REPORT OF THE CHIEF ASTRONOMER 601 



SESSIONAL PAPER No. 25a 



Individual Mountain-Ranges as Physiographic Provinces. 



Corresponding to these genetic explanations of the master-valleys, so far as 

 they can now be made, the intervening mountain-ranges can be considered as 

 forming fairly definite structural units. 



The Clarke-Lewis mountain group is made up of a locally warped and 

 broken synclinal block which is in overthrust relation to the Great Plains on 

 the east, and in what may be called ' horst ' relation to the block underneath 

 the Plathead valley. Following Suess, a ' horst ' may be defined as a crustal 

 block which stands in relief because it is bounded by lateral normal faults. 



Then, in order from east to west, we have the following physiographic 

 units which together make up most of the Cordillera at the Forty-ninth 

 Parallel: 



Ranges. ■ Physiographic Provinces. 



Hooky Mountain System . . . {^ g^^gSSS^t 



Pureell Mountain System The Purcell horst. 



Selkirk Mountain System The Selkirk monocline. 



Columbia Mountain System.. . . { H* g-^ sland -P hoei }^ volcanic cap. 

 J I The Midway volcanic cap. 



Belt of Interior Plateaus The Anarchist old-mountain plateau. 



Okanagan Range The Okanagan composite batholith. 



f The Pasayten monocline. 

 Hozomeen Range -J The Hozomeen horst (including merely the ridge of Mount Hozo- 



i. meen.) 



{The Skagit volcanic cap. 

 The Skagit composite batholith (including the Custer, Chilliwack 

 and Slesse plutonic bodies). 

 The Chilliwack province of folded Paleozoic sediments. 

 The Gulf of Georgia (Puget Sound) down-warp. 

 Vancouver Range The Vancouver complex. 



Front Range Syncline. — The Clarke and Lewis ranges furnish the most 

 interesting scenery on the whole Cordilleran section; in this respect their only 

 possible competitor is the Cascade range in the extreme west. Fortunately we 

 have the quality of the eastern ranges admirably portrayed in the ' Chief Moun- 

 tain Quadrangle ' sheet of the United States Geological Survey (topography 

 by F. E. Matthes and E. H. Sargent, 1900-1902). A part of each of the two 

 Front ranges is mapped within the quadrangle; the map may be profitably 

 consulted by one who wishes to appreciate the full individuality of these moun- 

 tains as compared with the ranges west of the Flathead. 



The relief is considerable. Waterton lake is given as 4,186 feet above sea, 

 about the altitude of the Great Plains in this latitude. The Flathead is about 

 4,000 feet above sea. Cleveland mountain in the Lewis range and six miles 

 south of the International line, is given as 10,438 feet in height. Within the 

 Boundary belt itself two of the highest summits are Mt. Thompson (9,926 feet) 

 and Starvation Peak (9,300 feet). A total range of over 6,000 feet is regis- 

 tered in the vertical relief; the mountain slopes generally run from 3,000 to 

 5,000 feet in height. 



