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Richardson mountains, springs up north of Peel river and extends down to the
Arctic coast, its eastern front following closely the valley of Peel river and rising

as an abrupt fault scarp out of the delta of the Mackenzie.

This physiographic province of the Mackenzie basin comprises three main
mountain groups, namely, the Rocky mountains, Mackenzie mountains, and the
Richardson mountains.

Rocky Mountains. The Rocky mountains occupy the southwestern portion
of the basin and extend as far north as the valley of the Liard river, where they
either die out or lose their lofty mountainous character in a region of foothills.
To the south they extend far beyond the limits of the Mackenzie basin into
southern Alberta and Montana. .

In the Mackenzie basin, as elsewhere, the Rocky mountains are made up of
a series of parallel ranges striking northwesterly and coinciding in trend with
the direction of the main mountain axis. e Between the ranges are deep longi-
tudinal valleys occupied by the smaller streams, and crossing them at right angles
are transverse gaps through which the major streams break eastward to the Great
Central plain. The transverse valleys are usually short in comparison with the
longitudinal valleys and only in a few instances do such transverse breaks preserve
their character so definitely through the whole breadth of the mountains as to
form direct passes. The most notable instance of this is the Peace river, which
cuts a deep, wide valley directly across the strike of the Rocky mountains and
draws much of its water from the country to the west of them.

Some of the loftiest summits of the whole Rocky Mountain system in Canada
are situated at the extreme southern portion of the Mackenzie basin at the head-

waters of the Athabaska river, where streams which flow eastward to the Atlantic,

northward to the Arctic, and westward to the Pacific interlock and have their
sources. Here, is a group of mountain peaks which exceed 10,000 feet in eleva-

tion and culminate in the highest point of all, mount Robson, 13,700 feet above

the sea. Between the Athabaska and Peace rivers not much is known of the
character of the Rocky mountains except that they are very rugged and high
and there are no known passes as low as the Yellowhead pass, 3,720 feet in
elevation. Approaching the Peace river, however, the mountains decrease in
height and width and are traversed by some low passes. Pine River pass, which
was estimated by Dawson’ to have an elevation of 2,850 feet above the sea,
traverses the ranges where the bordering summits do not rise more than 6,000
feet above the sea; and Peace river itself cuts a valley directly through the main
ranges of the Rockies, where their highest points barely exceed 6,000 feet in
elevation ard the valley bottom is less than 2,000 feet.

Less is known of the Rocky mountains north of Peace river than of any
other portion of the whole system. Points as high as 7,500 feet are mentioned by
McConnell? as occupying the region about latitude 57 degrees, but where the
ranges-have next been observed, at the Liard river, they are seen to have decreased
in height to such an extent that the highest points are not more than 4,000 feet
above sea-level. Only one of the main ranges of the Rockies is said to eross the
Liard river, near Riviére des Vents, and even this a few miles north of the river
becomes greatly reduced in height. The foothills, however, which border the main

1 Geol. Surv., Can., Rept. of Prog., 1879-80, p. 37 B.
2 Geol. Surv., Can., vol. VII, 1894, p. 16 C.

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