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scepticism respecting the Helvetian Interglacial Epoch is based, not upon any preconceived objection to the idea, but upon the failure of the hypothesis when I have put it to the test in this and other districts; and I find also that my experience in this particular runs parallel with that of many other investigators of the so-called "middle glacial deposits of England.

Marine Detritus in Glacial Gravels. From certain characters of the moundy gravels on Flamborough Head and in Holderness, such as their rudely linear arrangement, their indifference to the contours, and their relation to the middle or Purple boulder-clays, it appears most probable that they represent the material deposited along the margin of the ice-sheet by the surface-waters flowing from it and from the adjacent land. From the occurrence of more or less fragmentary marine shells in them, the gravels were, however, originally supposed to be of marine origin, and this view is still upheld by some geologists. It is the same question in which so many of the so-called middle glacial" sands and gravels of the British Islands are involved, and upon which there has been so much discussion. If it be permissible for me to reiterate the well-known argument by which the presence of marine shells in gravels of glacial origin is explained it may be outlined follows.

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Since the basins around our islands are known to have been occupied by the sea at the beginning of the Glacial Period, and since these basins were afterwards filled by ice-lobes, which, as we have seen, moved outward in many places upon the land, dragging with them much of the material of the old sea-floor, it is inevitable that a certain amount of marine detritus will occur in the deposits formed by the ice or derived from its melting. Just as we find shells, and sometimes even transported masses of marine deposits, intact in the Basement Clay, so we find marine relics likewise, though usually more scattered and less perfect, in the gravels derived from the same icesheet. This deduction is consistent with our knowledge of existing glaciers and ice-sheets; thus, Sir Archibald Geikie has recorded the presence of sea-shells in the moraine of a Norwegian glacier 2; Profs. E. J. Garwood and J. W. Gregory have found an excellent illustration of the same phenomenon in one of the Spitzbergen glaciers; and Prof. R. D. Salisbury, in describing the characteristic upturning of the layers, of ice at the end of one of the glacial lobes which descends into a shallow bay in North Greenland, gives the following instructive note on the conditions which he observed: "Here the upturning of the layers brought up shells from the bottom of the bay, and left them in marginal belts where the upturned layers outcropped. These shells were mingled with other sorts of débris. In one case their quantity could have been measured by some such unit as the wagon-load."

In our islands, as Prof. P. F. Kendall has clearly shown in discussing the drifts of Western England," it is only where the ice-lobes have passed over portions of the preexisting sea-floors that we find marine remains in the drift deposits; while in other places, at the same or lower elevations, where there is proof that the ice-flow was from the land, such remains are invariably absent.

The occurrence of these shells in a few places at high elevations, all explicable by consideration of the geographical circumstances, gave rise to the idea of a great mid-glacial submergence, and upon this idea the hypothesis of a mild interglacial epoch has mainly hinged. In Prof. Geikie's latest scheme this supposed submergence is, indeed, reduced to moderate limits, but it is still the essential factor in the argument.

The same idea of a moderate degree of submergence, accompanied by temperate conditions of climate, has been

1 Lamplugh. "Drifts of Flamborough Head." Quart. Journ. Geol. Sa.. vol. xivi. (1501), pp. 384-431. "Geological Sketches at Home and Abroad" (London, 1882), pp.

145 6.

"Contributions to the Glacial Geology of Spitzbergen." Quart. Journ, Geol. Soc., vol. liv. (1898), p. 210.

"Glacial Geology of New Jersey." Rep. Geol. Survey of New Jersey, vol. v. (102), p. 81. (The quoted italics are in the original.)

In the late Prof H. Carvill Lewis's "Glacial Geology of Great Britain and Ireland (London, 1894), Appendix A, pp. 425 43

applied by Mr. Clement Reid' to the shelly gravels of Holderness. Mr. Reid has also proposed to include the buried cliff-beds of Sewerby in the same interglacial stage; but as the gravels rise to nearly 100 feet above the level of the old beach in northern Holderness, and are separated from it by the Basement boulder-clay, I am sure that this correlation cannot be sustained.

These Holderness gravels are supposed to be absent from the coast sections, and it is suggested that they may lie below sea-level in this quarter; but this is not very probable, as they are found at an elevation of 50 feet within a few miles of the coast in southern Holderness, and the Basement boulder-clay rises well above sea-level in the cliffs at Dimlington. It is true that the gravels of the coast sections afford no support to the idea of a mild interglacial submergence, and are evidently of similar origin with the rest of the glacial deposits, but I can see no other reason against their correlation with the gravels of the neighbouring interior. Except in two or three limited tracts, the shells in the Holderness gravels are as fragmentary, and nearly as scanty, as in the moundy gravels of Flamborough Head, which from their character and position cannot be of marine origin. Even at the exceptional places referred to, where the fossils are more plentiful, there is a mixture of forms, including an abundance of the freshwater shell Corbicula fluminalis, which seems to denote their derivation from preexisting local deposits; and in the new section at Burstwick, described by Mr. T. Sheppard, these shelly gravels revealed the same close association with the boulder-clay that is so frequently displayed in the glacial gravels of the coast sections.

