Miocene System (Gr., 'less recent'). The name was applied by Lyell to that division of the Tertiary strata which contains a smaller proportion of recent species of Mollusca than the Pliocene System (q.v.), and a larger proportion than the Eocene. Of late years the lower part of the Miocene has been separated from that system, and now ranks as a separate system (see OLIGOCENE). No true Miocene deposits occur in Britain. Marine accumulations of this age are sparingly developed in Belgium (Black Crag), and cover considerable areas in the low grounds of Touraine (Faluns de la Touraine) in the west of France. In the Rhine valley Miocene beds extend from the Taunus southwards (Mainz Basin). These beds are chiefly of fresh-water origin—the lower portion being marine. A more important Miocene area is met with in the Vienna Basin. Here the lower series of beds is marine, while the overlying strata are less distinctly so, many of the fossils indicating brackish-water conditions. Another interesting development of Miocene occurs in Switzerland and South Bavaria—the beds being partly marine and partly of fresh-water origin. These are the more important European areas. In North America marine Miocene strata occur sparingly on the Atlantic borders of the eastern states; while fresh-water deposits of the same age are widely spread in the western states and territories. Miocene beds have been met with far within the Arctic Circle, in Greenland and Spitzbergen.
Life of the Period.—The flora of the earlier stages of the Miocene of central Europe is indicative of somewhat tropical conditions, the nearest representatives of many of the more characteristic plants being now confined to India and Australia. Palms seem at that time to have flourished over a large part of Europe, and with these were associated conifers (Sequoia, Libocedrus), evergreen oak, fig, laurel, cinnamon, various proteaceous plants (Banksia, Dryandra), olive, magnolia, maple, myrtle, mimosa, acacia, &c. Later on the climate became more temperate, for we meet with species of birch, alder, oak, beech, chestnut, plum, willow, poplar, &c. Among the more notable terrestrial animals of the Miocene were Dinotherium, Mastodon, Anchitherium, Hyotherium, species of rhinoceros, tapir, fox; a gigantic form of ant-eater (Macrotherium); Helladotherium, allied to the giraffe; Machairodus, a lion-like, sabre-toothed carnivore; various antelopes and deer with small horns and antlers; opossums, apes, and monkeys. The molluscs of the marine Miocene are all modern types—those of the older strata having a tropical or subtropical facies, while the shells in the younger strata seem, like the plants, to indicate milder climatic conditions.
In Miocene times the British area was probably dry land, and the same appears to have been the case with all northern Europe. The sea, however, overflowed the low grounds of Belgium and extended into north-west Germany. It is not unlikely, indeed, that most of the Low Countries, Hanover, and Sleswick-Holstein, were at that time submerged. In like manner the sea covered wide areas in the north-west and west of France, extending into the heart of the country now drained by the Loire and its affluents the Cher and the Indre, and stretching across the old district of Aquitania to the Mediterranean. Spain and Portugal then formed an island, considerable tracts in the south and east of Spain being submerged. From the Gulf of Lions a long arm of the sea passed up the valley of the Rhone, and swept north-east through northern Switzerland, sending a branch into the Mainz basin, and then traversing Bavaria, across which it continued to the wide sea which then occupied all the great plains of Hungary. Northern and eastern Italy were at the same time under water, as was also the case with many parts of eastern Europe and Asia Minor. Southern Europe was thus in the Miocene period an extensive archipelago, in which the plateaus of Spain and central France, the Alps, the Carpathians, &c. existed as islands. The most continuous land-mass was in the north of Europe: and if the Miocene of the Arctic regions, with its abundant flora, be of the same age as the Miocene of Europe, then we may infer that a vast area of the North Atlantic existed on dry land, across which migrations of the flora took place. Considerable movements of elevation seem to have occurred in Europe before the close of Miocene times, causing the sea to disappear from wide regions which it had formerly occupied. Thus, the Mainz basin and the sea that occupied much of northern Switzerland, &c. were replaced by fresh-water lakes, while the wide sea of the Vienna basin was much reduced in size, and eventually became freshened—the conditions resembling those that characterise the Black Sea.