684 GREAT SERPENTINE BELT OF NEW SOUTH WALES, 111., 



ness, the mineral has commenced to pass into tremolite. Usually 

 this is placed parallel to the vertical axis of the diallage, and 

 developed fairly evenly throughout the grain, giving it a peculiar, 

 mottled appearance. In other cases, the whole plate will have 

 passed into tremolite, forming a multiply twinned mass of parallel 

 amphibole-fibres. 



The normal types of highly altered, fine-grained eucrites in 

 hand-specimen are opaque white, with dull green spots, just like 

 the typical euphotides or saussuritic gabbros of the Alps and 

 Appenines; and, under the microscope, show the same features. 

 They consist of dusty diallage more or less completely changed to 

 tremolite, and dull grey-white saussurite traversed by small veins 

 of clinozoisite. The original twin-lamellae of the plagioclase can 

 still be seen in some cases, e.g., M.B., 327, from Upper Bingara. 

 Occasionally, the saussurite would be flaked with lighter spaces, 

 which consist of optically continuous prehnite. Rarely, hyper- 

 sthene is found in these rocks, a good instance occurring at the 

 old Paling Yard Diggings [N.T., 481]. The mineral is in rounded 

 grains, about 3 mm., in diameter, and is faintly pleochroic. In 

 this rock, the felspar has altered in an unusual manner The 

 cracks in some grains have been marked by the development of 

 grey-brown, dusty bands, increasing in number until the whole 

 mass becomes opaque. These pass into areas without sharp 

 demarcation, which consist of very finely divided prehnite(?), 

 while some of the diallage has passed into serpentine, partly 

 fibrous, and partly platy; the hypersthene is quite unaltered. 



In N.T., 469, from Moonbi, the felspar has changed entirely to 

 rather coarsely granular zoisite, with characteristic blue inter- 

 ference tint. The diallage is much strained, but is otherwise 

 unaltered. 



Another modification occurs at Upper Bingara, and is dis- 

 tinguished by the presence of much prehnite. This striking 

 mineral forms in veins; the individual grains are rarely as much 

 as 1 mm., in diameter. Its large, optical, axial angle, optically 

 positive character, straight extinction, and high refractive index 

 and birefringence are very characteristic. The saussurite, on 

 either side, is seen to have passed almost entirely into a fine 



