GEOLOGY OF THE COOMA DISTRICT, N.S.W. 205 
The age of the basalts, and the possibility of their extru- 
sion having continued into recent geological times, will be 
discussed later in connection with the physiography. — 
Diatomaceous earth.—There is a deposit of diatomaceous 
earth or tripolite about 1$ miles H.S.H. of Bunyan Railway 
Station (See Fig. 2). The deposit is referred to in Pitt- 
man’s ‘‘Mineral Resources of N. S. Wales,”’ p. 429, also in 
the Records of the Geological Survey of N.S. Wales, 1897, 
p. 128. 
From test-holes which have been put down, the deposit 
is believed to cover an area of 30 acres. It is situated in 
a hollow on the western side of Middle Flat, surrounded 
on the north and west by a ridge of slates and mylonized 
quartz-porphyry capped by Tertiary basalt. The deposit. 
is close to the surface, being covered by 18 inches to 2 feet 
of alluvium, chiefly basaltic soil, Under this is about 2 
feet of very hard buff-coloured ‘‘ mullock,”’ a kind of traver- 
tine containing numerous angular fragments of quartz and 
of diatomaceous earth. This is succeeded by another 2 
feet of massive tripolite of a pale creamy-white colour, 
then comes 3 feet of layered tripolite—‘‘slate,’’ as it is 
called—which is slightly denser than the other and shows 
stratification. Under this the deposit is alternately massive 
and stratified. At intervals, pipes of roughly elliptical 
section occur, filled with a hard, brittle brown clay, in 
which remains of bones, etc., are often found. Veins of 
wood opal are fairly frequent, yellow, red, and green in 
colour, and very light and brittle. The deposit is being 
worked, but not in systematic fashion, digging operations 
not being carried on to a greater depth than 10 or 12 feet. 
Travertine.—At Rock Flat, 9 miles 8.H. of Cooma, on 
the right bank of the creek, are situated the well-known 
Rock Flat mineral springs,* where carbonated waters rise 
1 For an account of these see Rec. Geol. Surv., N.S.W., 1889, p. 179. 
