178 



THE ROYAL SOCIETY OF CANADA 



a division may be made in the Rocky Mountains between an eastern 

 area in which later Palseozoi'c and younger sediments are predomi- 

 nant and a western one in which Cambrian and older strata are mostly 

 in evidence. The dividing line, where it crosses the Bow valley and 

 incidentally is opposite the deepest part of the present Alberta syn- 

 cline, is marked by a steeply dipping fault plane with a maximum 

 downthrow to the east estimated at thirty thousand feet. Westward 

 to the Beaverfoot valley this fault block is but slightly deformed and 

 dips gently westward. A thickness of five miles of material has been 

 removed from its eastern edge which could not have been elevated 

 and denuded within the same space of time that may be allowed for 



Figure 1 



The divisions of the Rocky mountains (areas marked by vertical lines represent 

 the earlier formed ranges) and outline of area occupied by Upper Cretaceous sedi- 

 ments (contour lines indicate shape of the bottom of the basin). 



