The soil to the east and north-west is principally a thick substratum of chalk, covered with a thin layer of earth. The subsoil of the centre is marl and shingle; and to the westward there are large beds of clay of very irregular character. Dr. Mantell, in his valuable work, “The Geology of the South-east of England,” says:—“The town of Brighton is situated on an immense accumulation of water-worn materials, which fills up a valley, or hollow, in the chalk. The diluvial deposit is bounded on the north-west by the South Downs; on the east it extends to Rottingdean, and is there terminated by the chalk; on the west it may be traced more or less distinctly to Bignor; on the south it is washed by the sea, and forms a line of cliffs from 70 to 80 feet high; these exhibit a vertical section of the strata, and enable us to ascertain their nature and position.” “The soil of the Downs,” says Young in his Agricultural Survey of Sussex, “is subject to considerable variation. On the summit it is usually very shallow, the substratum is chalk, and over that a layer of chalk rubble, and partially rolled chalk flints, with a slight covering of vegetable mould. Along the more elevated ridges there is sometimes merely a covering of flints, upon which the turf grows spontaneously. Advancing down the hills, the soil becomes deeper, and at the bottom is constantly found to be of very sufficient depth for ploughing: here the loam is excellent, generally ten or twelve inches thick, and the chalk rather broken, and mixed with loam in the interstices.”