The Kirmington Section.-There is, however, one case known to me in the east of England, and only one, in which an undoubtedly contemporaneous fauna occurs in beds intercalated with the boulder-clay series.3 At Kirmington, in North Lincolnshire, a brickyard is worked in a deposit of estuarine clay lying in the middle of a broad shallow valley which cuts across the Chalk Wolds about eight miles south of the Humber. Recent investigation by a Research Committee of the Association, in which I took an active share, has shown, somewhat unexpectedly, that the surface of the chalk at this place descends to present sea-level, and that the estuarine warp is underlain by more than 60 feet of drift, consisting of sand and chalky gravel, with two thick bands of tough clay containing far-travelled stones. The boring in which these beds were proved was insufficient to show precisely whether the stony clays possessed the distinguishing features of true till, but there can be no doubt as to their glacial character, since we know of no deposits of this kind in the east of England except those of glacial age. At the base of the estuarine warp, at 65 feet above Ordnance datum, we found a thin seam of silt and peat containing a few freshwater shells and plant remains, which, like the very scanty fauna of the overlying warp, give no precise indication of climatal conditions, though suggesting that the climate was cooler than at present. The estuarine bed is overlain by a coarse gravel of rolled flints, and in one part of the section this gravel is covered by 3 or 4 feet of red clay with far-travelled stones, resembling the Upper boulder-clay or Hessle Clay of Holderness. The character and fauna of the warp show that it must have been laid down between tide-marks, and we therefore gain an exact measure of the sea-level at the time of its accumulation, and also, I think, of the highest limit of marine submergence in this part of England during any stage of the Glacial Period.

The position of the deposit, at the fringe of the great sheet of drift, which covers the lowland east of the Wolds

1 "The Geology of Holderness." Mem. Geol. Survey (1885).

2 "On another Section in the so-called Interglacial Gravels of Holderness." Proc. Yorks. Geol, and Polytech. Soc., vol. xiii. (1895), pp. 1-14. 3 The freshwater deposit which I found some years ago at Bridlington, and at first thought to be probably intercalated with the boulder-clay, proved on fuller exposure to lie above the boulder-clay, with which it had become entangled by later disturbance. See Grol. Mag., dec. ii., vol. vi. (1879), p. 391; and Proc. Yorks. Geol. and Polytech. Soc., vol. vii. (1981). P. 389. 4 Rep. British Assoc. for 1904, PP. 272-4.

Europe to thicken and spread more rapidly toward the wes than toward the east, until finally the eastern portions were shrunken for want of sustenance, while the westerly lobes were still waxing thicker and stronger. The recent researches of Mr. F. W. Harmer into the probable meteorological conditions of the Glacial Period are full of suggestion in their bearing upon the changes which must have been brought about by the expansion of the ice-sheets. The subject is one of peculiar difficulty, but I believe that the solution of many of the problems connected with the Glacial Period is to be found along the lines of Mr. Harmer's investigations.

In considering this factor it is also especially interesting to find that Captain R. F. Scott is of opinion that the great shrinkage in the Antarctic land ice, of which he obtained such convincing evidence during the recent expedition, is due to the present excessive coldness, and consequent dryness, of the climate; and he assigns the former extension of the southern ice-sheets to a period of warmer and moister conditions. It would have been easy, had time permitted, to bring together numerous illustrations from Polar lands to show how strongly localised in many places are the conditions of existing glaciation; and such conditions must have been still more effective at lower latitudes. Hence we can readily imagine that, during the Glacial Period, differential growth and shrinkage might be brought about concurrently in areas not very wide apart, by local circumstances.

Waning Ice-sheets.-So far as the eastern side of England is concerned, I think that the epoch of maximum glaciation was reached, not when the East British lobe pressed farthest westward, but when the Pennine and North British ice advanced southward along its receding flank; and this stage is, I presume, equivalent to the "Polandian Glacia! Epoch " of Prof. Geikie's classification. It was at this time that the ice lapped highest around the slopes of the Jurassic and Cretaceous uplands of Yorkshire, causing that radical diversion of the surface-drainage which produced the remarkable effects first made known to us by the brilliant researches of Prof. P. F. Kendall in Cleveland,” and since traced by him and his fellow-workers at intervals wherever the margins of the ice-sheets have abutted against the slope of the land.

