242 ASSINNIBOINE AND SASKATCHEWAN EXPEDITION. 



with the flanks of the Eocky Mountains, trending first 

 north and then north-westerly. The North Branch and 

 the main Saskatchewan indicate approximately its low 

 northern boundary. 



SURFACE FEATURES. 



Lake Winnipeg, at an altitude of 628 feet above 

 the sea, occupies the lowest depression of this great 

 central basin, covering, with its associated Lakes Mani- 

 tobah, Winnepego-sis, Dauphin, and St. Martin, an area 

 slightly exceeding 13,000 square miles, or nearly half as 

 great an extent of the earth's surface as is occupied by 

 Ireland. 



The country possessing a mean elevation of one hundred 

 feet above Lake Winnipeg is very closely represented by 

 the outline of Pembina Mountain, forming part of the 

 eastern limit of the Cretaceous Series in the north-west 

 of America, as represented on the geological map. 



The area occupied by this low country, which includes 

 a large part of the valley of Eed Eiver, the Assinniboine, 

 and the main Saskatchewan, may be estimated at 70,000 

 square miles, of which nine-tenths are lake, marsh, or 

 surface rock of Silurian or Devonian age, and generally so 

 thinly covered with soil as to be unfit for cultivation, 

 except in small isolated areas. 



Succeeding this low region there are the narrow ter- 

 races of the Pembina Mountain, which rise in abrupt steps, 

 except in the valleys of the Assinniboine, Valley Eiver, 

 Swan Eiver, and Eed Deer's Eiver, to the level of a 

 higher plateau, whose eastern limit is formed by the 



Warren, Top. Eng., ordered by the Honourable Jefferson Davis, Secretary 

 of War, to accompany the Reports of the Explorations for a Railroad 

 Route to the Pacific. 



