646 ALFRED W. G. WILSON 



Bay, and part of the waters flow via the Cochrane River and 

 Wollaston Lake to Lake Athabasca, and eventually reach the 

 Arctic Ocean. Similar lakes, both large and small, with outlets 

 in two directions, are quite frequently found manywhere upon 

 the peneplain. 



b) Depressions co?itaining sedimentary deposits. — The occurrence 

 of valleys occupied by sediments which have been assigned to 

 the Cambrian has been reported by Low in Labrador and by 

 Tyrrell in northern Keewatin and eastern Mackenzie. Reference 

 has already been made to some of these in a previous section; 

 the occurrence of Paleozoic sediments in the basins of Lakes 

 Nipissing, Temiscaming, St. John, and Mistassinni has also been 

 noted. 



Low in describing these valleys in Labrador mentions that 

 the streams are often from 500 to 1,000 feet below the level of 

 the plateau. The heads of the valleys are from 100 to 300 

 miles from their mouths, and at the upper ends the rivers descend 

 from the level of the interior in a succession of heavy falls 

 through narrow gorges, where processes of erosion are at pres- 

 ent slowly extending and deepening the valleys. The valley of 

 the Hamilton River he describes as being from 700 to 1,200 feet 

 below the level of the plateau. In some cases these ancient val- 

 leys have been more or less filled with glacial debris, and the 

 modern streams for parts or all of their lengths have taken new 

 courses. 



Some of the depressions in which these sediments occur seem 

 to be ancient, broadly open valleys, and are considered by those 

 who have had the opportunity of studying the region in the field 

 as of pre-Cambrian age — In the case of Chesterfield Inlet, Tyrrell 

 notes that the sides are deep and in places cliffed. Back's descrip- 

 tion of the country immediately north of the east end of Great 

 Slave Lake would lead one to infer that the sides of this valley 

 were also well defined.^ 



In the Labrador regions the margins of the depressions in 

 which the pre-Cambrian sediments (so-called) occur are well 

 defined. This is strikingly true of the lower and partly sub- 



^ See also Fig. 9. 



