The plains appear to be divided into several stages by these cross ridges, which may have shut up the water of high floods in extensive lakes during the existence of which the deposits formed the surface of the present plains. Loose red sand also constantly forms low hills on the borders of these plains; and it seems to have been derived from the decomposition of the sandstone, and may be a diluvial or lacustrine deposit. Blue clay appears in the lowest parts of the basin, and forms the level parts of the plain, with concretions of marl in thin layers. This has every appearance of a mud deposit; but its depth is greater than the lowest part visible in the channel of the river. The parallel course of small tributaries joining rivers, which seem to be the middle drain of extensive plains, may have been marked out during the deposition of the sedimentary matter as tributaries, on entering the channel of greater streams, immediately become a portion of them; hence it is, the general inclination being common to both, that such tributaries do not cross these sediments of floods now termed plains in order to join the main channel or river now remaining. CHARACTER OF THE GOOBANG AND BOGAN. Thus the Goobang, on entering the valley of the Lachlan, pursues a parallel course until the ridge from Hurd's peak confines the plain on the west and turns the Goobang into the main channel. The Bogan, on the opposite side of the high land, may be said to belong to the basin of the Macquarie, although it never joins that river, but merely skirts the plains which, below Cambelego, may be all supposed to belong to the original bed of the Macquarie. Throughout its whole course of 250 miles the left bank of the Bogan is close to low hills, while the right adjoins the plains of the Macquarie. The basin of the Macquarie, as shown by its course near Mount Harris and Morrisset's ponds, falls northward, but that of the Darling to the south-west. It is not at all surprising therefore that the course of a tributary so much opposed, as the Macquarie is, to that of the main stream, should spread into marshes: still less that, on being at length choked with the deposit filling up these marshes, it should work out for itself a channel less opposed to the course of the main stream. Duck creek appears to be now the channel by which the floods of the Macquarie join the Darling, and in a course much more direct than that through the marshes. Hence the Bogan also, being still less opposed to that of the Darling, finally enters that river without presenting the anomaly of an invisible channel. In like manner, at a much lower point on the Darling, the course of the little stream named Shamrock ponds, so remarkable in this respect, may be understood. This forms a chain of ponds, or a flowing stream, according to the seasons, between the plains on the left bank of the Darling, and the rising grounds further to the eastward: but instead of crossing the plains to join the main channel