GEOLOGY OF THE COOMA DISTRICT, N.S.W. 183 
ing, and would indicate that the original granite was either 
very coarse grained or else porphyritic. That they are 
not products of recrystallization their sparing distribution 
would show. 
The blue gneiss.—The extent of this, particularly to the 
north, has not been fully traced. The investigated outcrop 
occupies a fairly large area some distance to the west of 
the Sydney road between Bunyan and Pearman’s Hill, and 
is well developed at the point where the Murrumbidgee, in 
emerging from its V-shaped gorge in the Berridale table- 
land, executes a sharp S-shaped bend. Like the Cooma 
gneiss, the blue gneiss sends out numerous tongues into 
the surrounding rocks, and inclusions are frequent, also 
what look like basic segregations. 
For the most part the rock shows well-marked foliated 
gneissic structure, but as one goes westward across the 
outcrop between Governor’s Hill and the Murrumbidgee, 
one notices that about + mile from the edge of the intrusion 
the rock loses its gneissic appearance and becomes granitic, 
resembling, in fact, a normal biotite granite. Here, too, 
it weathers into the great rounded tors characteristic of 
massive granite. At the southern end of the main intru- 
sion there is a porphyritic and relatively acid facies, with 
pink, simply-twinned orthoclase phenocrysts measuring up 
to $inch by +inch. As has been mentioned, numerous 
dykes of blue gneiss are found, usually with the strike of 
the schists. A long dyke-intrusion can be traced along the 
Mittagang Road from the Cooma Creek bridge nearly as 
far as the waterworks distributing reservoir about a mile 
out of Cooma; further on the same dyke appears in a rail- 
way cutting, crosses the Sydney road, and eventually 
disappears under the basalt behind Cooma Railway Station. 
A probable continuation of this dyke northward would 
make its total length somewhere about 6 miles. The width 
