375

ON THE GEOLOGY OF TH E BRISTOL DISTRICT.

By PROF. W. J. S OLLAS, M.A., F.R.S.E., F.G.S., &c.

Geologists possess,in the Survey Memoir, by Mr. H. B. Woodward, II complete handbook to this neighbourhood. In it descriptions of the localities which the excursion will visit a,re given in full det ail; to repeat them here would be a work of supererogation, and, con­ sequently, I shall only attempt in this paper to pres ent a sketch in broad outline of the geological history of the neigh bourhood. The earliest rocks which we shall examine ar e th e Old Red Sand­ stone, exposed on the summit of the Mendips, and in th e cliff from P ortishead to Olevedon ; they were deposited in an area of depression which was formed after the great post-Cambrian and pre-Silurian folding of our country, and which extended from th e Cambrian rocks of Wales on the west and north , to the line of Malverns on the east, and the Bristol Channel on the south. Outside the two latter boundaries was th e basin in which the Devonian rocks were contemporaneously deposited to the east and south. The lowest beds of the formation are chiefly red marls and shales which lie conformably on the older Silurian strata ; above these beds we find red sandstones, with red marls and cornstones, and above these conglomerates with red marls and sandstones, which form the highest beds of th e formati on, and pass conformably into th e Carboniferous Shales, as may be seen below Cook's F olly in the Avon section. The passage from marls through sandstone into conglomerates shows that the basin was becoming shallower , owing, probably, to deposition proceeding at a more rapid rate than depression ; the succession of the Lower Limestone Shales over the Old Red Sandstone shows, on th e other hand, th at depression was taking place at that time faste r than deposition could keep pace with it, and this relation (depression greater than deposition) ap­ pears to have continued into the Carboniferous L imestone times. The Cambrian and pre-Cambrian rocks, which furnished sediments for the Old Red Sandstone, consisted of arenaceous, argillaceous, and calcareous st rata, togethe r with various in trusive and erupted ign eous rocks. The origin of the ordinary sedimentary rocks of the Old Red Sandstone, such as sandstones, marls, and conglome- 2 D 876 W. J. BOL LAS ON THE GEOLOGY OF rat es, presents us with no difficulty; not SO, however, the red oxide of iron, to which it owes its colour, and the layers of " corn­ stone" or nodular limestone which characterise th e lower and middle parts of it. The cornstones are clearly inorganic, and have probably been formed by th e mechanical denudation and re-deposition of pre-Silurian limestone beds. The ferric oxide may have been derived in part from th e older red Cambrian beds, in part from the oxidised soil of igneous rocks, and in part from carbonate of iron introduced in solution by the action of decaying vegetation, and subsequently converte d, by the loss of carbonic acid and the addi­ tion of oxygen, into peroxide of iron, which was precipitated in the Old Red Sandsto ne sea. No fossils have been found in the Old Red Sandstone of this area, except the fishes Holoptychius and Coccosteus, of which scales and bones have been discovered near Portishead. To them, however, great interest attaches, and especially to H oloptychius, which resembled the existing Ceratodus, a fish showing strong tendencies towards the Amphibian type. P robably Ifoloptychius, if not in the direct line with, was at all events, closely related to, the forms from which the Amphibi ans of th e succeeding forma­ tion were derived. The Carboniferous format ion in this area consists of the follow­ ing members, th e thi ckness of which, in the Bristol Coal-field and the Avon section, is given in feet :- Coal Measures 5,000 Millstone Grit 1,000 Carboniferous Lim estone 2,500 Lower Limestone Shales 500 -9,000 Th e area (Fig. 1), in which it was deposited was the outcome of that of the Old Red Sandstone, modified by the general depression which it bad und ergone, and by various local changes of level, in cluding both elevation and depression. It was bounded on th e north by the now well-known central peninsula which stretched across the middle of England; Newent on the Malverns, and Haverfordwest, South W ales, being two points on the southern coast of the peninsula. On the south it was bordered by a continent, the north ern coast- line of which passed somewhere through the north-east of France, and THE BRI STOL DI STRICT. 377

