Eocene System, the lowest subdivision of the Tertiary group of sedimentary rocks, so named by Lyell (from the Greek cos, dawn; kainbs, recent), because the mollusks in these rocks present the first specific approximation to those of recent times.
From the Mediterranean basin to what are now the Pyrenees, Alps, Carpathians, and Caucasus, through Syria, Northern India, China, and Japan, open-sea conditions continued after the close of the Cretaceous (q.v.) epoch, and a massive limestone crowded with the characteristic foraminifer Nummulites (q.v.) was laid down. In Northern Europe the bed of the Chalk sea was raised so as to form several more or less distinct areas of deposit, and the outpourings of the great basalts of Auvergne, the Eifel, Antrim, Mull, Skye, and Iceland probably began. In Britain Eocene rocks are confined to the two centroclinal basins in the
Chalk, known as the London and Hampshire Basins. Paris is situated on a similar basin. Both the plants and the animals they contain point to "a climate almost tropical. Palms, nautili, cone, volute and olive shells, turtles, crocodiles, and sea snakes indicate this. Besides sharks and a few birds, Eocene beds have yielded a variety of mammalian remains, especially interesting from their generalised character, combining, as they do, features of various groups now distinct. Such are the Tillodontia (q.v.) and Eoltippus, the small ancestor of the horse, from the western United States, the tapir-like Paleeotheriuin of Europe and the lemuroid Canopithecns. The British Eocenes may be divided as follows: - Hampshire. London Basin.
Upper - Barton Clay. Upper Bagshot Sands.
Middle - Brac-lclesham, Bourne- Middle Beegshot Sands.
inontli, and Alum Bay Lower Bagsliot Sands.
Lower - Bognor Clay. London Sands.
Woolwich and Reading Woolwich and Reading Clay. Clay.
Thauet Sands. The lignites associated with pipe-clay in an old lake-basin at Bovey Tracey in Devonshire, and some at least of those between the great basalt sheets, 900 feet thick in Antrim, 3,000 feet thick in Mull, and extending into Greenland, are assigned to this period. [Bagshot Sands, London Clay, Thanet Sands.]