GEOLOGY AND PETROLOGY OF ENOGGERA GRANITE. 125 



uses Hatch's simple criterion^ then since the 

 Orthochise and Plagioclase felspars are present 

 in approximately equal amount the rock is an 

 adamellite. Further, the analysis of the Pink 

 Phase (Analysis I.) is remarkably close in all 

 its essentials to that quoted hy Hatch p. 179, as 

 "iv. Adamellite, Shap."* However, these 

 analyses also agree in differing somewhat 

 sharply, both in amount and proportion of the 

 alkalies, from Analyses I., II., and III., which 

 are presumably more typical adamellites.] 



(2.) A wide variability within both the light and 

 dark phases, which, however, is textural merely 

 and not chemical, as is seen by a comparison of 

 the mineral contents of specimens very dis- 

 similar texturally, which show^ plagioclases of 

 the same chemical composition and in which the 

 other minerals are identical. 



(3.) In addition to the former varieties we occa- 

 sionally get others which depart rather widely 

 from the more typical rocks in the proportion of 

 the minerals present. Of these, only one forms 

 outcrops of any importance, and this is remark- 

 able in that it appears to have some important 

 characteristics in common with each of the 

 phases. It is not so much a mineralogical 

 average of the Pink and Grej^ Phases as a 

 mineralogical mixture. At first sight it appears 

 to represent a connecting link between the 

 phases, but the discussion of this question is 

 deferred. The rock in question is to be seen 

 outcropping at the Quarry on Enoggera Creek. 



One might reasonably expect that such marked 

 chemical dift'erences as those shown in the analyses (El 

 and E4) of the tw^o phases would be reflected in their 

 distribution in space or in time. 



With regard to distribution in space, rocks represen- 

 tative of the Pink Phase cover roughly three-cpiarters of 

 the main Enoggera area of outcrop and all of the Green 



^ Hatch, "Petrology of Igneous Eocks,' ' p. 164. 

 * Op. cit. p. 171. 



