May 6.--Following the brook about four miles farther, I came to its source at a gentle slope of basalt. Plains stretched along both sides of its course, and even beyond it. Luxuriant reeds, Plothos, and several deep green trees, crowded round its head. Kangaroos, which abounded particularly along the scrub, had formed numerous paths through the high grass to the water's edge. I now directed my course to the W.N.W., but soon found myself checked by a dyke or wall of basaltic lava, composed of boulders and tabular blocks heaped over each other in wild confusion, and covered by scrub; it stretched from N.W. to S.E. I travelled round its edge to the southward, after having made a vain attempt to cross it. The outlines of the stream ran out in low heads into the flat table land, and there we met occasionally with springs and chains of water-holes which united lower down into a water-course, which, after following alternately the outline of the scrub, and turning into the stream of lava, became lost among its loose rocks. The lava was very cellular; the basalt of the table land solid. The whole appearance of this interesting locality showed that the stream of lava was of much more recent date than the rock of the table land, and that the latter was probably formed under water, whilst the cellular scorified lava was poured out into the open air. The stream of lava enlarged so much, and descended into so broad a valley, that I considered it to be the head of the Burdekin. I walked across it, in order to ascertain the presence of water, but found nothing but deep dry hollows surrounded with drooping tea trees, and the black basaltic rocks covered with wild bottle-tree scrub. It joined the valley of lagoons very much like the valley of the reedy brook, and seemed to unite with the latter, and to expand all over the large basin. Numerous headlands protruded from the table land into the valley of lagoons, between the stream of lava and reedy brook. Many of them were composed of quartzite and pegmatite [Graphic granite, composed of quartz and laminated felspar.--ED.], the detritus of which formed sandy slopes very different from the black and loamy soil of the table land and its plains. Several isolated hills and short ridges rise out of the basaltic floor of the valley of lagoons; they are composed of a different rock; and if it may be allowed me to judge by the colour and by analogy, I should say that they were pegmatite and quartzite. It would, therefore, appear that the valley of lagoons is connected with three streams of lava; one following down the river to the southward, a second coming down the valley of Reedy Brook from W.N.W., and the third coming from the N.W. The course of the Burdekin has no connection with this valley, but runs apparently along its eastern side, and divides the primitive rocks from the streams of lava; for I had not observed any lava on its left bank.