184 THE GEOLOGY OF THE CANOBOLAS MOUNTAINS, 



C.12. Dark greenish Trachyte. Loc: Watt's Pinnacle. 



Texture: holocrystalline; porphyritic, dopatic; base fine-grained, 

 and pilo taxi tic. 



Composition: the phenocrysts consist chiefly of microcline- 

 microperthite and anorthoclase, but smaller ones of jegirine- 

 augite and corroded magnetite are also present. The microcline 

 microperthite shows characteristic cross-hatching. The felspar 

 of the base is lath-shaped soda-sanidine. The segirine-augite 

 occurs in strongly pleochroic, corroded idiomorphs, and also in 

 the base as minute grains and rods. It is developing a uralitic 

 cleavage. 



Name: Pilotaxitic ^girine-Trachyte. 



C.23. Greenish Trachyte. Loc: east of Bald Knob. 



Texture: holocrystalline; porphyritic, trachytic with well 

 marked flow-structure. 



Composition: felspar forms about 80% of the rock; segirine- 

 augite about 15%; magnetite and other constituents about 5%. 

 These minerals have the same characters as in C.1'2. The felspar 

 and pyroxene crystallised together throughout, and hence 

 mutually interfere with one another's crystallographic develop- 

 ment. Secondary limonite and haematite are present. 



Name: Trachytic ^girine-Trachyte. 



Note: the difference between melanocratic trachytes (such as 

 C.12 and C.23) and leucocratic trachytes (such as X.631, C.13, 

 C.28) lies neither in texture, nor in the nature of the contained 

 minerals, but in the greater abundance of segirine and magnetite 

 in the former type, whereby it acquires its darker colour. 



C.8. Dark green aphanitic Trachyte. Loc: Cox's Gully, 

 south of The Old Man. 



Texture: holo- or hypocrystalline; porphyritic, perpatic: base, 

 very fine, microcystalline, even-grained, trachj^tic 



Composition: the felspar phenocrysts are strongly resorbed at 

 the edges, and are traversed by cracks filled with katapleiite. 

 Some consist of anorthoclase, others of microcline-microperthite. 

 They occasionally include biotite. Idiomorphic magnetite occurs 



