36 THE GLACIAL LAKE AGASSIZ. 



Coteau des Prairies. Next, a nearly equal extent, is the less elevated high- 

 land that gradually rises west of the Red River Valley, between it and the 

 Sheyenne River and Devils Lake. The northern half is a somewhat inter- 

 rupted, mountain-like escarpment, lying- mainly in JManitoba, whose top, 

 like the highland just mentioned, is the A'erge of plains that extend thence 

 westward, generally with a nearly level but slowly ascending surface, 

 excejjting where the}' are channeled and irregularly sculptured by stream 

 erosion. Occasional groups of hills also rise above the average height of 

 these plains, as Turtle Mountain and others farther northwest. Beneath 

 their thin covering of drift these billy tracts contain remnants of older for- 

 mations, of which the portions formerly continuous between these elevations 

 and on each side have been eroded and carried away. 



The accompanying maps, which form Pis. IX and X, giving altitudes 

 as determined chiefly by railway surveys upon the area of Lake Agassiz 

 and the adjoining country, show the extent and height of the Manitoba 

 escarpment, of portions of the Coteau des Prairies and the Coteau du 

 Missouri, and of the region extending eastward from Lake Agassiz to 

 Hudson and James bays and the great Laurentian lakes. 



THE COTEAU DES PRAIRIES. 



A large area extending from south-southeast to north-northwest in 

 southwestern Minnesota and the northeast part of South Dakota, and ter- 

 minating on the west side of the south end of Lake Agassiz, has an eleva- 

 tion from 500 to 1,000 feet above the Minnesota River, and from L300 to 

 2,000 feet above the sea. Upon this highland district are the sources of 

 the Lac qui Parle, Yellow Medicine, Redwood, and Cottonwood rivers, trib- 

 utary to the Minnesota; of the Des Moines River; and of the Little Sioux 

 and Big Sioux rivers, tributary t(j the Missouri. The outermost of the series 

 of terminal moraines of the waning ice-sheet, denominated the Altamont 

 moraine, generally lies on the highest portion of this area, which extends 

 in Minnesota from southeastern Noliles County in a nearly north-north- 

 west course, passing west of Worthing-ton, through southwestern ]\Iurray 

 County, the northeastern township of Pipestone County, and southwestern 

 Lincoln f!ountv, by the west ends of Lakes Benton, Shaokatan, and Hen- 



