252 B. N. A. BOUNDARY COMMISSION. 

Prof. Winchell, who has visited the locality, thus describes it:—“A 
continuous valley, between bluffs of the same form and appearance, and 
of nearly the same depth, connects the two lakes, giving the impression 
of one valley instead of two. The short interval constituting the divide 
between the two lakes is usually without water, but is often overflowed 
by the spring freshets, when a continuous overland watercourse is estab- 
lished between the Gulf of Mexico and Hudson’s Bay.” * 
581. The waters of the lake of the Red River Valley, even if ie 
attaining the level of the margins of the great alluvial deposit on the 
Boundary-line, would flow freely through this gap, which must then have 
formed a narrow strait, connecting the great northern lake, with that 
occupying the vallies of the Mississippi and Missouri; and at an earlier 
stage in the history of the continent, when the waters were deeper, the 
communication must have been quite free. In some parts of the loess 
deposit of the Missouri, the remains of fresh-water and land shells, 
mingled with bones of the Bison, the Mastodon and other lately extinct, 
or still surviving forms, have been found.t The fresh-water origin of 
the deposit is thus demonstrated, but the further difficulty at once pre- 
sents itself, that there is no trace of any efficient barrier southward to 
hold in the great lake now required, and if the depression of the con- 
tinent was such as to render a barrier unnecessary, the water filling 
the vallies must almost certainly have been that of the sea. This has 
been ingeniously accounted for by supposing that in such a comparatively 
land-locked area, the flow of fresh water from the rivers and streams 
would be sufficient to effect the exclusion of the salt. 
582. Information is wanting as to the nature of the barrier existing 
in the northern part of the great Red River Valley, which prevented the 
waters of the region from draining away, as they now do, by a hollow 
across the Laurentian plateau. It may probably, however, have con- 
sisted of moraine rubbish, or boulder-clay. On the supposition that the 
deposits were formed in a fresh-water arm of the sea, which opened 
southward, it cannot be supposed that any passage existed northward 
also, or the tidal currents would have rendered the entire area salt. 
583. The wide trough-like valleys, much depressed below the 
general level of the plains in which most of the rivers of the west flow, 
and in which the river itself is generally small and pursues a winding 
course, usually show a considerable thickness of nearly horizontal 
alluvial deposits, which, like that of the Red River Valley, have been 
*Second Annwal Report Geol. Surv. Minnesota. + Hayden. Final Report on Nebraska, p. 10. 
