S.), in a great accumulation of sand, at a height estimated between one hundred and fifty and two hundred feet, I observed many large sea-shells which I thought could not have been blown up by the wind to that height.
Mr.J.H.Blake has lately described these shells: he states that "inland toward the mountains they form a compact uniform bed, scarcely a trace of the original shells being discernible; but as we approach the shore, the forms become gradually more distinct till we meet with the living shells on the coast." ("Silliman's American Journal of Science" volume 44 page 2.)This interesting observation, showing by the gradual decay of the shells how slowly and gradually the coast must have been uplifted, we shall presently see fully confirmed at Lima.At Arica (latitude 18 degrees 28'), M.d'Orbigny found a great range of sand-dunes, fourteen leagues in length, stretching towards Tacna, including recent shells and bones of Cetacea, and reaching up to a height of 300 feet above the sea.("Voyage" etc.page 101.) Lieutenant Freyer has given some more precise facts: he states (In a letter to Mr.Lyell "Geological Proceedings" volume 2 page 179.) that the Morro of Arica is about four hundred feet high; it is worn into obscure terraces, on the bare rock of which he found Balini and Milleporae adhering.At the height of between twenty and thirty feet the shells and corals were in a quite fresh state, but at fifty feet they were much abraded; there were, however, traces of organic remains at greater heights.
On the road from Tacna to Arequipa, between Loquimbo and Moquegua, Mr.M.
Hamilton found numerous recent sea shells in sand, at a considerable distance from the sea.("Edinburgh New Philosophical Journal" volume 30page 155.)
LIMA.
Northward of Arica, I know nothing of the coast for about a space of five degrees of latitude; but near Callao, the port of Lima, there is abundant and very curious evidence of the elevation of the land.The island of San Lorenzo is upwards of one thousand feet high; the basset edges of the strata composing the lower part are worn into three obscure, narrow, sloping steps or ledges, which can be seen only when standing on them: they probably resemble those described by Lieutenant Freyer at Arica.The surface of the lower ledge, which extends from a low cliff overhanging the sea to the foot of the next upper escarpment, is covered by an enormous accumulation of recent shells.(M.Chevalier, in the "Voyage of the 'Bonite'" observed these shells; but his specimens were lost.--"L'Institut"1838 page 151.) The bed is level, and in some parts more than two feet in thickness; I traced it over a space of one mile in length, and heard of it in other places: the uppermost part is eighty-five feet by the barometer above high-water mark.The shells are packed together, but not stratified:
they are mingled with earth and stones, and are generally covered by a few inches of detritus; they rest on a mass of nearly angular fragments of the underlying sandstone, sometimes cemented together by common salt.Icollected eighteen species of shells of all ages and sizes.Several of the univalves had evidently long lain dead at the bottom of the sea, for their INSIDES were incrusted with Balani and Serpulae.All, according to Mr.G.B.
Sowerby, are recent species: they consist of:--1.Mytilus Magellanicus: same as that found at Valparaiso, and there stated to be probably distinct from the true M.Magellanicus of the east coast.
2.Venus costellata, Sowerby "Zoological Proceedings."3.Pecten purpuratus, Lam.
4.Chama, probably echinulata, Brod.
5.Calyptraea Byronensis, Gray.
6.Calyptraea radians (Trochus, Lam.)
7.Fissurella affinis, Gray.
8.Fissurella biradiata, Trembly.
9.Purpura chocolatta, Duclos.
10.Purpura Peruviana, Gray.
11.Purpura labiata, Gray.
12.Purpura buxea (Murex, Brod.).
13.Concholepas Peruviana.
14.Nassa, related to reticulata.
15.Triton rudis, Brod.
16.Trochus, not yet described, but well-known and very common.
17 and 18.Balanus, two species, both common on the coast.
These upraised shells appear to be nearly in the same proportional numbers--with the exception of the Crepidulae being more numerous--with those on the existing beach.The state of preservation of the different species differed much; but most of them were much corroded, brittle, and bleached: