328 ON THE ORIGIN OF SPECIES 



if far less well-stocked than Britain, scarcely more than 

 one would be so well fitted to its new home, as to 

 become naturalised. But this, as it seems to me, is 

 no valid argument against what would be effected by 

 occasional means of transport, during the long lapse of 

 geological time, whilst an island was being upheaved 

 and formed, 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 be sure to germinate and survive. 



Dispersal during the Glacial period. — r rhe identity of 

 many plants and animals, on mountain-summits, separ- 

 ated from each other by hundreds of miles of lowlands, 

 where the 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 to the 

 other. It is indeed a remarkable fact to see so many 

 of the same plants 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 several 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 inorganic, that 

 within a very recent geological period, central Europe 

 and North America suffered under an Arctic climate. 

 The ruins of a house burnt by fire do not tell their 

 tale more plainly, than do the mountains of Scotland 

 and Wales, with their scored flanks, polished surfaces, 



