Chap. XII.] THE GLACIAL PERIOD. 151 



well fitted to its new home, as to become naturalised 

 But this is no valid argument against what would be 

 effected by occasional means of transport, during the 

 long lapse of geological time, whilst the island was 

 being upheaved, and before it had become fully stocked 

 with inhabitants. On almost bare land, with few or no 

 destructive insects or birds living there, nearly every 

 seed which chanced to arrive, if fitted for the climate, 

 would germinate and survive. 



t)"^ 



Dispersal during the Glacial Period. 



The identity of many plants and animals, on moun- 

 tain-summits, separated from each other by hundreds 

 of miles of lowlands, where Alpine species could not 

 possibly exist, is one of the most striking cases known 

 of the same species living at distant points, without 

 the apparent possibility of their having migrated from 

 one point to the other. It is indeed a remarkable fact 

 to see so many plants of the same species living on the 

 snowy regions of the Alps or Pyrenees, and in the 

 extreme northern parts of Europe ; but it is far more 

 remarkable, that the plants on the White Mountains, in 

 the United States of America, are all the same with 

 those of Labrador, and nearly all the same, as we hear 

 from Asa Gray, with those on the loftiest mountains 

 of Europe. Even as long ago as 1747, such facts led 

 Gmelin to conclude that the same species must have 

 been independently created at many distinct points ; 

 and we might have remained in this same belief, had 

 not Agassiz and others called vivid attention to the 

 Glacial period, which, as we shall immediately see, 

 affords a simple explanation of these facts. We have 

 evidence of almost every conceivable kind, organic and 

 31 



