GEOLOGY AND PETROLOGY OF ENOGGERA GRANITE. ] 39 



are largely altered into chlorite. Biotiie is present as 

 uiinierous flesh flakes of a brown colour. The ferro- 

 magnesian minerals show a distinct tendency towards 

 segregation into definite groups. Magnetiie occurs as 

 fairly numerous crystals. Apatite is present as very small 

 needles generally included in the other minerals. Sphene 

 and Zircon are also present, but in much smaller amounts. 



Order of consolidation. — The order of consolidation 

 is not normal, and the various minerals "overlap" very 

 much more than is usually the case. Some of the plagio- 

 clases are definitely earlier than some of the hornblendes, 

 while others are ju.st as definitely later. The same over- 

 lapping is noticeable with hornblende and biotite. Even 

 some of the quartz crystals appear to be earlier than the 

 small flakes of biotite which partly surround them. The 

 ferro-magnesian minerals often appear as clusters illus- 

 trating the "together-swimming structure or synneusis 

 struktur" of Vogt'', which is characteristic of those 

 minerals segregated from the magma at an early stage. 

 But in this case they were certainly preceded by some at 

 least of the plagioclases. 



Name. — Granodiorite. 



{G. 18) 421. — Specimen of Grey Phase from the southern 

 of the two Kedron Brook outcrops. 



Megascopic. — A grey rock made up of small pheno- 

 crysts of felspar and a ferro-magnesian mineral set in a 

 very fine ground mass. 



Microscopic. — Holocrystalline, porphyritic with small 

 to medium phenocrysts set in a very fine-grained micro- 

 crystalline ground mass of quartz and felspar. Quartz 

 occurs as rounded and embayed phenocrysts from -5-1 mm. 

 in diameter. Orthoclase is present as medium-sized pheno- 

 crysts very much altered by weathering. Plagioclase is 

 present as medium-sized phenocrysts of Andesine very much 

 altered, Biotite is present as ragged crystals, and Horn- 

 hlende as long prisms both considerably altered. 



Name. — Granodiorite Porphyry. 



^"Magmatic Differentiation of Igneous Eocks, " Journal of 

 Geology, Vol. xxix. p. 321. 



