Whilst prosecuting my researches in the interior of the colony, I could not but be struck with the apparent connection between its geology and vegetation; so strong, indeed, was this connection, that I had little difficulty, after a short experience, in judging of the rock that formed the basis of the country over which I
was travelling, from the kind of tree or herbage that flourished in the soil above it. The eucalyptus pulv., a species of eucalyptus having a glaucus-coloured leaf, of dwarfish habits and growing mostly in scrub, betrayed the sandstone formation, wherever it existed, This was the case in many parts of the County of Cumberland, in some parts of Wombat Brush, at the two passes on the great south road, over a great extent of country to the N.W. of Yass Plains, and at Blackheath on the summit of the Blue Mountains. On the other hand, those open grassy and park-like tracts, of which so much has been said, characterise the secondary ranges of granite and porphyry. The trees most usual on these tracts, were the box, an unnamed species of eucalyptus, and the grass chiefly of that kind, called the oat or forest grass, which grows in tufts at considerable distances from each other, and which generally affords good pasturage. On the richer grounds the angophora lanceolata, and the eucalyptus mammifera more frequently point out the quality of the soil on which they grow. The first are abundant on the alluvial flats of the Nepean, the
Hawkesbury and the Hunter; the latter on the limestone formation of Wellington Valley and in the better portions of Argyle; whilst the cupressus calytris seems to occupy sandy ridges with the casuarina. It was impossible that these broad features should have escaped observation: it was naturally inferred from this, that the trees of New South Wales are gregarious; and in fact they may, in a great measure, be considered so. The strong line that occasionally separates different species, and the sudden manner in which several species are lost at one point, to re-appear at another more distant, without any visible cause for the break that has taken place, will furnish a number of interesting facts in the botany of New South Wales.
It was observed both on the Macquarie river and the Morumbidgee, that the casuarinae ceased at a particular point. On the Macquarie particularly, these trees which had often excited our admiration from Wellington Valley downwards, ceased to occupy its banks below the cataract, nor were they again noticed until we arrived on the banks of the Castlereagh. The blue-gum trees, again, were never observed to
extend beyond the secondary embankments of the rivers, occupying that ground alone which was subject to flood and covered with reeds. These trees waved over the marshes of the Macquarie, but were not observed to the westward of them for many miles; yet they re-appeared upon the banks of New-Year's Creek as suddenly as they had disappeared after we left the marshes, and grew along the line of the Darling to unusual size. But it is remarkable, that, even in the midst of the marshes, the blue-gum trees were strictly confined to the immediate flooded spaces on which the reeds prevailed, or to the very beds of the water-courses. Where the ground was elevated, or out of the reach of flood, the box (unnamed) alone occupied it; and, though the branches of these trees might be interwoven together, the one never left its wet and reedy bed, the other never descended from its more elevated position. The same singular distinction marked the acacia pendula, when it ceased to cover the interior plains of light earth, and was succeeded by another shrub of the same species. It continued to the banks of New-Year's Creek, a part of which it thickly lined.
To the westward of the creek, another species of acacia was remarked for the first time. Both shrubs, like the blue-gum and the box, mixed their branches together, but the creek formed the line of separation between them. The acacia pendula was not afterwards seen, but that which had taken its place, as it were, was found to cover large tracts of country and to form extensive brushes. Many other peculiarities in the vegetation of the interior are noticed in the body of this work, but I have thought that these more striking ones deserved to be particularly remarked upon.
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.