2 GEORGE V. SESSIONAL PAPER No 25a A. 1912 



CHAPTER II. 



SYNOPSIS OF THE REPORT. 



For the convenience of the reader a brief abstract of each of the following 

 chapters is here offered. As a rule, the petrography, which forms a large part 

 of each systematic section dealing with the rock formations, is not summar- 

 ized. 



Chapter III. — The necessity of subdividing the western mountain chain 

 of North America into relatively small orographic units is felt by the naturalist 

 who covers any large section of these mountains and then attempts to describe 

 the results of his observations. Such subdivision for a belt lying between the 

 Forty-seventh and Fifty-third parallels of latitude is suggested. 



For scientific writing the well recognized name ' Cordillera of North 

 America,' with the alternative, 'Pacific Mountain System of North America,' 

 is preferred for the chain as a whole. The many other alternative names for 

 the chain are listed. 



The existing nomenclature for the ranges crossed by the Forty-ninth Paral- 

 lel is inadequate and to some extent in confusion. An amplified nomenclature, 

 based as far as seemed possible on prevailing usage, is offered. The main 

 principle adopted is that of existing topographic relations, largely irrespective 

 of the genetic history or rock composition of the different ranges. Specifically, 

 the lines of delineation are the axes of the greater valleys and ' trenches ' in 

 the mountain complex. The Rocky Mountain Trench, the Purcell Trench, the 

 Selkirk Valley, and the Lower Okanagan Valley represent partial boundaries of 

 the Rocky Mountain system, and the Purcell, Selkirk, Columbia, and Cascade 

 Mountain systems at the Forty-ninth Parallel. The suggested subdivisions of 

 these systems for the region adjacent to the International Boundary include 

 the Lewis, Clarke, MacDonald, Galton, Flathead, McGillivray, Yahk, Moyie, 

 Cabinet, Nelson, Slocan, Bonnington, Valhalla, Tend D'Oreille, Priest, Kaniksu, 

 Bossland, Christina, Midway, Colville, Sans Foil, Okanagan, Hozomeen, and 

 Skagit ranges or groups. 



A small area of the Belt of Interior Plateaus is also represented in the 

 Boundary line section. In the preceding list the names in italics are proposed 

 by the present writer. The others date from the expeditions of Palliser, Daw- 

 son, Willis, Smith, Calkins, and MacDonald. The subdivision is illustrated with 

 sketch maps. 



Chapter IV. — The geological description begins with an account of the 

 Rocky Mountain Geosynclinal Prism, of which nearly all the mountains 

 between the Great Plains and the summit of the Selkirks are composed. Chap- 



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