122 ISLAND LIFE 



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 glacial epoch when it was continually increasing 

 in severity hardly a trace has been preserved, because each 

 succeeding extension of the ice being greater and thicker 

 than the last, destroyed what had gone before it till the 

 maximum was reached. 



Migrations and Extinction of Organisms caused hy the 

 Glacial Epoch, — Our last glacial epoch was accompanied 

 by at least two considerable submergences and elevations 

 of the land, and there is some reason to think, as we have 

 already explained, that the two classes of phenomena are 

 connected as cause and effect. We can easily see how such 

 repeated submergences and elevations would increase and 

 aggravate the migrations and extinctions that a glacial 

 epoch is calculated to produce. We can therefore hardly 

 fail to be right in attributing the wonderful changes in 



