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NOTES ON THE RH..ETlC BEDS AND LIAS OF GLAMORGANSHIRE.

By HORACE B. WOODWARD, F.G.S., of the Geological Survey of England and .

(Oommunicated by permission of the Director-General of the Geological Survey.)

(Read July 6th, 1888). It must at all times be a matter of especial interest to study a formation at the locality whence it derives its name ; and at we contemplate the English equivalents of the Rhretic formation to which in 1864 the name Penarth beds was given by Mr. Bristow.s It is, however, not unfrequently the case that at such a locality we do not find the most complete representation of the strata, and Penarth has not attained the fame of several other places as a hunting-ground for the collector of fossils. Each ex­ posure of the strata may indeed exhibit some particular feature of interest. The Bone-bed is best shown at Aust, the Monotis-bed at Westbury-on-Severn, the Ootham Marble near Bath, and the White Lias generally in Somerset. Nevertheless, at Penarth, and in the cliffs extending southwards to , the Rhretic beds are more clearly and prominently displayed than in any other part of Britain, not even excepting St. Audries and Blue Anchor near Watchet, where the beds attain a greater thickness. It is true that at Penarth Headland itself the beds are inaccessible, except to those who care to climb an almost perpendicular cliff; but observa­ tions made on the face of a precipice are not necessary in this case, for Natnre has produced undulations that bring the strata to the sea-level at two points as we proceed southwards to Lavernock (Fig. 1). With these advantages, Penarth has not attracted a great deal of attention. The sections were briefly described in 1860 by Dr. Wright,t but it was not until 1864 that a detailed account of the strata was published. This was the joint work of Mr. Bristow and Mr. Etheridge, and it was amplified later on in a series of

*•Geol. Mag.,' Vol. i (1864), p. 236. t •Quart.Journ. Geol. Soc.,' Vol. xvi, p. 381. 530 H. B. WOODWARD ON THE vertical sections published by the Geo­ logical Survey,* and III a paper com­ municated to the Oardiff Naturalists' Societyt in 1871 by Mr. Etheridge. The Rbretic beds along this coast-line, as in most other localities, present the ortho­ dox three-fold division; but here the uppermost portion consists for the most part of grey marls (12 to 20 feet thick) instead of the hard and compact layers of White Lias which we meet with in Somerset and Dorset. The Black Shales below (from 16 to 22 feet thick) present -', <'5 their ordinary features, yielding Avicula contorta and Cardium rhceticum, with bands of limestone containing Pecten »alo­ niensis, and thin Bone-beds at more than one horizon at and near the base. The ~ grey and tea-green marls (45 to 50 feet .0'" thick) are separated from the red and .~ '$ variegated Keuper Marls by a tolerably ~ well- marked and even colour-line. Near <:

