162 F, L. Stlllwell: 



PftrcK/raphicdl CJutrdrfer. 



Megascopieally the irninite is a grey rock, coarse grained, and 

 shows crystals of quartz, felspar and biotite. 



Microscopically the crystallinity of the rock is seen to be holo- 

 crystalline, and non-porphyritic, with crystals of variable size. 

 The average crystal size is medium, and the texture is hypidio- 

 morphic. The minerals present are quartz, biotite, plagioclase, 

 orthoclase, chlorite, muscovite, apatite, zircon, and magnetite. 

 The quartz is allotriomorphic and contains inclusions of apatite 

 and zircon. 



The plagioclase is mostly idiomoriDhic. A zoned crystal with- 

 out lamellar twinning has an extinction almost parallel to the 

 trace of cleavage, thus indicating andesine. The zones become 

 progressively more acid. The orthoclase is mostly untwinned 

 and cloudy. Tlie chief alteration product from the felspar is 

 kaolin, but a little secondary white mica and calcite has also 

 resulted. 



Biotite is abundant in large and small ragged crystals, and 

 contains inclusions of apatite, zircon and magnetite. 



Green chlorite is abundant as a decomposition product of the 

 biotite. Muscovite occurs in loose aggregates which appear to 

 be secondary. Apatite is plentiful in small colourless crystals 

 with low polarisation colours, which distinguish it from the less 

 abundant, prismatic and pointed crystals of zircon with its high 

 polarisation colours. The zircon also has a dark border. 



Magnetite occurs in grains throughout. 



The rock is not a true granite, differing from such in its 

 content of andesine. It is not a true grano-diorite, since the 

 plagioclase is not sufficiently predominant over orthoclase. It 

 may be described as an adamellite bordering near a grano- 

 diorite. 



Sub Older Basaltic Rocks. 



In section along the Moonee Ponds Creek below the older 

 basalt quarry, a thin bed of about 2 feet is to be seen under- 

 lying the older basalt and resting unconformably on the silurian. 

 It consists of a clay with much disseminated quartz grit, stained 

 brown by iron solutions from the basalt. It is interesting in 



