Petrology of Victorian Granites. 219 



is somewhat intense, it appears to be entirely free from inclusions. 

 The quartz and biotite present no features of interest. A small 

 quantity of apatite is shown in the slides. 



A vein about one inch thick traverses the quarry, it is a fine- 

 grained rock which appears, in the thin slide, to be composed of 

 grains of quartz on which a nionoclinic felspar is moulded. It 

 contains a small amount of mica, but there is no trace of horn- 

 blende. It is essentially an acid rock. 



A feature of interest in the quarry is a large sub-angular block 

 of quartzite contained in the granite. It appears identical in 

 microscopic character with metamorphosed rock occurring near 

 the junction of the syenite and silurian beds. 



Mo7tnt Martha Point. — The main rock here does not differ 

 from the syenite of Watson's quarry except that the hornblende 

 ■ is less frequently present. It is traversed by thin veins similar 

 to the one above described. It possesses some interest however 

 in the occurrence of (1) a vein of pegmatite, (2) dark ovoid-shaped 

 basic secretions. 



The pegmatite vein appears macroscopically to be composed of 

 felspar and quartz only, but the microscope shows the presence 

 of a minute quantity of biotite. The feLspar appears to \)% 

 exclusively orthoclase, and there is considerable intergrowth of 

 quartz and felspar. Hornblende is absent. 



The basic secretions occur in small ovoid masses rarely more 

 than a few feet in diameter. The normal form is a fine-grained 

 dark rock in which biotite is the prevailing mineral, variation 

 from this type arises from the occurrence in the rock of porphy- 

 ritic masses of pink felspar. Examined microscopically, the rock 

 is seen to be a crystalline granular aggregate of mica, quartz and 

 orthoclase, with a small amount of hornblende. [One slide failed 

 to yield any traces of hornblende]. The almost entire absence of 

 a triclinic felspar is noticeable. Sphene and apatite ai-e both 

 jDresent in small quantities. 



Drojuana. — Quarry on Arthur's Seat. — A fine-grained syenite 

 in which a pink felspar, quartz and mica are visible. In the thin 

 slide the nionoclinic felspar is seen to preponderate over the 

 triclinic, it is frequently twinned according to the Carlsbad law. 

 The triclinic felspar is occasionally an inclusion in the monoclinic. 

 Hyp-idiomorphic crystals of a light green hornblende showing 



