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Many gigantic specimens of the Ostraea Patagonica were collected in the Gulf of St. George. A good section of the lowest fossiliferous mass, about forty feet in thickness, resting on claystone porphyry, is exhibited a few miles south of the harbour. The shells sufficiently perfect to be recognised consist of: Pecten Paranensis, d'Orbigny, "Voyage, Pal." Nucula ornata, G.B. Sowerby. 6.
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.
Further inland, with the exception of the superficial gravel, the whole thickness of the truncated hills, which represent a formerly continuous plain 950 feet in height, appears to be formed of this white mudstone: here and there, however, at various heights, thin earthy layers, containing the great oyster, Pecten Paranensis and Turritella ambulacrum, are interstratified; thus showing that the whole mass belongs to the same epoch.
Out of these three beds, I procured the following twelve species, of which the two first were exceedingly numerous in individuals, as were the Terebratulae and Turritellae in certain layers: Ostrea Patagonica, d'Orbigny, "Voyage, Pal." Pecten Paranensis, d'Orbigny, "Voyage, Pal." Pecten geminatus, G.B. Sowerby. 5. Fusus Patagonicus, G.B. Sowerby. 8. Fusus Noachinus, G.B. Sowerby. 9.
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.
The shells included in these beds have been named for me by M. d'Orbigny: they consist of: Ostrea Patagonica, d'Orbigny, "Voyage" Part. Pal. 2. Ostrea Alvarezii, d'Orbigny, "Voyage" Part. Pal. 3. Pecten Paranensis, d'Orbigny, "Voyage" Part. Pal. 4. Pecten Darwinianus, d'Orbigny, "Voyage" Part. Pal. 5. Venus Munsterii, d'Orbigny, "Voyage" Pal. 6. Arca Bonplandiana, d'Orbigny, "Voyage" Pal. 7.
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.
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