SEDIMENTATION IN MACKENZIE RIVER BASIN 345 
observe the relative amounts of sediment on the two sides. On the 
east side the water was quite clear, the tip of an oar being visible 
as far down as its length. One third of a mile from the east bank 
the water showed a trace of sediment, the visibility in looking down 
into it along the side of an oar being noticeably less. ‘The suspended 
matter gradually increased toward the west bank for a quarter of a 
mile. The last third of a mile on the west side held so much sedi- 
ment that only indistinctly could the bottom of a cup 4 inches deep 
be seen through it. An oar could not be seen more than 3 or 4 
inches below the surface of the water. ‘At old Fort Wrigley, 140 
miles below the Liard, the water on the east side of the river is 
quite clear, no visible sediment is present, and visibility extends 
down 3 feet or more. On the west side the bottom of a cup 4 inches 
deep can be discerned through the water only very indistinctly. 
The contrast in driftwood also continues striking, being very 
abundant on the west and scarce on the east side.”’ This contrast, 
though in a somewhat less marked degree, extended as far as New 
Fort Wrigley, 160 miles below the Liard, the northern limit of my 
journey. At Fort Norman a large river brings the clear waters 
of the Great Bear Lake drainage basin into the east side of the 
Mackenzie. This large accession of clear water to the east side 
doubtless results in keeping the eastern half of the Mackenzie 
comparatively clear to the head of the delta. 
Thus we have the curious phenomenon of two rivers, one a 
clear and one a highly turbid stream, flowing side by side in the 
same channel without mixing except ina comparatively narrow zone. 
As a result the deposition of sediment differs markedly in amount 
and kind on the two sides of the Mackenzie. The islands of alluvial 
material which occur at various points in the river below the Liard 
are all confined to the western half of the stream. The abundant 
supply of drift logs which comes down the Liard furnishes a large 
amount of drift timber to the west bank of the Mackenzie. Com- 
paratively little of it lands on the east bank. 
DESTRUCTIVE AND CONSTRUCTIVE WORK OF THE RIVERS 
The Slave River carries vast quantities of sediment into Great 
Slave Lake. It enters the lake through several narrow channels, 