Farther southward this ice, augmented by the snowfall on its own broad surface, appears to have spread over the lower ground far beyond the bounds of the former invasion, covering most of East Anglia and the East Midland counties with a moving ice-cap, beneath which the Chalky boulder-clay was accumulated. The Upper boulder-clay of Yorkshire I consider to be the product of the same icesheet at its waning.

This final waning of the British ice-sheets, as I have elwhere attempted to show, must have been accompanied by conditions very different from the waxing stages. It appears from the evidence that the great ice-plateaus stil lingered in their basins even after the amelioration of the climate had progressed so far that no permanent snew could remain on hills that rose considerably above their level. Deprived of reinforcement, and wasting ever more rapidly as their surfaces were brought lower, the lobes must in all their embayments have passed into that cordition of "dead ice" with which the explorers of Polar regions have made us familiar. The englacial" load o detritus which the ice was powerless farther to transport was gradually dropped to the ground, and often modified and spread by gravitational movement in the saturated mass." The peculiar features of the upper part of the lowland drifts were thus explained many years ago by the late J. G. Goodchild, in his luminous description of the glacial

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and on the edge of an area west of the Wolds which appears to have escaped glaciation, sustains me in the opinion that it was accumulated during that temporary recession of the East British ice-lobe of which we have other evidence. Its proposed correlation with the Holderness gravels seems hardly tenable in the light of the fuller information which we now possess regarding the section. That the East British ice-lobe, during one of its phases, had the sea at its margin, has always appeared to me to be probable, and, I think, supplies an adequate explanation of the facts.

Under this interpretation the complex drifts between the Basement Clay and the Hessle Clay are regarded as the marginal products of the ice-lobe which filled the North Sea Basin during a stage when its eastern border began to lose ground by rapid wasting. By this recession a broad hollow was left between the hills and the ice-sheet, and into this hollow were swept the abundant washings from the glacier on the one side and from the bare land on the other, thus forming the irregular mounds and broad fans, of stratified material which run parallel with the receding ice-border. The sea at this time encircled the southern end of the ice-lobe, but its waters were restricted, in the area under consideration, to narrow estuarine inlets between the ice and the land.

The Upper Boulder-Clay.-Concurrently with this shrinkage of the East British ice-lobe there appears to have been a steady increase in the ice-caps which covered the broader upland tracks of the northern English counties. But all the evidence tends to show that the tongues descending eastward from these caps, from the time of the Basement Clay onward to the close of the glaciation, were persistently prevented from passing freely outward by the presence of the main lobe in the North Sea Basin. Upon the shrinkage of the main lobe they were deflected southward along the hollow between it and the hilly land, which, in time, they filled again to a somewhat higher level than before, the inosculation of the upper and lower Purple boulder-clays with the stratified drifts marking the gradual stages in this process. The magnificent cliffsections of the Yorkshire coast north of Flamborough reveal the continuous character of this glaciation, and there is no room anywhere to wedge an interglacial period into these sections. South of Flamborough, the interval between the withdrawal of the one mass and the advance of the other was longer, because the passage of the new invader to the eastward of the Oolitic hills was only gradually effected; and consequently it is in the interior of the Holderness recess that we find the greatest development of the stratified drifts. To imagine, with the interglacialists, that the North Sea Basin was emptied of its ice-sheet, and was then filled again just far enough to influence the flow of the local ice, without extraneous reinvasion of our coast, seems to me an unwarranted sacrifice of the evidence to the idea.

Local Shrinkage in the Ice-sheets.-There are many indications, especially in the Midland Counties and along the southern margin of the glaciated region, that the several lobes and tongues of ice of the Glacial Period in Britain did not all attain their maximum development at the same time, but that while some were creeping forward, others were shrinking back. To a certain extent this result may have been brought about simply by changes in the currents as the ice-sheets overwhelmed their erstwhile confining rims of bare land and opened up fresh avenues of discharge.

It appears to me, however, that the prime factor lay in the displacement of the areas of greatest precipitation during the course of the Glacial Period. As the plateaus of ice rose higher in the path of the moisture-laden aircurrents they must have gained increased effectiveness as condensers, thereby not only augmenting the snowfall in one quarter, but also diminishing the precipitation in the region to leeward. Hence I imagine that there would be a persistent tendency for the great ice-sheets of Western

1 "Drifts of Flamborough Head." Quart. Journ Geol. Soc., vol. xlvii. (1891), p. 421.

2 Glacialists' Mag., vol. i. No. 11 (1894), p. 231; and Mem. Geol. Survey, Isle of Man" (1903), p. 395.

1 "The Influence of Winds upon Climate during the Pleistocene Epoch Quart, Journ, Geol. Soc., vol. Ivii. (1901), pp. 405 476.

