GEOGRAPHICAL DISTRIBUTION 329 



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 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 supplanted 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 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 circum- 

 polar inhabitants, which we suppose to have everywhere 

 travelled southward, are remarkably uniform round 

 the world. We may suppose that the Glacial period 

 came on a little earlier or later in North America than 

 in Europe, so will the southern migration there have 

 been a little earlier or later ; but this will make no 

 difference in the final result. 



As the warmth returned, the arctic forms would 

 retreat northward, closely followed up in their retreat 



