34 



9. Hornblende Granitite. 



Min. Const. : Orthoclase, plagioclase, biotiie, hornblende? 

 quartz. 



Sp. Gr. 2-9. 



Macroscopical Characters. — The general ground mass of 

 this rock is of a pale greenish grey colour thoughout, with 

 but slight variation of tint. It has a perfectly fresh 

 appearance, although dull in lustre. The abundant niagnesian 

 mica forms a strong contrast to the general colouration, 

 being an extremely dark green, approaching black, with a 

 glimmering surface on the basal cleavages. It usually 

 occurs in aggregated bunches with occasional comparatively 

 large flakes. The hornblende is also dark in colour, but 

 it may be detected here and there by its longitudinal 

 striation. Of the several varieties of granitite which have 

 been observed in this district, that under notice is not only the 

 coarsest in general structure, but is also the most conspicuous 

 in colouration. It was obtained on the higher ground near 

 the 14-Mile Camp, associated with the augite-syenite. 



Microscopical Structure. — The dominant coloured consti- 

 tuent is biotite, a green hornblende being quite subordinate. 

 Hence we can hardly call the rock a hornblende-granite. 

 As granitites (biotite-granites) do not always carry biotite 

 exclusively, they may vary into hornblende-granitites, and 

 often contain a good deal more hornblende than the present 

 rock. There is a fair quantity of quartz and oligoclase- 

 andesine felspar with albite twinning. Plates of orthoclase, 

 optically continuous, sometimes enclose crystals of plagioclase 

 snd biotite. The mica is in irregular disjointed plates and 

 shreds, often bent and wavy, in colour deep brown, 

 bleaching to bronze and pale greenish yellow, retaining 

 always strong pleochroism. 



10. Gabbro without Olivine. 



Min. Const.: Diallage, enstatite, plagioclase felspar, titaniferous 

 iron. 



Sp. Gr. 2-88. 



Macroscopical Structure. — This is a dense crystalline 

 granular gabbro without any marked external peculiarities. 

 It is uniformly dark in colour ; the ground mass of the 

 rock is grey, with greenish-black irregular markings plenti- 

 fully distributed throughout its substance. It occurs in 

 masses of considerable extent in close proximity to the 

 serpentine belt, and is associated with some of the pyroxenite 

 rocks. 



Miser oscopical Structure. — A noncrystalline gabbroid 

 aggregate of pyroxene and felspar. The diallage pre- 



