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The rock consisted of a calcareous breccia, with water-worn pebbles. The carts had ascended to the crest without difficulty, and the descent to the country beyond was equally favourable. Halfway down, the dogs killed a female kangaroo, with a nearly full-grown young one, which she retained to the last, within her pouch.
There are just two distinct views under which we may consider all stalactical concretions formed; these are the incrustation of the calcareous substance concreting upon a foreign body, and the incrustation of the same substance upon itself. By the first any manner of shape may be formed, provided there be a solid body, upon the surface of which the calcareous solution is made to pass.
I shall accordingly proceed to treat of each family of rocks; first, in reference to those characters which are not chronological, and then in particular relation to the several periods when they were formed. Mineral Composition of Strata. Siliceous Rocks. Argillaceous. Calcareous. Gypsum. Forms of Stratification. Original Horizontality. Thinning out. Diagonal Arrangement. Ripple-mark.
As I have mentioned, the soundings from the great Atlantic plain are almost entirely made up of Globigerinae, with the granules which have been mentioned and some few other calcareous shells; but a small percentage of the chalky mud perhaps at most some five per cent of it is of a different nature, and consists of shells and skeletons composed of silex, or pure flint.
As we proceeded, the roof rose rapidly, so that the rocks overhead could not presently be seen by the light of the candle and lamp. Farther in, the roof became lower, and it was connected with the ground in places by natural columns of vast size, formed in the course of ages by the calcareous deposit of the dropping water.
The insidious cobra does not wear any calcareous covering beyond the frail tiny bivalves which guard the head a scandalously small proportion of its naked length but lines its tunnels with the materials whence shell is made, smooth and white as porcelain.
At about 20 miles we made an angle of the river where the left bank was 50 feet high. None of the usual indications of the neighbourhood of the Darling appeared here. No flats of Polygonum junceum, nor falls in the ground. The river was evidently encroaching on this high bank which consisted of red sandy earth to the depth of ten feet. Below this stratum was clay mixed with calcareous concretions.
The cemented mass is generally of a white colour, but in some few parts reddish from ferruginous matter; it is very hard, and is sonorous under the hammer; it is obscurely divided by seams, dipping at a small angle seaward; it consists of fragments of the corals which grow on the outer margin, some quite and others partially rounded, some small and others between two and three feet across; and of masses of previously formed conglomerate, torn up, rounded, and re-cemented; or it consists of a calcareous sandstone, entirely composed of rounded particles, generally almost blended together, of shells, corals, the spines of echini, and other such organic bodies; rocks, of this latter kind, occur on many shores, where there are no coral reefs.
Some mezquite trees appeared in front thinly covering the calcareous soil, but the twilight sun began to render less visible the objects here and there scattered over the plain. All at once the horse of Don Estevan came to a stand, and showed signs of affright.
With the exception of a few metamorphic ridges, the country between these two points, a distance of 400 geographical miles, belongs to the Pampean formation, and in the southern part is generally formed of the harder and more calcareous varieties.
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