BY W. N. BENSON. 349 



present. From this point, it may be traced across Reedy Creek 

 to the point where it is cut off by the important cross-fault men- 

 tioned below (.sec p. 351). This portion of the zone includes a 

 very unusual fades of keratophyre, namely, an aphanitic rock 

 with a semi-perlitic fracture. Microscopical examination proves 

 that this is a minutely crystalline variolite(si?e 1405, p. 369). 



The zone is then thrown to the east, about 600 yards, by the 

 above-mentioned fault, but, a short distance further to the south, 

 it has been thrown back to the west, and continues along the 

 eastern side of the Nemingha limestone across Cope's Creek. 

 In this portion east of Black Jack, it is not entirely uniform, 

 some portions being rather less acid than others (see, e.g., the 

 description of 1383, p.370). 



The keratophyre continues south of Cope's Creek, its intrusive 

 nature being rendered clear by the large block of limestone 600 

 yards south of the creek, which has been torn off from the 

 Nemingha horizon and enveloped by it. It may be traced from 

 this point down to Pipeclay Creek, where it is extremely sili- 

 ceous, and thence to Silver Gully. The features of this region 

 have already been briefly described (5, pp.137 and 154-5). Of 

 particular interest in this southern extremity of the keratophyre 

 zone is the occurrence of the Silver Gully keratophyre-complex 

 (jaspers, magnetite-keratophyre, etc.) which is intrusive into 

 the limestone. The brecciation of the keratophyre, and its pas- 

 sage into what seem to be breccias connected with the Nemingha 

 Red Breccias, are subjects well worthy of detailed study, which 

 the writer, by his removal from Australia, is unfortunately pre- 

 vented from making. 



The Dolerites. 



Three separate types of dolerite occur within this area, 

 grouped into three intermittent lines of intrusion. They may 

 be termed — reading from north to south — the Hypersthene-, the 

 Porphyritic, and the Albitic Dolerite. 



The Hypersthe7ie-Dolerite. — Thin belt of dolerites has been 

 already mentioned as lying a short distance below the Igneous 

 Zone. Its northernmost occurrence is by the river-bank in Por- 



25 



