REPORT OF THE CHIEF ASTRONOMER 459 



SESSIONAL PAPER No. 25a 



do not fully or directly answer the question but the mineralogical features of 

 the respective rocks are alike in so many special ways that one must believe in 

 a genetic bond between the masses. On comparing many thin sections from 

 type-specimens of each mass the writer lias found certain significant characters 

 in common, which are briefly noted in the following list : — 



a. An unusually beautiful polarization pattern in the essential microcline- 

 niicroperthite feldspars; these minerals are of sensibly identical nature in the 

 two bodies. 



o. In eacb mass the common recurrence of narrow sbells of olive-green 

 hornblende enclosing the pale green augite. 



c. The essentially similar nature of the hornblende whether as rims or as 

 independent crystals within the two masses. It varies somewhat in depth of 

 tint but is always of this scheme: 



a=pale grayish green. b=olive-green. 



C=olive-green. 

 Tbe extinction on (010) is slightly variable but the measurements always 

 Jan between 14° and 22°, indicating in all probability a common variety of born- 

 blende. 



d. In each mass tbe recurrence of essential brown biotite with sensibly 

 constant optical properties. 



e. The augite of tbe basified sbell in tbe batholith is a variety closely 

 similar to if not identical witb that characterizing the Ivruger body. 



We seem justified in concluding that, in spite of the strong chemical con- 

 trasts of the two masses, they have family traits suggesting that both belong 

 to one petrogenic cycle. 



Bikes Cutting the SimilJcameen Batholith. — The coarser phase of the Simil- 

 kameen granite is cut, not only by the younger phase and by apophyses of the 

 Cathedral granite, but also by a few basic dikes. One of these dikes has been 

 examined with the microscope and found to be a medium-grained hornblende- 

 diorite porphyrite, with phenoci'ysts of hornblende and andesine in a granular 

 ground-mass of plagioclase and hornblende microlites and quartz. 



The younger phase of the granite is cut by a few narrow dikes of black, 

 fresh-looking trap which is not porphyritic to the naked eye but, under tbe 

 microscope, shows phenocrysts of basic labradorite, Ab x An 2 , colourless augite, 

 and dark green hornblende. The rock is an augite-hornblende porphyrite 

 and all of these dikes are probably genetically connected with the porphyrite 

 cutting the coarser phase of the batholith. 



Cathedral Batholith. 



Older Phase. — The youngest of the batholithic intrusives is petrographically 

 the simplest of all. Its material is singularly homogeneous, both mineralogically 

 and textu'rally. The rock is a coarse-grained, light pinkish-gray biotite granite 

 of common macroscopic habit. Tbe essential minerals are microperthite, quartz, 



