the sea.

7665. B

2 Introduction.

The region is drained by the Ely, the Dawen, the Ewenny, and the Ogmore (Ogwr) rivers, and a few small streams which have independent courses into the sea (Fig. 2, p. 24). The Ely rises in the coalfield, on the north side of the Pontypridd anticline. Flowing across this and across the south crop it traverses the escarpment of the Carboniferous Limestone at Miskin, and thus gains the Cowbridge-Cardiff anticline. Thence it runs eastwards to Cardiff, along a valley which tends to follow the anticlinal axis. The Dawen rises on the north side of the Cowbridge-Cardifi anticline, but keeps its course across it to the coast at Aberthaw. The Ewenny and Ogmore rise in the coal-field and cross the south crop on to the Liassic plain, keeping a south-westerly direction to their union at Merthyrmawr, and thence to the sea.

Except for a colliery near Pont Clun, there are no mines in operation within the area under description, nor are there any large manufacturing towns, the population generally being occupied in agriculture. There are lime-works, however, at Stormy, Bridgend, Llanharry, and Aberthaw.

As would be anticipated from the geological conditions, there is much variety in the land in the northern part of the map. Calcareous soils, however, whether in the form of Triassic conglomerate or Liassic and Carboniferous limestones, predominate, and much of the land is, or has been, under the plough. The Lias which occupies most of the southern part of the map yields generally a stiffer claysoil, much of which is under pasture. Merthyr-mawr Warren, Newton Burrows, and Kenfig Burrows are large tracts of blown sand.

From a purely geological point of view, the relation of the Trias and Lias to the older rocks over which they were distributed constitutes one of the most interesting features in the region. In previous Parts of this memoir, it has been explained that these older rocks have been bent into sharp folds, ranging in an east and west direction, and that the flexures are obviously of pre-Triassic age, inasmuch as the Trias lies horizontally upon them. This fact is admirably illustrated in the Cowbridge-Cardiff anticline ; for that great upheaval was not only accomplished before the Triassic era commenced, but there was time for the removal of so much material along the axis of upheaval as to convert it into a valley, which subsequently was filled up by horizontal sheets of Secondary rocks. Especially interesting also are the proofs of the gradual submergence of many limestone-crags, which for a time formed islands in the Liassic waters.

It resulted from the unusual conditions under which they were laid down that the Secondary rocks assumed an abnormal character. The Keuper Marl passes into a limestone-breccia near its margin, the upper beds showing the change as fully as the lower. The Rhyetic group loses its character as a shale with thin limestones, and becomes a thick white and yellow sandstone distinguishable with difficulty from Millstone Grit ; while the Lias not only becomes conglomeratic near its margin, but assumes a variety of abnormal forms, some of which closely simulate Carboniferous Limestone,

Table of Strata. 8

The following subdivisions of the rocks and of the superficial deposits are distinguished by colour upon the map : —

Table of Strata.

Blown Sand

Alluvium

Peat VRecent and post-Glacial

Estuarine Mud

River Gravels (terraces) J

Boulder Clay and contemporaneous \r, . , Sand and Gravel /W

Lower Lias W .

Lower Lias of a literal type J ]

Rhaetic "j

j£e (Green and red marls passing into Trias Breccia and conglomerate J

Lower Coal series Coal Measures

Limestone and \Carboniferous Limestone

Shale J

Red sandstone with |old Red Sandstone

Quartz-conglomerate J

7665. B 2

Chapter It.

Old Red Sandstone. By T. C. Cantrill.

The Old Red Sandstone comes to the surface in someinliers at the western end of the Cowbridge-Cardiff anticline. The largest and most conspicuous is that which extends from Groes-faen on the north-east past Miskin Manor, and widens out in the high grounds of Hensol Park on the south-west. Much, however, of this outcrop is concealed by drift.

The beds consist of red sandstones and marls with impersistent bands, at about 150 feet from the top, of red quartzitic sandstone or grit containing numerous small quartz-pebbles. Blocks of these conglomerates abound on the fields immediately south of Llwyn-y- penau, but a road-cutting south of Crofftau shows only dull-red shales, marls, and sandstones, some of the last being micaceous. The next exposures occur at the northern extremity of Hensol Park, where the pebbly grits form the higher parts of a picturesque escarpment extending for a mile in a south-westerly direction. The grits dip about north-north-west at 25° to 30°, but at the south-west end of the ridge they roll over and dip south at 30° in a quarry opposite the western horn of the lake. Below the conglomeratic horizon there lie some thin-bedded red sandstones with thin grit-bands, which are exposed in some small quarries at the northern extremity of the Park. The beds above the conglomerates, though nowhere well seen, appear to be soft sandstones and marls.

The Old Red Sandstone mass of Hensol Park, although apparently consisting of an anticline the axis of which trends about east-northeast and west-south-west, has weathered out as a north-east and south-west ridge, the features seemingly ignoring the geological structure. This denudation dates probably from pre-Triassic times, when the ground no doubt stood up as a hill while the Triassic deposits were accumulating in the surrounding waters.

The conglomeratic beds and the overlying strata may be referred to either the Grey Grits of the Upper Old Red Sandstone, or to the plateau-beds* of the Brownstones of the north crop of the coalfield. The beds be-low the conglomerates resemble the Brownstones.

Still farther west a minute ir.lier of Old Red Sandstone occurs at Llwyn-iiwydog, on the west side of Morfa Ystradowain. The rock crops out on a wooded bank 100 yards south of the farm, and forms a scarp overlooking the marsh ; it consists of micaceous yellow and red gritty sandstone containing flakes of green marl. It dips about

The Country ;t round. AU-rthyr Tydfil (Man. 6W. Surv(-y), pp. C, 7.

Old Red Sandstone. 5

north 40° west, towards the lowest Carboniferous Limestone strata exposed in the farmyard. Along its south-east side the inlier appears to be cut off by a fault which throws down the lowest Carboniferous beds under the marsh.

Turning now to the southern side of the main anticline we have evidence of another exposure of Old Red Sandstone along the foot of the Carboniferous Limestone escarpment of Cottrell, though it is almost wholly concealed by drift. A faint feature parallel to the strike of the Lower Limestone may be attributed to the outcrop of the pebbly red quartz-grits which lie about 150 or 200 feet below the top of the Old Red Sandstone. Though they are nowhere exposed, some little debris which occurs on the slopes south of Ty'n-y-pwll suggests their presence.

The next section is afforded by the dingle south of Cae'r-wigau-isaf , soft red marly sandstones and gritty sandstones are visible about 100 yards south of the farm, and are followed at a higher horizon by yellow flags, exposed in a small quarry a few yards below Cae'r-wigau-ganol. The beds dip south 30° west at about 15°. These yellow flags appear to lie at about the same horizon as the pebbly red grits, and both are doubtless of Upper Old Red Sandstone age.

To the west of this dingle the country is so thickly overspread with gravelly drift as to make the course of the Old Red Sandstone outcrop a matter of inference. On the old series geological map (Sheet 36) it was represented as extending north-westwards over a large area north of Welsh St. Donats. There is, however, direct evidence that much of this ground is occupied by Lias (see p. 69), though the drift precludes our gaining a detailed knowledge of the structure.

The last exposure of Old Red Sandstone occupies the northern part of Stalling Down, near Cowbridge. The rock comes to the surface in a broad anticline trending a little north of east and south of west. Good sections are rare, but there is abundant debris of pebbly red grit scattered over the fields west of the Down, and on the Down itself there is a small quarry, some 300 yards northwest of Llan-Chwian-fach, in thin irregularly-bedded red sandstones and grits, containing a few small quartz-pebbles. All the sandstones appear to be more or less quartzitic and frequently pebbly. They no doubt belong to the upper division of the Old Red Sandstone.

Chapter Iii. Carboniferous Limestone Series.

(1). Eastern Part. BY T. C. CANTRILL.

The Carboniferous Limestone Series of the map under description shows a considerably greater development than that of the neighbourhood of Cardiff (Sheet 263). It presents the following descending sequence : —

Carboniferous Limestone Series.

Light-grey oolite, thick-bedded, forming about

half the mass. Dark-blue crinoidal limestone, thick-bedded,

Main Limestone.

forming the lower half. The lowest beds

are brown and grey earthy limestone, thinbedded, with shale -partings ; fossils (crinoids and spirifers) silicified.

/-Dark shales weathering yellow (200 to 300 feet)*

T T. Q, , including bands of limestone from a few

Lower Limestone Shales, J incheg tQ ( the Lower Qr

I " Bastard " Limestone).

From observations of dip at Crofftau, a mile east of Miskin, the thickness of the Main Limestone appears to be about 1,600 feet, and that of the Lower Limestone Shales about 275 feet, including 75 feet as the thickness of the Lower Limestone. North of Cardiff, on the contrary, the thickness of the Main Limestone amounted to only about 700 feet, and that of the Lower Limestone Shales to 150 or 200 feet.*

-There are numerous local modifications of these types of limestone ; sometimes the grey oolite takes on a darker hue owing to a greater amount of bituminous matter, and all the rocks are liable in places to a purple stain from the Trias. The Lower Limestone is usually a massive brown or purple oolite, frequently rich in crinoidal remains. Its upper and lower limits are thin-bedded and shaly.

All varieties of the limestone have been at one time or other extensively quarried and burnt for lime throughout the district, and several kilns were still in operation in the neighbourhood of Groesfaen. Mwyndy, and Miskin. The Llanharry Limestone Co. crush the rock, chiefly grey oolite, for roadstone, and also burn it for lime, at Llanharry Station on the Cowbridge railway. The limestone is worked for roadstone for local use at several small quarries.

The Country around Cardiff (Mem. Oeol. Survey), p. 22.

Carboniferous Limestone. 7

The Carboniferous Limestone forms the two limbs of the great Cowbridge-Cardiff anticline. On the eastern edge of the map this structure is obvious. For some two miles westwards of Cottrellthe basal scarp is easily traceable, and the dips gradually change from about south-south-east to south, and then to south-south-west, but beyond that distance, complications due to subsidiary folding set in ; and here too the limestone-base disappears under the Lias and drift southeast of Welsh St/Donats. The south-south-westerly dip persists as far as Pen-y-ffordd-fawr, where the limestone formerly quarried is probably not far above the base. Here again the outcrop is lost to view under a patch of Lias ; but it is clear that the limestone rolls over in a gentle anticline somewhere near Pen-y-flordd-fawr, for at Welsh St. Donats it dips north-west. The base therefore should trend towards the north-east ; but it must swing round again into a south-west direction and form a syncline somewhere between Welsh St. Donats and Ystradowain in order to gain its known position at Pen-llin Castle, where a southerly dip prevails. The faulted anticline of Pen-llin may be regarded as lying on the axis of the main anticline, and on this axis lies the approximately horizontal limestone of Pen-y-lan south-east of Llansannwr. North of this axis the general dip is towards the north-north-west, which carries the base past Llansannwr and Ystradowain where, however, a sharp syncline interrupts the regularity of outcrop. Beyond this point the minor folds die out and the base runs continuously across the district past Tal-y-garn, Miskin, and Groes-faen, where the northern limb forms a well-marked escarpment.

It thus appears that the great Co wbridge- Cardiff anticline not only loses intensity westwards, but also changes form. At its east end it spans a tract of Old Red Sandstone nearly four miles across in one grand arch, but westwards it buckles down into a series of minor parallel anticlines and synclines (Fig. 1) which overspread the same width of country with a corrugated sheet of limestone bordered by a strikingly sinuous margin.

It is still more difficult to trace the base of the Lower Limestone Shales which border the main mass of the limestone. Along the southern limb of the anticline near Cottrell the shales contain at their base a well- marked rock which gives rise to a minor escarpment. This Lower Limestone can be traced with some certainty westwards as far as the Lias area of Welsh St. Donats, but there its position becomes quite conjectural. The base presumably turns northwards in a sinuous line more or less parallel to the base of the Main Limestone and rounds the Old Red Sandstone of Hensol Park. Beyond this it continues in a north-easterly direction, but the Lower Limestone seems to have thinned out while a similar band makes its appearance at a higher horizon. The shales are shown on the map as occupying the low-lying core of the main anticline extending westwards from Morfa Ystradowain as far as Pen-llin, but this tract is almost wholly masked by drift and it is quite possible that some of it may be occupied by Old Red Sandstone.

The map forming Fig. 1 represents the probable outcrops of the Lower Limestone Shales and the base of the Main Limestone in the eastern part of the area, the overlying Secondary and glacial deposits being supposed to be removed. The boundaries where purely conjectural are dotted, and where more or less uncertain are broken.

Fig. 1. — Map of pre-Triassic Folds, BY T. C. CANTRILL.

of M/'/es t An tic//na/ Axes

-X- Syn cf/na / .Axes, indicates nip or Strata + indicates Horizontal Sb

At the north-east corner of the map the limestone-series emerges from beneath the Trias, and forms a gentle escarpment to Miskiii. Throughout this tract the beds dip usually about N. 15° W. at about -30C to -10°.

The Lower Limestone is well exposed in some deep old quarries at Maes-mawr, where it consists of blue, brown, and purple oolite irregularly dolomitized. Thin strings of galena in barytes occur. Between Groes-faen and Llwyn-y-penau two dip-faults break the continuity of the outcrop, both being westerly downthrows ; the eastern one produces a lateral displacement of about 100 yards, the western only 15 or 20 yards. The outcrop has been deeply quarried at Llwyn-y-penau, the highest beds being flaggy and alternating with shale. An old quarry immediately west of the house shows thick-bedded impure limestone resting on buff shale exposed for 6 feet. This is underlain by crinoidal limestone. In an old roadside quarry south-east of CrofTtau the limestone dips N. 10° W. at 30 ; but rolls over southwards in an anticline and is broken by a

Carboniferous Limestone. 9

small fault, probably a thrust, parallel to the strike and inclined towards the north at an angle of some 50° from the vertical. South of this fault the beds rise again to the south. The limestone in this quarry is clearly closer to the base of the Main Limestone than that seen at Llwyn-y-penau, and is possibly not the same band. Below it there come in shales, as we may infer from evidence afforded by sections south of Miskin. The shales overlying the Lower Limestone form a belt of flat ground at the foot of the Main Limestone escarpment, but are seldom visible.

South of Crofftau the outcrops of the Lower Limestone and the Shales are masked by gravel, through which the former has been quarried at several points, especially in Miskin Park. Near the village of Miskin a small section in buff shales overlying impure crinoidal limestone containing small gasteropods (? Natica) was exposed on the south side of the River Ely opposite the corn-mill, where limestone was formerly dug from under the drift gravel.

The Main Limestone throughout this tract east of the Ely is ex posed in numerous quarries and small outcrops. Light-grey oolite prevails in the upper part and a crinoidal rock in the lower. The lowest beds form a well-marked escarpment, and the underlying shales throw out several powerful springs ; one occurs west of Cwrt- y-carnau and several others at College. The top is concealed by drift and Trias, the latter everywhere slightly overstepping the base of the Millstone Grit ; the highest limestones exposed at Mwyndy appear to be grey oolite.

The existence of a large westerly downthrow at Miskin is assumed in order to explain the southward shift of the base of the limestoneseries between that place and Caer-gwanaf-isaf . The shift amounts to no less than 500 yards, which indicates a vertical displacement of at least 200 yards.

West of the Miskin Fault the Lower Limestone Shales are exposed at Caer-gwanaf-isaf. The Lower Limestone where quarried west of the farm is a grey oolite overlain by a few feet of shale. A red stain and traces of haematite may be attributed to the rock having been once overspread by Trias. Below, the limestone becomes flaggy and impure, as shown in some outcrops among the farm-buildings. A fault between the farm and the main road seems to be a downthrow west of several yards. On the fields at about 100 yards south of the old quarry a thin band of limestone appears to have been dug out, from which we must infer the existence of some thickness of shales with thin limestones below the Lower Limestone. This conclusion is confirmed by the fact that such beds were proved in a well near Bolgoed, and that at least 20 feet of shales under gravelly drift are shown in an adjacent gully, all at some distance south of the outcrop of the Lower Limestone. This latter cannot be traced beyond some swallow-holes about 400 yards west of Bolgoed, either having thinned out or being effectually concealed beneath the drift. Towards Ystradowain and Welsh St. Donats the position of the Carboniferous base becomes a matter of inference, owing to the prevalence of glacial gravel.

10 Carboniferous Rocks.

The Main Limestone between the Ely Valley and that of the Dawen is greatly obscured by drift, but between Miskin and Nant Dyfrgi is exposed in numerous old quarries, the impure nature of the basal beds and the silicified condition of the fossils being well shown at Pant-y-cwestau. At Tal-y-garn the limestone emerges from the drift as a bold escarpment in which are several quarries, notably one a few yards south-west of Adam's Well, where the rock is earthy and stained red. Between this exposure and Bryn Saddler, massive blue and grey oolite is quarried through the drift, and again north-east of Llwynau ; and a deep old quarry at Tal-y-garn Church exhibits similar rock under 6 feet of drift.

South-east of Rhyd-halog the lower beds are well exposed on the slopes overlooking Morfa Ystradowain, where dark bituminous crinoidal limestone underlain by grey and brown impure rock with silicified fossils was worked. At their base these beds become still more flaggy and earthy, and so tend to pass into the Lower Limestone Shales, of which traces are exposed.

The low ground followed by the railway at Rhyd-halog coincides with what appears to be a line of fault. The base of the limestone on the east side is too far south to fit on to the same line on the west side of the valley at Fforest-fach, which would be accounted for by an easterly downthrow. The fault, if it follows a south-southwesterly course, will serve also to account for the occurrence of pieces of yellow sandy shale with obscure fossils, presumably Carboniferous, in a ditch at the foot of the Old Red escarpment at Llwyn-nwydog. The Old Red Sandstone here (p. 4) dips in a north-westerly direction. Above this sandstone is a gap occupied by the beds, probably shales, on which stands the farm-house. In the north-western corner of the farm-yard a band of oolite crops out, dipping N. 40° W. This is apparently separated from the Main Limestone of Crofftau and Fforest-fach by some shales which can be seen in a swallow-hole at the first-named farm. It may lie at about the same horizon as the Lower Limestone where we last saw it at Caer-gwanaf-isaf.

The Main Limestone of the tract between Crofftau and Llanharry is opened up in numerous old quarries, and a good section is afforded by the Llanharry Limestone Co.'s workings in oolite near Llanharry Station. The actual top is overstepped by the Trias, but the highest beds exposed consist of grey oolite varied by a dark fine-grained rock ; at lower horizons a blue crinoidal rock prevails. The less pure limestones near the base are exposed in a large old quarry 150 yards south of Fforest-fach, and the lowest have been worked along a low feature extending north-eastwards from Crofftau, and in quarries just east of the farm-yard. From the farm a feature which presumably marks the base of the Main Limestone abruptly turns south-eastwards, and the next exposures are afforded by several old quarries by the side of the Cowbridge road ; the rock is chiefly crinoidal, but some dark oolite occurs. The beds dip south at 15° to 44°, as compared with N. 25° W. at Crofftau, there being an anticline a few yards south of that house.

Carboniferous Limestone. 11

The structure of the ground about Ystradowain is exceedingly obscure owing to the general prevalence of gravelly drift. Presumably the Main Limestone rises rapidly to the south, thus assuming a synclinal form, for it gives rise to a bold escarpment running southwestwards from Ash Hall towards Llansannwr. Several large blocks of grey faintly-oolitic limestone lying at the south-east corner of the Gaer near Ystradowain Church suggest the presence of the Lower Limestone Shales, but may be no more than boulders in the drift.

Half-a-mile farther to the south-west, however, between Llansannwr and Tre-rhingyll, the Lower Limestone Shales form the slopes of a small plateau capped by an outlier of the Main Limestone. A thick band of oolite emerges from the drift at Pen-cyrn, where it is quarried ; though rolling somewhat it is practically horizontal, and can be traced through old quarries along the wooded scarp running southwards. After a gap of several hundred yards a similar, and probably the same, band appears in a large quarry at Newton Farm, again in a horizontal position. It consists of thick-bedded crinoidal dark oolite exposed for at least 25 feet, under about 6 or 8 feet of flaggy beds. Beyond Newton Farm it is lost to sight under the drift. On the north-west side of the plateau, in Coed y Brain, oolitic limestones have been quarried in several places ; presumably they are interbedded in the shales, but none can be certainly identified with the band worked at Newton Farm. Above the limestone at Newton there is a considerable thickness of shales containing thin crinoidal limestones, as may be seen in the lane leading down from Pen-y-lan to Tre-betin, and in an old pit in the field above Newton Farm. These shales emerge from beneath the Main Limestone in the lane north of Coed y Brain.

The highest Carboniferous rock of the plateau is a crinoidal darkgrey earthy limestone containing Fenestella which is exposed in several small openings above Coed Pen-cyrn, and again in an old quarry on the upper edge of Coed y Brain. It is probably an outlier of the lowest bed of the Main Limestone. The shales between it and the next lower limestone would seem to be only 10 or 15 feet thick at Pen-cyrn, whereas above Newton Farm there must be at least 60 or 70 feet.

There are no exposures of whatever beds underlie the Newton limestone, and the low ground of Tre-rhingyll has been represented on the map as occupied by Lower Limestone Shales, but the uppermost beds of the Old Red Sandstone may possibly crop out beneath the gravel.

Most of the outcrop of the Main Limestone north of Ystradowain and Llansannwr is overspread with gravel. The highest rock exposed in Brigam Wood west of Llanharry is a light oolite, and most of the limestone in the neighbourhood of City is of the same character ; south of this, a dark crinoidal rock prevails. The lowest beds are well exhibited on the eastern side of the Dawen Valley at Llansannwr, and consist of the usual crinoidal earthy rock, with a band of purple oolite at about 180 feet above the base.

12 Carboniferous Rocks.

West of Llansannwr the Lower Limestone Shales emerge from beneath the Main Limestone, but are soon cut off on the south-west by a fault ranging towards Ham Farm ; and thence the base of the Main Limestone probably coincides with the edge of the gravelly and alluvial deposits of Pen-llin Moor as far as the Pen-llm Fault, which accompanies the dominant anticline of the district, and brings up the shales again.

South of this anticline the beds dip a little west of south, and the base of the Main Limestone gradually descends the fine wooded scarp below Pen-llm Castle. Its subsequent course is a matter of inference alone ; it presumably turns north-eastwards under the Lias of Maendy. The only evidence bearing on the question consists in a tradition of limestone having been worked through the gravel in the bottom of a dingle half-a-mile due west of Llwyn-du. There are signs of old quarrying operations on the west side of the dingle under the gravel, and two or three small pieces of crinoidal blue limestone (Carboniferous) which were lying here may indicate the presence of either the Main Limestone or a band in the Lower Limestone Shales. The latter interpretation has been adopted on the map. If it be correct the base of the Main Limestone must come on higher up the hill somewhere under the Lias of Bodlonga. It ultimately emerges from the Lias south-east of Welsh St. Donats (p. 7).

The limestone tract lying between Welsh St. Donats, Llanbleiddian, and Llantrithyd is traversed by the well-marked anticline of Stalling Down, where the Lower Limestone Shales, with a definite band of limestone at their base, wrap round a core of Old Red Sandstone. A small quarry on the west side of the Aberthin brook at Llan-chwian-fach north of Llwyn-celyn, shows some few feet of shale with thin limestones, over purple oolite exposed for 3 feet, all dipping about S. 30° E. at 28°. As Old Bed Sandstone debris occurs close by, the bed in the bottom of the quarry must be nearly if not quite at the base of the Lower Limestone Shales. Though it cannot be traced up the hill towards the south-west, it is occasionally exposed along the north-east side of the valley almost to the Court Farm at Aberthin. Above it there follow shales with thin seams of similar limestone ; some of the shales are very sandy and a thin bed of sandstone crops out on the side of the valley thirty yards south-east of the quarry at Llan-chwian-fach. The shales are well exposed in a gully 500 yards north of the same farm. The band of limestone shown on the map as running north-east to south-west, and crossing the same Aberthin brook 100 yards south-east of the farm, is a red and purple crinoidal oolite, and appears to be the same basement-bed brought up by a fault. It is exposed in the brook and in one or two quarries, in one of which it is at least thirteen feet thick. It is overlain by shales.

The lower beds of the Main Limestone at Llwyn-celyn are much disturbed, and a crinoidal limestone, formerly quarried there, is traversed by spar- veins, one ranging N. 52° W. and another a little north of east. These disturbances are probably due to the fault

Carboniferous Limestone. 18

which throws the Main Limestone against the Old Red Sandstone westwards of Llwyn-celyn. The fault does not appear to affect the Trias and Lias near Cowbridge, and therefore is probably of the same pre-Triassic age as the anticline withVhich it is associated; it cannot be traced east of Llwyn-celyn. Eastwards of this point the base of the Main Limestone can be readily followed past the ruins of Llan Chwian Castle, and along the wooded scarp crowned by the earthworks of Twr Gron ; and also on the north side of the valley till it joins the Cowbridge fault west of Pwll-y-daren.

The Main Limestone throughout this district exhibits the usual prevalence of dark crinoidal rock in the lower parts extending from Welsh St. Donats as far as the Cowbridge-Cardiff road ; south of that line light-grey oolite predominates. From an old quarry 500 yards south of Pwll-y-daren a tooth of Psephodus magnus, Ag. was obtained. The small inlier of light oolite, pierced by a cave, at Tre- Aubrey near Llantrithyd is the most southerly exposure of Carboniferous Limestone in the map, and must be high up in the series ; but whether the Millstone Grit comes on a little to the south beneath the Lias, or whether the limestone rises again in that direction there is no direct evidence to show.

The Lower Limestone Shales emerge from beneath the Lias southeast of Welsh St. Donats, and though their outcrop and that of the lowest horizons of the Main Limestone are everywhere concealed under an unbroken cloak of gravel, yet it is possible to recognise here and there their characteristic features. This is the case at Lilly pot north of Bonvilston, and the observation is confirmed by two small exposures of the Lower Limestone south of Ty'n-y-pwll, both of which are marked on the map. In one of them, at a small pond, impure crinoidal limestone is seen under three feet of pinkish-yellow sandy beds, all dipping south at 30° ; in the other, at a quarry by the side of the road half a mile north-west of Cottrell, some fifteen feet of crinoidal dark limestone with oolitic bands are exposed under gravel, the dip here being 20°. It is possible that some few feet of shales may underlie this limestone.* Some old quarries in Cottrell Wood well display the earthy lowest horizons of the Main Limestone ; the most westerly shows silicified fossils and at the bottom reaches shale. South of these sections the outcrop is overspread with gravel.

(2.) Western Part. By R. H. TIDDEMAN.

The central axis of "the Cowbridge-Cardiff anticline ranges from Pen-llin by Crack Hill, passing thence two- thirds of a mile south of Ewenny Priory and just north of Ogmore Castle. It next traverses the Merthyr Mawr Burrows and passes due west out to sea at Porthcawl. So much, however, is the limestone masked by patches of later rocks, that this line is by no means apparent without a careful study of the dips. Thus on the north side of the anticline, the actual

The Country around Cardiff (M em. Geol. Survey), pp. 23, 24.

14 Carboniferous Rocks.

top of the formation can be fixed in one place only, viz., in the railway and tramway opposite Angeltown Asylum, while on the south side its underground extent beneath the newer rocks is unknown, except for some three or four inliers.

Of these inliers, none of which had been previously detected, one consists of a narrow strip of limestone, one mile long, brought up between two faults. It is well seen in the Vale of Glamorgan Railway at Clemenston, and is here and there covered with patches of conglomerate which are apparently of Liassic age, but are not easily distinguished from the Carboniferous Limestone. Another example occurs as a large inlier of erosion in the south-east end of Clemenston Park, where, as the limestone dips north, there may be reason to suspect the existence of another anticline south of the large anticline mentioned. A third inlier is exposed in a small quarry, also with a northerly dip, half a mile west-north-west of Wick. A fourth which, however, is only doubtfully referred to a Carboniferous age, lies half a mile north of the last, and consists of tufaceous limestone with traces of conglomerate.

In lithological character the limestone varies greatly, but usually presents itself as a well-bedded rock, grey or black in tint, but varying to light-grey and drab -brown. White shelly limestone, such as is common in the north of England, is seldom seen, but fossils abound, especially in the lower beds, as at Pen-llin. Corals and large specimens of Productus occur in fine preservation, dotted over the beddingplanes, near Southerndown and Porthcawl. In many places a water-worn surface displays false bedding on a small scale, and in such cases the rock appears to consist almost wholly of small drifted shell-fragments.

Oolitic structure is common and occurs both high up and low down in the Carboniferous Limestone. Thus little else is seen in the road between Southerndown and St. Brides Major, and in Heol-y- Slough to the west of St. Brides, where the rock lies almost in the axis of a syncline and must be high up in the formation. Oolite exposed between Merthyr Mawr and Candleston, on the other hand, is in nearly the middle of the anticline and belongs to a much lower horizon. Another oolitic band of considerable thickness crosses Newton Down, between Laleston and Newton Nottage, and though high up in the limestone is by no means near the top. A singular cavernous bed, to a great extent filled up with chalcedonic silica, but containing also small crinoid ossicles, occurs near the base of the limestone at Pen-llin. Cherts are not uncommon, but are perhaps most abundant at the Witches' Point, Southerndown.

Some of the limestones of Mumbles Head and other parts of Gower (Sheet 247) exhibit pitted bedding-surfaces. The structure extends for some miles in Gower, but was first noticed in a quarry at Newton Nottage in the sheet under description, fourteen miles east of Gower. It characterises a high horizon in the limestone, and consists of a number of small pits irregularly distributed over one or more of the bedding-planes. Many of them contain a mass, or irregularly shaped nodule, apparently of dolomite, and their edges

Carboniferous Limestone. 15

in the immediate neighbourhood of the pit are frequently raised a little above the general level. A similar exposure will be found in the cliff north of Hutch wns Point west of Porthcawl. Two-thirds of a mile north of the point a conglomeratic bed has been noticed in the Carboniferous Limestone.

The topmost beds of the limestone, as seen in the small inlier near the County Lunatic Asylum, are associated with a marly limestone with trilobites, chert, and shale, which probably represent the radiolarian cherts and rottenstone-beds of Gower (Sheet 247), but owing to disturbances or slipping of the side of the cutting the succession is not well seen.

Few opportunities of measuring the thickness of the limestone occur in the Vale of Glamorgan, either the top or the bottom, or both, being generally hidden by Secondary rocks. Near Miskin where both are clear the breadth of outcrop of the Main Limestone indicates a thickness of some 1,600 feet. To this must be added 275 feet for the Lower Limestone Shales, making a total thickness of 1,875 feet for the Carboniferous Limestone Series.

Near Stormy it would appear that there must be a thickness of 4,500 feet of limestone, with little or no shale, in consideration of the fact that the limestone dips continuously northwards without any apparent break. There may, however, be some repetition by unknown faults.

The Lower Limestone Shales come to the surface in the centre of the anticline near Pen-llin, but nowhere further west. A bold scarp of the Main Limestone runs up below the castle from the alluvial flat, and crosses the little valley in which the village lies. The shales with interbedded limestones are well shown in the lanes which lead up from the river- plain, and like the limestone dip steadily southwards.

Sharp as the anticline is there is not room for these shales to turn over northwards and pass under the Main Limestone in that direction without faulting, and there is other evidence also of a fault running in an east and west direction. Springs rising from the alternating shales and limestones near Penllin Court quickly disappear on reaching the position assigned to it. The scarp referred to soon disappears westwards under Lias, but yellowish and greenish shales and clays with decalcified crinoidal limestones or rotten-stones are exposed for some distance west of the village. These strata have hitherto been mistaken for Rhsetic shales, and their correct identification throws a new light on the structure of the anticline. The fault referred to is probably the continuation of the lode which has been tried for lead at Llangan and other places.

Chapter Iv.

UPPER CARBONIFEROUS ROCKS. MILLSTONE GRIT. By A. STRAHAX.

The Millstone Grit, so far as it occurs within the limits of the area described in this volume, calls for little remark. An account of the part of its outcrop which lies north of the margin of the map will be found in the Geology of Pontypridd and Maesteg (GeoL Survey Memoir), p. 6, and in those parts where it lies within that margin there are few opportunities for examining it. Its thickness is believed to lie between 1,800 and 1,500 feet, and it consists mainly of shales with bands of grit or quartz -conglomerate. The lower part of it, as shown near the County Asylum, Bridgend, presents a sequence quite unlike that of the north crop, where a massive quartzconglomerate immediately succeeds the limestone. Here on the contrary shale was first laid down, and was followed only at intervals by sands, in this respect the section comparing more nearly with that of Gower (Sheet 2-i7). The remainder of the outcrop is concealed by Secondary rocks or drift.

Millstone Grit — continued. By T. C. CANTRTLL.

In the north-east corner of the map the Millstone Grit is not exposed, and its boundaries are laid down by inference from the coalworkings in ground lying to the north. The outcrop is soon overstepped by the Trias of Mwyndy, which passes over it on to the upper beds of the Carboniferous Limestone. Some of the haematiteworkings near Mwyndy after traversing the Trias encountered black shales, frequently stained red, which probably belong to the Millstone Grit. Detritus of similar shale with some pieces of quartzose sandstone was brought up from a trial-shaft in search of haematite, 1200 yards south-west of Llantrisant station. A little farther west, at old haematite-workings at Ty-du, dark-grey shale was brought up from the shafts together with some limestone which presumably immediately underlies it. West of this point the Millstone Grit is concealed under the Trias of Llanharry, and though it probably emerges again in the valley east of Llanilid it is everywhere covered with gravel.

Coal Measures.

By A. STRAHAN.

The Lower Coal Series enters the map under description at Pont Clun, and leaves it five miles to the west. For a general account of the South Crop reference should be made to the part of this Memoir referred to above, descriptive of the country around Pontypridd and Maesteg. So far as this small tract is concerned, a short extract from that volume will suffice. Several thick bituminous seams are known to occur, which as a group may be correlated with the principal steam-coals in the Rhondda Valleys, though individually they are not recognisable. The series commences with an impersistent and generally thin coal known as the Cribbwr-fach which lies a short distance above the Millstone Grit. The principal seams above the Cribbwr-fach are enumerated below in descending order : —

Bodwr-fach.: Slatog.

Bodwr-fawr.- Six-feet.

North and South Fawr; Nine-feet:

Trydedd.; Cribbwr-fawr.

In Coed-yr-Hendy attempts have been made to work the Cribbwr by level, and shafts, probably to the same vein, have been sunk through the Trias. On the south side of Coed-yr-Hendy a shaft sunk in search of haematite traversed a small thickness of Triassic conglomerate and then entered sandstone and shale stained red, but probably belonging to the upper part of the Millstone Grit. The base of the Coal Measures is accordingly shown as running through the southern part of Coed-yr-Hendy. At Pont Clun it is believed to be shifted by the Miskin Fault, the evidence for which is found in the limestone (p. 9).

The Cardiff Navigation Colliery is situated on an alluvial flat half a mile north-west of Pont Clun and was sunk through 21 yards of superficial deposits before reaching the rock (p. 103). The measures dip at 35° to the north, and the shaft intersected the Trydedd Vein at 150 yards from the surface, the Cribbwr, so called, at 210 yards, and ended in mine-ground at a depth of 280 yards. Three headings have been driven from the shaft northwards with the view of proving the North and South Fawr and Bodwr Veins, but all the coals were squeezed out and worthless with the exception of the Trydedd, which apparently owed its preservation to the fact of its being overlain by a strong rock. The sections proved in the headings agreed neither with one another nor with that proved in the shaft. The Trydedd has been worked continuously from its outcrop in Tre-castell Wood to beyond the shaft, but in spite of the general disturbance no large faults were found, and only two small overthrusts.

18 Carboniferous Rocks.

The Cribbwr Vein was estimated to crop out about 120 yards south of the Trydedd. Among many old slants and pits in Coed Tre-castell there seem to be only two crops of any importance, the one at 340 yards and the o£her at 450 yards south of the shaft. The more northern crop can be traced by old workings for about 1,000 yards westwards in the direction of Cwm-gran ; the other, as proved by shafts sunk through the Trias, appears to follow a parallel course. Both range for Gwaun Llanharry, where there are many old pits, about which nothing could be ascertained.

At Torgelli what was supposed to be the Cribbwr Vein \vaa reached at ninety yards depth in a shaft 180 yards north of the farmhouse, and again at 203 yards depth in the Llanharry Colliery, 500 yards north of the farmhouse, the dip apparently being one in three. The following section of the Torgelli Pit was furnished by Mr. David Evans, of the Meiros Colliery, while that of the Llanharry Pit was given from memory by a fireman to Mr. F. W. Dunn ; the Batter does not agree with other sections of the South Crop.

