CnxF. XI. DISPERSAL DURING THE GLACTAL PERIOD. 337 



stocked than Britain, perhaps not more than one would be so 

 well litted to its new home as to become naturalized. But 

 this, as it seems to me, is no valid arf^ument against "what 

 would be effected by occasional means of transport, during tlu; 

 long lapse of geological time, while the island was being up- 

 heaved, and before it had become fully stocked with inhabit- 

 ants. 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, 



Disjyersal durbuj the Glacial Period. 



The identity of many plants and animals, on mountain- 

 gunnnits, separated from each other by hundreds of miles of 

 lowlands, where Alpine species could not possibly exist, is one 

 of llie 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 remark- 

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

 the snowy regions of the Alps or Pyrenees, and in the extreme 

 jiorthern parts of Europe ; but it is far more remarkable that 

 the plants on the White Mountains, in the United States of 

 America, arc all the same with those of Labrador, and nearly 

 all the sanie, 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 

 Ijcen 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 exfjlanation of these 

 facts. We have evidence of almost every conceivable kind, 

 organic and inorganic, that, within a very recent geological 

 jx'riod, central Em-ope and North America suffered under an 

 arctic climate. The ruins of a house burnt by lire do not tell 

 their tale moni plainly than do the mountains of Scotland and 

 Wales, with their scored flanks, polishi^d surfaces, and perched 

 bowlders, of the icy streams with which their valleys W(M-e late- 

 Iv filled. So grcatlv has the climate of Europe clianged, thai, 

 in Northern Jtalv, gigantic moraines, left bv old glaciers, are 

 now clothed by tlie vine and maize, 'J'hroughout a larg(^ part 

 of the United States, erratic bowlders and scored rocks ])jainly 

 reveal a former cold j)eriod, 



Tlie former influence of the glacial climate on the distribu- 

 15 



