350 C. A. SUSSMILCH AND W. G. STONE. 



felsites east of the Cave limestone, even at points distant 

 from the junction. These facts have already been referred 

 to in discussing the age of the radiolarian cherts, and it is 

 quite possible that it was faulted against the limestone 

 along with the cherts, in which case it would be older than 

 the other igneous intrusions, which are of late Devonian 

 age. On the other hand its strike approximates to that of 

 the more acid intrusives occurring to the east of the Oave 

 limestone, and it could possibly, therefore, have resulted 

 from the same set of activities. In its petrological char- 

 acters, this rock much resembles the intermediate intru- 

 sive and effusive rocks associated with the Ordovician rocks 

 of the Orange District. Until more information is available 

 it is impossible to assign any definite age to this intrusion, 

 but there is some reason for thinking that it may be older 

 than the late Devonian (Kanimbla Epoch) intrusives, and 

 that it may even be Pre-Silurian in age. 



2. The Quartz Porphyrites. — These occur to the east 

 of the Oave limestone and intrude the underlying slates; 

 that they also intrude limestone is shown by the large 

 number of included limestone fragments which they contain, 

 but no actual intrusion into limestone was observed in the 

 area mapped. Two distinct types of porphyrite occur, one 

 of these has a reddish colour and will be referred to, for 

 the sake of convenience, as the Pink Porphyrite; the other 

 has a decidedly greenish colour and will be referred to as 

 the Green Porphyrite. Tbey are sufficiently alike in their 

 chemical and petrological character to be both classified 

 as quartz-porphyrites, but there are also differences both 

 chemical and petrological which will be referred to in 

 Part II. 



The pink porphyrite is a reddish aphanitic rock, typically 

 with but few phenocrysts of quartz; in places, however, 

 there is a considerable development of small phenocrysts 



