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Pauses also of vast duration may have occurred in the deposition of strata, allowing time for the modification of organic life throughout the globe, slowly brought about by variation accompanied by extinction of the original forms. Gryphaea incurva, Sowerby. Avicula inaequivalvis, Sowerby. Avicula cygnipes, Phil. Lower Lias, Gloucestershire and Yorkshire. a. Lower valve. b.
I will reiterate the evidence on the association of these several shells in the several localities. In the same bed, Rio Claro: Pecten Dufreynoyi. Ostrea hemispherica. Terebratula aenigma. Spirifer linguiferoides. Same bed, near Arqueros: Hippurites Chilensis. Gryphaea orientalis.
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.
Close to the junction between this upper black slate-rock and the upper red sandstone, I found the Gryphaea Darwinii, the Turritella Andii, and vast numbers of a bivalve, too imperfect to be recognised.
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