76 THE ICE AGE IN CANADA. 



cataclymic oscillations of level and a partial subsidence, 

 which is apparently still in progress.* 



For the evidence of this history I may refer to the 

 papers cited in the notes, f where abundant facts will be 

 found relating more especially to Canada, and, so far as 

 my reading extends, they will be found applicable, with 

 certain modifications of details, to other parts of the 

 northern hemisphere. 



In closing this section, I desire to refer to the map 

 (Fig. 6, B.) of the geography of North America in the 

 early Pleistocene, the height of the glacial period. At 

 this time I believe the northern half of North America 

 consisted of three large and mountainous islands, clad for 

 the most part with neve and glaciers, and surrounded by 

 ice-laden seas and straits. The conditions, it will be seen 

 at a glance, were most favourable to refrigeration, by 

 accumulation of floating ice in temperate latitudes, while 

 the arctic climate may have been little more severe than 

 at present, and the extreme opposite of those which 

 existed in the warm period of the early tertiary, when 

 the northern end of the continent was closed against the 

 arctic currents, and when the interior continental plateau 

 constituted a northern extension of the warm waters of 

 the gulf of Mexico. This map implies differential de- 

 pression of the western plains as compared with the 

 mountains, and of the northern as compared with the 

 southern portions of North America, and an opening for 



* According to Merrill and Lendenkeld (American Journal Science, 

 June, 1891), alternate depression to the amount of 150 feet and eleva- 

 tion to the amount of 400 feet have occurred in the valley of the 

 Hudson river since the glacial period. See also Acadian Geology, 

 article "Submarine Forests." 



t Also notes on Canadian Pleistocene, 1872; Acadian Geology, 1878. 



