GEOLOGY OF THE COOMA DISTIRICT, N.S.W. 203 
the syenite throughout its observed extent are free from 
gneissic structures, indicating that their crystallization 
took place during a period of comparative crustal stability. 
Since the Carboniferous appears to have been a time of 
intrusive igneous activity in central and southern New 
South Wales, it seems not unreasonable to assign these 
igneous rocks tentatively to that period. 
(e) TERTIARY AND RECENT. 
Olivine Basalt.—The latest evidences of igneous action 
about Cooma are to be found in the extensive flows of 
basalt which cover a considerable area of the surface of 
the country, and must have had a very much greater 
extent before erosion and denudation reduced the capp- 
ing to its present dimensions. Besides the large sheets, 
isolated residual patches of basalt, forming the charac- 
teristic table-topped hills, are to be found overlying the 
Berridale granite, the schists, and the slates and other 
Paleozoic rocks. Of the highest basalt residuals—the 
three hills known as The Brothers, about eleven miles 
south of Cooma—the Middle Brother is 100 feet higher 
than the next highest Trig. Station in the district, and 
about 700 feet above the general level of the country, but 
these figures of course do not necessarily indicate the depth 
to which the whole country was originally covered with 
basalt. The basalt hasa much greater extent to the south 
and §.H. of Cooma than to the north; it may be seen 
practically all the way along the road from Cooma to 
Nimitybelle and as far as Bombala. There is evidence of 
a number of successive flows, in the shape of terraced hills, 
sometimes as many as four terraces being distinguishable. 
Again occasionally one finds a flow of fresh basalt on top 
of an older and much decomposed flow. 
On the summit of the North Brother, and also, I under- 
stand on the Middle and the South Brother, the basalt is 
