116 CANADIAN FORESTRY ASSOCIATION 



by changes in the level of the continent, and consequently in the contours of the 

 former coast lines which limits the areas over which the trees could spread them- 

 selves. 



In the earlier times when great forests nourished over our polar regions, 

 this continent was somewhat more elevated than it is now, and the wide spreading 

 land of its most northern parts lent itself to the evolution and multiplication of 

 species the progenitors of the rich forest flora which still characterizes this 

 North American continent. 



While the way was clear and uninterrupted for these numerous species to 

 move gradually southward, as the climate cooled, and to establish themselves in 

 the latitudes most suitable to their requirements, it was impossible for their seeds 

 to cross the deep ocean which lay between their original home and the western 

 part of the old world. This barrier would be all the more complete because of 

 the probable existence of an ocean current corresponding with the Gulf Stream of 

 the present day, the northeasterly course of which would prevent them from 

 reaching the shores of Europe. There is also some evidence of the existence, after 

 the glacial epoch, of a counterpart of the Labrador current in the striking peculiarity 

 of the course of the eastern limiting line of the white cedar, which seems to indicate 

 that when this tree was spreading itself northward and eastward, it was stopped by 

 an Arctic current flowing south over Prince Edward Island and the isthmus between 

 Baie Verte and Chignecto Bay and thence on through the Bay of Fundy. Immed- 

 iately west of the white cedar line, as laid down by myself thirty years ago, this 

 species grows to perfection, while immediately to the east, it is entirely absent. 

 There is nothing in regard to soil, latitude, etc., that will account for this phe- 

 nomenon. 



Towards the central and southern portions of the North American continent, 

 the summer temperature for some time previous to the advent of the glacial epoch, 

 may not have differed greatly from that of the polar regions during the same period, 

 on account of the increasing length of the nights in going southward, which would 

 tend to reduce the mean solar heat of each day. Some species of trees may therefore 

 have been flourishing at the same time all the way from the north pole to the Gulf 

 of Mexico. 



The narrow and shallow strait of Behring, which now separates North America 

 from Asia Tias existed only in recent geological times. When that region of the 

 earth was only a little higher than it is at present, the two continents were 

 connected and the land animals travelled from one to the other. It was by this 

 route that the mammoth, the mastodon and other large mammals migrated from 

 south-eastern Asia into America. During that period the polar forests pushed 

 their way from their common starting-ground down the eastern shores of Asia and 

 the west coasts of America. It has been already mentioned that west of the Rocky 

 Mountains, about twenty-five species of trees are met with in Canada, which do 

 not occur to the east of them. The forests of the two sides of the Pacific, have 

 a closer resemblance to each other than either has to those of Eastern America. 

 On the Asiatic side of the Arctic Ocean an elevation of northern Siberia and the 

 bottom of the adjacent shallow sea would extend the land northward towards the 

 northern coasts of America and during the long period when the whole polar region 

 was enjoying a hot and afterwards a mild climate, due to the heat of the earth itself, 

 forests, like those of the present tropical and temperate regions would, no doubt, 

 flourish there, as well as in Northern America. As the climate cooled, the various 

 species would gradually migrate southward and settle themselves in the latitudes 

 best suited to their requirements all the way from the tundras to southern Asia. 



