380 THE GLACIAL LAKE AGASSIZ. 



tail Creek and the Oak and Little Saskatchewan rivers (p. 190). It was 

 deposited in this delta chiefly during tlie early Herman stages of the lake, 

 as is indicated by the elevation of the outer part of its principal expanse; 

 and its deposition continued until the ice-sheet was melted away on Riding 

 Mountain and the upper Assiniboine. The erosion of the Assiniboine Valley 

 above Brandon also supplied a considerable part of the delta. During the 

 ensuing stages of Lake Agassiz, to those of Gladstone and Bumside, 

 the border of this great delta was undergoing erosion liy the lake waves 

 and shore currents, by which its outer portion was spread in more gentle 

 slopes, extending farther into the lake, and much of it was swept southward 

 along the shore. 



By this erosion of the sloping face of the delta, and especially by 

 earlier transportation into the deep water of the lake while the gravel and 

 sand were being deposited in its western embayment between the Tiger 

 Hills and Riding Mountain, a large expanse of fine clayey sediment of the 

 same origin with this delta was spread far into the lake, extending to 

 the east beyond the Red River and to the south beyond the international 

 boundary. This deposit of lacustrine silt covers the till from the eastern 

 and southeastern limits of the delta, as before defined, to the low ridge first 

 east of the Red River, about 10 miles east of P^merson, while similnr sedi- 

 ments cover the central part of the Red River ^^lUey southward to Goose 

 Rapids, more than 100 miles east-southeast from this delta. Toward the 

 north and northeast, lacustrine sediments and subsequent alluvial deposits 

 associated with the Assiniboine delta cover the nearly flat country north 

 from Burnside, Portage la Prairie, and High liluff" to Lake Manitoba. On 

 this area the watershed between the Assiniboine and Lake Manitoba is very 

 low, and the river has sometimes overflowed its low banks, sending part of 

 its floods north to the lake, which in turn in its highest stages has occa- 

 sionally become for a sliort time tributary to the lower ])art of this river. 

 But the Transportation of the silt in the lake was of less extent in this 

 direction tlian to the east and south, as is shown by areas of till on both 

 sides of the Big Grass Marsh, west of Lake Manitoba, and from townships 13 

 and 14, range 5, southeast of this lake, eastward to Shoal Lake, Stonewall, 

 and Lower Fort Garry. 



