EELATIONSniP TO THE ICE-SHEET. 3 



and west borders of the Red Rh-er Valley and the base of the Riding and 

 Duck mountains. Its surface during storms was raised into waves which 

 formed well-defined beach ridges of gravel and sand, and these are found 

 at many successive levels, showing that the area and depth of the lake 

 were gradually diminished. Before these deserted shores and the inclosed 

 lacustrine area were examined in the field work for this report, their char- 

 acter had been observed and was generally attributed to lake action by the 

 immigrant fiirmers, wdio in many instances selected the beach ridges as the 

 sites of their dwellings. 



Intervals of small vertical amount divide the consecutive beaches, 

 from the highest to the lowest. Through the earlier and proliably greater 

 part of the dui'ation of the lake it outflowed southward bv the way of 

 Lake Traverse, Browns Valley, Big' Stone Lake, and the Minnesota River 

 to the Mississippi. Seventeen shore-lines on the northern ])ortion of the 

 lake area were formed contemporaneously with this southern outlet. I^ater 

 the lake was further reduced through stages shown liy fourteen shore-lines, 

 while it outflowed by successively lower avenues of discharge northeast- 

 ward. Finally it was reduced to lakes Winnipeg, ]\Ianitoba, and Winni- 

 pegosis, which are the lineal descendants and representatives of Lake 

 Agassiz. 



RELATIOXSHIP TO THE ICE-SHEET. 



The conditions to which Lake Agassiz owed its existence, however, 

 w^ere very unlike those of the present time. It could not have been held in 

 a landlocked basin, for there has been no subsidence of the country between 

 this area and Hudson Bay since the Glacial period. Instead, the area of 

 Lake Agassiz and all the region northeastward to Hudson Bay and Strait 

 have experienced a gradual uplift during the time of the departure of the 

 ice-sheet and subsequently. As shown by the northwardly ascending 

 shore-lines of this lake and by fossiliferous marine beds overlying the 

 glacial drift on the lower country adjoining Hudson Bay and along the 

 Ottawa and St. Lawrence rivers, the vertical extent of this uplift was 

 gi'eatest toward the north and east. It was little at Lake Traverse, but 

 amounted to 400 or 50U feet in Manitoba, and was approximately 500 to 

 600 feet on the southwest side of Hudson and James bays and upon all 



