GEOLOGY OF THE COOMA DISTRICT, N.S.W. 199 
Road at and past Middle Flat. Going about a quarter of a 
mile N.N.W. from ‘“‘Nitholme,’’ one observes that this 
porphyry is intrusive into the fine-grained variety; the out- 
crop is very wide, about one-half to three-quarters of a 
mile in places. Generally the rock is massive, but some- 
times it is a bit shattered at the periphery of the mass. 
Its intrusive character is shown near Rosebrook, where 
an isolated outcrop of it forms a conical hill sharply differ- 
entiated from the other porphyries and from the slates. 
This porphyry is a very handsome rock, abundantly por- 
phyritic in quartz and felspar, usually also with hornblende 
in varying amount. Quartz-porphyry was found in which 
practically all the base had been replaced by oxide of iron, 
leaving intact only the porphyritic quartz and felspars, 
and again in another place kaolinization had occurred, 
resulting in a soft white rock studded with quartz grains. 
Berridale granite.—Only a very small portion of the 
whole area of this was examined, and then not in great 
detail. It was only studied where it touched on the main 
area investigated. ) 
As one goes from Cooma to Berridale the granite is first 
met about 94 miles out. Great rounded monoliths of it 
strew the plain, and it can be seen stretching for a con- 
siderable distance on either side of the road most of the 
way into Berridale, the outcrop being occasionally con- 
cealed under small residual patches of basalt. On the 
Cooma side, the junction of the granite with the intruded 
Ordovician slates and quartzites has been to some extent 
eroded, and is masked by alluvial. 
The granite was also met witi along the Adaminaby 
road at a point 14 miles from Cooma, but a journey of 20 
miles south on the Bobundarah road failed to reveal any 
signs of it, so evidently the boundary of the outcrop takes 
a sweep to the south somewhere between the Berridale and 
Bobundarah roads. 
