152 DISPERSAL DUEING [Chap. XII. 



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, and perched boulders, of the icy streams with 

 which their valleys were lately filled. So greatly has 

 the climate of Europe changed, that in Northern 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 dis- 

 tribution of the inhabitants of Europe, as explained by 

 Edward Eorbes, 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 became 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 further south- 

 ward, 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 

 inhabitants would descend to the plains. By the time 

 that the cold had reached its maximum, we should have 

 an arctic fauna and flora, covering the central parts of 

 Europe, as far south as the Alps and Pyrenees, and even 

 stretching into Spain. The now temperate regions of 

 the United States would likewise be covered by arctic 

 plants and animals and these would be nearly the same 

 with those of Europe ; for the present circumpolar 



