24 president's address. 



thrust from behind, would be a heavy one, and, so far as I know, 

 without a parallel at the present day ; if the viscosity of the ice enabled 

 it to flow, as has lately been urged, 1 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. 2 Moreover, if the ice floated 

 across that channel, the thickness of the boulder-bearing layers would 

 be diminished by melting (as in Boss'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 

 broad valley, considerably more than 1,200 feet deep, which would 

 afford them an easy path to the Arctic Ocean, so that only a lateral 

 overflow, inconsiderable in volume, could spread itself over the western 

 plateau. 3 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 4 (which would 

 demand rather 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 proposed. 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 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. 5 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, till the depth 

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



1 H. M. Deeley, Geol. Mag., 1909, p. 239. 



2 E. Shackleton, The Heart of the Antarctic, ii. 277. 



8 It has indeed been affirmed (Brogger, Om de senglaciale og postglaciale nivaforand- 

 ringer i Kristianiafelted, p. 682) that at the time of the great ice-sheet of Europe the 

 sea-bottom must have been uplifted at least 8,500 feet higher than at present. This 

 may be a ready explanation of the occurrence of certain dead shells in deep water, 

 but, unless extremely local, it would revolutionise the drainage system of Central 

 Europe. 



< Geol. Mag., 1901, pp. 142, 187, 284, 332. 



5 See Warren Upham, Monogr. U.S. Geol. Survey, xxv. (1896). This explana- 

 tion commends itself to the majority of British geologists as an explanation of the 

 noted parallel roads of Glenroy, but it is premature to speak of it as ' conclusively 

 shown ' (Quart. Journ. Geol. Soc, Iviii. (1902), 473) until a fundamental difficulty 

 which it presents has been discussed and removed, 