FIG L 378 W. J. SO LLAS ON TH E GEOLOGY OF

near th e South of Corn wall and the South of Ireland. The South of E ngl and basin was in free communication with a wider European one. During a period of exceptional depression, the sea was clear th ough by no means deep, and beds of limeston e were deposited over nearly its whole extent. In thi s neighbourhood thick field-lik e growths of enerinites and rich banks of molluscs produced, by th eir growth and decay, the lower parts of th e limestone ; th ese at length yielded to a luxurious growth of corals, by which th e upper part of th e limestone was chiefly formed. Associated with the coralliferous beds are thick deposits of oolite, which may be seen in the Avon section, and thus th e association of coral reefs and oolitic deposits which exists at the present day, which existed in the Silurian period, and is so characterist ic of th e Jurassic forma­ tion, is again met with here. The quiet growth of the limestone was interrupted on one occa­ sion at least by an episode of ign eous activity, which has left its traces in th e thick beds of. volcanic ash associated with once vesi­ cular but now amygdaloidal basaltic lava, to be seen interbedded in th e limestone along the coast-se ction from 'Veston-super-Mare to Swallow Cliff. While th e Carboniferous Lim estone was forming over Somerset, a great river which I shall venture to call De la Beche's River,as th ose which entere d th ebasin of the North of England may be terme d Hull's Riv er and Phillips's River, flowed through the great southern con­ tin ent and emptied itself into our basin somewhere south of Corn­ wall and Devon; it soon brought to an end the conditions under which limestone had been formed over those counti es, building up by its deposit of sediment the great thickness of th e Culm Mea­ sur es. This continued accumulation of sediment brought the mouth . of the river continually farth er and farth er north , till at length its delta began to spread its seaward margin over Somerset and South 'Vales. Deposition was now in excess of depression, and the Mill-: stone Grit, with its th in bands of limestone and marine fossils (Producta scrobicula, &c.), is th e first sign of that enlargement of the delta which culminated in its extension over th e whole of th e western part of th e South English basin. On th e alluvial plain s or delt aic flats so formed, the Carboniferous vegetation extended itself from adjacent lands. The spores and debris from the Lyco­ pods, Ferns, Equisetums and Conifers accumulated on the g round, and in th e warm, moist climate, formed a fermenting mass, which both served as a hotbed, stimulating the germination of fallen THE BRISTOL DISTRICT. 379 spores, and led to such a complete decay of woody tissue as sufficed to obliterate nearly every trace of its structure. The more resinous spores and the bark of the trees resisted decay better, and are more frequently preserved. Wide tracts of the decayed and fermented mass were quietly de­ pressed beneath the water-level; shales and sands were strewn over it, and so far one coal-bed was completed. Deposition con­ tinued in excess of depression till a fresh land-surface arose, and a fresh coal supply was laid down; depression again ensued, and this series of processes was repeated as many times at least as there are coal beds (44) in our coal-field. At length the great geosynclinal which had been in progress throughout the whole of the Silurian, Old Red Sandstone, and Carboniferous times, and which extended from Ireland into Bel­ gium and Germany, was complete; tremendous pressure then set in from the South, and in the basin of the South and West of England thrust the great mass of Siluro-Carboniferous deposits against the buttresses afforded by the Pre-Silurian rocks of Wales on the West and North, and the Malvern range on the East. Thus, from an approximately horizontal position, they were folded up into great rolling curves (synclinals and anticlinals), sometimes sharply curved and even bent back on to themselves (reversed anti­ clinals), and fractured and displaced (faults both normal and re­ versed). The synclinals, or rather basins, exist now as the South Wales, Forest of Dean, Bristol, (Fig. 2,) Nailsea, and various other coal-fields, most of which are now concealed uuder newer strata; the anticlinals which separate the basins are to be seen in the Mendip range, which extends from Frome on the east to the Steep Holme on the west; in Broadfield Down which extends westwards to Swal­ low Cliff and the Flat Holme;' and in the curved ridge of the Durdham, Clifton, and Leigh Downs. Had these anticlinals attained their full height above the sea-level, unworn by denu­ dation, they would, in some cases, have risen to a height of 8,000 to 10,000 feet above their- present level. But they did not escape denudation, for this is the universal concomitant of elevation; and just as we have always to bear in mind the movements of the sea­ floor which accompany sedimentation, so we must always, in con­ sidering the result of elevation, take into account the opposing action of denudation. As the Mendip and its fellow anticlinals rose slowly into the air, they were incessantly acted upon by sub­ aerial denuding agents; rain and rivers did their worst upon them, 380 W. J. SOLLAS ON THE GEOLOGY OF

FIG. 2. SOMERSETSHIRE COAL-FIEJ,D AFTER THE POST-CARBONIFE1WUS DENUDA'l'ION.

