30 



green specks (chrome diopside ?), and still more rarely 

 patches of a talcose substance. In weathering the ex- 

 posed surface becomes a dull yellowish brown, which does 

 not penetrate deeply into the mass of the rock. This 

 pyroxenite occurs exposed in the road cutting on the sideling 

 across the Bald Hill, immediately west of and close to the 

 bridge across the Heazlewood River on the Waratah-Corinna 

 Road. The eastern portion of the road is apparently mainly r 

 if not entirely, composed of the rock, but its extension north 

 and south has not been traced. It is probably an intrusive 

 of considerable extent. 



4. Attgite-Syenite. 



Sp. Gr. 2-84. 



This is a plutonic rock of the intermediate group, in which 

 there is very little free quartz. The primary constituents are 

 orthoclase plagioclase, augite, hornblende, biotite, quartz, 

 secondary quartz, chlorite. 



Macroscopical Structure. — A somewhat handsome rock of a 

 comparatively fine granitoidal structure. It forms a 

 thoroughly crystalline mass, although the crystals of the 

 predominating essential minerals cannot be distinctly outlined 

 by the unassisted vision. It presents a remarkable resem- 

 blance to many gabbros, and might readily be mistaken for 

 such, if not carefully examined. It has an evenly distributed 

 mottled apperance on the surface of a fresh fracture, and for 

 a syenite is unusually dark in coloration. The prevailing 

 tint of the ground mass is a pale greenish-white, with 

 numerous extremely irregular and closely packed blotches of 

 a dull greenish-black, but with an occasional minute area of 

 reflecting lustre. The exposed portions of the rock are much 

 weathered to a dull greyish-white. As might be anticipated 

 with an intermediate rock of its nature, it is hard and 

 tenacious. It occurs as an eruptive mass of apparently 

 restricted extent, which forms portion of an abrupt hill of 

 medium elevation near the workings on the Bell's Reward 

 Silver Mine. Associated with it is a fine-grained hornblende 

 granitite, the whole being mainly flanked by the sandstone and 

 limestone of the locality, together with the serpentine-gabbro 

 rocks so abundant in the district. 



Microscopical Structure. — The predominating felspar is 

 orthoclase in simple tabular forms and carlsbad twins ; a 

 soda-lime felspar is present in considerable quantity, with the 

 extinction angles of oligoclase-andesine. The felspars are 

 turbid in their interiors, with the usual kaolinisation pro- 

 ducts, but the peripheral parts often remain perfectly clear 

 and transparent. The augite is pale green, often twinned 

 parallel to the orthopinacoid, with a second lineation parallel 



