GEOLOGY OF THE COOMA DISTRICT, N.S.W. 197 
The rock has been subjected to pressure subsequently to 
its consolidation; this has caused a good deal of shattering 
and alteration, in some cases changing the original appear- 
ance almost beyond recognition. From a field examination 
of the porphyries it has been concluded that there must 
have beenat least three distinct series of intrusions, possibly 
four. There is first of all the very much sheared type, 
exemplified in the Bushy Hill formation, now reduced to 
what Van Hise would call a quartz-porphyry slate,* quite 
schistose in structure. The cleavage pieces have a some- 
what greasy lustre, with dark green colour and greasy feel, 
due possibly to the development of chloritic minerals, 
Frequent eyes and lenticles of unshattered quartz, the relics 
of former phenocrysts, are scattered about the rock. 
Doubtless a certain amount of alteration is to be attributed 
to the mineralised waters which percolated through the 
porphyry at this place. Northwards right along the line 
of the Bushy Hill outcrop the porphyry is much ‘‘mylon- 
ized,’ in places so much so as to be recognizable only with 
difficulty. On Bushy Hill the cleavage planes are vertical, 
and no where has the departure from the vertical been 
found to be more than 40°. Very little in the way of ferro- 
magnesian constituents has been observed in the Bushy 
Hill porphyry. In addition to quartz, felspar occasionally 
appears as phenocrysts. 
Between “‘Rosebrook’’ homestead and the Umaralla 
River one passes over a couple of outcrops of porphyry of 
a light grey colour, with large and abundant phenocrysts 
of quartz, felspar, and a dark green chloritic-looking mica 
in small hexagonal plates. This rock is rather shattered ; 
it is intruded among Silurian slates and appears to be of no 
great extent. In the size and abundance of its quartz 
crystals it much resembles some of the “‘mylonized”’ 
* A Treatise on Metamorphism, p. 779. 