,

. UPpl!r (4al1Jfio.~ Jf •. ~ Pennant: . .., D Lower Ccal1lfwsww -c Illl!I XrDstone griL [:zJ Carbi limsscone t THE BRISTOL DISTRICT. 381 cutting out valleys, and leaving the intervening land between in steep hills and ridges, to attest, by surviving it, the waste which the surrounding country had undergone. The anticlinals, however much they might suffer, would clearly not in this way be worn down to any uniform or nearly horizontal plain; that is the work of the sea, it is the one great leveller. The waves produced by their incessant abrading action the ordinary features of a coast­ line around the elevated Siluro-Carboniferous land. Lofty cliffs bore witness to the extent of the land which had been destroyed and the beaches at their base layover the first beginnings of a plain of marine denudation. After the anticlinals had been sculptured into contour by rain and rivers, and outlined into con­ figuration by the sea, a long-continued depression ensued, the sea­ cliffs were more rapidly undermined and swept away by the power which had produced them; the valleys formed arms of the sea, the hills headlands which were continually undermined and sliced away. The sea completed the work which rain and rivers had commenced, the broad and lofty anticlinals disappeared, and a wide sea rolled over the cut-off edges of the strata which had formed them. The depression of the land not only accelerated the work of marine denudation, but it determined the main slopes of the plain of marine erosion, for, by the time the highest land had been destroyed and its remains submerged, the lower was out of reach of destruction far beneath the sea-level. Thus the denuded surface of the land would really be a sloping one, having for its maximum height a line corresponding in general direction with the line of maximum height of the largest original anticlinal, but some thou­ sands of feet below it. This will be rendered clearer by the fol­ lowing diagram ;- FIG. 3.

a, a, plain of marine denudation, having its maximum height at c, immediately below the summit A of the original fold. Thus great as is the power of denudation in its various forms, it is 882 w, J. SOLLAS ON TH E GE OLOGY OF quite incompetent to efface some of the moreimportant featur es which are first impressed upon th e land by th e power of elevation. On the sloping plain of marin e denudation sediments were laid down, the ruin ed sea-cliffs ground to pebbles and powder, fur nished beaches which followed close upon the sea as it stole across the land. These beaches are kn own to us now as the Magnesian conglomerates of th e Trias, and thus th e elevation of the Siluro-Carboniferous strata and the commencement of their depression occurred between the end of th e Oarboniferous and the beginning of th e Triassic times. The Trias beaches may be easily examined on the side of the new road from the Downs, where there is one consist ing of rounded boulders of limeston e, some of which are several feet in diameter, (Fig 4); and FIG. 4. d ---.... =------

a a a. Bed of Carboniferous Limestone at base of Lower Grit, brought down by a fault on th o north of Observatory Hill. b. Boulders and Pe bbles (in part subangul ar) of Carboniferous Limestone and Grit, some of th e boulders not much less than three tons in weight, cem ented by feruginous and calca reous mat ter. c. Oonglomerate or breccia containing more of the calcareous component. d. Calcareous component still mor e in excess. along the cliff section, from FIG. 5. P ortishead to Olevedon, (Fig. 5,) where they form a breccia of limestone frag­ ments as sharply angular as when they first fell from o their parent cliff into the sea; while some retain the slickensided surface of th e jointed limestone which fur- -I-.I.-..;....---_l-__-l.--L-L.a nished them as fresh as if d. Dolomiti c conglomerate. o. Old Red Sandstone. embedded yesterday. s, Shore. THE BR I STOL DI STRICT. 383

On the Clifton side of the Avon section, some of this beach material is seen as a dyke in the Carboniferous Lim estone, hav­ ing filled in an open j oint which was revealed by the great post­ Carboniferous denudation ( Fig. 6, T.) We may now proceed to give an account of the Triassic sea as it was when fully estab­ lished by long-continued depres­ sion. The British Trias was laid down in an inland sea, which covered the centre of England, and extended thence in three great processes, N.E., N.W. and S.W . (Fig. 7.) The S.W. gulf, which alone concerns us, was connected with the centr al sea through the Malvern Straits; on the west it was bounded by the Palreozoic land of W ales, Devonshire and Corn­ wall, into which it thrust two long arms westwards, one over the site of the Bristol Channel and the other along the middle line ' of the great Devonshire synclinal ; on the north and north-east it was bounded by the P alreozoic axis of London and Harwich, and on the south by some great land now un­ known to us. This inland sea was probably at one time in communication with the main ocean, but for the most part it was completely isolated from it. Swept by dry winds, it suffered excessive evaporation, its waters 38-1 W. J. SO LLAS ON THE GEO LOGY OF diminished in volume and became highly concentrated ; but whether in this area rock-salt was deposited in consequence we have here no certain proof, though much indirect evidence."

