REPORT OF THE CHIEF ASTRONOMER 35 



SESSIONAL PAPER No. 25a 



dominant importance of the Purcell Trench. That superb feature of the Cor- 

 dillera cleaves the mountains in so thoroughgoing a manner that a logical 

 grouping must regard the Purcell range as a member co-ordinate with the 

 Selkirk range. 



In the map the latter division is called the Selkirk system, because it 

 includes subordinate ranges. If, for purposes of exposition, this compre- 

 hensive character is not fixed for emphasis, the same Cordilleran member may 

 be called the ' Selkirk range.' Similarly, when the Purcell range is, in the 

 future, subdivided into its orographic units, it may bear the name ' Purcell 

 system.' ' Cascade range ' and "' Cascade system,' ' Coast range ' and ' Coast 

 system,' for example, may be profitably employed with the same distinctions. 

 In all these cases it is a matter of emphasis. 



The value of this distinction in common nouns, the great orographic 

 significance of the Purcell Trench, and the weight of much authority in previous 

 usages have caused the writer to suggest that the whole Purcell range be con- 

 sidered as co-ordinate with, and not part of, the Selkirk system. 



No systematic subdivision of the system has ever been attempted. In 

 discussing the geology of the system at the Boundary line there will be found 

 to be much advantage in recognizing its subdivision into units of more con- 

 venient size. A tentative scheme will therefore be proposed. 



Just north of the Porty-ninth Parallel a strong, though subordinate trench 

 runs meridionally along the middle part of the system. This trench is occupied 

 by the main Salmon river and by Cottonwood creek, which enters the West 

 Arm of Kootenay lake at Nelson. It divides the system into two broad ranges, 

 both of which are cut off on the north by the transverse valley enclosing the 

 West Arm and the outletting Kootenay river. The eastern range, for which 

 the name ' Nelson range ' is proposed (from the name of the chief town of the 

 district), is bounded on the east by the Purcell Trench and on the south by a 

 trench occupied by Boundary creek, Monk creek, and the South Fork of the 

 Salmon river. The western range may be called the ' Bonnington range,' from 

 the well-known falls which break the current of the Kootenay river. The 

 southern limit of this range is the Pend D'Oreille valley; the western limit, 

 the Selkirk Valley. (Figure 3.) 



In the preliminary paper the Slocan mountain group was stated to be 

 ' separated off definitely by the Slocan Trench, which is a longitudinal depres- 

 sion occupied by Slocan river, Slocan lake, and the creek valley mouthing at 

 Nakusp, on Arrow lake.' The definition was framed partly on the ground that 

 this mountain group includes the valley of Little Slocan river. On maturer 

 consideration the writer wishes to recall this definition and to propose the 

 name, ' Slocan mountains ' for the group east of Slocan river and Slocan lake. 

 The group west of the Slocan valley should probably have the name ' Valhalla 

 mountains,' which was entered by Dawson, in 1890, on his 'Reconnaissance 

 map of a portion of the West Kootanie District, British Columbia,' as the 

 title for the complex of high peaks west of Slocan lake. 



25 a— 3* 



