PROGRESSIVE UPLIFT FROM SOUTH TO NORTH. 481 



of the lake basin, reaching north to Gladstone, had been raised nearly to 

 its present height. Then followed a time, during the second third of the 

 lake's existence, in which the district that includes Riding and Duck moun- 

 tains and extends north to the mouth of the Saskatchewan was being rapidly 

 uplifted. But this later northward and northeastward advance of the wave 

 of upheaval had passed beyond the Saskatchewan before Lake Agassiz 

 was reduced to Lake Winnipeg, as is shown by the nearly level Niverville 

 beaches, the latest formed while the ice barrier remained. The rise of the 

 land approximately to its present height is thus known to have followed 

 close upon the glacial recession by which the land was relieved of the ice 

 weight. 



The remnants of the ice-sheet adjoining Hudson Bay were not melted 

 away until the Recent or post-Glacial epoch had begun in the northern 

 United States, their departure being possibly even nearer to the present 

 day than to the time of withdrawal of the ice barrier of Lake Agassiz. 

 Moving onward pari passu with the departure of the ice, the uplifting wave 

 of the earth's crast has raised the basin of Hudson Bay 300 to 500 feet 

 since the sea was admitted to it, and the upheaval there is not yet com- 

 pleted. Though doubtless slower than at first, it is still in progress, 

 according to Dr. Bell's observations, at a probable rate of 5 to 7 feet per 

 ceutmy. 



Tkree stages of the elevation of tliis region from its Champlain subsid- 

 ence are thus indicated by the beaches of Lake Agassiz and the fossiliferous 

 marine beds overlying the till about Hudson Bay, the first extending from 

 Lake Traverse to Gladstone and the south end of Riding Mountain, the 

 second reaching thence probably to the northern and northefistern limits 

 of the area that was occupied by Lake Agassiz, and the third aff"ectiiig 

 the basin of James and Hudson bays. On the common borders of these 

 contiguous areas the uplifts were of course interblended; but it seems to 

 be clearly shown by the Campbell and Niverville beaches that there was 

 essential rest from the uplifting movement, with n permanence of height 

 nearly as now, upon the southern part of the basin of Lake Agassiz while 

 its northern part was rising, and afterward upon the whole of this basin 

 while the country surrounding Hudson Bay has been elevated. A wave of 

 MON XXV 31 