FIG. 7.

Gypsum, however, crystallised out in abundance, and may he picked out in various forms from Aust Cliff. On the con­ tin ent to which this vast inland lake belonged, there lived a varied fauna, th e ancestors of the higher Vertebrata, and the descendants of the pro-Reptilia of Carboniferous times; there were reptiles which had branched off into ornithic forms, and others which had become true ostrich-like birds, and there were other reptiles more nearly in the right path, which had branched off into mammalian forms, and given rise to Monotremes and Marsupials. In our area * Since writing th is I have seen specimens of marl from Aust Cliff, bearing pseudomorphs of rock-sa lt-s-a n unexpected piece of direct evidence . FIG. 8. UPHILL, LENGTH OF CUTTING ABOUT HALF A MIl,E. AFTER A SECTION BY WILLIAM SAUNDERS, F.R.S. Uphil! Bridge. b ~ a a r e c, w eek Wharf ~c. ~ l~rifJ ~ ~~ -:"~~~=~~

~ ~~--~ -~==_._-----:;~~C''Y' l P F .F FF - F I-' ]'. F FF F f 1" a. L owrr Lias. c. Red Marl. e. Cnrbonifcron s Lim est one, j ·:FulIlt . b. 1'011:11'(11Bed s. d. Dolom it ic Conglomerat e. f. Trap Bods. .., ::r: I;l ~ t>l P :H;!-':l g-C ~ ;:; (D Bt·ds. 15' .., o ~ '"6 to<

~ I (D ~llil'·OIjII-'1:1T\i ~)I !'I i 1I IIil!\l ,/i1 ' 1, i ,., 11 1 q 1-- 'I' If/I I"" II 1/ \ ld ', I ', ' ';' '"0 e rill II(, ' IIi I II ' ,I : I, I i I 'I ',I I Q ...... :-' ~ ":j 1 ~

L--_---L.1_~...-'-I~11I~:.___'! ~LII)~;III ..---J..I1----,' 1 ''-..JI 'ii_II 111'11it I I i 1 ': p ~ ~ ~ - - ':7j -- - u:. <:> ,~~~ . ~ ~ r=: • t;."" ~ q ~~ ~ L>: ~~ ~~ t ':0'" r ....,

~ ~,~~ ~i ~ 1" 1;;1'" o ",f'.. h ~ t ~ z "'~ ~

~'!l> ~ ~ ~~ f '" ~. 0 ~~ J:.O s~ (; . {' 00 ~$' "" 386 W, J, SOLLAS ON THE GEOLOGY OF

FIG, 10, marsupial remains, 111icrolestes (Watobet) , Deinosaurian remains (Durdham Down), and ornithic footprints (Porthcawl, S. Wales) have alone been found j but of the abundant verti­ brate life of the period, the footprints of the Connecticut Valley, North America afford striking evidence. The lake itself, however, was a dead sea j its waters were as devoid of life as those of the Great Salt Lake of America, in which deposits similar to those of the Trias are form­ ---- Teag r ei!1'Lm..-vit ing at the present day. The continued depression of the Triassic area -- -f- 3 led at length to its submergence beneath th e Con­ tinental Sea, and the lifeless brine-pool which spread over the region was replaced by a wide sea teeming with various forms of life. The change from the red marls of the Keuper to the Tea­ green marls of the Rh eetic Beds, marks the commencement of the new conditions, As the depression slowly progressed, the change became more complete, and the Paper-shal es, with their -_._=-- bone-bed, and subsequently the alternating shales and limestones of the White Lias were laid down. The Rhretic Beds (Tea-green marls, A. eOlltOJ'ta shales and White Lias), will be seen at Uphill (Figs. 8 and 9), and at Aust (Fig. 10)­ the latter section far inferior to the magnificent

('""\:-':-'--~~'~-~~----'~~....-.L-'lZ0 Car~

SECTION OF AUST OLIFF. exposure along the shores at Penarth, south of Cardiff, but of great interest as being the source of the unique collection of Ceratodus teeth, which are preserved in th e Bristol Museum. THE BRISTOL DISTRICT. 387

