Slil'TEMBEK T, IQIOj 



NATURE 



:83 



strike," formed on the Kimeridge Clay, the eastern arm 

 of which was beheaded, even in pre-Glacial times, by the 

 sea.' As to Lake Oxford,- 1 must confess myself still 

 more sceptical. Some changes, no doubt, have occurred 

 in later Glacial and post-Glacial times ; valleys have been 

 here raised by deposit, there deepened sometimes by as 

 much as loo feet ; the courses of lowland rivers may 

 occasionally have been altered ; but I doubt whether, since 

 those times began, either ice-sheet or lake has ever con- 

 cealed the site of that university city. 



The submergence hypothesis assumes that, at the 

 beginning of the (ilacial Epoch, our islands stood rather 

 above their present level, and during it gradually sub- 

 sided, on the west to a greater extent than on the east, 

 until at last the movement was reversed, and they re- 

 turned nearly to their former position. During most of 

 this time glaciers came down to the sea from the more 

 mountainous islands, and in winter an ice-foot formed 

 upon the shore. This, on becoming detached, carried 

 away boulders, beach pebbles, and finer detritus. Great 

 quantities of the last also w'ere swept by swollen streams 

 into the estuaries and spre.id over the sea-bed by coast 

 currents, settling down especially in the quiet depths of 

 submerged Valleys. Shore-ice in Arctic regions, as Colonel 

 H. W. Feilden ^ has described, can striate stones and 

 even the rock beneath it, and is able, on a subsiding area, 

 gradually to push boulders up to a higher level. In fact, 

 the state of the British region in those ages would not 

 have been unlike that still existing near the coasts of the 

 Barents and Kara Seas. Over the submerged region 

 southward, and in some cases more or less eastward, 

 currents would be prevalent, though changes of wind ' 

 would often affect the drift of the floating ice-rafts. But 

 though the submergence hypothesis is obviously free from 

 the serious difficulties which have been indicated in dis- 

 cussing the other one, gives a simple explanation of 

 the presence of marine organisms, and accords with what 

 can be proved to have occurred in Norway, \\'aigatz 

 Island, Novaia Zemlya, on the Lower St. Lawrence, in 

 (rrinnell Land, and elsewhere,^ it undoubtedlv involves 

 others. One of them — the absence of shore terraces, caves, 

 or other sea marks — is perhaps hardly so grave as it is 

 often thought to be. It may be met by the remark that 

 unless the Glacial .Age lasted for a very long time and 

 the movements were interrupted by well-marked pauses, 

 we could not expect to find any such record. In regard 

 also to another objection, the rather rare and sporadic 

 occurrence of marine shells, the answer would be that, 

 on the Norway coast, where the ice-worn rock has 

 certainly been submerged, sea-shells are far from common, 

 and occur sporadically .in the raised deltaic deposits of 

 the fjords.' .An advocate of this view might also com- 

 plain, not without justice, that, if he cited an inland 

 terrace, it w^as promptly dismissed as the product of an 

 ice-dammed lake, and his frequent instances of marine 

 shells in stratified drifts were declared to have been trans- 

 ported from the sea by the lobe of an ice-sheet ; even if 

 they have been carried across the path of the .Arenig ice, 

 more than forty miles as the crow flies, from the Irish 

 Sea up the ^'alIev of the Severn, or forced some 1300 

 feet up Moel Tryfaen.' The difliculty in the latter case, 

 he would observe, is not met by saying the ice-sheet 

 would be able to climb that, hill " given there were a 



1 See for instance the courses ' f tHe Medway and the Beult over the 

 Weald rlay (C. Le Neve Foster and \V. Topley, Quart. Joum. Geol. Soc, 

 xii. fi86s), p. 445). 



2 F. W. Harmer. Quart. Journ, Geol. .Soc. Ixiit. (1907), p. 470. 

 » Quart. Journ. C.eol Soc.. xx.xiv. (1878). p. 556. 



^ See p. 23, and for the currents now dominint consult Dr. H. Ba^selt I ■< 

 Prof. Herdnian's Report on the Lanc.ishire Sea Fisheries, Trans. HioI. Soc. 

 Liverpool, xxiv. (iQIn). p. 123. 



■^ See '* Ice Work,'" p. 221, and GeoL Maz , 1000, p. 259. 



^ If, as seems probable, the temper.Tture was changing rather rapidly the 

 nld faun^ would he pauperised and the new one make its way but slowly 

 into the British fjor'^s. 



J Critics of the submergence hypotheses seem to find a difficulty in ad- 

 mitting downward and upward movements, amounting sometimes to nearly 

 1,400 feet during Plei-tocene .\ges ; but in the northern part of America the 

 upSeav.tl, at any rate, has .^mounted to about i.noo feet, while on the 

 western coast, beneath the loftv summit of Mount St. Elias. marine shell.s 

 of existing spec-es have been obt.iirfed some 5,000 feet above .sea level. It 

 is also admitted that in se\'eral places the pre-elacial surface of the land 

 was much above its present level On the Red River, whatever be the 

 explanation, foraminifers, radiolarians, and sponge spicules hav been 

 found at 700 feet above sea-level, and near Victoria, on the Saskatchewan, 

 even up to about 1,900 feet. 



