The shells out of the layers of brown limestone, included in the black calcareous shale-rock, which latter, as just stated, replaces the white siliceous sandstone, consist of:--Pecten Dufreynoyi, d'Orbigny, "Voyage" Part Pal.
Turritella Andii, d'Orbigny, "Voyage" Part Pal.
Astarte Darwinii, E.Forbes.
Gryphaea Darwinii, E.Forbes.
An intermediate form between G.gigantea and G.incurva.
Gryphaea nov.spec.?, E.Forbes.
Perna Americana, E.Forbes.
Avicula, nov.spec.
Considered by Mr.G.B.Sowerby as the A.echinata, by M.d'Orbigny as certainly a new and distinct species, having a Jurassic aspect.The specimen has been unfortunately lost.
Terebratula aenigma, d'Orbigny, (var.of do.E.Forbes.)This is the same variety, with that from Guasco, considered by M.D'Orbigny to be a distinct species from his T.aenigma, and related to T.obsoleta.
Plagiostoma and Ammonites, fragments of.
The lower layers of the limestone contained thousands of the Gryphaea; and the upper ones as many of the Turritella, with the Gryphaea (nov.species)and Serpulae adhering to them; in all the layers, the Terebratula and fragments of the Pecten were included.It was evident, from the manner in which species were grouped together, that they had lived where now embedded.Before making any further remarks, I may state, that higher up this same valley we shall again meet with a similar association of shells;and in the great Despoblado Valley, which branches off near the town from that of Copiapo, the Pecten Dufreynoyi, some Gryphites (I believe G.
Darwinii), and the TRUE Terebratula aenigma of d'Orbigny were found together in an equivalent formation, as will be hereafter seen.A specimen also, I may add, of the true T.aenigma, was given me from the neighbourhood of the famous silver mines of Chanuncillo, a little south of the valley of the Copiapo, and these mines, from their position, I have no doubt, lie within the great gypseous formation: the rocks close to one of the silver veins, judging from fragments shown me, resemble those singular metamorphosed deposits from the mining district of Arqueros near Coquimbo.
I will reiterate the evidence on the association of these several shells in the several localities.
COQUIMBO.
In the same bed, Rio Claro:
Pecten Dufreynoyi.
Ostrea hemispherica.
Terebratula aenigma.
Spirifer linguiferoides.
Same bed, near Arqueros:
Hippurites Chilensis.
Gryphaea orientalis.
Collected by M.Domeyko from the same locality, apparently near Arqueros:
Terebratula aenigma and Terebratula ignaciana, in same block of limestone:
Pecten Dufreynoyi.
Ostrea hemispherica.
Hippurites Chilensis.
Turritella Andii.
Nautilus Domeykus.
GUASCO.
In a collection from the Cordillera, given me: the specimens all in the same condition:
Pecten Dufreynoyi.
Turritella Andii.
Terebratula ignaciana.
Terebratula aenigma, var.
Spirifer Chilensis.
COPIAPO.
Mingled together in alternating beds in the main valley of Copiapo near Las Amolanas, and likewise higher up the valley:
Pecten Dufreynoyi.
Turritella Andii.
Terebratula aenigma, var.as at Guasco.
Astarte Darwinii.
Gryphaea Darwinii.
Gryphaea nov.species?
Perna Americana.
Avicula, nov.species.
Main valley of Copiapo, apparently same formation with that of Amolanas:
Terebratula aenigma (true).
In the same bed, high up the great lateral valley of the Despoblado, in the ravine of Maricongo:
Terebratula aenigma (true).
Pecten Dufreynoyi.
Gryphaea Darwinii?
Considering this table, I think it is impossible to doubt that all these fossils belong to the same formation.If, however, the species from Las Amolanas, in the Valley of Copiapo, had, as in the case of those from Guasco, been separately examined, they would probably have been ranked as oolitic; for, although no Spirifers were found here, all the other species, with the exception of the Pecten, Turritella, and Astarte, have a more ancient aspect than cretaceous forms.On the other hand, taking into account the evidence derived from the cretaceous character of these three shells, and of the Hippurites, Gryphaea orientalis, and Ostrea, from Coquimbo, we are driven back to the provisional name already used of cretaceo-oolitic.From geological evidence, I believe this formation to be the equivalent of the Neocomian beds of the Cordillera of Central Chile.
To return to our section near Las Amolanas:--Above the yellow siliceous sandstone, or the equivalent calcareous slate-rock, with its bands of fossil-shells, according as the one or other prevails, there is a pile of strata, which cannot be less than from two to three thousand feet in thickness, in main part composed of a coarse, bright red conglomerate, with many intercalated beds of red sandstone, and some of green and other coloured porcelain-jaspery layers.The included pebbles are well-rounded, varying from the size of an egg to that of a cricket-ball, with a few larger; and they consist chiefly of porphyries.The basis of the conglomerate, as well as some of the alternating thin beds, are formed of a red, rather harsh, easily fusible sandstone, with crystalline calcareous particles.This whole great pile is remarkable from the thousands of huge, embedded, silicified trunks of trees, one of which was eight feet long, and another eighteen feet in circumference: how marvellous it is, that every vessel in so thick a mass of wood should have been converted into silex! Ibrought home many specimens, and all of them, according to Mr.R.Brown, present a coniferous structure.
