H3 



Canadian part of the chain: namely, the Columbia, Fraser, 

 Peace and Liard — the last two being principal branches 

 of the Mackenzie river. The larger streams flowing in the 

 depression are: the Kootenay; the Columbia; the Canoe 

 river; the Fraser; the Parsnip and Finlay rivers (Peace 

 river system) ; and the Kachika river of the Liard system. 

 Many of them leave the trough by transverse gorges 

 cut in the adjacent mountains. The rivers enumerated, 

 as well as smaller ones not specially named, are arranged 

 in regular sequence, draining the trough in opposite 

 (N.W. and S.E.) directions. Although continuous 

 throughout its great length, the trough is not a valley 

 in the ordinary sense. It is like a trench dug by soldiers 

 in a hilly country; such a defensive work is not cut to 

 a uniform bottom grade but is man-deep whatever the 

 slope. This master form in the Cordillera may be appro- 

 priately described as a topographic trench. All the 

 mountains in Canada and in Montana lying to the north- 

 eastward of the trench have long been segregated as the 

 Rocky Mountain system, and the bounding trough has 

 been named the Rocky Mountain trench. 



A second trench, about 350 kilometres (220 miles) in 

 length, opens in the southeastern wall of the first near 

 Bea vermouth and runs southward. It is successively 

 drained by Beaver river, Duncan river, and Kootenay 

 river; for 120 kilometres (74 miles) it is occupied by the 

 fiord-like Kootenay lake. This trough rigorously separates 

 the Purcell Mountain range on the east from the Selkirk 

 system on the west and bears the name, Purcell trench. 

 The Purcell range is thus bounded, east and west, by 

 the two trenches; on the south it terminates at the loop 

 of the Kootenay river in Montana and Idaho. 



Near latitude 52 the Columbia river leaves the Rocky 

 Mountain trench and flows south, in a wide valley 500 

 kilometres (310 miles) long, to the Columbia lava-field of 

 Washington State. This part of the Columbia valley 

 may for convenience be called the Selkirk valley. Mid- 

 way in its course it bears the Arrow lakes, totalling 150 

 kilometres (92 miles) in length. East of the Selkirk 

 valley and west of the two master trenches is the Selkirk 

 Mountain system which, like the Rocky Mountain and 

 Purcell systems, extends into the United States. 



The rugged mountains to the west of the Selkirk 

 valley have been grouped under the name, Columbia 



