154 GREAT SERPENTINE BELT OF NEW SOUTH WALES, iv., 



the richly magnetitic areas lie in a matrix of quartz-keratophyre, 

 in which some, at least, of the quartz is of secondary origin. 

 Another of these rocks differs in that the magnetite occurs not 

 only in finely divided masses, but in irregular aggregates from a 

 tenth to a fifth of a millimetre in diameter. The rock(ll 10) has 

 a brecciated structure, and the magnetite is segregated chiefly in 

 long, irregular bands running between adjacent fragments, and 

 in close association with the secondary quartz and calcite. It 

 also occurs impregnating the central parts of some of the frag- 

 ments. Apart from the presence of magnetite, the rock is 

 similar to the quartz-keratophyres to be described below. 



The magnetite-keratophyre that lies north of the jasper band 

 differs from the above in having an amygdaloid al character. The 

 vesicles are filled with quartz, and sometimes have a selvedge of 

 chalcedony. The rock consists of a felt of albite-laths and small 

 phenocrysts in a matrix darkened by dust-like magnetite; the 

 latter is, for the most part, evenly distributed, but may be aggre- 

 gated around the vesicles. 



The magnetite-keratophyre of Silver Gully is similar to the 

 rock last described. It is associated with a small patch of dense, 

 slaggy, very heavy magnetite-keratophyre, similar to the most 

 ferruginous parts of the Hyde's Creek rocks. As already men- 

 tioned, this mass of keratophyre seems to pass into a locally 

 brecciated sill of dolerite, which extends about half a mile 

 northwards. This dolerite has been more or less silicified in 

 places, and more carbonates have been introduced. The dolerite 

 of the Hyde's Creek complex, though it is not so intimately con- 

 nected with the keratophyre, closely resembles the Silver Gully 

 rock. It is very acid; indeed it may be considered as a passage- 

 rock between dolerites and quartz-keratophyres: it consists of 

 albite, chloritised pyroxene, and abundant interstitial quartz, 

 together with a little ilmenite locally changed to sphene. The 

 rock is rather crushed, and carbonates have been introduced into 

 the zones of granulation. 



Adjacent to the dolerite in the Silver Gully complex, is a 

 fairly coarsely granular quartz and felspar rock which appears, 

 at its eastern side, to be a massive quartz-keratophyre-porphyry, 