* 'Rep. Brit. Assoc.for 1872,' Sections, p. 116. (See p, 538.) t • Proc, Geol. Boe.,' Vol. iii, p. 585. 532 H. B. WOODWARD ON THE case, it is natural that in some localities the beds are more inti­ mat ely connected with the Keup er Marls and at others with the lower lim estones of th e Lias. Between Axmouth and Lyme Regis, and again near Watchet, th e Grey Marls comprise bands of very dark grey, and even black, marly clays, that foreshadow the Black Shales that succeeded t hem. At the latter locality, inde ed, we hardly know where to draw the line between the Black Shales and the Grey Marls beneath them i while at Penarth we find th e Black Shales overlaid by anoth er division of grey marls and shales that lithologically resemble the nnderlying marls. Moreover, the lower Grey Marls, and even the Red Marls in places, contain bands of compact, more or less earthy limestone, that could not be distin guished lithologi­ cally from beds of White Lias. These facts show th e intimate connection of the series of beds in their sedimentary characters; and while we may admit that at Axmouth and Watchet th e Gr ey Marls present an aspect tha t would lead U8 to link them with the superincumbent Rheetic beds and Lias; in other localities, as at Bitton and Bath, and at W ainlode, near Tewkesbury, th eir cha­ racters appr oach more nearly to those of the Keuper Marls. P assing upward s to the Lias we find a difficulty at P enarth in fixing the precise boundary between the se strata and the Rh eetie beds. But where Nature has made no mark ed line of demarcation, it is perhaps needless for us to be concerned about th e matter. The Grey Marls that occur above the Black Shales repr esent the White Lias of other localities, and, in fact, we find some layers of W hite Li as in this division at Penarth, together with a band that reminds us of the Cotham Stone. The fossils include species of Ostrea, Modiola, Pleurophoru s, &c., for the most part poorly preserved, as th e fossils usually are in this port ion of the Rhretic series. On top of th ese Marls th ere is a bed of dark-g rey and brown paper-shales, from one to tWG feet thi ck, that forms what may be termed the debatable ground between the Rhaitic beds and the Li as. I should prefer to group it with the Lias, because a similar bed is found in-many localities on top of the White Lias, and in situ ations where it clearly belongs to the Lower Lias. At Penarth itself we cannot decide the matter, for the fossils Oetrea liassica and Modiola minima are common to the Rhretic beds and to Lower Lias. Resting on these paper-shales we find a series of even-bedded RHETIC BEDS AND LIAS OF GLAMORGANSHIRE. 533 argillaceous limestones and clays yielding the Ostrea and ~Iodiola in abundance, especially the former, so that th ey constitute the " Ostrea-beds " of some authorities - hero 12 or 15 feet thick. These merge upwards into similar beds th at contain many specimens of A mmonites planorbis, so that the mass of th e Li as above th e Rhretic beds, for 35 or ,10 feet, belongs to the zone of A mmonites planorbis, Those beds cap t he headland of P enar th, and are well shown at Lavernock point where they dip sea-ward; but rounding this headland towards the west we find the limestones paving the foreshore (where th ey exhibit their fossil treasures) and dipping westwards for a space, when they again rise, forming, in fact, a g entl e synclinal. Th e trough of this is filled with a third series of Grey Marls, not unlike those of the Rhretic beds, and I was at first much puzzled with them when examining a section on the new railway near Lavernock. These marls and marly clays, with in­ durated bands, about 40 feet thick, are overlaid by 25 feet of lime­ stones and clays. Unfort unately the upper part of the cliff west of Lavemo ck is not very accessible, and, as no fossils rewarded my labours, I could only infer that these marls and overlying limestones marked, in all probability, th e lower portion of the zones of Am­ monites angulatus and A. bucklandi-zones which are, to some extent, represented at P enarth, and are so well developed further westwards along the Glamorganshire coast. Th e cliffs along thi s further portion of th e land are well worth a visit. Passing Sully, we are remin ded of Conybeare, who was Rector from 1823 to 1836; and only last year I met two somewhat elderly men who had pleasant recollections of him and his geologi­ cal explorations. W e pass Barry Island, whose beauties, alas 1 are now sadly marred by the engineering operations for the new docks-works which practically unite th is tract with the mainland . Onwards past we come to a series of Lias cliffs that extend, with some interruptions at , to Dunraven and Southerndown, near the month of the Ogmore. These cliffs ex­ hibit, perhaps, the finest exposure of the Lower Lias Limestones in thi s country. We have not the complete sequence of Lias visible at Lyme Regis and Charmouth in Dorsetshire ; but here in South Wales the zones of Ammonites anqulatus and A. buckl audi (taken together) are much more fully and continuously exposed; It is true that 14 miles of cliffs showing the same set of beds, dis- 534 H. B. WOODWARD ON THE