Torgelli Pit.

Depth from Surface. YDS.

Third f Trydedd] Vein, 4 to feet - Old Nine-feet [ ? Slatog] Vein, 4 to feet Six-feet Vein, 5 to 6 feet -

Nine-feet Vein with a clod of 4 to 15 inches, 9 feet - - - ti() Cribbwr Vein with a clod of 4 to 15 inches, 7 feet - - - 96

Llanharry Pit.

(Dip said to have been about 15 inches to the yard).

Yds.

North Fawr Vein, trace of supposed 6 Coal, 3 feet - - 35

Third [ Trydedd J Vein - - 70

Slatog Vein 110

Six-feet Vein, coal 5 to 6 feet, holing 7 inches, and coal 1 to 1 £

feet - 140

Nine-feet Vein, coal 4 to 5 feet, holing 6 inches, and coal 2 feet - 167 Cribbwr Vein, soft carbonaceous shale-roof 9 inches, coal in beds

4 feet, clod 1 to 1£ feet, coal 3 feet 203

Coal, 7 inches 231

Sandstone, with water, proved to 18 yards in a borehole - - 252

A trial-pit, 930 yards a little north of west from the colliery, is said to have proved the Esgyrn Vein at a depth of five or six yards. This name is given to a coal which lies above the North Fawr near Tondu. The Cribbwr was found at two or three yards depth in Pen- y-waun farmyard, and the Six-feet Vein at six or seven yards depth in a pit 400 yards north-west of Pen-y-waun.

Farther north, near Bryn-y-cae, the South Llanharan Colliery was started, but abandoned without any coal being worked. Twu

Coal Measures. 19

shafts were sunk, and a section proved of which the following is an abstract :—

Abstract of Sinker's Journal of the South Llanharan Colliery.

(Communicated by Mr. F. W. Dunn.)

Depth from Thickness. Surface.

Yds. Ft. In. Yds. Ft. In.

Shale and thin rock

u

Coal

0

Shale

- 6

Coal -

- 0

Shale and thick sandstone

Lantern (Cannel

- - 0

O

/ 1

&

Shale

Coal

- 0

Shale

- 0

Coal

- 0

Shale and ironstone

Coal

- 0

Sandstone

Coal, inferior ...

- 0

Shale ...

- 0

G

Coal

- 0

Shale

- 0

Coal

- 0

Shale and ironstone

Bodwr-fach Vein

- 2

Shale .

- 8

Coal .

- 0

Shale .

- 0

Coal .

- 0

Shale .

- 0

The dip was fifteen inches to the yard near the top of the shaft, and ten inches to the yard near the bottom ; a slight correction, therefore, in the figures given above will be necessary. The identification of the Lantern and Bodwr-fach Veins is given as in the original. A vein, supposed to be the Lantern, was reached at twentythree yards depth in a shaft 150 yards south of the sinking, and was used for the engine. Several old pits in the fields eastwards appear to be on the crop of this vein, but there is nothing to indicate the crop of the Bodwr-facn. One of the higher veins crops out in a wood 500 yards south-west of Whitehall.

At Ty'n-y-caeau-fawr a trial was made for the Six-feet Vein. This same vein was got at twenty yards depth on the south side of the -Great Western Railway, and at sixty yards depth on the north side of the line in a shaft 300 yards west of the Mountain Hare (Sheet 248), but the Cribbwr and Nine-feet have not been proved. Following the railway eastwards we come to the workings on the Bodwr Veins at Brynau-gwynion.*

Geology of Pontypridd and Maesteg (Mem. Geol. Survey], pp. 43, 44. 7665. C 2

Chapter V. Trias.

INTRODUCTION. By A. STRAHAN.

The Triassic rocks of South Wales include representatives of the RluiBtic and Keuper formations, and rest upon a deeply denuded surface composed of strata ranging in age from Silurian to Coal Measures. For reasons given in a previous part of this memoir, the upper limit of the Keuper is drawn at the top of some green and buff shales with thin inorganic limestones, which constitute the " teagreen marls " of old authors.* Upon these rest the strata in which Avicula contorta makes its first appearance, and which accordingly are placed in the Rhsetic group under the name of the Avicula cantorta-zone.

Though no unconformity has been detected between the Keuper and Rhietic groups as thus defined, we have evidence of a somewhat abrupt change of physical conditions. The Avicula was closely followed, if not accompanied, by a true marine fauna, and, whereas the Keuper limestones are of inorganic origin and are associated with sediments in which fossils are extremely rare, the Rhsetic limestones consist largely of organic debris. The horizon at which the change took place can be readily determined to be constant over a large area in the south-west of England and in Wales.

To these facts may be added a further argument for the classification now adopted. In the region under description the Rhaetic strata exhibit a remarkable lithological change as they are traced westwards, the shales and limestones which constitute the group at Penarth being replaced by thick sandstones not unlike Millstone Grit at St. Mary Hill and thence westwards to Pyle. The " teagreen marls," on the contrary, show comparatively little change, when traced over the same ground, their aspect at their westernmost occurrence being much the same as elsewhere. It appears then that the conditions under which Keuper Marl was deposited prevailed uniformly over the whole region up to a certain date, but that after that date, when once the sea had gained access, the physical geography was changed and no such uniformity existed. Though the change was locally abrupt, and even accompanied by some slight erosion here and there, it would be easy to over-estimate its importance from a classificatory point of view. The green marls themselves mark the commencement of the change, for lithologically they strongly resemble parts of the Rhaetic, but, more than this, we find evidence high up in the Rhsetic of a brief recurrence

Country around Cardiff (Mem. Geol. Survey), p. 38.

Introduction. 21

of the conditions under which Keuper Marl was laid down, both in this and in other parts of the British Isles (p. 36). Nevertheless, the subsidence which led to the burying of the old rocks under Triassic and Jurassic sediments may have been continuous, for some cause other than re-elevation may have sufficed to restore temporarily the conditions which prevailed through Keuper times.

These conditions may be inferred to have been continental, for the reason that they indicate the existence of large tracts of water having no communication with the sea. The absence of such communication is proved by the nature of the material formed. A red clay, much of it devoid of bedding, but in parts evenly laminated, makes up the bulk ; bands of rock-salt, though not known in South Wales, occur elsewhere, together with bands or concretions of carbonate of lime and magnesia, sulphate of lime as gypsum and sulphate of strontia as celestine, the formation of all of which indicates a water in which surplus was removed by evaporation and not by overflow. The water moreover was so highly charged with iron-salts as to redden most of the rocks it touched. At its margin the clay inosculates with bands of talus roughly arranged in layers, but often scarcely at all waterworn. The preservation of footprints in this area, and of suncracks and rain-pittings elsewhere, proves that the water receded at times and was therefore shallow, which indeed might be inferred also from the nature of the marl. All these circumstances can be matched in the shifting sheets of shallow water which characterise many desert regions at the present day,* and it is interesting to find that in Leicestershire some of the granite-bosses upon which the marl there rests show a smoothed and terraced surface with signs of wind-polishing.f Probably lack of opportunity alone has prevented observation of a similar phenomenon in South Wales.

The paucity of organic remains in the Keuper Marl also suggests a desert environment. The character of the water may account for the absence of a lacustrine fauna such as teemed in the Purbeck and parts of the Wealden, but it would not explain the absence of plants, insects, and other organic remains which would have been washed or blown into it, had they existed in any abundance. It is to be noted also that the Keuper Marl of South Wales, though it fills depressions in the old land-surface, never assumes a fluviatile character. Nowhere can we point to a river-channel or a gravel such as could be attributed to a running stream ; everywhere, except of course in its literal type, it presents the same uniformity of red clay.

In its literal type the Keuper Marl consists of breccias or conglomerates, inorganic limestones and sandstones, the whole constituting the " Dolomitic Conglomerate " of old authors, a name which is

As suggested by Prof. Lapworth, Proc. Ged. Assoc., vol. xv., p. 388 (1898).;

f Report by Prof. Watts on an Excursion to Gharnwood For* st, Proc. Ged. Assoc.i vol. xvii., p. 379, and plate xviii; (1902); and Oeograph. Journal for 1903, p. 623

unsuitable lor reasons given elsewhere.* In this part ol Glamorganshire, these litoral modifications are exhibited not only in the Keuper Marl, as was the case further east, but in the Rhsctic and Lias also. The distribution of the litoral type, with other evidence, makes possible a fairly precise restoration of the geography of the region in Triassic and Liassic times. The features of that old landscape were due primarily to the effects of denudation upon the sharply folded Palaeozoic rocks. Then, as now. the Carboniferous Limestone formed scarps and the Old Red Sandstone stood up as rounded hills. Around and between these features the marl was spread out, mixed at its margin with the debris which fell from their sides. As the subsidence continued the marl and breccias extended further up the slopes, but though they had covered the small crags, they had failed to surmount the higher tracts when they were succeeded by the green marls. Gradually diminishing in size these same tracts can be easily recognised through the period of the green marls, of the Rlwtic, and of part of the Lias, but they all finally disappeared during the deposition of the Lower Lias. Subsequent denudation has so far disinterred the buried landscape as to admit of its partial reconstruction. The distribution of land and water at the moment when the Rharfic fauna overspread the region is given in the map forming Fig. 2.

The contents of the conglomerates are generally easy of determination. Carboniferous Limestone forms an overwhelming majority of the fragments in all of them, whatever rock they rest on, but some grit-pebbles occur abundantly in a few places and suggest by their perfect rounding that they have been derived from a pre-existing conglomerate, such, for example, as that which occurs in the lower division of the Old Red Sandstone of Llanishen.f Though in some bands the limestone-fragments also are well-rounded, they are more generally angular, and in this respect differ from those which fell into the Liassic sea. The one suggests scree that has fallen into water and been roughly sorted, but not rounded, the other a beach that has been exposed to surf.

The matrix of the conglomerate is generally a calcareous mud, with included fragments ranging from scarcely visible specks to large blocks. Presumably it was derived from the attrition of the limestone of the adjacent coasts, but the source of the red clay of which so much of the Keuper consists is not so obvious. Though its stratification proves that it was laid down by water, its distribution was not improbably, like that of the loess, due to wind. In South Wales much of the material might be attributed to the waste of the vast thickness of Coal Measures which overspread the region, which would also yield a water such as would account for the mineral contents of the marl. It is true that the Keuper Marl preserves its character in other parts of the kingdom where it spreads over other rocks, but it must be remembered that it was formed at a time when Coal

The Country around C.irdifT (Maruiir (Jcal. AV/vw/), p. 40. t The Country around Curd ill' (iMtrnoir (Jrol. Xnrrcy), 17.

Introduction. 23

Measures occupied a larger area than now, and when they were undergoing denudation on a vast scale.

There is abundant evidence, however, that an enormous mass of material had been denuded before the Triassic period commenced. In South Wales the thickness of strata removed before the Keuper Marl was laid down amounted in places to upwards of 7,000 feet. Near Cardiff, for example, where the Silurian rocks are laid open to a depth of 500 feet, the whole of the Old Red Sandstone as well as all the Carboniferous rocks had been swept away. In the area now under description, the denudation had reached the upper part only of the Old Red Sandstone, but all the Carboniferous rocks were probably thicker and the aggregate thickness removed may have been not much less than in the region referred to.

The map forming Fig. 2 shows the distribution of land and water at the close of the Keuper period, with the addition of the present coast-line and the courses of the principal rivers. The Keuper coast-line has been drawn by reference to the overlap of the Rhsetic and Lias. For example, it was considered that the fact of the Rhgetic or Lias lying directly upon the Carboniferous rocks at any spot proved that Keuper had never overspread that spot, inasmuch as we have no evidence of any pre-Rhaetic denudation to account for its absence. That spot would, therefore, form part of the Keuper land. On the other hand, the absence of Keuper at the present day on spots not overlain either by Rhsetic or Lias proved nothing, inasmuch as it might have been due to post-Liassic denudation. The coastline of the principal Keuper island could be fixed nearly all round by evidence of this description. Part of its southern margin, however, is doubtful ; we can say little more of it than that it must keep south of Wick and of Dunraven Castle, near both of which Lias rests on Carboniferous Limestone, and of Whitmore Stairs, where the Lias belongs to the litoral type, and may be inferred to rest on the older rock.

The coast of what we may call the mainland is doubtful almost everywhere. Near Llantrisant, the Keuper breccias end off against a steep Pennant scarp, and can scarcely have extended many yards beyond the line shown. Elsewhere we have proof that the Keuper extended close up to the scarp, and it has been assumed that its limits were determined by that great feature all through, the tract shown on the map. The limestone on either side of the Taff, near Taff's Well, is believed to have been overspread by the Trias on the evidence of the large deposits of haematite in it.

Certain rocks, such as those near Wenvoe, Cadoxton, and others, though submerged before the end of the Keuper period, formed islands till near the close, and have accordingly been indicated by stippling.

The rivers have been added to the map for the purpose of showing that their courses have no connection with the Triassic geography. For example the Ogmore and Ewenny on issuing from the Coal

*See also Ramsay, On the Denudation of South Wales (Mem. Geol. Survey} Vol. 1, p. 297 (1846).

24

Field, the margin of which approximately coincides with the coast of the Triassic mainland, cross the site of a Triassic strait in which Keuper Marl of normal typo was deposited, and then traverse a region in which Lias rests on Carboniferous Limestone, and which therefore was Triassic land. At their junction they enter an inlet of Trias which is indicated by two outlying patches, one on either

side of the river, but, with the exception of this short length, they show complete indifference to the Triassic features. The Dawe.n again rises in the Triassic strait referred to, but, so far from following it, cuts across the Triassic land southwards. The Ely also ignores the Triassic strait, but, on the other hand, it crosses the ridge of

Introduction. 25

Carboniferous Limestone by a gap which may be of Triassic age. The evidence, which is suggestive but not conclusive, is given on p. 29. The Cadoxton River rises in the site of a Triassic strait which separated the islands of Michaelston and St. Lythans in pre-Rhaetic times ; it flows not along the strait, but right across the Michaelston crag. These examples will suffice to show that the existing riversystem is independent of the Triassic features. It probably originated when the region was buried under Jurassic and Cretaceous rocks.*

One more point in connection with the map (Fig. 2) remains to be mentioned. The area of land shown as forming a Triassic island of course stood higher than the tracts on either side of it. It does not do so everywhere now, and a consideration of the changes of level which it has undergone enables us to estimate the effect of later earth-movements. The simplest method is to take the base of the Rhaetic as having been a Triassic contour-line, which it seems safe to do in view of the fact that it marks the incoming of the sea over a large tract of country. The base goes to or below sea-level at Penarth, Lavernock, and Barry. Thence northwards it rises to 200 feet at Leckwith and Dyffryn near St. Lythans, Llantrithyd and south of St. Hilary, the steady ascent northwards being easily detected in the valleys south of the two last-named villages. Near St. Nicholas it reaches 300 feet, and the eame height at Bonvilston ; at Tair Onen 400 feet, and at St. Hilary 300 feet. Here it reaches its greatest height, for farther north near Maes-y-leech it is 250 feet, and about 100 feet at St. Brides-super-Ely and Peterston, rising to 200 feet again a mile or two to the north. At Pendoylan it is 200 feet and three miles to the north 160 feet above the sea. The level in a faulty district from St. Mary Hill westwards ranges from 300 feet to about 180 feet near Pyle. Lastly, we may remark that the Rhaetic base sinks an unknown depth below sea-level south of Dunraven.

One fact comes out prominently from a consideration of these levels, namely, that there has been an uplift of the Rhaetic along the Carboniferous Limestone escarpment on the south of the anticline east of Cowbridge, as compared with the Rhaetic lying along the axis of the anticline. In other words, the post-Liassic anticline is parallel to but nearly three miles south of the pre- Triassic anticline. The uplift may be partly due to a fault, of which there is reason to suspect the existence, for farther west from Cowbridge to Southerndown the course of a fault producing such an effect has been traced on good evidence. Though the post-Liassic uplift diminishes westwards it can still be located in the Ogmore Valley, between Merthyr-mawr and Sutton, here again some distance to the south of the pre-Triassic anticline. For further details on the post-Liassic movements reference should be made to Chap, viii., Figs. 7 and 8.

Quart. Journ. Geol, 8oc.t vob Iviii., p. 218 (1902).

KEUPER (Eastern Part). By T. C. CANTRILL.

The Keuper of the eastern part of the map occurs in three areas determined by the position of the Cowbridge-Cardiff anticline, namely a tract around Pendoylan situated within the anticline, the strip extending along the outcrop of the Millstone Grit and base of the Coal Measures on the north of the anticline, and lastly the exposures which intervene between the anticline and the Lias plain on the south.

Within the Anticline.

The Pendoylan area is so largely concealed by drift that the nature of the underlying rocks is often doubtful, and it is even possible that part of the ground may be occupied by Old Red Sandstone.

The greatest thickness of Trias is exhibited in ground lying north-west of Pendoylan, and the following appears to be the general succession of the deposits :—

The lowest beds, consisting of red and purple gravelly somewhat incoherent conglomerates, make their appearance around Brynhelygen, though there are no good sections. The rock is made up of small often well-rounded pebbles of red and purple quartzite and sandstone embedded in a dark red sandy and ferruginous matrix. The pebbles at times are parallelepipeds with the solid angles rounded off. Associated with these conglomerates are beds of hard rocky marls containing calcareous concretions or ' race.' The conglomerates come to the surface at the side of Bryn-helygen farmhouse. About the year 1860 two trial- shafts in search of haematite were sunk here; one, which lies about 160 yards north-east of the house, is said to be 60 feet deep ; the other, in Coed Llwyn-Hywel,* to be 100 feet deep. In both, red rocky marl with ' race ' seems to have been the chief deposit proved ; haematite in workable quantity was not obtained. Conglomerates similar to those here described occur at Dyffryn-lloff, probably at about the same horizon.

A red marl succeeds these conglomerates and marls. It crops out at Clawdd-coch, where there are several old marl-pits, and may be traced across several fields southwards of the cross-roads nearly as far as an old barn a few yards north of Ty'n-y-cae.

Next follows a grey limestone of inorganic origin containing numerous more or less angular fragments chiefly of Carboniferous Limestone. This is seen at the old barn near Ty'n-y-cae, and it also crops out in the lane west of Tre-Dodridge.

Lastly, there come red and yellow sandy marls overlain by green marls, all containing thin bands of pebbly yellow rock and breccia, or even in places being wholly replaced by breccia. They represent the ' Tea Green Marls ' of old authors and form the top of the

In this wood there appears to be a small earthwork or camp.

Keit/per. 27

Keuper marls, being immediately succeeded by the Avicula contorta shales of the Rhaetic group. Red and yellow sandy marls with included fragments are exposed in an old pit at Ty'n-y-cae, and can be traced up the lane west of Tre-Dodridge.

At about 150 yards along the footpath running south-east from Ty'n-y-cae Rhsetic limestone can be recognised in the soil, but a little farther on the Keuper beds are brought up again by a fault which appears to range in a south-westerly direction and repeats most of the Keuper series. Thus, the red marls of Clawdd-coch recur immediately south-east of the fault, and are well-exposed in a quarry on the road to Pendoylan, while a pebbly limestone above them is worked for roadstone in the south part of the same quarry and can be traced thence to the south-west. It is probably this rock that is quarried also near the smithy a quarter of a mile southwest of Plwcau-Dafydd, where the following succession is disclosed.

Ft.

Breccia, thick-bedded, grey, of subangular fragments of Carboniferous Limestone in a calcareous matrix, exposed for - - 3

Rocky marls, hard, yellowish-green, with thin partings of softer, more shaly, and greener marl ; the upper two feet soft. Some of these beds contain small Carboniferous Limestone fragments - 9

Breccia, like the upper bed, but coarser and harder, exposed

for - - 10

Both the matrix and the contained limestone- fragments of the breccias are more or less dolomitic.

Some yellow rocky marls , once dug in some pits in a coppice west of the Lodge at Plwcau-Dafydd may be referred to the same or a slightly higher horizon ; while in the hedge on the western side of the roadside coppice immediately north of the Lodge there occur traces of the Avicula contorta shales.

A hard yellowish-grey breccia which may correspond to the grey limestone mentioned on p. 26 is shown in an old pit 200 yards northeast of Pendoylan Church ; with it are associated yellowish-green and grey rocky marls and pebbly grey limestone. They dip southwards and presumably underlie some buff, green, and red marls exposed at Ffynnon Cattwg 150 yards farther south, which cannot be' more than 50 feet below the Rhsetic base.

These details, together with the fact that pebbly green rocky marls were met with under the Avicula contorta shales in the trialpit at Ty-du, referred to on p. 69, make it clear that the topmost beds of the Keuper are liable to assume the literal type, though the Rhsetic group shows no such change for some distance farther west.

The remaining exposures of this area of Trias present less detail ; on the south some old pits east of Cae'r-wigau exhibit two types of rock : one, a coarse red conglomerate made up of pieces of red-stained Carboniferous Limestone and red sandstone probably of Old Red age, in a dark red calcareous matrix ; this is to be seen in an old

quarry on the hill-side '.\00 yards south of Maes-yr-haul. The other type is a yellow breccia exposed at Cae'r-wigau-isaf and at the adjacent mill. A little farther south. Old Red Sandstone props out in rlie brook (p. 5).

A few yards north-west of Llwyn-Gibbwn, some red gravelly conglomerate, exposed by the edge of the alluvium, apparently dips north at .°>20. an appearance which may be due to false-bedding ; it contains subangular pebbles of fine purple sandstone and quartzite, but no Carboniferous Limestone. Similar conglomerates, alternating with red marls, are exposed in the lane leading up to Llanwensan : while, from some small exposures and from the character of the soil, it appears that conglomerates extend past Gelli-wen and form a small outlier north of Llanerch. There are some doubtful indications of a small patch of breccia also at Tre-Gwilym, one-third of a mile south-west of Miskin.

The present limit of the Keuper can be traced near Groes-faen. South-oast of Llwyn-y-penaii an old quarry shows coarse wellcemented limestone conglomerate, and on its northern edge Old lied quartz-conglomerates which appear to be in place. Coarse breccia was quarried and apparently burnt for lime a little nearer (Iroes-faen, and red sandy marls and grey and pebbly limestone were brought up from an adjacent trial-shaft. Yellow breccia was got in pits south of the Church and crops out in the Cardiff road, between the Church and Ty-nant, and again at a pond 100 yards south of Cwrt-y-carnau, where it rests on the Carboniferous Limestone. At Ty-nant the breccia is overlain by cream-coloured earthy limestone ; the beds dip about east at 12° and in the bye-lane turning northeastwards are followed by buff shales, and green marls with thin rocky bands exposed near the mill. These rocks evidently correspond to the tea-green marls and dip towards the RluTtic shales which crop out on the east side of the brook.

The Keuper marl resumes its normal type near the Peterston Lias outlier, and exposures at Maendy .show tea-green marls overlying red marls.

With regard to the source of the debris which forms these conglomerates and breccias, it is clear that the Carboniferous Limestone detritus could have been derived from the neighbouring escarpments, but the source of the pebbles of purple and dark-red sandstones, grits, and quartzite is not so clear. They do not resemble the, quartzitic grits near the top of the Old Red Sandstone as seen at Hensol and west of Groes-faen ; but on the contrary their rounding suggests that they have come from a pre-existing conglomerate. Such conglomerates though they have not been certainly detected in the area under description have been found in some abundance in the Old Hed Sandstone of the arealying farther east.* It is even possible that some of the conglomerates attributed to the Trias in the foregoing descriptions may really belong to the Old Red Sandstone, such, for

The Countryaround Card ill' (lol. /S'nnv//) pp. 17, 20. Jh. Newport, pp. Hi, 17.

Keuper. 29

example, as those at Llwyn-Gibbwn and Llan-cos-lech. The possibility, of course, exists only in the case of those conglomerates which are devoid of pebbles of Carboniferous Limestone.

The original limits of the Trias may be inferred on the following evidence. The Carboniferous Limestone at Welsh St. Donats remained above the waters until the close of the Keuper, inasmuch as the Lias was the earliest sediment to be deposited upon it. Near Bonvilston for the same reason we infer that the limestone was not covered till Rhsetic times. The Trias margin must, therefore, have run between Pendoylan and Bonvilston, and thence east of Welsh St. Donats. It must then have kept eastwards of Ystradowain, but how far the Old Red hill of Hensol Park was covered, there is no means of deciding. The presumed outlier of Trias at Llanerch, though in the line of strike of the durable Old Red grits of Hensol Park, nevertheless lies in a hollow, which suggests a pre-Triassic valley running in the direction of Miskin and Pont Clun. The occurrence of red shale apparently brought up from a trial-shaft at Hendy-isaf, if it be not stained Millstone Grit, confirms this supposition, so that it is not unlikely that the Trias within the centre of the Cowbridge- Cardiff anticline was continuous along this depression with that to the north.

North of the Anticline.

This northern tract of Trias follows the outcrop of the Millstone Grit and the lowest beds of the Coal Measures. It has been cut through, however, by the Ely Valley, for it was not met with in the shafts of the Cardiff Navigation Colliery.

The deposit is largely concealed by drift, but may be examined in the old haematite-workings near Mwyndy and Llanharry. It consists chiefly of a well-cemented coarse conglomerate of large more or less rounded Carboniferous Limestone pebbles, ranging up to two feet in diameter at Llanharry. The pebbles are iron-stained, and embedded in a sandy, marly, calcareous, and ferruginous matrix. Occasional pebbles of purple grit such as make up the gravelly conglomerates of the Pendoylan area (p. 26) have been found, as for example at Rhyd-y-castell, north-east of Llanharry. If, as seems certain, they were derived from the Old Red Sandstone, they must have travelled westwards or northwards. It is noticeable that even where the Triassic conglomerates rest on Coal Measures they consist almost wholly of Carboniferous Limestone detritus. By this fact also a northward trend of the material is suggested. Nearer Cardiff, on the contrary, there is reason to suspect an eastward trend.*

With the coarse limestone-conglomerate there are often associated red marly sandstone containing calcite-crystals, single or in groups ; sandy marls with occasional detrital fragments ; and beds of unmodified red marl. The red marly sandstone is prevalent in the Bute

The Country around Cardiff (Mem. GeoL Survey), 1902, p. 40.

30 Trias.

haematite-workings at Mwyndy and at the Llanharry Iron Ore Works ; it contains haematite in streaks and also diffused through the rock.

All these deposits rest nearly horizontally on highly-inclined Millstone Grit and Carboniferous Limestone, and some of the old haematite excavations have revealed the steeply-sloping shore of limestone against which the Trias was laid down. At Llanharry village the sinuosities in the margin of the Trias are due to its having run up shallow inlets in the old coast-line.

Besides old quarries the old haematite-workings which extend westwards from Bro-fiscin-fach to Hendy, and again from Ty-du as far as Pen-y-waun on the north and Fron-wen on the south, yield many opportunities of examining these rocks. Farther west the conglomerate emerges from the drift as a ridge at Pen-y-coed-uchaf , but around Llanilid all the rocks are hidden by drift.

South of the Anticline.

To the south of the Co wbridge- Cardiff anticline the Keuper is frequently overlapped by the Rhaetic and Lias. A small quarry 100 yards south of Redland shows the Avicula contorta-sh&les overlying a hard yellow dolomitic rock of tea-green marl age, while Carboniferous Limestone, apparently in place, crops out on the opposite side of the road. Here then we can fix a point on the Keuper coastline, for the limestone-ground to the north was still above water at the close of the Keuper Marl period.

Coarse yellow breccia reappears in Bonvilston, and extends westwards as a tongue which evidently occupies an original Triassic channel. A cutting on the Cowbridge road shows the rock filling the channel to be a yellow conglomerate of subangular limestonedetritus. Its southern margin round the curious Carboniferous Limestone ridge of Leige Castle and Tilau can be clearly traced, and the junction is exposed near a footpath at 200 yards north-east of the latter farm. The hedge is rooted in a thin band of irregularlybedded buff fine-grained impure limestone containing fragments and pebbles of Carboniferous Limestone ; the lower part contains irregular patches of chert, attached to one of which was a pebble of Carboniferous oolite which had been converted into chert. This was cut for the microscope and the slide (E. 2867) is thus described by Dr. Flett :—

A fine example of oolitic chert in which the concentric structure of the oolitic grains is well preserved. The grains are composed of very fine grained chalcedonic silica, the matrix forms a coarser mosaic. Patches of carbonates occur in the heart of the grains and in the matrix ; they are probably dolomitic as they effervesce only slowly with acid and do not stain. The rhombohedral form, usually very perfect in dolomitic crystals, is not well seen. The oolitic grains are brownish, the cementing matrix clear and nearly colourless.

This Triassic breccia rests on an irregular and broken surface of dark-blue Carboniferous Limestone ; though exposed for several feet the dip in the latter is difficult to determine, but appears to be south-west at about 45°. The rock appears to be dolomitizecl.

Keuper. 31

There is an old kiln and quarry in the breccia north of Ty'n-y- coed, and a quarry 100 yards south-east of the farm shows the junction with the Carboniferous Limestone again, the Triassic basement-bed being a grey calcareous rock with much angular detritus. This is overlain southwards by thick-bedded sandy calcareous rocky marls and impure limestone, all more or less yellow. A buff rock containing few if any detrital fragments prevails here, and a specimen (E. 2866) taken from the roadside opposite Whitewell Farm is thus described by Dr. Flett :—

Dirty yellow, somewhat ferruginous limestone, which contains a few grains of quartz and areas of crystalline calcite with dolomite rhornbohedra. It appears to be made up mostly of small well-rounded limestone pebbles in a limestone matrix. The rock contains no fossils, and both the pebbles and the matrix are composed of a mosaic of small grains of crystalline calcite.

Probably all these rocks, and certainly the highest, belong to the tea-green marls.

West of Ty'n-y-coed the Keuper is overlapped by the Avicula conforta-shales, but its original margin ran westwards to Llantrithyd, where it reappears, filling up old channels in, and wrapping round knolls of, the Carboniferous Limestone. It consists of the usual yellow breccia, but in its upper part, which evidently represents the upper part of the tea-green marls, it contains bands of yellow and buff shales and rocky marls generally free from detritus. These rocks are well shown in the road north of the church and between the village and Tre-Aubrey, but north of the latter place are overlapped by the Rhsetic, never having extended over some of this ground. A small outlier however of yellow breccia north of Tair Onen shows that the Bonvilston Trias extended up a gulf as far as this point.

West of Tre-Aubrey the Keuper, brecciated up to its top, is overlapped by the Rhsetic and Lias, but it reappears at St. Hilary in the form of two narrow strips along the north side of a fault. It consists of greenish-grey breccia and pebbly marls, and is proved to be of teagreen marl age by the fact that it is immediately overlain by Rha3tic sandstones. The original margin comes out clearly, as shown on the map, between The Cross and the village of St. Hilary ; it emerge? from below the Rhaetic again at the Vicarage and must then have turned north-westwards.

The Dawen Valley near Llandough cuts down deep into the Trias, which is here at least 150 feet thick ; in the lower part, exposed in Coed-y-Grabla, it is a coarse limestone-conglomerate with a red tinge. The deposit is pebbly to its summit, but farther offshore, in the valley half a mile south-west of Llandough, and again at How Mill, green and buff more or less rocky marls of the normal type may be detected just below the Rhsetic base. Occasionally grey fine-grained limestone occurs, as in an old quarry on the westtern side of the Dawen Valley north-west of How Mill.

At Llanbleiddian the original limit of the Trias ran westwards towards Nash, but the Lias spreads northwards over it.

The Cowbriclge Keuper appears to have been deposited at the extremity of an inlet which ran north-westwards and northwards from

32 Triaif.

St. Hilary as far as Aberthin, but the margin there turned sharply south-westwards under Cowbridge, past Llanbleiddian Castle, and thence south-westwards, there being no reason to think that the Keuper extended over Xewton Moor. A coarse red breccia which forms the lower part makes the bold scarp of Coed-y-llwyn, where it must be at least 100 feet thick. As shown in the Cardiff Koad south of Slade it contains pockets of red marl only a few feet below its top. It is remarkable to how small an extent detritus from the Old Red Sandstone enters into the composition of the breccia even at only a few feet distance, as may be observed in the small outlier south of Aberthin. The breccia has been quarried and apparently burnt for lime on the north side of a dry valley north of Slade.

The highest part as shown in the railway immediately south of the bridge on the Aberthin road is a massive grey rock made up of angular and rounded fragments of oolitic and crinoidal Carboniferous Limestone. The fragments, which range in size from mere grains to pieces two inches across, are embedded in a fine-grained grey or dark cream-coloured calcareous matrix, probably more or less dolomitic. Chert also occurs in strings and concretionary nodules. The actual top of the breccia is exposed on the east side of the cutting at about nineteen yards south of the bridge ; the uppermost six inches consist of hard dark cream-coloured or pale-brown rock, comparatively free from detrital fragments, and fine-grained and flinty in fracture. This is overlain by a trace of sandstone, followed by palegreen marls, one foot eight inches thick (p. 45).

At the south end of the same cutting, which crosses the Lias outlier of Cowbridge, the Keuper is represented by an impersistent band, one foot thick, of grey hard breccia containing fragments of Carboniferous Limestone, chert, and quartz. This conformably underlies the Rhsotic beds and rests unconformably on the Carboniferous Limestone. The pebbles, some of which are subangular, range up to one inch in diameter. In places strings and patches of chert are present, and chert seems here and there to take the place of breccia. The surface of the Carboniferous Limestone is fissured and contains strings of chert, and the Triassic basement-bed is so firmly cemented to it that the exact junction is difficult to locate. The older rock is dark-grey and crinoidal, and dips 8. 30° \Y. at 45°, whereas the breccia and the overlying Rhaetic and Lias beds clip about X. 10° W. at 20°, thus showing considerable post-Liassic movement along the line snewn in Fig, 1>. The rapid southerly thinning of the Keuper is here evident, and may be ascribed to an approach to land or to a paucity of detritus.

KKI TKR— continued. (Western part.) By A. STRAHAN, from notes by R. H. TIDDEMAN.

A largo tract of Trias runs along the north side of the Cowbridge- Cardiff anticline by Coychurch and Coity. It consists almost wholly of conglomerate, often coarse, packed with fragments of Carboniferous Limestone and a few other rocks. Haematite has been found

Keuper. 33

below these conglomerates at Rhythin, but attempts to work it appear to have met with no success. On St. Mary Hill Down the conglomerate is immediately overlain by, as well as faulted against, Rha3tic beds.

At Coychurch also the same sequence may be observed, but the yellow tint of the uppermost part of the conglomerate indicates that it represents the tea-green marls. One and a half miles further north the green marls resume their normal aspect as shown in a claypit at Hendre : —

Hendre Clay-pit.

Ft.

Sandy beds - - - - 3

Green and yellow marl - - 15

Hard marl with race and gypsum - - 2

Clayey red marl -2

Clay and marl, proved in a well - 30

A thin impersistent band of quartz-sand occurs in places near the bottom of the pit, but except for this the section differs little from those observable in East Glamorgan. The fact is interesting, for it shows that the Keuper deposits had space to develop in normal form in the strait which separated the Triassic island from the mainland of the Coal Field (Fig. 2, p. 24). At Coity conglomerate is faulted against Rhaatic and Lias except for a small space occupied by red marl at and east of the church.

The Keuper near Cwrt Colman consists in part of red marl ; it is faulted down on the north against Millstone G rit, but passes southwards under yellow and green shales and marls, which, however, seem to be thin.

At Pyle a complete sequence can be obtained in the Keuper as well as in the Rhaetic group. A pit close to the " Pyle Inn " shows a Rhsetic sandstone (p 55), while a steep slope down to the house exposes characteristic green Keuper marls which lie immediately below the sandstone. Below these again come red marls, which in a railway east of Pyle Inn Quarry contain a band of limestone between two beds of conglomerate. The limestone (3821) is described by Dr. Flett as granular, coarsely crystalline and without organic structures, but with a few grains of quartz. The green marls are well developed again on the south side of the Porthcawl Railway on the road to North Cornelau ; buff and grey marls, with black and green shales and thin nodular limestones, being visible in several places close along the Rhaetic base. From beneath these come red marls normal in aspect and sequence, but at North Cornelau conglomerate sets in, and the whole of the Keuper which circles round Newton Down by Ivenfig to Newton Nottage consists of that literal type. The fact that red marl formed the marginal Keuper deposit a mile to the east of Cornslau well illustrates the extremely sudden variations to which the formation is subject in this region. It may be noticed, however, that the conglomerates have 7665, D

:u T

clustered chiefly along the west and south sides of Xowton Down while near Cardiff they are more abundant on the eastern sides of some of the limestone-inliers.*

The rocks which project here and there through the sand of Kenfig Burrows nearly all consist of Triassic conglomerate. In some bands the pebbles are well rounded, and include grit as well as limestone ; in others rounded material alternates with angular breccia. Specks of galena are not uncommon.