NO. 2 13 I, VOL. 84] 



sufficient head behind it."' That ice can be driven up- 

 hill has long been known, but the existence of th& 

 " sufficient he£id " must be demonstrated, not assumed. 

 There may be " no logical halting-place between an uplift 

 of ten or twenty feet to surmount a roc/te inoutonnee and 

 an equally gradual elevation to the height of -Moel 

 Tryfaen," yet there is a common-sense limitation even to 

 a destructive sorites. The argument, in fact, is more 

 specious than valid, until we are told approximately how 

 thick the northern ice must be to produce the requisite 

 pressure, and whether such an accumulation would be 

 possible. The advocates of land ice admit that, before it 

 had covered more than a few leagues on its southward 

 journey, its thickness was less than 2000 feet, and we 

 are not entitled, as I have endeavoured to show, to pile 

 up ice indefinitely on either our British highlands or the 

 adjacent sea-bed. The same reason also forbids us largely 

 to augment the thickness of the latter by the snowfall on 

 its surface, as happens to .Antarctic barrier ice. Even if 

 the thickness of the ice-cap over the Dumfries and Kirk- 

 cudbright hills had been about 2500 feet, that, with every 

 allowance for viscosity, would hardly give us a head 

 sufificient to force a layer of ice from the level of the 

 sea-bed to a height of nearly 1400 feet above it, and at 

 a distance of more than 100 miles. 



Neither can we obtain much support from the instance 

 in Spitsbergen, described by Profs. Garwood and Gregory, 

 where the Ivorv Glacier, after crossing the bed of a valley, 

 had transported marine shells and drift from the floor 

 (little above sea-level) to a height of about 400 feet on the 

 opposite slope. Here the valley was narrow, and the 

 glacier had descended from an inland ice-reservoir, much 

 of which was at least 2800 feet above the sea, and rose 

 occasionally more than a thousand feet higher." 



But other difliculties are far more grave. The thick- 

 ness of the chalky Boulder Clay alone, as has been stated, 

 not unfrequently exceeds 100 feet, and, though often 

 much less, may have been reduced by denudation. This 

 is an enormous amount to have been transported and 

 distributed by floating ice. The materials, also, are not 

 much more easily accounted for by this than by the other 

 hypothesis. A continuous supply of well-worn chalk 

 pebbles might indeed be kept up from a gradually rising 

 or sinking beach, but it is difficult to see how, until the 

 land had subsided for at least 200 feet, the chalky Boulder 

 Clav could be deposited in some of the East Anglian 

 vallevs or on the Leicestershire hills. That depression, 

 however, would seriously diminish the area of exposed 

 chalk in Lincolnshire and A'orkshire, and the double of it 

 would almost drown that rock. .Again, the East Anglian 

 Boulder Clay, as we have said, frequently abounds in 

 fragments and finer detritus from the Kimeridge and 

 Oxford Clays. But a large part of their outcrop would 

 disappear before the former submergence was completed. 

 Yet the materials of the Boulder Clay, though changing 

 as it is traced across the country, more especially from 

 east to west, seem to vary little in a vertical direction. 

 The instances, also, of the transportation of boulders and 

 smaller stones to higher levels, sometimes large in amount, 

 as in the transference of " brockram " from outcrops near 

 the bed of the Eden valley to the level of Stalnmoor Gap, 

 seem to be too numerous to be readily explained by the 

 uplifting action of shore-ice in a subsiding area. Such a 

 process is possible, but we should anticipate it would be 

 rather exceptional. 



Submergence also readily accounts for the above-named 

 sands and gravels, but not quite so easily for their occur- 

 rence at such very different levels. On the eastern side 

 of England gravelly sands may be found beneath the 

 chalky Boulder Clay well below sea-level to three or four 

 hundred feet above it. Again, since, on the submergence 

 hypothesis, the Lower Boulder Clay about the estuaries 

 of the Dee and the Mersey must represent a deposit from 

 piedmont ice in a shallow sea, the mid-glacial sand (some- 

 limes not very clearly marked in this part) ought not to- 

 be more than "forty or fifty feet above the present Ordnance 

 datum. But at Manchester it reaches more than 200 feet, 

 while near Heywood it is at least 425 feet. In other 



1 P. F. Kendall in Wright's " Man and the Gl.-tcial P rlod." p. 171. 



2 Quart. .Tour. Geol. -Soc. liv. (iSqB), p. 20s. Eirlier obs;] 

 some upthrust of materials by a glacier are noted on p. 219. 



