159 



was washed into the geosyncline fron land masses located 

 in the longitudes of Montana and Wyoming. 



In Arizona, Colorado, and elsewhere in the United 

 States, the early Cambrian was a time of erosion following 

 local deformation in the Rocky Mountain Geosynclinal 

 area; and in the late Middle Cambrian a re-submergence, 

 contemporaneous with the marine transgression elsewhere, 

 restored conditions of sedimentation in the zone. In 

 British Columbia and Alberta, however, there appears to 

 be perfect conformity throughout the Cambrian. Opinions 

 differ as to the existence of an erosional break at the base 

 of the Lower Cambrian in the Rockies. Walcott has 

 announced the existence of an unconformity in the rocks 

 of the Bow valley but later observations by Dr. Allan and 

 by the present writer indicate that the break at this horizon 

 must in any case be local and does not represent a long inter- 

 val of time. 



As yet it is impossible to locate the line of maximum 

 thickness for the geosynclinal. In the railway section 

 the Beltian and Lowei Cambrian strata grow thinner as 

 they are followed eastward into the Rocky mountains, 

 where the Middle and Upper Cambrian strata have their 

 greatest known strength. 



Next to the clastic material won from the adjacent 

 lands, the most abundant constituent of the Rocky Moun- 

 tain Geosynclinal is carbonate, chiefly limestone with some 

 true dolomite. All of the pre-Ordovician carbonate- 

 rock and most of the younger limestone and dolomite 

 seems to be best explained as chemical precipitates. The 

 total of the maximum thicknesses recorded for the carbon- 

 ate rocks is more than 6,000 metres (20,000 feet). 



Though contemporaneous vulcanism is recorded in this 

 great prism at various horizons of the 49th Parallel section 

 as well as elsewhere in the United States, it has added 

 very little to the bulk of the geosynclinal at the Canadian 

 Pacific section. So far as now known, the only occur- 

 rences of lava are those found in the Beltian Cougar 

 formation. 



In the Pennsylvanian (Carboniferous) period the 

 geosyncline was enlarged both eastward and westward 

 on a scale probably surpassing the marine transgression 

 of the Middle Cambrain. Pennsylvanian sediments, 

 chiefly limestone, were laid on the prism and in yet greater 

 thickness limestones, shales, and more silicious beds were 



