DARWIN ON THE ORIGIN OF SPECIES 131 



of the great continents and oceans has since prevailed, 

 and it is now recognised that the means of dispersal oi 

 species are greater than was once supposed. 



The discovery, about the year 1846, of the marks of 

 ancient glaciers in all parts of northern Europe, and the 

 acceptance of an Ice Age, had a still greater influence 

 upon the teaching of naturalists. Edward Forbes 1 put 

 forth a glacial theory to account for the present distribu- 

 tion of plants of northern origin. Glacial cold, he main- 

 tained, had driven the arctic flora far southward. When 

 more genial conditions returned, most of the northern 

 plants retreated towards the Pole, but some climbed the 

 mountains and gave rise to an isolated alpine flora. 

 Darwin, whose unpublished manuscripts had anticipated 

 Forbes's theory, believed that the whole earth became 

 chilled during the Ice Age, and that the fauna and flora 

 of the temperate zone reached the tropics. His argu- 

 ment, which is contained in chap. xi. of the Origin oj 

 Species, is now generally accepted in principle, though 

 opinions differ on many points of detail. Some think 

 that he extended too widely the effects of glacial cold, 

 exaggerated the resemblance of the arctic and alpine 

 fauna and flora, and attributed the extinction of the 

 northern species in the intermediate plains too exclu- 

 sively to climatic causes. 



One paragraph in the extremely condensed discussion 

 on geographical distribution which we find in the Origin 

 of Species calls attention to the dominance of forms of 

 life "generated in the larger areas and more efficient 

 workshops 2 of the north." The power which inhabitants 



1 GeoL Survey Memoirs, 1846. 



2 By a curious and no doubt accidental coincidence, Darwin 

 employs the same remarkable metaphor which had occurred to 

 lordanes in the sixth century A.D. lordanes calls the north the 

 officina gentium. 



