BY W. N. BENSON. 371 



remains, though most is replaced by albite or calcite. There are 

 also small pheiiocrysts of fresh augite and magnetite. The ground- 

 mass is extremely tine-grained, witii a traehytic structure dotted 

 with tlnely crystalline magnetite. 



The karaiophyrrs proper^ which consist essentially of acid plagio- 

 clase, are rather less abundant than other rocks. They usually 

 have present in them some other mineral, and as this becomes suf- 

 ticiently important to distinguish the rocks, the necessity' arises of 

 adding a qualifying mineral name to the term keratophyre. The 

 keratophyre on the border of Portions 35 and 36, Loomberah, is 

 one of these containing the least amount of minerals other than 

 albite. It consists of minute laths of albite in pilotaxitic to traehy- 

 tic groundmass, in which a few small phenocrysts of albite-mag- 

 netite and chlorite apparently replace augite. The felspars of the 

 groundmass are also associated with a very small amount of inter- 

 stitial quartz, and there appears to be a small intergrowth of the 

 felspar-laths with quartz, forming little irregularly-shaped patches 

 with the same optical orientation throughout. The groundmass is 

 cut by a few fine-gTained veins of clear albite. The most felspathic 

 of the keratophyres associated with the Nemingha Red Breccia 

 (No. 1123) is a highly porphyritic rock with phenocrysts of plagio- 

 clase, now albite, with a large amount of calcite, a little perfectly 

 fresh augite, and *i few large grains of magnetite lying in a 

 groundmass of very finely traehytic felspar, dotted with magnetite 

 dust and containing a very little interstitial quartz. Finely divided 

 calcite is also distributed in cloudy masses throughout the rock, 

 which has evidently been gi-eatly affected by carbonating solutions. 

 No. 1413. from near the head of Bog Hole Gully, indicates the most 

 felspathic member of the group of ferruginous keratophyres, 

 recalling the features of the brecciated keratophja-es from Hyde's 

 Creek (No. 1296, described in an earlier paper; 5, p. 151), though 

 the nodular structure is not so well developed. It conies from 

 near the southern end of the eastern mass of keratophyre. The 

 more ferruginous types of this series are considered below. 



Qu((rtz-l'eratoi}]ii/res are more numerous. Some, such as No. 

 1134 from the mass of keratophyre east of Black Jack, contain 



