90 Dr. Dawson on the Flora 



" If we attempt to speculate on tlie manner in which the pecu- 

 liar species of plants now established on the ] highest summits of 

 the White Mountains, were enabled to reach those isolated spots, 

 while none of them are met with in the lower lands around, or 

 for a great distance to the north, we shall find ourselves trying 

 to solve a philosophical problem which requires the aid not of 

 botany alone but of geology, or a knowledge of the geographical 

 changes which immediately preceded the present state of the 

 earth's surface. We have to explain how an Arctic flora con- 

 sisting of plants specifically identical with those which in- 

 habit lands bordering the sea in the extreme north of America, 

 Europe and Asia, could get to the top of Mount Washington. 

 Now geology teaches us that the species 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 portion of the existing 

 mountains, valleys, plains, lakes, 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 

 mollusca flourished, of which the fossil remains occur about 500 

 feet above the level of the sea at Montreal. Lake Champlain 

 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 con- 

 stituted 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 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 Siberia, Lapland, Greenland, and 

 Labrador, scaled the heights of Mount Washington, because the 



