INTERGLACIAL EPOCHS. 255 



It will be remembered that Scotland, during the climax of 

 the Ice Age, was smothered in a thick sheet of ice, which coa- 

 lesced in the east and north-east with the Scandinavian mer de 

 glace, while towards the west it occupied what is now the bed 

 of the sea, overflowed the Outer Hebrides, and extended into the 

 Atlantic Ocean for an unknown distance, but probably as far as 

 the present 100-fathom line. The bottom-moraine of this ice- 

 sheet is the well-known till or boulder- clay so abundantly 

 developed, especially in the Lowlands. It is very remarkable 

 that this ancient bottom-moraine contains now and again patches 

 of river- and lake-alluvia, together with beds of peat : and from 

 these have been obtained remains of mammoth, great Irish deer, 

 horse, urus, various insects, sticks of oak, birch, etc., and frag- 

 ments of other plants, and freshwater entomostraca. In other 

 places, we find in beds between the till, marine shells ; and in 

 certain localities the till itself contains sea-shells scattered 

 through it. If the till be a bottom-moraine, how can we possibly 

 account for the presence of those remarkable intercalated fossili- 

 ferous beds? The inferences to be drawn are obvious — the 

 freshwater beds are relics of old land- surfaces— while the interca- 

 lated shell-beds represent what was formerly the sea-bottom. 

 But these inferences draw after them certain conclusions, which, 

 however startling they may appear, follow no less surely as a 

 perfectly logical sequence. In the work already referred to, I 

 have described a number of interglacial beds, and pointed out 

 their meaning. From the position occupied by some of the 

 deposits, it can be proved, 1st, That the great ice-sheet melted 

 away from the Lowlands ; 2d, That there supervened a climate 

 capable of nourishing sufficient vegetation to induce mammoths, 

 Irish deer, horses, and great oxen to occupy the country; 

 3d, That the climate again became arctic, and another immense 

 mer de glace overflowed the Lowlands and buried under a new 

 accumulation of boulder-clay or bottom-moraine such parts of 

 the land-surface as it did not erode. If we reflect for a little, we 

 can hardly fail to be impressed with the magnitude of the cli- 

 matic changes which are thus indicated. We must first consider 



