On the Included Pebbles of the Upper Neocomian Sands of The

414 Waller Keeping—The Upicare and Potion Pebble-beds. was startled by news that Mammoths were still living, and that a Cossack had traced some to their haunts. This sensational news, I need not say, was not confirmed. I notice that Mr. Skertchly, in his recent work on the Fen district, in which he has embodied so much valuable and interesting information, has gravely suggested that it is possible Mammoths may have been living quite recently in Siberia, grounding his argument on the above-quoted passage of Bell. I need not say that no Russian naturalist holds such a view, and that the popular legends are undoubtedly the natural outcome of the remains of these huge beasts being found under such curious conditions. The nature of these conditions, and the very interesting light they throw upon the most recent geological changes in the Northern hemi- sphere, we will discuss in another paper. Here it will have sufficed to collect the evidence showing how very early and widespread was the knowledge of the existence of the Mammoth, and to report some of the curious legends which the indigenes of Siberia have built up out of it.

V.—ON THE INCLUDED PEBBLES OF THE UPPEK NEOOOMIAN SANDS OP THE SOUTH-EAST OF ENGLAND, ESPECIALLY THOSE OF THE UPWAKE AND POTTON PEBBLE BEDS.1 By "WALTER KEEPING, M.A., F.G.S., Lecturer on Geology in the University of Cambridge. T has often appeared to me that in working out the ancient physical I features of the earth in former periods of its history, too little attention has been given to one simple set of evidences which are of wide-spread occurrence, and, frequently, of very clear and decided meaning. I refer to the included rock-fragments of conglomeratic deposits. An appeal to these fragments would, I believe, often bring out clearly-written facts of no small value for the elucidation of the nature of ancient sea-margins, as compared with the much- involved palffiontological evidences with which we are made so much more familiar. Any particular rock exposed along the coast-line, or brought down to the sea by rivers, becomes more or less wide-spread along the shores and over the sea-bed as it is rolled into pebbles by the action of marine tides and currents, and scattered, it may be, by floating agents ; and thus a series of pebbles in geological deposits shows the nature of the old sea-cliffs and neighbouring lands, and may serve to prove the original physical continuity of deposits now completely isolated. Also a further interest attaches to these fragments as relics, scanty it may be, of those great masses of rock-formations which have been destroyed by the denudations of past ages. Bearing in mind these interests, a series of pebbles has been gathered together by Prof. Hughes and Prof. Bonney, myself, and other geologists from the Neocomian Pebble beds of Upware (near Cambridge), Potton (Beds), and elsewhere, the results of which are embodied in the following account. To Professor Bonney I am par- 1 Read before the Cambridge Philosophical Society, May 3, 1880.

Downloaded from https://www.cambridge.org/core. INSEAD, on 01 Mar 2018 at 09:58:37, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016756800148253 Walter Keeping—The Upware and Potton Pebble-beds. 415 tioularly indebted for the generous gift of his notes already written upon this subject. The Potton and Upware Nodule beds have been already described by Professors Bonney and Seeley, Mr. Teall and Mr. Walker, and it is sufficient here to state that the deposit is a pebble bed or (when hardened by carbonate of lime or limonite) conglomerate, with a matrix of quartz sand, usually ferruginous, sometimes shelly and calcareous. The great majority of the pebbles are the phosphatic nodules or ' coprolites ' themselves, for the extraction of which the bed has been worked for the last ten or twelve years. These are of various ages, principally Upper Jurassic, but some of them are fragments of older Neocomians which were saturated with