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may be reduced to the above general type; the lower beds being more argillaceous.

The Italian tertiaries constitute a triple series, but the lower and upper terms appear only at particular points.

Sicilian, or upper tertiaries, best seen in the Val di Noto (and Calabria), consist of thick limestone (700 or 800 feet), rising in the hill of Castrogiovanni to 3000 feet elevation; shells nearly all of existing species; white calcareous sand, sandy limestone, and conglomerates.

Subapennine, or middle tertiaries, of very great thickness, consisting of innumerable laminæ of marls, calcareous and argillaceous, blue or brownish, like the mud now gathered on the bed of the Adriatic; some sandstones, limestones, and gypsum are locally traceable: 40 per cent, of the shells belong to existing species.

Superga, or lower tertiaries, consisting of fine green sand and marl, resting on conglomerate, full of boulders of primary rocks; unconfirmed beneath the subapennine marls, and containing only a small proportion of recent shells.

The relation of these tertiary to the subjacent cretaceous groups has again been the subject of an elaborate investigation by Murchison. Taking the limestone of La Spezia and Carrara (of Lower Jurassic age) to be the oldest of the Italian secondaries, we have above the ammonitico rosso and the cretaceous series, this latter being well exhibited on the flanks of the Venetian Alps and about Nice. In these localities they are covered conformably by tertiary accumulations, characterized by nummulites, and devoid of types of secondary fossils. In such sections it is only by the sequence and combinations of the forms of life that the separation of tertiary and secondary strata can be safely attempted, nor can a hard line be drawn where nature has employed the softening pencil.^[1]

Geographical Extent, and Physical Geography.—

1. Geol. Proc., 1849. See also the addresses of De la Beche, 1849, and Lyell, 1850, on this subject.