The elevation of Darling Downs--about 1800 to 2000 feet, according to the barometrical observations of Mr. Cunningham--renders the climate much cooler than its latitude would lead one to suppose; indeed, ice has frequently been found, during the calm clear nights of winter. During September and October, we observed at sunrise an almost perfect calm. About nine o'clock, light westerly winds set in, which increased towards noon, died away towards evening, and after sunset, were succeeded by light easterly breezes; thunder-storms rose from south and south-west, and passed over with a violent gust of wind and heavy showers of rain; frequently, in half an hour's time, the sky was entirely clear again; sometimes, however, the night and following day were cloudy. The plains, as we passed, were covered with the most luxuriant grass and herbage. Plants of the leguminosae and compositae, were by far the most prevalent; the colour of the former, generally a showy red, that of the latter, a bright yellow. Belts of open forest land, principally composed of the Box-tree of the Colonists (a species of Eucalyptus), separate the different plains; and patches of scrub, consisting of several species of Acacias, and of a variety of small trees, appear to be the outposts of the extensive scrubs of the interior. There are particularly three species of Acacias, which bestow a peculiar character on these scrubs: the one is the Myal (A. pendula)--first seen by Oxley on Liverpool Plains, and afterwards at the Barwan, and which exists in all the western plains between the Barwan and Darling Downs--whose drooping foliage and rich yellow blossoms render it extremely elegant and ornamental. The second, the Acacia of Coxen, resembles the Myal (without its drooping character), its narrow lanceolate phyllodia rather stiff, its yellowish branches erect. The third, is the Bricklow Acacia, which seems to be identical with the Rose-wood Acacia of Moreton Bay; the latter, however, is a fine tree, 50 to 60 feet high, whereas the former is either a small tree or a shrub. I could not satisfactorily ascertain the origin of the word Bricklow [Brigaloe, GOULD.], but, as it is well understood and generally adopted by all the squatters between the Severn River and the Boyne, I shall make use of the name. Its long, slightly falcate leaves, being of a silvery green colour, give a peculiar character to the forest, where the tree abounds. Oct. 1.--After having repaired some harness, which had been broken by our refractory bullocks upsetting their loads, and after my companions had completed their arrangements, in which Mr. Bell kindly assisted, we left Jimba, and launched, buoyant with hope, into the wilderness of Australia.