BASALTIC AND ALLIED ROCKS, 501 
wholly of red sandstone, excepting a layer of basaltic conglomerate 
below. Near the middle of the cliff, at one place, the sandstone has 
the ordinary gray colour of the Wollongong rock. The other shows 
the basalt overlying the sandstone, and separated from it by three feet 
of basaltic conglomerate. 
The red sandstone, which in these sections lies between the two beds 
of basalt, appears to be an upper layer of the Wollongong sandstone, 
while the grayish rock below the basalt is identical in characters and 
in its fossils with the fossiliferous layer of Wollongong Point. 
This stratification is well seen also at Keelhogue. ‘The porphyritic 
and amygdaloidal basalt form a bed which may be traced for half a 
mile along the bed or margin of a stream. At either end we find it 
overlaid nearly horizontally by sandstone ; and five hundred yards far- 
ther up the stream the coal shale and its fossils are abundant. 
Between Black Head and Shoalhaven there was no exposed section 
in which the relations of the basalt could be studied. But in Mount 
Coolomgata, it appears in a bed, and overlies sandstone containing 
fossils hke that of Black Head. This fossiliferous layer is seen at a 
height of three hundred and fifty feet. Above it, the basalt continues 
for eighty or one hundred feet, and then there follows sandstone 
again. ‘The rocks correspond apparently to the lower sandstone 
layer, the lower basalt, and the second sandstone layer. 
When first examined by the writer, the basalt was supposed to form 
a dike ; but on examining the other side of the hill, I found the same 
alternation of sandstone and basalt, and could not discover any appear- 
ance of the latter cutting through the former. ‘The case appeared 
anomalous, for the coast of Kiama had not then been studied. But 
afterwards it was obvious that we have in Coolomgata only a conti- 
nuation of the stratification at Black Head, interrupted by a fault of 
one or two hundred feet. 
Descending towards Shoalhaven, from the height called Brough- 
ton’s Head, (see Map,) back from the coast ten miles, we passed over 
some outcropping basalt, which for sixty or eighty feet intersected the 
sandstone. Whether a dike or not was not ascertained. 
This alternation of basaltic beds and sandstone has been described 
as occurring in Van Diemen’s Land, and the rocks present there the 
same characters as in Illawarra. 
The beds of basalt, which we have followed along the shores, cover, 
with small exceptions, the whole region between Black Head and 
Point Bass, and compose the mountain spurs which here radiate from 
126 
