2 GEORGE V, SESSIONAL PAPER No. 25a A. 1912 



CHAPTER XII. 



INTRUSIVE ROCKS OF THE SELKIRK MOUNTAIN SYSTEM. 



Erom the Great Plains to the Pureell Trench the igneous-rock geology of the 

 Boundary section shows relative simplicity. It has centred principally around 

 the discussion of the Pureell Lava formation and the basic sills and dikes of the 

 Pureell mountain system. Crossing the trench westward we enter a region where 

 igneous rocks become areally important and, because of their petrographical 

 variety and complicated relations, deserve considerable attention. All the rest of 

 the Boundary belt, from the Pureell Trench to the Fraser flats at the Pacific may 

 be described as an igneous-rock field. It is not always possible to treat of the 

 many intrusive and extrusive bodies in groups corresponding to the various 

 mountain ranges crossed by that long belt. In somes cases the igneous-rock 

 bodies are crossed by the master valleys which have been taken as the convenient 

 lines of separation between the ranges. This is true of several of the igneous- 

 rock units which, in part, make up the Selkirk system at the Forty-ninth Parallel. 

 It happens that the larger areas covered by these bodies occur in the adjacent 

 Rossland mountain group of the Columbia system, and it is appropriate to discuss 

 such areas in the following chapter devoted to the geology of the Rossland moun- 

 tains. In that chapter will, then, be described the formations which have been 

 mapped under the names ' Rossland Volcanic group,' ' Beaver Mountain Volcanic 

 group,' ' Trail batholith,' ' Sheppard granite,' and ' Porphyritic olivine syenite.' 

 (Maps No. 7 and 8.) 



In the present chapter there will be noted in some detail two granitic bodies, 

 named the Rykert and Bayonne batholiths; several stocks which appear to be 

 satellitic to the Bayonne batholith ; a sill or dike of very abnormal hornblende 

 granite which cuts the Kitchener quartzite near Corn creek; sills and dikes of 

 metamorphosed basic intrusives cutting the Priest River terrane; numerous 

 lamprophyric dikes and sills and other basic intrusions, together with a few acid 

 dikes and sills cutting the younger sedimentary formations as well as the Priest 

 River terrane; and a boss of monzonite near the main fork of the Salmon river. 

 No attempt will be made to describe these bodies rigidly in their order of age or 

 geographical arrangement, though the usual procedure of taking them up in the 

 order from east to west will be followed. The difficult problem of their succes- 

 sion in geological time will be discussed in a following section. 



The Irene Volcanic formation has already been described in its natural place 

 as a member of the Summit series. Further reference to it is unnecessary except 

 in the general summary on the igneous rocks of the Selkirks. 



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