I. EOCENE OF BRITAIN. (1.) LOWER EOCENE.--The base of the Eocene series in Britain is constituted by about 90 feet of light-coloured, sometimes argillaceous sands (_Thanet Sands_), which are of marine origin. Above these, or forming the base of the formation where these are wanting, come mottled clays and sands with lignite (_Woolwich and Reading series_), which are estuarine or fluvio-marine in origin. The highest member of the Lower Eocene of Britain is the "London Clay," consisting of a great mass of dark-brown or blue clay, sometimes with sandy beds, or with layers of "septaria," the whole attaining a thickness of from 200 to as much as 500 feet. The London Clay is a purely marine deposit, containing many marine fossils, with the remains of terrestrial animals and plants; all of which indicate a high temperature of the sea and tropical or sub-tropical conditions of the land. (2.) MIDDLE EOCENE.--The inferior portion of the Middle Eocene of Britain consists of marine beds, chiefly consisting of sand, clays, and gravels, and attaining a very considerable thickness (_Bag-shot and Bracklesham beds_). The superior portion of the Middle Eocene of Britain, on the other hand, consists of deposits which are almost exclusively fresh-water or brackish-water in origin (_Headon and Osborne series_). The chief Continental formations of Middle Eocene age are the "Calcaire grossier" of the Paris basin, and the "Nummulitic Limestone" of the Alps. (3.) UPPER EOCENE.--If the Headon and Osborne beds of the Isle of Wight be placed in the Middle Eocene, the only British representatives of the Upper Eocene are the _Bembridge beds_. These strata consist of limestones, clays, and marls, which have for the most part been deposited in fresh or brackish water. II. EOCENE BEDS OF THE PARIS BASIN.--The Eocene strata are very well developed in the neighbourhood of Paris, where they occupy a large area or basin scooped out of the Chalk. The beds of this area are partly marine, partly freshwater in origin; and the following table (after Sir Charles Lyell) shows their subdivisions and their parallelism with the English series:-- GENERAL TABLE OF FRENCH EOCENE STRATA. UPPER EOCENE. _French Subdivisions._ _English Equivalents._ A. 1. Gypseous series of Mont 1. Bembridge series. Montmartre. A. 2. Calcaire silicieux, or 2. Osborne and Headon series. Travertin Inférieur. A. 3. Grès de Beauchamp, or 3. White sand and clay of Sables Moyens. Barton Cliff, Hants. MIDDLE EOCENE. B. 1. Calcaire Grossier. 1. Bagshot and Bracklesham beds. B. 2. Soissonnais Sands, or 2. Wanting. Lits Coquilliers. LOWER EOCENE.