If we strike a line to the N.W. from Sydney to Wellington Valley, we shall find that little change takes place in the geological features of the country. The sand-stone of which the first of the barrier ranges is composed, terminates a little beyond Mount York, and at Cox's River is succeeded by grey granite. The secondary ranges to the N.W. of Bathurst, are wholly of that primitive rock; for although there are partial changes of strata between Bathurst and Moulong Plains, granite is undoubtedly the rock upon which the whole are based: but at Moulong Plains, a military station intermediate between Bathurst and Wellington Valley, limestone appears in the bed of a small clear stream, and with little interruption continues to some distance below the last-mentioned place. The accidental discovery of some caves at Moulong Plains, led to the more critical examination of the whole formation, and cavities of considerable size were subsequently found in various parts of it, but more particularly in the neighbourhood of Wellington Valley. The local interest which has of late years been taken in the prosecution of geological investigations, led many gentlemen to examine the contents of these caverns; and among the most forward, Major Mitchell, the Surveyor-General, must justly be considered, to whose indefatigable perseverance the scientific world is already so much indebted. The caves into which I penetrated, did not present anything particular to my observation; they differed little from caves of a similar description into which I had penetrated in Europe. Large masses of stalactites hung from their roofs, and a corresponding formation encrusted their floors. They comprised various chambers or compartments, the most remote of which terminated at a deep chasm that was full of water. A close examination of these caves has led to the discovery of some organic remains, bones of various animals embedded in a light red soil; but I am not aware that the remains of any extinct species have been found, or that any fossils have been met with in the limestone itself. There can, however, be little doubt but that the same causes operated in depositing these mouldering remains in the caves of Kirkdale and those of Wellington Valley. About twenty miles below the junction of the Bell with the Macquarie, free-stone supersedes the limestone, but as the country falls rapidly from that point, it soon disappears, and the traveller enters upon a flat country of successive terraces. A schorl rock, of a blue colour and fine grain, composed of tourmaline and quartz, forms the bed of the Macquarie at the Cataract; and, in immediate contact with it, a mass of mica slate of alternate rose, pink, and white, was observed, which must have been covered by the waters of the river when Mr. Oxley descended it.