106 THE ROYAL SOCIETY OF CANADA 



The best that can be said for this evidence is that it indicates that the 

 Kishenena formation is probably of Eocene age, and to that extent 

 it indicates that the Laramide revolution is probably not later than 

 Eocene in date. 



Stewart has shown that the Laramide revolution has deformed 

 strata which he correlates with the Fort Union of Montana, and he 

 dates the Laramide disturbance as post-Fort Union (41, d). The 

 Fort Union formation is generally accepted as Eocene (47, a) and if 

 this be so, the Laramide revolution is not older than early Eocene. 

 Schuchert, however, argues with a good deal of force from the evi- 

 dence given by Stanton (47) for the Cretaceous age of the Fort Union 

 formation (48). An excellent discussion of the debatable strata 

 between the Cretaceous and the Tertiary is given by Rose in his report 

 on the Wood Mountain-Willowbunch Coal Area, Saskatchewan (54). 



The most definite statement regarding the date of the Laramide 

 revolution in this region that can be made from the evidence in hand is 

 that it is later than Fort Union and earlier than the quartzitic con- 

 glomerate of the Cypress hills. Neither its earlier nor its later limit 

 can be more definitely stated than this. A reasonable interpretation 

 of the stratigraphie evidence summarized above places the Laramide 

 revolution as not earlier than the uppermost Cretaceous, nor later 

 than the latest Eocene. 



Before proceeding to a discussion of the present structure of the 

 Rocky mountains and its origin, it may be noted that the history of 

 the region as described here agrees closely with its physiographic 

 development as deduced by Schofield from facts gathered in the 

 Selkirk and Rocky mountains. For the Tertiary and later history, 

 worksby Dawson (13,14), Willis (45), Daly (12), (46), Stewart (41), and 

 Schofield (49) may be consulted. 



Structural Geology 



Structural Features of the Region 



General 



The Rocky mountains between the International Boundary and 

 the Crowsnest pass may be divided structurally into three areas. 

 These structural areas, the geographic relations of which are shown in 

 Fig. 1, will be designated as the western area, the central area, and 

 the eastern area. From the boundary to the North Kootenay pass 

 the three areas are clearly defined; north of this pass the eastern 

 area is characteristically developed, but the distinction between 

 the central and the western areas is not at present clear, if indeed 

 a distinction exists in this part of the region. 



