[MACKENZIE] HISTORICAL AND STRUCTURAL GEOLOGY 109 



great length and unusual steepness. These faults are associated 

 with strong folds (34), (41), (24, c). The faulting is more pronounced 

 in the vicinity of the Crowsnest pass than it is near the boundary 

 where the Cretaceous rocks are not disturbed to the extent that they 

 are both to the north and to the south of the international line. The 

 principal faults of the area are shown in Fig. 1. As the hypotheses 

 of the development of the present structures of the region are largely 

 dependent on the characteristics of these faults, they will be described 

 in some detail. 



Reverse Faults 



Extent. — These faults extend for miles, many of them for dozens, 

 and some of them for scores of miles, and throughout nearly the whole 

 of their extent they closely parallel the strike of the rocks. At their 

 ends, however, where they vanish in folds, there is of necessity a 

 discordance in strike. 



Characteristics of the Parting Surface. — There is surprisingly 

 little disturbance of the strata in the neighbou^^hood of these faults, 

 and breaks of several thousand feet displacement take place on what 

 is apparently a single surface, or in a zone at the most not over a 

 few feet thick. A similar effect has been noted by Stebinger in Mon- 

 tana (40, a). Occasionally along the course of a fault there are what 

 may be termed "zones of regional brecciation" where there is much 

 minor reverse faulting along the line of a single break. Two of such 

 zones are shown on Rose's map of the Blairmore area, one east of 

 McGillivray ridge and one on York creek, and I have seen similar 

 occurrences in the foothills south of the Blairmore area. It is possible 

 that this "regional" brecciation is a more common occurrence than 

 has been recognized, but in general, the faults are probably simple 

 breaks. 



Near the main line of the Canadian Pacific Railway in the Rocky 

 mountains McConnell has noted that faults occur "without much 

 preliminary bending" (21, a). It is worth noting in this connection 

 that one of Cadell's experimental results was that reverse faults often 

 develop on the application of horizontal pressure without previous 

 folding (7). 



Dip. — Apart from their great length, the high angle of dip of 

 these faults is their most striking characteristic. Though low angle, 

 faults have been recognized in the eastern structural area, they are 

 exceptional (24, c), (41, e). These low angle thrusts are readily 

 recognized by their sinuous outcrops, whereas the steeper reverse 

 faults are remarkably straight, even in a region of considerable 



