888 THE GEOLOGY OF THE NANDEWAR MOUNTAINS, 



present. The magnetite appears to be partly secondary after 

 arfvedsonite. 



Name : Nepheline-Acmite-Syenite Porphyry, allied to Solvs- 

 bergite. 



A rock closely allied to the preceding is N.8 (Pl.L, fig. 3), 

 which also occurs as a rolled specimen in Bullawa Creek. It is 

 holocrystalline, porphyritic, with a fine-grained base, and has a 

 trachytic fabric inclining to camptonitic. 



The felspar phenocrysts have lozenge-shaped outlines in the 

 sections like the felspar of rhomben-porphyr. They are twinned 

 on the Carlsbad plan and exhibit a very fine polys3^nthetic 

 twinning as Avell which shows that they belong to the species 

 anorthoclase. The refractive index is less than that of canada 

 balsam. Reddish iron ores (hsematite) occur in dendritic aggre- 

 gates secondary after a hornblende of the riebeckite group. 

 The base consists essentially of lath-shaped microlites of sanidine, 

 between which are studded minute stunted rods of segirine, a 

 little primary as well as secondary magnetite, and some inter- 

 stitial quartz. 



This rock is a somewhat decomposed solvsbergite. It difiers 

 from N.27 mainly in that it is more decomposed and contains a 

 little quartz instead of nepheline. 



Still more closely allied to N.27 is another rolled specimen, 

 N.9, from Thor's Creek. Its texture is the same. The pheno- 

 crysts consist chiefly of orthoclase, occasionally of microperthite. 

 The orthoclase of the base is allotriomorphic in more or less 

 rounded grains. There are numerous haematite or ferrite 

 skeletons replacing w^hat was originally a hornblende. Both 

 idiomorphic primary, and dusty secondary, magnetite occur. 

 Apatite is abundant and ^girine occurs sparingly in the base. 

 The segirine is of a bright malachite-green colour, strongly pleo- 

 chroic, but of a colour so deep as to almost obscure birefringence. 



This rock must be referred to the species Solvsbergite. 



N.ll. Loc: branch (E.) of Oakey Creek under Mount Odin. 

 (Pl.L, fig.4). 



