BY H. I. JENSEN. 877 



sheets of trachyte with the hornblende completely metamorphosed 

 to ferrite or haematite while it has not been subjected to any 

 more weathering than adjoining arfved^onite trachytes. 



Wohleriie (?), a yellow mineral in acicular crystals, nonpleo- 

 chroic or but slightly so; double refraction strong; refractive 

 index medium. This mineral shows the characteristic yellow 

 cracks of wohlerite and is apparently the product of the pneu- 

 matolytic action which broke down the katophorite molecule. 

 It is more abundant in tegirine-ferrite trachytes than in the rocks 

 rich in arfvedsonite. 



Lavenite (?) or Rosenbuschite (I) appears to be present in some 

 of the rocks, but has not been identified with certainty. 



Tridymite occurs occasionally in vesicles; often yellowish, 

 almost isotropic opal is seen; occasionally banded chalcedony 

 replaces it. 



Aleionite (i) (or an allied scapolite mineral such as wernerite 

 or marialite) in clear glassy or milky-white crystals, showing a 

 good cleavage, weak double refraction and medium refractive 

 index, is sometimes present. 



Where quartz is very rare or wholly absent, sodalite (or 

 nosean), nepheline and katapleiite have occasionally been 

 observed to occur. 



In the phonolitic rocks of the Nandewar region we find, in 

 addition to those occurring in the trachytes, nepheline, a mineral 

 of the sodalite group, cancrinite, katapleiite C?), geisikite (^), 

 liebuerite C?), zeolites and calcite. Analcite often occurs. 



ii. The Ali-syenites, porphyries and porphyrites contain many 

 of the above-mentioned minerals, but in the more basic varieties 

 soda-lime felspars predominate as phenocrysts, and albite or 

 potash-soda felspar (anorthoclase, soda-sanidine) in the ground- 

 mass. In different rocks different soda-lime felspars are met 

 with varying from albite to medium labradorite. 



In some reddish-coloured varieties of syenite-porphyry occurr- 

 ing in sills about Bullawa Creek the felspar phenocrysts have a 

 refractive index less than Canada balsam. In outline they are in 

 some rock-varieties like orthoclase,in others they give rhombic sec- 



