296 ANNUAL OF SCIENTIFIC DISCOVERY. 



living at present on the earth are older than many parts of our existing 

 continents ; that is to say, they were created before a large part of the 

 existing mountains, valleys, plains, lakes, rivers,' and seas were formed. 

 In 1833, 1 announced my conviction that such must be the case in Sicily. 

 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 fossil 

 shells of living, but northern, species are entombed. It is clear, 

 that a great portion of Canada, and the country surrounding the 

 great lakes, were 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 Montreal. Lake Cham- 

 plain was a gulf of the sea at that period, large areas in Maine 

 were under water, and the White mountains must 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 established. 



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 birthplace, and spread 

 gradually from its original centre, 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 " specific centres," 

 there is no difficulty in comprehending how the cryptogamous plants 

 of Siberici, Lapland, Greenland, and 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. 

 But the cause of the occurrence of arctic plants of the phanogamous 

 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, effect a passage over 

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

 of winter would be fatal to them. We must suppose, therefore, that 

 originally they extended their range in the same way as the flowering 

 plants now inhabiting arctic and antarctic lands disseminate themselves. 

 The innumerable islands in the polar seas are tenanted by the same 

 species of plants, some of which are conveyed as seeds, by animals, 

 over the ice, when the sea is frozen in winter, or by birds ; while a still 

 larger number are transported by floating icebergs, on which soil contain- 

 ing the seeds of plants, may be carried, in a single year, for hundreds 

 of miles. A great body of geological evidence has now been brought 

 together to show that this machinery for scattering plants, as well as 

 for carrying erratic blocks southward, and polishing and grooving the 

 floor of the ancient ocean, extended in the western hemisphere to 

 lower latitudes than the White Mountains. When these last still 

 constituted islands, in a sea chilled by the melting of floating ice, we 

 may assume that they were covered entirely by a flora like that now 



