BY W. N. BENSON. 675 



chemical composition of this rock is of the normal serpentine- 

 character (See analysis, Table ii. ). 



Finally, the completely changed rock is seen in N.T., 491, from 

 the same locality. All the bastite has passed into antigorite, its 

 former position being indicated by areas in which the magnetite- 

 dust occurs in parallel bands. In the remainder of the rock, the 

 magnetite is in the irregular bands and kernel-aggregates, charac- 

 teristic of ordinary olivine-serpentine mesh-structure. The posi- 

 tion of the pseudospherulites of antigorite is quite without rela- 

 tion to the magnetite-bands, and, consequently, without any 

 reference to the original cleavage of the pyroxene-minerals, of 

 which they are the second derivative. Moreover, the appearance 

 of the interwoven sheaves, both in the olivine and pyroxenic 

 areas, as combined with the straight extinction of the antigorite, 

 which makes just those portions that are at right angles, in the 

 45° position, in polarised light, gives so close a similarity to 

 what has been termed " gitter struktur " as to strongly sup- 

 port Professor Bonney's contention, that this structure is more 

 apparent than real, and by no means a valid indication of the 

 presence of pyroxene(36). This rock also contains a small amount 

 of carbonate. 



Antigorite-serpen tines also occur in the northern region, but 

 differ in structure from those described above. A good example 

 of these is M.B., 319, which occurs in Hall's Creek, fourteen miles 

 south of Bingara. This is a dark green rock, with a granular 

 fracture. It consists of blade-like, platy antigorite, usually 

 arranged standing perpendicularly to a parallel series of cracks. 

 Often the arrangement is much more irregular. Scattered about 

 the rocks are irregular grains of chromite. The rock passes, in 

 the spaces of an inch, into a mass of fibrous, radiating, -pale green 

 tremolite. The small width of passage-rock is very beautiful in 

 microscopic section, the antigorite being interspersed with long 

 prisms, diamond-shaped cross-sections, or isolated, radiating 

 aggregates of tremolite-prisms (Plate xxvi., fig. 10). The tremo- 

 lite is frequently surrounded by that most perplexing, greenish 

 decomposition-product, which Lacroix, while retaining the original 

 name bowlingite, considers to be probably a variety of idding- 



