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.