BY W. N. BENSON. 601 



opal and chlorite. This rock is on the borderline between the 

 quartz-dolerite-porphyrites and keratophyres, and, like the adja- 

 cent dolerite proper, it has not been albitised. 



A more typical keratophyre is that occurring near Gap Creek, 

 half a mile east of this spot (1136). Its composition is shown by 

 the analysis given on p. 602. Its texture is very net-like; there 

 is no sign of flow-structure, though the ragged felspar-laths some- 

 times give a sort of ophitic texture with the small amount of 

 augite, with which they are associated. The latter is now mostly 

 changed to chlorite. The felspar also forms small, interstitial, 

 spherulitic aggregates. Quartz is very abundant, both interstitially 

 and in small veins, but there are no chalcedonic phases. The com- 

 position of the felspar, as calculated from the analysis, is 

 Or^AbyoAnijj, equivalent to Aby4Ani6. 



In addition to this, there are a few occurrences of highly crushed 

 quartz-albite-porphyrites, in Portions 168, 213, and 171, Nemingha. 

 These consist {e.g., 1326, 1332) of broken phenocrysts of albite 

 (probably), with all the optical effects of great strain, and a 

 groundmass of finely granular, and intergrown, strained quartz 

 and albite. There is rarely also a little biotite in spangles and 

 crystal-plates, wisps of fibrous, pale green actinolite, both in pheno- 

 crysts and base, and a little magnetite and titanomorphite. A 

 similar rock occurs on the north side of Housefield's Hill, 

 Woolomol, forming a, vein in the Middle Devonian rocks. The 

 whole appearance of these rocks strongly recalls that of the albitic 

 veins in the serpentines near Bingara, and it is not clear whether 

 they should really be classed with the Devonian keratophyres(16, 

 p. 691). 



Chemical Characters of the Spilite-Keratophyre Series. 



The chemical features of these rocks will be illustrated by the 

 following table, which should be compared with the tables given 

 in previous parts of the series (16, p. 704; 17, p. 139), 



13 