phosphate in the Upper Neocouiian sea; none of them are proper to the bed itself. But besides these there is a scattering of other pebbles and rock-fragments, devoid of phosphate, which in the course of the workings are separated out by hand picking and thrown aside; and it is to these, as being but little known, though of peculiar interest, that we would now call particular attention. The following are found :— 1. Fragments of older Cretaceous rocks ; mostly a dark-coloured, nearly black, ferruginous grit rock l occurring in irregular fragments often as much as three inches across. It contains numerous casts of Neocomian fossils, Cucullcea donningtonensis (MS.), Cardium sub- Mllanum, etc. Boiled fragments of the Wealden Endogenites are also not infrequent in the Potton sands, and I have lately found it at Upware. 2. Pebbles from various Jurassic rocks, such as rolled fragments of limestone and chert, which have doubtless come from many of the Lower Oolites; argillaceous limestone, which may have been derived from concretions in Kimmeridge-clay or Oxford-clay, or even from the Lower Lias ; and arenaceous rocks such as occur sometimes in the Lower Oolites of the Midlands. One large pebble of pale yellow sandstone (3 inches diam.) has yielded a few fossils ; namely, a mytiloid shell, and a transverse bivalve of doubtful affinities. The age of the rock is uncertain, but the balance of opinion would refer it to some part of the Jurassic period. Fragments of chert from these rocks are described below. Besides these however, we find the following, obviously from a more ancient source :— 3. Small pebbles from about the size of a filbert downwards to a hempseed. These are abundant, so that often a dozen or more may be detected upon the face of a hand-lump of the phosphate rock. Quartz, apparently vein-quartz, is not uncommon ; but the majority .are angular or subangular fragments of hard, highly siliceous, fine- grained rocks, mostly dark coloured, many of which are simply chert, resembling that common in the Mountain Limestones of Derbyshire, the rest being highly indurated argillites (Lydian stone and 1 This rock, and its fossils, are dsscribed more fully in another work on '' The Fossils and Palacontological Affinities of the Xeocomian Deposits of Upware and Brick- hill," not yet published.

Downloaded from https://www.cambridge.org/core. INSEAD, on 01 Mar 2018 at 09:58:37, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016756800148253 416 Waller Keeping—The Upicare and Potion Pebble-beds. Hiilleflinta). These Lydian stones are often banded by zones of different colour, texture, and hardness. 4. Larger pebbles (i.e. diameter more than an inch). These are much rarer, probably not more than one per cent, of the whole. The following have been collected at Potton, and may now be seen in the Woodwardian Museum. a. Vein-quartz.—These are the most common, five or six of them being found to one of the rest. They are fairly well rounded, and, as a rule, do not exceed three inches in diameter. Traces of metallic ores are sometimes seen in them. 6. Fragments of hard vein-breccia; slaty and quartzose varieties, sometimes with geodic cavities. c. Quartzite. —A very compact, hard, light-coloured variety, much resembling that from the Bunter conglomerates. These do not attain quite the size of the others. d. An angular fragment of white saccharoidal quartzite measuring 4 x 2J x 2| inches, spotted with pale pink felspar crystals, and imperfectly laminated with layers of white mica. e. One specimen only. A subangular, dark-coloured pebble of fine-grained, altered grit, with veiny patches of quartz. /. Altered Grit.