218 Proceedings of the Royal Society of Victoria. 



Warburton, near old township. — A iine-grained granite rich in 

 biotite. Orthoclase somewhat destitute of crystal boundaries 

 occurs in larger plates and greater quantity than the triclinic 

 which appears to be an acid-oligoclase. The latter shows good 

 zonal structure and is twinned according to both albite and peri- 

 cline laws. It has well-marked crystal edges except when it 

 occurs as an inclusion in the orthoclase, in those cases the edges 

 are often ei'oded. Zircon and apatite are rather frequent, quartz 

 is free from inclusions except mica. 



Somerto7i. — Southern end of outcrop, about 3| miles N.N.W. 

 of Broadmeadows Station. — A medium-grained granitite with 

 white felspar, bottle green quartz and biotite. In the slides it is 

 apparent that the monoclinic felspar is subsidiary to the triclinic 

 variety. The latter has good crystal boundaries and has resisted 

 alteration better than the orthoclase. Quartz is well represented, 

 and the rock is very rich in apatite. Biotite is largely altered to 

 chlorite. A small amount of muscovite is present, it appears as 

 an alteration product of orthoclase. 



Frankston. — On the eastern side of Port Philip Bay are three 

 isolated granitic areas, Frankston, Mount Martha and Dromana. 

 It is possible that at one time they formed a continuous chain. 

 At Dromana the hills attain, at Arthur's Seat, a height of 970 

 feet, and at Mount Martha and Mount Eliza close on 600 feet. 

 The isolated areas are separated on the shore line by tertiary 

 beds, and are bounded easterly by Upper Silurian rocks into 

 which they have intruded. The rock from Frankston is a 

 medium-grained granitite showing a pink felspar, quartz and 

 biotite. Orthoclase and plagioclase felspar are about equally 

 represented in the slide, the biotite and quartz are normal. No 

 traces of apatite, zircon or other accessory minerals could be 

 found. 



Mount Alariha. — Watson's Quarry. A medium-grained 

 syenite showing white felspar, clear quartz, biotite and long pris- 

 matic crystals of hornblende. The dominant felspar is monoclinic, 

 it contains as inclusions triclinic felspars with rounded edges. 

 The triclinic felspar is an acid oligoclase with a maximum extinc- 

 tion angle, measured from the twin line, of about 10°. Horn- 

 blende is present in moderate quantity ; the terminal faces of 

 prismatic sections are for the most part wanting ; the pleochroism 



