150 



strength and complication, including the presence of local 

 unconformities, this prism is already known to extend from 

 Colorado to Western Alaska. Throughout the length 

 of the Cordillera in Canada and Alaska as well as in the 

 United States proper, the Rocky mountains are almost 

 wholly composed of the prism; hence this gigantic unit 

 has been named the Rocky Mountain Geosynclinal. On 

 its back have been deposited, unconformably, local geosyn- 

 clinals of late-Mesozoic and of early Tertiary dates. 

 These have major axes parallel to that of the older, greater 

 prism and parallel to the general axis of the Cordillera. 

 The whole, compound assemblage of sediments forms the 

 Eastern Geosynclinal Belt of the Cordillera. 



On the other hand, the chief sedimentary rocks of the 

 Coastal system of mountains — including the Coast range 

 of Alaska and British Columbia, the Vancouver range, 

 the Olympic mountains, the Cascade range, and the Sierra 

 Nevada of California — are of Carboniferous (Pennsyl- 

 vanian), Triassic, and Jurassic age. These beds were 

 deposited in a broad, very long zone of subsidence. The 

 sedimentation was not continuous; there are local uncon- 

 formities in the series. Yet, as a whole, this deposition 

 was long-continued and on a regional scale within the 

 geographical zone described. Since, moreover, the clastic 

 strata were deposited in Pacific water and represent 

 detritus largely from the Eastern Belt, the whole complex 

 prism may be called the Main Pacific Geosynclinal. After 

 a late-Jurassic orogenic revolution affecting this entire 

 prism, local areas of the now deformed zone were down- 

 warped and received heavy loads of sediment in the form 

 of Cretaceous and early Tertiary geosynclinal prisms. 

 These, along with the much greater Main Pacific Geosyn* 

 clinal, form the Western Geosynclinal Belt of the Cordillera. 



Between the two belts, on the line of the Canadian 

 Pacific Railway, lies the Shuswap Terrane, the third and 

 last of the major sedimentary provinces. Its rocks are 

 of Pre-Cambrian (pre-Beltian) age. In our section, the 

 eastern limit of the terrane is at Albert Canyon on the 

 western slope of the Selkirks; its western limit is a few 

 miles below the outlet of Little Shuswap lake, in the Belt 

 of Interior Plateaus. 



Along the railway, the Rocky mountains form a syncli- 

 norium, broken by numerous faults and by occasional 

 zones of mashing. The eastern limb of the synclinorium 



