NO. 4 PRE-DEVONIAN SEDIMENTATION 173 



Ozarkiaii, Upper and Middle Cambrian limestones and Lower Cam- 

 brian sandstones, arenaceous and siliceous shales. 



Limestones 9,400 feet (2,865.1 m.) 



Sandstones and shales 3,900 feet (1,188.7 ni.) 



The formations of the Robson Trough are of the general character 

 of those of the Glacier Lake and Bow Troughs. They differ in details 

 and contained faunas, but there is sufficient similarity to lead to the 

 conclusion that they were deposited in connecting troughs of the 

 Cordilleran Geosyncline and possibly in a more or less continuous 

 trough that extended from north of the Robson District to south of 

 the Bow Valley. 



It is to be regretted that we do not have a section of the pre- 

 Devonian formations east of the Moose Pass fault, as it is possible 

 that not only a great thickness of LIpper Cambrian strata is present, 

 but also Ozarkian, Ordovician, and possibly Silurian. The Silurian 

 occurs to the north in Alaska and to the south in the Beaverfoot- 

 Brisco-Stanford Range of British Columbia, and the Devonian in the 

 ridges east of the Upper Cambrian and northeast of Henry House. 



It is to be noted that in the Robson and Glacier Lake Districts 

 the known Upper Cambrian rocks are east of the Continental Divide 

 and in the Bow-Kicking Horse area they are west of the divide. 



