Earths are derived from rocks

1137. Earths are derived from the rocks which are exposed at the surface of the globe, and soils are earths mixed with more or less of the decomposed organised matter afforded by dead plants and animals. Earths and soils, therefore, must be as various as the rocks which produce them; and hence to understand their nature and formation it is necessary to begin by considering the geological structure of their territorial surface, and the manner in which earths and soils are produced. We shall next consider in succession the Nomenclature, Quality, Use, and Improvement of Soils.