located 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. At any rate, the observations re­ corded are meagre in the extreme, for they amount to such brief references that I was unaware, until I reached the spot, that the celebrated "Aberthaw lime" was obtained from beach-boulders and not procured from the rock in situ. It may be mentioned that many beds of limestone in the neighbouring cliffs are much jointed; hence they break up into small masses, which are readily rounded by the action of the sea. The cliffs exhibit a series of argillaceous limestones, shales and marls, which must attain a thickness of nigh 200 feet, and for 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 diversi­ fied by faults modifying the strike of the ledges, or by heaps of boulder-shingle that lie here and there on the surfaces of the plat­ forms. It is very instructive to observe the distribution of the fossils, for we have the Lias well exposed both in plan and in .section, and may notice how the organic remains occur in groups or colonies, abundant now and again at various levels. We can picture the evidence obtained in a quarry, where a P entacdnite-bed, a Grypha'a-bed, and a Lima-bed might be noted in succession j but here on the foreshore we may observe groups of these fossils, sometimes in family clusters, at others intermingled, and at many different horizons, while the same bed appears quite unfossiliferous over the greater portion of its exposure. Such evidence warns us not to place too great reliance on the persistency of fossil-beds, and it explains why organic remains abundant at a certain locality at one time, have become rare later on, when the beds have been ex­ tensively worked. On the whole this great series of limestones is singularly barren, but this appears to be the rule with strata that are thickly developed. Compare, for instance, these rocks with the attenu­ ated Lias near Radstock; or the thick beds of Inferior Oolite near Cheltenham, with their very fossiliferous but scantily-developed equivalents in Dorsetshire. When we approach Dunraven we come to the confines of a very RHlETIC BEDS AND LIAS OF GLAMORGANSHIRE. 535 debatable tract of Lias-a district that has been much visited by geologists, and much written about also. We come, in fact, to an altered condition of the Lower Lias, not necessarily an " abnormal" condition, as it has been termed, but to a tract where the beds were deposited under different sedimentary conditions, and in a tolerably distinct zoological province. We have, in fact, marginal deposits, to which the term Lias-conglomerate was appropriately given by Sir Henry De la Beche. It will be unnecessary here to give all the views of different geologists on the age and relations of these beds, but it may be observed that from Dunraven onwards to Southerndown and Sutton we find the ordinary beds of Lower Lias limestone and shale resting conformably on a series of bluish-grey conglomeratic limestones, termed the Southerndown beds, that pass downwards into pale, more or less tufaceous limestones and con­ glomerates, known as the Sutton stone and Conglomerate. The whole of this conglomeratic series was in I 866 claimed as Rhretic by Mr. E. B. Tawney, but his view was shortly afterwards contested by Mr. Bristow, Mr. Charles Moore, and Prof. Tate, who maintained that the beds were truly a portion of the Lower Lias. As regards their precise palreontological equivalents opinions still differ, for it is questioned whether they represent the zone of Ammonites planorbis or that of A. angulatus ; while Dr. Duncan, who included the White Lias and the zone of A. planorbis under the term Infra-Lias, applied this vague term to the conglomeratic beds of Sutton and Southerndown. Ultimately Mr. Tawney re­ linquished his view of the Rhsetic age of these beds, and the question seemed settled for a time. Mr. Etheridge, however, remained in a state of uncertainty, for in his paper 011 the Penarth beds (before mentioned) he observed that the precise position of the Sutton stone was still an open question, while in 1884 Mr. R. F. Tomes, who had many years before written about the beds, returned to the discussion of the snbjeet,* and, in company with Mr. W. O. Lucy,t maintained that the Sutton stone was the equivalent of the White Lias. In order to thoroughly understand the stratigraphical relations of the beds, much time (and so far as my own experience goes, at least ten days) must be devoted to the cliff-sections, which in the area under dispute extend only a distance of about two miles. But * 'Quart. Journ. Geol, Soc.,' Vol. xl, p. 353. t 'Proc, Ootteswold Club,' Vol. viii, p. 254. 536 H. B. WOODWARD ON 'l'HE much of the cliffs can only be examined at low spring-tides, and by scrambling over ragged rocks. It is necessary to note the beds in detail at every available point, and it is then manifest that the bluish-conglomeratic (Southerndown) beds increase in thickness as we proceed from Dunraven towards Sutton, but they shade down­ wards into the White Sutton stone and conglomerate without any line of demarcation. The beds, moreover, are faulted in several places, and in positions which render exact measurements of the beds most difficult. It is, however, clear that the White Sutton stone and Con­ glomerate form the base of the series, resting irregularly, and in hollows, on the upturned edges of the Limestone, so that the thickness varies considerably at different points, from 25 to 40 feet. Commencing west of Southerndown, these beds may be traced from Sutton to the cliffs at Pant-y-Slade, near West, where they are overlaid by a considerable thickness of blue con­ glomeratic limestones; thence they descend to the sea-level by the large Fairy Cavern. Here three faults affect the beds; and the White Sulton stone is repeated in one instance on the foreshore, but is carried out of sight beneath the main mass of the Southerndown Cliffs. There the bluish conglomeratic limestones are exposed at the base of the cliffs and on the foreshore below the ordinary beds of Lower Lias. As we proceed towards Dunraven Castle, higher and higher beds of the Lias are exposed in the cliffs, and then again we meet with a considerable fault which brings up the Sutton stone and Conglomerate, and the , in the headland known as the Witches Point, Dunraven. Thence round to the little bay south of Dunraven Castle, we may trace the sequence again of Carboniferous Limestone, covered irregularly by White Sutton stone and Conglomerate (passing horizontally into greyish and bluish-grey beds in places), and overlaid by the more conspicuously blue conglomeratic limestones (Southerndown beds), above which come the ordinary beds of Lias Limestone and Shale. These ordinary beds of Lower Lias, which extend along the cliffs before noted to near Barry Island, clearly belong to the zones of Ammonites bucklandi and A. angulatus, yielding these fossils, together with Gl'yphcea incul'va, Lima gigantea, Pentacrinites, etc. The only specimens of A. anqulatus which I obtained came from the base of this series near Dunraven, but Mr. Moore notes it from the conglomeratic beds below, together with Lima gigantea, Oetrea RHlETIC BEDS AND LIAS OF GLAMORGANSHIRE. 537

