1150. Diluvial soils. This is a term generally applied to accumulations of sand and gravel which are found in various parts of the kingdom, and which appear to have been deposited by water, but which have never hardened into the consistency of rocks. Though there is generally some connexion between the diluvial soils and the rocks on which they rest, this is not always the case; for, as Morton observes, 'we find in that which rests on the new red sandstone, not only rolled fragments of that stratum, but also of most of the primitive rocks. These are principally in the shape of boulder stones or large gravel, and the sand and earthy parts are mostly from the red sandstone. This accumulation in the neighbourhood of Nottingham and Mansfield is, in many places, upwards of one hundred feet in depth.' (Morton on Soils, 4th edition, p. 10.) Diluvial soils are, generally speaking, remarkable for their poverty, but under proper management most of them may be made productive. Thus, the tenacious clayey gravel which is found in Bedfordshire and other places may be improved by the addition of chalk, or chalk and sand. The diluvium which rests on a clayey subsoil may be improved by drainage and deep ploughing; and the siliceous sands of Norfolk and Suffolk may be improved by mixing them with chalk marl. In some cases where a siliceous sand is found on a subsoil of chalk, chalk marl, or plastic clay, the surface soil, Morton observes, may be permanently improved by digging up a portion of the subsoil, and spreading it over the surface soil, though in most other cases it injures the surface soil to mix it with the subsoil.