GEOLOGY OF THE JENOLAN CAVES DISTRICT. 353 



3. The Quartz-Felsites. — These are more highly acidic 

 in composition and occur in smaller intrusions than the 

 quartz porphyrites. As shown ou the map they occur 

 between two large intrusions of green porphyrite, and one 

 of them, at least, appears to be genetically connected with 

 this rock, although this counection is not shown on the 

 map. These felsites are well exposed in the road cuttings 

 at the head of Hinchman's Oreek ; some are unquestionably 

 intrusive, but one of them, which is only about twelve feet 

 thick, lies conformably between the bedding planes of the 

 slates, just like a contemporaneous flow. This occurs at 

 the point marked H on the map, although the actual occur- 

 rence is not shown. An adjoining felsite intrusion is simply 

 crowded with fragments of limestone, which must have 

 been brought from some distance, as there is no limestone 

 occurring in the immediate vicinity. Quite a number of 

 felsite dykes (or ? silis) occur at this locality, but as it 

 would be impossible to show them all on the map, they are 

 represented thereon as two intrusions; they alternate with 

 slates. 



4. The Diorites. — One outcrop of diorite has been noticed; 

 it occurs on the track leading down Jenolan Creek at the 

 place marked J on the map. The rock is fine-grained, 

 almost aphanitic, and is much altered. It exhibits no 

 features of special interest. 



Part II. Petrology and Analyses. 

 By W. G. Stone. 



A. The Rhyolite Porphyry (Quartz-porphyry. 



B. The Andesites. 



(a) Andesite (non-porphyritic type). 



(b) Augite-Hornblende- Andesite (porphyritic type). 



(c) Augite-Lamprophyre. 



C The Quartz-Porphyrites. 



(a) Granophyric-Quartz-Porphyrite (pink variety). 

 (6) Quartz-Porphyrite (green variety). 



D. The Quartz-Felsites. 



W— December 1, 1915. 



