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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.
Its composition is peculiar, as it is chiefly formed of small pieces of pumice, obsidian, and trachyte, in beds alternating with loam, ferriferous sand, and fragments of limestone. It is evidently of marine formation, as Sir William Hamilton, Professor Pilla, and others have detected sea-shells therein, of the genera Ostræa, Cardium, Pecten and Pectunculus, Buccinum, etc.
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.
And day after day the creatures will grow more tame, the serpula will not dart back into his case when you approach, nor the pecten close his beautiful shell as your shadow passes over it. Moreover, the habits of the creatures grow more entertaining as you become familiar with them, and even the dull oyster begins at last to show some signs of individual character.
By many able palaeontologists the species of fossils, more than fifty in number, were declared to be more Eocene in their appearance than Cretaceous. But M. Hebert found in this formation at Montereau, near Paris, the Pecten quadricostatus, a well-known Cretaceous species, together with some other fossils common to the Maestricht chalk and to the Baculite limestone of the Cotentin, in Normandy.
Pecten Valoniensis. Dfr. 1/2 natural size. Portrush, Ireland, etc. Avicula contorta. Portlock. Portrush, Ireland, etc. Natural size. The principal member of this group has been called by Dr. Wright the Avicula contorta bed, as this shell is very abundant, and has a wide range in Europe.
I heard of a great gypseous formation in the Cordillera; and a collection of shells made there was given me. These shells are all in the same condition, and appear to have come from the same bed: they consist of: Turritella Andii, d'Orbigny, "Voyage" Part Pal. Pecten Dufreynoyi, d'Orbigny, "Voyage" Part Pal. Terebatula ignaciana, d'Orbigny, "Voyage" Part Pal.
Ostrea Patagonica, d'Orbigny, "Voyage, Pal." Ostrea Alvarezii, d'Orbigny, "Voyage, Pal." Pecten Paranensis, d'Orbigny, "Voyage, Pal." Pecten Darwinianus, d'Orbigny, "Voyage, Pal." Pecten actinodes, G.B. Sowerby. 6. Casts of a Turritella. The four first of these species occur at St. Fe in Entre Rios, and the two first in the sandstone of the Rio Negro.
From specimens and notes given me by Lieutenant Stokes, it appears that the lower bed consists of soft muddy sandstone, like that of S. Josef, with many imperfect shells, including the Pecten Paranensis, d'Orbigny, casts of a Turritella and Scutella.
The great oyster is here numerous in layers; the Trigonocelia and Turritella are also very numerous: it is remarkable that the Pecten Paranensis, so common in all other parts of the coast, is here absent: the shells consist of: Ostrea Patagonica, d'Orbigny; "Voyage Pal." Venus meridionalis of G.B. Sowerby. 4. Crassatella Lyellii, G.B. Sowerby. 5. Cardium puelchum, G.B. Sowerby. 6.
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