CHAP, vn.] 



THE QLACIdL EPOCH. 



119 



brought about. The higlier peaks of the Alps and even 

 of the Pyrenees, contain a number of plants absolutely 

 identical with those of Lapland, but nowhere found in 

 the intervening plains. On the summit of the White 

 Mountama, in tlie United States, eveiy plant is identicjil 

 with species growing in Labrador. In tliese cases all 

 ordinary means of transport fail. Most of the plants 

 have heavy seeds, which could not jiossibly be carried 

 such immense distances by the wind ; and the agency of 

 birds in so effectually stocking these Alpine heights ia 

 equally out of the question. The difficulty was so great, 

 that some naturalists werj^ driven to behcve that these 

 species were all separately created twice over on these 

 distant peaks. The determination of a recent glacial epoch, 

 however, soon olfcred a much more satisfactoiy solution, 

 and one that is now universally accepted by meu of science. 

 At this perigd, when tlie mountiiins of Wales were full 

 of glaciers, and the mountainous parts of Centml Enropi.*, 

 and much of America north of the great lakes, were 

 covered with snow and ice, and had a climate resembling 

 tluit of Labrador and Greenland at the present day, an 

 Arctic flora covei'ed all these regions. As this epoch of 

 cold pfissed away, and the snowy mantle of the country, 

 with the glaciers that descended from every mountain 

 summit, receded up their slopes and towards the north 

 pole, the plants receded also, always clinging as now to 

 the margins of the perpetual snow line. Thus it is that 

 the same species are now found on the summits of the 

 mountains of temperate Europe and America, and in the 

 banen north-polar regions. 



But there is another set of facts, which help us on 

 another step towards the case of the .Javanese mountain 

 flora. On the higher slopes of the Himalaya, on the tops 

 of the mountains of Central India and of Abyssinia, a 

 number of plants occur which, though not identical with 

 those of Eurui>ean niountains, belong to the same genera, 

 and are said by botanists to represent them; and most 

 of these could not exist in the Tvarni intervening plains. 

 Mr. Darwin believes that this class of facts can be 

 explained in the same way ; for, during the greatest severity 

 of the glacial epoch, temperate forms of plants wiU have 



