160 THE ORIGIN OF SPECIES 



this same belief, had not Agassiz and others called vivid 

 attention to the Glacial period, which, as we shall imme- 

 diately see, alfords a simple explanation of these facts. 

 We have evidence of almost every conceivable kind, 

 organic and inorganic, that, within a very recent geologi- 

 cal period, central Europe and North America suffered 

 under an arctic climate. The ruins of a house burned 

 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 bowlders, of the 

 icy streams with which their valleys were lately filled. 

 S6 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 bowlders and 

 scored rocks plainly reveal a former cold period. 



The former influence of the glacial climate on the 

 distribution 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 became fitted for the inhabi- 

 tants 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 in- 

 habitants 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 