A quarry west of Newton Nottage which is indicated on the map by a dip of 4° shows a coarse gravelly conglomerate resting on finegrained calcareous flags with small angular fragments of limestone. The flags show foot-prints and ripple-marks and closely resemble a slab which formerly lay in the village, but was subsequently transported to the Cardiff Museum. That slab bore the impressions of five footprints, which were figured and described by Prot. Sollas as being those of a Dinosaur, Brontozoum ThomasiJ The occurrence of footprints proves that the flags were laid down on a foreshore that was occasionally dry. The conglomerate is terminated at Porth-cawl by a fault, but an interesting proof of its former existence to the west of the fault is found in a Triassic cave near Lock's Common. The cave wras rilled in with Triassic gravels, marls and travertin.

Small patches of Triassic conglomerate lie on either side of the river at Ogmore. A larger mass is intersected by the coast-line near Sutton. Some of the included blocks of Carboniferous Limestone must fall but little short of ten tons in weight, which suggests that the deposit is quite local. Further proof may be obtained of the same fact within a few yards, for at the top of the hill where the Lias comes on there is no Trias under it. It. follows that the hill formed an island in Triassic times and that the deposits of that age thinned of! against its flanks.

The Country aroun I Cardiff (Memoir (Ic.ol. Siircct/) 1902, p. 40. t (}n irt. Joiirn, (J<">1. Sue., vol. xxxv., p. 511 (ISU).

Chapter Vi.

TRIAS continued.— RRMTW BEDS.

Introduction.

By A. STRAHAN.

It will be understood from the remarks made on p. 20 on the classification of the Keuper that the Rhsetic group is taken as commencing with the strata in which Avicula contorta makes its first appearance, and that it does not include the uppermost green marls, or " tea-green series " of old authors. Allusion was made also to the fact that, apart from a litoral modification in the immediate neighbourhood of Triassic land, the Keuper marls retain their normal aspect to their westernmost limit, wherever there was room for their proper development, as for example in the neighbourhood of Pyle.

Such was not the case with the Rhsetic, though the extent of open water was greater than in Keuper times. The shales and thin limestones which constitute the normal type at Penarth, and in the south of England and Wales generally, begin to give place near Cowbridge to massive sandstones, often simulating Millstone Grit, nor so far westwards as they have survived do they tend to revert to the normal type. As a first stage in the change the Rhsetic shales assume the character of calcareous marls and limestones, or more generally of oolitic limestone containing so much sand as to weather into a sandstone. The development of massive oolite has been noticed in the Lias also, as an indication of near- shore conditions (p. 59),* and it is interesting to find the Rhaetic strata assuming the same condition, and thus differentiating themselves from the Keuper in which oolitic limestone is not known. Chert, however, which abounds in the litoral type of Lias does not occur in the Rhsetic.

Another type of rock which is developed in the Rhsetic Beds resembles the Sutton- stone which is conspicuous in the Lias towards the western part of the area. It may be described as a massive limestone composed of fragments of shells and corals firmly cemented by calcite. When deposited it was probably a shell-marl, made up of the debris of shells living in the neighbourhood, but drifted into a mass. It usually contains fragments of Carboniferous Limestone and in this as in its general character constitutes such a rock as would be formed perhaps not on the beach, but close along a shore that was not exposed to heavy surf. Glauconite occurs sparingly in the Sutton-stone. This mineral appears at the present

See also The Country around Cardiff (Memoir Gwl. Survey), p. 69. 7665. D 2

36 Rhcetic.

day in greatest abundance in comparatively shallow water along nigh and bold coasts where no rivers enter the sea and where accumulation is not rapid. The distribution of these litoral types in the Lias and Rhaetic differs from that of the litoral Keuper in the respect that they covered a wider area. The Keuper breccias are clustered along the Keuper coast-lines, but the Rhaetic and Liassic oolites and the Sutton-stone were laid down in wider belts.

The change undergone by the Rhaetic from shales into sandstone is capable of more than one explanation. In the first place the area of exposed Carboniferous Limestone was contracting. The island shown in Fig. 2 had only slightly diminished in size, but all the others had disappeared. The coast-lines therefore consisted mainly of Millstone Grit and Coal Measures. But we may also suppose that the opening of a communication with the sea effected a change in the circulation of the water. Currents such as could not exist in the land-locked Keuper water would come into action and the distribution of sediment would be changed. The sandstones have been described as an estuarine form of Rhaetic, but it is perhaps wiser to avoid the use of the expression. They are not confined to the strait shown in Fig. 2, but appear both to the south and east of its eastern entrance. Their fossils, though not abundant, are all species which occur in the normal type of Rhaetic strata.

Mention was made on p. 20 of a temporary recurrence of Keuper Marl conditions in the Rhsetic period. The evidence for this consists in the interbedding of some thin bands of red and green marls, indistinguishable from the Keuper Marl, in the upper part of the Avicula contorta zone. This interbedding has been noted in several places west of Bridgend, and especially in the church-quarry near Pyle (p. 55). A similar recurrence was found in the upper part of the Rhaetic group of Belfast by Mr. R. Tate, who remarks that but for the well- marked succession and the presence of Cardium rhceticum the strata might have been referred to the Keuper.* It is noteworthy also that a fresh-water fauna has been described by Mr. E. Wilson in parts of Somerset at apparently the same horizon. j- The reasons for supposing the Keuper Marl to have been deposited in landlocked waters have been given on p. 21. It must be supposed that the sea was temporarily shut out again from a part of the Rhsetic area, either by the formation of sand-banks or some other barrier, or by a slight re-elevation of the land.

The identification of the sandstones of Pyle as Rhaetic was due to Bristow and Etheridge, and the Rhsetic boundaries were added in 1864 to the Old Series Map 36, by Bristow and Mr. H. B. Woodward. The strata were described in detail by E. B. Tawney in 1865, in a paper which was one of the earliest of a long series on the Rhaetic question. The following list includes the more important of those which have a bearing upon the Lower Lias and Rhaetic rocks of South Wales.

Quart. Journ. Geol Soc., vol. xx., p. 107, 1864. f Quart. Journ. Geol, Soc.; vol xlvii., p. 548, 1891,-

Introduction. 37

Wright, T. On the zone of Avicula contorta, and the Lower Lias of the south of England. Quart. Journ. Geol. Soc., vol. xvi., p. 374.

Bristow, H. W. On the Rhaetic or Penarth Beds of the neighbourhood of Bristol and the south-west of England. Geol. Mag., vol. i., p. 236. Also Rep. Brit Assoc. for 1864 (pub. 1865), Sections, p. 50.

Jones, J., and Tomes, R. F. [Letters on the Sutton Beds of Glamorganshire.] Proc; Cotteswold Club, vol. iii;, p. 191.

Tawney, E. B. On the Western Limit of the Rhaetic Beds in South Wales, and on the position of the " Sutton Stone," with a note on the Corals by P. M. Duncan. Quart. Journ. Geol. Soc., vol. xxii., p. 69.

Bristow, H. W. On the Lower Lias or Lias -Conglomerate of a part of Glamorganshire. Quart. Journ. Geol. Soc., vol. xxiii., p. 199.

Duncan, P. M. On the Madreporaria of the Infra-Lias of South Wales, Quart. Journ. Geol. Soc., vol. xxiii., p. 12.

A Monograph of the British Fossil Corals. Second Series, Part 4,

No. 1. Corals from the Zones of Ammonites Planorbis and A. Angulatus in theLiassic Formation [S. Wales, pp. 6-23, 27-35]. Pal. Soc.

Moore, C. On Abnormal Conditions of Secondary Deposits when connected with the Somersetshire and South Wales Coal-basins ; and on the age of the Sutton and Southerndown Series. Quart. Journ. Geol. Soc., vol, xxiii., p. 449.

Tatc, R. On the Fossiliferous Development of the Zone of Ammonites angulatus, Schloth., in Great Britain. Ib. p. 305.

Duncan, P. M. A Monograph of the British Fossil Corals. Second Series, part 4., No. 2. [Liassic] Appendix : Note on the Age of the Sutton Stone and Brocastle, etc., Deposits," p. 69. Pal. Soc*

1868.;

Duncan, P. M. First Report on the British Fossil Corals. Rep. Brit. Assoc. for 1868, p. 75. [Sutton and Brocastle, pp. 99-110.]

1872,

Etheridge, R. On the Physical Structure and Organic Remains of the Penarth (Rheetic) Beds of Penarth and Lavernock, etc. Trans. Cardiff Nat. Soc., vol. iii., part 2, p. 39.

Lee, J. E. Notice of Veins or Fissures in the Keuper, filled with Rhaetic Bonebed, at Goldcliffe, in Monmouthshire. Rep. Brit. Assoc. for 1872, Sections p. 116. [See also his Notebook of an Amateur Geologist, 1881, p. 72, and plates 171, 172.]

Moore, C. The Liassic and other Secondary Deposits of the Southerndown

Series. Trans. Cardiff Nat. Soc., vol. viii., p. 53. Toines, R. F. On the Stratigraphical Position of the Corals of the Lias of the

Midland and Western Counties of England and of South Wales, Quart,

Journ. Geol% Soc.. 1878. vol. xxxiv., p. 179.-

38 Trias.

Storrie, John. The Fossils at Penarth (Rhsetic and Lias). Trans. Cardiff Nat. Soc. vol. xiv. p. 100.

Tomes, R. F. A Comparative and Critical Revision of the Madreporaria of the White Lias of the Middle and Western Counties of England, and of those of the Conglomerate at the Base of the South Wales Lias. Quart. Journ. Gaol. Soc., vol. xl., p. 353.

Lucy, W. C. Southerndown, Dunraven, and Bridgend Beds. Proc. Cotteswold Nat. Field Club for 1884-5, p. 254.

Duncan, P. M. On the Astrocoenise of the Sutton Stone and other Deposits of the Infra-Lias of South Wales. Quart. Journ. Geol. Soc.., vol. xlii., p. 101.

Woodward, H. B. Notes on the Rhsetic Beds and Lias of Glamorganshire- Proc. Geol. Assoc., vol. x., p. 529. See also Rep. Brit. Assoc. for 1888, p. 900.

Tomes, R. F. Description of a new Genus of Madreporaria from the Sutton

Stone of South Wales. Quart. Journ. Geol. Soc., xlix., p. 574. Woodward, H. B. The Jurassic Rocks of Britain, vol. iii. The Lias of

England and Wales, Yorkshire excepted. If em. Geol. Survey.

Howard, F. T. Notes on the Base of the Rhaetic Series at Lavernock Point. Trans. Cardiff Nat. Soc., vol. xxix., p. 64.

Howard, F. T. The Geology of the Cowbridge District. Trans. Cardiff Nat. Soc., vol. xxx.

Strahan, A. Geology of the South Wales Coal Field.- Part 1. The Country around Newport. Mem. Geol. Survey.

Strahan, A. and T. C. Cantrill. Geology of the South Wales Coal Field. Part 3. The Country around Cardiff. Mem. Geol. Survey.

Eastern Part. By T. C. GANTRILL.

An outcrop of Rhaetic strata fringes the Liassic tract from Bonvilston to Cowbridge and also the eastern side of the Liassic plateau near Welsh St. Donats. The same rocks form an outlier at Pendoylan, and border the Lias outliers of Peterston and Castell-y- mynach, which lie partly within the eastern edge of the map.

Rkretic. 39

Castell-y-mynach Outlier. — The Rhsetic beds are visible only along the eastern bank of a stream at Ty-nant, near Groes-faen. At a spring on the southern edge of a wood between the mill and the Cardiff road, there may be seen dark shelly limestone with Protocardium rhceticum, black shale, and very dark coarse sandstone with remains of Gyrolepis Alberti, the whole being some 20 feet thick, and resting on buff rocky marls belonging to the tea-green marls of the Keuper. They evidently belong to the Avicula contorta zone, but whether they are succeeded by any representative of the White Lias could not be determined. They are not noticeably modified by literal conditions, a fact which suggests that the original Rhsetic margin lay some distance farther north.

Peterston Outlier. — The Rhaetic shales are poorly exposed in a brook between Maendy and Allt-isaf. South of the first-named farm on the top of the tea -green marls there follow with a sharp line of demarcation beds referable to the A. contorta zone, the lowest being an impure limestone, about two inches thick, which weathers into friable ferruginous earth and contains fragments of what appears to be buff Keuper marl. Upon this there rest grey, dark, and black shales, with a line of calcareous nodules, and bands of limestone containing Pecten valoniensis. A few yards farther up stream thin-bedded cream-coloured limestones and shales and shelly marls crop out which probably represent the White Lias ; the Lias comes on a little farther east.

Bonvilston to Cowbridge. — The Rhsetic outcrop enters the map east of Bonvilston. Black paper-shales overlie the Keuper at Redland (p. 30), and may be detected in the sides of the road for some distance towards Blackland. Pieces of dark limestone containing Pecten and Protocardium, and traces of black paper-shales, may be found in the low ground north-west of Coed-yr-Aber. North of Redland Wood no Keuper rocks are exposed, and the Rhaetic soil can be recognised so close to the brow of a large quarry in Carboniferous Limestone as to suggest that the Keuper is here wholly overlapped, as shown on the map.

Black shales with Pecfeft-limestone containing fish-remains (Gyrolepis Alberti, Ag.) crop out at two wells on the north-west side of the Lias outlier south of Bonvilston, and similar beds can be traced southwards along Llancarfan Brook nearly as far as Abernant. On the west side of this valley the outcrop spreads out east of Leige Castle and overlaps the Keuper, so as to rest directly on the Carboniferous Limestone. The actual junction may be seen in a small roadside section 200 yards north-west of Ty'n-y-coed. The section shows one foot of brownish and greenish-yellow clay with fragments of black paper-shales, and near the bottom a weathered band, one inch thick, of dark limestone containing Pecten valoniensis and fishteeth. The clay rests on decomposed Carboniferous Limestone, with crinoid ossicles. The Rhsetic beds dip south at about 5° while the Carboniferous Limestone dips in the same direction at 15° to 20°. Although both here and at Redland Wood the Rhsetic strata

40 Trias.

come into contact with the old land, yet they show no lithological change such as appears farther west. They seem to have been laid down on a gently sloping shore devoid of coarse debris.

Small exposures of the black shales with Pecfen-limestones which have yielded a scale of Gyrolepis Alberti may be detected around Castell-ar-Foel, and just within Llantrithyd Park a piece of limestone yielded Pecten valonicnsis ? and a reptilian bone.

Thence south-westward the Rhaetic beds locally disappear, but as the Lias shows no signs of literal modification, and as there is consequently no reason to suppose the Rhsetic to be overlapped, the disappearance is attributed to a fault. They emerge south-east of Wren Castle, and here for the first time exhibit signs of the oncoming of a more arenaceous type in the intercalation of bands of greenishgrey sandstone. These may be traced southwards along the valley, but are especially well shown in a road- cutting at Tre-gyfT, though the beds undulate gently down the road westwards at such an angle that only a few feet are exposed They consist of sandstone with Protocardium philippianum and Avicula contorta, blue sandy marls, a thin conglomeratic band containing pebbles of Carboniferous Limestone and chert, and black limestone with Pecten valoniensis. Several sandstone-blocks lying by the side of the cartroad to Tregyff are covered with casts of worm-burrows, with a few impressions of Avicula contorta.

This accession of sandy sediment becomes much more pronounced as we trace the outcrop westwards and northwards, and is due to the influence of some sand-bearing currents invading the area of deposit from the west rather than to the immediate proximity of a coast-line of Carboniferous Limestone cliffs.

Simultaneously with this appearance of sandstones in the Avicula contorta zone, thin bands of white flaky limestone like Sutton-stone, containing fragments of Carboniferous Limestone and broken shells, develop in the White Lias zone, this modification making its first appearance between Tre-Aubrey and Ty-draw. Sandstone, sometimes pebbly, predominates at Ty-fry, and is exposed at Ffynnon-y- cae, but between Ty-ganol and Pentre it contains some Pecten-lime- s tones. The Rhsetic outlier at Pentre is thrown down by a fault which passes through an old quarry, now a pond, 200 yards east of the road ; on the north side of the quarry is exposed Carboniferous Limestone, sparry, and containing traces of galena, but on the south, four feet of dark-brown Rhsetic shales are shown under limestone, while fragments of limestone containing fragments of shells and bone lie on the adjacent hedgebanks.

A bare surface of Carboniferous Limestone upon which the road at Ty-uchaf runs is remarkably smooth and is probably the waterworn floor on which the Rhsetic deposits were laid down. Three hundred yards north of Pentre two small old marlpits or quarries show sandy limestone and shales, yellow sandstone, and dark limestone containing fragments of what looks like carbonised wood. Farther north, on the extremity of the Lias, and 300 yards southeast of Tair Onen, there is a large excavation encumbered with

Ahcetic. 41

growing timber ; the floor at the east end is formed of a nearly horizontal bedding- surf ace of conglomerate, the well-rounded pebbles therein being mostly of Carboniferous Limestone, with a few of chert, and more rarely some small rounded fragments of black carbonaceous matter, possibly wood. At a higher horizon, yellow clay is to be seen on the western bank of the pit, and above it are large blocks of white flaky limestone resembling Button- stone, above which the Orea-beds of the Lias crop out. The conglomerate here probably belongs to the Avicula contorta zone ; the rock like Sutton-stone is probably at the top of the Rhaetic, but may be at the base of the Lias.

At Tair Onen a brown rotten sandstone, white or pale-green and calcareous where unweathered, has been quarried ; it contains Carboniferous Limestone fragments and casts of Pecten valoniensis. On the south-west this sandstone is apparently overlapped by Lias of litoral type, which abuts directly against the Carboniferous Limestone ; but it emerges again north of Garn, and is to be seen in an old quarry one furlong west of the second milestone from Cowbridge. It is succeeded by pebbly limestones and light-coloured marls poorly exposed in old pits north of Garn.

In and near St. Hilary the Rhaetic sandstones are frequently exposed, e.g., in the sides and floor of the lane north of Coed Hills, where they yield Pullastra arenicola, and at The Cross, where they contain thin streaks of black shale of the ordinary type. The highest beds, as may be seen along the southern edge of the tongue of Lias west of Garn, consist of fine-grained limestones and a conglomerate or bone-bed, the latter poorly exposed in an old pit 350 yards south-east of Eastdown. From this rock Schizodus ? has been obtained. A bone-bed is recorded by Buckland and Conybeare* as occurring " at the village of St. Hilary, near Cowbridge."

The Rhaetic outcrop extends southwards as far as Gigman Bridge near St. Mary Church Road Station, grey sandy and oolitic Rhaetic limestones cropping out in the lane east of the bridge. North of the station a deep and long cutting traverses 'a gentle anticline in thinbedded Lias limestones and shales (Ostrea-beds) ; at the bottom some soft dark shales and marls are brought up for a length of about 500 feet, though nowhere exposed for a greater depth than three feet. They differ wholly in appearance from the overlying Oraz-flags, and are evidently Rhaetic. The following details were noted at about the middle of the anticline : —

Railway -cutting north of St. Mary Church Road Station.

Ft. In.

Limestones, thin-bedded, blue, somewhat nodular, or breaking into blocks ; 2 to 6 inches thick, with shale partings 3 to 4 inches thick - - 10 to 15 0

Limestone-flags, 2 to 6 inches thick, with thin partings of shale ; strongly jointed ; full of Ostrea liassica. (The Orea-beds) - 94

Trans. Geol< tioc. Series 2, voU i. (1824), p, 301,

Ft. In.

1. Shales. dark-brown, lissilo. soft -

'2. Marl, hard, dark-grey, shaly Q

3. Shales. grey ,-,

Rn.Tir 4. Marl, dark-grey, hard. becoming in places a lime.itone 3

Shales, grey 4

(i. Marl, grey, lianl 4

7. Mails, shaly. dark-grey, exposed for 1 0

A few oysters occur in beds '2 and 4. Dr. F. L. Kitchin has identified the following additional fossils : In bed 2, Modiola minima, Ccrithium sp. ; in bed 4, Ccrithium sp., Protocardium, Modiola minima, Pleuromya sp., Phasianetta ? Plcurophorus elongatus, Protocardium philippianum ?

Bed 1 appears to represent the laminated limestone or ' slate ' which lies immediately below the CMrea-beds at Penarth, and the grey shales and marls below it correspond to the blue marls with Modiola. etc., which are found at the top of the RlhTtic group of that section.

South of the station a shallow cutting traverses the Ostrca-bcds, and, farther on, a gentle anticline which brings up to view about six and a half feet of the underlying R ha? tic shales and marls, as shewn in Fig. 3.

Railway-cutting south oj St. Mary Church Road Station.

Ft. In.

LIAS Limestones, thin-bedded, flaggy, blue ; (the Ostrea-hcds) 10 0 / Shales, brown, thin, and platy 8

Marl, light-brown, fossils 4

Shales, brown, with impersistent limestone ; Outre a

liassica, Modi old 9

Marls, light-brown 3

p j Shales, brown and blue ; Osirea liaxica and other fossils

not determinable, including gasteropoda 3 0

Limestone, hard, line-grained, light-blue, highly fossiliferous — Modiola minima ? Protocardium philippia n u in . Pie uropJi or us ? 6

Oolite, f sandy, blue-hearted, but weathering to a brown

sandstone ; exposed for - 1 0

The fossils have been identified by Dr. F. L. Kitchin.

A small fault crosses the cutting obliquely a little south of the centre of the anticline, having a direction of about W. 30" X., and a downthrow X. 30 E. of five feet. Beyond this fault Ili<- dip, about 4° or 5°. soon brings down the Osf/ra-beds to the level of the rails ; and not far beyond this these flaggy limestones take on a stronger dip, and more nodular limestones weathering to a lighter buff colour are thrown against them by a concealed fault probably of ten feet or so. Beyond this fault for about 115 feet distance the section is obscured, but then flags resembling the Ostrca-buds reappear and dip obliquely to the cutting at about 30°. They soon flatten however, and a little farther on are cut by a fault which, although it makes little show, has a considerable downthrow north and brings up again the Rha'tic beds, the sandy oolite being exposed for a depth of about ten feet. A few yards farther on two small faults

Rhcetic.

®

,2 ,2 -a cs '% a

cross the cutting ; the more northerly, which has a downthrow south of four feet, is clearly visible on the west, but not on the east side of the cutting ; the other has a downthrow in the same direction of two feet nine inches. A point of interest about this latter is that the fault-plane shifts laterally southwards for four feet eight inches on passing downwards from the soft marls into the harder sandy oolite, there having evidently been some horizontal movement of the soft over the hard beds along the bedding-planes. Beyond this point the Ostrea-beds and the overlying more nodular limestones gradually descend to the bottom of the cutting.

The most noteworthy fact exhibited by this cutting is the replacement of a large part of the soft Rhaetic marls and shales, as seen at Penarth, by massive sandy oolite. The replacement may be regarded as an intermediate stage in the conversion of the normal type of Rhaetic into soft yellow sandstones as developed at St. Hilary and west of Cowbridge. The oolite probably represents the nodular beds, number 5, and some of the beds beneath, of the south end of the Cowbridge cutting (p. 47). It has been sliced (E. 3252) and examined under the microscope, and is thus described by Dr. Flett : —

Oolitic limestone with a few shell fragments. The oolitic grains have in

44 Trias.

most cases a centre of calcite of or quartz which seem to be rounded grains around which a deposit of oolitic character has formed. There is little room for doubt that the rounded quartz is of detrital origin, and the calcareous fragments are sometimes crinoidal, sometimes pieces of limestone. The cementing matrix is granular calcite. There are also one or two pieces of felspar in the heart of oolitic grains.

The existence of oolitic structure in the Rhaetic strata — then included in the Lias — was noticed by Buckland and Conybeare. Speaking of the Lias of the south-western districts of England they remark that " between the white lias and the black shale, are strata of dark-grey marl sometimes perfectly stony, and then acquiring a granular and coarsely- oolitic structure. In this state it is known by the name of corn-grit."* The authors do not state where this oolitic rock occurs ; but Murchison,f a year or so later, quotes this paper by Buckland and Conybeare as the source of his knowledge of the existence of oolitic Lias at Cowbridge.

Farther along the Rhgetic outcrop towards Cowbridge there are road-sections between How Mill and The Herberts and elsewhere which show sandy limestones with traces of black shale underlying the Ostrea-beds of the Lias and overlying green rocky marls, the topmost beds of the Keuper. On the edge of the valley east of Llandough Rectory the Rhaetic sandstone has been quarried for additions to the church and schools. Thence the outcrop can be followed as far as the north-west corner of Coed-y-castell, 200 yards east of Newhouse ; but the occurrence on the fields below the house of pieces of sandstone, one containing fish-remains, indicates that the Rhaetic extends thus far before it is overlapped by the Lias.

Rhaetic strata at Cowbridge were first recognised by Mr. F. T. Howard J in 1897 ; they were laid open on the construction of the Aberthaw railway, which intersects the Lias outlier and shows it to consist of a syncline ranging in an east and west direction. The beds are exposed at the southern end of the Cowbridge railwaycutting, and there are good reasons for believing that certain rocks which crop out at the northern end of the same cutting are also of Rhaetic age.

North end of the Cowbridge railway-cutting.

FT. IN. 10. Limestones, hard (south of Gardiff-road bridge) ;

Ostrea and other lamellibranchs, about - 45 0

I J 9. Sutton-stone (north of Oardiff-road bridge) - - 70

v 8. Limestones, thin-bedded, blue ; Ostrea liassica ? - 90 7. Limestones, thicker-bedded, impure and marly ;

Ostrea liassica ; about 40

6. Marls and shales, hard, friable, calcareous, greenishbuff, with occasional pebbles ; Cardium ? 00

Riletic ?

5. Limestones, sandy (? oolitic) ; Cardium? - - 50 4. Rock like Sutton-stone, white, pebbly, with shell-fragments and a coral 26

Trans. GeoL Soc., series 2, vol. i. (1824), p. 300. t Trans. Geol. Soc., series 2, vol. ii. (1826), p. 362.

% The Geology of the Cowbridge District. Tranti Cardiff Natt Soc., vol. xxx, (1897-8)*

Rhcetic. 45

Ft. In.

(3. Marls, pale-green - 1 8

2. Sandstone, impersistent 1. Breccia, exposed for 6 0

The top of the breccia (1) is exposed on the east side of the cutting nineteen yard south of the Aberthin Road bridge ; it consists of dark cream-coloured rock (see p. 32). Adhering to its somewhat uneven surface there are one or two inches of (2) pale-green very finegrained calcareous sandstone visible at about fifteen yards south of the bridge. Four yards farther on, however, there rests directly on the breccia pale-green, soft, friable calcareous marl (3), which contains at its base small well-rounded pebbles of Carboniferous Limestone, chert and quartz. No fossils having been seen in either the green sandstone or the green marl, it is difficult to determine their age ; the former may be Rhsetic and the latter a reversion to Keuper Marl conditions, such as we have at Pyle (p. 36); but on the whole it is perhaps safer to regard them as Keuper.

Above these doubtful beds succeeds (4), a massive white or lightgrey limestone containing rounded and angular fragments of Carboniferous oolite up to eight inches in length, but averaging about one or two inches. In the apparently amorphous matrix of the lighter coloured parts there are numerous small cavities such as might be due to the dissolving out of shell-fragments, but some of the hollows are evidently due to the decomposition of small fragments of impure limestone, and in such cases contain a loose brown or yellow material. In this condition the rock corresponds in character to Sutton-stone as described on p. 59.

Above this comes (5) an obscurely oolitic sandy limestone, brown but blue-hearted, and irregularly bedded ; it contains a few small detrital fragments of limestone, together with an occasional cast of a lamellibranch (possibly a Cardium), and fragments of what appears to be wood. Treated with acid, this rock leaves a considerable residue of fine sand which consists chiefly of rounded grains of quartz, some few angular chips of brown chert, and occasional fragments of felspathic material. The quartz-grains were presumably derived from a distant source, but the angularity of the chert-chips suggests a local origin.

The strata seen next consist of alternating buff marls and shales (6), with a thin conglomerate of small limestone-pebbles ; they contain a few dwarfed oysters, some fragments of wood, and casts of small lamellibranchs.

Above these, finely oolitic limestones (7) and (8) set .in again, averaging nine inches to a foot in thickness ; they contain a few specimens of Ostrea, probably 0. liassica, and continue as far as the north side of the Cardiff Road bridge.

With regard to the systematic position of these poorly fossiliferous beds, it is safe to regard everything above the top of bed (3) as post-Keuper ; but whether beds (4),( 5), and (0) are Rhsetic or not is uncertain. That they are of this age is suggested by the strong probability that bed (8) with, possibly, (7), represents the Ostrea beds of the Lias.

46 Trias.

Above the beds last described, there lies a rock having the same general characters as bed (4), but devoid of large fragments of limestone ; it crops out immediately north of the Cardiff Road bridge. Above it, and south of this bridge, the cutting enters very hard thicker-bedded limestones without many pebbles, and without marl or shale partings. At about thirty or forty yards south of the bridge, and forty feet above the base of the Lias as seen at the south end of the cutting, and presently to be described, the limestonesare unusually massive, and contain angular chips of chert ; but at the axis of the syncline, near the milepost 23, they are more evenly stratified, and average only about one foot in thickness ; here also one or two thin bands of fine conglomerate occur. A rock half-way up the west side of the cutting yields ossicles of Pentacrinus, with Ostrea (cf. irregularis, Miinst.), 0. liassica, and another species of Ostrea large and coarseribbed, and somewhat resembling 0. multicostata. This horizon is about sixty feet above the base of the Lias, and is markedly fossiliferous, though the specimens are broken and difficult to extract.

Fig. 4. — Section at south end of Cowbridge Cutting. By T. C. CANTRILL.

N.

Old Lane.

Level of Rails.

L.L. Lower Lias limestones.

RH ETIC. d, shales and marls, c, limestones, b, marls, a, black shales. KEUPER. K, T.reccia. C.L., Carboniferous Limestone. F., Fault. Length of section about 160 feet.

Between Bridges 27 and 28 lower beds come into view, consisting of oolitic blue limestones varying from two to six inches in thickness, and separated by thin shale-partings ; Ostrea liassica occurs in profusion, but in poor preservation. Chert-nodules abound, but there are no foreign fragments.

That the lowest of these limestones are the Ostrea-beds is put beyond doubt by an examination of some shales, marls, and limestones which rise from beneath them. These make their first appearance half-way between bridges 27 and 28 ; they are shown to a depth of seven feet on the eastern side of the cutting and extend for twenty- four feet, when they are thrown out of sight on the south by an east and west fault which brings down the Lias. The beds exposed are number? 1 to 5 of the following section (p. 47).

At forty-seven feet south of the fault they reappear, which enables us to ascertain the throw of the fault to be ten yards. In this second exposure, which extends for. a horizontal distance of about seventy feet, the cutting traverses the whole group and shows that it is about twenty feet thick. It proves also that it rests on a thin and impersistent grey* breccia, apparently Keuper, and that this in turn reposes unconformably on the Carboniferous Limestone. The accompanying sketch illustrates the unconformity.

Mr. F. T. Howard* gives an illustration of this cutting, and records details of the Rhaetic beds in his paper on Cowbridge.

The complete succession of the beds here in descending order is as follows : —

South end of the Cowbridge Cutting.

LOWER LIAS, Ostrea beds. Ostrea liassica.

FT. Ix.

inch

RHTIC. 19 ft. 8£ in.

shale -

1. Shale ; fissile, dark-brown, weathering cream

colour, fossils

2. Marl ; hard, brownish-green, fossils and wood

3. Marl ; friable, light-brown, more shaly at base

Limestone ; pebbly and highly fos-

oiliferous - - 1£

Shale -parting - - - 1

4. I Limestone ; few fossils - - 3£

Shale-parting - - - - £

Limestone, few fossils - - 4

Marls, hard - - 4

5. Limestone ; impure, nodular, few fossils

6. Limestones ; marly, thin-bedded, with

partings ... ...

7. Marl or marly limestone ; hard, brown -

8. Marls and shales, alternating ; brown

9. Limestone, impersistent ; with pebbles of limestone

and chert. Fish- teeth - inches to

10. Marl ; a few limestone-pebbles and fish-teeth

11. Marl; fine-grained, with flinty fracture ; pebbles

up to three-quarters of an inch in length -

12. Limestone ; shelly and pebbly, like Sutton-stone

13. Marl ; hard, buff ... 3 inches to

14. Marl ; similar

15. Marl ; harder, pebbly, fossils

.16. Shales; black, locally sandy, pebbly at base. 10 in. to 1 0

1 2J

Trias.

Breccia ; grey, hard, with cherty patches ; fragments of limestone, chert, and quartz

Carboniferous Limestone;

The shale and marl (1 and 2) weather away from the overlying Osfrea-flags in such a way as to render the junction highly conspicuous. The shale is crowded with obscure remains of a small lamellibranch, and contains also Avicula and Modiola. It probably represents some dark-grey and brown paper-shales which occur in

Trans. Cardiff Not. Soc., vol. xxx (1897-8).

Tria*.

a similar position at Penarth, and which Mr. H. B. Woodward groups with the Lias. The marl (2) resembles Bed 6 of the section at the north end of the cutting.

Bed 9, which is a markedly conglomeratic band, thins out on the east side of the cutting among sandy marls, while a similar pebbly rock comes in immediately below and underlies the first for a distance of ten inches, passing northwards into marls. Bed 12 differs in no obvious respect from the Sutton-stone of the Lias ; the included limestone -pebbles range up to one and a half inches in diameter.

The following fossils have been determined by Dr. F. L. Kitchin :—

Rhcetic Fossils, South end of Cowbridge Cutting.

Bed 1. Modiola, Avicula.

„ 2. Modiola minima, Sow., Pleuromya ?, Cerithium sp., Area ?, and indeterminable lamellibranchs, gasteropods, and wood fragments.

3. Protocardium pTiilippianum ? Dunk.

4. Modiola minima, Sow., Ostrea, Pleuromya ?, Schizodus.

9. Saurickthys acuminates, Ag., Gyrolepis Alberti, Ag. Pecten valoni-

ensis, Defr.

10. Gyrolepis Alberti, Ag.

15. Cardium cloacinum, Quenst., Pecten valoniensis, Defr. Myophoria . nov. sp. ? (cf. eleyans, Alberti). Protocardium.

This section differs from that of Penarth in that the thickness of Rhaetic beds is ten feet less, in the greater development of marls of the White Lias type at the expense of the black paper-shales, and in the occurrence of conglomerates.

The Ostrea-beds are less readily recognised at the north end of the cutting owing to their modified character and the scarcity of Ostrea, but are probably represented by some limestones, containing a few specimens of that fossil, which have been quarried in the yard of Slade Farm. Again, according to a measurement made at the south end of the cutting, the base of the Lias ought to lie about twenty feet below the top of the seven-foot band of Sutton-stone at the Cardiff Road bridge. There is, therefore, space enough for not only the Os£rea-beds, but also some part of the Rhaetic group. The distance is only 500 yards, yet there is only the faintest likeness between the two sections. All that can be attempted in the way of correlation is to point out that Bed 6 at the north end resembles Bed 2 at the south.

Presumably these Rhaetic strata are soon overlapped, for no certain evi dence of their existence elsewhere round the Lias outlier has been obtained.

The Lias beds in the cutting, judged by their aggregate thickness, represent not only the Osraz-beds and overlying limestones of the A. planorbis zone, but also part of the overlying marls and shales (Lavernock Shales) of the zones of A. angulatus and A. BucJclandi of Penarth ; all, however, have assumed the condition of hard limestones.

f The Jurassic Rocks of Britain, vol< iii,-, p. 119, Mem, Geol, Surv,.

Rhcetic, 49

An analysis of one of the Rhaetic limestones overlying the black shales at the southern end of the Cowbridge cutting was made at St. Mungo's College, Glasgow, under the superintendence of Prof. T. Rhymer Marshall, for Mr. F. T. Howard, with the following results : —

pia,.

lO'OJ-

06

- 78-97

.Oo

MgCO;5 Moisture, etc.

