28TH APRIL.--Masses of a ferruginous rock extended across the river bed like a dyke, in a N. W. and S. E. direction; and as the river here broke through these rocks, changing, at a sharp angle, its course to the S. W., it seemed probable that the general course from above might be parallel to these rocks. Continuing along the bank, we found the reaches large, full of water; the country clear of scrub and covered with luxuriant grass. One singular flat sweeping round to the W. S. W. was covered with the rich grass PANICUM LOEVINODE. The tropical PEROTIS RARA, a delicate grass, producing long purple tufts of reflexed bristles, was also here observed. The general direction of the river was towards the N. W., and whenever it took any turn towards the east, I continued to travel northward, and thus, on three occasions, came upon its bank again, cutting off detours I must otherwise have described in following its course. We encamped on a beautiful spot, the sight of which would have rejoiced the heart of a stockholder. A fresh westerly breeze blew during the day, and we were as free from the annoyance of heat, as if we had been in England during the same month. Latitude 27 deg. 32' 37" S. The direction of the river's course was uncommonly straight, and its long sweeping reaches, full of water, seemed capable of being rendered available for the purpose of forming water communications. The surface of the adjacent country presented a thin deposit of sand, near the river, attesting the great height to which its waters sometimes rise; and minor features of ground near, showed, in their water-worn sections, that they had been wholly deposited by the river. Thermometer, at sunrise, 39 deg.; at 4 P. M., 69 deg.; at 9, 48 deg.;--with wet bulb, 46 deg..