37

into it from the north and all are short, rapid, and unnavigable. On the south ~

side the streams, though larger, are small, and none of them is navigable by
canoes for any great distance except Old Fort river. The principal inflowing
streams are Stone or Black river at the east end, and Athabaska river at the
-west end. In periods of flood Peace river also flows into the lake by way of
Quatre Fourches river, but normally this and the Rocher river are outflowing
streams.

Athabaska lake formerly extended much farther west over the basins
of lake Mammawee and lake Claire, but Peace and Athabaska rivers have
gradually built up deltas at their mouths and cut off these two lakes from the
main lake.

Towards the eastern end of the lake the water is clear and pure, but at its
western end it is rendered turbid by the material discharged into it by Athabaska
river.

Athabaska lake is usually not free from ice until the middle of June and it
begins to freeze over again early in October. The ,western end, however, at
the mouth of Athabaska river, is usually open early in May.

Great Slave Lake

Great Slave lake, according to Cameron,! has a superficial area, including
islands, of over 12,000 square miles and ranks fourth among the great lakes
of the continent, being exceeded in size only by Superior, Huron, and Michigan.
No complete survey of the shores has yet been made, but the lake is estimated
to have a total length of 288 miles and its greatest width exceeds 60 miles.

Originally it had the form of a great cross, with one arm penetrating east-
ward into the Laurentian plateau, two others stretched north and south along

the contact between the Laurentian plateau and the horizontal sedimentary ~

rocks of the lowland, and the fourth extended westward over the flat-lying rocks
of the lowland. The southern arm extended southward up the valley of Slave
river, but has now been silted up by the material carried in by that stream.

The eastern portion of the lake has a very irregular outline and is dotted
by numerous rocky islands. Its shores are bold, rocky, and sparsely wooded,
and on the north side rise in places to a height of 1,000 feet above. the lake.
Tnto the north side, Hoarfrost river precipitates itself over a precipice 60 feet
in height, and at the east end Lockhart river enters, after flowing from Artillery
lake in a series of rapids. On the south side the only tributary of importance
js Taltson river which enters near Slave river and drains most of the region
between this arm of the lake and Athabaska lake. |

The northern arm of the lake is over 100 miles in length, but is narrow
and filled with islands. Its shores are rocky and are nowhere very high.
Yellowknife and Grandin rivers are the only important streams discharging
into it and neither is navigable except for canoes.

The western arm presents a greater expanse of water, unbroken ‘by islands,
than either of the other divisions. “Its southern shore has a gentle, sinuous out-
line and is characterized by low banks and gently shelving beaches which are

often thickly strewn with boulders. The banks . . . . are often built up of

drift timber. The northern shore is more uneven and is indented with several
deep bays.”? This arm is bordered on both sides by a flat, wooded country, which
on the south side rises inland a few miles to some low rounded hills.

1 Geol. Surv., Can., Sum, Rept., 1916.
2McConnell, R. G., Geol. Surv., vol. TV, 1888-89, p. 66 D.

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