150 ENOGGERA GRANITE AND ALLIED INTRUSIVES. 



hornblende usually in excess of biotite, is lacking in pink 

 orthoclase, and contains a marked quantity of pyrites. 

 Like the former type, it varies someAvhat both texturally, 

 and in the proportions of its constituent minerals. For 

 convenience this phase of the granites may be called the 

 granodiorite type. This variety usually occurs as segrega- 

 tions in the former (using the term in its broadest sense), 

 these segregations varying in size from patches a few square 

 inches in area to huge masses covering many square yards. 

 A common size measures about ten feet in diameter. These 

 segregations do not favour any particular shape, rounded,, 

 angular, and very irregular patches, all being common. 

 Larger outcrops of this granodiorite type also occur, 

 one area in the north-western portion of the mass 

 measuring some acres in extent. 



In connection with this natural division of the granites 

 into these two fairly distinct groups, it is interesting to 

 quote Saint-Smith on the "" Stanthorpe " granite. 

 " Speaking generally," he writes, " the ' Stanthorpe ' 

 granite is characterised by a markedly pink colour, due to 

 the abundance of pink orthoclase felspar, which is seen 

 through the rock. This colouration does not, however, 

 persist over the whole area examined, for at Wilson's 

 Downfall the rock has a preponderance of long, white fel- 

 spars having a marked orientation. So pronounced is the 

 difference between these two varied types of the same 

 rock-mass. . . ."^ 



The Green Hill Area is composed of rocks of the first 

 or adamellite type. They are for the most part very acid, 

 of a pink colour, and consist of phenocrysts of quartz, pink 

 orthoclase, white plagioclase, biotite, and a very little 

 hornblende, set n a fine-grained pink aplitic groundmass. 



The Kedron Brook Area differs from the one just 

 described in that it contains rocks which bear a general 

 resemblance to the granodiorite type of the Enoggera 

 Area. Th y contain plagioclase in excess of orthoclase, 

 the pink variety of the latter mineral being entirely absent. 

 They vary in colour from light to dark grey, but are all 

 fine-grained porphyritic rocks. Both pyrites and pyrr- 

 hotite occur as accessory minerals. 



I. Op. cit. p. 40. 