"Results of the National Antarctic Expedition." Geograp" Jeans vol. xxv. (1905), p. 306.

3 A System of Glacier-Lakes in the Cleveland Hills. Quart. I norm Geol. Ser., vol. Iviii. (1902), pp. 471-571.

4 "The Geology of the Isle of Man." Mem. Geol. Sumeg (1,03). JF 395-7

5 The flow of loose material at the surface when saturated by water Sabeen recently studied by J. G. Andersson (Upsala), who cites many remai able illustrations of the phenomenon, and proposes to apply to it the "solifluction. Journ. Geol., vol. xiv. (1906), pp. 91-112.

the hills and the ice-border; and in this hollow a mass of stratified drift was deposited. From its terraced aspect and the occurrence of scattered shells, I thought at first that this deposit might be of marine origin; but examination in detail convinced me, as it had previously convinced Prof. P. F. Kendall,' that the phenomena could only be explained by regarding the stratified material as marginal overwash from the ice-front. As in Yorkshire, the association of the boulder-clays with the stratified drift is in most places so intimate that again the evidence for the continuous presence of the ice-sheet in the surrounding basin seems irrefragable.

deposits in the Vale of Eden,' and his conclusions have been supported by the researches of Dr. N. O. Holst in Southern Greenland, where there was found to be the same difference between the unoxidised ground-moraine and the overlying oxidised material of "englacial" origin as between the lower and upper boulder-clays in areas of ancient glaciation. In adopting this explanation we must recognise that the uppermost boulder-clay of an extensive" area was not formed at exactly the same time in every part, but was accumulated progressively as a marginal residue during the emergence of the land from its icy cloak.

Late Glacial and Post-Glacial Deposits.-Of the glacial and interglacial epochs of Prof. Geikie's scheme later than the "Polandian it is admitted that no indication has been found in Yorkshire. There seems, on the contrary, to be evidence of steady amelioration in the climate, as the glacial deposits opposite the mouths of the Wold valleys are overlain, first by great deltas of chalky gravel, denoting torrential floods, probably from the seasonal melting of heavy snows; and then, in the hollows of these gravels, or of the boulder-clay itself, we find freshwater marl and peat that were deposited in the many lakelets and marshes that dotted the Holderness plain; and in the lower layers of certain of these freshwater deposits the leaves of the arctic birch (Betula nana) have been detected, indicating a climate colder than at present.

In East Yorkshire, then, we appear to have a continuous record of the events from the beginning to the end of the Glacial Period; and yet, if I read the sections aright, we can find no place into which a single mild interglacial epoch can be intercalated.

Let us now more briefly consider certain glaciated areas within the influence of the " West British "ice-lobe which I have personally investigated.

DRIFTS OF THE ISLE OF MAN.-From its isolated position in the midst of the Irish Sea, the Isle of Man constitutes an excellent gauge or glaciometer, on which is recorded the course of events within the basin occupied by the West British ice-lobe. In carrying out the geological survey of this island I made a close examination of its glacial deposits in every part, and have stated the results rather fully in a recently published memoir.*

We find here, as in Yorkshire, that prior to the glaciation there was a sea-margin at approximately its present level and, where the coast is composed of "solid" rocks, in approximately its present position. In this sea, marine deposits indicative of cold conditions were accumulated, and were afterwards displaced and mingled with the boulder-clay of an ice-sheet that gradually filled the basin and swept southward, or south-south-eastward, over the very summit of the island. At its maximum the surface of this ice-sheet stood more than 2000 feet higher than present sea-level. The difference between the altitude attained by this ice and that of the East British lobe in the same latitude is especially noteworthy. In Yorkshire the eastern ice did not reach much above 800 feet on the flanks of the Cleveland Hills, declining to 500 feet or under off Flamborough Head. The higher land which surrounds the Irish Sea Basin may be in part responsible for this difference, but I think that it must have been mainly due to the heavier precipitation in the west.

Then followed a declining stage in the glaciation, during which the ice-sheet shrank away from the hills, which were never again covered. Owing to local circumstances that are readily recognisable, the recession of its margin was relatively accelerated in the northern part of the island, so that a broad hollow was formed there between

1 "Ice Work in Edenside. Trans. Cumberland Assoc., No. 12 (1886-7),

pp. 111-167.

2"Dr. N. O. Holst s Studies in Glacial Geology," by Dr. J. Lindahl, American Naturalist, Aug. 1888. pp. 705-712. It should be noted, however, that Prof. R. D. Salisbury did not find this difference apparent in the moraines of North Greenland glaciers. See Journ. Geol., vol. iv. (1896), PP. 8c6-7.

By Dr. A. G. Nathorst, at Bridlington; and by C. Reid, at Holmpton. "Geology of Holderness, pp 78 and 85.

