156 PROCEEDINGS OP THE ROYAL SOCIETY OF QUEENSLAND, 



(b) Other Queensland Areas. 



The division of the granitic rocks of the Enoggera 

 district into two phases — the earlier typically grano- 

 dioritic (the Gre^y Phase) and the later somewhat more 

 alkaline (the Pink Phase) — seems to be reflected in all those 

 granitic rocks of Queensland of wiiich analyses are avail- 

 able. Not only is this twofold development widespread 

 geographically ; in time, too, it appears to be wonderfully 

 persistent. As far north as Charters Towers and as far 

 back as Early Devonian, these two distinct phases are met 

 with. 



The plutonic rock nearest to the Enoggera area, of 

 which a chemical analysis exists, is the Mountain Camp 

 Quartz ]\Iica Hornblende Diorite, which lies within 3 or i 

 miles of the main Enoggera outcrop (see analysis E.3). 

 This rock has a handsome appearance and makes an excel- 

 lent building stone. It was selected by Professor H. C. 

 Richards as the most suitable granitic rock available for the 

 construction of the base of the new Brisbane Town HalL 

 Mineralogieally this rock most closely resembles the Pink 

 Phase, although it is, of course, considerably less acid and 

 does not carry enough pink orthoclase to give the charac- 

 teristic colour. The chemical analysis gives added weight 

 to the mineralogical evidence, for though it is remarkably 

 like that of the Grey Phase (E.4) in most respects, in the 

 all-important matter of the alkalies it shows its true relation- 

 ship to the Pink Phase, the Na„0 being slightly in excess of 

 the KoO. The variation diagrams, too, point clearly to its 

 relationship to the Pink Phase. 



The remaining comparisons must necessarily be general 

 in their nature. So little has been done in the study of the 

 plutonic rocks of Queensland that little in the way of 

 detailed correlation is possible. 



j\[r. Reid-° has described from the Charters Towers 

 goldfield a series of granodiorites and associated rocks of 

 Lower Devonian or pre-Devonian age, all of which show 

 rather low alkalies with a decided excess of NaoO over KjO. 

 and which are followed by an aplitic granite which "is 

 intrusive in the granodiorite" and the analysis of which 

 shows high alkalies with the potash in excess of the soda. 



=°"The Charters Towers Goldfield," Qld. Geol. Surv. Pub. No. 

 256, p. 6fi. 



