(i) Geologic - The smallest, formal lithostratigraphic unit of sedimentary rocks. The designation of a bed or a unit of beds as a formally named lithostratigraphic unit generally should be limited to certain distinctive beds whose recognition is particularly useful. Coal beds, oil sands, and other layers of economic importance commonly are named, but such units and their names usually are not a part of formal stratigraphic nomenclature. (ii) Agronomic - A raised (usually) cultivated area between furrows or wheel tracks of tractors specially prepared, managed and/or irrigated to promote the production of a planted crop.