Nowhere in our locality do the Rhretic Beds approach 100ft. in thickness, and yet their contained fauna leads us to correlate them with the Upper St. Cassian beds which, in the Rheetian Alps, attain a thickness of some 3,000 or 4,000 feet. The latter were deposited at a great distance from the land in a more rapidly sub­ siding area; the English beds near the coast-line of the sea, over a sea-bottom which sunk forty times more slowly. The depression which led to the planing across of the Carboniferous rocks and to the deposition of the Trias and the Rhretic, continued through­ ont the whole of the Liassic and a part of the Oolitic period, and so a mass of sediment, continuous from the Trias to the Inferior Oolite, buried the Carboniferous rocks out of sight, and formed far above the old plain of denudation, a plain of deposition which swept from the east of England away west, to end against the lofty hills of Wales. At length, near the close of the Jurassic period, elevation set in, pressure came from the east, and forced the Jurassic rocks against the Welsh buttresses on the west; a low anticlinal resulted, with its axis, in this region, situated over the eastern edge of the Bristol Coal-field, and having a long gentle slope to the S.E., and a shorter, perhaps steeper, slope to the W. This anticlinal was then subj ected to denudation, and rolled pebbles were carried from it into the Wealden delta during the Neocomian period; afterwards it was depressed, and the waters of the Upper Neocomian sea began to cut a plain of marine denudation across it. The Cretaceous sea completed the work which the Neocomian had begun, and deposited its sediments over the denuded plain; nor can one doubt on looking east towards the Chalk hill of Long Knoll, near Maiden Braidley, that the higher beds of the Creta­ ceous must originally have extended right over the Oolitic rocks of this locality, and have crossed, in all probability, the Bristol Chan­ nel to abut against the east of Wales. In Tertiary times great crust movements again occurred, and led to the formation of a low anticlinal of Cretaceous rocks, similar in character to that of the previons and Oolitic anticlinal. Between the western face of this anticlinal and the older rocks of Wales, lay the depression of the Bristol Channel; down this western face, which formed the short steep slope of the anticlinal, the rivers of our district began to flow towards the West, and emptied themselves into the trough of the Bristol Channel-one of these rivers being the Avon. Two es­ carpments were formed -one at right angles to the dip of those 388 W. J. SOLLAS ON THE GEOLOGY OF beds having the steeper westward slope, the other of those having the gentler eastward dip. The small patch of Cretaceous rocks at the west was soon removed, and so completely that not a vestige of it remains in our area; the escarpment on the east receded more slowly, but still has made considerable progress. The Oolitic rocks thus became subsequently exposed, and likewise gave rise to two escarpments; that on the west has almost entirely but not quite been destroyed; and patches of Inferior Oolite (Dundry Hill, 760 feet above sea level), and Lias still remain as outliers over our coal­ field to assure us of their former wide extension, which otherwise we might have been tempted to regard as a mere dream of the imagi­ nation. The Trias remains as a wide-spreading sheet or sheets, which cover up and conceal the greater part of our coal-field, but enough has been removed to reveal to us in places the main features of the old Carboniferous plain of marine denudation (Fig. 11). Be­ fore alluding to this, however, it may be as well to point out that the river Avon, which commenced to flow down the steeper side of the Cretaceous anticlinal westwards, succeeded. in cutting its way through the Chalk, Oolite, Trias, and finally entered the Carbo­ niferous strata, wearing out for itself a channel which was broad in the softer and narrower in the harder rocks. Subsequent to'the formation of its bed, and while it was being gradually deepened, the Mesozoic rocks were removed, and finally the Coal Measures on the east of the Clifton limestone were denuded away over a wide area down to the level of the river. side. Thus the low-lying plain east of the Clifton gorge was formed after the gorge itself, and this is the reason why the Avon, instead of flowing over this plain and emptying itself into the sea at Nailsea, flows through the higher country of the Downs by a gorge which, at first sight looks as though it had been specially prepared for its passage. It will do no harm to repeat that the low-lying ground to the east of the gorge was high-lying ground at one time, which directed the Avon right athwart the hard Carboniferous Limestone. When it had done this, and so led to the formation of the gorge, it was removed by general atmospheric denudation, and the gorge, left without its scaffolding, became as great a puzzle to the unscientific as the bridge which spans it was to a thoughtful American, who conjec­ tured that it had been elevated by balloons I Reverting to the main features of the old Carboniferous plain of marine denudation, as revealed by the later waste, which has FIG. 11.

