72 THE ICE AGE IN CANADA. 



sively shown by several geologists* that in this period 

 the valleys of the great American lakes were excavated, 

 and that the ancient St. Lawrence flowed without any 

 lakes to the sea. The present great lakes are partly 

 dammed up by glacial deposits, and partly produced by 

 warping or differential elevation. It may now be con- 

 sidered as fully established that the great American lakes 

 are not the result of glacial action, but that they are old 

 river valleys excavated in periods of continental elevation, 

 and now dammed up by accumulations of debris and by 

 differential elevation occurring in the Pleistocene period. 

 In the great depression of that period, they spread 

 far more widely than at present, as indicated by the 

 old terraces around them, some of which, according to 

 Spencer, are 1,700 feet above the present water level, and 

 may indicate a period when the whole American land was 

 much lower than at present. (See Spencer, Journal 

 Geol. Society, Vol. XLVI., 1890.) Further, Dr. G. M. 

 Dawson f has shown that in this and previous periods of 

 continental elevation the great fiords and canons of 

 British Columbia w^ere cut out, and quite recently 

 Pettersen has ably applied the same explanation to the 

 fiords of Norway. The latter says : " I have, therefore, 

 after the most careful researches here, yard by yard, and 

 extending over many years, come to the conclusion that 

 the Balsfjord is not of glacial origin, hut formed an incision 

 or depression in the mountains of older origin than the 

 glacial age. And this conclusion, I believe, may, in the 

 main, apply to the question of the formation of all fjords in 



* Newberry, Hunt, Spencer. 



t Superficial Geology of British Columbia, 1878. Later Physio- 

 graphical Geology of the Rocky Mountains of Canada, Trans. R.S.C., 

 1890. 