42 62

The rock is therefore a somewhat sandy magnesian limestone.

Pendoylan Outlier. — In the Pendoylan outlier sections are poor. A well recently sunk in a field on the west side of the main road, eighty yards north-west of the school, is said to be fourteen feet deep ; it passed through the Rhaetic black paper-shales with Pecten-limQstones containing spines and tubercles of Acrosalenia? and fish-remains, and entered cream-coloured rocky marls, presumably the top of the Keuper. Pieces of Pectew-limestone occur at a pond 100 yards south-east of the vicarage, and debris of black papershales and limestone along the western edge of a coppice at Plwcau- Dafydd, apparently bounded on the east by a small fault which throws down the Lias. A minute Rhaetic outlier south-east of Ty'n-y-cae on the north-west side of the Cowbridge Fault has been already referred to on p. 27.

The outcrop of Rhaetic beds which runs from this fault northwestwards is largely conjectural, the whole country being buried under drift. It was to be expected, however, that the tea-green marls and breccias exposed in the lane leading westwards from Tre-Dodridge would be succeeded by Rhaetic at the foot of the rising ground occupied by Coed Leyshon, and this expectation was fulfilled on the sinking of .a small pit in search of coal, about the year 1888, in the north-east corner of the field containing the foundations of Ty-du, close to an ancient entrenched mound on the Cwm Farm. The shaft passed through some gravel into black paper-shales containing Rhaetic fossils (shell-fragments and a tooth of Sauriehthys acuminatus, Ag.), and then into pebbly green rocky marls, the top of the Keuper, How far to the north-west this outcrop extends is problematical, but it is certainly overlapped before it reaches Ystradowain.

Western part. By A. STRAHAN, in part from notes by R. H. TIDDEMAN.

The Rhaetic outcrops which have been described in the foregoing pages lie south of the Triassic island shown on the map forming Fig. 2. The survival of this island into Liassic times is proved by the fact that neither Rhaetic nor Keuper were deposited upon it, and we therefore have to cross to its northern margin to regain

7665. E

50 Trias.

a Rhaetic outcrop. Though the map shows the distribution of the land at the close of the Keuper, it serves in great part also to illustrate the close of the Rhaetic period. A good deal of land had disappeared near St. Hilary and Bonvilston, as can be seen by the fact that the Rhaetic overlaps the Keuper at those places, and no doubt the island had shrunk in other places also, but the general distribution of land and water remained much the same. The tract now to be examined occupies the site of the Triassic strait shown on the north side of the Rhaetic island. It will of course be understood that the present outcrop of the Rhaetic strata has been determined by unequal upheaval and denudation, and does not coincide with the original margin.

The change in the Rhaetic sediments, the progress of which has been traced near Cowbridge, here reaches a further stage. Sandstones have taken the place of the sandy oolitic limestones, and shales have become quite subordinate. The exposures range from St. Mary Hill to Pyle, and will be described in geographical order from east to west.

West of Pencoed a strip of Rhaetic beds has been let down between two faults ranging west-north-west. The strata consist mainly of sandstones which have been worked for building- stone at Saunder's Quarry on the south side of the brook and at Hendre Quarry on the north side, where they have also been used for silica in firebrick making. The rock may be described as a rather fine-grained freestone, white but with light-greenish bands. Ripple-marks are not infrequent on the bedding-planes. The rock from a trial-drift a little to the north of Saunder's Quarry contained Puttastra arenicola, while scales and fragmentary bones of Gyrolepis Alberti, Ag. were collected in the road to Dyfiryn. In the Hendre Quarry about 30 feet of sandstone are exposed, the lower part being massive and the upper part more thinly bedded. The rock rests upon the Keuper Marls (tea-green beds) described on p. 33.

A small outlier of this rock is faulted in on the top of Coed Mwstwr. A yellow limestone-conglomerate,which can be seen west of the fault, and presumably crops out also round the east side of the outlier, may represent the tea-green marls in their literal type, though the Hendre section showing these strata in their normal type is only about 600 yards distant. By comparing the levels of this outlier with the Hendre rock, we ascertain that the throw of the fault between them cannot be less than 100 feet. It probably increases eastwards, but it is lost to view under the drift of the Ewenny valley. The fault which throws the Hendre rock on its north side against Millstone Grit is probably much greater.

In approaching the St. Mary Hill Rhaetic outcrop from Coychurch we pass a quarry in the Ostrea-beds, 300 yards east of the mill at Persondy. They dip to the south-west and from beneath them there rise in succession White Lias, green Rhaetic marls with a red band, and then the sandstone which forms the lower part of that group. This is followed by a space in which the uppermost green Keuper Marls probably crop out, and then by light-coloured

Rhcetic. 51

conglomerate. The sandstone has yielded obscure fossils (Mollusca) with bone-fragments and scales of Gyrolepis Alberti. On St. Mary Hill Down huge blocks of the Rhaetic sandstone are scattered about, giving much the appearance of a Millstone Grit moorland. The sandstone lies in the form of a compound anticline, striking eastsouth-east and much broken by strike-faults. It probably rests on conglomerates. The joints of several of the blocks are covered by a quartzose fault-rock.

In these sections the occurrence of red and green marls high up in the Rhsetic group should be noted especially. In appearance they precisely resemble red Keuper Marls and, though thin, they may be recognised at intervals all the way to Pyle. The conclusions to be drawn from this recurrence of the Keuper Marl type of sediment have been previously mentioned.

The road from Coychurch to Coity runs for the most part on the Rhsetic outcrop. The sandstone is exposed occasionally and forms a scarp below the road. To the south of the road gentle slopes lead up to the outcrops of the upper Rhastic strata and the Ostrea-beds which are visible in a few little quarries.

In Coity a road-section west of the Castle exhibits sandstones and shales with greenish colouring and a little red mottling. The strata at first sight much resemble Keuper, but they yield Modiola minima in abundance, a fossil which is plentiful in the upper part of the Rhsetic group. A fault close by brings up red marl and conglomerate which are certainly Keuper. The massive sandstone which forms the lower part of the Rhsetic group crops up in several places in the village.

At Quarella this sandstone is extensively worked for building and other purposes. The rock is white or pale-green and is sawn into large slabs and blocks. Of the two quarries which are being worked the deeper lies to the south of the lane and yields the following section : —

Mr. M'GauVs Quarry, Quarella.

Ft. In.

Lower / Blue limestone, Ostrea liassica and Pleuromya - 0 2 Lias I Glay, about - 1 0

Clayey limestone representing the Cotham Stone, variable grey and green clay with variable cal- Rhsetic-] careous bands which have been burnt for cement -

making. Lima sp. and other lamellibranchs - 2 6 Hard and soft white and pale-green sandstone, used

for building, grindstones, etc., seen to 35 0

The stone from this quarry has been examined under tbe microscope by Dr. Flett, who furnishes the following description :

3816. An impure, rather fine-grained, pale-green sandstone, consisting of small grains of quartz and felspar, with a little chert, iron-ores, chlorite, zircon, etc. The green colour arises from the presence of a chloritic (?) mineral in the fine-grained material between the sand-grains, and partly also in the weathered felspars. The rock contains a few pieces of tourmaline and practically no carbonates.

52 Trias.

In a pamphlet on the Quarella Quarries* it is stated that the three best beds are the White Bed, 10 feet, the Grey Bed, 4 feet, and the Green Bed, 9 feet thick. The average densities are, White Bed 2-33, Green Bed 2'39, Grey Bed 2'40, and top rock 2'46.

The White rock absorbed 6 per cent, of its weight of water, the Green 4*5 per cent., the Grey 4'33 per cent., and the top rock 3*25 per cent., after having been immersed in water for 12 hours. The cement by which the grains are bound together in the rock is siliceous. Two six-inch cubes of the, white and green stones crushed respectively at 546' 4 and 438*4 tons per square foot, according to Mr. D. Kirkaldy. An analysis by Mr. J. S. Merry gave the following result : —

Silica - 91-20 .

Alumina - - - 3-35

Protoxide of Iron 0-58

Lime - 1-23

Magnesia - - - 0-25

Combined Water 2-57

Loss, and possibly a little Soda - - 0-82

Another quarry to the north shows, under some gravel and loam, a massive sandstone, fifteen feet thick, underlain by twenty feet of more rubbly sandstone. Exposures of the sandstone may be seen in the river south-west of the Quarella railway-bridge, and again at the bend south-east of the asylum.

A large quarry opposite the Angeltown Asylum was opened for building-stone for that structure. The section is now obscured, but Rhsetic fossils may be seen in the quarry-rubbish.

The railway-section at Cwrt Colman, which was described in detail by E. B. Tawney in 1865,'f is now partly overgrown, but some of the beds examined by him on the south side of the railway can now be seen on the north side. The following descending section is constructed from the descriptions given in his paper (loc. cit., p. 71.)

Cwrt Colman, south side of the Great Western Railway.

Section by E. B. Tawney.

Ft. In.

White, pale-green and yellow sandstones and sands - - 17 0

Shales, marls and sandstones - 9 0

Three beds of siliceous limestone with fish-scales, Anomia. Shales - 3

Soft chocolate-coloured sandstone with Avicula contorta and

Pecten valoniensis 1

Dark shales 3 0

Siliceo-micaceous limestone with irregular marly surfaces.

An occasional quartz-pebble and reptilian bone with

an abundance of teeth and scales of the fishes named

(op. tit.) The Aust Bone-bed. Two inches to 3

Shales, including a grey and green marly limestone, the

grey part being full of shells - 3 0

White or yellowish massive sandstone with a few small

quartz -pebbles ; coprolites at the top - - - - 8 to 10 0

Quarella Quarries, Bridgcnd, 1893.

t Quart. Journ. Geol. 8oc., vol. xxii., p. 70 (1866).

Rhcetic. 53

All these strata were referred by Tawney to the Rhsetic group, and the scarcity of calcareous and aluminous matter as compared with Penarth was commented on. For the reason stated the details could not be verified, but a somewhat different succession can now be determined in a road south of Melin Cwcw. We there obtain in descending order : —

f Blue limestone with Ostrea liassica, Pleuromya crowcombeia ? Tate ( non Moore, and a coral (Ostrea-beds).

Buff marlstone weathering white, probably representing the Gotham

Stone. Green marls with a band of red marl, closely resembling Keuper

Marl.

Calcareous sandstone, several feet thick. Tough shelly limestone, in part resembling Sutton-stone.

Rhaetic Beds.

The strata exposed in the north side of the railway-cutting evidently rise from beneath these, and themselves rest on the thick Rhsetic sandstone which forms the crest of the hill of Cwrt Colman. They include the bone-bed referred to by Tawney and some soft strata. In this locality again the observation that red and green marl are associated with the upper part of the Rhsetic group is confirmed. Higher up the valley some old pits show black shales resting on graen limestone and white marly limestone. The green limestone is full of shells, which, however, cannot be broken ot, but there is little doubt that the strata belong to the upper part of the Rhaetic series.

The following results of microscopic examination of specimens from this neighbourhood have been furnished by Dr. Flett :—

3818. Melin Cwcw ; in upper part of the Rhsetic, among green marls. Very fine-grained grey limestone, with a few rounded spots and elliptical areas of crystalline calcite. This looks as if it had been originally a fine limestone- mud. When treated with acid it leaves a considerable amount of fine yellow argillaceous residue. I can find no organic structures in it.

3820. Melin Cwcw [the "tough shelly limestone" of the section given above]. Shelly limestone, in which the numerous shell -fragments have been replaced by a mosaic of crystalline calcite similar to that of the matrix. The rock has throughout a highly crystalline character, but the outlines of the shells have been preserved. A few rhombohedra of ferriferous dolomite (?) are present.

3822. Melin Cwcw, close to 3820. [A very shelly limestone which looks like a sandstone.] Shelly limestone, with worn shell-fragments which internally consist of a coarse calcite -mosaic, though the external form is retained. Dissolves in acid, leaving only a small residue. Matrix also of crystalline calcite ; a few grains of dolomite.

3815. South of the railway and south-west of Cwrt Colman. Greenish, cherty, concretionary or brecciated limestone. The green colour is due to glauconite or chlorite. In the green matrix lie irregular fragments of compact creamy limestone. The rock shows no fossils, and the appearance of the slide would lead to the opinion that it is concretionary, as coarsely crystalline and finely crystalline patches alternate, and there are traces of cavities filled with caleite, chlorite, and chert.

54 Trias.

The Rhaetic outcrop broadens out southwards to Laleston. The ground north-west of the village is underlain by sandstone, but above that rock there are indications of black shale, and there was formerly an exposure of limestone, the age of which led to dispute. The only section appears to have been the Laleston Churchyard Quarry referred to by Tawney (op. cit., p. 77). According to him it showed Sutton limestones beneath " the Monofo's-beds," and in sonn shales there he found spines and portions of the test of an echinoderm (Hemipedina ?). His complete list from the locality " Laleston " (op. cit., p. 79), included the following species : — Avicula contorta, Portl., Axinus elongatus, Moore, A. cloacinus, Moore, Myophoria poster a, Qu., Modiola minima, Anatini precursor, Qu., Monotis decussata, Ostrea liassica, Strickl., Hemipedina sp. On this evidence Tawney identified the rock as Rhaetic and quoted it in support of his contention that the Sutton-stone was of that age.

Moore, however, redescribed the quarry in the following year.* He found in it a block containing an abundance of Lima gigantea, Plicatida intusstriata and Ostrea liassica, and stated that the bed is crowded with a coral, not, however, the species of the Sutton-stone of Brocastle. Upon it there rested 1 foot of marl with perfectly preserved impressions of plants, together with Entomostraca and Monotis decussata in abundance. He further points out that Monotis decussata had been proved by him to range above the Rhaetic, and states his belief that the rock belongs to the horizon of Ostrea liassica. To this we may add that the'occurrence of Lima gigantea and of corals supports Moore's view. The quarry is now covered up so far as the lower rocks in it are concerned, and no other exposure has been made.

At Cae Tor the OsZraz-beds have been quarried. Beneath them there is some red and black marl, and then a coarse calcareous grit with a few pebbles, in close association with a shelly and detrital limestone containing fragments of corals, molluscs and echaioclerms, together with small fragments of an older granular limestone and grains of quartz. Dr. Flett finds under the microscope that there ia also secondary quartz, sometimes with good crystal outlines, replacing the calcareous material of the rock. The rock lies upon or close above Triassic conglomerate, and is presumably of Rhaetic age ; but it is evidently a beach-deposit, for it thins out within a few yards to the south on the shores of the island shown in Fig. 2, p. 24. Presumably it is below the limestone of the Laleston quarry, but there is no direct evidence of their relations. The Stormy Down sections, though they come next in geographical order, will be better considered after a discussion of the fine exposures at Pyle.

A quarry to the south-east of the house formerly known as Pyle Inn was opened about the year 1896, to get stone for railwayviaducts, etc., It yields a section of the lower part of the Rhaetic group, extending nearly if not quite to its base.

Quart. Journ, Geol. Soc,, vol. xxiii., p, 519 (1867V

Rhcetic. 55

" Pyle Inn."

FT, IN. Soft drab and green sandstone with shell-beds. Natica pylensis,

Cylindrites oviformis, Myophoria - 12 0

Ochreous bed 4

Fine sand 13

Green and grey clay - 36

Calcareous nodular bed. Acrodus minimus 3

Shales 13

Calcareous nodular bed with fish-remains ... 3 Shales - 1 8 Fine whitish sandstone with plants, and at top a seam of quartzpebbles with remains of Hybodus and Acrodus ; seen to - 12 0

The uppermost green marls of the Keuper are exposed in a slope leading down to the house, just below the lowest rock reached in the quarry.

The Rhaetic sandstone has also been much quarried west of Pyle Church, the outcrop having been followed for a considerable distance. Much stone was got here for the building of the modern residence at Margam Abbey. Near the entrance a white sandstone is seen to a thickness of 6 or 7 feet, with casts of Pullastra arenicola near its base. Upon it then rests a greenish marl with about 6 inches of red marl, corresponding, no doubt, to the green and red marls previously noted at Cwrt Colman and St. Mary Hill. Further on in the quarry the sandstone, where it has been more recently worked, shows brightgreen marly partings with ripple-marks, and yields Anatina precursor, Myophoria, and Axinus doacinus, while Natica has been obtained from the quarry-rubbish. The occurrence of the green and red marls next above this sandstone, suggests that that rock lies high in the Rhaetic group, and probably corresponds to the upper of the two sandstones in the " Pyle Inn " quarry, which also yielded Natica and other fossils.

Of the many scattered openings on Stormy Down the greater number have been made in search of sand for silica-bricks. One

Some of the beds in the lower part of this quarry were stated by Tawney in his paper already quoted (Quart. Journ. Geol. Soc., vol. xxii., p. 70.) to be " very similar to the white Keuper sandstone near Bridgend," and on page 72 (op. cit.) he shows that he is referring to the Quarella stone, and that h3 regards that rock as bing low down in the Keuper. That the Pyle and Quarella stone are similar is true, but that they are not of Keuper but of Rhaetic age is proved by the evidence given in these pages. Tawney remarks that he is obliged to dissent from an opinion expressed by De la Beche in the Geological Survey Memoir, vol. 1, p. 252, that the sandstones near Pyle Church are inferior to the red marl. The words used by De la Beche were, " we here find, near the church, greenish grey, grey and red sandstones, and we also observe these to be covered by red or variegated marls in the same vicinity, supporting lias." It seems certain that De la Beche referred to the green and red marls visible in the church- quarry above the sandstone, and not to the Keuper marl. Tawney also noticed these variegated strata in the churchquarry, and remarked of them, " These belong to the Avicula contorta series, and not to the Keuper." It would seem, then, that there was really no disagreement between these eminent observers as to the stratigraphical position of the variegated marls.

50 Triti*.

of these, lying south-west of the chemical works, shows about 20 feet of massive sandstone, much like a Carboniferous sandstone, but resting on and containing thin seams of greenish clay. A little further west there is a scarp of somewhat similar sandstone, and close beneath it a swallow-hole into limestone, which at first sight looks like Carboniferous Limestone, but which on closer examination proves to be a purely chemical deposit devoid of organic remains. The sandstone seems to represent the lowest sandstone of the " Pyle Inn " Quarry, while the limestone is probably of Keuper age.

Further east, sandstones with green and yellow clays are exposed in a long line of excavations. Some of the sandstones are brightgreen and ripple-marked, with a resemblance to the upper beds of the Pyle Inn " Quarry. They contain casts of Avicula contorta, Pleuromya ? and other lamellibranchs, in an extremely fragile condition. A disturbance runs through the excavation in an eastsouth-east direction.

The '; Little Cement Quarry " on the edge of the Down, southsouth-east of the Stormy Works, shows a bed of extremely shelly white limestone, resembling those which occur on both sides of the valley three-quarters of a mile west of Cwrt Colman. There, however, the shelly limestone lies above a white marly limestone, whereas here it lies below such a rock. The material thrown out in deepening a well close by yielded Natica pylensis, Myophoria sp. (cf. poster a, Moore) and Cylindrites oviformis. The white marly limestone is similar to the rock formerly used for making cement. A specimen has been examined under the microscope by Dr. Flett, who reports as follows : —

3819. Green-spotted fine-grained argillaceous limestone, with more or less of a nodular concretionary structure. It contains no organic structures, but the fine matrix is traversed by irregular patches and veins of clear crystalline ealcite. It leaves an abundint fine argillaceous residue after treatment with acid.

Some Rhsetic marls were formerly used for cement at Stormy Works and were exposed at the time of Mr. Woodward's visit to the locality, though they are no longer visible. He gives the following section : —

Stormy Cement Works.

Lias; S" P- 7-1.

Ft. In.

f Limestone-shales - --08

Hard compact limestone (like Sun-bed) 0 10

Shaly parting- Rhac'tic J Hard compact and rather shaly limestone - 0 8

Beds. Black shales with thin bands of limestone, Pcctcn valoni- [ part of J I cnsi$ 1 0

(Jrey and greenish marls with hard nodules (formerly I used for cement) seen to depth of - -36

The thick Ilhnritic sandstones form an escarpment of coarse white and yellow conglomerate near the top of Stormy Down. On some of the big blocks casts of lamellibranchs may be seen, but in other

Rkcetic. 57

respects the stone might be taken for Millstone Grit. Such blocks are scattered all across the Down, and it was in one of these that the impression of a large reptilian jaw was discovered by Mr. John David. The specimen was presented to the Museum of Practical Geology, and has been described by Mr. E. T. Newton as a left dentary bone of a megalosauroid reptile, Zanclodon cambrensis* There is scarcely room for doubt that the specimen occurred in true Rhsetic strata of the zone of Avicvla contorta.

Anatina precursor, Quenstedt, and MyopJioria postera, Quenstedt, from the Rhsetic sandstone of Stormy Down ; Pleurophorus elongatus, Moore, Gervillia precursor, Quenstedt, and Anatina sp. from the sandstone at Ty-fry, are preserved in the Cardiff Museum.

Quart. Journ. Geol. Soc., vol. liv., p. 646, 1899.

Chapter Vii.

Lias.

INTRODUCTION. By A. STRAHAN.

The map under description includes the western part of a broad tract of Lias which occupies much of the Vale of Glamor an, and of which the eastern pari was described in a previous part of this Memoir.*

The following table gives in descending order the Liassic zones existing in South Wales. They belong to the lower part of the Lower Lias.

Zone of Ammonites [Arietites] semicostatus. „ „ „ Bucldandi.

„ ,, [Schlotheimid] angidatus.

„ ., [Psiloceras] planorbis (including the Ostrea-beds).

The Lias alone of the Secondary rocks existing in South Wales covered the whole area embraced in this map. The island however which forms so prominent a feature in the Triassic map (forming Fig. 2, p. 24), and which survived through Rhsetic times with its main features little changed, remained above water during part of the period of the Lower Lias. The proof of its survival lies chiefly in ths changing character of the Liassic strata as they approach its shores. No doubt the lower strata thinned out against the land, as did the Rha?tic and Keuper before them, and were overlapped by higher beds as the subsidence proceeded, but from the fact that the Liassic strata, whether shales or limestones, tend to pass into massive limestones of which the horizons are extremely difficult to determine, it has proved impossible to work out the overlapping in detail. Though the existence of the island therefore is abundantly evidenced by the fact that Lias rests directly on the Carboniferous Limestone, and contains abundant wave-worn detritus derived from it, the moment of its disappearance cannot be determined, further than that it probably ceased to exist during the period of the zone of Ammonites angulatus.

It will be understood that what was the highest ground in Liassic times is not necessarily the highest ground now, owing to post- Liassic earth-movements. For example, a post-Liassic antic-line

*The Country around Cardiff (Mem. Geol. Survey), chap. vii.

f In this table the original names of the zones are retained as a matter of convenience. The names now used for the zone-fossils are added in square brackets.

Introduction. 59

has raised the Liassic base near Bonvilston to about 300 feet above sea-level, and the denudation which ensued has removed the Lias from a tract about six miles long. Further north, though there are patches to prove its former extension, the Lias has suffered still more from subaerial waste, so that its present margin gives no clue to the position of the original shore-line. The absence of marginal types of limestone suggests that the shore lay a good deal farther north, though at the same time it is hardly probable that the Lias overlapped the Pennant scarp. Of the two types of Lias therefore, the normal occurs throughout all the part of the map which lies south of a line drawn through St. Mary Church to the coast between Dunraven and Marcross. The same type is found also near Bridgend and north of Pendoylan. The intervening area, covering the site of the Triassic island referred to, has been and is still in part occupied by Lias of litoral type.

To the normal type a description given of the Cardiff Lias is equally applicable here. It consists in its lower part of hard slabby limestones, crowded with Ostrea, passing up into evenly bedded alternations of limestone and shale crowded withal m. [Psiloceras] planorbis. Above these lie some thick sha1 s or marls, almost devoid of limestones, which belong to the zone of Am. angidatus, but which we may conveniently call the Lavernock Shales, and these are followed again by strata in which limestones predominate, and which belong to the zone of Am. Bucklandi. To the varying resistance offered by these rocks to denudation much of the Liassic scenery is due. The Osrea-beds stand cut as a platform and low escarpment founded upon a slope of the softer Rhsetic shales, while the limestones of the Am. Bucklandi-zone form a second and inner scarp and overlook wooded slopes occupied by the shales of the zone of Am. angulatus.

The litoral type includes a variety of limestones, and conglomerates or breccias. Generally it is characterised by an absence of shale and consequently by a more massive bedding than the normal type, by the prevalence of oolitic : tructure, and by an abundance of chert in nodules or as a replacement of the carbonate of lime in fossils. Many of the limestones assume the character of the Sutton-stone, as was the case with some of the Rhsetic strata. This rock, which has been much used in the neighbourhood for building, may be described as a shell-sand or shell-marl, mixed with a variable amount of small detritus from the Carboniferous Limestone. It has been cemented by partially crystalline calcareous matter, which, however, has not always filled all the inter-granular spaces, so that the rock has a cavernous and tufaceous appearance. The shells consist, so far as the fragments can be recognised, of the fossilsproper to the horizon, and are chiefly lamellibranchs but sometimes include much coral-debris. The type of rock occurs not only in mass, as a local basement-bed to any of the lower Liassic zones, but appears in thin bands among both Rhsetic and Liassic limestones of normal type. It often contains large angular or rounded fragments of Carboniferous Limestone sparsely scattered through it, and in this and other re-

60 Lias.

spects constitutes a near-shore deposit such as might have been anticipated under Liassic conditions. Some evidence of coralgrowth also has been obtained by Mr. Tiddeman round an inlier near Wick. Galena occurs frequently both in Sutton-stone and in the other conglomeratic limestones both Liassic and Triassic. It usually appears as strings or isolated crystals formed in place in the matrix, nofc as derived fragments. At Candleston, according to De la Beche, it fills the cavities left in Sutton-stone by the disappear mce of shells, and at Dunraven it enters into the joints of the jet-like plants contained in the Lias limestone.*

Specimens of Sutton-stone from Sutton (E. 1253 and E. 3827), and Tair Onen near Cowbridge (E. 3829), have been submitted to examination under the microscope by Dr. Flett, who reports as follows :—

One of these specimens is a compact white or slightly creamy limestone full of broken fragments of shells of mollusca and brachiopods. There is little crystalline calcite, but when the broken surface is examined with a hand-lens many small rounded grains are visible ; they resemble the oolitic grains of oolitic limestones. The rock, however, is not an oolite; these grains are rounded shell-fragments which are coaled with a thin layer of fine crystalline calcite. Most of the limestone is composed of small pieces of shells of molluscs and brachiopods with d6bris of corals. A few broken echinodermal plates may also be seen. The cementing material is crystalline calcite in fine granular mosaic. E. 3827 shows angular cavities in the handspecimen which appear to have originated from the removal of shell-matter in solution. It contains also pebbles of a dark -coloured limestone, one of which is well rounded and nearly an inch in diameter. This differs a good deal from the Sutton-stone in structure and composition; it is more crystalline and is full of crinoidal fragments, and tests of foraminifera.

The included fragments in the literal Liassic rocks consist exclusively of Carboniferous Limestone. Though generally waterworn and often in this respect contrasting with ,the cliff- talus which forms the marginal type of Keuper, angular material occurs also in thin bands. The scarcity of rocks other than limestone is remarkable when we consider that only the crests of a few of the limestoneridges remained above water, whereas there must have been a long shore close by formed of Pennant. The Liassic marginal deposits of that shore have all been removed by denudation ; apparently they were strictly confined to its neighbourhood, from which we may infer that locally at least the Liassic sea was not troubled by powerful tides or by heavy surf. The inference' is supported by the character also of the normal Liassic sediments.

It follows from the fact that the Liassic sea was encroaching upon subsiding land that each zone overlaps its predecessor. Consequently the base of the Lias, at any point where it rests upon the older rock, may not be the true base of the formation, and as a fact the Ostrea-beds are rarely present save where the Rhaetic group exists beneath. In such cases the abnormal character of the local basement-bed makes its zonal identification extremely difficult.

Memoirs of the Geological Survey, vol, I, pp, 9-72, 273,

Introduction. 61

The following history of a discussion on the relations of the Sutton-stone of Button and Southerndown is by Mr. H. B. Woodward.*

Introduction — continued. By H. B. WOODWARD.

The peculiar characters of the basement-beds of the Lower Lias, where they rest on the Carboniferous Limestone, at Southerndown and Dunraven near Bridgend, and at other localities in Glamorganshire, were pointed out many years ago by De la Beche ; he noticed that the limestones became more or less conglomeratic, and were associated with a whitish limestone known as Sutton Stone.f

Since the recognition of the Rhsetic beds in this country (1860-61), there has, however, been much discussion on the age of the " Lias conglomerate " of South Wales, and on the question whether the Rhsetic beds are or are not represented in it.

In 1863 Mr. R. F. Tomes " claimed for the basement-beds a date corresponding to the Rheetic age," on account of the presence of Plicatula intusstriata% ; but this view proved to be based on an insecure foundation, as the species occurs sometimes abundantly in the Lower Lias.

In 1866 E. B. Tawney expressed his opinion that the whole of the Conglomerate series was Rhsetic in age § ; he divided the beds as follows : —

2. Southerndown Series (about 50 feet thick at Southerndown and about

12 feet at Dunraven). 1. Sutton Series (about 40 feet thick).

The ordinary beds of Lower Lias, overlying the Southerndown Series, were grouped by him in the zone of Ammonites Bucklandi.

lawney's conclusions were shortly afterwards contested by Charles Moore,|| H. W. BristoWjIT and Prof. Ralph Tate,** who maintained that the beds were Lower Lias ; while Prof. P. M. Duncanft adopted a sort of compromise by applying to the strata the term Infra-Lias, which includes both White Lias (Rhaetic Beds) and the zones of A. planorbis and A. angulatus.

Bristow, who maintained that the beds belonged to the Lower Lias, disputed the sequence pointed out by Tawney, urging that there was but one series, by whatever name it may be called ; the Southerndown Series being merely the easterly prolongation and the representative of the Sutton Stone, and the total thickness being from 35 to 37 feet. He admitted, however, that as the Sutton Stone reposes on the upturned edges of the Carboniferous Limestone, and fills up irregularities and undulations in that rock, the thickness is somewhat variable in different places.

Subsequently Tawney abandoned his view on the Rhsetic age of the deposits, JJ and for a time the question appeared to be settled. In 1884, however,

Jurassic Rocks of Britain (Geol. Survey Memoir], vol. iii., pp. 99, 100.

t Mem. Geol. Survey, vol. i. pp. 269, &c. ; Geol. Observer, Ed. 2, pp. 482, &c.

j Proc. Cottesw. Club, vol iii. pp. 191, 202.

§ Quart. Journ. Geol. Soc., vol. xxii. p. 69.-

Ibid., vol. xxiii. p. 511 ; and Proc. Bath Nat. Hist. Club, 1865.

f Ibid., vol. xxiii. p. 199 ; see also pp. 202, 203.

Ibid., p. 307.

ft Quart. Journ. Geol. Soc., vol. xxii. p. 89 (1866) ; vol. xxiii. p. 15 (1867) ; vol. xlii. pp. 101, 113, 139 (1886) ; andSupp. to Fossil Corals, Palceontogr. Soc.

JJ This statement is made on the authority of Mr. Etheridge. Quart. Journ. Geol. Soc.t vol. xl. p. 375 (1884).

62 Liti*.

Mr. Tomes expressed his conviction that the conglomerate-bed at Stormy Down near Bridgend " is the true representative of the Sutton Stone of Sutton and West, of the ; Guinea ' led of Bint on and Graf ton in Warwickshire, and of the White Lias of that county and the West of England ; vf a view taken also by .Mi1. W. ('. Lucy.;;; who had accompanied Mr. Tomes on a visit to the South Wales district. At the same time Mr. Llliei'idge, who had previously considered that the Sutton Stone and white conglomerate might be of Rh;ctic age, observed that their precise position was still an open question. §

Xo doubt sonic difficulty is experienced in making out the precise relations of the white Sutton Stone and conglomerate to the ordinary Lower Lias of the area. This arises in part from the cliffs being to a great extent inaccessible, while portions of the coast can only be visited for a short time when the tides are at their lowest ; and we have to scramble over ragged rocks. Moreover the strata themselves are subject to variations, and are shifted in three or four places by faults, in situations where it is difficult to estimate the precise amount of the displacement. By measuring the strata in detail at several points, I was enabled in time to make out the sequence, and to satisfy myself that while the white Sutton Stone and conglomerate (with occasional bluish modifications) form the base of the series, both at Sutton and Dunraven, these beds pass up insensibly into the blue and grey conglomeratic (Southerndown) beds, which are overlaid by the ordinary beds of the Lower Lias. The sequence, therefore, that was pointed out by Tawney is correct, although the Sutton beds merge upwards into the Southerndown Series without any definite plane of demarcation (see Fig. 5). The total thickness of the conglomeratic series, where it could be definitely measured, varies from lift}' to eighty feet, but it increases still more in its western development between Sutton and Southerndown.

The whole of these beds may be regarded as the basement-beds of the Lower Lias, representing the Os£rea-beds and other portions of the zone of Ammonites planorlis, and including perhaps portions of the zone of A. angulatus. They are overlain conformably by limestones and shales exhibiting the ordinary characters of Lower Lias, and belonging partly to the zone of A. angulatus, but mainly to that of A . Bucklandi.

Eastern Part. By T. C. CANTRILL.

The Lias of the eastern part of the area covered by the map forms a broad belt fringing the coast, and lies generally south of the Cardiff- Cowbridge anticline ; it also extends from Cowbridge in a north-

t Quart. Joiirn. Hoc., vol. xl. pp. (18S4) ; sec also vol. xxxviii. p. 411 (1882).

T I'roc. Cottetw. Club, vol. viii. p. 2.14 (1SS.~>).

$ Qwirt. Journ. Hoc., vol. xl. p. ;J7.~> (LSS4) ; .see also Proc. Cardiff Xat. -W-., vol. iii., pp. 30 (52 (1872).

o d

ft

P3

Pq

m

m

64 Lias.

easterly direction in outlying tracts partly covering the core of the anticline. The succession agrees closely with that given by Mr. H. B. Woodward for the Penarth district.

General Section of the Coast of South Glamorgan.

Ft. In.

Zones of / Blue and brown limestones, in beds up to 2 feet,

A. semicostatus, averaging 1 foot or less, with shale part-

A. Bucldandi, ings ; Gryphcea arcuata, Lima, etc. At

and / least - 200 0

A. anguiatus ] Grey marls and shales with occasional nodules

[ Bucldandi- and bands of limestone (Lavernock Shales).

group.] About - - 40 0

Limestones and shales, alternating. A. plan-

Zone of J orbis. About 22 0

A. planorbis. Limestone-flags (Ostrea-beds) with shale-part-

V ings. Ostrea liassica - - - - - 15 0

The superposition of the relatively hard beds of the zone of A. planorbis upon the Rhsetic marls and shales gives rise to a low escarpment ; while the limestones of the A. Bucklandi- group overlying the Lavernock Shales produce a bolder scarp which forms the edge of the Liassic plain of the coast-tract. The steep clayey slopes leading up to the scarp are occupied by hanging woods, such as Coed Garn-lwyd north of Llancarfan, Coed Arthur and Coed-y-Colwn near Llantrithyd, the woods south-east of St. Hilary, and Draenog and Arglwydd Woods at St. Mary Church.

The Lias of the coast shows no indications of having been laid down near a shore, but farther northwards it develops an oolitic structure, and includes small rounded fragments, usually of Carboniferous Limestone and chert, occasionally in such size and number as to constitute a coarse conglomerate or breccia. At the same time shale -par tings disappear and the rock becomes massive and hard, while bands of Sutton-stone often make their appearance. The breccias are well-marked in the Osrea-beds and also in the overlying beds of the Bucklandi-gTonp. It has been already pointed out (p. 59) that the Sutton-stone type of limestone occurs in both Rhsetic and Lias, and as it rarely yields recognisable fossils, the determination of the age of an isolated exposure of the rock is often difficult.

The Os£rea-beds enter the map near Blackland, south-east of Bonvilston, as a low escarpment in which are several small old quarries. They can be traced along the south side of Coed-yr-Aber to a large quarry near Greendown.

