664 ALFRED W. G. WILSON 



Lawrence, even at a time when no significant amount was pas- 

 sing over the subdivide between the basin and the river. This 

 ice-stream, moving in a well-defined channel, would deepen and 

 widen the pre-existing river gorge. It thus seems probable that 

 the Saguenay gorge may be regarded as the channel of a glacial 

 distributary from the St. John basin, and that it was in existence 

 prior to the advent of the ice, as a stream channel similar in 

 form to those which exist farther northeast and show no signifi- 

 cant modification of form due to ice-action. 



With reference to the older valleys, north of the main divide 

 in Labrador, containmg pre-Cambrian sediments, the descriptions 

 available are inadequate to enable one to determine whether 

 they have been significantly widened and deepened by ice- 

 erosion. In the case of the old valley of the Hamilton River 

 lateral tributaries plunge or cascade over the margin into the 

 main valley. This may be true of other similar valleys. It has 

 already been intimated that the lack of adjustment between the 

 tributary and the main valley may be due to relatively recent 

 downfaulting of graben blocks. 



Reference has already been made to the possible origin of 

 the submerged gorge of Lake Temiscaming and the Ottawa 

 River valley above Mattawa. 



There are also a number of minor gorges, such as those 

 mentioned by Barlow as occurring on the peneplain west of 

 Lake Temiscaming, whose courses are in some cases transverse 

 to hard and soft strata alike ; or others, such as the gorge on 

 the Upper Abitibi mentioned by Parks, which may be the chan- 

 nels of superposed streams, may have been eroded along the 

 line of weak dike-rocks, or may be due to some other cause. 



4. The origin of the smooth fresh surface of the Archcean rocks. — 

 As has been intimated in the previous description of the pene- 

 plain, the old soil cover of subaerial origin has everywhere been 

 removed. For this has been substituted a covering of material, 

 much of which undoubtedly was derived from the Archaean ter- 

 ranes, but almost all of which has been brought to its present 

 resting-place by the aid, direct or indirect, of the Pleistocene ice- 

 sheets. Uncovered Archaean bosses often project above this 



