No. 7.] DANA — DISCHARGE OF LAKE WINNIPEG. 439 



The heights on Minnesota River are (Winchell's Report) : 



Surface of bordering plateau near Big Stone Lake 1,125 



At Mankato, 145 miles south 975 



At Shakopee, 50 miles northeast 925 



At junction Avith the Mississippi 800 to 820 



7. The slope of the hike-bottom prairie is northward, toward 

 Lake Winnipeg; and, from the 49th parallel, according to 

 Dawson, it is nearly six inches per mile ; the mean slope from 

 Moorhead in Minnesota, 150 miles south of the 49th parallel, 

 is little less than one foot per mile. 



The slope of the bordering plateau nortliward from Lake 

 Traverse to Lake Winnipeg, 315 miles, is about one foot per 

 mile; for 1,125-810=315. 



The slope of the bordering plateau along the Minnesota from 

 Big Stone L'ike to Mankato (145 m.) is southward and about 

 one foot per mile; for 1,125-975=150. 



8. Tlie material of the lake-bottom, where examined by Mr. 

 Dawson, is mostly yellowish chiyey earth or loess, containing 

 calcareous matter enough to effervesce freely with acids; the 

 upper portion is rarely so coarse as to be called sand, though 

 sometimes an arenaceous clayey material ; that of the border is 

 also somewhat arenaceous. Tlie depth of this lake-bottom de- 

 posit is generally 40 feet or more over the central portions, but 

 it thins towards the sides. This point is illustrated in the plate 

 facing p. 248 in Dawson's Report. He represents the loess as 

 overlying stratified drift and boulder clay. The surface of the 

 prairie rises somewhat toward the sides ; but whether the de- 

 pression is more than would result from the drying (and conse- 

 quent contraction) of so much wet loam after the disappearance 

 of the lake, is not ascertained. It is rare to find anything like 

 pebbly areas or pebbles over it. 



9. The outline of the lake-bottom prairie has the appearance 

 of being, so far as it extends, the outline of the great Winnipeg 

 Lake, and is so recognized by Warren, Dawson and others. 



10. The material of the bordering high plateau alono- both 

 the Red River portion and the Minnesota is coarse gravel and 

 sand ; much of it unstratified till, much, more or less stratified ; 

 and the upper surface is often pebbly or stony, with occasional 

 boulders. 



Roseau River, for 25 miles east of the western edo-e of the 

 plateau, says Dawson (p. 214), has cut deeply into the plateau 



