No. 1.] DAWSON — GLACIATION OF BRITISH COLUMBIA. 39 



valleys, attributing most of the canons of the region he has ex- 

 amined to their action. He draws attention to the V-shaped 

 gorges which become U-shaped in their upper reaches, and sup- 

 poses that the former were cutout by flood waters accompanying 

 and following the first period of glaciation, while in the latter we 

 have the unaltered work of the glaciers of the second period, 

 stating that the work of erosion in these valleys has been ab- 

 solutely trivial since the glaciers left them. It is also advanced 

 in support of these views that many if not most of the canons 

 of which the age can be determined, have been cut out since 

 Pliocene times, and that in the surfaces of the Archaean masses 

 which must have stood out as islands during long geological 

 periods, nowhere shew the junction of newer formations with 

 them, to follow other than broad rounded curves. 



To this theory of the origin of canons and mountain-valleys 

 it may be objected that whatever be the case in the fortieth 

 parallel area, vast post-glacial erosion and the formation of deep 

 valleys and gorges since that period have elsewhere been dis- 

 covered ; that glaciers are never now found to exert such active 

 erosive power, and that the idea that so sluggish and inert a portion 

 of a glacier as its nevS should produce the great amphitheatrical 

 valleys or cirques of the central mountain regions, seems incon- 

 ceivable. Further, the post-pliocene age of the canons, supposing 

 it to be correctly assigned to them in all cases, may mean nothing 

 more than that the progressive elevation of the plateau area by 

 which the cutting down of canons may be explained, was most 

 active about that time. Canons and fjords are in any case 

 rather exceptional phenomena, they occur only, on any hypothe- 

 sis, in regions long raised above the sea level, and the chances 

 that such features should be preserved during a depression of 

 the land and afterwards brought to light in the particular por- 

 tions of the lines of contact of newer and older rocks exposed by 

 denudation, are exceedingly small. 



