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Close to Conchalee, a gravel-plain is fronted by a lower and similar plain about sixty feet in height, and this again is separated from the beach by a wide tract of low land: the surfaces of all three plains or terraces were strewed with vast numbers of the Concholepas, Mesodesma, an existing Venus, and other still existing littoral shells.
On another hill, some miles distant, and 648 feet high, I found shells of the Concholepas and Trochus, perfect, though very old, with fragments of Mytilus Chiloensis, all embedded in reddish-brown mould: I also found these same species, with fragments of an Echinus and of Balanus psittacus, on a hill 1,000 feet high.
On the bare surface of the calcareous plain, or in a thin covering of sand, there were lying, at a height from 200 to 252 feet, many recent shells, which had a much fresher appearance than the embedded ones: fragments of the Concholepas, and of the common Mytilus, still retaining a tinge of its colour, were numerous, and altogether there was manifestly a closer approach in proportional numbers to those now lying on the beach.
Kent, the assistant-surgeon, was so kind as to make for me some measurements with the barometer: he found many marine remains along the shores of the whole bay, at a height of about twenty feet; and from the hill of Sentinella behind Talcahuano, at the height of 160 feet, he collected numerous shells, packed together close beneath the surface in black earth, consisting of two species of Mytilus, two of Crepidula, one of Concholepas, of Fissurella, Venus, Mactra, Turbo, Monoceros, and the Balanus psittacus.
In the valley of Chaneral, a similar bed occurs in which, differently from that of Coquimbo, I observed many shells of the Concholepas: near Guasco the same calcareous bed is likewise met with. In the valley of Guasco, the step-formed terraces of gravel are displaced in a more striking manner than at any other point.
Of marine animals there remain to be noticed a small Octopus, a Loligo, two Chiton, Patella, Crepidula, Pilcopsis, Fissurella, Calyptræa; of Concholepas, only empty shells; a large Mytilus, a small Modiola, Turritella, Turbo, Balanus; and a Holothuria of the variety Psolus.
The state of preservation of the different species differed much; but most of them were much corroded, brittle, and bleached: the upper and lower surfaces of the Concholepas had generally quite scaled off: some of the Trochi and Fissurellae still partially retain their colours.
Kent observed that there were beds formed exclusively of the Mytilus Chiloensis: this species now lives in parts never uncovered by the tides. At considerable heights, Mr. Kent found only a few shells; but from the summit of one hill, 625 feet high, he brought me specimens of the Concholepas, Mytilus Chiloensis, and a Turbo.
The shells embedded in the calcareous beds forming the surface of this fringe-like plain, at the height of from 200 to 250 feet above the sea, consist of: Venus opaca. 2. Mulinia Byronensis. 3. Pecten purpuratus. 4. Mesodesma donaciforme. 5. Turritella cingulata. 6. Monoceros costatum. 7. Concholepas Peruviana. 8. Calyptraea Byronensis.
Out of several Cirripedes, which are anomalous both in structure and development, Cryptophialus minutus must be mentioned here; Darwin found it in great quantities together in the shell of Concholepas peruviana on the Chonos Islands.
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