372 THE GLACIAL LAKE AGASSIZ. 



The western and southern limits of the phateau are those ah-eady noted, 

 and on the east its boundary runs north and northwest from Treherue to 

 Sydney and Neepawa. The area of the phateau is aljout 1,300 square 

 miles, and the eastern slope adds to this fully two-thirds as much, making 

 the total area of this delta somewhat more than 2,000 square miles. 



The thickness of the Assiniboine delta is seldom shown by wells, 

 which generally obtain ;i plentiful supply of water upon this area within 

 moderate depths, ranging from 10 to 50 feet. In some localities, however, 

 near the great valley that the Assiniboine has cut through the delta, the 

 plane of saturation probably lies nuich deeper, and wells nuist be sunk 100 

 feet or more to obtain water. Better measures of the depth of these gravel 

 and sand deposits are supplied by the valleys of the Assiniboine and other 

 streams, which are eroded in their deeper portions 100 to 200 feet below 

 the top of the delta plateau before reaching the underlying till. Deep 

 ravines are especially numerous on the northern part of the delta, where 

 many springs issue near the plane of junction between the porous gravel 

 and sand beds and the till, giving rise to the Squirrel, Pine, and Silver 

 creeks, which flow northeast to the White Mud River. The descent of 200 

 to 300 feet made within a few miles upon the eastern face of the delta is a 

 further indication of its tliickness, Avhicli reaches its maximum at the verge 

 of the plateau. In the vicinity of the outcrop of Niobrara beds on the 

 Assiniboine, in section 36, township 8, range 11, the thickness of the delta 

 gravel and sand appears to be about 200 feet; and it probably ranges from 

 100 to 200 feet along the outer limit of the plateau tlu-ough the greater 

 part of its extent of more than 50 miles. The average thickness of this 

 very extensive delta is probably between 50 and 75 feet. Computing its 

 volume for an average of 50 feet on an area of 2,000 square miles, it is 

 found to be about 20 cubic miles. 



Fig. 16 presents a section crossing the central part of the Assiniboine 

 delta, along the line of the Canadian Pacific Railway from Brandon to 

 Poi-tage la Prairie. 



Fifty miles east-southeast from Brandon the highest portions of the 

 surface of the delta south of the Assiniboine and east of the Cypress, where 

 it has not been heaped in sand hills by the wind, are 1,225 to 1,240 feet 



