118 



ISLAND LIFE. 



[part. I. 



one was deposited, but no interglacial deposits have yet been 

 found. In North America more complete evidence has been 

 obtained. On the shores of Lake Ontario sections are exposed 

 showing three separate beds of " till " with intervening stratified 

 deposits, the lower one of which has yielded many plant 

 remains and fresh-water organisms. These deposits are seen to 

 extend continuously for more than nine miles, and the fossil - 

 iferous interglacial beds attain a thickness of 140 feet. Similar 

 beds have been discovered near Cleveland, Ohio, consisting, first 

 of " till " at the lake-level, secondly of about 48 feet of sand 

 and loam, and thirdly of unstratified " till " full of striated 

 stones — six feet thick. ^ On the other side of the continent, in 

 British Columbia, Mr. G. M. Dawson, geologist to the North 

 American Boundary Commission, has discovered similar 

 evidence of two glaciations divided from each other by a 

 warm period. 



This remarkable series of observations, spread over so wide 

 an area, seems to afford ample proof that the glacial epoch did 

 not consist merely of one process of change, from a temperate 

 to a cold and arctic climate, which, having reached a maximum, 

 then passed slowly and completely away ; but that there were 

 certainly two, and probably several more alternations of arctic 

 and temperate climates. 



It is evident however, that if there have been, not two only, 

 but a series of such alternations of climate, we could not 

 possibly expect to find more than the most slender indications 

 of them, because each succeeding ice-sheet would necessarily 

 grind down or otherwise destroy much of the superficial deposits 

 left by its predecessors, while the torrents that must always 

 have accompanied the melting of these huge masses of ice 

 would wash away even such fragments as might have escaped 

 the ice itself It is a fortunate thing therefore, that we should 

 find any fragments of these interglacial deposits containing 

 animal and vegetable remains ; and just as we should expect, 

 the evidence they afford seems to show that the later phase of 

 the cold period was less severe than the earlier. Of such 

 deposits as were formed on land during the coming on of the 

 1 Dr. James Geikie in Geological Magazine, 1878, p. 77. 



