+ gio = 
. 
254 B. N. A. BOUNDARY COMMISSION. 
of the Winnipeg group of lakes, and the great valley of the Red River 
itself, can be explained; the river cutting downward and westward on 
the sloping surface of the Laurentian rocks, at the expense of the Creta- 
ceous strata, and later, of the limestones of the Devonian and Silurian. 
The subsequent blocking up of the southern exit, and changed direction of 
flow, being a phenomenon only similar to that which is known to have 
taken place with the Great Lakes of the St. Lawrence. 
587. The altitude of Lake Winnipeg is about 710 feet. That of the 
surface of the prairie on the forty-ninth parallel, 786 feet, the depth of 
the alluvial deposits and drift being unknown. At Fargo, the elevation 
of the surface of the prairie is 900 feet, but that of the surface of the 
underlying Cretaceous beds, as proved by boring, is only 680 feet, and the 
rod may not have descended in the deepest part of the old valley. The 
surface of the ground forming the watershed between Traverse Lake and 
Big Stone Lake—as already stated—is only from 960 to 970 feet, and here 
the continuation of the great drift ridge of the Coteau should cross the 
valley. The present surface of the Mississippi at St. Paul is 670 feet. 
Prof. Thomas has drawn attention to the general direction of the tribu- 
taries of the Red River; asa rule those on the west side flow south-east, and 
those on the east side south-west, till they approach the main stream, 
when some of them tend abruptly northward.* This is a sugestive fact, 
as indicating the primitive southern slope of those parts of the hollow 
least encumbered by drift or alluvium. . 
The evidence with regard to the former drainage of the Lake of the 
Woods region, and the course of the tributaries of the Red River, has 
already been fully stated. + 
588. Exactly how the glacial period was introduced, in the area in 
question, or by what phenomena its beginning was marked, it is now 
very difficult, if not impossible to tell. Nor can any reliable estimate of 
its duration be formed, for the effect ofthe later periods has been, not merely 
to obliterate more or less many of the former physical features of the couns 
try, but such as to cover up and conceal those which antecedent glaciation 
may have produced. There is nothing to show, however, that glacial 
*U. S. Geol. Surv. Territ., 1872, p. 283. 
t Since the above was written, I find that similar conclusions have been arrived at by Major General 
G. K. Warren, and published by him as ‘‘ An Essay concerning important Physical Features exhibited in 
the Valley of the Minnesota River, and upon their signification ” being part II. of Report on Minnesota 
River, submitted to Brig. Gen, A. A. Humphreys, Chief of Engineers, Oct. 31,1874. I am indebted to 
Maj. Gen. Warren for copies of his essay, to which I would refer, as throwing very important light on 
some phenomena connected with the glacial period. It is very gratifying to find my conclusion as to the 
former southern outflow of Lake Winnipeg, &c., borne out by an entirely independent study of the Min- 
nesota River, which must have carried its waters. I cannot agree with Gen. Warren, however, in making 
the formation of the great southern outlet post-glacial [loc cit. p. 8,] as 1 think the evidence of its pre-glacial 
formation is complete, and that it was after the glacial period re-occupied. 

Ly 
