Mica Slate.—Colour dark brown, approaching red; mica glittering. The hills enclosing Pondebadgery Plain at the gorge of the valley of the Morumbidgee, are composed of this rock. They are succeeded by
Sandstone.—Which rises abruptly from the river in perpendicular cliffs, of 145 feet in height.
Jasper and quartz.—Colour red and white. Forms the slope of the above sandstone, and may be considered the outermost of the rocks connected with the Eastern or Blue Mountain Ranges. It will be remembered that jasper and quartz were likewise found on a plain near the Darling River, precisely similar to the above, although occurring at so great a distance from each other.
Granite.—Light red colour; composition of a small isolated hill, to all appearance wholly unconnected with the neighbouring ranges. This specimen is very similar to that found in the bed of New-Year's Creek.
Breccia.—Silicious cement, composed of a variety of pebbles. Formation of the most WESTERLY of the hills between the Lachlan and Macquarie Rivers. This conglomerate was also found to compose the minor and most westerly of the elevations of the more northern interior.
Chrystallised Sulphate of Lime.—Found embedded in the deep alluvial soil in the banks of the Morumbidgee River, in lat. 34 degrees 30 minutes S., and long. 144 degrees 55 minutes E. The same substance was found on the banks of the Darling, in lat. 29 degrees 49 minutes S., and in long. 145 degrees 18 minutes E.
A reference to the chart will show that the Morumbidgee, from the first of the above positions, may be said to have entered the almost dead level of the interior. No elevation occurs to the westward for several hundreds of miles. A coarse grit occasionally traversed the beds of the rivers, and their lofty banks of clay or marl appear to be based on sandstone and granitic sand. The latter occurs in slabs of four inches in thickness, divided by a line of saffron-coloured sand, and seems to have been subjected to fusion, as if the particles or grains had been cemented together by fusion.
The first decided break that takes place in the level of the interior occurs upon the right bank of the Murray, a little below the junction of the Rufus with it. A cliff of from 120 to 130 feet in perpendicular elevation here flanks the river for about 200 yards, when it recedes from it, and forms a spacious amphitheatre that is occupied by semicircular hillocks, that partake of the same character as the cliff itself; the face of which showed the various substances of which it was composed in horizontal lines, that if prolonged would cut the same substance in the hillocks. Based upon a soft white sandstone, a bed of clay formed the lowest part of the cliff; upon this bed of clay, a bed of chalk reposed; this chalk was superseded by a thick bed of saponaceous earth, whilst the summit of the cliff was composed of a bright red sand. Semi-opal and hydrate of silex were found in the chalk, and some beautiful specimens of brown menelite were collected from the upper stratum of the cliff.
A little below this singular place, the country again declines, when a tertiary fossil formation shows itself, which, rising gradually as an inclined plain, ultimately attains an elevation of 300 feet. This formation continues to the very coast, since large masses of the rock were observed in the channel of communication between the lake and the ocean; and the hills to the left of the channel were based upon it. This great bank cannot, therefore, average less than from seventy to ninety miles in width. At its commencement, it strikingly resembled skulls piled one on the other, as well in colour as appearance. This effect had been produced by the constant rippling of water against the rock. The softer parts had been washed away, and the shells (a bed of Turritella) alone remained.
Plate 1, Figures 1, 2, and 3, represent the selenite formation.