"The Geology of the Isle of Man" (1903). Mem. Geol. Survey.

Following closely upon this local deposition of stratified drift, there appears to have been a limited readvance of the ice, which brought about the accumulation of an upper boulder-clay on parts of the low ground. But, unlike the Upper Clay of Yorkshire, this bed lies well within the limits of the lower clays, both in extent and elevation; and it seems to denote only a slight augmentation of the persisting ice-sheet, which was thus enabled to close in again upon the lower flanks of the hills.

The end of the glacial invasion was marked by similar conditions to those found in Holderness. Great fans of flood-gravel were spread out around the mouths of the upland glens; and the hollows in the drift-plain were occupied by lakelets, now mostly obliterated by an infilling of marly and peaty sediments. Among the plants found in a bed near the base of one of these hollows is a northern willow (Salix herbacea), along with the remains of a minute arctic freshwater crustacean (Lepidurus glacialis); and similar remains were also found in a peaty layer interbedded with the flood-gravels.

Here, then, is another area in which the drifts are fully developed and magnificently exposed in cliff sections, but still yield no proof of the supposed interglacial epochs or of the marine submergence.

IRISH DRIFTS.-During recent years, while attached to the staff of the Geological Survey in Ireland, I had occasion systematically to examine the drifts of four separate and typical areas. With my colleagues of the Irish staff, the mapping of the superficial deposits was carried out in the country around the cities of Dublin, Belfast, Cork, and Limerick. The results, which have been fully stated in recent publications of the Survey, differ only in detail from those already dealt with, and need not detain us long.

Cork District.-In the south of Ireland, the infra-glacial beach, with its associated cliff and shore-line, discovered by Messrs. H. B. Muff and W. B. Wright, is essentially similar to the buried cliff at Sewerby and at almost exactly the same level. The presence of the old beach-line within the submerged valleys or rias of this coast proves that the valleys were excavated during some earlier stage of elevation. In its eastward extension the beach, with its covering of sub-aërial land-waste or "head," is overlain by the shelly boulder-clay of the West British ice-lobe; but in the south-west of Ireland, where the glaciation was from landward, this boulder-clay is absent, and its place is taken by a till of more local origin. The Cork district appears to have lain not far within the southerly bounds of the ice-sheets, and its valleys were filled to the brim almost entirely with ice from the interior of Ireland. Where the products of this ice are seen in contact with the shelly drift, as in the vicinity of Youghal, the latter lies undermost; but the evidence implies that the two ice-sheets were coexistent, and there is no indication of any break in the glaciation. Both here and in the Dublin district there appears to have been a shrinkage in the West British lobe while the Ivernian ice was still advancing, which again

1 "On the Glacial Geology of the Isle of Man." Yn Lioar Manninagh, vol. i. pt. 12. pp 297-438.

2 Mems. Geol. Survey: "The Geology of the Country around Dublin" (1903); "The Geology of the Country around Belfast" (1904); "The Geology of the Country around Cork and Cork Harbour" (1905); "The Geology of the Country around Limerick (in press).

Wright and Muff, "The Pre-glacial Raised Beach of the South Coast of Ireland." Sc. Proc. Roy. Dublin Soc., N.S., vol. x. pt. 11 (1904), PP. 250-324.

Wright and Muff, op. cit., p. 272.

points to a shifting westward of the area of greatest precipitation.

Owing to its peripheral position, the Cork district seems to have been set free from its ice-mantle much earlier than the more northerly parts of Ireland; and if there had been marine submergence later than the period of maximum glaciation, it should have left clear traces in this area. But we found, instead, that all the deposits newer than the boulder-clay were unmistakably of fluviatile or sub-aërial origin, and occupied positions that they could not have maintained if any submergence had occurred.

Dublin District.-In the Dublin district the lower shelly boulder-clay was carried for some distance inland during an early stage in the glaciation, but afterwards there was a great outpouring of the Ivernian ice from west-northwest round the northern flank of the Dublin Mountains. As the Pennine ice was deflected southward on reaching the North Sea Basin, so was this Ivernian ice deflected southward parallel to the coast in the Irish Sea Basin, the persistence of ice-lobes within the basins being the only adequate explanation in both cases.

The shelly gravels associated with the Dublin drifts are of peculiar interest, since they occur at heights ranging up to 1200 feet above sea-level, and are typical of the other high-level shelly drifts of the "West British" basin, including the much-discussed deposits of Moel Tryfaen and Macclesfield. The position of these gravels on the flanks of the Dublin Mountains at the margin of the heavily drift-covered country, their moundy outlines, sporadic development, disregard for contours, character of the fauna, relationship to the boulder-clay, and, in fact, every feature they possess, tell against the possibility of these gravels being of marine origin or other than the marginal deposits of the ice-sheet. Gravels at much lower levels in the same district that are associated with the ice-flow from the interior of the country contain no shell frag

ments.

