648 ALFRED W. G. WILSON 



out on the coast, that hanging lateral valleys may be due to the 

 deepening and widening of the main valley by an ice-stream ; 

 but many of the type of depressions here referred to not only lie 

 in regions which can never have been at the edge of the ice- 

 sheets when they were in motion (or at least at their points of 

 discharge) , but seem to be completely inclosed by the bounding 

 scarps except for the narrow outlet through which the present 

 drainage passes. 



In the majority of cases there is not suf^cient available evi- 

 dence to warrant an extended discussion of this very interesting 

 problem. 



c) Gorge and canyon valleys. — Narrow, steep-sided valleys and 

 gorges, sometimes many miles in length, sometimes only extend- 

 inar for short distances, are of frequent occurrence in various 

 parts of the peneplain. Reference has already been made to a 

 number of them which are known to occur in the Labrador area, 

 through which the drainage of the interior upland passes down 

 to Hudson Bay, to the River St. Lawrence or to the Atlantic 

 Ocean. One of the most interesting of these is the gorge of the 

 Hamilton River, described by Low' as occurring above the more 

 broadly open, partly submerged pre-Cambrian valley (so-called) 

 of the lower part of the same river. The numerous rivers which 

 enter the Gulf and River St. Lawrence from the northwest in 

 every case pass through deep, steep-sided valleys, often canyons 

 with unscalable walls, at times cut to a depth of over one 

 thousand feet below the level of the peneplain. The valley of 

 Moisie has been described by Hinde, the Bersimis by Low, the 

 Saguenay the best-known of all, by Laflamme and Dumais. 



Farther west the depression occupied by the lower part of 

 Lake Temiscaming and the Ottawa River as far down as Mattawa 

 seems to belong to this category. In the immediate vicinity of 

 Lake Temiscaming there are a number of other gorges and 

 valleys, the former much narrower and smaller than the Temis- 

 caming depression, cut beneath the surface of the plain, at times 

 even across weak and hard rocks alike, independent of the 

 structure. 



' See above p. 641. 



