618 DEPARTMENT OF TEE INTERIOR 



2 GEORGE V., A. 1912 



' In the later Pliocene a very marked reelevation of the Cordilleran 

 region evidently occurred, leading to the renewed activity of river erosion, 

 the cutting out of deep valleys and canyons, and the shaping of the surface 

 to a form much like that held by it at the present day. This elevation in 

 all probability affected the coast as well as the interior, and it would 

 appear that the rivers for a time extended their courses to the edge of the 

 continental plateau.' * 



Dawson's statement as given and his more detailed accounts in the govern- 

 ment reports on the belt show quite clearly that the accordance of levels among 

 the many flat-topped massifs of the belt cannot be directly connected with the 

 Eocene peneplanation. The same fact is at once apparent from an inspection of 

 the Kamloops and Shuswap sheets of the Canadian Geological Survey. In 

 those maps it is seen that a very large proportion of these typical areas of the 

 belt is underlain by the nearly or quite horizontal post-Eocene volcanics, and that 

 their structure alone amply explains the flatness of very many of the' larger 

 plateaus. This relation of surface to structure is like that explaining the 

 flatness of the Columbia lava-field of the United States. Dawson's maps and 

 reports show that the Eocene eroded surface must now, over large areas, be far 

 below sealevel, while over other large areas the flat denudation-surface truncat- 

 ing the Triassic and Paleozoic terranes of the belt is more than 6,000 feet above 

 sea. We may, therefore, safely exclude the view that the present accordance 

 in the levels of the many plateaus in the belt is to be explained by pre-Miocene 

 baselevelling. There are, however, plenty of local areas in the belt, as at 

 Anarchist mountain, where the deformed Paleozoics are truncated by surfaces 

 so flat as fairly to be called peneplains or extremely old mountains. For the 

 enormous denudation there represented we have pre-Eocene time at our dis- 

 posal in making explanation. 



It seems clear, therefore, that, genetically speaking, we cannot call this 

 part of the Cordillera, between the Coast range and the Columbia mountain 

 system, a single plateau, unless it can be shown, in opposition to Dawson, that 

 the accordance of summit levels among the different massifs is due to post- 

 Miocene peneplanation. For this reason it is expedient to review the arguments 

 of Russell, Willis, and Smith, who agree in advocating a Pliocene pene- 

 planation in the Cascade range and on a great scale similar to that just 

 suggested for the Belt of Interior Plateaus. The hypothesis of these United 

 States geologists should, however, be considered in the light of the actual 

 topography of the Okanagan, Hozomeen, and Skagit ranges. The further 

 discussion of this matter of Tertiary peneplanation will, therefore, be postponed 

 until we have made a brief study of the remaining ranges crossed by the 

 Boundary belt. 



Olcanagan Range.- — The local baselevels for the Okanagan range are found 

 in the Similkameen at about 1,200 feet above sea and the Pasayten river at about 

 3,900 above sea. These streams occupy the valleys which respectively delimit 



* G. M. Dawson, ibid., p. 90. 



