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of the height of land'* and though such a two-fold division might be made in the
Mackenzie basin alsa, we have not’as yet sufficient information of the topography
to enable us to make it. The boundary of the plateau :is marked by a series of
north facing escarpments which extend from near Fort Smith on Slave river
northwesterly along the south side of Great Slave lake and thence at an equal
distance along Mackenzie river to the Liard in longitude 122 degrees. Here the
escarpment is lost, although from McConnell’s? observations it may swing south-
west along the valley of Liard river. South of Fort Smith the plateau seems to
merge into the Laurentian plateau.

Unlike the escarpment in Manitoba it is here not coincident with the eastern
boundary of the, Cretaceous rocks, but is built mainly out of Paleozoic limestones
which overlie softer shales and so, in the course of erosion, give steepness to the
slope. The smaller streams that break through from the plateau to the lowland
all do so with high falls or strong rapids. Falls exist along this line on Little
Buffalo river, Hay river, and Beaver river, and strong rapids occur at corre-
sponding points on Buffalo river, Trout river, and the Liard. The larger streams,
namely the Peace and the Athabaska, are, however, graded throughout and cut
picturesque, terraced valleys in the plateau, that become gradually deeper and
deeper to the southwest as the mountains are approached. For example, the
valley of Peace river at Fort Vermilion is only about 100 feet deep, whereas
at the mouth of Smoky river 300 miles farther upstream it is 700 feet deep and
has a width of about 2 miles.

The top of the escarpment stands about 400 feet above the level of the adja-
cent lowland and the surface then rises gradually southwest and west to the foot-
hills of the Cordillera. The slope, however, is so gradual that the smaller streams
which have not the power to cut graded valleys from the plateau to the low-
land, are comparatively sluggish in the plateau and are rapid and broken only
where they descend through the escarpment. The surface, therefore, is mono-
tonous and outcrops of the solid rocks are rare, and because the drainage is
immature, muskegs are abundant and lakes fairly numerous. There are also
many areas of open prairie land, especially in the basin of Peace river where
settlement by agricultural communities is rapidly taking place.

The surface of the plateau is relieved by several higher plateaus or ridges
which rise 1,000 or 2,000 feet above it. Of these, Caribou mountain, or as it
should more correctly be called, Caribou plateau, is situated between Peace river
and Great Slave lake east of Hay river and covers an area of about 8,000 square
miles. From the incomplete knowledge we have of its general character it
appears to be a remnant of an older plateau, which is separated from the Lauren-
tian plateau by the wide plains of Slave river above which it rises ‘to a heignt
of about 2,500 feet. The slopes on the north and east sides are said to be rather
steep. On the south they are more gentle, and on the west they are still more
so. The plateau is said to contain a number of lakes and is forested by a stunted ©
growth of spruce similar to that which grows on.the borders of the Barren lands
or near the timber-line in the mountains.

Buffalo Head hills, which lie south of Peace river, rise abruptly from the
plateau about 50 miles west of Wabiskaw river to an elevation of about 2,500
feet above the sea and, running in a south-southwesterly direction, die abe

‘Dowling, D. B., Physical geography of Canada; Thirteenth report of the Geographic

Board of Canada, 1914.
2Geol. Surv., Can., vol. IV, 1888-89, pt. Bi.

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