Geological Observations on South America. Darwin Charles

high) through plains B and A and the River of Guasco at the Town of Ballenar.)

      On the northern side of the valley the summit-plain of gravel, A, has two escarpments, one facing the valley, and the other a great basin-like plain, B, which stretches for several leagues northward. This narrow plain, A, with the double escarpment, evidently once formed a spit or promontory of gravel, projecting into and dividing two great bays, and subsequently was worn on both sides into steep cliffs. Whether the several escarpments in this valley were formed during the same stationary periods with those of Coquimbo, I will not pretend to conjecture; but if so the intervening and subsequent elevatory movements must have been here much more energetic, for these plains certainly stand at a much higher level than do those of Coquimbo.

       COPIAPO.

      From Guasco to Copiapo, I followed the road near the foot of the Cordillera, and therefore saw no upraised remains. At the mouth, however, of the valley of Copiapo there is a plain, estimated by Meyen ("Reise um die Erde" th. 1 s. 372 et seq.) between fifty and seventy feet in height, of which the upper part consists chiefly of gravel, abounding with recent shells, chiefly of the Concholepas, Venus Dombeyi, and Calyptraea trochiformis. A little inland, on a plain estimated by myself at nearly three hundred feet, the upper stratum was formed of broken shells and sand cemented by white calcareous matter, and abounding with embedded recent shells, of which the Mulinia Byronensis and Pecten purpuratus were the most numerous. The lower plain stretches for some miles southward, and for an unknown distance northward, but not far up the valley; its seaward face, according to Meyen, is worn into caves above the level of the present beach. The valley of Copiapo is much less steeply inclined and less direct in its course than any other valley which I saw in Chile; and its bottom does not generally consist of gravel: there are no step-formed terraces in it, except at one spot near the mouth of the great lateral valley of the Despoblado where there are only two, one above the other: lower down the valley, in one place I observed that the solid rock had been cut into the shape of a beach, and was smoothed over with shingle.

      Northward of Copiapo, in latitude 26 degrees S., the old voyager Wafer found immense numbers of sea-shells some miles from the coast. (Burnett's "Collection of Voyages" volume 4 page 193.) At Cobija (latitude 22 degrees 34') M. d'Orbigny observed beds of gravel and broken shells, containing ten species of recent shells; he also found, on projecting points of porphyry, at a height of 300 feet, shells of Concholepas, Chiton, Calyptraea, Fissurella, and Patella, still attached to the spots on which they had lived. M. d'Orbigny argues from this fact, that the elevation must have been great and sudden ("Voyage, Part Geolog." page 94. M. d'Orbigny (page 98), in summing up, says: "S'il est certain (as he believes) que tous les terrains en pente, compris entre la mer et les montagnes sont l'ancien rivage de la mer, on doit supposer, pour l'ensemble, un exhaussement que ce ne serait pas moindre de deux cent metres; il faudrait supposer encore que ce soulevement n'a point ete graduel;…mais qu'il resulterait d'une seule et meme cause fortuite," etc. Now, on this view, when the sea was forming the beach at the foot of the mountains, many shells of Concholepas, Chiton, Calyptraea, Fissurella, and Patella (which are known to live close to the beach), were attached to rocks at a depth of 300 feet, and at a depth of 600 feet several of these same shells were accumulating in great numbers in horizontal beds. From what I have myself seen in dredging, I believe this to be improbable in the highest degree, if not impossible; and I think everyone who has read Professor E. Forbes's excellent researches on the subject, will without hesitation agree in this conclusion.): to me it appears far more probable that the movement was gradual, with small starts as during the earthquakes of 1822 and 1835, by which whole beds of shells attached to the rocks were lifted above the subsequent reach of the waves. M. d'Orbigny also found rolled pebbles extending up the mountain to a height of at least six hundred feet. At Iquique (latitude 20 degrees 12' 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 30 page 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. I collected 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: the upper and lower surfaces of the Concholepas had generally quite scaled off: some of the Trochi and Fissurellae still partially retain their colours. It is remarkable that these shells,