The extreme western end of a small outlier of Ostrea-beds just enters the map at Redland. There is a larger outlier of the same beds south of Bonvilston, the thin-bedded limestones and alternating shales being well-shown in some shallow old quarries north-east of Langlon Wood. The eastern limits of this outlier are obscure ; there are some indications of a prolongation of the beds eastwards, or there may be a small separate outlier north of Coed-yr-Aber.

The Jurassic Rocks of Britain, vol. iii., p. 121 (Mem. Geol. Survey),

Eastern Part. 65

Towards Leige Castle and around Castell-ar-foel the Orea-beds are thin, and indeed at the latter locality they may be absent altogether, if we are right in identifying as Lavernock Shales some buff shales exposed in a pit 100 yards north of Carmel Chapel.

South-west of Castell-ar-foel the Ostrea-beds and the Lavernock Shales are faulted out, but the former reappear south-east of Wren Castle, and may be seen in quarries south of Tre-gyff, also south-west of Green, and in cuttings on the Cowbridge-Aberthaw railway a little farther west (pp. 42, 43). They have been quarried also at Ystumelaid and near Cross Barn, and are well-exposed in a railway-cutting north of St. Mary Church Koad (p. 41). West of Ty-fry they are evidently closely approaching their original margin.

The Lias north of the Pentre fault consists of the Osfrea-beds alone, except perhaps for a few feet of nodular limestones seen at Coed Hills ; it is generally more or less pebbly and impure, and contains bands of Sutton-stone, composed of the comminuted shells of Ostrea and other fossils. It has been quarried 250 yards southeast of Tair Onen ; and near a kiln several feet of white Sutton-stone rest on flags of a more than usually shelly character. Towards Garn also the Lias presents much the same aspect, and inasmuch as in the direction of Tair Onen it overlaps the Rhsetic Beds we infer that the shell-beds and Sutton-stone have been formed close to the original shore-line. Occasional traces of galena occur in these rocks, and have given name to two of the fields.

An old quarry 250 yards south by east of Eastdown shows flaggy limestones with a few specimens of Ostrea and Modiola, and several thin bands of light-coloured limestone containing small pebbles of dark limestone. This Lias is possibly faulted down against Rhsetic sandstones on the north. About 150 yards south-west of St. Hilary Cross a wedge of Lias, only a few yards broad, has been let down along the line of the Pentre fault.

The Ostrea-bQds of an outlier at Old Beaupre are somewhat sandy ; they are exposed by the side of the river under the walls of the old castle. The same beds in another outlier east of How Mill have been quarried along the edge of the valley north of the mill.

West of the Dawen Valley the Osrea-flags are exposed at Sandpit near Gigman Bridge, and can be traced thence along the west side of the valley to a quarry in the fields north of The Herberts Farm. Mr. F. T. Howard in his paper on the " Geology of the Cowbridge District " gives the following section, in descending order : —

Section at The Herberts, Llandough-juxta-Cowbridge.

FT. IN. 3. Hard limestones, containing many specimens of Lima,

Pentacrinus, and gasteropoda, much calcified - - - 5 0 2. Coral-limestones in three bands, the lowest being the richest. The corals are in the position of life. A few fossils of other genera, principally Ostrea and Modiola 1 ft. to 1 2 1. Typical Ostrea -limestones full of Ostrea liassica - 40

Trans, Cardiff Nat, tioc., vol. xxx, (1807-8). 7665. F

(iii /, nil-:

The coral max be Thecoftmilia irmjuhiris, Duncan (7\ Duncani, Tomes), according to Mr. rC. T. Newton.

Thin-bedded blue limestones with shale-partings, somewhat higher in the series, are exposed in a quarry on the south side of the road ; here Mr. Howard observed Lima, Cardinia, and A. [Arietites] BucMandi.

West of Llandough the lowest Lias exposed in the Llannhangel Valley contains corals but few oysters. North of the village the 0,s-/Vm-beds are well exposed in a quarry o(JO yards S.S.lv of Newhouse. This is probably the quarry referred to by Mr. Howard* as showing below the Os£/fea-beds " from two to three feet of yellowish impure limestones and dark blue shales, differing widely from the very fossiliferous Ostrea limestones above," and he surmised that these lower beds might be a portion of the White Lias.

South-west of Xewhouse there is a working quarry in what appear to be chertv 0,s7/vv/-f1ags ; due west of the same farm there is an old quarry in ihiggy limestone, and a few yards south of Bryn-hyfryd is a third. Some or all ol these are probably "the quarnes at Llanbethian " described by Moore."!* 'The following rnarised foini of his section, taken in descending order

Quarries at Llanbleiddian.

Limestones containing .1. jJanorln's, Nerito'ims i/n, l/r/iia. ( 'lif'iu n//~;/n, ('nrditn, l.tnin, PtcJin yW///.r, He.

Limestones containing Oxtrca liaxxicn, Cnrdinin, Limn

nfcd, Thf'.Cafinnlut, Mmttlicnltin, etc. - 7

Lime stones Mix/t'iifd Indium, I*UUKI f;< tinxl/'Hihtx. Teiq.,

i -a [>/>llii.r. I'lirntnln nrii ini nntn , Limit //it/ti He. - 1 O

The middle group of limestones was supposed by Moore to represent the 0,sf/'eY/-beds. The fossils do not support this view.

From Bryn-hyfryd the edge of the Lias descends rapidly into the village of Llanbleiddian, overlapping the Rhsctic Beds (p. 44) and Trias (p. and then resting directly on the Carboniferous Limestone, which is exposed in the road immediately south of Llanbleiddian Cottage. We have here evidence of post-Liassic folding along an east and west axis, for since the overlap proceeded from south to north up an inclined plane of Carboniferous Limestone, we should expect to find the edge, of the Lias, where in direct contact with thr Carboniferous Limestone, at a greater altitude than where underlain by Kh;ctic and Trias, and not at a lower, as is actually the case. Several exposures west of Bryn-hyfryd, however, show northerly dips which prove the post-Liassic movement and explain the circumstances. They mark th - northern side of the post-Liassic anticline shown in Kig. '2.

Some of the Liassic rocks here contain pebbles of dark limestone. Without these they would be difficult to distinguish from the Carboniferous Limestone, as, for example, along the southern slope of Llanbleiddian Hill.

O]t. elf.

t Quart. Jaiirti. ,W-.. xxiii. (1S07), pp. IS-

Eastern Part. 67

Along the north side of this same hill alternating limestones and shales, probably of a higher horizon than the Ostrea-beds, are thrown down by the Cowbridge fault against the Carboniferous Limestone. From below this normal type the literal variety emerges and is well-exposed in quarries on the Llantwit Major road 350 yards from the Westgate Inn, Cowbridge. The quarry at work in 1898 on the north-west side of the road shows a blue-hearted brown oolite, flaggy in the upper part and containing Carboniferous Limestone pebbles in several of the bands. An old quarry a few yards nearer Cowbridge in lower beds yielded a few specimens of Ostrea, probably 0. liassica, ranging up to T6 inches in length. All these rocks may be referred to the Ostrea-beds, though their aspect is somewhat abnormal, and they are perhaps thickened by detritus of the Carboniferous Limestone. The junction of the two formations can be seen in the Llantwit road 50 yards from the Westgate Inn, where it was sketched by De la Beche,* and a minute outlying patch of the same pebbly Lias caps Gibbet Hill near by.

The junction is better exposed in a large quarryf 200 yards southwest of Llwyn-helyg House, where 4 or 5 feet of nearly horizontal Lias lie on Carboniferous Limestone dipping at 25°. On the south side of the valley and 90 yards south of this quarry the basal crags of the Lias consist in part of the Sutton-stone variety containing shellfragments and small cubes of galena. The basement-beds are well exposed along the Bridgend road, and irregularly- bedded well developed oolite has been quarried in a coppice 250 yards beyond the first milestone from Cowbridge. Much of the Lias east of Llwyn-helyg House is more or less conglomeratic.

The Cowbridge Lias outlier, so far as it has been opened up in the fine railway-section, has been already described on p. 46. The Ostrea-ftags and overlying A. planorbis limestones and shales, and also part if not the whole of the Lavernock Shales of the A . Bucklandi-zone, are all represented by hard and massive limestones, but it is doubtful if any of the overlying limestones of this zone are present. This agrees with the opinion of Moore,} who was disposed to assign the Cowbridge Lias to a lower horizon than that of either Sutton or Brocastle on account of the general absence of the coral-fauna of those localities. It must not be overlooked however that corals occur at the Herberts and also s:uth-west of Llandough in or immediately above the Ostrea-beds.

Moore gives details of a quarry which was being worked about the year 1867 " immediately opposite the railway-station " ; this was probably a deep quarry 180 yards south-west of the entrance to the old station in the High Street, and just behind the school in the Broadway. In it he saw compact crystalline limestone to a depth of 30 feet ; the lower beds were somewhat thicker-bedded and contained ' flint ' layers or nodules. The fossils recorded were

Mem. Geol. Surv., vol. i., Fig. 36, p. 274 (1846).

t Figured by Mr. Howard, Trans. Cardiff Nat. Soc., vol. xxx. (1897-8).

+ Quart. Joum. Geol. ,SYx?., vol. xxiii. (1807), pp. 517-8.

7665. F 2

68 Lias.

Plicatula acuminata, Ostrea intusstriata, 0. liassica, Pecten polluxy Lima gigantea, Cardinia, Astarte, etc. Close to this quarry he mentions another in somewhat higher, thinner, and more rubbly beds ; this was probably one on the north side of the Broadway a few yards west of the school. The coral ThecosmUia Michelini, Terq. and Piette, was abundant in one of the beds here, and numbers of Entomostraca were present in the matrix between the corals. Ostrea intusstriata, Em., and Neritopsis exigua, Terq., are recorded also. Moore failed to find ammonites in any of the Cowbridge Lias and realise i the resulting difficulty of fixing its horizon. "Small sections in different parts of the outlier show that oolitic structure and bands of Sutton-stone type are frequent ; in the Cardiff road south of Slade this latter type of rock rests on Triassic breccia. A similar junction may be found in the road at Porth-y-green east of Llanbleiddian Castle, the Triassic breccia here being only a few inches thick.

A small outlier on the north side of the dry valley north of Slade consists of light-coloured obscurely oolitic limestone, and a faulted strip of grey oolite is well exposed in an old quarry 250 yards south of Aberthin. Both outliers have been referred to the Lias, with some doubt, however, in the absence of fossils.

At the western end of Cowbridge the Lias extends north-eastwards across the Dawen Valley, being faulted on the south against Carboniferous Limestone, Trias, and Old Red Sandstone. North - west of Aberthin it is overspread with glacial gravel, and consequently its limit is conjectural ; but at that village it can be seen to rest directly on the Carboniferous Limestone and Lower Limestone Shales. Here the prevalent type is Suttonstone, more or less pebbly and frequently containing specks of galena, as, for instance, in the lane near Court Farm. A minute outlier of the same type of rock occurs south of the Welsh St. Donats road about half-way between that village and Aberthin. North of Aberthin this literal type gives place to normal limestones and shales which, being evidently higher than the Ostrea-loads and probably than the Lavernock Shales also, may be assigned to the A. BucJdandi-gToup. Here and there the Lias presents its normal characters even close up to its margin, as for instance in the fields north-east of Aberthin. Between Prysc and Maendy the rock is normal, but west of the Llantrisant road at the latter place a deep quarry shows flaggy blue limestones, some of which are pebbly, while there are also pebbly whitish rocks of the nature of Suttonstone ; chert-nodules also occur in some of the bands. These being probably the Orea-beds, the normal type seen at Prysc at a higher level may be referred to iheA.BiccJdandi-loads. The adjacent railwaycutting shows a small exposure of thin-bedded grey faintly- oolitic rock under a few feet of gravel. This may be an exposure referred to by Moore.*

Quart. Journ. Oeolt Soc,, vol. xxiii, (1867), p. 519,

Eastern Part 69

At Bodlonga also flaggy limestones, probably the Ostrea-beds, have been quarried, but both here and at Maendy it is possible that some of the limestones and shales overlying the Ostrea-beds are represented also. The small outlier at Pen-y-lan south-east of Llansannwr consists chiefly of limestones resembling Sutton-stone.

The direction of dip at Bodlonga suggests that the Lias extends eastwards under the drift-covered ground at Bwlch-gwyn and Llwyn-du to join that at Cwm now to be described. In a brook bounding the south side of the field at Ty-du on the Cwm Farm (p. 27), some thin-bedded limestones, which may be either high Rhoetic or low Lias, are just visible at the mouth of a small runnel issuing from Ffynnon-yr-hebog, a strong spring just inside Coed Leyshon. A few yards farther up the main stream there are overgrown workings probably in the same rocks. On following up the edge of the wood several small swallow-holes will be noticed, and finally thin-bedded Lias limestones and shales under gravel are exposed in a dingle on the edge of Coed Leyshon, 200 yards eastby-south of Cwm Farm. These beds lie probably just above the horizon of the Lavernock Shales and presumably belong to the lowest part of the A. BucJdandi-group. They present no indications of literal conditions. This exposure necessitates the conclusion that the drift-covered escarpment ranging north-west and southeast of Cwm must be the edge of a Lias plateau occupying the heathcovered ground of Mynydd-y-glew. Two small trial-pits, said to have been for coal, were made many years ago on this plateau ; one just within the western edge of Coed Leyshon directly west of Ty-fry farm, the other on the heath just outside the south-west angle of Coed-y-marlau ; at both pits nothing but gravel is now to be seen. %

The boundaries of this Liassic plateau are largely conjectural, except at one point, where they are defined by an outcrop of Carboniferous Limestone at Welsh St. Donats. Wherever exposed, except at Cwm, the beds are conglomeratic and of the literal type. Thus, a roadside quarry 300 yards north of Pwll-y-daren shows nine feet of white conglomeratic Sutton-stone, while at a pond near the farm-house a band full of angular fragments of Carboniferous Limestone appears among otherwise normal clays and limestones. South of the Cowbridge fault, which crosses the road between the pond and the farm-house, Sutton-stone with traces of galena reappears, while a little farther east, and 200 yards west of Pen-y- ffordd-fawr, flaggy blue limestone containing abundant Ostrea liassica but associated with Sutton-stone and breccia have been extensively quarried. Farther to the south-east there are several sections in similar limestones, all of which may be referred to the Ostrea-beds.

Tawney* records PlicatuLa intusstriata, Emm., Ostrea multicostata, Miinst., Pecten suttonensis, Tawn., and Lima tuberculata, Terq., from the ' Sutton Series ' of Welsh St. Donats, which he then regarded as Rhsetic.

Quart. Journ. Geol. Soc., vol. xxii. (1866), p. 69, See p. 80.

70 Lias.

How far to the east the Lias extends is very uncertain ; a large swallow-hole a few yards north of Cwrt-newydd, and another, named Trial Shaft on the six-inch map (Glamorgan 42 S.W.), with a small stream flowing into it, near the roadside at Ffald-wen, indicate the presence of limestone beneath the gravel, but whether Lias or Carboniferous cannot be stated.

On the small Lias outlier at Plwcau-Dafydd, Pendoylan, thinbedde I limestones and shales, the former containing ossicles of Pentacrinus, are exposed in the road, and in the fields 150 yards south-east of the house there are some old workings in the Ostfrea-beds.

On the western edge of the Peterston outlier the Orea-beds are poorly exposed ; thin-bedded limestones and shales, probably belonging to a higher horizon, crop out in a lane east of Gwern-y- cae-uchaf ; the Lavernock Shales are doubtfully present, and cherty more massive limestones, probably of the BucMandi-zone, have been quarried at Allt-las.

The western edge of the Castell-y-mynach outlier is concealed by drift. The Rhsetic is recognisable at Ty-nant, but the junction with the Lias is not exposed.

The Lavernock Shales can be easily recognised, wherever the Lias retains its normal characters, round the northern margin of the Liassic plain bordering the coast, as a wood-clothed slope between the Ostrea-beds below and the plateau of the A . BucJdandi-beds above. Good sections are rare ; the best being those afforded by the Cowbridge-Aberthaw railway in two cuttings, one south of Nant Tregyff, the other south-west of Coed-y-colwn. Brown shales and marls with nodules, and occasional thin bands, of limestone are exhibited in both.

The overlying thicker-bedded limestones of the A. BucJdandigroup of zones occupy the greater part of the area bordering the coast ; they gently undulate in all directions and a dip of more than 5° is exceptional. Sections are numerous, as the limestone was formerly burnt for lime and used as building-stone. Now it is quarried chiefly for road-metal. It forms a soil which is suitable for the plough, and much of the district is still in an arable condition. Good sections are exposed on the Cowbridge-Aberthaw and the Vale of Glamorgan railways, but the magnificent coast-section affords the best view of the beds. The limestones are generally about eight inches, but occasionally as much as two feet thick, with shale-partings ; they belong chiefly to the zone of A. Bucklandi.

East of Roose Point the beds dip south-west at angles ranging up to 25°, but the effect of this dip is counteracted by numerous small faults trending about W. 10° N., and throwing down N. 10° E. At the Point the beds dip south, and farther west this changes to south-east, the Point thus marking a synclinal axis. Joints are conspicuous on some of the rock-platforms on the foreshore. Gryphcea arcuata, Lima gigantea, and ossicles of Pentacrinus abound. The genera] south-easterly dip continues as far as a gentle anticline at Andrew's Pant near Pleasantharbour, beyond which it becomes south-westerly.

Western Part, 71

The limestone for making Aberthaw Lime was gathered from the shingle on the shore near Watch-house Point, and not from quarries. Of late years the works have greatly declined.* Pebbles are shipped to be used as a flux in the iron -works (see also p. 87).

Limestone is quarried and burnt at St. Athan Road Station, and quarried half-way between Lower Porthkerry and Tre-Dwgan. At Limpert Bay the coast is formed of an alluvial flat bordered on the seaward side by an old beach of limestone-pebbles, which, at the Ocean House, are burnt for lime. West of this bay the cliffs reappear ; between Summerhouse Point and Stout Point a slight seaward dip has caused them to slightly overhang at several places ; and near the latter they attain an altitude of 160 feet.

Western Part. By A. STRAHAN. From Notes by R. H. TIDDEMAN.

South of Coity the Lias,'] where it rests on the Rhsetic sandstone described on p. 51, is oolitic in its lower bands and contains chert. North of St. Mary Hill village the Oraz-beds follow the Rhsetic in normal sequence, but south of the village the Lias overlaps the Rhsetic and passes on to the Carboniferous Limestone. It then assumes the condition of Sutton-stone. Fragments of black chert, small pebbles of white quartz and specks of galena occur in it according to Bristow,f and it yielded to Mr. Woodward Cardinia suttonensis, Lima, Modiola, Ostrea liassica, Pinna, and Pecten suttonensis.

Thence southwards bedded and shelly conglomerate forms the local basement-bed, superimposed on Lower Limestone Shales at Pen-llin, but on the Main Limestone elsewhere. A shaft sunk in an unsuccessful search for lead at Gelli-araul, near Llangan, proved a greater thickness of conglomerate than might have been anticipated. The following account of it is given by Moore. J " At the surface were regularly bedded, but finely conglomeratic dense limestones with thin intervening beds of marl. ... In the marls, Potticipes rhomboidalis, Moore, and Pentacrinites are frequent. Following the above limestones, the Sutton Stone was passed through, from which were obtained Patella Dunkeri, Terq., and Pecten pollux, Tawn.

" Immediately below the Suttonstone unstratified conglomerates were found, and passed through to the depth of 150 feet, and still continued when the mine was abandoned. In the stratified

H. B. Woodward, " The Jurassic Rocks of Britain,'' vol. iii. (1893), pp. 117-118 (Mem. Geol. Survey).

t Quart. Journ. Geol. Soc., vol.- xxiii. p, 204 (1867).: + Ibid., p. 533.

72 Lias.

beds above the Suttonstone, there are many species of Cardinia arid Pentacrinus ; and I also obtained the following :—

Ammonites angulatus Orthostoma avena, Terq.

Lepidotus -scales Pleurotomaria lens, Terq. Pollicipes rhomboidalis, Moore Turbo rotundatus, Terq.

Entomostraca, 2 spp. Trochus Juliani, Terq; Astarte irregularis, Terq: „ Langanensis, Moore.

Ostrea arietis.- Trochotoma clypeus, Terq;

Anomia irregularis, Terq. Astrocoenia gibbosa, Martin*

Gardita tetragona, Terq. Thecosmilia Michelini, Terq.

The conglomerates were considered by Moore to be of Liassic age. Mr. Woodward compares the section to that in the ravine of Pant- y-Slade (p. 76), where also the conglomerate was locally thick.

At Colwinston the marginal Lias consists of conglomeratic and gravelly limestone, much of it consisting largely of shell-debris. The regular run of these litoral rocks suggests that the Carboniferous peninsula of Pen-llin corresponds in form to a Liassic promontory at one stage of the subsidence. The description is continued by Mr. Woodward in the " Jurassic Rocks of Britain " (vol. iii, p. 118), as follows : —

" At Bridgend the limestones of the Lower Lias have been extensively quarried for building-stone and for Blue Lias lime, which has been put on the market under the name of ' Aberthaw lime.' The railway-cutting also shows fine sections of the beds, and these were described in detail by Charles Moore, who recorded an alternation of 476 beds of limestone and marl. The lower portion of the series is worked in the quarry, but we do not see the base of the Lias ; blue earthy limestones were the lowest beds to be seen, and they are overlaid by compact and earthy bluish-grey and yellowish limestones. Altogether upwards of seventy-six beds of limestone were exposed in the quarry, for the most part in thick beds with comparatively little clay. The fossils which I obtained, included Gryphcea arcuata (and broad varieties), Ostrea irregularis, Lima gigantea (large specimens), Pholadomya ambigua, Homomya, Uni~ cardium cardioides, and Pleurotomaria. By the entrance to the quarry from the railway, the Lias contains lenticular nodules of chert or siliceous limestone, in which Dr. Hinde (to whom I sent specimens) found rod-like sponge-spicules. Ammonites BucHandi occurred here, and I obtained also a large specimen of Cerithium nodulosum at the base of the railway-cutting.*

" Moore published a list of the fossils obtained by him, including Ammonites angulatus, A. Conybearei, and (in the higher beds) A. semicostatus and A. sauzeanus.\ He also noted a number of Gasteropoda. The beds correspond with those seen in the cliffs between Dunraven and Aberthaw, and, like them, include portions of the zone of A. angulatus, the zone of A. BucJdandi, and that of A. semicostatus"

The fossils were named by Messrs. Sharman and Newton, f Quart* Journ. Geol. Soc., vol. xxiii., pp. 513-517.

Western Part. 73

The Lias here is much disturbed. In the Great Western Railwaycutting a southerly dip of 10° to 30° prevails, and is accompanied by some crushing. A new cutting on the Aberthaw railway shows that this dip forms part only of several sharp undulations. The folds range generally east and west.

From Bridgend westwards the Lias is of the normal type, and the Orea-beds can be recognised wherever opportunity occurs. Near Tythegston, however, where the Lias overlaps the Rhsetic group, this ceases to be the case, there no doubt being a progressive overlap also among the Liassic zones. The lowest bed is a hard oolitic limestone, creamy or dark -grey, and by no means easy to distinguish from Carboniferous Limestone, on to which, moreover, it is often welded. Grypncea arcuata occurs not far from the local base near Merthyr-mawr, and proves that the Lias sequence is not complete.

At Brocastle the Lias crosses the Carboniferous massif, much of the rock apparently being of the normal type. The shore -deposits, however, reappear along the road to Corntown. Here, in an old quarry now much obscured, on the north side of the road 700 yards west of Brocastle House, Moore found Liassic conglomerate resting on Carboniferous Limestone.

The succeeding pages of this chapter, with the exception of the passages in square brackets, are taken from the Jurassic Rocks of Britain, vol. iii. (The Lias of England and Wales), chap, iv., by H. B. Woodward.

Western Part—continued. BY H. B. WOODWARD.

At Brocastle, again, there is a rich Coral fauna, containing in fact more species than have been found in the Sutton-stone, although a certain number are common to the two deposits. From this locality Moore obtained a very rich collection of fossils, but, as he remarks, most of these proved to be new, and therefore they afford but little evidence for correlating the beds with other zones in this country. However the presence of Gryphcea arcuata, Lima gigantea, Ostrea liassica, together with several species'of Cardinia, recorded by Moore, suggest an early stage of the Lower Lias, and agree generally with his grouping of the beds in the zone of Ammonites angulatus, a position also assigned to the mon the evidence of the Corals.* Mr. Tomes has expressed the opinion that the "Brocastle bed has been to some extent re-assorted, and this is not improbable : f undoubted evidence of the reconstruction of beds is met with in the Lower Lias of the Radstock district. Among the Corals (which have been worked out mainly by Prof. Duncan) are species of Astrocosnia (Stylastrcea), Isastrcea, Montlivaltia, Thecosmilia, etc.

Moore, Quart. Journ. Geol. Soc., vol.- xxiii., p. 521 (1867) ; Duncan, Ibid.; p.- 17. See also Rev. H.- H. Win wood, Proc. Bath Nat. Hist. Club, voL vL, p. 218.

t Quart; Journ. Geol Soc., vol. xl, p. 357 (1884):

74 Lias.

The quarry is practically disused, and the conglomeratic beds of Lias are mostly obscured. It is however, possible, to trace these beds abutting irregularly against the Carboniferous Limestone, as represented by Moore. The older rock is a dark blue crystalline and compact limestone, containing Spirifers and Encrinites. The Lias beds comprise greyish-brown granular limestones, and conglomeratic layers having a matrix of pale and compact limestone. Cherty masses here and there occur in the weathered soil on top of the Carboniferous Limestone.

West of Longland, about eight feet of coarse pale grey granular and brecciated limestones have been opened up by the roadside, and at the lime-kiln to the south, beds of conglomeratic Lias abut against the Carboniferous limestone.

[The existence of an outlier of Lias at Pyle village is evidenced by small exposures in a tramway, 450 yards west of St. James Church.

The Stormy outlier of Lias is faulted along its southern margin and not well exposed along the north side where it rests upon Rhsetic beds, but has been laid open at the Cement Works, where the following section was measured by Mr. Woodward (Jurassic Rocks of Britain, vol. iii, p. 114) : — ]

Stormy Cement Works.

Ft. In.

( Brown clay Hard compact blue limestones and shales with

Unicardium, etc. 36

Even beds of shaly limestone and shales - - 20

Lower Lias. Zone of .1 mmonites

plauorbis.

Dark-blue shaly limestones ; near their base beds of blue limestone and shale containing Ostrea liassica and Modiola minima, about - - - 18 0

Conglomeratic bed ; pale-grey and bluish brecciated and shelly limestone, about - - - - 0 10 Rhajtic Beds. See p. 56.

Bristow, who regarded the conglomerate as the attenuated representative of the Sutton Series, noted its thickness as two feet, and described the bed as a " hard, siliceous, and shelly blue conglomerate."*

From the Lower Lias here I obtained Ostrea irregularis, and poor specimens, identified somewhat doubtfully with Ammonites Joknstoni and Pholadomya glabra. Moore recorded A. [Psiloceras] planorbis, Lima gigantea, L. tuberculata, Ostrea arietis, and Pecten pollux (suttonensis)."\ These fossils compare well with those from the beds at Sutton and Southerndown.

Coast Section, Sutton to Aberthaw.

The Sutton Stone has been extensively quarried near Sutton, more especially between Sutton and Sealawn, on both sides of the road, and again on the slopes facing the Black Rocks near Pant-y-

Quart. Journ. Geol. Soc., voL xxiii. p. 204 (1867)g j- Quart. Journ. Geol. Soc., vol. xxiii. p. 520 (1867),

Coast Section. 75

Slade. The principal working in 1887, was immediately south of Tusker Cottage, and the section was as follows : —

Ft. In.

/Hard grey and white shelly limestones, with occasional pebbles of Carboniferous Limestone, and near the base a band of tolerably compact blue limestone ..-GO

Les' Massive bed of white more or less tufaceous stone of variable character, with fibrous structure here and there, and much jointed and broken up in places. (Sutton Stone proper) 7 0 or 80

The more abundant fossils are Ostrea multicostata, Plioatida intusstriata, Pecten suttonensis (or pollux), and Cardinia suttonensis ; but these are not very common, and in many instances the shells have been dissolved away, leaving the rock in a cavernous condition. I also obtained Gryphcea, Hinnites, Lima hettangiensis, Astrocc&nia gibbosa, and lignite.

Galena has been observed in several places in the Sutton Stone and overlying conglomeratic beds. De la Beche remarked that it occurs not only in the mass of the stone, but in joints of jet-like plants, and in cavities left by the dissolution of shells. He noted also that in some localities the stone is dolomitic, a specimen having been obtained at " Pare, two miles north-west of Bridgend."

Along the coast west of the Black Rocks near Sutton, we come upon the Sutton beds, resting directly on the Carboniferous Limestone ; and the general dip of the newer beds being in a southeasterly direction, the stone which at Sutton rises to an elevation of 200 feet, gradually descends to 50 feet and less above sealevel.

On the coast here (west of Pant-y-Slade), the beds consist of white shelly conglomeratic and tufaceous stone, containing Ostrea, corals, etc. ; they are variable in character, being in places coarsely conglomeratic ; they show honey-combed weathering, and they rest irregularly on the Carboniferous Limestone. The basementbed is generally the more conglomeratic, containing often large boulders of Carboniferous Limestone in a creamy limestone-matrix ; but bids with no pebbles lie in places directly on the older rock. The conglomeratic series contains curious sparry veins, sometimes tinged with a greenish colour. Corals derived from the Carboniferous Limestone, as well as fragments of chert and limestone also occur.

The connection between the white Sutton beds and overlying bluish-grey conglomeratic limestones of the Southerndown Series, may be traced in the ravine known as Pant-y-Slade, that descends to the coast from a point north-west of the farm buildings of West. (See Fig. 5, p. 63). Forming the higher ground here, and exposed in three scarps at successively lower levels along the borders of the

Mem. GeoL Survey, volg i.: pp.: 272, 273 ; see also Bristow, Quart Journ. Geol. Soc., vol.- xxiii. p. 199 ; and " Catalogue of Rock Specimens in the Museum of Practical Geology," Ed. 3, p. 123.

vfi Liaa.

ravine, there may hi1 seen a series of blue ilaggy compact and crystalline limestones, more or less conglomeratic or brecciatecl, and containing angular fragments of Carboniferous Limestone and chert. Some of the bi'ds indeed are not unlike Carboniferous Limestone in texture,* and intercalated with them are thin shaly beds. The sequence in these upper beds is not sufficiently clear for detailed measurements, and it is quite possible there may be some repetition by faults. It is, however, probable that we have here a thickness of 70 or 80 feet (if not more) of conglomeratic Lias above the Sutton Beds : a view that coincides with the evidence obtained elsewhere along the coast, that the conglomeratic scries thickens towards the west, and this agrees with the observations of Charles Moore. f

The lower beds in ihe coast section, merge downwards into the white Sut ton-stone Series, as seen i i the following section of the cliff east of the Pant-y-Slade ravine :—

( .Bluish brecciatcd chert)' limestones with veins Pr. IN. ( of calc -spar - - 0 (3

/Palo brecciatcd limestone with fibrous structure ,'5 U .Bluish-grey and pale, brecciated limestones 3 0

Compact bluish limestone more or less conglomeratic, passing into white tut'aceous and shelly limestone, with iibrous structure: Pc'icn. siuttonensis - [) U

Thick beds of pale tufa ceo us limestone with iibrous structure, and with conglomeratic bands here and there - 10 0 to lii 0

Massive beds of pale brecciated limestone, passing down into conglomerate of irregular thickness: Pcclcn sultonensis, Oxtrca mu.Hi- , costata, Corals - 5 to 10 0

( 'arbonifrrous Limestone.

It may be questioned whether the top 6 feet of strata, here included with the Sutton Series, should be so grouped ; the evidence obtained at Witches Point favours the view adopted, but the question is of no importance. We have, however, near Sutton, a thickness of from 25 to 40 feet of strata that may be assigned to the Sutton Seri"S, as their thickness increases eastwards in places according to the irregularities on the surface of the Carboniferous Limestone. There can be no question of the intimate connection between, the Sutton air I Southerndown Series ; and the higher beds of blue conglomeratic limestone seen here, arc similar to those seen above the white Sutton Beds on the southern side of Witches Point, where the thickness of the Southerndown Series is much reduced.

The higher beds in the Pant-y-Slade ravine have not proved to be fossiliferous, so that we are not in a position to state whether the greater thickness of the conglomeratic beds is due solely to an

See also l)e la JJeche, Mtnt. (Jcnl. ,S'///r., vol. i., p. 272: Quart. Jour 11. G'eol. tioc., vol. xxiii., pp. 520, 5.'} I ; Tomes, LI>i<L, vol. xl. p, 357.

Count Section. 77

expansion of the Southerndown Series, or (as seems probable) to the occurrence as we proceed westwards, of conglomeratic beds at higher stages in the Lower Lias.

As we pass eastwards along the coast, over the irregular surface of the Carboniferous Limestone, we find the pale Button Beds banked up against the older rock (see Fig. 5), and at the base of the first cave they occupy a large hollow eroded in that rock, and descend to the beach-level. Here the Sutton Beds are 40 feet or more in thickness, and it may be noted that the lowest bed of conglomerate is very coarse, and of a bluish colour, similar to the basement-bed on the further side of Witches Point.

Beyond this first cave the Carbcniferous Limestone again rises, and we may readily follow the jale Sutton Beds, which appear in marked contrast with the dark bluish-grey Carboniferous rock beneath. Both groups have an easterly dip, and the stratification in places is fairly conformable, but further east the Carbonif rous Limestone rolls over abruptly in the same direction, ar.d the discordance between it and the overlying strata is great.

The Sutton Beds appear now as massive strata assuming a brown aspect where weathered, and the lower layers are very irregular in thickness. We can fix no divisional plane between them i nd the overlying Southerndown Beds, for the cliffs, which rise to a height of nearly 150 feet, are for the most part perpendicular. The Sutton Beds, however, gradually descend to the sea-level by the large " Fairy Cave."* To the east of this, their prolongation on the foreshore is terminated by a fault ; but they are again upraised, for a space, a little further on by another fault, being seen only in ledges on the foreshore. Thence they do not reappear intil we come to the cliffs on either side of the Witches Point at Dunraven, as observed by Tawney and others.

From the Fairy Cavern eastwards, we can again note the upward succession of the beds from the base of the Sutton Series into the lower portion of the Sou herndown Beds, but the cliffs above are inaccessible. Here we find on top of th3 Carbcniferous Limestone, a thickness of 25 feet of pale conglomeratic limestones, alternating with pale limestones like the Sutton stone. These, as at Sutton, are surmounted by grey and bluish-grey limestones (4 feet 6 inches thick), which form a connecting link with ihe conglomeratic lime- ! tones of the Southerndown Series above. In these the limestones become streaked with indurated shaly bands, whi h present a wavy appearance. Here the highest bed we can reach is about 50 feet above the Carboniferous Limestone ; it is a limestone with prominent fucoidal markings, but bands of this nature occur at various horizons in the Southerndown Series, and also in the ordinary beds of Lias above.

Passing by the faulted tract to ihe east, where three great buttresses of rock with perpendicular faces are presented to view, we

See Sections by Tomes, Quart. Journ. Geol. Soc., vol. xl., p. 357 ; and , Proc, Cotteswold Club, vol, viii., Section D., p. 254,

78 Lias.

come to what may be termed the main section of Southerndown, for 1 he beds may be traced eastwards continuously, past Southerndown beach to the cliff by the fault west of Dunraven Castle. That in this division of the cliffs the sequence is clear, may be proved by detailed measurements of the beds at either end of the beach ; and by observing the continuity of a thick and prominent band of limestones (with little shale), that occurs near the upper part of the Southerndown cliff and appears again on the Dunraven side of the little bay. (See Fig. 5).

In the entire section about 180 feet of ordinary Lower Lias limestones and shales have been exposed, and of these beds about 100 feet are shown in the Southerndown cliff. These beds rest on a series of hard and more massive beds of bluish conglomeratic limestone and shale (Southerndown Series) that form the base of the cliffs ; and, as the strata undulate, the sequence can be traced upwards from the lowest bed exposed on the foreshore at the western end of the bluff, and again further eastwards, where the ledges and platforms of rock stretch out seawards for some distance. Unfortunately in these exposures we do not find evidence of the white Sutton Stone and conglomerate anywhere along the base of the cliffs or foreshore. Bristow's section was evidently taken from this portion of the cliffs, and consequently it did not show the Sutton Stone that underlies the Southerndown Beds. He notes the occurrence of an irregular layer of black chert, in addition to the derived fragments of this rock ; and W. D. Conybeare noted that specimens of Gryplicea, coated with chalcedony, were to be found in the Lias of this area.* In order to make clear the sequence we must carry our investigations further eastwards beyond the Witches Point.

