At daylight I climbed the highest tree I could find on the eastern bank of the river, in order to get a peep at the surrounding country. The prospect, however, was but limited. The landscape presented to my view, was an almost uninterrupted level; open woodlands, with here and there a few grassy spots, were its prevailing features. I could see nothing of the river itself beyond the reach in which the boats were lying; its upper extremity bore South by West and was about half a mile from our halting place. I made a discovery in climbing this tree, which I hoped to make available in our farther ascent of the Fitzroy, should we be so fortunate as to accomplish its further exploration, or in any similar circumstances during our examination of these untrodden wilds. It was this, and I mention it, as the hint may be useful to others: I found our enemies the mosquitoes did not resort to the higher portions of the tree, and that by climbing some thirty feet from the ground, a night's repose, or at least a night undisturbed by their attacks might be obtained. Hastening back to the boats, we pushed on, but were some time getting to the end of the reach, the shallowness of the water rendering our advance difficult and tedious; entering at length the next, which trended South-West for about half a mile, the river gradually widened out until it attained a breadth of about half that space. An extensive flat of sand fronted the eastern bank, which was very low, and though now dry, bore undoubted marks of being not unfrequently visited by floods. The western bank of the next reach was low and broken, evidently forming a group of low grassy islands when the river is in a higher state. Some yellow sandstone cliffs, from ten to sixteen feet in height, formed the opposite bank of this reach, which extended barely a quarter of a mile, in from a South by East to a South by West direction; and varied in width from one to two hundred yards. We now entered a lake-like reach of the river, trending south for a mile and a quarter, having a breadth of about a hundred yards, and a depth in many places of twelve feet; being twice that which we had usually found in any of the lower reaches, with scarcely any stream. Soon after entering this remarkable sheet of water, we noticed a rock formation in its western banks; this we found to be a coarse-grained red sandstone, with fragments of quartz, and extended for nearly a quarter of a mile along the edge of the water. Over many parts of it was a coating of a dark and metallic appearance, about three inches thick; and the surface in places presented a glazed or smelted appearance. Mr. Darwin, in his work upon volcanic islands, page 143, alludes to this formation, under the head of "Superficial ferruginous beds," and thus concludes his observations: "The origin of these superficial beds, though sufficiently obscure, seems to be due to alluvial action on detritus abounding with iron."