September i, 19 io] 



NATURE. 



281 



found, roughly speaking, in Spitsbergen, which, since its 

 mountains rise to much the same height, should give us 

 a general idea of the condition of Britain 'in the olden 

 time. 



What would then be the state of Scandinavia? Its 

 present temperature ranges on the west coast from about 

 45° in the south to 35'^ in the north.' But this region 

 must now be very much, possibly iSoo feet, lower than 

 il was in , pre-Glacial, perhaps also in part of Glacial, 

 times. ^ If we added 5° for this to the original 15°, and 

 allowed so much as 18° for the diversion or the warm 

 current, the temperature of Scandinavia would range from 

 7° to —3°, approximately that of Greenland northwards 

 trom C'pernivik. But since the difference at the present 

 day between Cape Farewell and Christiania (the one in 

 an abnormally cold region, the other in one correspond- 

 ingly warm) is only 7'^, that allowance seems much too 

 large, while without it .Scandinavia would correspond in 

 temperature with some part of that country from south 

 of Upernivik to north of Frederikshaab.^ But if 

 Christiania were not colder than Jakobshavn is now, or 

 Britain than Spitsbergen, we are precluded from com- 

 parisons with the coasts of Baffin Bay or \'ictoria Land. 



Thus the ice-sheet from .Scandinavia would probably 

 be much greater than those generated in Britain. It 

 would, however, find an obstacle to progress westwards 

 which cannot be ignored. If the bed of the North Sea 

 became dry land, owing to a general rise of boo feet, that 

 would still be separated from Norway by a deep channel 

 extending from the Christiania Fjord round the coast 

 northward. Even then this would be everywhere more 

 than another 600 feet deep, and almost as wide as the 

 Strait of Dover.' The ice must cross this and afterwards 

 be forced for more than 300 miles up a slope, which, 

 though gentle, would be in vertical height at least 600 

 feet. The task, if accomplished by thrust from behind. 

 would be a heavy one, and, so far as I know, w-ithout 

 a parallel at the present day ; if the viscosity of the ice 

 enabled it to flow, as has lately been urged,® we must be 

 cautious in appealing to the great Antarctic barrier, 

 because we now learn that more than half of it is only 

 consolidated snow.' Moreover, if the ice floated across 

 that channel, the thickness of the boulder-bearing layers 

 would be diminished by melting (as in Ross's Barrier), 

 and the more viscous the material the greater the tendency 

 . for these to be left behind by the overflow of the cleaner 

 upper layers. If, however, the whole region became dry 

 land, the Scandinavian glaciers would descend into a 

 Lroad valley, considerably more than 1200 feet deep, which 

 would afford them an easy path to the .Arctic Ocean, so 

 Ihat only a lateral overllow, inconsiderable in volume, 

 ;ould spread itself over the western plateau.' .An attempt 

 to escape this difficulty has been made by assuming the 

 existence of an independent centre of distribution for ice 

 and boulders near the middle of the North Sea bed * 

 fwhich w^ould demand 1 ather exceptional conditions of 

 temperature and precipitation) ; but in such case either 

 the .Scandinavian ice would be fended off from England, 

 or the boulders, prior to its advance, must have been 

 dropped by floating ice on the neighbouring sea-floor. 



If, then, our own country were but little better than 

 Spitsbergen as a producer of ice, and Scandinavia only 

 surpassed southern Greenland in having a rather heavier 

 snowfall, what interpretation may we give to the glacial 

 phenomena of Britain ? Three have been prooosed. One 

 asserts that throughout the Glacial Epoch the British Isles 

 generally stood at a higher level, so that the ice which 

 almost buried them flowed out on to the beds of the 



1 J» js 44'42° at Bergen, 38*48° at Bodo, 35'42'at Hammerfest, 41*36° at 

 Christiania and Stockholm. 



■- For particulars see Geol. Ma^.t 1899, p. 97 (W. H. Hudleston) and 

 p. =82 (T. G. Bonney). 



•* Christiania and Cape Farewell (Greenland) are nearly on the same 

 latitude. 



■* For details see do^. Mar.. i''>99. pp. 97 and 282. 



•'' H. M. Deeley, Gt't>/. ^fag., 1909. p. 2^0. 



I E. .Shackleton, " The Heart of the .'Antarctic." ii., p. 277. 



" It has indeed been affirmed (Hiogger, Om cff seitglaciaU og fcstg^aciale 

 nha/orandrtn^er i Kristianinfilteti , p. 682) that at the tim- of the g-eat 

 ice-sneet of Europe the sea-bottom must have been uplifted at I'-asl 8:00 

 feet higher than at present. This may be a ready explanation of the occur- 

 rence of certain dead shells in deep water, but. unless extremely local, it 

 would revolutionise the drainage system of Central Europe. 



'^ Ceol. Mag., 1901, pp. 142, 187, 284, ^32. 



