10 THE ICE AGE IN CANADA. 



coasts would raise the temperature of their waters. Any 

 change that would allow the equatorial current to pursue 

 its course through to the Pacific or along the great inland 

 valley of North America, would reduce the British seas to 

 a boreal condition. 



" The boulder formation and its overlying f ossiliferous 

 beds prove, as I have in previous papers endeavoured to 

 explain with regard to Canada, and as has been shown by 

 other geologists in the case of other regions, that the land 

 of the northern hemisphere underwent in the later 

 tertiary period a great and gradual depression and then 

 an equally gradual elevation. Every step of this process 

 would bring its modifications of climate, and when the 

 depression had attained its maximum there probably was 

 as little land in the temperate regions of the northern 

 hemisphere as in the southern now [while that which 

 remained above water was high and mountainous].* This 

 would give a low mean temperature and an extension to 

 the south of glaciers, more especially if at the same time 

 a considerable arctic continent remained above the waters 

 [as a gathering ground], as seems to be indicated by the 

 effects of extreme marine glacial action on the rocks 

 under the boulder clay. These conditions, actually indi- 

 cated by the phenomena themselves, appear quite sufficient 

 to account for the coldness of the seas of the period, and 

 the wide diffusion of the gulf stream caused by the 

 subsidence of American land, or its entire diversion into 

 the Pacific basin,f would give that assimilation of the 



* The important question of differential elevation has been solved in 

 great part since this was written, aud would much strengthen the 

 argument. 



t This is often excluded from consideration, owing to the fact that 

 the marine fauna of the gulf of Mexico differs so much from that of the 



