Some of these caves have been examined by Sir T. Mitchell in the Wellington Valley, about 210 miles west of Sidney, on the river Bell, one of the principal sources of the Macquarie, and on the Macquarie itself. The caverns often branch off in different directions through the rock, widening and contracting their dimensions, and the roofs and floors are covered with stalactite. The bones are often broken, but do not seem to be water-worn. In some places they lie imbedded in loose earth, but they are usually included in a breccia. The remains found most abundantly are those of the kangaroo, of which there are four species, besides which the genera _Hypsiprymnus_, _Phalangista_, _Phascolomys_, and _Dasyurus_, occur. There are also bones, formerly conjectured by some osteologists to belong to the hippopotamus, and by others to the dugong, but which are now referred by Mr. Owen to a marsupial genus, allied to the _Wombat_. [Illustration: Fig. 126. _Macropus atlas_, Owen. _a._ permanent false molar, in the alveolus.] [Illustration: Fig. 127. Lowest jaw of largest living species of kangaroo. (_Macropus major._)] In the fossils above enumerated, several species are larger than the largest living ones of the same genera now known in Australia. The annexed figure of the right side of a lower jaw of a kangaroo (_Macropus atlas_, Owen) will at once be seen to exceed in magnitude the corresponding part of the largest living kangaroo, which is represented in fig. 127. In both these specimens part of the substance of the jaw has been broken open, so as to show the permanent false molar (_a._ fig. 126.) concealed in the socket. From the fact of this molar not having been cut, we learn that the individual was young, and had not shed its first teeth. In fig. 128. a front tooth of the same species of kangaroo is represented. [Illustration: Fig. 128. Incisor of _Macropus_.] Whether the breccias, above alluded to, of the Wellington Valley, appertain strictly to the Pliocene period cannot be affirmed with certainty, until we are more thoroughly acquainted with the recent quadrupeds of the same district, and until we learn what species of fossil land shells, if any, are buried in the deposits of the same caves.