OLDER PLIOCENE FORMATIONS.

We must now carry back our retrospect one step farther, and treat of the monuments of the era immediately antecedent to that last considered. We defined in the fifth chapter, the zoological characters by which the strata of the older Pliocene period maybe distinguished, and we shall now proceed at once to describe some of the principal groups which answer to those characters.

Subapennine strata—The Apennines, it is well known, are composed chiefly of secondary rocks, forming a chain which branches off from the Ligurian Alps and passes down the middle of the Italian peninsula. At the foot of these mountains, on the side both of the Adriatic and the Mediterranean, are found a series of tertiary strata, which form, for the most part, a line of low hills occupying the space between the older chain and the sea. Brocchi, the first Italian geologist who described this newer group in detail, gave it the name of the Subapennines, and he classed all the tertiary strata of Italy, from Piedmont to Calabria, as parts of the same system. Certain mineral characters., he observed, were common to the whole, for the strata consist generally of light brown or blue marl, covered by yellow calcareous sand and gravel. There are also, he added, some species of fossil shells which are found in these deposits throughout the whole of Italy.