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 feel. 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. 1 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. 
