A name commonly assigned to a class of solid substances composing, in various states of combination, the crust of the globe; the general qualities of which are, that they are incombustible, not convertible into metals by the ordinary methods of reduction, and their specific gravity not exceeding five times that of water. The number of these substances is ten; viz. barytes, strontites, lime, magnesia, alumina, or clay, silica, glucina, zerconia, yttria, and thorina. But although these substances are generally termed earths, the experiments of Sir H. Davy have shown that a portion of them, viz., barytes, strontites, and lime, as well as the alkalies, potash and soda, are, in reality, combinations of metallic bases with oxygen and lead, and determine, by most probable analogies, that the whole of them belong to the metallic class.