SEDIMENTATION IN MACKENZIE RIVER BASIN 357 
penetrating the crystalline schists while two others stretched north 
and south along the junction of these with the newer sedimentaries, 
and the fourth extended itself over the flat-lying Devonian to the 
west.”’ Lake Athabasca lies almost entirely within the limits of the 
pre-Cambrian rocks. 
Inspection of the map (Fig. 1) will show that the drainage of an 
enormous area in Northwestern Canada, extending from the interior 
of the Rocky Mountains region far into the pre-Cambrian area west 
of Hudson Bay, passes through Lake Athabasca and Great Slave 
Lake. Practically all of the vast quantity of sediment which is 
annually stripped from this extensive area is left in these great 
settling basins. A noteworthy feature of this lacustrine sedimenta- 
tion is the extreme inequality of its distribution. Probably 95 
per cent of the immense volume of sediment which enters Great 
Slave Lake is poured into the south side of the lake. The streams 
entering the north side of the lake are nearly all small and com- 
paratively insignificant. In the course of a survey of the north 
shore of the west arm of Great Slave Lake, A. E. Cameron found 
that “‘throughout the entire 136 miles of shore line between the 
Mackenzie River and the north arm only one stream, and it a very 
minor one, was found entering the lake” (manuscript). The streams 
which do enter the north shore of the lake lose most of their sedi- 
ment in passing through small lakes before reaching Great Slave 
Lake. On the south shore, besides the Slave, which is one of the 
great sediment-bearing streams of the continent, three other 
rivers enter, each of which has a considerable volume. These are 
the Taltson, the Buffalo, and the Hay. It is the zone of lake bottom 
bordering the 150 miles of the south shore receiving these streams 
which takes the great bulk of the river-borne sediment. Great 
Slave Lake opposite the mouth of Slave River, which carries the 
great bulk of the silts entering the lake, has a width of more than 
60 miles. Little or none of the sediment brought in by the Slave 
has any chance of being deposited in the northern half of the 
lake. Coastwise currents, however, distribute the silts from the 
Slave and other south-shore streams widely along the south-shore 
bottom zone. It is probable that along the shore line between the 
Hay and the Buffalo rivers the prevailing direction of the coastwise 
