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262 B. N. A. BOUNDARY COMMISSION. 1 
are chiefly borrowed from a careful study of the region south of the — ; 
great lakes of the St. Lawrence, but as he includes the valley of the Red 
River, and the entire North-west, in his deductions, its mention here may 
not be inappropriate. The most suggestive part of the paper is that in 
which—like Mr. Belt— he traces the necessary production of a great — 
inland sea, or lake, as the foot of such an ice-sheet as that supposed, 
gradually retreats northward down an inclined plane. 
605. Ingenious as this hypothesis undoubtedly is, its inapplicabiliijels 
the phenomena and physical features of the region now under considera- 
tion, must be at once apparent. The great depth to which submergence took 
place is one of the most patent difficulties. From the description of the 
Red River Valley ali eady given, it will be evident that the entire drainage 
of the great lake must have passed southward byit. There is here no 
range of mountains to be crossed, and unless the retreat of the glacier 
Was very rapid, no reason can be assigned, why a channel once formed, 
should not have been cut down through the gentle swell of the watershed, 
and remained the permanent exit of the drainage of the country. Again, 
the distribution of northern erratics in lines fixed by the altitude of the 
country, and their equal spread over the central and marginal regions of 
the plains, and the interpenetration of the eastern and western drift, do 
not admit of explanation on the supposition of a southward ‘moving ice 
sheet ; nor does the surface of the country show any trace of the progress 
of such a mass. The whole question is a very interesting one, and it 
would seem probable that a solution once arrived at, will be found to 
apply equally to North America and Northern Asia. 
Post-Glacial Phenomena. 
606. The existence of a period characterized by great rainfall, or 
pluvial period, has been very generally supposed for the West. Such an 
event may probably have supervened at the end of the epoch of glacia- 
tion, but it would seem that much of the evidence brought to pee its 
occurrence is not of the most unexceptionable nature. 
607. Chief among the phenomena which at first sight seem to imply 
the action of large bodies of running water, are the great vallies which the 
streams of the prairie country, themselves often so insignificant, have 
produced in the yielding strata. These vallies, like that of the Pembina 
River, are sometimes more than three hundred feet in depth below the 
plain, and over a mile in width; and are frequently depressed more than 
one hundred feet below the general surface. The stream generally occu- 