SECTION ACROSS THE MEXDIP HILLS TO A POINT EAST OF 'l'HE CLIFTON DOWNS-19 MILES.

(REDUCED FROM A SECTION BY PROFESSOR RAMSAY).

M.,ut.ip "i114 "l ==t'l I:d I:d ... "l o'" e- ;:: I-l'" :;I:d ~ ~ ~ Coal~!".easur<'4" _ 1. Ink Oo7it£ 3. N r:wRed.Sands tone c.... ~ o. R.S . OlO..Red.San4.fwne I_I 2. .Lieu lEI 4. Dolomitic wngloma-a.te ~ c. L. CarbonifU"Ol.l.SLUnur.oru

The dotted lines above the section represent that part of the strata which was removed by tbe Post.Carboniferous Denudation. Those below, the extension of the strata beneath the ground. The straight line drawn from Dundry over the Downs represents the former extension of the Inferior Oolite in that direction. ee 00 <0 390 W. J. SOLLAS ON THE GEOLOGY OF stripped it of a good deal of its Mesozoic covering, one may point out first that its line of greatest altitude lies (as theory would pre­ dict) somewhere along the summit of the Mendip ridge, and that thence it slopes away on every side towards the sea. Standing on 'Valton Down, and looking south, the tops of Carboniferous Lime­ stone hills can be clearly seen reaching up to a straight line which (lips evenly downwards from the Mendip and Broad Down range to the top of the Steep Holme, thence to the Flat Holme, and still further west till, as we know, it ends below the Trias of Penarth, and then rises again north and west, to culminate in the Vans of Brecon and Caermarthenshire. Thus as a whole, and as it exists now, this plain of marine denudation may be said to slope from the Mendips westwards to the Bristol Channel, and then to rise again into the hills of Wales. The depression of the Bristol Channel would thus seem to have been marked out before Triassic times. But we have now to guard against a misconception involved in our use ot terms; the plain of denudation can only be so regarded by a very liberal interpretation of the meaning of the term "plain," for it was excavated in some places into great hollows, and in others' rose up into swelling prominences. These irregularities are clearly shown by the variations in the level of the base of the scattered patches of Trias on the older rocks; thus, not to ~o far from Bristol, the Trias of Durdham Down rests upon a limestone surface 200feet above the river Avon. At Pyle, two or three miles west, the Trias rests on the Old Red Sandstone, not many feet above the river, and whilst the line from the Mendips to the summit of the Steep Holme (Carboniferous Limestone) lies from 1,000 feet to 200 feet above the sea level, the Trias from Clevedon to Portishead descends almost to the sea level. The irregularities so proved may have been produced at the same time as the plain of marine denudation, though some may have been caused by subsequent earth movements which, acting along the old axis of elevation, exaggerated the foldings which had bern previously produced. To return to the post-Cretaceous denudation, after the Bristol Channel had been established, and the Avon and its parallel rivers or " pills," as they are locally termed, flowed west, the scenery of our area acquired its present character j but during the period of Palreolithic man, the country stood much higher above the sea THE BRISTOL DISTRICT. 391

than it does now; the Avon gorge, in common with the rest of the district, was 600 feet higher above the sea level than at present, and the Bristol Channel formed a wide and fertile valley, watered by the ancient Severn. Subsequently great depression ensued, one by one the six hundred feet by which the country had, in Palseolithic times, surpassed the present height, were submerged, and still the depression continued till the land sunk to at least 25 feet below its present level. At this level it appears for a while to have remained stationary, allow­ ing time for the denudation of cliffsand the accumulation of beaches, one of which, now 25 feet above high-water mark, is to be seen at Anchor Head and Birnbeck Cove (Fig. 12), Weston-super-Mare. Finally a movement of elevation set in, as indicated by the raised position of the beach just mentioned, which ceased, however, after the land had risen 25 feet. Since tben the country has apparently enjoyed a period of repose.

FIG. 12.

SKETCH BY MR. DAY OF RAISED BEACH IN BIRNBECK COVE, WESTON-SUPER-MARE. 1866. "Geol. Mag," Vol. iii, p. 115.

H. W. L. High Water Level. c. Ancient Sand dunes. 25 feet. 25 feet above H. W. L. d. The "Head." a. Modern Beach. e. Ancient Cliff. b. Ancient Beach. j. Carboniferous Limestone.

2 E