REPORT OF TEE CEIEF ASTRONOMER 393 



SESSIONAL PAPER No. 25a 



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and interstitial quartz are the primary accessories. The rock may be classified 

 as a biotite-hornblende diorite. 



Granodiorite. — The granodiorite sends apophyses into the diorite and at a 

 few points encloses blocks of it, so that their relative age is determined. The 

 granodiorite is rather coarse-grained and of a reddish-gray colour much lighter 

 than that of the diorite. The constituent feldspars include basic andesine near 

 Ab 4 An 3 (dominant), with orthoclase and microperthite. The other essentials 

 are quartz, biotite, and hornblende, each of which has optical characters like 

 those of the respective minerals in the older diorite. This rock too is notably 

 crushed and altered. Epidote, calcite, and kaolin are very abundant secondary 

 constituents. 



Diorite and granodiorite disappear on the east under the Tertiary arkose 

 and lavas, so that the whole original extent of these plutonic bodies is not 

 known. 



A larger area of somewhat crushed granodiorite is exposed on the slope 

 south of the confluence of Bock creek and Kettle river. In that area some 

 three square miles of the Boundary belt are underlain by the granodiorite which 

 seems to have the field relations of a typical stock or batholith. The body 

 extends for an unknown distance south of the Boundary line. It sends a con- 

 spicuous, wide apophysis northward to the Kettle river at the ' Riverside Hotel.' 

 This great dike cuts the Anarchist phyllites and seems to be continued beyond 

 the river by a strong dike of the same rock, cutting limestone and quartzite. 



Petrographically this granodiorite is practically identical with that cropping 

 out at the forks of Bock creek but has a basified contact -phase recalling the 

 quartz diorites. 



Dunite. — Dunite, generally altered to serpentine, occurs at two different 

 localities in the valleys of Bock creek and Kettle river. One mile up the river 

 from their confluence several large outcrops of heavily slickensided serpentine 

 and talc, shown microscopically to have been derived from a pure olivine- 

 chromite rock, were found. The structural relations and total area of this body 

 could not be accurately determined. On the west and southwest it is either 

 covered by Tertiary conglomerate or cut off by the chonolith of rhomb- 

 porphyry. On the east the serpentine disappears beneath the river gravels and 

 it was not found in place beyond the river. 



In the deep gorge of Bock creek, immediately below Baker creek, a some- 

 what less obscure occurrence of the dunite was discovered. In spite of the pro- 

 found crushing to which the dunite and its country-rocks have been subjected, 

 it seems clear that the dunite forms an intrusive dike at least 100 feet wide, 

 striking in a general northeast-southwest direction. A yet larger dike, 

 measuring 300 feet in width, crops out on the slope a half-mile west of the forks 

 of the creek. Both dikes cut the Anarchist phyllite and associated rocks. The 

 dunite is like that on the Kettle river, which is, therefore, probably also a great 

 dike and contemporaneous with the dikes on Bock creek. 



The dike at the canyon has been studied with more care than the others 

 and has been subjected to chemical analysis. In general, the rock is massive, 



