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Updated: June 5, 2025
The shells of the older pliocene give from thirty-five to fifty; those of the newer, from ninety to ninety-five per cent. of existing species. The pachydermata of the preceding era now disappear, and are replaced by others belonging to still existing families elephant, hippopotamus, rhinoceros though now extinct as species. Some of these are startling, from their enormous magnitude.
We have seen that most of the fossil shells of the Older Pliocene strata of Suffolk which are of recent species are identical with testacea now living in British seas, yet some of them belong to Mediterranean species, and a few even of the genera are those of warmer climates.
Geology is not in a position either to prove or disprove this, and it remains only a speculative interpretation of the fact We know at least that there was a great uprise of land in Europe and North America in the Pliocene and Pleistocene and may leave the precise determination of the point to a later age. At the same time other local causes are not excluded.
South America is the home of a peculiar order of mammalia of the edentata, to which belong the sloth, the armadillo, and the like. All its predecessors are to be found also in the Pliocene strata of South America, and only there; and mostly in gigantic, but otherwise completely related, forms.
Hence, we may suppose that the organisms which now live under latitude 60 degrees, lived during the Pliocene period further north, under the Polar Circle, in latitude 66-67 degrees; and that the present arctic productions then lived on the broken land still nearer to the pole.
The Red Crag contains, as stated in the table, eight northern species, all of which recur in the Norwich Crag, with the addition of four others, also inhabitants of the arctic regions; so that there is good evidence of a continual refrigeration of climate during the Pliocene period in Britain.
The more ancient portion of Vesuvius and Etna originated at the close of the Newer Pliocene period, when less than ten, sometimes only one, in a hundred of the shells differed from those now living.
The Italians generally have not this paludal notion, for experience taught them long ago that malaria is produced nearly everywhere in marshy districts as well as in those which might almost be called arid; in a volcanic soil as well as in the deposits of the Miocene and Pliocene periods and the ancient and modern alluvia; in a soil rich in organic matters as well as in one containing almost none; in the plains as well as on the hills or mountains.
Forests might be torn up by such a flood, and thus the occurrence of the numerous trunks of trees dispersed irregularly through the trass can be explained. The manner in which this trass conforms to the shape of the present valleys implies its comparatively modern origin, probably not dating farther back than the Pliocene Period. Volcanic Rocks of the Upper Miocene Period. Madeira. Grand Canary.
Even in the Eocene, about five per cent of marine shells were of species still living, and in the Pliocene the proportion had risen to more than one half. Fishes were of modern types. Teleosts were now abundant.
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