93 



Kilometres Lake Agassiz. The sediments at the south 

 end of this basin were brought in very rapidly 

 by a strong system of drainage across the Cret- 

 aceous plateau to the west, and the erosion 

 of the soft rocks of that region provided abun- 

 dant material for filling inequalities in the rock 

 surface forming the bed of the lake. At its 

 highest stage Lake Agassiz extended southward 

 to Lake Traverse in Minnesota and drained 

 to the Mississippi valley. At Winnipeg, the 

 depth of water was about 560 feet (170 m). 

 Beaches along the western margin were formed 

 at several stages of the lake recession and these 

 show an upwarping of the crust. A vertical 

 projection of the beaches accompanying this 

 description shows graphically the amount of 

 this movement. The subsidence of the lake, 

 with the retreat of the ice barrier to the north- 

 east, did not at once alter the direction of 

 drainage, and the southward flow was main- 

 tained for several stages owing to the upwarp 

 to the north. An outlet northward was found 

 while the water was 240 feet (73 m) deep 

 over the position now occupied by the city 

 of Winnipeg. 



In going westward from Winnipeg the rise 

 is very slight across the lower part of the old 

 lake basin, and, since the railway ascends 

 to the rim of the basin on the delta of the prin- 

 cipal stream tributary to the lake, beaches 

 are not strongly in evidence. These are how- 

 ever strongly marked both to the north and 

 south and are indicated in the accompanying 

 illustration. 



55 m. Portage la Prairie — Altitude 851 ft. (259 m). 



88 km. 



62 m. Burnside — Altitude 869 ft. (265 m.). 



100 km. Shortly after passing Portage la Prairie the 

 railway crosses a succession of beaches of the 

 ancient glacial Lake Agassiz: the Burnside 

 beach four miles west of Portage la Prairie, 

 and the Gladstone beach two miles (3.2 km.) 

 beyond Burnside near Rat creek. 

 70 m. Bagot — Altitude 936 ft. (285 m.). 



112 km. 



