BY W. N. BENSON. 677 



(y). The carbonation of the serpentine naturally resulted in the 

 freeing of a considerable amount of silica, so that the rocks of 

 this group may be considered as overlapping, to some extent, 

 those of the next group, (8) the silicated rocks. They are de- 

 veloped to a great extent between the Folly and Quackanacka 

 Creeks, near Nundle, and occur at intervals along the western 

 side of the intrusion, from Crow Mountain northwards, forming 

 very large masses near the head of Hall's Creek, " Red Rock/' 

 and on Myall Creek, near Bingara. The Folly Creek rocks are 

 pseudomorphous after massive bastite-serpentine. They consist 

 of talc and carbonate in varying proportions, with dusty mag- 

 netite, which is so disposed as to show conclusively that it was 

 developed during serpentinisation, prior to the carbonation, for 

 it lies in the mesh-structure of olivine-serpentine, on the parallel 

 lines of bastite-serpentine. 



In N.T., 280, and, to a less degree, N.T., 176, 294, and 297, 

 the bastite pseudomorphs can be seen, in hand-specimen, as large, 

 purplish-grey plates, splitting along the original bastite-cleavage. 

 Microscopically, they are composed partly of fine, matted talc, 

 with a general arrangement parallel to the lines of magnetite, 

 and partly of roughly idiomorphic carbonate-crystals without 

 regular orientation, though, in some, the magnetite-lines are the 

 major diagonals of their cleavage-rhombs, i.e., the original bastite 

 cleavage-planes become the basal planes of the carbonate-crystals. 

 Occasionally [e.g., N.T., 176], there is developed a little micaceous 

 mineral parallel to the same bastite-cleavage, with a marked 

 green to yellow pleochroism. It is probably clinochlore. The 

 olivine-serpentine ground-mass is also composed of talc and car- 

 bonates, the latter being more irregular in shape, and appearing 

 occasionally to replace residual olivine. The arrangement of talc 

 is sometimes radial, generally matted. The chromite-grains, in 

 the specimens examined, are usually granophyric, and analysis 

 shows that one [N.T., 280] contains 0-55 per cent, of chromic 

 oxide (See Table ii., p.705). 



The schistose carbonate-rocks show also, though not so de- 

 finitely, their derivation from serpentine by chemical changes. 

 The rock near the Trevena Mine, on Folly Creek, is strongly 



