
-. 
he 
GLACIAL PHENOMENA AND SUPERFICIAL DEPOSITS. 235 
Red River, but wanting the backing of the Lignite Tertiary plateau, it 
appears to become more diffuse, and spreads more widely over the 
country. The drift deposits do not form the high ground, but are merely 
piled upon it; and it seems to be based at no very great depth on a 
nucleus of hard paleozoic rocks, over which the Cretaceous is generally 
thinly spread, but which appear at the celebrated Pipe Stone Quarry 
and elsewhere. From what I can learn, it would appear that the 
so-called Coteau de Prairies and Coteau de Missouri, between which a 
distinction is often here made, are parts of the same great feature. Their 
elevation is similar, and nearly the same as that of the Coteau on the 
Line, and they are equally characterized by the immense profusion of 
erratics, with which they are strewn, and by basin-like swamps and 
lakes. 
542. The following description of the Coteau south of the Line, by 
Prof. Thomas, is the best I have been able to find for that,region, and 
will be valuable as a term of comparison. ‘The surface of the country 
between the valley of the Red River on the east, and Missouri River on 
the west, may be described, in general terms, as consisting of high, roll- 
ing prairies, intersected by the vallies of a few streams which run south, 
But this general contour is interrupted by two elevated plateaus, which 
stand high above the general level, as monuments reared by the vast 
aquatic forces of the past, as if to give us some idea of their stupendous 
power. The smaller of these elevated plains, the Coteau des Prairies, 
extends from a point about forty miles west of the north end of Lake 
Traverse, latitude 46°, longitude 97° 30’, southward, expanding and 
somewhat dividing towards its southern extremity. The western arm of 
this southern extension encroaches close upon James River Valley, about 
latitude 44° 15/, where it ends; the other arm reaches south-east, passing 
down on the east side of the head waters of Big Sioux, and graduaily 
fades out in the southwest corner of Minnesota. The elevation of its sur- 
face averages nearly 2,000 feet above the level of the sea, varying from 
1,860 feet, to 2,040 feet, showing arise above the plains east of it of about 
800 feet, and above the valley west of it of 700 feet. The other plateau 
is the Coteau of the Missouri. This hugs the valley, and follows the 
course of the Missouri, northward from Fort Sully to the great bend of the 
river near the mouth of the Yellowstone. Here it it recedes, and extends in 
a northwest direction into British Possessions, where it gradually fades 
out and is lost (?). It varies in width from thirty to fifty miles, and in 
height from 1800 to 2000 feet above the sea; but the surface is more irre- 
