204 



laiometxes hence the appropriate name, Dogtooth moun- 

 tains, for this division of the Purcells, situated 

 between Quartz creek and the Columbia. A 

 narrower, tightly compressed syncline forms 

 the adjacent lower and less rugged range, 

 called the Prairie Hills. That mountain group 

 overlooks the broad Beaver River trough 

 which, between Six Mile Creek (68 -o mis.) 

 and a point many miles south of Beaver Creek 

 (78-0 mis.), is an anticlinal valley excavated 

 in the relatively friable rocks of the Cougar 

 formation. 



The Purcell mountain system is thus essen- 

 tially a mass of Beltian strata folded with 

 comparative regularity. The Cordilleran strike 

 (here N. 30 W.) is generally well preserved 

 throughout the whole area covered in this 

 part of the Purcell system, as it is in the much 

 broader section mapped at the International 

 Boundary, far to the south. However, the 

 folds show local disorder ; they were accompanied 

 by subordinate fractures and, where closely 

 appressed, by mashing and by the development 

 of slaty cleavage. 



Three kilometres beyond Donald, soon after 

 crossing the river, the railway enters a long 

 series of rock cuts, where the river leaves the 

 main trench, and is cutting a long canyon 

 across the folded and mashed Paleozoics. On 

 the right bank of the river, for a distance of 

 many kilometres, is a mountain block separated 

 from its structural equivalent, the Dogtooth 

 range, by a late Glacial diversion of the river 

 from the broad trench on the east. The 

 Paleozoic shales and limestones, standing at 

 high angles, can be seen in the walls of the 

 canyon. Near the tunnel marked as 54-6 

 miles from Field, fossils of late Upper Cambrian 

 age, including an Illenurus and a genus like 

 Dicellocephalus, have been found in abundant 

 calcareous nodules formed in shale and impure 

 limestone. 



The strata grow more and more disordered 

 until the great Trench fault is reached, at a 



