448 THE ICE AGE IN NORTH AMERICA. 



least 1,470 feet thick there, and to have gradually risen in ele- 

 vation as one vast plateau, like that which at the present time 

 covers the interior of Greenland. Among the Alps it attained 

 almost incredible dimensions. The present snow-fields and 

 glaciers of these mountains, large though they are, form no 

 more than the mere shrunken remnants of the great mantle of 

 snow and ice which then overspread Switzerland. In the 

 Bernese Oberland, for example, the valleys were filled to the 

 brim with ice, which, moving northward, crossed the great 

 plain, and actually overrode a part of the Jura Mountains, for 

 huge fragments of granite and other rocks from the central 

 chain of the Alps are found high on the slopes of that range 

 of heights.* 



More recently the late Professor H. Carvill Lewis studied 

 the field in Great Britain, and published conclusions some- 

 what different from those which had been before accepted. 

 He traced, according to the summary given by Upham, a 

 terminal moraine "across southern Ireland from Tralee on 

 the west to the Wicklow Mountains and Bray Head southeast 

 of Dublin ; through the western, southern, and southeastern 

 portions of Wales ; northward by Manchester, and along the 

 Pennine Chain to the southeast edge of Westmoreland, thence 

 southeast to York, and again northward to the Tees, and 

 thence southeastward along the high coast of the North Sea 

 to Flamborough Head and the mouth of the Humber." f 



Professor Lewis propounded the theory that the supposed 

 glacial deposits in England south of this line of terminal 

 moraine were to be explained as water- deposits in a glacial 

 lake produced by the damming up of the Humber Kiver and 

 a slight elevation of the earth at the Straits of Dover. It 

 is proper to say, also, that in this theory Professor Lewis had 

 been in part anticipated by Professor Boyd Dawkins, who 

 had written as follows : 



The ice at this time was sufficiently thick to override 

 Schihallion, in Perthshire, at a height of 3,500 feet, and the 



* «5 Text-Book of Geology," pp. 885, 886. 



f "The American Geologist," vol. ii, 1888, p. 3*75. 



