84 G. M. DAWSON — ROCKY MOUNTAIN KEGION IN CANADA 



Dr. Whiteaves. They include a number of still living forms, but may 

 be regarded as Pliocene or later Miocene.* 



Physical History of the Region 



It will now 1)6 endeavored to briefly review the orographic changes 

 and the conditions of deposition of which the geological column gives 

 evidence — in other words, to touch in outline the main facts of the phys- 

 ical history of the Rocky Mountain region of Canada. 



As for the Archean, it need onW be said that here, as in nio^t parts 

 of the world, we find beneath any rocks that can be assigned to the Cam- 

 brian in the most extended sense of that term, and a})parently separated 

 from these rocks by a great break and unconformity, a crystalline series 

 or "fundamental comi)lex'' composed of plutonic rocks with highly 

 metamorphosed and vanishing sedimentary rocks in seemingly inex- 

 tricable association. The similarity of this basal series in different parts 

 of the world is so great as apparently to imply world-wide and approx- 

 imately contemporaneous conditions, of a kind perhaps differing from 

 any that can have occurred at later periods. The region here described is 

 not, however, an ideal one for the study of these Archean rocks, because of 

 the extreme metam()ri)hism by which much newer formations have often 

 been affected in it ; nor has any series yet been defined that appears here 

 to bridge the gap between the Archean and the strata that may with pro- 

 priety be attached to the Cambrian. 



In the earlier series of dei)osits assigned to the Cambrian, we discover 

 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 under- 

 going denudation, and it is along this axis that they are still chiefly ex- 

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

 buried beneath accumulating strata, they have been brought to the sur- 

 face again by succeeding ui)lifts 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 geosyncline, 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 preva- 



*See Report, of Progress. Geol. Siirv. Can., 1878-79, p. 87 B. 