The fine coast sections between Killiney and Bray show the usual features of a lower shelly boulder-clay brought in obliquely from the seaward and an upper boulder-clay derived from the landward ice; and they show, too, that the so-called "middle glacial gravels are merely local modifications of the glacial series, interwoven with the boulder-clays and of contemporaneous accumulation. this district there is again strong evidence that the land remained above sea-level during the final waning of the ice, and that it has not since undergone any submergence, except to a depth of not more than 10 feet above present

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estuarine clays which overlie this peat demonstrate a more recent submergence to a depth of not more than 15 or 20 feet above present sea-level. This degree of submergence is marked also by the raised beach which almost everywhere fringes the north-eastern coast of Ireland, and there is no adequate evidence for any other epoch of submergence in Ireland between the beginning of the Glacial Period and the present time.

Limerick District.-In the country around Limerick we had to deal with the products of the Ivernian sheet-ice only, uncomplicated by exterior invasion; and here not even the staunchest supporter of Interglacial deglaciation and submergence could have found a basis for his hypothesis. Although the drifts occur thickly on low ground falling to sea-level, as well as on the hills, and although they include numerous eskers and broad fans of sand and gravel, not a single shell fragment has been discovered in them, nor any other indication of marine agency. On the other hand, there is abundant evidence that the boulderclay and the stratified drift were formed contemporaneously, the one by the ice-sheet itself, and the other by the floodwaters in and around it. Another noteworthy point in this district is that, in spite of its proximity to the west coast, with the broad estuary of the Shannon offering at present an open passage thereto, the general movement of the land-ice was south-eastward across the low ground, trending inland, and not toward the coast. It appears, therefore, that the ice-sheet at the mouth of the Shannon was sufficiently thick to dominate that of the country to the east in this part of Ireland. Farther to the northward, however, and also to the southward, it is known that ice-lobes passed outward toward the Atlantic.

I think that this review of the testimony from the areas which I have closely investigated will serve to show how extraordinarily elusive is the evidence for even the prin cipal Interglacial epoch of the proposed scheme. I shall venture to claim that in each of these areas all the available data concerning the superficial deposits were systematically examined in the field and conscientiously sifted, without prejudice towards one opinion or another. Yet the only support which has been found for the Interglacial hypothesis is from a single section in North Lincolnshire, and although in this case the facts give some encouragement to the idea, they can be as readily explained without recourse to it.

In view of some evidence which we have still to consider, it is especially remarkable that in the range of magnificent coast sections, not of these areas alone, but of the whole of our islands, there is not, so far as I am aware, a single known occurrence of fossiliferous land deposits, peaty or otherwise, interbedded with boulder-clays; and we have, therefore, to depend entirely upon much less satisfactory exposures in the interior of the country for evidence of this kind.1

After the experience above recorded, it is inevitable that I shall approach the remainder of the British evidence for the Interglacial hypothesis in sceptical mood, though, I hope, without dogmatism. In discussing this evidence from districts of which my personal knowledge is scanty, or altogether wanting, I shall perforce have to depend mainly upon the literature of the subject, although I am fully aware that of the opinionative churning of this literature there has already been more than enough.

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East Anglia. In East Anglia, the original opinion that the shelly "middle glacial sands and gravels represent a mild interglacial epoch of submergence is no longer prevalent. Mr. F. W. Harmer points out that both the mollusca and ostracoda they contain are generally of a boreal or arctic character; and my colleague, Mr. H. B. Woodward, after extensive field-experience of these deposits. concludes that they are inseparable from the associated

sea-level.

Belfast District.-In the country around Belfast the glacial phenomena presented the same general features. The principal constituents were again-a shelly boulderclay, brought in from the northward, interlocked in a few places with moundy gravels, also containing a few shell fragments; and a contemporaneous drift in the hilly interior of more immediately local origin, associated with gravels of like composition and without any marine relics.

The only new feature was the presence of a mass of unfossiliferous sand and laminated clay in the recess at the head of Belfast Lough, which appears to have been deposited in a glacially dammed lake during the waning phase of the glaciation. This deposit is in places interbedded with and partly overlain by boulder-clay. Its relation to the surrounding drifts seems only explicable under the supposition that the oscillating margin of the ice-lobe was continuously present in the vicinity; and nowhere in the district did we find any evidence to suggest that there were epochs of glaciation separated by warm interglacial episodes.

