40 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



Another important, though small, natural subdivision of the system is 

 limited on the north, east, and south by the Selkirk Valley ; on the west, by the 

 lower Kettle valley, and by a short trench running from Lower Arrow lake to 

 Christina lake and the Kettle river at Cascade. This group may be called 

 the Rossi and mountains. (Plate 3.) 



Again for convenience, the mountains occurring between Christina lake 

 and the North Fork of Kettle river will be referred to as the Christina range. 

 (Figure 4.) 



The more northerly part of the Columbia system is yet too imperfectly 

 known to permit of subdivision in a systematic way. 



BELT OF INTERIOR PLATEAUS. 



As we have seen, the belt of Interior Plateaus is of primary importance 

 in the systematic orography of the Cordillera. (Plate 6.) It is difficult of 

 delimitation. On nearly all of its boundaries the belt fades gradually into the 

 loftier, more rugged ranges encircling it. Its limits have been compiled 

 and drawn on the map (Plate 3.) after a study of Dawson's numerous 

 reports of exploration. The limits are to be regarded as only approximate. 

 The plateau character is obscure at the Forty-ninth Parallel, but the 

 roughly tabular form and considerable area of Anarchist mountain, imme- 

 diately east of Osoyoos lake, seem to warrant the slight extension of the belt 

 across the International line. The southernmost limit of the belt is an irregular 

 line following — (1) the main Kettle river valley; (2) a quite subordinate trench 

 occupied by Myers creek and Antoine creek, in the state of Washington; (3) 

 a part of the lower Okanagan valley; and (4) the Similkameen-Tulameen 

 valley. 



CASCADE MOUNTAIN SYSTEM AND ITS SUBDIVISION. 



Usage, both official and popular, has gone far toward finally establishing 

 the nomenclature for the immense ranges lying west of the Columbia lava 

 plain, Midway mountains, and belt of Interior Plateaus. The Cascade range 

 is now defined on the principle of continuity of crests, not on the basis of 

 rock-composition. At the cascading rapids of the Columbia river the range is a 

 warped lava plateau ; in northern Washington it is an alpine complex of schists, 

 sediments, granites, etc. In British Columbia, Dawson adopted the name ' Coast 

 range ' to enforce the view that the granite-schist British Columbia moun- 

 tains on the seaboard should be distinguished from the lava-built Cascades, as 

 originally named, at the Columbia river. It has, however, become more and 

 more evident, as the study of the Cordillera progresses, that rock-composition 

 can never rival crest continuity as a primary principle in grouping the western 

 mountains. Meanwhile, . the name 'Coast range' has survived, and is, in fact, 

 the only name officially approved by the Geographic board of Canada for any 

 principal division of the Cordillera 



