MOULD, in agriculture, a general name for the soft earthy substance with which the dry land is generally covered, and in which all kinds of vegetables take root and grow. It is, however, far from being an homogeneous substance; being compounded of decayed animal and vegetable matters, calcareous, argillaceous, and siliceous earths, all mixed together in various proportions, and with the different degrees of moisture, constituting all the varieties of soil throughout the world. All kinds of mould contain some inflammable substance, which remains in them from the decayed animals and vegetables; and they are more or less black in proportion to the quantity of phlogiston they contain. The black mould yields by distillation a volatile alkali and oil.