—A fine quartzo-felspathic grit of dark colour with small black specks—much resembling some of the grit in the Lower Cambrians of Wales. Two specimens found ; the largest is a long pebble with the greatest diameter about 3J inches. Prof. Bonney states that in his specimen are several groups of minute belonites much resembling tourmaline. g. Hard sandstone so indurated as to be almost a quartzite ; light yellowish or whitish colour. These attain a somewhat greater size than (a) ; they have evidently been a good deal rolled, but are more irregular in shape. They appear identical with a rock common in the Cambridgeshire drift, which comes, I believe, from the Carbon- iferous series. h. Indurated shale and Lydian stone. — Most of the fragments which have hitherto been designated Lydian stone are, I believe, more correctly chert. We have, however, met with some which appear properly to belong to this group of highly altered rocks. t. Well-rounded oval pebbles of pale yellow, fine-grained argillaceous sandstone, sometimes micaceous and thinly laminated. h. An irregular, oblong fragment of Cambrian or Silurian pale slate measuring 2| x 1| X | inches, its contours sharply angular and joint-hacked. It is made up of two distinct zones of rock :—(1), a pale olive-coloured soft shaly rock, really a slate, splitting at a high angle across the plane of the fossils; and (2), a half-inch of fine-grained felspathic, ash-like grit crowded with fossils. The . specimen has now been broken up and I am able to identify from it— Favosites fibroms, var. ramulosus, Phillips. Orthis elegantuta, Dalman. ,, testudinaria, Dalraan ? „ biforata, Schlotheim. * Strophomena, sp. (same as one from the Dalquorhan sandstones; 6/404, of the Cambridge Catalogue). '

Downloaded from https://www.cambridge.org/core. INSEAD, on 01 Mar 2018 at 09:58:37, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016756800148253 Walter Keeping—The Vpware and Potton Pebble-beds. 417 I. Chert.—These fragments also not seldom exceed (a) in size, and are more distinctly subangular in form, being sometimes rude parallelopipeds with rounded sides and angles. Colour pale grey to almost black ; also red and yellow. Several distinct types occur which prove to be of two different ages, namely, Carboniferous and Jurassic. The majority, I believe, have come from the Mountain Limestone, for we find in them numerous fragments of Crinoid ossicles (arm joints, and round-sectioned columns), minute shells, Athyris, Polyzoa, large sponge spicules and (?) Chmtetes. These are white, grey, or black-coloured; opaque or translucent. But others, for the most part of reddish yellow colour and opaque, or but slightly translucent, are Jurassic, yielding muricated Cidaris spines fragments of shells and hinge of Inoceramus ; Pecten, and other, Lamellibranchs.1 m. A pebble in the cabinet of Prof. Bonney, who thus describes it:— " Devitrified Pitchstone.—This remarkable specimen was found by Miss Forster, of Newnham Hall. In form it was a flattened pebble rather compressed on one side, about 3f" by 3J" diameter, and nearly 1|" in greatest thickness. When brought to me it had been broken into two, the fresh surfaces showing a perfectly compact structure of pale pinkish-buff colour marbled with vein-like markings, a few specks of quartz being also visible. It was evident that the markings very closely resemble a fluidal structure, and the rock a Ehyolite. Hoping to place this beyond doubt, I had a thin section cut, and then found that the structure was very similar to that of some of the " devitrified Pitchstones " described by Mr. S. Allport. With transmitted light it seems to be a tolerably clear glass, in which is a quantity of opaque dust,—red with reflected light, and probably Fe2O3,—which is often aggregated in wavy, cloud-like irregular bands. There are a few larger grains of the same. With crossed Nicols the glass breaks up into the usual mosaic of light and dark granules of a rather irregular form characteristic of a devitrified glass. It has some resemblance to fragments in certain of the Charnwood agglomerates, but a still closer to slides cut from devitrified pitchstones from the Wrekin, to which (allowing for the paler colour) it has to the eye a considerable likeness. It must, however, be admitted that macroscopically, and to some extent microscopically, the rock resembles a specimen, given to me by Dr. Hicks, from Treffgarn (Pembrokeshire), which Mr. T. Davies con- siders of sedimentary origin. Still, though the above-described is a little anomalous, I think it more likely to be a true igneous rock. I have lately found another pebble of the same kind." At Upware the larger pebbles are much rarer than at Potton, only a very scanty sprinkling of 2-inch pebbles being seen upon the heaps of rejected rubbish. The phosphatic masses themselves are 1 Jurassic chert occurs in England in the Purbeck and Portland beds of Wiltshire and the Isle of Portland. Mr. E. B. Tawney tells me of beds of chert in the Lower Lias of Glamorganshire ; and in the North of England Mr. J. F. "Walker, of Sidney College, kindly refers me to such deposits in the Coralline Oolite near Malton. DECADE II.—VOL. VII.—HO. IX. 27

Downloaded from https://www.cambridge.org/core. INSEAD, on 01 Mar 2018 at 09:58:37, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016756800148253 418 Walter Keeping—The TTpicare and Potton Pebble-beds. also markedly smaller at Upware, so that there is much reason to believe we are here further from the source of the pebbles than at Potton. Amongst the non-phosphatic fragments we find the same tile-like fragments of ironstone, pebbles of dark grit, and other relics of an older Neocomian deposit as at Potton; of the Jurassic rocks, fragments from the underlying Coral Rag are most conspicuous, especially in the basement bed. Of the pebbles of more ancient rocks we also find the same prevailing types as at Potton ; vein-quartz and quartzite are especially abundant, also chert of many varieties. The indurated argillites are also common, and jasper is occasionally found. Some fragments of a pale micaceous laminated grit occur, which may well have had the same origin (Upper Cambrian or base of Silurian, Sedgwick) as the specimens i and k from Potton. Other Localities.— Following the outcrop of the Upware and Potton ivonsand series southwards to Brickhill and Farringdon, the same small pebbles of quartzite, chert, and Lydian stone occur, vein- quartz being most abundant at the latter place. Again, at Godal- niing and Folkestone quartz pebbles are abundant, and the " dark- coloured shiny stones " of Mr. Meyer' appear to be our cherts and Lydian stones. In the Lower Greensand of Redcliffe and Shanklin, Isle of Wight, there occur irony grit, compact quartzite, reddish quartzite and jasper. Thus we find that a certain set of pebbles characterizes the Upper Neocomian beds of the East and South of England. A more remarkable fact is, that in the Neocomian rocks of North Germany we again find the same set of pebbles, including the characteristic subangular polished chert fragments and the phosphatic nodules. The Neocomian rocks of Berklingen and Shceppenstadt, near Bruns- wick, contain beds of calcareous conglomerate with phosphatic nodules, irony fragments, and subangular chert, scarcely distinguish- able in general appearance from the Upware conglomerate. The Portlandian conglomerate of the country around Swindon must also be noticed here, on account of its included pebbles. This bed, which is well seen on Bourton Hill, is a calcareous conglomerate with scattered pebbles very similar in appearance to the Upware conglomerate. The pebbles are almost exclusively chert, mostly dark coloured, some jaspery. I have not been successful in the search for organisms in them under the microscope. Pebbles of syenite, greenstone, chert (?) and other rocks are described from the conglomerate beneath the Gault, discovered in the Kentish Town Boring. The original homes of the pebbles.—In the unpublished work before referred to, I discuss the origin of the phosphatic and other Neoco- mian pebbles, and come to the conclusion that while some of them (Ammonites deshayesii, Endogenites, as also many of the indigenous species) seem to be of southern origin, others, namely, the dark grits with fossils, point to northern deposits, such as the Lower Neoco- mian sands of Tealby, as their original home. 1 Geol. Assoc. Report, Dec. 4, 1868.

