2 GEORGE V. 



SESSIONAL PAPER No. 25a 



A. 1912 



CHAPTER VII. 



STRATIGRAPHY OF THE SELKIRK MOUNTAIN SYSTEM (IN PART). 



SUMMIT SERIES. 



Excluding the igneous rocks, the principal formations encountered in the 

 Nelson range within the ten-mile belt may be grouped in three divisions. The 

 rocks belonging to the oldest division, called the Priest River terrane, are found 

 only on the eastern slope of the range. The rocks of the youngest division 

 are confined to the western side of the range and to the valley of the Pend 

 D'Oreille river, to and slightly beyond its confluence with the Columbia. 

 This younger principal division may be called the Pend D'Oreille 

 group. Lying between these two divisions both geographically and 

 stratigraphically, is the Summit series, a large part of which is the equivalent 

 of the whole Purcell series. The present chapter is devoted to a summary 

 description of the Summit series. It will be followed by a chapter of the corre- 

 lation of all four of the great series so far discussed, and then the systematic 

 account of the formations occurring in the Selkirks at the Boundary will be 

 resumed. 



In order to facilitate a rapid understanding of the Summit series a tabular 

 view of the formations is here presented: — 



Formation. 



Lone Star 



Beehive 



Ripple 



Dewdney 



Wolf 



Monk 



Irene Volcanics. . .. 

 Irene Conglomerate 



Thickness in 



feet. Dominant rocks. 



Top. erosion surface? 



2,000+ 



Phyllite and quartzite. 



7,000 



Quartzite. 



1,650 



Quartzite. 



2,000 



Quartzite, with conglomerate. 



2,900 



Silicious grit, sandstone, and conglomerate, 



5,500 



Quartzite, phyllite, and conglomerate. 



6,000 



Efiu6ive greenstones. 



5,000 + 



Conglomerate. 



32,050 + 



Base, unconformity with Priest River terrane. 



Irene Conglomerate Formation. 



The basal member of the Summit series is a conglomerate, outcropping 

 on the summit and slopes of Irene mountain. It has, accordingly, been named 

 the Irene Conglomerate formation. Excellent exposures are numerous along 

 the outcrop from the International line to the Bayonne batholith, eight miles 

 distant. (Plate 16.) The most instructive section was found on the long 



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