/ London clay. Wanting. | | Woolwich and \ / Argile Plastique. | Reading beds, or > \ Glauconie Inférieure. Lower Eocene. < Plastic clay. / | | Oldhaven beds. | \ Thanet sands. Sables Inférieurs. The Woolwich and Reading Beds, or the Plastic Clay of older writers, consists of extensive beds of sand with occasional beds of potter’s clay, which lie at the base of the Tertiary formation in both England and France. Generally variegated, sometimes grey or white, it is employed as a potter’s earth in the manufacture of delf-ware. In England the red-mottled clay of the Woolwich and Reading Beds in Hampshire and the Isle of Wight is often seen in contact with the chalk; but in the south-eastern part of the London basin, Mr. Prestwich shows that the Thanet Sand (consisting of a base of fine, light-coloured sand, mixed with more or less argillaceous matter) intervenes between the Chalk and the Oldhaven Beds, or in their absence the Woolwich and Reading beds, which lie below the London Clay. The Thanet Sands derive their name from their occurrence in the Isle of Thanet, in Kent, in the eastern part of which county they attain their greatest development. Under London and its southern suburbs the Thanet sand is from thirteen to forty-four feet thick, but it becomes thinner in a westerly direction, and does not occur beyond Ealing.[85] [85] “Memoir of the Geological Survey of Great Britain. The Geology of Middlesex, &c.;” by W. Whitaker, p. 9. The Woolwich and Reading beds in the Hampshire basin rest immediately on the Chalk, and separate it from the overlying London Clay, as may be seen in the fine exposure of the Tertiary strata in Alum Bay, at the western extremity of the Isle of Wight, and in Studland Bay, on the western side of the Isle of Purbeck, in Dorsetshire. In the London basin the Woolwich and Reading beds also rest on the Chalk, where the Thanet Sands are absent, as is the case, for the most part, over the area west of Ealing and Leatherhead. The beds in question are very variable in character, but may be generally described as irregular alternations of clays and sands--the former mostly red, mottled with white, and from their plastic nature suitable for the purposes of the potter; the latter also of various colours, but sometimes pure white, and sometimes containing pebbles of flint. The Woolwich and Reading beds are called after the localities of the same names; they are fifty feet thick at Woolwich, and from sixty to seventy feet at Reading.