The section of the beds at Southerndown, traced westwards from the fault seen in the cliffs east of Southerndown beach, and near Dunraven Castle, is as follows : —

Ft. In.

/Limestones and shales (mostly inaccessible). Unicardium cardioides and Gryphcea arcuata

7 in lower beds About 100 0

Thick and prominent mass of irregular limestones

Ammonites I -. r , if\

P ,7 ,. and marly clays 10 0

Alternate bands of earthy, compact, and shelly limestone, and dark shale : yielding Ammonites [Arietites] Bucklandi, Gryphcea arcuata, Ostrea, Unicardium, lignite- - - - 05 0

Hard grey and conglomeratic limestones with thin shaly beds. Gasteropods abundant in different layers of limestone. Cerithium, Littorina, Gryphcea arcuata - - - - 56

Hard grey limestones, conglomeratic, and with

obscure shaly layers. Ammonites, lignite - 43

Hard blue and grey limestones, with occasional conglomeratic beds, cherty limestone, and indurated shale - - 24 3

Southerndown

Beds

Conybeare and Phillips, Geol, Eng. and Wales, p. 265 ; see also J. J. Conybeare, Ann. Phil., 1822, p.- 336,

Coast Section. 79

Ft. In.

Hard blue limestone, with chert fragments ; Southerndown ) Gasteropods - 10

Beds. Hard blue conglomeratic limestones, with in-

( durated shaly bands. Seen to depth of - - 13 0

Tawney estimated the thickness of the Southerndown Series in this section at 50 feet ; so that our measurements well agree.

In the south-eastern angle of the bay, on the western side of Witches Point, there is a fault and much disturbance of the strata. The Lower Lias limestones and clays on the north, are brought abruptly against the conglomeratic beds of Lias, the Sutton Stone and conglomerate, and the Carboniferous Limestone on the south : and the downthrow on the north must amount to about 100 feet. The beds on the northern side of Witches Point are for the most part inaccessible, but their general arrangement may be studied from the shore. The white conglomerate is seen to rest irregularly, and with varying thickness, on the Carboniferous Limestone, which here contains many nodules and lenticular bands of chert, and exhibits an undulating anticlinal structure. (See Fig. 5.) Beyond the Witches Point the beds are more accessible at low-tide, and here the Sutton Stone inosculates with the older rocks, having undercut it in places ; a feature also observable near Sutton.

The main mass of white stone and conglomerate forming massive beds, here occurs at the base, as in the cliff at Panty-y-Slade ; it is from 20 to 25 feet thick, but above are nearly 20 feet of blue, bluishgrey, and pale-grey limestones that contain the same fossils and cannot be separated from the Sutton Series. Higher still, we can just trace the more decidedly bluish limestones, more or less conglomeratic (Southerndown Series), that underlie the ordinary beds of Lower Lias.

Along this part of the coast the sequence is interfered with by an occasional dislocation of the beds. On the eastern side of Witches Point there is a cavern, excavated in the white Sutton Beds which rest on the Carboniferous Limestone. The basement Sutton conglomerate contains fragments of chert, and pebbles or boulders of Carboniferous Limestone. It is here 9 feet thick, and is overlaid by about 18 feet of pale limestones more or less brecciated. We are unable to trace the sequence continuously from this point, as a little further north there is a small fault or joggle, the precise throw of which it is difficult to determine, but it appears not to exceed about 4 feet on the further side towards Dunraven. It suffices, however, to carry the Carboniferous Limestone out of sight. From this point we are enabled again to trace the beds upwards from the Sutton Beds to the ordinary Lower Lias ; for although there is another fault that traverses the cliffs in an oblique direction, with a downthrow of about 8 or 9 feet on the west or south-west, yet we are at no loss in comparing the beds on either side of this displacement. The beds adjoining the fault present a massive and wall-like appearance, and some of the higher layers of the Southerndown Series present, where weathered, a curiously ragged, cavernous, and

Lias.

crinkly appearance, standing out in marked contrast from the softer earthy limestones and marls of the Lower Lias above them. (See Fig. 5.)

Section of the Cliffs from below the Flag Staff, Dunraven, to the cavern near the Witches Point.

Ft. In.

/Hard limestones, much jointed, and dark bluishgrey and blue-black shales, with Gryphcea Zone of arcuata, Pholadomya ambigna, P. glabra;

Ammonites J Irregular and nodular pale earthy limestones, Bucldandi, dark shales and marls, with Ammonites angu- &c. lotus, Gasteropods, Gryphcea arcuata, Lima

gigantea, Unicardium cardioides. (Here and there we find bands crowded with G. arcuata.}

Hard and somewhat irregular bluish-grey limestones, with sparry veins, shaly beds, fucoidal markings, and occasional fragments of Carboniferous Limestone. Lima gigantea, LI tuberculata, Ostrea - - - - - 59

Southerndown J Hard and irregular grey limestones with little Series. or no shale, with sparry veins, and occasional

fragments of Carboniferous Limestone - - 40 Compact grey limestones, with shaly layers : conglomeratic in places. Ostrea liassica, O. multicostata, Lima gigantea, spines of Echini, lignite - 4 0

'Hard compact pale-grey and bluish-grey limestones passing in places into a bed like Sutton Stone. Pecten suttonensis, Ostrea multicostata 6 0

Hard bluish -grey and compact limestones, conglomeratic and brecciated : massive beds.

Pecten suttonensis 76

Sutton Series; Compact bluish-grey limestones, wedge-bedded

in places 5 7

Compact blue limestones, brecciated in places ; passing down into pale -grey brecciated limestone, like Sutton Stone. Shelly in places - 5 0

Buff, pale-grey, and bluish-grey limestones,

passing down into white conglomerate. About 15 0

It will be noted that beneath the ordinary limestones of the Lower Lias, we come to, first, a series of hard and more or less conglomeratic limestones that yield Lima gigantea, L. tuberculata, and other fossils. These are from twelve to fourteen feet thick. They rest on a series of bluish-grey and pale-grey limestones, more massive in appearance, that pass down gradually into the white conglomerate. In the upper part of this lower series, which is mainly bluish in colour, we may note the horizontal change of a compact blue limestone into pale-grey stone of the character of Sutton Stone, showing that the test of colour is one not to be entirely depended upon. This, moreover, is shown by the fact that the lowest bed of conglomerate, beneath the white Sutton Stone and conglomerate, is here and there decidedly blue. Moreover, some of the compact blue limestones yielding Pecten suttonensis, present characters resembling the highest

Coast Section. 81

beds noted in the section at Pant-y-Slade, beds which there and elsewhere along the coast, form a sort of passage from the white Sutton Stone upwards into the blue conglomeratic Southerndown Beds.

It is clear that wherever the base of the conglomeratic se ies is exposed, we find the white Sutton Stone and conglomerate (of varying thickness) resting on the Carboniferous Limestone. No attempt is made to correlate particular beds in the Southerndown Series of Dunraven with those under Southerndown, because of the blending of these divisions, and the absence of any definitely marked lithological or palaeontological horizons.

Undoubtedly the pale creamy and white colour of the Sutton Stone and cmglomerate has led to the supposition that the beds represent the White Lias. In texture, however, the Sutton Stone differs very much from that rock. It should, moreover, be noted that at Penarth the White Lias is i epresented mainly by grey shaly marls, twelve feet or more in thickness, and does not exhibit a mass of compact white limestones such as we find in Somersetshire. Again at the Stormy Cement Works, between Bridgend and Pyle, the White Lias is but feebly developed, and its probable representative is overlain by a thin bed cf conglomerate that occurs at the bass of the Lower Lias. In other localities in this district, as observed by Bristow, the Rhaetic Beds are exhibited in close proximity to the conglomeratic Lias. Bearing in mind the fact that in places the Rhsetic Beds merge almost imperceptibly into the Lower Lias, it would perhaps be wrong to state dogmatically that no portions of th) White Lias are represented in the conglomeratic Lias of South Wales ; but at Subton we have no evidence that this is the case. No specimens of Protocardium philippianum, or Lima precursor have been obtained, but the fossils that do occur include species elsewhere obtained from the basement-beds of the Lower Lias.

Modifications of the Lower Lias have been noticed elsewhere on Broadfield Down and near Shepton Mallet, where the strata rest in similar situations on the Carboniferous Limestone. The beds and the fossils found near Shepton Mallet are so like those of the Sutton Stone that they could not be distinguished.* This is remarkable, as there is no evidence of any original continuity over the intervening area between beds of this character. The identity is due to the similar origin of the strata, both being largely due to the direct destruction of the Carboniferous Limestone, thus originating as shore-deposits of calcareous mud with which angular detritus was occasionally mixed. In other cases where the Lower Lias rests directly on the Carboniferous Limestone, and at the same time presents its ordinary characters, we may infer that the beds were probably laid down on submarine shelves or platforms of the older rock.

£ The appearance of the beds in the cliffs of Sutton and Southern- d:wn changes much, according as the layers come within the

See also Moore, Trans. Cardiff Nat. Soc., vol. viii. 1877, p. 56.

7665. G

82 Lias.

influence of the sea,* also where they are much weathered or present joints or fault-faces. Where the Southerndown Beds have been long exposed in the cliffs, they present often a wavy or crinkly appearance which is not exhibited on freshly cut faces ; the fact being that softer shaly or marly partings are eroded, and the irregularities of the limestone-bands are made more manifest. The Southerndown Beds are more divided in some places than in others by partings of shale. The surfaces of beds just uncovered by the sea present a smooth appearance, and are blue or bluish-grey in colour, while further on, the platforms, long exposed to the action of the sea, have become brown, rough, and honeycombed. Many beds above and below the chief Gryphcea-bed under Southerndown are " fucoidal " at the base, and also here and there on the surface. There is no definite horizon of Gryphsea, nor of Fucoidal beds, nor even of Gasteropods.

Concerning the organic remains, fossils as a rule are not abundant, and those that are present in the conglomeratic beds of Lias, are difficult to extract, owing to the hardened nature of the rocks. In the lower portions of the Sutton Stone and conglomerate, and especially in the conglomerate exposed above the Carboniferous Limestone, on the coast near the Black Rocks and Pant-y-Slade, corals are not uncommon. Some are identical with forms found in the Alpine Trias. The most abundant species is Elysastrcea Fischeri, which, according to Mr. Tomes, appears " in some places in great masses, the corallites of which, either more or less closely packed, or in disjointed branches, penetrate the stone through and through. "f Many other species of corals have been obtained, and although in Mr. Tomes's opinion many of them " must be assigned to a period antecedent to that at which those beds were formed, "J yet the lithological characters of the rocks, and the absence of clayey sediments, suggest that favourable conditions for coral-growth may have existed at the time. It is therefore possible that the peculiar character of the Sutton Stone may have been due in part to the waste of coral-beds : the calcareous mud being mixed with the debris of corals. Higher up in the series, where clay-beds come in, we lose the coral-fauna. The Southerndown Beds on the coast contain but few corals, and the two species recorded are also found in the Sutton Beds.§

The development of coral-life seems to have been local, so that wd cannot attempt definite correlations, based on the occurrence of the many species, with beds in other parts of this country, for, except in Skye, nowhere else in the basement-beds of the Lower Lias have these organic remains been found in such abundance.

That the induration of the beds is not to any extent due to the action of sea-water, may be judged from the fact that where the ordinary beds of the Lias pass down to the sea-level, they do not exhibit any marked differences.

t Quart. Journ. Geol. Soc., vol. xl. p. 368.

J Ibid., p. 354, and remarks by Prof. Bonney, p. 375.

§ See Duncan, Quart. Journ. Oeol. Soc., vol. xxii. p. 15 (1866).

Coast Section. 83

Only one species (Thecosmilia rugosa) has been recorded from both White Lias and Sutton Stone.

The evidence of the Ammonites is important. Moore indeed included- .[Schlotheimia] angulatus in his list of Sutton Stone fossils, but in his sectionof the strata he notes the occurrence of this species on top of the Sutton Stone — at least 18 feet 3 inches from the base ; and in considering its horizon it is necessary to bear in mind the varying thickness of the beds where they rest in the hollows of the Carboniferous Limestone. Of the two species recorded from the Sutton Series by Tawney, the one named A. suttrmensis (a form which, according to Prof. Tatef, is allied to A. Johnstoni) was found about 20 feet above the base of the series, both at Dunraven and at the Sutton quarries ; while the fragment named A. dunravenensis was found about 30 feet above the base of the Sutton Series at Dunraven. We have therefore no actual record of the discovery of an Ammonite in the main mass of the Sutton Stone itself. In many localities, however, Ammonites [Psiloceras] planorbis, which characterise 5 the lowest zone of the Lias, is not found in the bottom-beds ; and these have in places been separated under the name of Ostrea-beds, being conspicuous for the prevalence of Ostrea liassica.

The two above-mentioned Ammonites, however, evidently occur in the beds which shade off from the white Sutton Stone and conglomerate into the bluish grey Southerndown series, and thus confirm the view that the Sutton and Southerndown beds constitute one palseontological series.

The bed with Gasteropods, that occurs at the base of the ordinary beds of Lias at Dunraven, may correspond with that marked as the top of the Southerndown beds under Southerndown. There are, however, at least three distinct bands of limestone in the Southerndown Series that yield Gasteropods. The more prominent bed, about 1 foot thick, occurs about 18 inches below the highest conglomeratic bed (top of Southerndown Series) under Southerndown. It is a greyish limestone containing conglomeratic seams, and is well seen in ledges on the foreshore, becoming darker and rougher in appearance away from the cliffs. It has been planed off at somewhat different levels and inclinations. Tawney noted a bed with a great number of large specimens of Chemnitzia, about 16 feet from the top of the beds which he grouped with the Southerndown Series : his description well applies to the bed above noted, and, as he remarks, it is not possible to extract specimens owing to the toughness of the limestone. J

Pecten suttonensis of Tawney, which is one of the most abundant fossils in the Sutton Stone, was regarded by Moore as the Pecten Pollux of d'Orbigny, while Tate considered it to be the same as P. valoniensis, Def ranee. It is a somewhat variable form. It occurs

Quart. Journ. Geol. Soc., vol. xxiii. pp. 526, 530 ; see also notes by Sir W. V. Guise, Proc. Cottesw. Club, vol. iv. p. 109 ; and Ibid., p. 84. f Quart. Journ. Geol. Soc., vol. xxiii. p. 309. t Quart. Journ. Geol. Soc., vol. xxii. pp. 75, 76.

7665. y 2

84 Lias.

in the beds at Shepton Mallet and also in the peculiar cherty modifications of the Lower Lias at Harp tree Hill. At the last-named locality this species occurs together with Ostrea midticostata and Cardinia suttonensis, two of the most abundant Button Stone fossils, and in the same beds at Harptree there occur A. [Psiloceras] planorbis and A. [P.] Johnstoni (torus), furnishing strong corroborative evidence that the Button Stone should be included in the zone of Ammonites planorbis* A. [Psiloceras] Johnstoni has been found in beds like the Sutton Stone, at Shepton Mallet.

From the published lists of fossils it is difficult to decide what were the precise horizons of all the species. Thus Tawney has given lists from the Sutton and Southerndown Series at various localities ; Prof. Tate has given a list of fossils from the Sutton Stone, with a revision of Tawney's species ; and Moore has done likewise, although his revisions differ in several respects from those of Prof. Tate. Moore has also given lists from the conglomeratic Lias above the Sutton Stone at Southerndown, and lists from Brocastle, &c.f So much difference of opinion exists on the identification of some species, that it is best only to give those about which no doubt has been expressed.

The following fossils have been recorded from the Sutton Stone : —

Ammonites (see p. 83).

Neritopsis exigua.

Patella.

Pleurotomaria.

Trochus.

JCardmia suttonensis. jGryphsea. JHinnites. JLima hettangiensis.

J tuberculata.

JOstrea irregularis.

multicostata.

JPecten suttonensis. JPIicatula intusstriata. JAstroccenia (Stylastraea) gibbosa.

reptans.

Cyathocrenia incrustans. JElysastreea Fischeri.

Montlivaltia.

Rhabdophyllia recondita.

Thecosmilia mirabilis.

rugosa.

suttonensis.

The following species have been recorded from the Southern down Series : —

Am. [Schlotheimia] angulatus. Belemnites acutus. Cerithium nodulosum. Littorina ? clathrata. Cardinia.

Gryphaea arcuata. Lima duplicata.

Lima gigantea.

- tuberculata. Ostrea liassica.

- multicostata (arietis). Pecten suttonensis. Plicatula intusstriata. Echinodcrm spines.

Geol. East Somerset (OeoL Survey Memoir], p. 108. See also Moore, Quart. Journ. Geol. Soc., vol. xxiii. p. 492. W. W. Stoddart noted the occurrence of Sutton Stone fossils in the Zone of Ammonites planorbis of the neighbourhood of Bristol, but unfortunately he included the White Lias in that zone. Quart. Journ. Geol. Soc., vol. xxiv. p. 203.

t Tawney, Quart. Journ. Geol. Soc., vol. xxii. p. 79 ; Tate, Ibid., vol. xxiii. p. 309 ; Moore, Ibid., pp. 530, etc.

Specimens so marked were obtained by myself, and identified by Messrs. Sharman and Newton,

Coast Section. 85

The ordinary beds of Lower Lias above the Southerndown Series at Dunraven, have yielded the following species : —

*Am. [Schlotheimia] angulatus.

[Arietites] Bucklandi.

[ ,, ] Gonybearei.

[Aegoceras] laqueolus ?

[Arietites] semicostatus.

Belemnites acutus.

Cerithium. *Turritella (cast). *Gryphaea arcuata.

Lima duplicata.

gigantea.

Hermann!.

*0strea multicostata (arietis). *Pholadomya ambigua.

glabra.

*Unicardium cardioides.

Rhynchonella calcicosta.

Pentacrinus tuberculatus.

From Dunraven onwards to Aberthaw, the coast is bounded by cliffs exhibiting the blue and brown argillaceous limestones, shales, and marls that overlie the conglomeratic Lias of Southerndown. On the eastern side of the Dunraven headland, the conglomeratic beds dip away beneath the beach, being repeated for a short distance by the oblique fault (before mentioned, p. 79.), and by another fault a little further on ; beyond which they are not seen again along the coast-sections.j

These cliffs exhibit, perhaps, the finest exposure of the Lower Lias Limestones in this country. We have not the complete sequence of Lias visible at Lyme Regis ; but here in South Wales the zones of Ammonites angulatus and A. Bucklandi (taken together) are much more fully and continuously exposed. It is true that li miles of cliffs, showing the same set of beds, dislocated here and there by faults, seem a little monotonous ; and as fossils are neither very varied nor very abundant, we cannot wonder that the cliffs for the greater part of the distance are but little visited by the geologist. The beds must attain a thickness of quite 200 feet, and for a great part of the way the limestones stand out also in ledges and platforms along the foreshore, so that our progress along these natural pavements is a very happy one, excepting where it is diversified by faults that modify the strike of the ledges, or by heaps of boulder-shingle that lie here and there on the surfaces of the platforms.

The following general sequence is shown : and the upper beds being more jointed and open, springs are thrown out at their junction with the bluer beds : —

Yellowish argillaceous limestones ; about 55 bands, on the whole thicker than the beds below and with less clay — the limestones here and there exhibiting rhomboidal

Zone of

Ammonites

Bucklandi,

etc.

jointing.

Bluish-grey limestones ; about 80 comparatively thin and on the whole irregular bands, alternating with thin clays, shales, or marls. Southerndown Series, etc.;

Species obtained by myself, and identified by Messrs. Sharman and Newton ; some of these and other species are recorded by Moore.

f [Except at Whitmore Stairs, where Mr. Tiddeman has found some limestones full of fragments of chert and limestone brought to view in the foreshore in the crest of an anticline.]

J These beds are very similar in character to the Black Limestone locally known as " Aberdo Limestone," in the upper part of the Carboniferous Limestone of Flintshire. A. Strahan, Geol. Rhyl (Mem. Geol. tiurv., Sheet 79t N.W.), pp. 15, 16.

86 Lias,

The lower division attains a thickness of about 80 feet estimated from the top of the conglomeratic series ; and in the first cliff beyond the angle formed by the Dunraven headland, the lower beds are shown to a height of about 70 feet, and the upper occupy about 50 feet above. The cliffs between the gullies of Cwm-mawr and Cwm-bach, rise to a height of 200 feet, so that the limestone-series here exceeds that thickness, though not perhaps to any great extent. We do not however notice any beds in the cliffs as far as Aberthaw, that indicate higher divisions of the Lower Lias, and, judging by the fossils, the beds belong to the zones of Ammonites angulatus, A. Bucklandi, and A. semicostatus, and mainly to that of A. Bucklandi.

On the whole the beds are tolerably flat, but with a general inclination (interrupted by a gentle anticlinal) towards Nash Point. Approaching this point, a thick mass of limestones appears on the top of the yellow beds in the cliffs, forming a conspicuous band as at Southerndown, and this caps the buttress of Nash Point. Here, then, the cliff is formed of a thick mass of limestones, resting en tolerably thick beds of limestone, bluish and yellowish, and these again on bluish limestones, on the whole even-bedded with here and there crinkly layers and thin partings of shale. The limestones form thick ledges and pavements of rock, varying in direction with the inclination of the beds, and the changes produced here and there by faults. Gryphcea arcuata, Lima gigantea, anl Ostrea, occur, often in clusters, together with Pentacrinus, small ammonites and occasionally lignite. Pholodomya appears not uncommon in the higher jointed beds, fallen masses of which lie on the beach.

The cliffs below the Nash lighthouses, show the thick mass ot limestones towards the upper portion of the cliffs, and this is let down to lower levels here and there by faults which thus counteract the influence of the dip. In one instance, not far from Dunraven, a small fault, which displaced the upper beds 2 or 3 feet, was lost towards the base of the cliff, the layers of limestone being just separated, then simply bent, and finally no appearance of disturbance was visible. (See Fig, 6.) I have seen similar faults in the Purbeck beds near Swanage. They appear to be due to irregular compression of the beds, and not to the effects of landslips.

Immediately east and west of St. Donat's Point, the beds are somewhat faulted and tumbled. There is however no great displacement, and the ledges display Gryphcea arcuata, Lima gigantea, A. [Arietites] Bucklandi, and lignite. From the higher beds I obtained A. [Arietites] Conybearei. There is a considerable accumulation of coarse boulder-shingle here, and Jarge blocks are taken away for building purposes, and occasionally to be burnt for lime. Some of the beds exhibit fucoidal markings.

The beds south of Llantwit-Major are much jointed ; in fact the beds showing rhomboidal jointing come down to the beach, and the blocks are worked off by the sea in huge masses. These are readily broken up and rounded, so that the ledges of rock are in many places irregularly covered by accumulations of boulder-shingle. From

Coast Section. 87

Dan twit to Stout Point the beds are tolerably level and unbroken — the highest part of the cliffs being 146 feet. There is a slight seaward dip, and this continues towards Summerhouse Point, where the cliffs overhang in places. A short distance east of the Camp, the cliff ends, the last beds seen here being 8 or 10 feet of jointed limestones and clays.

From a short distance east of Summerhouse Point to the east of the River Daw, at East Aberthaw, there are no cliffs, the coast being bordered by alluvial flats, hillocks of blown sand and a high beach of boulder-shingle. It is this shingle, composed of rolled limestone derived from the cliffs further west, that has furnished and still furnishes the celebrated Aberthaw lime. All the " lime " shipped, goes away in the form of pebbles (3 or 4 inches in diameter), and those are reckoned the best that are taken between high- and lowwater mark, where washed by the sea. The trade has of late years

FIG. 6. — Fault in Lower Lias, east of Dunraven Castle, Glamorganshire.

considerably declined, in fact, since the introduction of railways, the lime from places inland has come more and more into use ; but I was informed that about seventy years ago (1827-1837) there were sometimes twentyjvessels in the " Port," that had come to take away the stone for lime.

It is curious that the stones gathered from thet higher part of the beach, where they are sun-dried, are said to be not so good for hydraulic lime ; but they are burnt for local purposes at the limekiln near Ocean House, West Aberthaw, where " lump lime " and " ground lime " are prepared.

East of the River Daw, by Pleasant Harbour, the platforms of rock contain Gryphcea arcuata, and Lima gigantea. The cliffs for some distance show hard blue limestones in tolerably thick beds, dipping gently eastwards, and yielding the same fossils together with Ammonites.

[To this account by Mr. Woodward we now add that evidence has been obtained by Mr. Tiddeman that the Lias rests directly upon the

88 . Lias.

Carboniferous Limestone at Wick. The older rock is shown in four inliers referred to on p. 14. The Lias in the case of the inlier half a mile west-north-west of Wick assumes a rag-like character near its base, and corals become abundant in some bands. A fifth, however, which is only doubtfully referred to a Carboniferous age, lies half a mile north of the last, and consists of tufaceous limestone with traces of conglomerate. These sections, taken in connection with an exposure of conglomeratic limestones at Whitmore Stairs, form the evidence for extending the dry land in Keuper times as far south as is shown in Fig. 2.]

Chapter Viii.

Faults And Disturbances

By A. STRAHAN.

Though frequent reference has been made in the preceding chapters to the faults and disturbances by which the rocks have been brought to their existing structure, it will be convenient now to summarise our conclusions with respect to them. They may be divided at once into two main principal groups, namely, those which preceded the deposition of the Secondary strata, and which therefore affect the Carboniferous rocks only, and those which were of later age than the latest Lias represented in the district, and which affect all the rocks. The first group belongs to the powerful system of east and west folding which reached its greatest intensity in Somerset and Devon. It began after the close of the Carboniferous period and concluded before the Trias commenced. It therefore coincided with what was in this part of the world a prolonged continental period. To it was due the stupendous denudation undergone by the older rocks, and the unconformity between them and the Secondary rocks which is so finely displayed in the Vale of Glamorgan.

Pre-Triassic Disturbances.

In the adjoining Sheet (263) we had evidence of a series of anticlines ranging through Cardiff, Cadoxton, and Barry.* One only of these is exposed to view in this western part of the Vale of Glamorgan, namely, that which brings to the surface Silurian rocks near Cardiff and Old Red Sandstone near Cowbridge. The evidence of its pre-Triassic age is found in the fact that the Triassic rocks did not share in the upheaval, but that, on the contrary, they rest at low inclinations on the upturned edges of the deeplydenuded Palaeozoic rocks. This relation is well shown in the haematite-workings illustrated in Figs. 9 J.O and 11, pp. 108, 109, and can be seen or inferred in a multitude of other places.

It is to be noticed also that pre-Triassic denudation was especially active along the Cowbridge-Cardiff anticline. The crest was so deeply eroded as far west as the neighbourhood of Cowbridge that a valley was formed along the axis of upheaval. Further west, however, where the anticline tends to die away, the arch remained unbroken, and this surviving part of the crest, with what may be

The Country around Cardiff (Geolt Survey Memoir), 22|

HO Fimlts Disturb me cs.

called the foundations of the ruined arch east of Cowbridge, subsequently formed the Triassic island shown in Fig. 2. The anticline, as far west as Pendoylan, took the form of a single broad arch, but in that neighbourhood became compound. The main axis of upheaval runs by Pen-llin, where it brings the Lower Limestone Shales to the surface, and thence to near Porth-cawl (p. 13), but subsidiary anticlines branch off to the north and south, as shown in Fig. 1. The folding was accompanied, no doubt, by some faulting, and at Pen-llin a fault which throws the shales against the Main Limestone passes under Lias apparently without affecting it ; the fault on the south, of Stalling Down also has not been detected in the Secondary rocks of Cowbridge.

To the north of the anticline the Upper Carboniferous rocks come on in succession, all dipping north except in some local undulations. But at a distance of about six miles from the axis we reach the synclinal region of Ton-yr-fail and Llandyfodwg, which again is followed by the anticline of Pontypridd and the Moel Gilau Fault.* With these, however, except that they form part of the same system of disturbances, we are not now concerned. To the south of the anticline there lies a region of gently-undulating Secondary rocks, under which the structure of the Palaoozoic rocks is unknown, but in which the possibility of the existence of a coal-field claims attention.

The evidence available in the area described in this volume is scanty. Near Wick the Carboniferous Limestone dips north, which suggests that other anticlines lie south of the Cowbridge-Cardiff anticline. In the adjoining Sheet on the east (2()3) the proof of such being the case is more conclusive, for the existence of at least two other anticlines is evidenced at Cadoxton and Barry, while a fourth traverses Flat Holme, all of them trending east and west. It would seem, therefore, that the Pala3ozoic floor under the Secondary tract is more likely to be formed of folded Lower Carboniferous rocks than of a syncline of Coal Measures.

Post-Liassic Disturbances,

The later system of disturbances in this region takes a direction somewhat unusual in South Wales. Generally the most prominent faulting has been the north-north -westerly system which cuts through the Coal Measures and, to a less degree, the Secondary rocks, while the leading disturbances belong to the W.S.W. system, of which the Vale of Neath furnishes a notable example. Here, on the contrary, some of the faults run due east and west, and others west-north-west ; north and south faults are exceptional, and the Neath system is unrepresented. We arrive then at the fact that there is some agreement in direction between the earlier and the later disturbances, and it becomes of interest to determine how far there may be coincidence in position also, in view of the theory

The Country around Pontypridd (Gc.nl . vrroj Mviwiir), Chapter V1J I.

Post-Liassic.

that lines of weakness once established have proved lines of faulting or folding at successive geological periods.

Turning to the Cardiff - Cowbridge anticline, we are met with the fact that it does not strictly coincide with the axis of upheaval of later times. The Rhsetic base, which forms a convenient datum - line, lies at a lower level on it than either to the north or south of it. Moreover, one of the principal lines of post- Liassic upheaval, which runs through Bonvilston to the south of Cowbridge, keeps about three miles north of the line of principal pre-Triassic upheaval, and coincides with no pre-Triassic anticline. This post-Liassic anticline is followed northwards by a syncline at Llanbleiddian (p. 66), which again corresponds to no syncline in the older rocks, but lies partly over the site of the Stalling Down anticline. From this neighbourhood a fault runs westwards through the Lias to St. Bride's Major, but, except that it runs east and west, it shows no connection with the structure of the older rocks ; on the other hand the fault in the older rocks near Pen-llin is not recognisable in the Lias. Again a post-Liassic anticline crosses the Ogmore considerably south of the anticlinal axis in the Carboniferous Limestone.

i-O

£ S

O

o"

H

Faults <(vd Disturbances.

s £

d

Post-Liassic. 93

The sections forming Figs. 7 and 8 have been drawn with a view to illustrating the differences in the structure of the newer and older rocks. In. Fig. 7 it will be noticed that the Keuper and Ehaetic thin out from south to north and leave the Lias in contact with the Carboniferous Limestone. Here, therefore, we can fix a point on the Khsetic shore-line. But the surface of the ilhsetic land, as thus determined, descends to a lower level than the shore-line, obviously in consequence of the subsequent formation of a syncline. That syncline, however, is not situated over a syncline in the older rocks, though, no doubt, the dip of those rocks must have been slightly modified by it. Similarly Fig. 8 shows Triassic conglomerate on the shore south-west of Sutton, but Lias resting directly on the Carboniferous Limestone at Sutton. The Rhaetic shore-line therefore ran between the two spots. The conglomerate comes in onOgmore Down and at Lalestoii, but between the two, though the surface of the Carboniferous rocks sinks to sea -level, there is neither Keuper nor Khsetic below the Lias. Here again, therefore, we find what was Khsetic land lying lower than what was Rhaetic sea, in consequence of post-Liassic movements, and in this case the post-Liassic syncline is not situated on a syncline in the older rocks.

These instances show that the disturbances in the Secondary rocks cannot be trusted to indicate the structure of the older rocks. There is certainly no correspondence in detail, and in view of the fact that the Vale of Glamorgan is an anticlinal region as regards the older rocks, but still part of a basin of Secondary rocks, there would appear to be no correspondence in the broader features either.

The tract of Secondary rocks, entending from St. Mary Hill to Pyle, is traversed by a number of faults with a general west-northwesterly direction, which run obliquely to the strike of the underlying Carboniferous rocks. In fact, no connection exists between the superimposed structures of the Secondary and those of the Carboniferous Rocks. The later rocks lie in a trough eroded along the northern limb of the Cowbridge-CardifT anticline, so as to rest partly upon the Carboniferous Limestone and partly on the Millstone Grit. Their existence is due mainly to the fact that pre-Triassic denudation had led to the formation of a strait as shown in Fig. 2, but their survival is due partly also to the faults.

One of these faults forms the Triassic boundary from Llanilid westwards, while another, parallel to it, forms the Liassic boundary north of Bridgend and the Triassic boundary thence westwards to Kenfig. These are downthrows to the south, and though there are intermediate faults with downthrows north, the generalisation holds good that southerly downthrows characterise the northern margin of the Secondary tract. The south side, on the contrary, is characterised by faults with a northerly downthrow. One, for example, bounds the Lias of Stormy on the south, while others throw the Rhaotic and Trias against the Carboniferous Limestone towards Laleston. The faults, therefore, may be said in a general way

94 Faults and Disturbances.

to border the trough, which amounts in the present case to saying that they tend to run along the original margins of the Secondary rocks. A similar coincidence has been noticed in the neighbourhood of Belfast, where it has been attributed to differential movement having been set up between the older and newer rocks by the shrinking and consolidation of the latter.

Chapter Ix. Glacial Deposits.

Introduction. By T. 0. CANTRILF.

The glacial deposits which occur in the area embraced by this map airi almost restricted to the northern parts of the district, and do not extend to the south of St. Mary Church or of Merthyr-mawr.

Most of the material is of a gravelly nature, but locally it becomes more clayey, as along the north-eastern margin of the map. There appears to be no difference in age between the Gravel and the Boulder Clay, for the one passes laterally into or give s place to the other in such a way that no hard and fast line can be drawn between them. As a general rule, however, the gravelly material prevails near the outer margin of the glaciated region.

The Boulder Clay generally forms featureless slopes, whereas the Gravel usually gives rise to hummocky ground, diversified by numerous mounds and hollows, the latter often occupied by small ponds or peatflats.

That the present southerly margin of the glacial deposits approximately coincides with the original limit of the ice-flow may be inferred from the remarkable absence of drift-material in the soil of the coast-region, the only exceptions being a boulder of dark-green brecciated felsite, 2 feet 6 inches across, by the roadside at Pentre near Llantrithyd, half a mile south of the present drift-margin ; another of quartz-felsite and of about the same size which lay in the village of St. Athan, and was removed about the year 1897 to Barry ; and lastly two small patches of sand and gravel in the Dawen valley near St. Mary Church.

The materials of both the Gravel and the Boulder Clay are almost wholly of local origin, the only known exceptions being the boulders mentioned above ; another, 6 feet long, of quartz-felsite, which lies in a field 620 yards S. 23° W. of Newton House near Cowbridge ; and the boulders from Pencoed discussed on p. 100. To them may be added the supposed chalk- flints which occur in many parts of the Vale of Glamorgan, but the origin of which is not certainly proved*.

With these exceptions the boulders are rounded or subangular pieces of Pennant and other Coal Measure grits, Millstone Grit and Carboniferous Limestone, together with pebbly grits derived from the upper part of the Old Red Sandstone and some red

The Country around Cardiff (Geol. Survey Memoir), p. 78.

96 Glacial Deposits.

grits from the lower part of the same formation. These materials, some of which have been transported from the north side of the Coal Field, are mixed in van-ing proportion with fragments of Trias and Lias of local origin.

Eastern Part. By T. C. CANTRILL.

The Boulder Clay which extends along th northern margin of the map as far westward as Llanilid presents few good sections ; it may be seen, however, at the old haematite-workings at Mwyndy, but gives place to gravel at Pont Clun in the Ely valley, where sand and gravel have been proved to a depth of 64 feet (p. 103). Farther west much of the Coal Measure ground of Coed Trecastell, Gwaun Uanharry, and Mynydd Hywel Dico is covered with a stiff impervious yellow clay-with-stones which appears to be a boulder-clay derived largely from the Coal Measure shales and sandstones, but which is with difficulty distinguished from those rocks in a weathered condition.

