486 NEW SOUTH WALES. 
sandstone; and in some places the passage of the red into the gray 
may be observed. ‘Through much of the distance, however, beds of 
basalt constitute the shore bluffs. The relations of the sandstone and 
basalt will be particularly described in the pages on the latter rock. 
At Black Head the rock is identical in appearance with that of Wollon- 
gong. Between this point and Shoalhaven, a distance of nine miles, 
the coast is a sand beach. But near the latter place stands Mount 
Coolomegata, an isolated elevation, five hundred feet high, which con- 
sists of the same rock, but having a grayish-red colour and a rather 
coarse texture, approaching to pebbly. 
The greenstone or basaltic boulders and pebbles of this rock in 
Illawarra, way be traced to the basaltic rocks of the same region. 
The porphyritic variety contains tabular crystals of feldspar half an 
inch square, so thickly disseminated as to form at least one-third of 
the whole mass. In the amygdaloid, the ovoidal nodules were so 
numerous as to make it resemble a puddingstone; and its nature was 
farther disguised by a bleaching of the surface to a light grayish- 
green. ‘These nodules were calcareous and averaged half an inch in 
length, though some were two or three inches. 
This amyedaloid actually occurs in place at Keelhogue, presenting 
the same characters in every particular; and a porphyritic rock is 
also met with in the same region, similar to that above described, 
excepting a smaller proportion of imbedded feldspar crystals. ‘This 
locality is situated to the west of Wollongong, not far from the foot of 
the Illawarra range, near the residence of the Attorney-General. 
The imbedded minerals of the rock, as far as known, are few and 
unimportant. Some small nodules 
or crystals of pyrites occur at Wol- 
longong; and chalcedony, quartz 
crystals, and calc spar are met with, 
constituting fossils and occasional- 
ly filling seams. 
Concentric Structure.—A_ con- 
centric structure is more frequent 
in these rocks than in those of the 
coal series above, and in some 
places the examples of it are quite 
remarkable. The general cha- 
racter of it when connected with 
cracks or fissures in the rock is 
