THE LA URENTIAN PENEPLAIN 663 



side, below and above this gorge, would suggest that the Labra- 

 dorite hills here referred to rise as a monadnock above the level 

 of the plain, and that the stream to cut through them must have 

 been superposed upon them. 



Whether these gorges were developed by catastrophic pro- 

 cesses, or owe their origin to antecedent or superposed streams, 

 or to some other cause, a few of them have probably been mod- 

 ified by subsequent ice-action. In all cases they lie in a position 

 transverse to the direction of ice-motion. In many cases, partic- 

 ularly toward the northeast, the probability is that the ice, 

 retarded in its progress from central Labrador by the ascent of 

 the main divide, had little effect. Toward the center and west- 

 ern part of this division of the plain, in the vicinity of Lake St. 

 John and elsewhere, the effect of the glacial ice in modifying 

 these valleys is more apparent. Writing of his ascent of the 

 Betsiamites River, Low mentions incidentally a tributary of this 

 river which "descends into the valley by a beautiful falls, over 

 one hundred feet high" (20, p. 6). The main valley varies in 

 width from a quarter of a mile to over a mile, and is more or 

 less filled with glacial debris. The relation of this tributary lat- 

 eral valley to the main valley certainly suggests that the main 

 valley has been significantly widened and deepened by a glacial 

 distributary from the interior. The best-known of the gorges is 

 that of the Saguenay. It is a typical fiord valley with ice-scoured 

 sides. Its relation to the St. John basin suggests that it owes 

 its present form to the scouring by an ice-stream which made its 

 way outward from the basin. The Labrador ice, although 

 retarded in its flow by the ascent of the main divide, would 

 attain a considerable thickness in this basin after it had passed 

 the divide. Although it probably, at one time, passed over the 

 St. Lawrence swell, the main ice-stream, after leaving the St. 

 John basin, moved toward the southwest. If, however, there 

 existed a deep river canyon leading outward from the basin, 

 similar to the many found farther northeast, the depth of ice in 

 the basin and the tendency for the pressure to force the ice out- 

 ward in every direction along the lines of least resistance would 

 cause an ice-stream to pass out in this direction toward the St. 



