Metaniorphic amd Plutonic Rocks at Omeo. 121 



analagous to the structure of the rocks lately described. lu 

 places the quartz also surrounds portions of felspar. Most 

 usually the felspar has been converted into small flakes of 

 alkali mica, which lie at various angles to each other. The 

 result simulates portions of mica schist enclosing quartz 

 grains. On the whole this rock is very quartzose, the grains 

 being angular to rounded, and in places showing strain. 

 Between the grains, and also bordering the felspar, there are 

 in places small flakes of brown mica which extend down 

 into fissures, and which are, therefore, probably secondary in 

 formation. There are in this rock hexagonal and imperfect 

 crystals of iron ore, and also a few scarce crystals which I 

 refer, upon grounds before stated, to Zircon. 



At about two hundred yards from this spot is the 

 boundary of the Granites, and there being on the one side 

 massive rocks with faint traces of foliation, and on the other 

 well-marked porphyritic granites. I have here marked on 

 the section a second possible contact (x\) In order to 

 compare the doubtful rocks with the porphyritic granites 

 which they adjoin on the north-east side, I made a 

 quantitative analysis of both samples. The first to be 

 described is the one on the north-east side — that is to say, 

 on that side on which the schists are found. The sample is 

 a rather fine-gTained, crystalline granular rock, dark grey in 

 colour, vrith in places lighter portions, giving it a slightly 

 schistose appearance. 



An examination of a thin slice of this rock gave me the 

 following results, and I found it to be composed of the 

 following minerals : — 



(a.) Orthoclase in eroded crystals, most of which have 

 been much altered to muscovite, which either is scattered 

 through the crystal or entirely replaces it. In parts the 

 orthoclase crystals have been broken up, and much of the 

 resulting debris has gone to produce mica. The orthoclase 

 was formed before the triclinic felspars, which have been 

 altered in an analogous manner to the former. The low 

 extinction angles of the plagioclase indicate albite or 

 oligoclase. Muscovite occurs not only as alteration products 

 replacing felspars, but also as larger flakes and crystals of an 

 earlier formation. Intergrown with the muscovite, but also 

 independently of it, is a brown pleochroic magnesia mica 

 which, where unaltered, is much corroded and " tattered," 

 and where altered, has been converted into a pale-coloured 

 chlorite. As is very common in this chloritisation, the 



