COTEATT DES PRAIRIES AND JNIANITOBA ESCARPMENT. 35 



prominent than this, excepting perhaps the ascent along the similar and 

 parallel Coteau du Missouri. The latter, ho;^ever, lacks the accompani- 

 ment of such a continuous brokd depi'ession beside it. This wide valley, 

 occupied by Lakes Winnipeg, Manitoba, and others, and by the Red and 

 Minnesota rivers, varying in elevation from 710 to 1,100 feet above the 

 sea, is the base of the slowly ascending expanse of the great plains ^\■llich 

 rise thence westward to a height somewhat exceeding 4,000 feet above the 

 sea-level at the foot of the Rocky Mountains, on the international boundary. 

 Most of this elevation is attained by a gradual slope, averaging 4 or 5 feet 

 per mile throughout the distance of 730 miles from the Red River to the 

 mountains; but at two lines, extending from south to north or north- 

 west, first on the west side of this valley and again in the Coteau du 

 Missouri, 100 to 20() miles farther west, the surface rises more rapidly sev- 

 eral hundred feet within a few miles by a terrace-like ascent. The first 

 was the western shore of Lake Agassiz, and continuing- south and s<5utheast 

 held the same relation to an earlier glacial lake which occupied the basiu 

 of the Minnesota and Blue Earth rivers. 



The southern portion of this line of elevation is the massive and high 

 Coteau des Prairies. Its lower continuation from the head of the Coteau 

 des Prairies, west of Lake Traverse, for the next 1 75 miles northward, bears 

 no name, and is scarcely more conspicuous, or in some parts even less so, 

 than the moderate ascent that forms the opposite border of the Red River 

 Valley in Minnesota. Farther north this line of higher land lises abruptly 

 300 to 500 feet in Pembina Mountain, and from 500 to 1,000 feet or more 

 in Riding and Duck mountains and the Porcupine and Pasquia hills. All 

 of these are successive parts of a very remarkable terrace-like escarpment, 

 called by Mr. J. B. Tp-rell the Manitoba escai-pment,^ stretching from North 

 Dakota by the west side of Lakes Manitoba and Winnipegosis to the Sas- 

 katchewan River. Its portions thus differently named are divided by deep 

 and broad valleys eroded by intersecting sti'eams. 



This whole belt of highland, reaching in a nearly direct north-north- 

 west course about 800 miles, may thus be considered in tkree parts. At 

 the south a quarter of its length is the great plateau-like ridge of the 



1 Am. Geologist, Vol. VIII, pp. 19-28, July, 1891. 