Downloaded from https://www.cambridge.org/core. INSEAD, on 01 Mar 2018 at 09:58:37, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016756800148253 Walter Keeping—The Upware and Potion Pebble-beck. 419 A glance at the map will show that the Upware and Potton beds rest upon members of the Upper and Middle Oolites, and most of the Jurassic pebbles, phosphatic or otherwise, are doubtless of local origin. But some of the Portlandian masses with Cyrena (?) rugosn, etc., are decidedly southern, identical with the Swindon Portlandians ; and a particular set of shells, including Pholadomya turaida, Ag., and Myoconcha portlandica, Blake, are remarkable as occurring also as derived fossils in a band of the Portlandian group at Swindon.1 Bunter beds, capable of furnishing pebbles such as many of our quartzites, and likely to have been exposed at that time, lie roughly between two lines drawn N. and N.W. from Potton. The hard sandstone pebbles g, are likely to be from the Coal-measures, and many of the remainder are probably of Silurian, Cambrian, and pre- Cambrian ages. The set of fossils in the pale slaty pebble Te, points to the Bala or the May Hill group; the general appearance of the rock being nearest to the Shropshire Caradocs ; but it is more perfectly cleaved than the Onny river-beds. This occurrence of Lower Palseozoic fossils is also of value as supporting evidence of the nature of the indurated argillites or Lydian stones h, many of which closely resemble the more earthy varieties of dark chert. Many of the quartzites c, and the rhyolite n, are probably of similar primeval date. We have already seen that the chert was derived from both the Carboniferous and Jurassic periods. In reasoning from these materials concerning the details of their accumulation, it is of the first importance to determine whether the pebbles were obtained directly from the parent rock in Neocomian times, or only indirectly from earlier pebble beds j and, again, we must consider wether they were carried to their present positions solely by marine currents, or had been brought down from the land by rivers. Some of the quartzites are like those of the New Eed Sandstone pebble beds, and were probably thus derived, but the majority of the rocks are not similar to those of common occurrence in the older conglomerates.2 In connexion with the abundant angular chert fragments, a specially noteworthy fact is the absence of any trace of the mother-limestone itself; and yet the Mountain Limestone is a very durable rock under wave action, and there is nothing in the Upware deposit to hinder the preservation of any included calcareous fragments. Perhaps the best evidence of the direct origin of some of the older pebbles is the fragment of fossiliferous Lower Palaeozoic rock, whose very angular contour excludes any theory of repeated transport. The general physical features of the Neocomian period are pretty well known, and an outline of some of these facts will here be of service to us in discovering the source of the more ancient pebbles. 1 See Blake on the Portlandian rocks of England, read before the Geological Society, January, 1880. 2 It is indeed remarkable that in the New Eed Sandstones we know of no such accumulations of chert pebbles, derived from the Mountain Limestone, to correspond with the abundant flint pebble and gravel beds of Tertiary and modern times. There must surely be some such deposits somewhere hidden in the New Eed.

Downloaded from https://www.cambridge.org/core. INSEAD, on 01 Mar 2018 at 09:58:37, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016756800148253 420 Walter Keeping—The Up ware and Potton Pebble-beds. The present westerly line of shallow water, sand and pebble beds, marks closely enough the ancient west coast-line. The Northern Neocomian Sea (Anglo-Germanic), extending E. and W. from Yorkshire to Brunswick was freely open to the north, but gradually shallowed to the south over Norfolk and Cambridge, till it beat upon the shores of the ancient east and west ridge of Palaeozoic rocks (the Harwich axis), now hidden under the Cretaceous and Tertiary deposits. By gradual depression and denudation this ridge came to form only an imperfect barrier, perhaps a scattered chain of islands marking oif the Northern Sea from the Southern (or Anglo-Parisian) basin, the two seas surging together through newly-made channels.1 It is to this old ridge that I look for the origin of most of the more ancient pebbles found in our Neocomian deposits; as well from the inadequateness of other theories as from the likelihood of such a source of supply in itself. The other rock surfaces of the period can be restored with some certainty. The rocks of the country to the west of the Upper Neocomian shore-line were of much the same general character as at present. The same series of Jurassic rocks overspread the country to the north-west and south-west, only ranging further west than at present; and the New Red Sandstone was also more wide- spread than now. The Mountain Limestone of Derbyshire and the ancient rocks of Charnwood were also to some extent exposed. Now, regarding this country as a source of pebble supply, we find a large area of Jurassic and New Red rocks, and single, isolated, and distant patches of primary rocks. But looking at the pebbles in the Upware and Potton sands, we find, after eliminating the Upper Jurassic fragments of local cliff origin, that the older Jurassic and New Red pebbles are but scantily represented, while Mountain Limestone chert, and other older Palaeozoic rocks are abundant. The Derbyshire Mountain Limestone is, therefore, 1 believe, utterly inadequate as a source of supply for the quantity of chert in our Neocomian deposits, and still less was the Charnwood inlier capable of supplying the quantity of Lower Palaeozoic pebbles. The pebble bed discovered in the Kentish Town deep-boring tends further to show that many of the more ancient rock fragments were not derived from any existing exposure. There, nearly thirteen feet below the base of the Gault, occurs a " hard red conglomerate, with pebbles of syenite, greenstone, trap, quartz, hornstone. red claystone porphyry, and fossilifer.ous schist from the size of a marble to that of a cannon ball.". Some of the lower beds also contained pebbles, but these are small. White quartz is named as the material of these in one case, and small angular fragments of chert (?) in another.2 And these beds probably rest upon the old Pakeozoic ridge. But little of the constitution of this ancient ridge and barrier has yet been directly revealed. Its date being Post-Carboniferous, we should naturally expect large exposures of Mountain Limestone 1 In earlier Cretaceous times (Lower Jieocomian) the two seas could have com- municated only by their common union with the Atlantic in the west. 2 Mem. Geol. Suryey, vol. iv. p. 498.

