356 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



Tertiary. The great resemblance of this granite to the aplitic type apophysal 

 from the Trail batholith suggests a genetic connection between that batholith 

 and the stocks, as if the latter are satellites from the former, in the same fashion 

 as the Summit stocks, Lost Creek body, and Bunker Hill stock are satellitic 

 to the great Bayonne batholith. Yet it is possible that the Sheppard granite is 

 not closely associated in age with the Trail granodiorite. The two are genetically 

 •connected perhaps only in the sense that the same underground conditions under 

 which the aplite of the batholithic apophyses was developed, prevailed also at 

 the later date when a new magmatic invasion affected the region. If this be 

 true, the Sheppard granite may have been a differentiate from a more basic 

 magma like the Trail granodiorite but younger than that batholith and not 

 exposed in the Boundary belt. 



PORPHYRITIC AUGITE-OLIVINE SYENITE. 



Just south of the point where the Crowsnest line of the Canadian Pacific 

 railway turns out of McRae creek valley and enters that of Christina lake, the 

 railway cuttings for some 600 feet cross a peculiar basic rock which deserves 

 special note. It is a stock-like body, intrusive into crystalline limestone and 

 schists of the Sutherland complex. To each side of the railway track the expo- 

 sures are poor and the exact ground-plan of the body could not be discovered in 

 the time available for its study. A larger mass of the same rock occurs as an 

 intrusive mass, about a half mile in diameter, at the head of Fifteen-mile creek 

 north of the Pend D'Oreille river (see map). Erratic boulders of the 

 rock are to be found on the flat west of the Alice mine, north of Creston, and 

 clearly come from a third locality. The repeated discovery of this unusual rock 

 at widely separated points shows tbat its peculiar structure is not merely a local 

 accident but the persistent product in the crystallization of a definite magmatic 

 type. 



The rock at the Christina lake locality is a fresh, dark gray to greenish or 

 bluish-gray, medium-grained to rather coarse-grained aggregate of augite, 

 olivine, biotite, plagioclase, and orthoclase; in this aggregate relatively enor- 

 mous phenocrystic foils of dark green biotite lie embedded at all angles. The 

 irregular surfaces of the mica-foils range in diameter from 1 cm. to 3 cm. or 

 more, while their thickness is seldom over 1 mm. As the rock is fractured under 

 the hammer the broken surfaces are so generally bounded by the cleaved pheno- 

 crysts that the rock is decidedly facetted in a striking way. 



Though the rock is almost perfectly fresh, the lustre of the large biotites is 

 rarely higher than the metallic; the lustre is impoverished by a very marked 

 magmatic corrosion of the biotites which, in thin section, have an apparent 

 poikilitic structure in consequence. The more minute biotites of the ground- 

 mass have the usual high lustre of the micas. The optical angle of the pheno- 

 crystic mica is (2 E) about 15° ; that of the ground-mass mica is over twice as 

 large (2 E = about 35°). Both are highly pleochroic in tones from dead-leaf 

 yellow to deep reddish-brown. 