The conditions in this district subsequent to the disappearance of the ice-sheets are recorded in the post-glacial deposits at the head of Belfast Lough, which have been carefully investigated by Mr. R. Lloyd Praeger. A bed of peat, passing considerably below sea-level, proves that at first the land stood higher than at present, while the 1 "Report on the Estuarine Clays of the North-east of Ireland." Proc. Roy. Irish Acad. (3), vol. ii. (1892), pp 21 -289.

1 I did, indeed, at one time think that I had discovered an ancient wil with land shells between two boulder-clays in the cliffs of Filey Bay. uf after much examination I found that it was a recent soil, covered by a huge slip of houlder-clay from the upper part of the cliff and then exposed in section by the cutting back of the coast.

"The Iater Tertiary History of East Anglia," Pra. Gol Any vol. xvii (1902), pp. 458-462; and "Pleistocene Deposits of Fast Anglia" Proe. Yorks Geol, and Polytech. Sec., vol. xv. (1904), p. 322.

-an

drifts acknowledged to be of glacial origin, and that their curiously mixed assemblage of shells does not represent a contemporaneous fauna.' "Helvetian These beds form part of the interglacials of Prof. Geikie's scheme. Midland Counties.-In the North Midlands, Mr. R. M. Deeley, in classifying the complex drifts of the Trent Basin, has sought to explain these deposits as the product of several successive glacial and interglacial epochs, but the correlation of these supposed epochs with those of Prof. Geikie is found difficult." posits classed as interglacial are unfossiliferous; and the All except the latest of the deevidence for glaciation later than this fossiliferous deposit ancient river-gravel of the Derwent containing mammalian remains (hippopotamus, elephant) '—is very questionable. The recent work of the rhinoceros, and Geological Survey in the district, in which I am taking part, confirms Mr. Deeley's opinion that the basin was invaded by ice-lobes from different quarters, which attained their maxima at different times. It is also found that there are areas which apparently lay beyond the reach of these lobes, and remained unglaciated." In these circumstances, the simplest explanation of the facts seems to be that the marginal area was sometimes exposed and sometimes ice-covered by the different flows in their oscillations during a single prolonged period of glacial conditions. There is no evidence of marine submergence in the district, though the whole of it lies much below the level attained by the shelly "middle glacial" stratified drifts of the country to the westward.

997

Farther south, Mr. W. Jerome Harrison, after a lengthy investigation of a wide area centring around Birmingham, finds that the drifts were the product of three great icelobes-the 44 Arenig Glacier," the "Irish Sea Glacier," and the "North Sea Glacier "; and he concludes that there has been no marine submergence and that "the district affords no proof of any interglacial' period." North-western Counties.-The glacial deposits of West Lancashire, Cheshire, and North Wales are essentially analogous to those of the Isle of Man. "middle glacial" submergence has figured largely in the The supposed voluminous literature of this part of the country; and Prof. Geikie, by supposing that certain Welsh and Yorkshire cave deposits of doubtful age are interglacial, and that an undefined part of the glacial sands and gravels indicates interglacial submergence, is able to picture a glaciation, a "Helvetian" mild interglacial epoch with Saxonian a wide land surface succeeded by marine conditions, and then a later "Polandian" glaciation from the quarter as the first." studied this district most closely are agreed that the interBut the investigators who have stratification of the boulder-clay with the sands and gravels is so intimate and so many times repeated that the deposits must have been practically contemporaneous and of common origin; and the differences of opinion that have arisen are on the question whether these drifts as a whole have been deposited by the sea or by land-ice. The case for the land-ice hypothesis and for the unity of the glaciation has been admirably summarised by Prof. P. F. Kendall. 19

66

same

The systematic researches of the late J. G. Goodchild in Edenside,11 and of Mr. R. H. Tiddeman in North 1 "The Glacial Drifts of Norfolk." Proc. Geol. Assoc., vol. ix. (1887), pp. 111-129.

The Pleistocene Succession in the Trent Basin." Quart. Journ. Gent Sec, vol. xlii. (1886), pp. 437-480. "The Glacial Succession." Geol. Mag, dec. iii., vol. x. (1893),

PP: 31-35

H. H. Arnold-Bemrose and R. M. Deeley, "Mammalian Remains n Derwent River Gravels." Quart. Journ. Geol. Soc., vol. li. (1896),

pp. 497-510.

C. Fox Strangways, Mem, Geol. Survey: "Country between Derby, ' &c. (1905), p. 41.

Summary of Progress of Geol Survey for 1905."

7 "The Ancient Glaciers of the Midland Counties." Proc. Geol. Assoc., vol. xv. (1898), pp. 400-408.

8"Great Ice Age," 3rd ed., pp. 367-374.

eg.-G. E. De Rance, Rep. Brit. Assoc. for 1893, D 779: A. Strahan, Quart, Journ. Geol. Soc., vol. xlii. (1886), p. 383; T. Mellard Reade, Quart. Journ. Geol. Soc., vol. xxx. (1874), pp. 35-37; and ibid., vol. xxxix. (1883), pp. 123-127.

