
218 B. N. A. BOUNDARY COMMISSION. 
Lake, and finding the lowest part of its rim in the pre-existing notches 
across the junction of formations at Rat Portage, would pass over, and 
pursue its way by the Winnepeg River to Lake Winnepeg. This river 
does not follow a true river-valley, but falls rapidly westward through a 
series of rock-basins, which often lie transverse to its course; passing 
down the slope of the Laurentian axis, and accommodating itself to the 
surface of a country previously shaped by other agency. The subsequent 
great spread of the Lake of the Woods, southward, must have been due 
chiefly to the action of the waves on the incoherent drift material, a pro- 
cess which is still going forward rapidly. : 
Drift deposits of the Second Prairie Plateau West of the Red River, and 
of Turtle Mountain. 
495. In proceeding westward with an examination of the drift and 
superficial deposits, those of the Red River Valley would next claim 
attention. As, however, they belong to a later period, than those of the 
higher’region to the west, and represent a distinct phaze in the great 
series of physical changes which have passed over the interior of the 
continent, it will be better to reserve them for subsequent consideration. 
Beginning at the. Escarpement of Pembina Mountain, the western shore 
of the former Great Lake of the Red River Valley—I shall describe those 
sections of the later deposits which seem to be typical. 
» 496. The surface of the second prairie steppe, appears to be almost 
everywhere thickly covered with drift deposits, and the undulations and 
slight irregularities of its outline, are in the main due to the arrangement 
of these surface materials, and though no doubt somewhat modified by 
sub-aerial waste, does not seem to have been much changed in this way. 
Over large areas, no system of coulees or stream vallies is to be found, and 
the generally undulated surface, must be due to original inequality, of de- 
position, denudation having acted only in removing a certain quantity of 
the material from the rounded hillocks, into the intervening gentle hollows. 
Such an arrangement, implies not only the porous nature of the subsoil, 
but is in accord with the comparatively very small rain-fall of the region, 
and would tend to show, that at no time since its emergence has the rain-fall 
been very great. The drift material is found generally to consist in great 
part of local debris, derived from the immediately underlying soft forma- 
tions, but this is always mixed with a considerable quantity of far-trans- 
ported material, which is generally most abundant in the upper layers. 
Large erratics are in some localities very plentifully strewn over the plain, 
