216 Proceedings of the Royal Society of Victoria. 



sufficiently thin slide cannot be obtained without reducing the 

 rock to a very fragmentary condition. The decomposition which 

 the felspars have in most cases undergone often makes the exact 

 determination of the plagioclase felspars quite impossible. So 

 far as possible specimens typical of the locality under examina- 

 tion liave been sliced and are described in the following paper. 



The extent and boundaries of the gi^anite outcrops are not 

 given as information on this point, can be more easily and 

 accurately obtained from the geological maps of Victoria, issued 

 by the Department of Mines, and only brief reference is made to 

 the other field relations. 



Harcourt. — A granitite showing a white felspar, greenish 

 quartz and black mica. The twinning planes of the triclinic 

 felspar are visible to the naked eye. Under the microscope it is 

 seen that monoclinic and triclinic felspars are fairly equally dis- 

 tributed through the slide. The triclinic felspar has the more 

 perfect terminal faces, often shows zonal structure and occurs as 

 an inclusion iu the monoclinic felspar. Measurements suggest 

 that the triclinic felspar is oligoclase. The orthoclase felspar 

 shows Carlsbad twinning and intergrowth with a triclinic felspar, 

 probably albite. Apatite occurs in slender prisms and as grains 

 included in the biotite. This granitite is intrusive into the 

 Lower Silurian rocks, the latter being, according to Mr. E. J. 

 Dunn, r.G.S., altered in the neighbourhood of Bendigo for a 

 distance of 25 chains from the granitite. Similar contact meta- 

 morphism has not yet been noted in the deepest mines of the 

 Bendigo field. 



Traawofll, 7 miles E. of Tallarook. — A coarse-grained granitite, 

 rich in quartz, and showing a white felspar and biotite, the latter 

 mineral often in perfect hexagonal crystals. Under the micro- 

 scope it is seen that the triclinic felspar is as well represented as 

 the monoclinic, that it has better crystal definition and that it 

 occurs as an inclusion in the monoclinic felspar. Both felspars 

 are much decomposed, but the triclinic felspar shows the less 

 alteration of the two. A small amount of apatite is present ; 

 muscovite occurs in minute clusters and is probably a secondary 

 product. 



Millpark, X. of Preston. — A fine-grained granitite showing a 

 white felspar, quartz, and biotite. In the thin slide triclinic 



