SEDIMENTATION IN MACKENZIE RIVER BASIN 359 
outlet channels of the Peace empty directly into Slave River, but 
the Quatre Fourches channel, which branches off above the Slave 
River outlets, empties into Lake Athabasca. Ordinarily by far 
the greater part of the Peace River water flows directly to Slave 
Lake via Slave River; but a conjunction of low water in Lake 
Athabasca and high water in the Peace River may for a time 
reverse the direction of flow in the upper Slave River and turn all 
of the Peace River outflow into Lake Athabasca. Such a reversal 
of drainage involves the temporary obliteration and reversal of 
Little Rapid, located about 25 miles north of Lake Athabasca in 
Slave River. Father Lafebre, of the Catholic Mission, informs me 
Pomel 
Hs 
Fic. 13.—A double beach of a and drift wood, shore of Great Slave Lake 
that he has observed this reversal in May. It thus appears that at 
times the whole of the combined volume of sediment carried by the 
Peace and the Athabasca is dumped into Lake Athabasca. When 
this reversal of current near the head of the Slave River occurs, it 
is evident that the deposition of sediments must proceed in the 
western part of Lake Athabasca at an enormously increased rate. 
Under these special conditions the whole of the Peace River sedi- 
ment, nearly all of which ordinarily reaches Great Slave Lake, 
stops in Lake Athabasca. During the unusual seasons when the 
Peace River contributes largely to the Lake Athabasca sediments, 
the annual layers of silt would not only be thicker than those 
ordinarily laid down but would also probably have a much greater 
easterly extension. 
