BE POET OF THE CHIEF ASTROXOMEK 197 



SESSIONAL PAPER No. 25a 



The observations of Dawson, MoCounell, and McEvoy serve to warrant 

 the belief that the western rim of the geosynclinal may be traced through the 

 whole length of British Columbia to the Sixtieth Parallel of latitude. The study 

 of British Columbia geology impresses one, however, with the difficulty of 

 locating this rim with precision. For hundreds of square miles together the 

 beds of the geosynclinal are either buried out of sight by younger formations 

 or have been replaced by batholithic intrusions on a gigantic scale. Even 

 where, in many places, the Belt-Cambrian rocks are exposed, they have been 

 so metamorphosed by crushing and by thermal action that the true nature and 

 relation of the beds is very obscure. In each one of the following cases, there- 

 fore, the location of the rim of the geosynclinal is to be considered as only 

 approximate. Future investigation may show that errors as great as fifty 

 miles in longitude may have been made in these locations. The scale of the 

 geosyncline is, however, so great that the main conclusions regarding the posi- 

 tion and extent of the huge down-warp and of its sedimentary filling are con- 

 sidered as approximately correct. 



At the Canadian Pacific railway section Dawson himself placed the western 

 rim of the geosynclinal within the area occupied by the present Columbia 

 system. 



' In the earlier series of deposits assigned to the Cambrian, we dis- 

 cover evidence of a more or less continuous land area occupying the 

 position of the Gold ranges and their northern representatives and aligned 

 in a general northwesterly direction. The Archean rocks were here 

 undergoing denudation, and it is along this axis that they are still chiefly 

 exposed, for although they may at more than one time have been 

 entirely buried beneath accumulating strata, they have been brought to 

 the surface again by succeeding uplifts and renewed denudation. We 

 find here, in effect, an Archean axis or geanticline that constitutes, I 

 believe, the key to the structure of this entire region of the Cordillera. 

 To the east of it lies the Laramide geosyncline (with the conception of 

 which Dana has familiarized us), on the west another and wider geosyn- 

 cline, to which more detailed allusion will be made later. 



' Conglomerates in the Bow River series indicate sea margins on the 

 east side of this old land, but these are not a marked feature in the 

 Nisconlith, or corresponding series on its western side. Fossils have so 

 far been discovered only in the upper part of the Bow River series, but 

 the prevalence of carbonaceous and calcareous material (particularly in 

 the Xisconlith) appears to indicate the abundant presence of organisms of 

 some kind at this time. 



' Although no evidence has been found of any great physical break, 

 the conditions indicated by the upper half of the Cambrian are very 

 different from those of the lower. Volcanic materials, due to local erup- 

 tions, were accumulated in great mass in the region bordering on the 

 Archean axis to the west, while on the east materials of this kind appear 

 to be mingled with the preponderant shore deposits of that side of the 



