338 THE ORIGIN OF SPECIES 



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 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. 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 

 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 follov/ 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 farther and farther 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 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 woulc be nearly the same 

 with those of Europe; for the present circumpolar inhabitants, 

 which we suppose to have everywhere travelled southward, are 

 remarkably uniform round the world. 



As the warmth returned, the arctic forms would retreat north- 

 ward, closely followed up in their retreat by the productions of 

 the more temperate regions. And as the snow melted from the 

 bases of the mountains, the arctic forms would seize on the cleared 

 and thawed ground, always ascending, as the warmth increased 

 and the snow still further disappeared, higher and higher, while 

 their brethren were pursuing their northern journey. Hence, when 

 the warmth had fully returned, the same species, which had lately 

 lived together on the European and North American lowlands, 

 would again be found in the arctic regions of the Old and New 



