i5i 



is thrust at least n kilometres (7 miles) over somewhat 

 deformed Cretaceous strata. The western limb terminates 

 in a master-fault running in the general line of the Rocky 

 Mountain trench. This fault, with downthrow of at least 

 5 kilometres (3 miles), is likewise the eastern limit of a 

 second synclinorium forming the Purcell mountains and 

 the eastern part of the Selkirks. The western limit of this 



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Looking south from Mt. Tupperto Mt. MacDonald and Mt. Sir Donald (background), 



showing part of the summit syncline of the Selkirks as shown in the Sir Donald 



quartzite forming the great escarpment. Photograph by Howard Palmer. 



broad flexure is a relatively simple monocline extending 

 from the summit of the Selkirks to the primary uncon- 

 formity at Albert Canyon. 



Each synclinorium is unsymmetric, with older strata 

 exposed on the western edge than on the eastern. This is 

 particularly striking in the Selkirks, where the Shuswap 

 terrane is exposed on the west, below the basal beds of the 

 Beltian system, while the Cambrian quartzites appear at 

 the surface not far west of the fault in the Rocky Mountain 

 trench. The maximum amount of uplift registered in the 

 railway section has charactertized the eastern part of the 

 35069— 4A 



