176 THE GEOLOGY OF THE CAXOBOLAS xMOUNTAINS, 



Note: this specimen and the preceding, X.625j are clastic 

 fragments out of the tuff-beds. 



No.X.638. Vesicular, bluish-grey Trachyte. Loc: Forbes 

 Road, near Molong Road. 



This rock varies in grain-size from cryptocrystalline to micro- 

 crystalline, and has pilotaxitic fabric. Its components are 

 felspar, jegirine, arfvedsonite, and laavenite(!). 



No.X.631. Compact, bluish-grey Trachyte. Loc: east side of 

 Plowman's Farm. 



Texture : holocrystalline, porphyritic, perpatic, with very fine 

 even-grained trachytic base. 



Composition : the dominant constituent is felsjmr. As minor, 

 yet essential, constituents, there are quartz, arfvedsonite, and 

 barkevicite. The felspar phenocrysts consist of cryptoperthitic 

 anorthoclase of prismatic habit. The felspar of the base consists 

 of lath-shaped microlites of sanidine (soda-rich?). The amphibole 

 in poikilitic aggregates is pleochroic in brownish-yellow, greenish- 

 blue, and blue-black. The brownish tints come mainly from the 

 edge of each grain, and appear to be due to a rim of barkevicite 

 surrounding each arfvedsonite grain. Secondary leucoxene and 

 quartz are present. 



Name : Trachytic Arf vedsonite-Comendite. 



No.X.630. Soda-Trachyte. Loc: north side of Young Man. 



Handspecimen : compact, fine-grained, bluish rock, with a few 

 phaneric crystals. 



Texture: holocrystalline, with trachytic fabric in the fine even- 

 grained base. 



Constituents : (a) felspar of two generations, (b) quartz,, 

 (c) riebeckite, (d) wohlerite. The phenocrysts consist of anortho- 

 clase. They are of orthophyric habit, more or less corroded, and 

 show shadowy extinction from ultraraicroscopic twinning. They 

 are optically negative and almost uniaxial; a lies near the a axis. 

 The felspar of the base consists of lath-shaped sanidine microlites 

 with Carlsbad twinning. Quartz is a rather abundant con- 

 stituent in the base; it is quite allotriomorphic, and often com- 



