608 GREAT SERPENTINE-BELT OF NEW SOUTH WALES^ V., 



altered breccia, made up of many differing portions, each uniform 

 within itself. The more finely granular fragments consist of small 

 short prisms of hornblende with a roughly parallel arrangement, 

 in a groundmass of small, equant, untwinned grains of quartz, and 

 (probably) andesine; occasionally, there are large, irregular plates 

 of an indeterminable felsjDar. Surrounding each such fragment is 

 a zone of larger crystals of hornblende, among which are frequent- 

 ly small patches of fresh, new-formed, colourless pyroxene, making 

 irregular poikiloblastic plates. These have very oblique extinction, 

 and a large optic axial angle. Rarely there are also poikiloblasts 

 of hornblende. In the irregular groundmass between the frag- 

 ments, there are also irregular prismoids of hornblende, granular 

 and poikiloblastic secondary augite, poikiloblastic, dusty, twinned 

 plagioclase, and abundant, usually untwinned oligoclase-ande- 

 sineC?) in the matrix. Rarely, also, there are poikiloblasts of 

 quartz that are quite free from strain-effects. Magnetite is scat- 

 tered about. 



Slide 1137, from the same locality, differs from 1134 in the pre- 

 sence of large porphyroblasts of andesine. The secondary augite 

 at times shows a sieve-structure, but more usually forms solid 

 grains, or scattered granules. Erdmannsdorfer has described the 

 development of secondary enstatite in the altered diabases by the 

 granite of the Harz(28, pp. 17-1 9). The pyroxene in the rocks 

 just described, though it is augite, seems also to be secondary; it is 

 certainly not residual, and as it occurs only in rocks quite close to 

 the granite, it is probably developed under the effects of contact- 

 metamorphism. Erdmannsdorfer observes that the degree of 

 metamorphism necessary to produce secondary pyro!xene is greater 

 than that necessary for the change of afigite into fibrous amphi- 

 bole(28, p. 37); the present rocks seem to exemplify this conclu- 

 sion. 



In the altered limestone of Seven-Mile Creek, is a green fel- 

 spathic rock (1372), which is probably an altered pyroclastic 

 inclusion. It consist of large poikiloblastic grains of andesine, 

 dotted with small grains of diopside, here and there aggregated 

 into dense masses. Scattered about there is also sphene in irregu- 



