Fig. 181: Chama squamosa. Barton Series (_Sands and Clays_), A.4 Table—Both in the Isle of Wight, and in Hordwell Cliff, Hants, the Headon beds, above-mentioned, rest on white sands usually devoid of fossils, and used in the Isle of Wight for making glass. In one of these sands Dr. Wright found _ Chama squamosa,_ a Barton Clay shell, in great plenty, and certain impressions of marine shells have been found in sands supposed to be of the same age in Whitecliff Bay. These sands have been called Upper Bagshot in the maps of our Government Survey, but this identification of a fossiliferous series in the Isle of Wight with an unfossiliferous formation in the London Basin can scarcely be depended upon. The Barton Clay, which immediately underlies these sands, is seen vertical in Alum Bay, Isle of Wight, and nearly horizontal in the cliffs of the mainland near Lymington. This clay, together with the Bracklesham beds, presently to be described, has been termed Middle Bagshot by the Survey. In Barton Cliff, where it attains a thickness of about 300 feet, it is rich in marine fossils. It was formerly confounded with the London Clay, an older Eocene deposit of very similar mineral character, to be mentioned (p. 263), which contains many shells in common, but not more than one-fourth of the whole. In other words, there are known at present 247 species in the London Clay and 321 in that of Barton, and only 70 common to the two formations. Fifty-six of these have been found in the intermediate Bracklesham beds, and the reappearance of the other 14 may imply a return of similar conditions, whether of temperature or depth or of a muddy argillaceous bottom, common to the two periods of the London and Barton Clays. According to M. Hebert, the most characteristic Barton Clay fossils correspond to those of the Gres de Beauchamp, or Sables Moyens, of the Paris Basin, but it also contains many common to the older Calcaire Grossier. SHELLS OF THE BARTON CLAY. Certain foraminifera called Nummulites begin, when we study the Tertiary formations in a descending order, to make their first appearance in these beds. A small species called _ Nummulites variolaria,_ Fig. 190, is found both on the Hampshire coast and in beds of the same age in Whitecliff Bay, in the Isle of Wight. Several marine shells, such as _Corbula pisum_ (Fig. 158), are common to the Barton beds and the Hempstead or Lower Miocene series, and a still greater number, as before stated, are common to the Headon series. Fig. 182: Mitra scabra, Fig. 183: Voluta ambigua, Fig. 184: Typhis pungens, Fig. 185: Voluta athleta, Fig. 186: Terebellum fusiforme, Fig. 187: Terebellum sopita, Fig. 188: Cardita sulcata, Fig. 189: Crassatella sulcata, Fig. 190: Nummulites variolaria. MIDDLE EOCENE, ENGLAND.