ORIGIN OF SYDNEY SANDSTONE. 525 
required, therefore, a continued gradual subsiding of the Jand. The 
sands are mostly granitic; even the several ingredients of the granite 
may be distinguished, and we must therefore look to granite ridges 
for its origin, and probably to those of the south and west. In this 
respect, these rocks differ from those below the coal, which are to a 
large extent, where exposed in Illawarra and at Harper’s Hill on the 
Hunter, made from basaltic material. 
It is justly a matter of astonishment that through the whole of 
these deposits we find no remains of marine life. But it is a general 
case that in seas with a sandy bottom, mollusca are of rare occurrence ; 
and when they are met with, the dead shells are generally worn out 
by the trituration. Many instances of this kind are mentioned in the 
Report on Coral Islands, instances where the sands were within a few 
hundred feet of reefs of growing corals and shells, and yet no frag- 
ment of shell or coral larger than a grain of sand could be detected.* 
Such facts are common about all the islands bordered by coral reefs, 
and at first they naturally excited much surprise. At Hanalei on 
Kauai, are deposits very closely resembling those of the Sydney sand- 
stone, even to the inclined layers of deposition and absence of fossils. 
In this case, however, the rock is of beach origin. 
The formation of this sandstone in steep banks beneath a sea, as 
supposed by Darwin to account for the configurations of the valleys, 
may well be doubted.t Such a result may take place when the sands 
are chemically agglutinated, as in the case of calcareous sands by lime. 
But accumulations of siliceous sand, except when eddied by currents 
on a small scale, are not thus formed in isolated deposits, with inter- 
vening channels or valleys a thousand feet or more in depth: a broad 
current, gulf-stream like, sweeping over the region, could hardly have 
occasioned the eddyings required by the hypothesis of Mr. Darwin. 
The eruptions of basalt during the progress of these depositions, and 
also subsequently, were not numerous. ‘The island of Nobby, at the 
mouth of the Hunter River, has been described as a fine example of 
the influence of heated dikes on clays and sandstone when under 
water. 
Many fissures, shakings of the earth, and probably many earth- 
quake waves, accompanied these effects. The regular structure of the 
sandstone, as shown in its transverse fissures, may be connected in some 
degree with the course or direction of the tension, causing elevation, one 
of the lines being formed in the line of the movement, and the other trans- 
* Page 149, and elsewhere. t Volcanic Islands, p. 136. 
132 
