366 GEOGEAPHICAL DISTRIBUTION, Chap. XI. 



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 then 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. Through- 

 out a large part of the United States, erratic boulders, 

 and rocks scored by drifted icebergs and coast- ice, plainly 

 reveal a former cold period. 



The former influence of the glacial climate on the 

 distribution of the inhabitants of Europe, as explained 

 with remarkable clearness by Edward Forbes, is sub- 

 stantially as follows. But we shall follow the changes 

 more readily, by supposing a new glacial period to come 

 slowly on, and then pass away, as formerly occurred. As 

 the cold came on, and as each more southern zone became 

 fitted for arctic beings and ill-fitted for their former 

 more temperate inhabitants, the latter would be sup- 

 planted and arctic productions would take their places. 

 The inhabitants of the more temperate regions would 

 at the same time travel 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 inhabitants would descend 

 to the plains. By the time that the cold had reached 

 its maximum, we should have a uniform arctic fauna 

 and flora, covering the central parts of Europe, as far 