A similar deposit occurs to the east of Groesfaen, and to the north of Peterston Station, but gives place westwards in the lower ground to gravelly drift. Here and elsewhere the gravelly type of drift often shows so clayey or loamy a matrix as to be inseparable from the boulder-clay type.

In a gravel-pit on the north side of the valley west of Warren Mill, near Welsh St. Donats, the pebbles consist chiefly of Pennant sand- s one, but include some of Old Red grit, with a few of vein-quartz and ironstone. In another, south-west of Mountain Lodge, Pennant sandstone again predominates, and sandy gravel of the same character has been dug to a depth of 8 feet, 400 yards north-east of Talygarn. At Ty-draw, north of Bryn Saddler, on the west side of the railway, a ballast-pit shows coarse gravel with Pennant pebbles ranging up to 6 inches in length, and gravel has been dug also farther north, between the railway and Tyle-garw.

Near Ystradowain there are old pits at Rhyd-halog, one in loamy Pennant gravel by the roadside near the railway-bridge ; another, 400 yards south of the farm, has been opened on a terrace-like flat some 20 feet above the stream ; it shows on one side yellow sand with pebbles of coal, and on the other about 10 feet of gravel. At Castell-y-mwnw 3 near Llanharry station the e is a small gravel and sand-pit 7 feet deep in which similar pebbles occur in the sand ; and in another pit, 200 yards farther to the north-east, clean Pennant gravel with layers of sand is exposed for six feet. Farther west, at New Forest House south of Llanharry, a roadside exposure shows a few feet of subangular gravel chiefly of Pennant sandstone, but containing in addition several ironstone-nodules, one or two fragments of red sandstone, and several pieces of yellow g it and sandstone, probably derived from the Coal Measures.

The gravel assumes a markedly moundy form near its southern limit, especially along the high ground extending westward from

Eastern Part. 97

Cottrell past Welsh St. Donats and Ystradowain to Llanilid. On the lower ground it sometimes loses this character, while becoming more clayey and tending to assume the featureless surface associated with Boulder Clay, as in the Ely Valley; but along the courses of the streams it appears to become sandy. At Cae-rhingyll, however, east of the river Ely, a large mound, standing up conspicuously from the surrounding alluvium, appears to consist of gravel. A similar mound lies east of Pendoylan village.

Yellowish clayey gravel is exposed to a depth of some 40 feet in a deep dingle coming down from the west to Cae'r-wigau Mill south of Pendoylan. Prof. Edgeworth David* gives the following percentages of boulders in a brown sandy boulder-clay at Pendoylan :— Carboniferous sandstone 51, Lias 18, Rhaetic 9, red Triassic sandstone 9, Millstone Grit 5, Carboniferous Limestone 4, light-green dolomitic conglomerate 4. In addition to these he records a few chalk-flints.

South and west of Pendoylan the gravel rises up and over the Carboniferous Limestone escarpment and Liassic plateau of Welsh St. Donats, and becomes remarkably moundy — a character well exhibited on Mynydd-y-glew (north-east of Welsh St. Donats), and on the high ground about a mile south-west of Llanharry. The same character is noticeable about Llanilid. In all these localities there lie between the mounds small hollows many of which are occupied by peat. On Mynydd-y-glew one of these peat-bogs named Fawnog on the map was evidently till recently a pool, and there are two others, known as Megan-felin and Pysgodlyn-mawr, which still contain water. This gravel offers no resemblance to a terminal moraine along its southern margin, but thins off to a knifeedge.

West of Welsh St. Donats the margin gradually descends into the Dawen Valley near Cowbridge ; it forms the terrace of gravelly soil on which the town is built and there terminates. Two outliers, however, near St. Mary Church, suggest that it may have extended ,' everal miles farther down the Dawen Valley. In the more northerly of these, which lies on some flat ground north-east of How Mill, the only exposure is furnished by a small sand pit in a field on the northwest ide of the road to St. Hilary, .300 yards from the mill. It shows 6 feet of clean brownish-yellow sand containing a few pebbles of quartz and other rocks, several chalk-flints, and a small block of quartz-pebbly grit probably from the Old Red Sandstone. The base of this outlier must be about 35 feet above the alluvium of the Dawen at How Mill.

The second outlier caps some rising ground west of Gigman Mill, the base of the deposit being about 30 to 40 feet above the alluvium, and about 10 or 20 feet lower than that of the other outlier. It has been opened up to a depth of 10 feet in a sand-pit 450 yards west-south-west of Gigman Mill. The yellow sand therein exhibited contains numerous pebbles of yellow sandstone, red sand-

Quart. Journ. GeoL Soc;, vol. xxxix. (1883), p. 39.- 766S. H

stone, vein-quartz, chert, black shale probably from the Coal Measure.-, and several (supposed) chalk-flints. In another small pit north-west of this, and just on the edge of the wooded side of the Dawen Valley, there is a small block of quartz-pebbly grit. Subangular fragments of what appears to be chalk-dint occur in the soil of the small tributary valley one-third of a mile east of Old Beaupre.

These isolated patches seem to be relics of a tongue of sandy gravel which once extended southwards along the Dawen Valley for some distance beyond the main ma-s of drift. Not only, however, has the gravel been in great part removed, but the valley has been considerably deepened by post-glacial erosion. The mass of the material is such as might have been carried by effluents from the ice-sheet, but the occurrence of a few larger boulders is difficult to explain except on the supposition that ice in some form, for a time at least, reached the spot.

North of Cowbridiie the high Carboniferous Limestone escarpment of Pen-llin limits the drift-covered area. The part of the Dawen Valley known as Pen-llin and Newton Moors is covered with a gravelly deposit which presents the composition of glacial gravel, while at the same time it has the form of an alluvial fiat. It may be supposed that the river, before it was confined to an artificial channel, meandered and smoothed down such irregularities of surface as may have existed. Much of the material therefore might equally well be regarded as drift or as alluvium. Along the foot of the escarpment there lies some brown loam which may be nothing but rain wash.

The onlv known far-derived boulders which occur within the eastern part of the map-area are the Pentre boulder near Llantrithvd. the Newton boulder near Cowbridge. and the St. Athan boulder.

The Pentre boulder lies at the corner of a short lane on the west side of the road leading north from Pentre. and yards north of Tv-iu-haf : it rests on bare Carboniferous Limestone at an altitude of feet above 'runance Datum, and half a mile south of the southern limit of the drift. IT is unaccompanied by any other drifted material. It measures 2i-x:2xlJ feet. Under the microscope a slice [E. iN'>sj of the rock is described by Mr. Teall as a dark-£re-?n brecriated felsite. composed of a few porphyritic crystals of felspar :orthoclase) and fragments of crystalline felspar-rock in a finely-crystalline matrix largely composed of felspar. It was probablv a tutt. The source of the boulder is not known.

The Newton boulder stands at the north end of a field at 6:20 yards distance S. :2:3: W. from Newton House between Cowbridge and Llaiisannwr. at about 100 feet above Ordnance Datum. It rests on glacial clayey gravel near the southern limit of the drift. It measures 6 x 4J feet, and is partially embedded in the ground. Under the microscope [E. 3-S26] it is described by Dr. Flett as a riuanz-felsite \virh phenoerysts of quartz, orthoclase. and plagiocla?e, in a felsitic matrix which i? somewhat brerciateH.

Wr.Nfr.rn /V/V. 99

The St. A than bouMc.r has a somewhat remarkable history. According to tradition it once lay somewhere to the south of Gileston, at or about sea-level. It was taken to the village of St. Ath&n, where it remained for some time, and was thence removed about the year 1897, under the superintendence of Mr. Storrie, to the Romilly Park, Barry, where it now lies. It measures about 3 feet 10 inches x 2 feet 8 inches x 2 feet. A small fragment of the boulder has been sliced [E. 3830] and examined under the microscope, and is described by Dr. Flett as a quartz-felsite with quartz and felKpnr phorioorysts. Dr. Flett adds that all three boulders are very similar to one another and may without difficulty 1)6 believed to have been derived from the same area.

Large blocks of Old Red pebbly grit and pebbly yellow sandstones or grits from the Coal Measures occur not infrequently on the drift-covered areas. The following list gives details of some of the largest which have been noticed in the eastern part of the district : —

Pencyrn, east of Llansannwr, pebbly brown grit, 4 ft. x 3 ft. X 2J ft. ; Grippy, City, near Llansannwr, coarse yellow grit, 2J ft. ; ' Careg-lwyd,' New Forest House, Ystradowain, Pennant, 3 ft. x 3 ft.; 500 yards S.W. of Ty'r-capper, Llansannwr, Pennant, 3 ft. ; Mur-y- llengau, Ystradowain, Coal Measure sandstone, 3J ft. ; 300 yards south east of Ty-chwith, Ystradowain, Old Red Sandstone, 2J ft. ; 200 yards N.W. of Ash Hall, Ystradowain, Pennant, 6 ft.x3J ft. ; 350 yards S.S.E. of Llwyn-y-penau, near Groes-faen, Pennant, 4J ft. x 4 ft. ; 300 yards S.S.W. of Allt-y-Cawri, near Miskin, Pennant, 10 ft. x 7 ft. x 5 ft. ; 350 yards east of Rhyd-halog, near Talygarn, Keuper conglomerate, 4J ft. ; one-third of a mile west of Brigam, near Llanharry, Pennant, 3 ft. All have been derived from ground lying to the north-east, north, or north-west.

Western Part. By A. STRAHAN, from Notes by R. H. TIDDEMAN.

At Llanilid there is a great assemblage of gravel-mouuds. These however give place towards the north-east to a boulder clay, which it is difficult to separate from weathered Coal Measures. In its western part the gravel appears to have been rearranged by the Ewenny, and the material around Tre-groes is classed somewhat doubtfully as a river- gravel. At Groes on the west side of the Ewenny a well was sunk eighteen yards in clay to water.

Lower down the Ewenny Valley there is a mass of undoubted boulder clay. It extends from near Coychurch south-westwards along the north bank of the Ewenny and reaches over towards the Ogmore Valley, where however it is partly covered up by gravel. It consists of a reddish clay with small stones of which the greater part are Pennant rock, but among which there occur foreign boulders and yellow partly-rolled flints. The clay where most free from stones has been much used for pottery, and is said to have been 7665. H'2

100 Glacial Deposits.

worked for this purpose since Roman times. The clay is covered in places by gravel which has a more or less flat surface, and is not easily distinguished from a river-gravel.

In a pit 100 yards north of Pencoed Station a similar clay has been worked for making bricks and tiles. It is overspread by a gravelly drift which is nearly 20 feet thick at the north end of the pit, but only six to 10 feet at the south end.

This gravel is packed with rounded boulders of Pennant, many striated, with some pebble/ grits. It is bluish or brownish and contains lenticular bands of grey sand or nefi gravel with coaldust. Below it and separated clearly from it by a somewhat undulating plane lies a deep-red and purple clay with few boulders and extremely stiff. This is said to be 28 feet thick and to rest on sand. This pit is abandoned.

A new pit opened 300 yards further north shows a similar red clay containing many bands of fine sand much twisted and contorted, and also small pockets of sand which appear to be disconnected relics of crumpled-up bands of sand. A little of the gravelly drift with Pennant lies here and there on top of the red clay, and over all there is much rainwash containing prostrate tree-trunks. Possibly some of the superficial disturbances are due to tree-roots, but those evidenced in the red clay are too deep and large for such an origin.

It is clear that there are two drifts at Pencoed of different origin. The newer is a Coal Measure drift of the usual South Wales type, and has moved southwards. The older contains little if anything from the Coal Field, but is made up largely of red marl, probably from the Trias, and has been disturbed, not improbably by the over-riding of the ice moving southwards. Its source appears to have lain to the west on the following evidence :

In the pit near Pencoed Station fragments of marine shells, now preserved in the Cardiff Museum, were obtained by Storrie from some sand. Though too much broken and worn for determination they were believed to be Cyprina, and their character as glacial fragments was considered unmistakable. So far this constitutes the only record of shell-fragments occurring in the South Wales glacial deposits, though they abound in North Wales and in several parts of England. Th3 explanation is not far to seek. The South Wales ice-sheet had its birth among the hills in and north of the Coal Field, and travelled southwards or south-westwards. Such material as it carried was picked up on the journey. In all the regions where shell-fragments occur there is reason to believe that th-3 ice was advancing from sea towards land. It may be inferred that the Pencoed drift was not the product of the main South Wales ice-flow.

In the same deposit Storrie also found a large number of igneous boulders, now preserved in the Cardiff Museum. They have been examined by Mr. F. T. Howard, by whom the following descriptions ae supplied. The specimens were divided into eight groups, and slices from each group examined under the microscope.

1; Gabbro. Showing at places interstitial micropegmatitic structure.-

The lath-shaped felspars are enclosed by augite (ophitic structure), fairly well developed, and somewhat decomposed.

Pan. 101

The augite is in part fresh and presents definite crystal-faces and a very characteristic basal striation. There are also serpentinous pseudomorphs after the rhombic pyroxene, sometime intergrown with the augite ; crystals of epidote, probably produced by the alteration of the felspar ; magnetite and haematite.

2. Fdspathic Ash. This rock appears to be composed of very angular fragments of felsite. Some include porphyritic crystals of quartz and felspar (both orthoclase and plagioclase). The base is greyish in colour with portions of a greenish tint.

One fragment shows rnicrospherulitic structure marked by the typical black cross when the nicols are at right angles to one another.

Small grains of magnetite are scattered through the slide. The rock originally was glassy, but subsequently became " devitrified."

3. Felsite. The ground mass originally glassy is now completely devitrified. There are many porphyritic quartz-crystals usually rounded, some much

corroded and indentated, and possessing internal cavities. A few are broken, probably subsequent to cooling.

Large porphyritic crystals of plagioclase felspar are present, the majority being decomposed. They exhibit the characteristic polysynthetic twinning, and occasionally the pericline type.

Small patches of a yellowish green chlorite occur throughout the slide.

4. Porphyritic Basalt. Much decomposed.

The large crystals of plagioclase felspar are tabular ; some are broken and others much weathered.

The ground mass is also composed of minute lath-shaped felspars, dark brown in colour without augite. This feature would place the rock near the a ndesites.

There are greenish decomposition products (chlorite ?), which may have entirely replaced the original augite.

Two oval vesicles are also filled with chalcedony.

5. Basalt. Containing large lath-shaped felspars, some well-preserved, others decomposed. Few exhibit polysynthetic twinning. One crystal i. broken, and the parts separated.

There are small grains and crystals of augite and magnetite. Largercrystals of augite or another ferro-magnesian mineral are replaced by a green decomposition product (serpentine ?).

6. Brecciated Felstone. The slide exhibits flow-structure, and the crushed appearance may have been produced during the cooling of the rock.

A few good orthoclase felspar crystals with the typical Carlsbad twinning are seen, and small broken quartz -grains are scattered through the slide. The rock contains regular oval spaces.

7. Altered Basalt. Once contained many vesicles now filled up by secondary minerals, especially calcite and zeolites. Some are slightly greenish, polarising from brown to red, others are dark green in colour under crossed nicols.

Viridite has replaced a ferro-magnesian mineral, probably a rhombic pyroxene, and in part appears hi the cavities.

Some original porphyritic crystals remain which look like felspars, though multiple twinning is not distinct.

8. Ash. Basic in character ; very green in colour.

The fragmental portions originally belonged to a glassy scoriaceous basalt. The vesicles and cracks are rich in opacite. The palagonite portions contain strings and aggregates of chalcedony. Small crystals of plagioclase occur in the basalt, and the pyroxene is replaced by fibrous serpentine.

With respect to the source of these rocks, Mr. Howard remarks that No. 1 is identical with the gabbro of St. Davids Head. No. 2 is a common type in North Wales. No. 3 somewhat resembles the pre-Cambrian rocks of St.Davids. No. 6 is similar to the Bala rocks of Pwllheli, but there is a group near St. Davids also with closely allied characters. No. 7 is probably from West Pembrokeshire.

102 Glaeicd Deposit*.

No. 8 resembles rocks of the Ueyn Promontory in Carnarvonshire, but has more probably been derived from Skomer Island. " An andesitic boulder in its microscopic characters is extremely like a rock on the north side of the Neck, while a boulder of porphyritic basalt can be fairly matched in a bed at Skomer Head."

The same author in conjunction with Mr. Small writes : —

" According to Mr. Storrie the sedimentary rocks found at Pencoed likewise indicate an ice movement quite distinct from the general southerly one of the district, for whilst they include representations of the local Millstone Grit, Pennant Grit, and Carboniferous Limestone, as well as Keuper, Rhietic, and Lias rocks, there are also a number of Old Red Sandstone pebbles and cleaved rocks and grits belonging to the earlier Palaeozoic strata.

It appears then that in the similarity of the igneous rocks at Pencoed to the rocks of Pembrokeshire, in the presence of shell fragments, in the distribution of the flints, we have a set of phenomena which can be best explained by an easterly movement of the ice along the area of the Bristol Channel, and it may well be that the curious mixture of granites, porphyritic rocks, and quartzites to be found on the shores of Flat Holm is due to the same cause."*

It would be premature to enter here into the history of the glaciation of Western Wales and the basin of the Irish Sea, but we may add that the hypothesis put forward by Messrs. Howard and Small has received support from facts observed lately in Gower and on the Carmarthen coast. There also we obtain proof of an eastward movement of the drift near the shore of the Bristol Channel, though the ice-sheet generated in South Wales moved south-westwards and southwards.

The flints referred to were discussed in a previous part of this memoir.f As then explained they closely resemble chalk-flints, but no positive proof that they are so has ever been furnished. They occur in the Vale of Glamorgan, but, as remarked by Messrs. Howard and Small, are most numerous in the area which would be least affected by the Brecknock and Coal Measure drift, between the valleys of the Ogmore and Taff. They are found sparingly also in the raised beach in Gower, which is of earlier date than the local glacial drift.

The gravel which lies on the eastern side of the Ogmore north of Bridgend takes the form of a terrace, and is only separated from the gravel below Bridgend by a slight break. The pebbles consist chiefly of Pennant, but it is often covered with a foot or two of loam. The terrace shows a general gradient corresponding in direction and amount with that of the river, which gives it a resemblance to a river-terrace, but its composition and distribution indicate that it was the work of an effluent from the ice-sheet rather than that of the Ogmore, and it is accordingly classed among the glacial deposits.

Notes on "Ice Action in South Wales," by F. T. Howard and E. W. SmalL Trans. Cardiff Not. Soc., voL xxxiL, 1899-1900. f The Country around Cardiff (Gtol. Survey Memoir), pp. 78, 79 (1902).

ioa

Chapter X.

POST-GLACIAL DEPOSITS. By A. STRAHAN.

The post-glacial deposits include blown sand, estuarine mud and alluvium, peat, calcareous tufa and river-gravels (terraces).

River Gravels. — The southern end of the gravel- terrace between the Ely and the Clun enters the northern margin of the map. A larger tract borders the Ewenny near Pencoed, where, however, it is doubtfully distinguished from glacial gravel. In several cases difficulty has been experienced in deciding whether a gravel-flat bordering a stream should be classed as glacial or alluvial. At Pen-llin, for example, the origin of a broad expanse of gravel is doubtful (p. 98), and the same difficulty arises at Pont Clun and south of Miskin Manor. At Pont Clun the depth of the gravel was proved in the shafts referred to on p. 17. Though forming what looks like an alluvial flat, the greater part of the deposit is likely to be of glacial origin. The surface of the ground is 150 feet above Ordnance Datum.

Cardiff Navigation Colliery.

FT. IN. Soil and clav ' 18

Rough gravel

Mixture

Quicksand

Rough Gravel

Clay mixed with fine gravel

Fine clayey sand

Coal Measures, p. 17

Estuarine Mud and Alluvium. — The fluviatile alluvium of the Dawen merges into brown Scrobicularia-cl&y at Marsh House, and in this form extends eastwards to the old watch-house, as a turfcovered flat. It is, however, being invaded by shingle. Westwards from the river a flat of similar origin forms the Lays. This tract is protected from the sea by dunes, and is in parts thinly overspread by blown sand. Some years ago Mr. Woodward noted on the foreshore, half a mile west of Limpert, Scrobicularia-claky resting on white calcareous tufa with Helix, this in turn lying on Lias.

Blown Sand. — East of the Dawen a narrow strip of blown sand accompanies the shingle at far as the old watch-house. West of the river the dunes fringing the Lays rise to thirty feet in height. The

104 Post-Glaeud Deposits.

source of the sand is not obvious unless the alluvial tract formerly extended over Limpert Bay, as suggested by the observation refe red to above.

There is doubt also whence came the sand of Newton Burrows and Merthyr Warren, unless it be supposed that there has been some alteration of the coast within the last one or two hundred years. Blown sand occurs generally where there is a broad alluvial foreshore, exposed to the south and west, as, for example, as Aberavan. No such alluvial tract exists at Newton, and it must be supposed either that the shore between tide-marks has yielded the sand, or that an alluvial tract once existed, but has been destroyed by the sea. Two facts rather favour the latter hypothesis. In the first place the quantity of sand is too great for the source on the first hypothesis, and in the second, it is stated that within the memory of living men the Tusker Rock was a sheep-pasture, though it is now covered by every tide. The subsoil of the pasture must have been some easily eroded material, and was presumably an alluvial deposit such as occurs in so many parts of the Bristol Channel. It may be inferred that it formed the last relic of a wider alluvial tract.

The Kenfig Burrows form the southern end of a belt of blown sand which borders the shore as far as Swansea, with interruptions only where the principal rivers break through. The general drift is eastward. That the sand has made great inroads since Roman times might be inferred from the fact that the Roman Road known in different parts as the Water Street and Heol-las was taken across a tract now occupied by high dunes. It is possible, however, to date its movements more precisely.

The Parliamentary and Municipal Borough of Kenfig is now represented by a few scattered cottages with a population of about 300.* The charters are preserved in a room in a building known as the Town Hall, the lower part of which has been used as an inn. The earliest is a charter of Thomas, Lord le Despencer, dated 16th February, 1397, but there were earlier charters which have been lost. In 1232 the place was attacked by the Welsh. The town was situated half a mile north-north-west of the Town Hall, as shown upon the Ordnance Map, and is supposed to have been abandoned in the fifteenth century on account of the encroachment of the sand. It is the general opinion that the sand made great advances in the sixteenth century. It is still encroaching upon the southern end of the village. Kenfig Pool is a broad sheet of water ponded up between the drift on which Kenfig village stands and the sand encroaching from the west. Its greatest depth is about eleven and a half feet, and the water is fresh. It has existed in almost its present form since 1876, but is smaller than, and slightly different in outline to, the pool of 1814.

This account is based on various papers in the Archceologia Cambrensis. See also A Topographical Dictionary of Wales, by Samuel Lewis. 4to. London, 1845.

Post-Glacial Deposits. 105

Beneath the sand, where it has been blown off the original surface, Mr. Tiddeman has found many chips of flint, together with arrows, lance-heads, scrapers, awls, and disused flakes, and ocasionally ancient pottery.

Peat. — Many of the drift-hollows are occupied by peat ; notably in the neighbourhood of Llanilid. A peat-flat, once a pool, named Fawnog on the map, occurs about a mile east of Welsh St. Donats. A small peat-bog, lying in a valley south-west of Hensol Park, gives rise to two small streams which flow in opposite directions. Morfa Ystradowain is an extensive peat-bog lying on glacial gravel. It now drains by Nant Dyfrgi northwards into the Ely at Pont Clun, but before the deposition of the gravel, the water may have equally well turned southwards by Ystradowain and Maendy to the Dawen.

Calcareous Tufa. — An irregular bed of calcareous tufa has been deposited at Garn-lwyd north of Llancarfan by a calcareous and slightly ferruginous spring which issues in front of the house. Gas, presumably atmospheric air, is evolved.

On the coast a trace of tufa-cemented shingle sticks to the face of the Lias cliff, six feet above the top of the present shingle, about 150 yards west of Font-y-Gary Cave near Aberthaw. Either the shingle must once have been banked up higher against the cliff than now, or the deposit may represent the raised beach which is shown in many places in Gower, and is always cemented. In view of the waste undergone by these cliffs the latter supposition is hardly possible. Some tufa observed on the foreshore by Mr. Woodward has been already mentioned (p. 103.)

Chapter Xl Economic Products.

Building Stone and Road Metal.

The Quarella Stone, described on p. 51, and the Sutton-stone described on p. 60, are the principal building-stones. The former was once quarried near Pyle also (p. 55). Lias limestone is used for road-metal, but locally only, the Carboniferous Limestone being more durable. The latter is worked for this purpose at Llanharry.

Lime, Cement, and SUica.

Lias limestone is used largely for both lime and cement at Stormy and Bridgend. The well-known Aberthaw lime was obtained by gathering pebbles of this limestone from the beach at that place (pp. 71, 87). The Carboniferous Limestone, and in fact all the other limestones, were formerly burnt in a multitude of places, each farmer preparing lime for his own use. Now all the kilns are abandoned save those on a line of railway, as at Llanharry. Rhgetic sandstone has been used for making silica-bricks at Stormy.

The following analyses of Lias limestones are quoted from the 'Jurassic Rocks of Britain/ vol. iii., p. 292, by H. B. Woodward, to which reference should be made for a general account of the economic products of the L!as.

Aberthaw.* Bridgend. f Carbonate of lime - - - 86-0 76-0

Carbonate of magnesia - Alumina

Silica

Oxide of iron Moisture, organic matter and loss

2O 4-0

100O 100O

Galena.

Traces of galena occur in veins associated with barytes in the Lower Limestone Shales at Groes-faen. At Pentre, north of Llantrithyd, several veins of calcite cross the road on the line of the fault shown on the map. Galena was worked here about fifty years

Analysis published by Mr. H. Keid, Manufacture of Portland Cement 1877, p. 56 ; see also R. Phillips, Ann. Phil., ser. 2, vol. viii., 1824, p. 72 ; and A. Voelcker, Journ. Bath and W. of England Soc., ser. 2, vol. vi., p. 228.

f Analysis published by Mr. H. Reid.

Bcematitet 107

ago, and it is said to have yielded more silver than is usual in the district. Some has been got also by shafts and levels on the south side of the valley east of New Beaupre, where a few feet of Triassic breccia overlie the Carboniferous Limestone. There are two old shafts also 200 yards north of New Beaupre. The more ambitious attempt to work galena at Llangan has already been mentioned (p. 71). An east and west vein containing barytes and specks of galena has been tried also near Twmpath, and there is a row of deep shafts along the base of the Lias, west of Pen-llin Court. The Carboniferous, Triassic, and Liassic limestones all contain specks or threads of galena more or less abundantly, especially near the uncomfortable junction, but the ore has not been found in paying quantity.

Hcematite. By T. C. CANTRILL.

The haematite-deposits extend along the junction of the Millstone Grit shales and Carboniferous Limestone from the north-east corner of the map near Mwyndy nearly to Llanharry. Those rocks, dipping steeply northwards, are unconformably overlain by Keuper conglomerate, and over much of the ground there is a coating of glacial drift which is said to have attained a thickness of 120 feet at some of the workings.

The haematite at Llanharry was known and worked en a small scale in very early ages, for Dr. Watson* records that at Llechau had been found old workings which by their form seemed to be of Roman origin, and that some small amphorae of coarse red pottery, undoubtedly Roman, were found a few years before in the bottom of an ancient stall-working at Ty-isaf, and he gives a section and plan of one of the old workings. That the Romans worked the haematite near Mwyndy seems certain from the finding of a coin of Antoninus Pius (A.D. 138-161) and a piece of earthenware charged with figures of greyhounds, hares, etc., near Miskin in 1752, under some iron-cinders which were being re-smelted.f It is probable that the cinders referred to are those still to be seen in heaps in a field on the west side of the River Ely 100 yards above the bridge at Miskin. There is a smaller heap at Hendy-isaf nearer to Pont- Clun. Old beds of cinders have been met with at the Mwyndy Mine ; and in old workings in the adjoining Bute Mine, reopened in 1854, ancient tools and human remains are said to have been found. Several masses of charcoal-iron cinder lie by the side of the footpath 250 yards south-west of Fron-wen, Llanharry.

Leland, in the Itinerary (circ. 1540), refers to the making of iron as being then in progress in a " park " named Glinog in the district south of Llantrisant. This name is apparently not now known,

Geologist, vol. ii. (1859), p. 241.

The Rev. W. Harris, in Archceologia, vol. ii., p. 1.

Economic Products.

but Dr. Watson conjectured that the mine referred to by Leland might be the same as one then (1859) working at Cornel-y-parc, Mwyndy. The word " pare " forms part of several place-names in the immediate vicinity.

The position of the iron- ore relatively to the Triassic and Carboniferous rocks is shown in some sections by Mr. Stephen Vivian,*

FIG. 9. — Transverse Section of Mwyndy Mine. BY S. VIVIAN.

which are here reproduced by permission of the Council of the South Wales Institute of Engineers.

The ore usually occurs as an alteration product, in the form of irregular masses which have replaced the upper part of the Carboniferous Limestone. Upon it rest the shales which constitute the lower part of the Millstone Grit. It thus has a fairly regular roof,

FIG. 10 — Transverse Section of Mwyndy Mine. BY S. VIVIAN.

though downwards it shades most irregularly into, and includes masses of, unaltered limestone.

Occasionally the Keuper conglomerate becomes so rich in iron oxides as to be worth working, as at the Trecastell Mine, where a

Trans. S. Wales Inst. Eng., vol. xiv., plates 24, 25, 26,

Hcematite.

small patch of ore occurred between the conglomerates and the shale, some forty yards north of the regular ore-bed. Ore has been found also in small veins and fissures in the conglomerat 3.

The conglomerat 3 generally consists, as at Mwyndy, of a mass of subangular and rounded pebbles, chiefly of Carboniferous Limestone, but with some of sandstone, embedded in a red ferruginous and calcareous marly matrix. Occavsionally the pebbles become small, rare, or absent ; and the rock then takes the form of a hard reeky calcareous marl. At its contact with the underlying limestone or shales this rock becomes highly ferruginous, and at the old Llanharry Iron Ore Works it contains streaks of haematite and nests of calcite. There is a notable absence of magnesian compounds.

A specimen of this red ferruginous and calcareous marl from the disused workings at the Llanharry Iron Ore Works has been examined by Mr. H. H. Thomas. The insoluble residue after treatment of the rock with acid was divided by specific gravity solution

FIG. 11. — Transverse Section of Trecastle Aline. BY S. VIVIAN.

into two parts. The part with specific gravity less than 2'8 consisted chiefly of impalpable marly sediment which, with a little detrital quartz, made up the bulk of the rock. The other part consisted almost wholly of a heavy sulphate, probably of barium.

A specimen of a red ferruginous limestone was taken from the north side of the road from Llanharry Station to the village, at twenty yards east of the junction of the road from Ystradowain, and close below the base of the fine red breccia of the Keuper. Mr. H. H. Thomas finds that the residue after treatment of the rock with hydrochloric acid forms a very small percentage and is mainly detrital quartz, the grains in some cases having a secondary growth of silica completing the crystalline form. These crystals are beautifully sharp doubly-terminated short prisms. Besides the quartz there are a few grains of brown tourmaline and also of pale garnet.

That the Triassic water was the source of the iron here, as in so other many regions,* seems certain. The replacement of the calcium

The Country arounr] Newport (Geol. Survey Memoir], p. 25.

Econom ic Product*.

carbonate by an iron-salt would be guided by the impervious shales, which would hold the water up in the base of the conglomerate, or cause it to circulate along the top of the limestone below, according to local circumstances, while the depth to which the alteration of the limestone proceeded was determined by fissures, beddingplanes, etc.

The ore occurs as the hydrated purple-brown ferric oxide known as limonite, and as the harder anhydrous ImMuatite. The latter, which was more abundant at Mwyndy than at Trecastell, is generally more siliceous and is called k blue iron.' The chief points of difference in the two varieties are as follows* : —

Limonite. Hu-matite.

(Treeustell.) (Mwyndy.)

Peroxide of iron - 74-71 70-f>7

Silica 3-S(> 18-36

Carbonic acid 4-1) '2-71 Water combined - 7 -64

The replacement has affected only the uppermost beds of limestone ; and rarely extends far below the Triassic base, the greatest depth hitherto reached being about 100 yards. At Mwyndy the ore extended vertically downwards into the limestone in a deep pocket, and both here and at the adjoining Bute Mine several gashveins cut southwards into the limestone for 100 or 150 yards, with a width of 5 to 15 yards, and a depth of 20 to 50 yards. When followed along the strike, the main ore-bed rarely persists more than 100 or 200 yards.

The ores are stated to have yielded '>0 to 50 per cent, of metallic iron, the residue being largely siliceous or calcareous. Dr. Watson remarks that botryoidal forms of haematite are notably absent, while fine specimens of quartz-crystals are common. The ( raddle' of the Ulverstone district is not found here.

It was found that the ore became less siliceous at the greater depths, and that it changed much in hardness, so that in places it could be got with the pick. In colour it varied from red and brown to blue, grey, and yellow. A small quantity of yellow ochre was sold for colouring purposes, and a little manganese ore was found at the Trecastell Mine. Lead- and copper-ores occurred but rarely. Messrs. W. Vivian and J. H. Collins t have described and figured some crystals of calcite and quartz containing inclusions of ironoxides from the Mwyndy Mine.

Mines east of the River Ely.

The easternmost workings on this map occur north of Bro-fiscinfach, and old openworks and shafts can be found as far west as Cefn-yr-Hendy, but the most extensive works were carried on at

From The. Iron Ores of Great Hritain, and Ireland, by J. D. Kendall, 8vo., London, 1893, p. 13.

J- 3/t'n. Mag.t vol. i., pp. 18, 19, and 117.-

Hcematite. Ill

the Bute Mine on the west side, and at the Mwyndy Mine on the east side of the Llantrisant-Cardiff Road.

The modern period of these mines appears to have commenced in 1854 and 1855 respectively, and Dr. Watson probably referred to them in 1859 when speaking of mines at Hendy and Cornel Park. In 1884 operations appear to have stopped, and in 1896-7 all the works had been long abandoned. The ore was first got by open-works, till the cover of drift and conglomerate became over 100 feet thick. Slopes or drifts were then opened, following the ore down a dip of about 30° to 40° ; but after a time shafts were sunk some distance to the deep, and horizontal adits driven from them southwards to the ore.

The quantity of water encountered, which, at times, amounted to 20,000 tons a day, proved a great hindrance to the success of the mines. It is said that 1,500,000 tons of ore were won from the Mwyndy, Bute, and adjacent mines, with average value of 12s. to 14s. per ton.

At Maes-y-felin, Pont-Clun, trials were made by the Dowlais Iron Company in search of haematite, but the quantity met with was not sufficient to be worth getting. One of the shafts lies about 200 yards south-west of Llantrisant Station ; the tip is composed mainly of black shale, with apparently no Triassic deposits. The absence of the Trias in this valley was inferred on other evidence also, obtained while the mapping was in progress.

Mines west of the River Ely.

The Trecastell Mine at Ty-du, according to Mr. Vivian, was opened up by the Mwyndy Iron Ore Company about the year 1884. Thick glacial gravel overspreads the rocks, and much water was encountered, amounting to a yield of about 6,000 tons a day, unaffected by rains. All the ore was obtained from one large pocket, 60 yards long by 35 broad, by means of a pit sunk to the deep and adits driven southwards to the ore. The beds dip a little west of north at about 35°. The ore is particularly rich, and is calcareous rather than siliceous. An analysis of a picked sample showed over 62J per cent, of metallic iron. Some of the limestone brought up from the shaft, and now lying in heaps on the site of the works, has been found by Dr. Pollard to be a ferriferous dolomite, compose of carbonates of magnesia, lime and iron, with a little manganese and some ferric iron.

The supposed Roman workings at Llechau and Ty-isaf have already been mentioned.

The Llanharry Iron Ore Works, half-way between Llechau and Llanharry, were opened some time prior to 1885, at which date they were alluded to by Mr. Stephen Vivian as having yielded a few thousand tons of ore worked on the crop. The deposit appears to have proved to be of limited extent, but of good quality. All operations had ceased previous to 1899. There are no mines west of Llanharry.

112 Water Supply.

The foregoing account of the mines has been based largely on the following publications.

A list of works dealing with the South Wales Hccnuitite Deposits.

1859. WATSON, J. .1. W. — The Haematitic Deposits of Glamorganshire.

Geologist, vol. ii. (1859), p. '241. 18(51. ROGERS, E., SALTER, J. W., ETC. — The Iron Ores of South Wales.

being Part JIT. of " The Iron Ores of Great Britain." Mew. Gfol.

