第24章 ON THE ELEVATION OF THE WESTERN COAST OF SOUTH AME

The Concholepas is much the most abundant, and the best preserved shell;but I extracted perfectly preserved specimens of the Fissurella biradiata, a Trochus and Balanus (both well-known, but according to Mr.Sowerby yet unnamed) and parts of the Mytilus Chiloensis.Most of these shells, as well as an encrusting Nullipora, partially retain their colour; but they are brittle, and often stained red from the underlying brecciated mass of primary rocks; some are packed together, either in black or reddish moulds;some lie loose on the bare rocky surfaces.The total number of these shells is immense; they are less numerous, though still far from rare, up a height of 1,000 feet above the sea.On the summit of a hill, measured 557 feet, there was a small horizontal band of comminuted shells, of which MANYconsisted (and likewise from lesser heights) of very young and small specimens of the still living Concholepas, Trochus, Patellae, Crepidulae, and of Mytilus Magellanicus (?) (Mr.Cuming informs me that he does not think this species identical with, though closely resembling, the true M.

Magellanicus of the southern and eastern coast of South America; it lives abundantly on the coast of Chile.): several of these shells were under a quarter of an inch in their greatest diameter.My attention was called to this circumstance by a native fisherman, whom I took to look at these shell-beds; and he ridiculed the notion of such small shells having been brought up for food; nor could some of the species have adhered when alive to other larger 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.Above this height, shells became very rare, though on a hill 1,300 feet high (Measured by the barometer: the highest point in the range behind Valparaiso I found to be 1,626 feet above the level of the sea.), I collected the Concholepas, Trochus, Fissurella, and a Patella.At these greater heights the shells are almost invariably embedded in mould, and sometimes are exposed only by tearing up bushes.These shells obviously had a very much more ancient appearance than those from the lesser heights; the apices of the Trochi were often worn down; the little holes made by burrowing animals were greatly enlarged; and the Concholepas was often perforated quite through, owing to the inner plates of shell having scaled off.

Many of these shells, as I have said, were packed in, and were quite filled with, blackish or reddish-brown earth, resting on the granitic detritus.Idid not doubt until lately that this mould was of purely terrestrial origin, when with a microscope examining some of it from the inside of a Concholepas from the height of about one hundred feet, I found that it was in considerable part composed of minute fragments of the spines, mouth-bones, and shells of Echini, and of minute fragments, of chiefly very young Patellae, Mytili, and other species.I found similar microscopical fragments in earth filling up the central orifices of some large Fissurellae.This earth when crushed emits a sickly smell, precisely like that from garden-mould mixed with guano.The earth accidentally preserved within the shells, from the greater heights, has the same general appearance, but it is a little redder; it emits the same smell when rubbed, but I was unable to detect with certainty any marine remains in it.This earth resembles in general appearance, as before remarked, that capping the rocks of Quiriquina in the Bay of Concepcion, on which beds of sea-shells lay.I have, also, shown that the black, peaty soil, in which the shells at the height of 350 feet at Chiloe were packed, contained many minute fragments of marine animals.These facts appear to me interesting, as they show that soils, which would naturally be considered of purely terrestrial nature, may owe their origin in chief part to the sea.