644 ALFRED W. G. WILSON 



Valleys similar to these, containing sedimentary rocks, are 

 also known to occur in the Labrador area. Low has reported 

 the finding of sediments, provisionally classed as Cambrian, in 

 the valleys of the Kaniapiskau and the Upper Hamilton Rivers. 

 A somewhat similar series of sediments, the Manitounuck Series 

 of Bell, occur along the east coast of Hudson Bay — lying below 

 the level of the edge of the interior plateau, dipping seaward at 

 low angles, presenting a well-defined cuesta front toward the 

 plateau. In places the foot of the cuesta is submerged, but the 

 unsubmerged portions form a series of coastal islands. 



A series of sediments, for the most part classed as Cambrian, 

 also occur in the Mistassinni basin. Ordovician outliers are 

 found in the Lake St. John basin ; Ordovician and Silurian strata 

 occur in the northern part of the deep valley before noted as 

 being occupied by Lake Temiscaming. Ordovician strata are 

 also found in the Lake Nipissing basin. North of Lake Superior, 

 particularly to the south and west of Lake Nipigon, is a well- 

 developed series of non-fossiliferous ferruginous sandstones and 

 dolomites resting upon the peneplain, and showing typical cuesta 

 form. Subsequent to the development of the cuesta form on 

 these sedimentary outliers they seem to have been over- 

 flowed with diabase sheets, and in some cases the earlier land 

 form has been preserved beneath the more recent flow. 



5. Topographic depressions. — A comparative study of the various 

 depressions which go to make up the relief of the peneplain sur- 

 face, as it is today, suggest a provisional recognition of three 

 distinct types. 



a) The broad, shallow depressions between the more or less 

 hummocky or undulating ridges which occur upon the upland 

 itself, and which are probably in the main of contemporaneous 

 origin with the surface of the peneplain, and are presumably due 

 to local differential erosion, and subsequent denudation. 



b^ Broad, open depressions, which are generally in part occu- 

 pied by sediments provisionally classed as Cambrian. 



<:) Deep, narrow channels, in places gorges, with steep, often 

 inaccessible sides, distinctly incised beneath the level of the 

 adjacent upland. (These are of two types, short and relatively 

 shallow, and long and generally deep.) 



