GEOLOGY OF THE JENOLAN OAVES DISTRICT. 367 



The augite occurs in typical stumpy crystals and is not 

 quite so fresh looking as the phenocrysts. It is more 

 abundant than the biotite. 



The biotite is of a brown colour, and rather plentifully and 

 regularly scattered through the groundmass. It is unaltered 

 with fairly strong pleochroism; has a somewhat smudgy 

 appearance, the outline of the crystals being indefinite, 

 seldom distinctly idiomorphic. 



Besides apatite the only other accessory minerals are 

 iron ores, consisting chiefly of pyrite as small crystals and 

 grains generally associated with the serpentine patches. 



It will be seen that this rock differs from the porphyritic 

 augite-hornblende-andesite of the Cave House in (a) con- 

 taining a fair amount of biotite, (b)containing no hornblende^ 

 (c) its lamprophyric texture. 



C. The Quartz Porphyrites. 

 As already pointed out in Part I, two distinct varieties 

 of this rock occur, which owing to their colour were 

 referred to as the pink and green varieties respectively. 

 It will be seen from the following description, that not only 

 do they differ in colour, but to some extent also both in 

 their structure and chemical composition. The pink variety 

 has a granophyric structure and quartz phenocrysts are 

 not conspicuous. This will be described as a granophyric- 

 quartz-porphyrite. The green variety does not display any 

 granophyric structure, but is crowded with small quartz 

 phenocrysts. 



The classification of rocks of this type i.e., of hypabyssal 

 occurrence and of intermediate chemical composition, is 

 a vexed question. If classified on a chemical and 

 mineralogical basis only, a system some petrographers are 

 strictly following, they would be placed with the dacites, 

 e.g., the green variety with the magmatic name Tonalose 