397

Lancashire and Yorkshire,' failed to bring to light any evidence for this great Helvetian" break in the glaciation; nor have the later investigations farther southward, among which we may mention those of Prof. T. J. Jehu in Pembrokeshire, and of the Geological Survey in South Wales, shown any other result.

In support of the hypothetical Helvetian land surface in the north-western region, Prof. Geikie lays stress upon the discovery of a muddy deposit containing undetermined vegetable remains and diatoms in the boulder-clay near Ulverston, in North Lancashire. This material, pene

4

trated in borings for iron ore, was first described by Mr. J. Bolton, more than forty years ago, as occurring beneath the "pinel (boulder-clay) and just above the Carboniferous Limestone; Miss E. Hodgson shortly afterwards gave reasons for believing that the " introduced into the cavernous top of the limestone by muck "" had been recent streams which drain underground; and eighteen years later Mr. J. D. Kendall recorded further borings, which seem to show that the material sometimes occurs a few feet above the base of the boulder-clay; but his suggestion that the outcrop of the bed in question may be represented by the submerged forests occurring above the boulder-clay on the foreshore at Walney, Dring, and St. Bees indicates a misapprehension of the evidence. that the great mass of boulder-clay, in one place 70 feet Prof. Geikie infers thick, above the "muck boulder-clay, and the bottom clay, rarely more than 3 or represents the Polandian quite contrary to the usual relations of the boulder-clays 4 feet thick, the Saxonian glaciation; but this reading is assigned to these epochs; and, indeed, the whole case is too indefinite to carry any weight.

Another peaty deposit to which an interglacial age has been assigned was observed many years ago near Macclesfield by Dr. J. D. Sainter," but in this instance the bed by a few feet of coarse bouldery gravel, which, from its occurred above all the boulder-clays, and was covered only topographical position, is probably of fluviatile origin and of late-glacial or post-glacial age.

7

Northern Counties.-In Northumberland and Durham, so far as I am aware, no indication of the Helvetian interglacial epoch is forthcoming. The boulder-clays, with their interbedded sands and gravels, are like those of the North Yorkshire coast, and have received similar explanation. Dr. D. Woolacott, in his recent description of glacial sections in Northumberland, remarks: available evidence. "So far as the goes there does not seem to be anything pointing to an interglacial period or periods. The deposits of sand and sandy clay intercalated in the true boulder-clay are, as a rule, most irregular in position, and vary laterally in thickness." Southern England.-In the South of England, beyond the area of actual glaciation, evidence for an interglacial epoch has been brought forward from two or three localities, where deposits of very limited extent, partly of marine and partly of freshwater origin, have yielded a fauna and flora indicative of comparatively warm conditions.

Of these, the most important is a marine deposit containing a molluscan fauna of southerly facies, which occurs on the coast of Sussex near Selsey. The case for its interglacial age has been stated by my colleague, Mr. Clement Reid, who observed numerous large erratic boulders resting on a floor of Eocene beds in a temporary exposure on the foreshore, and infers that these boulders represent a period of glacial conditions anterior to the deposition of the bed containing the temperate-climate shells, while a later period of glaciation is inferred from the presence of the "Coombe-rock," or chalky rubble, overlying the shellbed. This interpretation of the section has, however,

1 Quart. Journ. Geol. Soc., vol. xxviii. (1872), pp. 471-401. The Glacial Deposits of Northern Pembrokeshire." Soc. Edinburgh, vol. xli. (1904), pp 53-97

3 Quart. Journ. Geol. Soc., vol. xviii. (1862), pp. 274-7.

Trans. Roy

4 Quart. Journ. Geol. Soc., vol. xix. (1863), pp. 19-31.
Quart. Journ. Geol. Soc., vol. xxxvii. (1881), pp. 29-39.
Geological Rambles round Macclesfield" (Macclesfield, 1878),

6

10 In G. F. Wright's "Man and the Glacial Period" (London, 1892), PP. 145-153, and in H. Carvill Lewis's "Glacial Geology of Great Britain and Ireland" (London, 1894). pp. 394-434.

Op. cit., and Quart. Journ. Geol. Soc., vol. xxxi. (1875), pp. 55-99.

NO. 1920, VOL. 74]

pp. 65-7.

7 Quart. Journ. Geol. Soc., vol. Ixi. (1905), p. 68.

8 On the Pleistocene Deposits of the Sussex Coast." Quart. Journ. Geol. Soc vol. xlviii. (1892), pp. 344-61. See also "The Origin of the British Flora" (London, 1899), chap. iv. et seq.

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