230 THE GLACIAL LAKE AGASSIZ. 



300 to 500 feet below its present level; that the Ottawa basin was de- 

 pressed 400 to 500 feet; the St. Lawrence Valley, about 250 feet at the 

 mouth of Lake Ontario, at least 560 feet at Montreal, and 375 feet opposite 

 the Saguenay ; and the country bordering- the Gulf of St. Lawrence, about 

 200 feet at the Bav of Chaleurs, with diminishing amount thence to the 

 east and south, ceasing in Nova Scotia and southeastern Massachusetts. In 

 the Mackenzie basin, evidences of marine submergence since the Glacial 

 period have not been found; but thev are discovered, up to heights of 100 

 to 300 feet, on the Pacitic coast of the drift-bearing area. It is probable, 

 however, that these elevations of marine deposits are not full measurements 

 of the depression under the ice-load. The nearly complete uplifting of the 

 basin of Lake Agassiz while the ice-sheet was retreating' from it and was 

 still the barrier of the waning glacial lake proves that the reelevation 

 closely followed the departure of the ice, and suggests that in the districts of 

 these marine beds some uplifting may have been done "while the ice above 

 was becoming thin, but had not wholly disappeared, or at least before its 

 retreat had opened ways of ingress for the sea. 



Depression and reelevation of the basin of Lake Agassiz shown hy differen- 

 tially uplifted beaches. — If we next seek a measure of the subsidence of the 

 basin of Lake Agassiz while it was ice-burdened, no marine beds above 

 the drift in this district can aid in giving an answer, but we must look 

 to the known amount of northward uplifting of the once level beaches, and 

 from tliis differential elevation it seems well-nigh sure that the maximum 

 depression which this basin underwent failed to sink its lowest part, the 

 shallow bed of Lake Winnipeg, to the sea-level. The central and northern 

 portion of the area of Lake Agassiz, where the great lakes of Manitoba are 

 now outspread, was depressed apparently 400 or 500 feet, carrying' the pres- 

 ent shores of Lake Winnipeg down to an altitude of only 300 or 200 feet 

 above the sea; but the bed of this lake, which is less than 100 feet deep, 

 was still abo-s^e the ocean. The amount of si;bsidence here is thus found 

 to be harmonious with that of other parts of our glaciated area which bor- 

 dered the oceans and Hudson Bay. As a whole, the ice-enveloped portion 

 of the continent is seen to have sunk slightly more in its central region than 

 on its boundaries. The vertical extent of the maximum known depression. 



