As a dark-coloured soil is also found in the ridges about some of these lakes we must look deeper for the original cause of such depressions in those extensive plains; and may attribute them either to cavities or protuberances in the lower rocks, which may not have been sufficiently filled or covered by the superincumbent deposits: or they may be due to partial subsidences in a thin stratum of limestone.
CHANGES ON THE SEACOAST. PROOFS THAT THE COAST WAS ONCE HIGHER ABOVE THE SEA THAN IT IS AT PRESENT. PROOFS THAT IT WAS ONCE LOWER. AND OF VIOLENT ACTION OF THE SEA.
The sea, probably when higher relatively to the land than it is at present, appears to have acted with some violence in isolating various points along the eastern coast; most of which we now find curiously analogous, in their situation on the southern sides of inlets, and in being now united to the mainland by mounds of sand.
AT WOLLONGONG.
The point of Wollongong was formerly an island and is now only connected by drifted sandhills with the site of the township.
CAPE SOLANDER.
Cape Solander, the south head of Botany Bay, on which Captain Cook first landed, was evidently once an island though at present connected with the mainland by the neck of sand which separates Botany Bay from Port Hacking.
PORT JACKSON.
The south head of Port Jackson has also been isolated but is again connected with the shore of Bellevue between Bondi Bay and Rose Bay, by drifted hills of sand. The north head appears to have been likewise isolated.
BROKEN BAY.