GEOLOGY OF ERUPTIVE AND ASSOCIATED ROCKS, POKOLBIN. 387 



be Carboniferous, it may be conveniently be treated here. 

 It outcrops in a long narrow band along the eastern face 

 of the range between Mount Bright and Mount View. The 

 typical rock is medium-grained, with a slight preponderance 

 of light over dark coloured minerals. At the northern 

 limit of the occurrence two extremely well marked types 

 of local differentiation products occur, the first being a 

 basic modification, much darker in appearance than the 

 general type. From examination of hand-specimens the 

 ferro-magnesian constituents hornblende and biotite are 

 seen to predominate, forming about 80 per cent, of the rock, 

 while the remainder consists of plagioclase, pink orthoclase 

 and a little quartz. A short distance away a further 

 modification appears in the shape of a pink aplite, consist- 

 ing of porphyritic laths of plagioclase, showing albite and 

 carlsbad twinning, in a fine-grained base of quartz and 

 felspar with subordinate biotite. Pyrites in very small 

 crystals is abundantly distributed. The aplite in places 

 also contains irregular small patches of tourmaline, and 

 large segregations of the same mineral showing fibrous 

 radial structure also occur, probably as a result of pneu- 

 matolytic action. The final phase of differentiation of the 

 grano-diorite magma is represented by a pegmatite. This 

 rock is extremely coarse in texture and consists of an 

 intimate intergrowth of allotriomorphic to subidiomorphic 

 quartz and pink felspar. At this northern end the grano- 

 diorite is cupriferous, the copper minerals being in close 

 association with the pegmatite. Azurite, malachite, pea- 

 cock ore, pyrites, etc., have been obtained near the upper 

 boundary of the grano-diorite, but the workings are now 

 abandoned. Attempts to find copper near the Mount View 

 end of the outcrop have proved unsuccessful. 



Rhyolite and rhyolite tuffs are the earliest of the Upper 

 Carboniferous volcanic series, and form the greatest part 



