254 Burling — Purcell Range and Rocky Mountains. 



Art. XXII. — The Relations Between the Purcell Range 

 ""and the Rocky Mountains in British Columbia, Canada; 

 by Lancaster D. Burling. 



During a trip along the Canadian Pacific Railway from 

 Field to Glacier, British Columbia, in 1915, the writer 

 formulated a working hypothesis to explain the strati- 

 graphic and structural interrelations of the Rocky Moun- 

 tain and Purcell Range sections. This differs from those 

 which have been proposed but succeeding observations 

 have more and more convinced him that the hypothesis 

 has elements of plausibility which warrant its presenta- 

 tion, together with such corroborative evidence as he is 

 able to recall. 



In order that we may understand the general relations 

 it may be stated briefly that the Rocky Mountains and the 

 Purcell Range, two mountain systems lying respectively 

 east and west of the Columbia River Valley at Golden, 

 differ markedly in the lithologic character of the rocks of 

 which they are composed. The western rocks are marked 

 by igneous intrusions, the sandstones are not so clean, and 

 there has been considerable metamorphism. In the 

 Rocky Mountains to the east there is little metamorphism 

 and igneous activity appears to be confined to single small 

 centers such as the Ice River valley occurrence south of 

 Field. 



Speaking generally the Rocky Mountains section (to 

 the east) is dominantly calcareous; the Purcell Range 

 section (to the west and nearer to the source of the sedi- 

 ments) is dominantly arenaceous. And between the two 

 there is a relatively narrow belt of crumpled shales in 

 which the Rocky Mountain (Kootenay-Columbia River 

 valley) trench has been cut. 



In the western portion of this intervening shale zone is 

 a fault-contact which represents the trace of the plane 

 along which the shales have been overthrust by the elas- 

 tics of the Purcell Range. (Students will recall that 

 Termier has here postulated thrust faulting of large mag- 

 nitude to account for the relations of the rocks of the 

 Purcell Range to those farther west.) Between the shale 

 zone and the Purcell elastics the change in lithology is 

 abrupt; eastward the change from shale to limestone is 

 gradual and progressive. 



For a long time the rocks in the Purcell Range were 

 believed to be unfossiliferous, but there has been grad- 