North and Irish Seas. The Boulder Clays represent its 

 moraines. The stratified sands and gravels were deposited 

 in lakes formed by the rivers, which were dammed up by 

 ice-sheets.' A second interpretation recognises the presence 

 of glaciers in the mountain regions, but maintains that the 

 land, at the outset rather above its present level, gradually 

 sank beneath the sea, until the depth of water over the 

 eastern coast of England was fully 500 feet, and over the 

 western nearly 1400 feet, from which depression it slowly 

 recovered. By any such submergence Great Britain and 

 Ireland would be broken up into a cluster of hilly islands, 

 between which the tide from an extended Atlantic would 

 sweep eastwards twice a day, its currents running strong 

 through the narrower sounds, while movements in the 

 reverse direction at the ebb would be much less vigorous. 

 The third interpretation, in some respects intermediate, 

 was first advanced by the late Prof. Carvill Lewis, who 

 held that the peculiar Boulder Clays and associated sands 

 (such as those of East .Anglia), which, as was then 

 thought, were not found more than about 450 feet above 

 the present sea-level, had been deposited in a great fresh- 

 water lake, held up by the ice-sheets already mentioned 

 and by an isthmus, which at that time occupied the place 

 of the Strait of Dover. Thus these deposits, though 

 indirectly due to land-ice, were actually fluviatile or 

 lacustrine. But this interpretation need not detain us, 

 thoiigh the former existence of such lakes is still main- 

 tained, on a small scale in Britain, on a much larger 

 one in North .America, because, as was. pointed out when 

 it was first advanced, it fails to explain the numerous 

 erratic blocks and shell-bearing sands which occur far 

 above the margin of the hypothetical lake. 



Each of the other two hypotheses involves grave difficul- 

 ties. That of great confluent ice-sheets creeping over the 

 British lowlands demands, as has been intimated, climatal 

 (onditions which are scarcely possible, and makes it hard 

 to explain the sands and gravels, sometimes with regular 

 alternate bedding, but more generally indicative of strong 

 current action, which occur at various elevations to more 

 than 1300 feet above sea-level, and seem too widespread 

 to have been formed either beneath an ice-sheet or in 

 lakes held up by one, for the latter, if of any size, would 

 speedily check the velocity of influent streams. Also the 

 mixture and crossing of boulders, which we have described, 

 are inexplicable without the most extraordinary oscilla- 

 tions in the size of the contributing glaciers. To suppose 

 that the Scandinavian ice reached to Bedfordshire and 

 Herts, and then retired in favour of north British glaciers, 

 or vice versa, assumes an ainount of variation which, so 

 far as I am aware, is without a parallel elsewhere. So 

 also the mixture of boulders from South Scotland, the 

 Lake District, and North Wales, which lie, especially in 

 parts of Staffordshire and Shropshire, as if dropped upon 

 the surface, far exceeds what may reasonably be attributed 

 to variations amplified by lateral spreading of mountain 

 glaciers on reaching a lowland, while the frequent presence 

 of shells in the drifts, dozens of miles away from the 

 present coast, implies a rather improbable scooping tip of 

 the sea-bed without much injury to such fragile objects. 

 The ice also must have been curiously inconstant in its 

 operations. It is supposed in one place to have glided 

 gently over its bed, in another to have gripped and torn 

 out huge masses of rock.- Both actions may be possible 

 in a mountain region, but it is very difiicult to understand 

 how they could occur in a lowland or plain. ' Besides 

 this, we can only account for some singular aberrations 

 of boulders, such as Shap granite well above Grosniont 

 in Eskdale, or ' the Scandinavian rhomb-porphyry above 

 Lockwood," near Huddersfield, by assuming a flexibility 

 in the lobes of an ice-sheet which it is hard to match at 



1 See Warren Upham, Mnnogr. U.,S. Gcol. Survey, xxv. (1896). This 

 explanation commends itself to the maiority of British geologists as an ex- 

 planation of the notfd parallel roads of Glenrov, but it is premature 10 speak 

 of it as "conclusively .sho»n " (Quart. Journ. Geol. Soc, Iviii. (1902) p. 473) 

 fundamental difficulty which it presents has been discussed and 



d. 



is a very dubious hypothesis (see Geot. 

 us relations of the drift and chalk in 

 lometimes supposed to prove the same 

 3 hesitation in saying that the chalk 



.„, _,. , _„ it is in the Isle of Wight. 



» .About half-way .across England and 810 feet above sea-level. P. F. Ken- 

 dall, Quart. lourn. Geol. Soc, Ivii. (1902), p. 498. 



'■^ That this has occurred a^. Cr 

 Maz-, 1905, pp. S97, 524). The 

 the'islands of iMoen and Riigen 

 action. Knowing both well, I h; 



NO. 2 13 I, VOL. 84] 



