236 B. N. A. BOUNDARY COMMISSION. 
gular than that of the other Coteau, portions of it rising as much as 200 
feet above the general average. The general elevation corresponds very 
closely with that of the Coteau des Prairies, showing very clearly some 
relation between the origin of the two. On each are numerous small 
lakes, mostly impregnated more or less with saline matter, and at many 
points on each boulders are quite plenty.”* 
543. Dr. Hayden, treating of the same region, writes: “North of 
the Missouri River, from the Big Sioux River to Fort Clarke, there are 
districts where one might walk for miles across the plains, and over the 
hills without stepping upon the ground, so closely paved is it with worn 
or partially-worn boulders.” + Prof. Winchell describes the extreme 
south-eastern part of the Coteau, near Lake Traverse, as characterized 
in a similar way, by the abundance of erratics, which, though some 
limestone boulders occur, are chiefly of granite.t Minne Wakan, or 
Devil’s Lake, in the watershed region of northern Dakota, may be but 
a larger example of the kind of lakes characteristic of the Coteau. Its 
waters are saline, and its shores appear to be fringed with innumerable 
boulders of great size. 
544. Inthe Missouri Coteau, we find a natural feature of the first 
magnitude. A mass of glacial debris and travelled blocks, with an 
average breadth of, perhaps, thirty to forty miles, extending diago- 
nally across the central region of the continent, with a length of about 
eight hundred miles. It would appear to go far toward satisfying the 
requirements of the theory which accounts for the glaciation of northern 
America and Europe, by the southward progress of a great polar ice-cap. 
It may be supposed that a projection of this great ice-sheet, filled the 
whole northern part of the interior of the continent, from the high 
ground at the foot of the Rocky Mountains on the west, to that of the 
Laurentian plateau to the east. It would be supplied by ice generated 
in the polar regions, and fed also by that of the Rocky Mountains and 
Laurentian axis at its sides, and may be supposed to have passed south- 
ward, impressing on the country all the features which now characterize 
it, and especially excavating the basins of the great series of lakes which 
lie along the western base of the Laurentian. | Hemmed in on the 
west by the higher ground of the watershed, it may be supposed to have 
been forced eastward, and leaving the Coteau as a gigantic lateral 
moraine, to have sent a tongue far southward in Dakota and Minnesota 
— 


*U.S. Geol, Surv. Territ., 1872, p. 294. + U.S. Geol. Surv. Territ., 1867-69, p. 174 
t Second Annual Report Geol, Surv. Minn., 1874, 

“a 
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