~ 
GEOLOGY OF THE COOMA DISTRICT, N.S.W. 195 
lenticular patches, the most southerly of which crosses the 
* Greenhill Road a little to the west of Rock Flat Creek. 
Here there are seen to be two intermittent outcrops of two 
distinct kinds of limestone, separated by slates, and some- 
times 40 yards apart. The main outcrop is of light blue 
limestone, massive and fossiliferous, the other harder, of a 
deeper blue, flaggy, unfossiliferous, and much intersected 
with veins of white secondary calcite. Occasionally this 
band is broken up into smaller bands, about 4 inches wide, 
interbedded with the slates. The limestone is traversed 
by cracks or joints striking a little west of north. The dip 
appears to be easterly on the western side, and -westerly 
on the eastern, the angles in both cases being very high. 
Caves are said to exist in the limestone, fairly extensive 
and containing stalactites. 
The main outcrop of the limestone is constantly attended 
by quartz-porphyry on both sides, which has very probably 
intruded and to some extent destroyed part of the limestone. 
A certain amount of assimilation may have taken place; a 
specimen of quartz-porphyry collected from near the junc- 
tion showed under the microscope numerous little patches 
of what look like epidote. Along the eastern boundary of 
the limestone, however, the quartz-porphyry (and possibly 
the limestone too) has been converted into a kind of iron- 
stone, thus destroying any evidence of contact effects. 
This ironstone is indeed more or less characteristic of the 
limestone outcrop, and where the latter cannot be traced 
ironstone is often found. The occurrence is suggestive of 
a metasomatic replacement. 
There is in the limestone abundant development of 
Favosites, both the large massive and the small dendroid 
species, also Heliolites, Tryplasma, Pentamerus, and 
Stromatopora. The fossils are in general well preserved. 
Hast of the limestone there is a further development of 
slates. Between Rosebrook homestead and the Umaralla 
