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‘ Mackenzie Lowland. The lowland portion of the Great Central plain of the
Mackenzie basin commences in the lower part of Peace river and the extreme
western end of lake Athabaska, whence it extends as a narrow band down the
valley of Slave river to Great Slave lake. Its eastern boundary here as well as
north of Great’ Slave lake is the border of the Laurentian plateau. It embraces
the basin of the western end of Great Slave lake and continues thence down the
valley of Mackenzie river to the Arctic coast, its eastern boundary being as far
as known the Laurentian plateau, and its western Mackenzie mountains and the
escarpment of the Peel plateau. A re-entrant of the lowland extends up the
valley of Liard river as far at least as Fort Liard.

. The limits of the lowland on the south are well defined and marked by a
distinct topographic break at the escarpment of the Alberta plateau. North of
Liard river the lowland reaches on the west to the base of Mackenzie mountains
which are here not bordered by an elevated plateau belt. North of Nahanni river,
however, the long narrow ridge of Franklin mountains divides the lowland into
two parts by separating a strip 20 to SO miles in width, through which the
Mackenzie flows, from the main portion of the lowland lying in the drainage
basin of Great Bear lake. Franklin mountains are believed to die out about lati-
tude 66 degrees, and from this line northward the lowland is bounded on the
west by the escarpment of the Peel plateau and farther north by Richardson
mountains, whereas on the east its limits are unknown though it probably extends
across the height of land into the watershed of Anderson river.

So far as it is possible to determine from our imperfect knowledge of the
eastern portions of the lowland there is no well-defined and continuous break
between the lowland and the Laurentian plateau such as occurs in the west, but
the plateau, as a rule, dips gently westward under the overlapping edges of the
flat-lying sedimentary strata which constitute the bedrock of the lowland.

The elevation of the lowland at the west end of Athabaska lake is about 700
feet above the sea and the slope of the surface from that point to the Arctic
averages about 8 inches to the mile and is so gradual that from Fort Smith to
the Arctic ocean, a distance of over 1,300 miles by the river, steamers with a
draft of 5 feet are able to run without encountering any obstructions from rapids
ormallgs +4 hua!

The surface as a rule does not stand much above the main water courses or
the great lakes and the banks of these are rarely more than 200 feet in height.

The great bodies of water, Great Slave and Great Bear lakes, occupy areas
of depression in the surface of the lowland, and another long narrow depression,
not, however, now filled with water, lies along the base of Mackenzie mountains
from Fort Liard to the mouth of North Nahanni river.

Rising above the general level of the lowland are a number of hills and
mountain ranges varying in height from a few hundreds of feet to about 4,000

feet. Such ranges are: Horn mountain, northwest of Providence; Franklin
mountains, between the Mackenzie and Great Bear lake; Grizzly Bear mountain
and Scented Grass hills on the shores of Great Bear lake; Reindeer hills, east of
the delta; and a-number of other short ranges or isolated hills. :

These ranges are the only features that rélieve the monotony of an otherwise
flat plain which holds on its forested surface innumerable lakes and muskegs, and
through which the smaller streams meander in shallow valleys. Only in the

1McConnell, ‘R. G., Geol. Surv., Can., vol. IV, 1888-89, pp. 57 D and 89 D.