1146. The nomenclature of soils of this description is very simple, and is naturally taken from the earth which predominates in the soil. Thus, soil in which argillaceous matter abounds is called clayey soil; that which is formed from chalk or any kind of limestone is called calcareous; and the siliceous soils are called sandy. It is, however, necessary to use precision in applying those terms. Thus, as Sir H. Davy has observed, the term sandy soil should never be applied to any soil that does not contain at least seven-eighths of sand; sandy soils which effervesce with acids should be distinguished by the name of calcareous sandy soils, to distinguish them from those that are siliceous. The term clayey soil should not be applied to any land which contains less than one sixth of impalpable earthy matter, not considerably effervescing with acids ; the word loam should be limited to soils containing at least one third of impalpable earthy matter copiously effervescing with acids. A soil, to be considered as peaty, ought to contain at least one half of vegetable matter.