Surv. 1872. VIVIAN', W. — The Mwyridy Mines. Trans. Cardiff Nat. Hoc., vol. Hi.,

pt. i., p. 70. 187<>. VIVIAN, W. — Note on Paragenetic Formations of Carbonate of Lime

and Oxide of Iron, and of Quartz and Oxide of Iron, at the Mwyndy

Iron Mines, Glamorganshire. With Note on the Specimens by

J. H. COLLINS. Min. Mag., vol. i., no. 1, p. 18. 1877. VIVIAN, W. —Further Notes on the Oxides of Iron, enclosed in Quartz,

at Mwyndy. Glamorganshire. Ibid., no. 4. 117. 1882. MEADK. R.— The Coal and Iron Industries of the Tinted Kingdom.

8vo. Loud.

WETHERED, K. — On the Origin of the Haematite Deposits in the Carboniferous Limestone. Geol. Mag., p. 522. .884. VIVIAN, S. — The Haematite Deposits of the Southern Outcrop of the

Carboniferous Limestone of South Wales. Proc. *S'. Wales InM.

Eng., vol. xiv., p. 164. [Discussion, p. 211.] 1893. KENDALL, J. D.— The Iron Ores of Great Britain and Ireland. 8vo.

Land. 1895. HOWARD, F. T.— The Haematite Deposits of South Wales and the

theories regarding their formation. Trans. Cardiff Nat. tioc.

vol. xx vi., pt. i., p. 47.

Water Supply.

Eastern Part. By T. C. CANTRILL.

In the eastern part of the area surf ace -springs are chiefly utilised for the source of water. There are no deep wells, and draw-wells are exceptional. The best springs are those thrown out along the junction of pervious and impervious strata, for example, between the topmost pebbly grit of the Old Red Sandstone and the underlying more marly beds ; between the Lower Limestone and the Old Red Sandstone ; and between the Main Limestone and the Lower Limestone Shales. The Keuper conglomerates also, and sometimes the marls, yield some good springs. Faults, especially where they bring pervious against impervious strata, generally throw out water.

Many small springs issue along the edges of the drift-deposits, but they are usually less reliable. Among these may be mentioned the Silver Well and the Bowmen's Well at Cowbridge, which, apparently, are fed from the gravelly terrace on which the town i s built ; the former is much drawn upon by a pump in the High Street. A strong but intermittent spring, in the valley between Prysr- and Aberthin. bursts up through gravel, but probably has its source in either the Lias or Carboniferous Limestone.

With respect to the springs thrown out by the " solid rocks," we find a little water issuing from the base of the pebbly grits of Old Red Sandstone south-east of Llwyn-y-penau near Groes-faen, and at Kennel Grove in Heiisol Park. The Lower Limestone throws out water at Llan-chwian-fach east of Cowbridge, and south of Crofftau near Miskin Manor, and a good spring issues from the base of the Main Limestone a quarter of a mile north-east of Groes-faen. A powerful issue occurs at about the same horizon at Pant Wilkin, east of Cowbridge. Other strong limestone-springs are Adam's Well at Talygarn ; another 350 yards north-east of Llwynau, Bryn Saddler ; and another situated on the edge of the alluvium 200 yards north-west of Rhyd-halog, near Ystradowain. There is a strong spring on the edge of the alluvium of the Ely between Hendyisaf and Miskin, and others near the river immediately west of Miskin, all being situated close to the supposed course of the Miskin fault. Another line of fault appears to account for the issue of Ffynnon Elan from Carboniferous Limestone near Ystradowain, and for two strong springs at Llwyn-nwydog farther north. A slightly chalybeate water issues from Coal Measures, and probably from the crop of the Drydedd Vein, north of Tyle Garw near Pont Clun.

Two strong issues of water flow from the junction of the Keuper conglomerate and the Carboniferous Limestone at Llechau near Llanharry Station, and form Felin-fach Brook. The conglomerate again, 200 yards west of Ty-du, yields a strong supply which is utilised for the supply of Bryn Saddler, the water probably being held up in it by the underlying shales of the Millstone Grit and Coal Measures. Ffynnon Deilo south of Pendoylan issues from the same rock, but Ffynnon Cattwg, east of the church, is thrown out by Keuper Marl, and another, on the edge of the alluvium of the Da wen north of How Mill, by brecciated tea-green marls overlain by Rluetic sandstone. Whitewell, south of Bonvilston, issues from Keuper breccia and evolves bubbles, probably of atmospheric air.

The base of the Lias throws out a strong spring 250 yards south of Bonvilston, at Coed-y-Castell near Llandough, and at Ffyrmonyr-hebog at Cwm near Pendoylan. Another spring issues from a slightly higher bed in the Lias south of Ystum-elaid near Llantrithyd.

The limestones of the A. BucMandi-zoue give egress to water along the top of the Lavernock Shales and along the alluvial flats. Such springs abound in the coastal region, and among them may be mentioned a highly calcareous and somewhat ferruginous spring at Garn-lwyd, near Llancarfan (p. 105), and another at Pistyll-hill northwest of the same place; St. Mary's Well and the slightly hepatic Eye Well at St. Mary Church ; and several good springs on the west side of the Peterston outlier. Lias faulted against Carboniferous Limestone gives rise to the Brewer's Well at Llantrithyd. The Good well atFlemingston and St. John's Well at St. Athan are situated in valleys in the Lias. The Eagle's Well is utilised for the supply of Boverton.

7665. T

114 Water Supply.

The following records of well-sections in the eastern part of the area .have been obtained :— -

Peterston, 200 yards west of the station ; fifteen feet in brown sandy gravel and quicksand.

Peters Urn, 350 yards south-west of Oroes-y-parc ; fourteen feet in clayey gravel with flints.

Peterston, at Tre-rhedyn, on the Pendoylan road ; thirteen feet in gravel.

Pendoylan, 150 yards north-west of the church ; over fourteen feet deep, commencing in black paper-shales (AvicuLa contorta-zone) and ending in Keuper Marl (tea-green beds).

Prysc, Welsh St. Donats. Two wells at the top of the hill, said to be seventyeight and seventy-two feet deep respectively, and the latter said to end in " dark shale ; " they probably commenced in Lias of the A. Bucklandi-zone and failed to reach the horizon of the supposed Ostrea-beds which crop out at Maendy (p. 68).

City, Llansannwr, 100 yards west of the rectory ; thirty-three feet in gravel and probably some limestone -debris and eighteen feet farther in Carboniferous Limestone.

Argoed-isaf, Llansannwr ; thirty -six feet in gravel.

Fforest-fawr, Ystradowain ; six feet in " gravel " (probably limestonedebris), thirty-three or thirty-six feet farther in Carboniferous Limestone.

Cowbridge, at the station ; twenty-six feet in gravel and more than four feet farther in rock, probably Keuper breccia.

Western Part.

By A. STRAHAN, from Notes by K. H. TIDDEMAN.

Tn the western part of the map, mention may be made of the following springs :—

From the Lias. — Ffynnon Fair, a good spring in a dingle west of Monk-nash. Ffynnon y Grotto, and another close by, in Factory Brook, west of Llanbleiddian. A large spring in Llysworney. Chwech Ffynnonau, 400 yards north-west of Sixwells south of Nash. Large springs at Great Frampton, said to be polluted. Springs at Sigingstone. The Wound Well and the Eye Well in Cwm Marcross, supposed to have healing properties ; a thorn-tree close by is hung with votive rags. Spring west of Capel near St. Donat's. Mid Well which forms the supply for Llantwit-Major. Ffynnon-wen, at the base of the Lias, 500 yards east of Peran-pren, west of Cwrt Colman.

From Keuper. — Large springs in the cliff on the south side .of Sker Point. St. David's well and Ffynnon-fawr at Nottage. St. John's Well at Newton Nottage (see also p. 115). Waun-y-mer, south of Kenfig Burrows, strong in winter, but nearly dry in summer. Ffynnon -y-mer, a good spring at Pen-yr-heol south-east of Kenfig Burrows.

From Carboniferous Limestone. — Great issues of water 650 yards east of Ogmore Castle, where it is pumped for the supply of Bridgend; and others to the west of the castle. The Lias of this region is a massive limestone, adhering to and much resembling the Carboniferous Limestone. The two rocks are equally liable to swallow -holes and to underground waterchannels. Springs issuing from them may contain any proportion of contaminated surf ace-water*. Ffynnon Tre-Brenin, south of Nottage ; the water in a quarry close by is said to be affected in level by the tide. Porth-cawl Dock, a large spring visible at low tide. Springs in foreshore south of Newton Nottage, see p. 115.

At Ty Maen, South Cornelau, there is a well sixty -three feet deep in Carboniferous Limestone ; a band of clay in the limestone, 200 yards northeast of South Cornelau, throws out*water. A well 300 yards south-west

Dr. Bulstrode's Report to the Local Government Board upon the Water Supply of Bridgend, and upon the relation thereto of tlv prevalence of Enteric Fever, 1903.

Western Part. 115

of 'Grove commences in Keuper conglomerate and has been sunk to a depth of sixty feet. A well at Heol-las in Keuper is twenty feet deep. A shaft 370 yards west of Ty'n-y-cae, north of Newton Nottage, was originally sunk in search of iron-ore, but has been re-opened in an attempt to get water. A well 450 yards north-east of Nottage Court has been sunk 140 feet, commencing in Keuper conglomerate ; a spring at a depth of thirty -two feet yielded 700 gallons per hour. The height of the surface above Ordnance Datum is about forty-eight feet. The spring therefore is a little above the level of the water in St. John's Well.

St. John's well at Newton Nottage has long been known to ebb and flow in sympathy with, but not simultaneously with, the tide. It was described and the movements of the water observed in 1898 by H. G. Madan, from whose paper* the following account is taken.

The well is 500 yards from the shore and separated from it by sand-dunes and a pebble-ridge. The sand rests on Keuper conglomerate and this on Carboniferous Limestone. Between the two rocks a considerable body of water flows seaward, and bursts out on the foreshore. It is this water which is tapped in the well. The well is thirteen and a half feet deep and its bottom is eight feet above Ordnance Datum. From a number of hourly and half-hourly observations Madan ascertained that the movements of the water in the well were as regular as those of the tide, but that they lagged behind the tide almost exactly three hours.

The water contains the rather high proportion of 27 '2 parts per 100,000 of sodium chloride, but shows the same proportion when at its highest as when at its lowest level.

The interpretation of these phenomena presents no serious difficulty. The water contained in the Keuper conglomerate and Carboniferous Limestone " is in free communication with the sea, along the line where the conglomerate crops out below high-water level on the shore.

The tidal wave, on reaching the outcrop, is taken up by the water in the permeable strata and propagated landwards, but with a greatly diminished velocity, owing to the resistance to its motion offered by the solid, though porous, stratum of conglomerate. . . . Hence we have high water in the well three hours later than high water in the sea " (op. cit., p. 305).

Two other wells in the village are said to ebb and flow synchronously with St. John's Well. There is said to be a similar well on Flat Holm f (Sheet 263).

Quart. Jo-urn. Geol Sot., vol. liv., p. 301 t Proc. Geol. AMOC., vol. xi., p. 214 (1890).

Index.

Aberdo Limestone, 85. Cae'r-wigau, 5, 27, 28 ; glacial, 07.

Abernant, 3D. Cue Tori 51.

Aberthaw, 85 -87 ; lime, 71, 72, lot; ; Calcareous Tufa, 105.

tufa, 105. Abortliin, 12, 32, os ; spring, 112. Adam's Well lo. I 13. Allt-isaf, 3'. Allt-las, 70.

Allt-y-Cawri, laoial, 99. Analyses, -1!), :2, IOC, llo. Andrew's Pant, To. Aimvltown Asylum, 14-10, 52. Arglwydd \Vood, 04. Argoed-isal I I I. A .ill Hall ! 1 ; glacial, 99. Aust Hour U,l:,2.

Candleston, II. oo.

Carboniferous Limestone, (5-15 ;

springs, 1 12-115. Cardiff Museum, 34. Cardiff Navigation Colliery, 17,103. Carmel Chapel, 05. Castell-ar-foel, 40, 05. Castell-y-mwnws, glacial, 90. Castell-y-mynach, 3!), To. Cave, 13.

( VI n-yr-li'Midy, 1 lo. I 'ement' Works, 50, Y-l, 1 00. Chalk- flints, 95, 9V, 98, 102. Cherl, 5!), 72. Cli \vech I'Yynnonau, 1 14. Clemenston, 1 4.

City, 11 ; glacial, 99 ; well, 114. Clawdd-coch, 20, 27. Coal Measures, IT- 19. Coal-trials in lxh;etic, 49 ; in Lias,

Coed Arthur, 04. Coed Garn-hvyd, 04. Coed Hills, 41, 05.

marry, 25 : anticline, -S9, 9o.

Jarytes, 8, 100, 1 07.

'.lackland, 39, (J4.

>lack Kocks, 71, 75, 82.

Jlown Sand, 1O3 ]O5.

iodlonga, 12, 09.

>odwr Seams, 1 7, 19.

Jolu'oed.

Joiiney, Ilev. Prof. T. C., 82.

vilston, 13, 25, 29, 30,39, 50, 59, Coed Leyshon, 49, 09.

04, : spring, 113. Toed Llwyn-Hywel, 26.

'overtoil, \vater-supp]y, 113. Coed Mwstwr, 50.

loiilders, 95-102. Coed Trecastell, glacial, 90.

Moulder (.'lay, 95-97. Coed-y-Brain, 11.

lowman's Well, 112. Coed-y-castell, 44 : spring, 113.

>re\ver's Well, 113. Coed-y-Cohvn, 64, 70.

'.ridgend, 59, 72,73,75,93, loO: Coed-y-( Arabia, 31 .

glacial 102; water-supply, 114. Coed-y-llwyn, 32.

Jrigani Wood, 11 ; glacial, 99. Coed-y-niarlan, 09.

'.ristow, Mr. II. W., 36,37,61,71, Coed-yr-Aber, 39, 04.

74, 75, si . (Joed-yr-Uondy, 17.

iroadlield Down, 81. (1oity,'32. 33, 51, 71.

Jroc.a.stle, 73, s I. Colleuc, (J.

Jro-iiscin-tach, 3o, llo. Colliii,-, Mr. .1. H., llo, 112.

3,'on.foiouiil Thn-ni<t*'i, 34 Jrynau-gwynion, 19. Jryn-helygen, 20. Jryn-hyt'ryd,

>ryn Saddler, |o; glacial, 90 ; spring, ( 'ornelaii, 33.

( '.)! i nst OH, , 2.

Conybeare, Jtev. W. D., 4 1, 78.

Conybeare, Hev. .1. .1., 78.

Coral -growth in Lias, Oo, 82, 88.

I >ryn v cae, I s.

I'.n'ck la iid llev. I Vol. W., II, 44. P.uililiim' S|i me, lot;. Bnlstrode, Dr. II. T.. I I 1. liilte Mine, 3D. 0!>, |O7, llo, 111.

i. :J3, . ,Ui1 incline, 8!),

'orm;l-y-parc, |os. 111. ConitoNvn, 73. ( 'ot ham St >1U', 53. Cottrcll 5, 7, 13 : glacial, 97. Court K.irin, 12, 08. Co \vbrid-r, 5, 13. 25, 31,32, 35, 39, I I 48, On, Oli 08 ; glacial 95, 97 ; springs, 113, 114. (.'owhridge-Carditt' anticline, i, 2, 4,

7, 13, 89 93. Coyphnivh, 32. 33, ">o, .)i i.tnial, 99,

m

Crack Hill, 13.

(Jribbwr-fawr Coal, 17-19.

Crofftau (Miskin), 4, 6, 8, C.

Crofftau (Ystradowain), 10.

Cross, The, 41.

Cross Barn, 65.

Cwm, 69 ; spring, 113.

Cwm Farm, 49.

Cwm-gran, 18.

Cwm-mawr, 86.

Cwrt Colinan, 33, 52, 53; spring,

Cwrt-newydd, 70. Cwrt-y-carnau, 9, 28.

David, Mr. J., 57.

David, Prof. E., 47.

Dawen Valley, 2, 11, 24, 68, 103, 113 ;

glacial, 95, 97, 98. De la Beche, Sir H. T., 55, 60, 61,

67, 75, 76.

Disturbances, 89-94. Dolomite, 8, 14, 111 ; in Lias, 75. Draenog Wood, 64. Duncan, Prof. P. M., 37, 38, 61, 73,

Dunn, Mr. F. W., 18, 19. Dunraven, 23, 25, 59-63, T7-80, 83-

Dyffryn, 25, 50. Dyffryn-lloff, 26.

Eagle's Well, 113.

Earth-movements, 58, 59, 66, 89-91. Eastdown, 41, 65. Ebbing and flowing wells, 115. Ely Valley, 2, 9, 24, 113 ; glacial, 96,

97 ; gravel, 103 ; haematite, 107. Esgyrn Vein, 18. Estuarine Deposits, 103. Etheridge, Mr. R., 36, 37, 61, 62. Evans, Mr, D., 18. Ewenny Priory, 13. Ewenny Valley, 2, 23, 50; glacial,

99 ; gravel, 103. Eye Well, 113, 114.

Fairy Cave, 77. Faults, 89-94. Fawnog, 105 ; glacial, 97. Ffald-wen, 70. Fforest-fach, 10. Fforest-fawr, well, 114. Ffynnon Cattwg, 27, 113. Ffynnon Deilo, 113. Ffynnon Elan, 113. Ffynnon Fair, 114. Ffynnou-fawr, 114. Ffynnon Tre-brenin, 114. Ffynnon- wen, 114. Ffynnon-y-cae, 40. Ffynnon-y-Grotto, 114. Ffynnon-y-mer, 114. Ffynnon-yr-hebog, 64, 113.

Firebricks, 50.

Flat Holme, 90 ; glacial, 102 ; spring,

Flemingston, 113. Flett, Dr. J. S., 31, 33, 43, 53, 54, 56,

60, 98, 99.

Flint implements, 105. Fron-wen, 30, 107.

Galena, 8, 34, 40, 60, 65, 67-69, 71

75, 106, 107. Gareg-lwyd, 99. Garn, 41, 65. Garn-lwyd, 105, 113. Gelli-araul, 71. Gelli-wen, 28. Gibbet Hill, 67. Gigman Bridge, 41 65. Gigman Mill, glacial, 97. Gileston, glacial, 99. Glacial Deposits, 95-102. Glauconite, 35. Glinog, 107. Goodwell, 113. Gower, 14, 102. Gravel, glacial, 95-102 ; of rivers,

Great Frampton, 114. Green, 65. Greendown, 64. Grey Grits, 4. Grippy, glacial, 99. Groes, glacial, 99. Groes-faen, 4, 7, 8, 28, 39, 106 ;

glacial, 96, 99 ; springs, 113. Grove, 115. 'Guinea' bed, 62. Guise, Sir W. V., 83. Gwaun Llanharry, 18 ; glacial, 96. Gwern-y-cae-uchaf, 70.

Haematite, 30,32,33, 107-112.

Ham Farm, 12.

Harptree Hill, 84.

Harris, Rev. W., 107.

Hendre, 33, 50.

Hendy, 30.

Hendy-isaf, 29, 107-111.

Hensol Park, 4, 7, 28, 29, 105, 113.

Heol-las, 104, 115.

Heol-y-Slough, 14.

Herberts, The, 44, 65, 67.

Hinde, Dr. G. J., 72.

Howard, Mr. F. T., 38, 44, 47, 49, 65,

67, 100-102, 112.

How Mill, 31, 44, 65, 113 ; glacial, 97. Hutch wns Point, 15.

Infra-Lias, 61. Jones, Mr J., 37.

Kendall, Mr. J. D., 112 Kenfig, 33, 34, 93.

Is'Dex.

Kenfig Burrows, 104, 114. Keuper, 20, 23-24 ; springs, 112-115. Kirkaldy, Mr. D. 52. Kitchin, Dr. F. L., 42, 48.

Laleston, 14, 54, 92, 93.

Langlon Wood, 64.

Lantern Vein, 19.

Lavernock Shales, 59, 65, 67, 70.

Lays, the, 103.

Leckwith, 25.

Lee, Mr. J. E., 37.

Leige Castle, 30, 31, 39, 65.

Leland, John, 107.

Lewis, Mr. S., 104.

Lias, 58-88 ; springs, 112-114.

Liassic geography, 58, 59, 88, 93.

Lilly pot, 1, 13.

Lime, 6, 71, 72, 8T, 106.

Limpert Bay, 71, 103, 104.

Llanbleiddian, 12, 31, 32, 66, 68, 91 ;

springs, 114. Llancarf an, 39, 64 ; tufa, 1 05 ; spring,

Llan Chwiau Castle, 13. Llan-chwiau-fach, 5, 12. Llan-cos-lech, 29.

Llandough, 31, 44, 65-67, 91 : spring,

Llandyfodwg, 90.

Llanerch, 28, 29.

Llanfihangel, 66, 91 .

Llangan, 15, 71, 107.

Llanharry, 6, 10, 11, 16, 29, 30, 106 ; iron ore workings, 30, 107-112 ; glacial, 96, 97, 99 ; springs, 113.

Llanharry Colliery, 18.

Llanilid, 16, 30, 93, 105 ; glacial, 96, 97, 99.

Llansannwr, 7, 11, 12, 69 ; glacial, 99 ; wells, 114.

Llantrisant, 16, 23, 107, 111.

Llantrithyd, 12, 13, 25, 31, 40, 64, 106 ; glacial, 95 ; spring, 113.

Llantwit-Major, 86 ; water, 114.

Llamvensan, 28.

Llechau, 107, 111 ; springs, 113.

Llwynau, 1 0.

Llwyn-celyn, 12, 13.

Llwyn-du, 12, 69

Llwyn-Gibbwn, 28, 29.

Llwyn Helyg, 67, 91.

Llwyn-nwydog, 4, 10 ; springs, 113.

Llwyn-y-ixmau, 4, 8, 9, 28 ; glacial, 99 ; spring 113.

Llysworney, springs, 114.

Local Government Board Report,

Lock's Common, 34.

Longland, 74.

Lower Limestone Shales, 106.

Lucy, Mr. W. C., 38,62, 77.

Madan, Mr. H. G., 115.

Maendy, 12, 28, 39, 68, 9.

Maes-ma wr, 8.

Maes-y-felin, 111.

Maes-y-leech, 25.'

Maes-yr-haul, 28.

Manganese, 110.

Marcross, 59; spring, 114.

Margam Abbey, 55.

Marshall, Prof. T. R., 49.

Meade, Mr. R., 112.

Megan-felin, glacial, 97.

Merry, Mr. J. S., 52.

Melin Cwcw, 53.

Merthyr-mawr, 13,14, 25, 73 ; glacial,

Merthyr Warren, 104.

M'Gaul, Mr., 51.

Michaelston-le-pit, 25.

Mid Well, 114.

Millstone Grit, 16.

Miskin, 6-10, 15, 28, 29 ; fault, 9, 17 ; glacial, 99 ; gravel, 103 ; ironworks, 107.

Miskin Manor, 4 ; spring, 113.

Moel Gilau Fault, 90.

Monk-nash, spring, 114.

Monotis-beds, 54.

Moore, Mr. C., 37, 54, 61, 66-68, 71- 74, 76, 81, 83, 84.

Morfa Ystradowain, 4, 7, 10, 105.

Mountain Hare, 19.

Mountain Lodge ; glacial, 96.

Mumbles Head, 14.

Murchison, Sir R. L, 44.

Mur-y-llengau, glacial 99.

Mwyndy, 9, 16, 29, 107-112 ; glacial,

Mynydd-y-glew, 69 ; glacial, 97.

Mynydd Hywel Dico ; glacial, 96.

Nant Dyfrgi, 10, 105.

Nash, 31 ; springs, 114.

Nash Point, 86.

New Beaupre, 107.

New Forest House, glacial, 96.

Newhouse, 44, 66.

Newton boulder, 98.

Newton Burrows, 104.

Newton Down, 14, 33, 34.

Newton, Mr. E. T., 57, 66, 84, 85.

Newton Farm, 11.

Newton House ; glacial, 95.

Newton Moor (Cowbridge), 32;

glacial, 98. Newton Nottage, 14, 33, 34 ; springs

114, 115.

Nine-feet Vein, 17-19. North Fawr Vein, 17, 18. Nottage, springs, 114, 115.

Ocean House, 71, 87. Ochre, 110.

Ogmore Valley, 2, 23, 25, 34 ; 99, 102.

Ogmore Castle, 13 ; springs, 114.

Old Beaupre, 65 ; glacial, 98.

Old Bed Sandstone, 4, 5.

Oolitic structure, in Carboniferous Limestone, 6, 10-15 ; in Rhaetic, 41 --46 ; in Lias, 59, 64, 71, 73.

Pant Wilkin, spring, 113. Pant-y-cwestau, 10. Pant-y-Cwteri, 92. Pant-y-Slade, 63, 72, 74-76, 79, 81,

Peat, 105.

Pembrokeshire, boulders, 102. Penartb, 20, 25, 48. Pencoed, 50 : glacial, 95, 100-102 ;

gravel, 103a

Pencyrn, 1 1 glacial, 99. Pendoylan f 5-27, 29, 38, 49, 59, 70,

90 ; glac;aJ, 97 ; springs and wells,

113, 114. Pen-llin, 7, 12-15, 71, 72, 90, 91,

107 ; glacial, 98 ; gravel, 103. Pentre, 40, 106 ; boulder, 98. Pen-y-coed-uchaf, 30. Pen-y-ffordd-fawr, 7, 69. Pen-y-lan, 7, 11,69. Pen-y-waun, 18, 30. Persondy, 50. Peterston, 25, 28, 38, 39, 70 ; glacial,

96 ; spring and well, 113, 114. Physical features, 1, 2. Pistyll-hill, 113. Pleasantharbour, 70, 87. Plwcau-Dafydd, 27, 49, 70. Pollard, Dr. W., 111. Pont Clun, 17, 29 ; glacial, 96 ;

gravel, 103; iron-ore, 107, 111;

Pontypridd anticline, 90. Porth-cawl, 13, 15, 34, 90; spring,

Porthkerry, 71. Porth-y-green, 68. Pottery clay, 99, 100. Prysc, 68; spring and wells, 112,

P\vll-y-daren, 13, 69. Pyle, 20, 25, 33, 35, 54, 55, 74, 81,93,

Pysgodlyn-mawr, glacial, 97.

Quarella Quarry, 51, 52, 106.

Radstock, 73.

Raised Beach, 105.

Redland, 30, 39, 64.

Red Marl, 20-34 ; in Rhaetic beds, 21, 36, 51, 53, 55.

Rhaetic beds, 20, 21, 35-57 ; shoreline, 24, 35, 36, 40, 49, 50, 93.

Rhyd-halog, 10; glacial, 96, 99; spring, 113,

Rhyd-y-castell, 29.

Rivers, 2.

River Gravels, 103.

Road Metal, 6, 100.

Rogers, Mr. E., 112.

Roman iron-workinsrs, 107 ; pottery,

Roose Point, 70.

St. Athan, glacial, 95, 99 ; spring,

St. Athan Road Station, 71. St. Bride's Major, 14, 91. St. Bride's-super-Ely, 25. St. Davids, boulders, 101. St. David's Well, 114. St. Donat's Point, 86. St. Donats, spring, 114. St. Hilary, 25, 31, 32, 41, 43, 50, 64,

St. Hilary Down, 1. St. John's Well, 113-115. St. Lythans, 25. St. Mary Church, 59, 64 ; glacial, 95,

97 ; springs, 113. St. Mary Church Road Station, 41,

42, 43, 65. St. Mary Hill, 20, 25, 33, 50, 51, 71,

St. Mary's Well, 113. St. Nicholas, 25. Salter, J. W., 112. Sandpit, 65.

Sandstones in Rhaetic, 40-44, 50, 51. Saunder's Quarry, 50. Scrobiculartct-dKy 103. Sealawn, 74. Sharman, Mr. G., 84, 85. Shells in Drift, 100, 102. Shepton Mallet, 81, 84. Sigingstone, spring, 114. Silica, 50, 55, 106. Silver Well, 102. Six-feet Vein, 17-19. Six wells, 114. Sker Point, spring, 114. Skomer Island, boulders, 102. Slade, 32, 48, 68. Slatog Vein, 17, 18. Small, Mr. E. W., 102. Soils, 2.

Sollas, Prof. W. J., 34. South Cornelau, well, 114. Southerndown, 14, 25, 61-63. Southerndown Series, 61-63, 75-85. South Fawr Vein, 17. South Llanharan Colliery, 18, 19. Springs, 112-115. Stalling Down, 5, 12, 90, 91. Stoddart, Mr. W. W., 84. Stormy, 15, 74, 81, 93, 106. Stormy Down, 55-57, 62.

Storrie, Mr. J., 3?, 99. 100. l-.£. Tv-ganol, 40.

Sniu Point, 71. 57. Tvle-nv : :

Summerliou*e Point. 71. 87. Tv-i??.!, 107.

Sun-bed, 56.

Siuton. 31. 6U-63, ,4 i 7, 92. !3

Sutton- -tune. 3.\ .p, 41, 4.\ 47. i>.

Table strata. 3.

TatT> Well. 23.

Tair On. MI. 1. 31. 41

Tal-y-garn. 7. : glacial,

>pring, 113.

Tate, Prof. K.. 36. 37. 61. 8; Tawney. Mr. K. R. 3ri. 37.

Tea-given Mark Teall, Dr. .1. .1. H.. 98. Terraces, of rivers, U>3. Thomas. Mr. H. H.. 109. 'liddeman. Mr. K. H, 71-73. 85. 81

88. K>5, 114. 115. Tilau. 30. Tome-. Mr. P. F, 37. 38. 61. 62. 7:

Ton-yr-fail. 9". Torgelli Colliery. 18. TreAubrey. 13.' 31. 4". Tre-betin. 11. Tivcale Mine. K7 111. Tre-castell Wood, 17. 18.

Tre-grofghu-ial. 99.

Tre-G\\ ilyrn. 2V.

Tri'-gyrt'. 4". I',:.. 7".

Tre-rhingyll, 11.

Trias, 20-57.

Trydedd Vein. 17. IS.

Tu>ker L'ottage ,5.

Tusker l!ock._P>4.

l. iron. 13.

Ty-chwith. glacial. 9;*.

Ty-draw. 4M : glacial.

Ty-du (Llantri>ant). If.. 3". Ill

Ty-du (PendoylanX 27. 4!'. f.n. Tv-frv. 57. 65. 69.

well 1 1

v-n.mt , 2 3', ,0. y'n-y-caeau-tawr, 19. y'n->'-coed. 31 . 39.

v 'r-eapper, glacial. M9. 'ythegston, 72.

Ty-uchaf. 40 : glacial. 98.

Vivian. Mr. S.. 108 112. Vivian. Mr. W.. 110, 112.

Warren Mill, glacial. 9ti.

Watch-house Point. 71.

Water Street. 104.

Wator Supply. 112 1 15.

Watson. Dr. .!. J. W.. 107, 108, 110-

Waun-y-iner. spring. 114. Well-sections, 114, 115. Welsh St. Donats. 5, 7. 9. 12. 13. 29,

38, 68. 69 : glacial. W. 97 : peat.

1U5 : wells. 114. Wenvoe. 23. West. 75,

Wethered. Mr. K.. 112. Whitehall. 19.

White Lias. 39. 40. 48. 50, f.2. 66, SI. White well, 113. \Vhite\vell Farm. 31. Whitmoir Stair-. 23, 85. Wick. 14. 23. 60, 88, MM. Wilson. Mr. K., 3;.

in\N 1. Rev. 11. H.. 73.

Witches Point. 14. 153. 76 80. Woodward. Mr. H. 1... 36. 38, 48. 56.

Hl-64. 71-87, 1"3. 105, PK;. Wound Well. 114. Wren Castle. 40. 05. Wright. Dr. T.. 37.

V-tradowain. 7. H. 11. 2!. Hi : glacial. 96. H7, 9H : spring and well. 113. 114.

Ystum-elaid, 65 ; Airing. 113.

Z-'iie- in the Lias ">v. "'-(. t;i.

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93 NW - - N. and E. of LEEDS and near TADCASTER. By W. T. AVELINE, A. H. GREEN (and Others).

93 SE, 94 SW COUNTRY between YORK and HULL. By J. R. DAKYNS, C. Fox-STRANGWAYS, and A. G. CAMERON. 1*. 6d.

94 NW - - DRIFFIELD. By J. R. DAKYNS and C. FOX-STRANGWAYS. 9d.

94 NE - - BRIDLINGTON BAY. By J. R. DAKYNS and C. Fox-STRANGWAYS. Is.

95 SW, SE - SCARBOROUGH and FLAMBOROUGH HEAD. By C. Fox-STRANGWAYS. (2nd Ed.) 4s. Qd.

95 NW - WHITBY and SCARBOROUGH. By C. Fox-STRANGWAYS and G. BARROW. Is. 6d.

96 SE - - NEW MALTON, PICKERING, and HELMSLEY. By C. FOX-STRANGWAYS. Is.

96 NE - - ESKDALE, ROSEDALE, &c. By C. FOX-STRANGWAYS, C. REID, and G. BARROW. Is. Qd.

96 NW, S W - NORTHALLEETON and THIRSK. By C. FOX-STRANGWAYS, A. G. CAMERON, and G. BARROW. Is. &d.

97 SW - - INGLEBOROUGH. By J. R. DAKYNS, R. H. TIDDEMAN, W. GUNN, and A. STRAHAN. 2s.

97 NW - - MALLERSTANG. By J. R. DAKYNS, R. H. TIDDEMAN (and Others). 3s. 6d.

98 NE - - KENDAL. By W. T. AVELINE and T. Me K. HUGHES. 2nd Ed. by A. STRAHAN. 2s.

102 SW - - APPLEBY, ULLSWATER, &c. By J. R. DAKYNS, R. H. TIDDEMAN, and J. G. GOODCHILD. Is. Crf.

104 SW, SE - NORTH CLEVELAND. By G. BABBOW. Is. 6d.

107 - CARLISLE. By T. V. HOLMES. Is. 3d.

108 SE - - OTTERBURN and ELSDON. By HUGH MILLER. 2s. 6d. 108 NE - - CHEVIOT HILLS. By C. T. CLOUGH. Is. 6d.

108 SW - - PLASHETTS and KIELDER. By C. T, CLOUGH. Is.

110 SW - - WOOLER and COLDSTREAM. By W. GUNN and C. T. CLOUGH. Is. 6d.

110 NW- - NORHAM and TWEEDMOUTH. By W. GUNN. 6d.

110 NE - - COAST SOUTH of BERWICK-ON-TWEED. By W. GUNN. 9d.

110 SE - - BELFORD, HOLY ID, and FARNE ISLANDS. By W. GUNN. 2s. U.

Sheet Memoirs Of New Series Maps.

123 - - STOKE-UPON-TRENT. By W. GIBSON and C. B. WEDD. Price Is. 6d.

155 - ATHERSTONE and CHARNWOOD FOREST. By C. FOX-STRANGWAYS. 2s.

156 - - LEICESTER. By C. Fox-STRANGWAYS. 3s.

231 - - MERTHYR TYDFIL. By A. STRAHAN, W. GlBSON, and T. C. CANTRILL. Is. 6d.

232 - ABERGAVENNY. By A. STRAHAN and W. GIBSON. 2s.

248 - - PONTYPRIDD. By A. STRAHAN, B. H. TIDDEMAN, and W. GIBSON. Is. 6rf.

249 - - NEWPORT, MON. By A. STRAHAN. 2s.

263 - CARDIFF. By A. STRAHAN and T. C. CANTBILL. 2s. 3d.

268 - READING. By J. H. BLAKE and H. W. MONCKTON. Is. M.

298 - SALISBURY. By C. REID (and Others). Is. 3d.

314 - KiNGWOOD. By C. REID (and Others). Is.

315 - - SOUTHAMPTON. By C. REID. Is 6d. 317 - CHICH .fcSTER. By C. REID (and Others). Is. 325 - - EXETER. By W. A. E. UssHEU. 2s.

328 - - DORCHESTER. By C. REID. Is.

329 - BOURNEMOUTH. By C. REID. 4r7. HM - BOGNOR. By C. REID. 6d.

:5:;i - - EASTBOURNE. By C. REID. Gd.

k 350 - KING8J3KIDGE and SALCOM'BE. By W. A. E. USSHER. Is. 6d.