liassica, several gasteropods, and other fossils. There can be no question, therefore, of their Liassic age. With regard to the Sutton stone, fossils are by no means so abundant, but it is note­ worthy that two species of Ammonites were described by Mr. Tawney, one resembling A. johnstoni, but both so poorly preserved that opinions differed on their identification. These specimens (and one also of A. angulatus recorded by Mr. Moore) were taken from the upper portion of the Sutton Series, 18 to 30 feet above their base. Hence the beds at this horizon may be regarded as repre­ senting the limestones with A. planorbis at Penarth, or at any rate the upper portion of that zone where it passes into the zone of A. anqulatus; The stone at Sutton yields more especially Ostrea multicostata, 0, intusstriata, Pecten suttonensis or P. pollux, and Cardinia sui­ tonensis, as well as numerous . The corals were most of them new to this country. They are, however, many of them, known from the so-called Infra-Lias of the continent, but do not help us in our comparisons of the strata with other English beds. The other fossils present a Liassic rather than a Rhretic facies, and lead us to group the mass of Sutton stone with the " Ostrea. beds" before noted at Penarth, which form the lower part of the zone of Ammonites plano] bie. Oysters are somewhat troublesome forms to deal with, especially in the fossil state, and the authorities have differed much in their identification of the Sutton species, but Ostrea liassica has been recorded, together with other species by Mr. Moore. I may men­ tion that I have found Ostrea multicostata and Cardinia suttonen­ sis, two of the most abundant fossils of the Sutton stone, in the same beds of Lower Lias, together with Ammonites planorbis and A. johnstoni. The locality was Harptree, on the Mendip Hills, and here the Lower Lias presents some remarkable cherty modifi­ cations. It is unnecessary to enter further into this subject. The suggestion that the Sutton stone represents the White Lias appears to have been based to some extent on a lithological resemblance, perhaps mainly on the fact that the beds are pale, for the texture of the Sutton stone differs considerably from the ordinary beds of White Lias. When we remember that at Penarth the upper portion of the Rheetic series consists mainly of grey marls, and when we see it at VOL. X., No.9. 39 538 ON THE RH.E 'rIC BEDS AND LIAS OF GLA1>lORGANSHIRE.

Stormy Down, near , to comprise only one or two bands of compact white limestone, th ere is no suffi cient reason to regard th e 30 or 40 feet of White Sutton stone as Rhastic on the ground that it consists of pal e beds at th e base of the Lia s. At Stormy Down th ere is a thin conglomeratic band at th e base of the Lia s Lim estones, which th ere belong to the zone of Ammo­ nites planorbis, and thi s band occurs on top of the beds that are admitted to represent th e White Lias. It has been t aken to correspond in a feeble way with th e Sutton Congl omerate. There is no reason to dispute this, but a conglomeratic band suggesting a local chang e in conditions sho uld be grouped rather with th e over­ lying than with th e underlyi ng beds, and hence we need not hesitate to place it and the Sutton stone also in th e Lower Lia s. The peculiar characters of the Sutton stone may be due to it s being derived largely from islets of Carb oniferous Limestone, and to th e limestone-mud being mixed to some extent with th e debris of corals. NOTE.-Since writing the above (see p. 531), I have had tb e opportunity of visiting Goldcliff, in Monmouthshire, and of seeing the Bone-bed described by MI'. Lee. (See also his •Note-hook of an Amateur Geolog ist,' 1881, p. 72, and plates 171 and 172. H e, however. omitted to point out that the Bone-bed there occurs beneath three feet of the g reenish-grey marls, which are thus shown to be intim ately link ed with the A nicuia-contorta Shales above.- H . B. W.]

NOTE ON THE SOUTH W ALE S COAL-FIELD. By F . W. RUDLER , F.G.S., President. During the approaching visit of the Association to South W ales exccptional facilities will be offered for makin g an E xcursion into th e h-art of this coal-field, und er th e able guid ance of Mr. Will iam Galloway, of Cardiff. To those who are about to avail th emselves of this opportunity, it may be useful to possess a general sketch of the phy sical characters and geological structure of tb e district about to be visited. While occupying th e greater part of Glamorganshire, the coal-field of South Wales st retches t o a greater or less extent into th e four neighb ouring counties of Monmouth, Br ecknock, Carmarth en, and Pe mbroke. As seen on a geological map th e Coal-measures