CHAP. V.] MIGRATION OF PLANTS. 71 



less obvious to any naturalist who has studied the structure of 

 North America, and observed the wide area occupied by the 

 modern or glacial deposits before alluded to,* in which marine 

 fossil shells of living but northern species are entombed. It is 

 clear that a great portion of Canada, and the country surround 

 ing the great lakes, was submerged beneath the ocean when 

 recent species of mollusca flourished, of which the fossil remains 

 occur more than 500 feet above the level of the sea near Mon 

 treal. I have already stated that Lake Champlain was a gulf 

 of the sea at that period, that large areas in Maine were under 

 water, and, I may add, that the White Mountains must then 

 have constituted an island, or group of islands. Yet, as this 

 period is so modern in the earth s history as to belong to the 

 epoch of the existing marine fauna, it is fair to infer that the 

 Arctic flora now contemporary with man was then also estab 

 lished on the globe. 



A careful study of the present distribution of animals and 

 plants over the globe, has led nearly all the best naturalists to 

 the opinion that each species had its origin in a single birth-place, 

 and spread gradually from its original center, to all accessible 

 spots fit for its habitation, by means of the powers of migration 

 given to it from the first. If we adopt this view, or the doctrine 

 of &quot; specific centers,&quot; there is no difficulty in comprehending how 

 the crypto gamous plants of Siberia, Lapland, Greenland, andj 

 Labrador scaled the heights of Mount Washington, because the 

 sporules of the fungi, lichens, and mosses may be wafted through 

 the air for indefinite distances, like smoke ; and, in fact, heavier 

 particles are actually known to have been carried for thousands 

 of miles by the wind. But the cause of the occurrence of Arctic 

 plants of the phcenogamous class on the top of the New Hamp 

 shire mountains, specifically identical with those of remote Polar 

 regions, is by no means so obvious. They could not, in the 

 present condition of the earth, effect a passage over the inter 

 vening low lands, because the extreme heat of summer and cold 

 of winter would be fatal to them. Even if they were brought 

 from the northern parts of Asia, Europe, and America, and 

 # Ante, p. 33. 



