276 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



of the Wood River series in his report will be found to match fairly well with 

 the account of the Pend D'Oreille group just given. 



About one hundred miles to the northward and north-northwestward of the 

 Boundary section at the Pend D'Oreille are considerable areas of stratified 

 rocks referred by Brock to the Cache Creek series or to the Slocan series which 

 he regards as probably equivalent to the Cache Creek-t In that region the 

 Cache Creek series is made up of ' dark argillites, greywaekes, quartzites and 

 limestone, with some eruptive material ' ; the description of the Slocan series 

 is in similar terms. In the Kamloops district, still farther northwestward, the 

 Cache Creek beds are well exposed and there they have been studied in some 

 detail by Dawson. His summary statement of their succession is as follows : — 



■ The lower division consists of argillites, generally as slates or schists, 

 cherty quartzites or hornstones, volcanic materials with serpentine and 

 interstratified limestones. The volcanic materials are most abundant in the 

 upper part of this division, largely constituting it. The minimum volume 

 of the strata of this division is about 6,500 feet. The upper division, or 

 Marble Canyon limestones, consists almost entirely of massive limestones, 

 but with occasional intercalations of rocks similar to those characterizing 

 the lower part. Its volume is about 3,000 feet. 



' The total thickness of the group in this region would therefore b<? 

 about 9,500 feet, and this is regarded as a minimum. The argillites are 

 generally dark, often black, and the so-called cherty quartzites are probably 

 often silicified argillites. The volcanic members are usually much decom- 

 posed diabases or diabase-porphyrites, both effusive and fragmental, and 

 have frequently been rendered more or less schistose by pressure.'* 



Much of the Cache Creek series is fossiliferous and definitely Carboni- 

 ferous (Pennsylvanian), but Dawson points out that the lower beds may include 

 formations somewhat older than the Carboniferous. He emphasizes, after 

 many years of experience, the great constancy of the series from the Yukon 

 boundary of British Columbia southward throughout the length of British 

 Columbia. 



In view of these various facts it seems to be the best working hypothesis 

 that these greatly metamorphosed rocks of the Pend D'Oreille group roughly 

 correspond to the Cache Creek series and that they are in large part of Car- 

 boniferous age. The lower schists may include sediments of any age from the 

 Carboniferous to the Silurian inclusive. There is no evidence of unconformity 

 with the Summit series; the Pend D'Oreille schists seem, on the other hand, 

 to pass gradually into the underlying Lone Star schists. Because of the special 

 local intensity of thermal and dynamic metamorphism it must be long before 

 the correlation of the Pend D'Oreille group is anything other than hypothesis. 

 Yet, as in so many cases, the tentative correlation seems to be better than none, 



t R. W. Brock, Explanatory* notes to West Kootenay sheet, issued by the Geo- 

 logical Survey of Canada, 1902. 



* G. M. Dawson, Bull. Geol. Soc. America, Vol. 12, 1901, p. 70. 



