686 GREAT SERPENTINE BELT OF NEW SOUTH WALES, iii., 



to the vertical axis of the diallage up into veins, where it becomes 

 twisted and irregular. Sometimes it is without definite orienta- 

 tion, and exhibits the thorn-structure. The clinozoisite occurs 

 in isolated grains, and is very irregularly distributed. The 

 grains are unusually large, sometimes 2 mm., in length. They 

 are prismatic in habit, usually twinned singly or multiply, and 

 such twinning throws the basal cleavage-lines, on each side, into 

 a herring-bone or zigzag pattern. Optically, it is distinguished 

 by its high refractive index, low anomalous birefringence, low 

 extinction, and large, optical, axial angle. The grains are usually 

 surrounded by prehnite (Plate xxvi., fig.ll). 



South of Bingara, there are a number of other peculiar modifi- 

 cations of gabbro. In the field, they are remarkable for their 

 density; they are either greenish-white in character, or trans- 

 lucent and grey, and are spotted with greyish or greenish ser- 

 pentine-masses pseudomorphous after pyroxene. M.B., 36, of the 

 translucent grey type, has a specific gravity of 3*420, while that 

 of the unaltered gabbro, N.T., 118, is 2-930. The rock consists 

 entirely of garnet locally darkened by the segregation of dusty 

 particles. It contains lakelets of antigorite representing the 

 residue of the original pyroxenes, for there can be no doubt that 

 the garnet has encroached considerably on the pyroxene-bound- 

 aries. The chemical composition of this rock is given in Table 

 iii. The whitish rocks [e.g., M.B., 43] differ from this, in that 

 there is a considerable development of prehnite in little scales, 

 quite invisible in ordinary light. 



The garnet-gabbros are also developed at Bowling Alley Point, 

 as for instance, N.T., 261, which consists of minute grains of 

 colourless garnet and serpentine. In this connection may be 

 mentioned Mr. Porter's discovery of well crystallised, colourless 

 garnet (topazolite) in the serpentine of Sheep Station Creek, in 

 the same neighbourhood. 



A most interesting slide [N.T., 486] from the mass east of 

 Cobbadah, shows that decomposition of the pyroxene is not an 

 essential part of the process of garnet-making. The rock, which 

 is aphanitic, pale green and translucent, consists of a few dis- 

 torted, but otherwise unaltered diallage-crystals in a ground-mass 



