requently concretions of indurated marl, are found. Coal appears in the
bed and banks of the Wollombi, near Mr. Blaxland's station, and at no
great distance from his farm is a salt spring, also in the bed of this
brook. The waters in the lesser tributaries, on the north bank of the
river Hunter, become brackish when the current ceases. In that part of
the bed of this river, which is nearest to the Wollombi (or to Wambo
rather) I found an augitic rock, consisting of a mixture of felspar and
augite.

FOSSILS OF THE HUNTER.

Silicified fossil wood of a coniferous tree, is found abundantly in the
plains, and in rounded pebbles in the banks and bed of the river, also
chalcedony and compact brown haematite. A hill of some height on the
right bank, situate twenty-six miles from the seashore, is composed
chiefly of a volcanic grit of greenish grey colour, consisting
principally of felspar, and being in some parts slightly, in other parts
highly calcareous when the rock assumes a compact aspect. This deposit
contains numerous fossil shells, consisting chiefly of four distinct
species of a new genus, nearest to hippopodium; also a new species of
trochus; Atrypa glabra, and Spirifer, a shell occurring also in older
limestones of England.*

(*Footnote. These shells having been submitted to Mr. James De Carl
Sowerby, I am indebted to that gentleman for the following description:

Class Conchifera. Order, Dimyaria. Genus Megadesmus.

Valves equal, inequilateral, thick, their edges even; umbones nearly
central; hinge sunk, with an antiquated area and one ? or two ? large
teeth in each valve; ligament external, large; impressions of the
abducter muscles strong, nearly equal, united by the impression of the
mantle, at the posterior extremity of which is a small shallow sinus; no
lunette.

A genus of heavy shells in some respects resembling Astarte, in others
especially in having a striated area within the beaks, Hippopodium, from
which it is distinguished by the position of the umbones and the presence
of a thick tooth in the hinge. There appear to be four species, which may
be named Megadesmus globosus (Plate 2) M. laevis (figure 1) M. antiquatus
(figure 2) and M. cuneatus (figure 3 Plate 3) the cuneatus differs from
antiquatus, only in having the shell a little contracted towards the
anterior side.

The large shell (Plate 4 figures 1 and 2) is near to Isocardia, but Mr.
Sowerby would not venture to say it belongs to that genus