412 ORIGIN OF SPECIES 



living at distant points, without the apparent possibility of 

 their having migrated from one point to the other. It is in- 

 deed 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 atten- 

 tion 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 in- 

 organic, 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, and perched boulders, 

 of the icy streams with which their valleys were lately filled. 

 So greatly has the climate of Europe changed, that in North- 

 ern Italy, gigantic moraines, left by old glaciers, are now 

 clothed by the vine and maize. Throughout a large part of 

 the United States, erratic boulders and scored rocks plainly 

 reveal a former cold period. 



The former influence of the glacial climate on the distribu- 

 tion of the inhabitants of Europe, as explained by Edward 

 Forbes, is substantially as follows. But we shall follow the 

 changes more readily, by supposing a new glacial period 

 slowly to come on, and then pass away, as formerly occurred. 

 As the cold came on, and as each more southern zone be- 

 came fitted for the inhabitants of the north, these would take 

 the places of the former inhabitants of the temperate regions. 

 The latter, at the same time, would travel further and fur- 

 ther southward, unless they were stopped by barriers, in 

 which case they would perish. The mountains would become 

 covered with snow and ice, and their former Alpine inhabit- 

 ants would descend to the plains. By the time that the cold 



