BY W. H. BRYAN, B.SC. 149 



New England, as described by E. C. Andrews. i and the 

 ** Stanthorpe " granite of Saint-Smith. ^ However, in the 

 case under consideration, the various phases can all be 

 assigned to one of two main types. 



Of these types, the one which forms the major 

 portion of the outcrop of the Enoggera Area fs' a 

 rock of a fairly uniform flesh-colour, which is only 

 relieved by a minority of ferro-magnesian minerals 

 — these constituents, however, being very variable. 

 XJsually the rock is holocrystalline and porphyritic. with 

 medium-sized phenocrysts of quartz, pink orthoclase, 

 white plagioclase and black mica set in a fine-grained 

 aplitic, flesh-coloured groundmass. Hornblende is some- 

 times present, but is always subordinate to the biotite. 

 Occasionally the porphyritic character disappears, and in 

 its place appears a medium-grained holocrystalline rock, 

 which in all other respects resonbles the normal tyj^e. 

 In this rock the orthoclase is slightly in excess of the 

 plagioclase, while in the commoner porphyritic phase the 

 plagioclase phenocrysts are considerably in excess of the 

 orthoclase. This apparent div^ersity is however compen- 

 sated for in the groundmass of the latter tyjje, which is 

 rich in orthoclase. The accessor}^ minerals usualh' present 

 are apatite in considerable amount, magnetite, and zircon. 

 Pyrites is usually absent. From this short description 

 the rock is evidently comparable in structure and minera- 

 logical character with specimens of a granite from Bolivia 

 which is described by Mr. G. W. Card,^ and is a represent- 

 ative of the great '" Acid " series of New England granites, 

 and also with the '' typical ' Acid' " granite described b}' 

 him.^ 



The second tjqDe of granitic rock met with in the 

 Enoggera Area, is usua'ly considerably less acidic than that 

 just described, it has a much greater proportion of ferro- 

 magnesian minerals (often in two generations), has 



1. New England Cieolociy. Records of Geol. Survey of N.S W. 

 Vol VIII. Part 2, pp. 116-117. 



2. Geology and Mineral Resources of the Stanthorpe, Ballandean 

 .and Wallangarra District. Qland. Geol. Survey Pub. No. 243, p. 39. 



3. Geol. Survey of N.S.W. Records, Vol. VIII, p. 219. 



4. Mineral Resources of N.S.W., No. 14, p. 23. 



