On the European continent, marine Pliocene beds are found in Belgium and Italy. The former deposits greatly resemble our Crags, whilst the latter are of interest on account of the mixture of volcanic beds with marine sediments in Sicily, showing that the formation of Etna commenced in Pliocene times. Various deposits formed in inland basins are found in France and Germany, but the most remarkable occur in the Vienna basin, where Caspian conditions prevailed over large areas, and the ordinary strata alternate with chemical deposits of which the best-known are the celebrated rock salt masses of Wieliczka, near Cracow. At the same time volcanic activity was rife to the south of the Carpathian mountains. Other deposits, which are partly referable to the Pliocene period, occur in Greece at Pikermi, and in India in the Siwalik hills; these are celebrated for their remarkable mammals, as are the Pliocene strata of the Western territories of North America. The occurrence of marked earth-movements since Pliocene times is indicated by the nature of the deposits of Barbadoes, where radiolarian cherts have furnished two echinids which are described by Dr Gregory as deep-sea forms. These beds were once referred to the Miocene period, but there is good reason for assigning them to a later date, and correlating them with the Pliocene beds of other areas, in which case there must have been a considerable uplift in this region since Pliocene times, a fact of great theoretical importance.
The climatic conditions of Pliocene times show steady fall of temperature. The early Pliocene beds of Britain were deposited during the prevalence of warmer temperatures than those which now exist in the same area, but during later Pliocene times, the temperature was at first similar to that now prevailing, and afterwards distinctly colder, and we find in the upper Pliocene beds the remains of organisms of a northern type. In the uppermost deposit of the Cromer 'Forest' Series, the arctic birch and arctic willow indicate the commencement of the cold which culminated in the succeeding 'Great Ice Age.'
The flora and fauna. Little need be said of the Pliocene fossils: the flora approaches that of present times, and the invertebrates are in most cases specifically identical with those now living. The vertebrates alone differ markedly from living forms, being chiefly of extinct species, and in many cases belonging to extinct genera. It is interesting to find that the mammalian fauna of Pliocene times resembles the existing fauna of the area in which the beds are found, a fact long ago observed by Darwin. Thus the European Pliocene mammals are like existing European forms, whilst in Australia the mammalian terrestrial fauna consists of Marsupials, and in South America there are Edentata of Pliocene age[108].
[108] The Pliocene fauna of Britain is described by Mr Searles V. Wood in the Monographs of the Palæontographical Society.
THE PLEISTOCENE ACCUMULATIONS.
Classification. The term Pleistocene, as used here, is approximately equivalent to the expressions 'Glacial Period' and 'Great Ice Age' of some writers; but I have adopted it in preference to these expressions, because it may eventually be possible to define the Pleistocene period in such a manner as to give the term a strictly chronological meaning, whereas the other terms indicate the existence of climatic conditions which must have ceased in some areas sooner than in others. At present, climatic change gives us the best means for separating the accumulations formed subsequently to the Pliocene period over large parts of the Eurasian land-tract, and the most convenient division of these continental accumulations is to refer them to three periods, viz.:—
The Forest Period (in which we are now living).
The Steppe Period.
The Glacial Period.