Downloaded from https://www.cambridge.org/core. INSEAD, on 01 Mar 2018 at 09:58:37, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016756800148253 ' Prof. T. Rupert Jones—Notes on a Well at Wokingham. 421 along its boundaries; and I regard the chert pebbles above described as relics of such rocks, they having been separated out from the mother-limestone by the delicate sifting power of running water. The shaly rocks of the Harwich deep boring probably belong like- wise to the Carboniferous period, and those of Meux's Brewery are true Devonian. The recent deep boring at Turnford also discovered Devonian rocks, and that at Ware Silurian (Wenlock Limestone), and the relations of these beds are such that, as Mr. Etheridge •writes, " Should the dip of these Hertfordshire Silurians prove to lie to the south, we may anticipate the more ancient series further north towards Cambridge."1 The dip of the Hertfordshire Silurians is proved to lie to the south, and thus we find the details of the ancient barrier, so far as yet known, strongty supporting our independent conclusions that the more ancient Palasozoic pebbles were derived from this source. And at this period the old dividing ridge must have been suffering active marine denudation from waves, and the wash of strong currents between the two N. and S. seas; the advancing waters steadily widening the gaps in the old barrier as it gradually disappeared beneath the sea surface. The conditions were therefore peculiarly favourable to the formation of pebble beds, and then it was that our Upware and Potton pebbles were formed, the Jurassic ones mainly from the western shores in Cambridgeshire and Bedfordshire, and the Carboniferous and older Palaeozoic from the destruction of the ancient barrier.2 The Rhyolite pebbles may have been obtained, like many of the quartzites, indirectly through the New Eed Sandstone. Lastly, inquiring what we can learn from these fragments as relics of beds since destroyed by denudation, we find the Jurassic chert pointing to the former existence of Jurassic limestone near to this area, and the abundance of Mountain Limestone chert proves a great denudation of the Carboniferous formation. But little evidence appears bearing upon the question whether Coal-bearing beds now form part of the Palseozoic ridge; but the more ancient pebbles testify to the existence of the older Silurian and Cambrian rocks beneath the Cretaceous series near Cambridge, as independ- ently predicted by Mr. Etheridge. The almost exclusive presence of chert in the Portlandian pebble beds of Berkshire suggests that only the Carboniferous rocks were exposed to denudation in Upper Jurassic times, the Mountain Lime- stone wrapper being not yet eaten through so as to expose the more ancient core-rocks of the axis.

VI.—NOTE ON THE WELL LATELY SUNK AT WOKINGHAM, BEKKS. By Prof. T. EUPERT JONES, F.R.S., F.G.S. AVING been favoured by Mr. T. M. Quill, who has of late successfully completed an artesian well at Wokingham, with opportunitieH s of examining the specimens brought up from the well, and with his own notes on the progress and results of the boring, ! Popular Science Eeview, 1879, vol. iii. p. 293. 2 Mr. J. J. Harris Teall suggested, in 1875, that the Lydian stone came from Palaeozoic rocks to the east.—Sedgwick Prize Essay, 1875, p. 38.