882 THE GEOLOGY OP THE NANDEVVAR MOUNTAINS. 



Mr. Saunders also kindly forwarded me a slide of another rock 

 of the same kind obtained from a depth of 2,015 feet in the bore- 

 hole at Narrabri. This rock is holocrystalline, hypidiomorphic 

 granular, medium-grained, and porphyritic in augite, magnetite 

 and felspar, The felspar consists of lath-shaped labradorite 

 crystals; the augite is highly titaniferous and occurs in fine 

 reddish-brown idiomorphic crystals which frequently enclose 

 felspar in an ophitic manner. Titaniferous magnetite occurs in 

 corroded phenocrysts ; ilmenite is also present. Apatite is 

 common as inclusions in both the augite and the felspar. 

 Large patches of the base consist of a clear colourless isotropic 

 mineral with a low refractive index. This mineral was the last 

 to consolidate, and is probably analcite. The rest of the ground- 

 mass consists of the second generation of the minerals already 

 mentioned. 



Name : Ophitic Analcite-Olivine-Dolerite or Diabase. 



N.19. Loc: edges of laccolite. Dingo Creek. 



Handspecimen dark basaltic-looking rock with white amyg- 

 dules. 



Texture holocrystalline, uneven-grained but fine-grained with 

 pilotaxitic fabric. 



Composition : this rock consists of basic labradorite felspar 

 in laths decomposing to analcite, zeolites and other products, 

 automorphic but somewhat corroded grains of titaniferous augite, 

 very corroded and rounded olivine grains, idiomorphic magnetite 

 granules, analcite and decomposition-products. The white 

 amygdules consist of analcite and zeolites. 



Name : Pilotaxitic Olivine Basalt (or Diabase). 



N.56 consists of a fine-grained basalt exactly like N.19, and 

 occurs on the borders of the basic laccolite at the head of 

 Bobbiwaa Creek. 



N.57, collected from the core of the same Bobbiwaa laccolite, 

 is a coarse-grained dolerite (or diabase) exactly like N. 17, 

 described above. 



