= 
260 B. N. A. BOUNDARY COMMISSION. 
ward by the high ground beyond the position of the present Saskatchewan 
River. At this time, the north and south branches of the Saskatchewan 
formed separate rivers, and divided between them the whole of the 
drainage of the third plateau. Turtle Mountain, and other similar accumu- 
lations of drift, and the high hills of the Cretaceous, overlooking Manitoba 
Lake, formed islands or shoals, The edge of the Pembina escarpment 
and the second steppe next becoming the shore, the united waters of 
the Saskatchewan, the Assineboine, and other smaller streams, flowed 
eastward into the inlet of sea-water, occupying the lowest prairie level, 
which, as the elevation continued, became that great lake of the Red 
River Valley, the history of which has been already traced. There is 
evidence, too, to show that as the Laurentian region rose above the water, 
it was again covered with glaciers for a short time; but that these did 
not last till the very close of the submergence, appears to be shown by 
the very fine character of a!l the later deposits of the Red River Valley. 
The few fragments of rocks which are found, being not more than may, 
with probability, be attributed to the ice of the great lake itself. 
602. In attributing the glacial phenomena presented by the central 
plateau of the continent, almost entirely to sea borne ice-bergs, I have 
adopted that explanation which appeared on consideration of the facts, 
to embrace them best, and which would account for them most simply. 
In so doing I am in accord with Dr. Hector, and also I believe with Dr. 
Hayden; who have studied the phenomena most extensively on the 
ground. That some circumstances, however, give at least negative 
evidence against marine glaciation, must be admitted. The most 
important of these is the complete absence, so far as I have observed, of 
any marine animal remains in the drift. Thisis found equally over the 
entire western portion of America, and though it has been supposed to 
show that the drift was deposited in fresh water, this explanation does 
not seem to remove the difficulty. It is impossible to imagine a sub- 
mergence so great in amount as to overflow nearly all the barriers, with 
the continued exclusion of salt waters; and though the absence of 
marine shells is remarkable, on one supposition, that of lacustrine forms 
is almost equally so, on the other. That molluscous remains might have 
been preserved, had they been imbedded in the deposit, is shown by the — 
occurrence of specimens of Cretaceous or Tertiary Ostreas. The non- 
occurrence of molluscs in great deposits older than the drift, and known 
to be of marine origin, is however, an accepted fact ; and in such conglo- 
meritic beds as those of the drift, it is most frequently observed, Recent 




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