Was occupied in descending the river to the Geraldine Mine, cutting off several bends of the river, and making such additions to our sketch of the outward route as circumstances would admit. RETURN TO PERTH. 23rd June. We all arrived safe at the hospitable residence of Mr. W. Burges, on the Irwin; the following day being occupied in making up the accounts connected with the expedition, which, including the whole of the cash expenditure, did not exceed 40 pounds, which sum had already been subscribed by a few settlers interested in the undertaking. Quitting the Irwin on the 1st of July, and proceeding by way of Dandaragan and Toodyay, I arrived, with Mr. Roe and chainer Fairburn, in Perth on the 10th instant, having accomplished a journey of nearly 2000 miles in 107 days. On reviewing the foregoing report, I find it necessary to add a few observations on subjects that could not well be introduced into the body of the narrative. GEOLOGY OF COUNTRY. In the first place, viewing the geographical and geological features in combination, the tract of country contained within the 114th and 118th parallels of longitude, and the 24th and 27th degrees of south latitude, may be considered as an inclined plane, the eastern edge of which has an elevation of about 1700 feet above the level of the sea. Commencing from the coast, the first 100 miles is almost exclusively of tertiary sandstone formation, which the process of denudation has, in many instances, converted into either stony or sandy tracts, rarely fertile, except when subject to the influence of frequent inundation. This region seldom gives rise to rivers or watercourses; the flat-topped ranges, which are often found towards the eastern limits of this formation, do not generally exceed 500 or 600 feet in altitude, and are only those portions of country that have not as yet yielded to the waste of time, or the constant action of rivers, which, rising in the higher lands more to the eastward, rapidly abrade, and in their onward course remove the soft and porous sandstone from their bases. In the deeper valleys, towards the eastern edge of these sandstones thin beds of oolitic limestone, containing numerous fossil shells, occasionally occur; also gypsum and clayey shales, with other indications of the probable existence of coal in the vicinity; following the series appears a compact, fine-grained amorphous sandstone, having an almost flinty fracture; this rock, in a few miles, gives place to granite and gneiss, frequently broken up by the upheaval of whinstone and porphyritic trap hills, having an elevation of from 100 to 500 feet above the plain. As we proceeded eastward, the eruptive rocks became more numerous; chlorite slate, veins of quartz, chert, and variegated jasper, frequently forming the summits of the most elevated hills, while, on the general level of the plain, are occasionally found thin beds of ancient lava.