344 E. M. KINDLE 
as the Birch Mountain projects shieldlike from the south into the 
low land between the Peace and the Athabasca rivers. 
The banks of the Mackenzie for the first 200 miles below 
Great Slave Lake are in some places very low, particularly near the 
head of the river, though rising 50 to 150 feet above the stream in 
many places. But the materials in which the channel is cut are 
nearly everywhere either glacial drift or Devonian shales. It will 
be pointed out later that the till banks of the Mackenzie give rise to 
certain peculiarities of the river which are not found in the Slave, 
lower Peace, and Athabasca rivers, whose channels are cut largely 
in lacustrine beds. 
RELATIVE TURBIDITY 
The major part of the great volume of water comprising the 
upper Mackenzie River is gathered by two large rivers, the Peace 
and the Athabasca. The latter stream is filtered through Atha- 
basca Lake before joining the Peace. The Peace, united with 
the Athabasca under the name of the Slave River, pours its flood 
of sediment-laden water into Great Slave Lake, which discharges 
it, freed of its burden of floating trees and suspended mud, into the 
head of the Mackenzie River. The filtered waters of the Slave and 
half a dozen other considerable streams which flow into Great 
Slave Lake unite in the upper Mackenzie to form a stream which, 
in both volume and clarity, is comparable with the upper St. 
Lawrence. This clear river issuing from the lower end of Great . 
Slave Lake receives no stream of notable size for 150 miles, to the 
point where it is joined by the Liard from the west. The Liard 
drains a great area including all the easterly valleys of the Rocky 
Mountains between the head waters of the Peace and the Yukon. 
The large volume of the Liard is characterized by a high degree of 
turbidity. Its muddy waters join the clear waters of the Mackenzie 
at Fort Simpson, but for more than 160 miles below Simpson they 
fail to mix except in a limited zone near the middle of the river. 
During the canoe trip down the Mackenzie observations regarding 
the relative clarity of the water on the two sides of the river were 
made repeatedly. The following excerpts from my notes indicate 
the contrasts observed. Twenty-five miles below the mouth of the 
Liard River, a crossing from the east to the west bank was made to 
