66o ALFRED IV. G. WILSON 



The gorge-like valleys, free from Paleozoic sediments, and the 

 canyons, one would be inclined to think, date their origin from 

 a time subsequent to the planation period. Their immature 

 form, as compared with the broader pre-Cambrian valleys (so 

 called), and the absence of any Paleozoic sediments between 

 their walls suggest this. Most of them are pre-glacial, but some 

 few are post-glacial. 



The processes by which they were excavated no doubt were 

 various. Mention has already been made of the opinions of 

 Agassiz and Bell that some of them owe their origin to the 

 erosion of soft disintegrated dike rocks. This may be true in a 

 few isolated cases. In the great majority of cases, however, 

 particularly of the larger of these gorges, other and more gen- 

 eral processes must have been in operation. 



Given time enough, there can be no question but that the 

 normal processes of river erosion could produce these deep 

 canyons or steep-sided valleys. So far as we know at present, 

 this seems to have been the process by which most of the deep 

 gorges and canyons cut below the level of the Labrador pene- 

 plain were excavated. Low notes with respect to the canyon of 

 the Hamilton, just below the Grand Falls, that the river in its 

 erosion of this gorge has been guided by two series of joint 

 fractures, so that the canyon has a somewhat zigzag course. Mr. 

 Low has also drawn the writer's attention to the fact that there 

 are several instance where an old valley has been blocked by 

 glacial debris, and the streams flowing in the upper portions of 

 the valleys are turned aside, and have already cut well-defined 

 canyons, in some cases of considerable length, in the crystalline 

 rocks. It is to be noted that the canyon of the Hamilton River 

 enters the older valley, to which reference has already been 

 made, from the north side. The old valley continues inland for a 

 considerable distance beyond the junction of the present Hamil- 

 ton River, via the canyon, with the lower part of the stream in 

 the older valley. Mr. Low regards this canyon as of post- 

 glacial origin and due to erosion by the large stream which now 

 rushes through it. 



The problem of the origin of the deep canyons across the 



