BAHIA BLANCA.

The Beagle arrived on the 24th of August, and a week afterwards sailed for the Plata. With Captain Fitzroy's consent I was left behind, to travel by land to Buenos Ayres. I will here add some observations, which were made during this visit, and on a previous occasion, when the Beagle was employed in surveying the harbour. Not much can be made out respecting the geology. At the distance of some miles inland, an escarpment of a great argillaceo-calcareous formation of rock extends. The space near the coast consists of plains of hardened mud, and broad bands of sand-dunes, which present appearances, that can easily be accounted for by a rise of the land; and of this phenomenon, although to a trifling amount, we have other proofs.

At Punta Alta, a low cliff, about twenty feet high, exposes a mass of partly consolidated shingle, irregularly interstratified with a reddish muddy clay, and containing numerous recent shells. We may believe a similar accumulation would now take place, on any point, where tides and waves were opposed. In the gravel a considerable number of bones were embedded.