221 



Kiomlt'res ^he town ne s m the ' Selkirk Valley, ' namely, 



that part of the Columbia river valley which 

 bounds the Selkirk mountain system on the 

 west and separates it from the long Columbia 

 system, which across the valley rises to heights 

 approaching 9,000 feet (2,743 m -)- This long 

 depression has a complex history and is of com- 

 posite origin, though the details of neither have 

 been worked out. Over most of Revelstoke 

 mountain, north of the town, the strikes average 

 about N.N.W. — S.S.E., a Cordilleran direction 

 corresponding probably to fault-blocking during 

 one of the post-Cambrian periods of mountain- 

 building. Across the river the strikes average 

 nearly E. — W. At its eastern bank, 5 kilometres 

 above Revelstoke, these structural lines are 

 found in close proximity, indicating a N. — S. 

 fault on which the river is located. Other local 

 evidence agrees with the view that this part 

 of the Selkirk valley has been formed by erosion 

 on a longitudinal fault of unknown but possibly 

 considerable throw. The downthrow is prob- 

 ably on its eastern side. 



Along the branch railway to Arrowhead, 

 44 kilometres southward from Revelstoke, one 

 may observe the prevailing low dips in the 

 Shuswap terrane. 



From Revelstoke to Kamloops the mile-posts 

 are numbered in a new series, beginning in the 

 east, and distances are stated accordingly. 



At the crossing of the river one notes its 

 increase of size, accomplished in its 300-kilo- 

 metre journey from Beavermouth where it was 

 last seen. In that distance the river has rounded 

 the northern end of the Selkirk range, and it 

 is here flowing south toward the lava fields 

 of Washington State. After running over one 

 of the terraces characteristic of this valley, 

 the train reaches some extensive artificial cuts 

 in the Tonkawatla paragneiss. (See page 123.) 



The normal orthogneisses, developed as thick 

 sills and many dykes cutting the sediments and 

 problematic basic schists, begin to appear as 

 the low divide of the Columbia range is approa- 

 ched, near Clanwilliam. 



