ALPINE AND ARCTIC PLANTS 437 



rivers, and seas were formed. That such must be the case in 

 regard to Sicily I announced my conviction in 1833, after first 

 returning from that country ; and a similar conclusion is no 

 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, in which marine shells of living but 

 northern species are entombed. It is clear that a great portion 

 of Canada, and the country surrounding the great lakes, was 

 submerged beneath the ocean when recent species of molluska 

 flourished, of which the fossil remains occur about 500 feet 

 above the level of the sea at Montreal. Lake Cham plain was a 

 gulf or strait of the sea at that period, large areas in Maine were 

 under water, and the White Mountains must then have consti- 

 tuted 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 this, was then also established 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 centre to all access- 

 ible 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 specific centres, there is no difficulty in compre- 

 hending how the Cryptogamous plants of Siberia, Lapland, 

 Greenland and Labrador scaled the heights of Mount Washing- 

 ton, 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 Phcenogainous class on 

 the top of the New Hampshire 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 eff'ect a 



