124 PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 



II. GENERAL PETROLOGY. 



The rocks dealt with fall into two main groups — viz., 

 the granitic and granodioritic rocks forming the outcrops 

 at Enoggera, Green Hill, and Kedron Brook, and intrusives 

 of a rhyolitic and porphyritic nature which are intimately 

 associated with the former series, and which are believed to 

 be genetically related to them. 



The former group is called locally the "Enoggera 

 Granite, ' ' and is best known from the building stone which 

 has been very largely used in and about the city of Bris- 

 bane, and which is obtained from a quarry on the left bank 

 of the Enoggera Creek. This rock has been dealt w'ith by 

 Professor H. C. Richards, D.Sc, mainly from the economic 

 aspect.^ This particular variety cannot, however, be 

 regarded as typical either of the group of granitic rocks as 

 a whole, or even of those forming the outcrop of the 

 principal Enoggera area. 



The most marked feature of the granitic group petro- 

 logically is the wide variation of type to be met with for 

 such a restricted area of outcrop. This variability is both 

 chemical and textural. Mineralogically the variation is 

 not so marked, the different rock types resulting rather 

 from differences in the proportion of the minerals present 

 than in actual difl'erences in character and appearance of 

 the minerals themselves. 



In the face of such wide differences in the field it is at 

 first difficult to generalise, but it seems to the writer that 

 this variability can be revolved into — 



(1.) Two main phases, which for convenience we 

 may term the Pink and the Grey, which dift'er 

 chemically as shown by a comparison of the 

 Rock Analyses El and E4, and mineralogically 

 in the proportions of the minerals present. 



[These were referred to in the earlier part 

 of this paper (p. 150) as the "adamellite type" 

 and " granodiorite type" respectively. While 

 the author has every reason still to regard the 

 "Grey Phase" as being essentially granodioritic, 

 he now doubts the wisdom of referring to the 

 "Pink Phase" as an adamellite type. If one 



- Proc. Eoyal Soc. Qld. Vol. XXX. p. 101, and Plate X., fig. 13. 



