GEOLOGY AND PETROLOGY OF ENOGGERA GRANITE. 131 



(III.) PETROGRAPHY. 



(a) The Pink Phase. 



This phase is characterised by its high acidity and the 

 consequent presence of quartz in considerable amount; by 

 its pink orthoclase, which is usually slightly in excess of a 

 white soda rich plagioclase, and which gives the rock its 

 typical colour ; and by biotite, which is usually present 

 though not in any great amount. Hornblende is either 

 absent or rare. Pyrites is absent. Associated with the 

 Pink Phase proper are modifications of it of an aplitic and 

 granophyric nature, which occur generally near the margins 

 of the granite and capping the higher hills, and sometimes 

 as distinct intrusions through the Pink Phases. These 

 modifications are slightly later in time of intrusion than 

 the typical pink rocks, and are almost certainly the equi- 

 valents of the "Euritic" series of Andrews and the 

 "Aplites and Sandy Granites" of Saint-Smith in New 

 England and Stanthorpe respectively {see Table II.). In 

 the Enoggera area they are so intimately associated with 

 the Pink Phase proper that it does not seem advisable ta 

 treat them as a separate group. 



The following descriptions give some idea of the rock 

 types found in this phase. 



The bracketed numbers refer to the special " ' Enoggera ' ' 

 collection of rocks, while the other numbers are those of 

 the collection of ^licroslides. Both are the property of' 

 the Geology Department, University of Queensland. 



(Ct.1) 141. (See Micro-photograph PI. II., No. 1, and 

 analysis El.) 



Specimen from southern part of main Enoggera mass. 



Megascopic. — A pink holocrystalline, porphyritic rock, 

 composed of medium-sized phenocrysts of quartz, pink 

 orthoclase, white plagioclase and black mica set in a fine- 

 grained flesh-coloured ground mass. 



Microscopic. — The porphyritic character of the rock is 

 marked and the proportion of phenocrysts to ground mass 

 somewhat variable (Sempatic to Dopatic of Iddings). The 

 ground mass is made up for the most part of quartz and 

 felspar, sometimes irregularly intergrown. with occasional 



