106 THE GLACIAL LAKE AGASSIZ. 



valley plain doubtless also consists of Cretaceous shales, perhaps chietly 

 the Niobrara and Fort Benton formations, beneath the envelope of glacial 

 drift. Farther east and southeast, througli northern and central j\Iinnesota, 

 it seems certain that at least many Cretaceous knobs and hills thus far had 

 escaped the general Tertiary- and early Pleistocene denudation, but most of 

 them were leveled during the Ice age and mingled with the glacial ch-ift. 

 Westward from the Pembina and ilanitoba escarpment the Fort Pierre 

 formation generally constituted the preglacial surface, and is now the floor 

 on which the ch-ift lies, until it is succeeded by the Laramie series. This 

 again includes especially enduring beds, which have caused the preservation 

 of extensive outlying areas, as the Turtle ilountain and probably other 

 masses of hills farther north, situated many miles east of the principal 

 Laramie outcrop. In the same way that tlie Fort Pierre formation makes 

 the escarpment west of the valley of the Minnesota and Red rivers and the 

 Manitoba lakes, the Laramie beds, underlying the drift, make the greater 

 part of the ecj^ually prolonged terrace-like highland of the Coteau du Mis- 

 souri from South Dakota northwesterly through North Dakota, Assiniboia, 

 and Saskatchewan. Numerous outliers exist, however, east of the main 

 course of this coteau, in the region crossed by the North Saskatchewan 

 River. 



The course of the preglacial rivers flowing from the Cretaceous area 

 west of Lake Agassiz, after the late Pliocene uplifting of the continent, 

 probably coincided approximately with the present avenues of ch-ainage 

 throughout the region north of the international boundary, in the Assini- 

 boine, Saskatchewan, and Athabasca basins. In North and South Dakota, 

 the present channel of the Missouri River, as shown by Gen. G. K. Warren^ 

 and by Prof. J. E. Todd, dates only from the Glacial period, this great 

 stream having- been turned aside by the ice-sheet to the west and south 

 from its preglacial course, which may have occupied the valley of the 

 James or Dakota River, nearly parallel with tlie Missouri of to-day, or 

 perhaps continued east to the most southern bend of the Souris River, or 

 to the- Sheyenne and Red rivers. Professor Todd finds also in the topog- 

 raphy of that region evidence that in preg-lacial time the great tributaries 

 coming from the west to join this part of the Missouri, namely, the Cannon 



'Annual Report of the Chief of Engineers, U. S. Army, for 1868, pp. 307-3T4. 



