SOIL SURVEY

-179-Organic - An order of soils that have developed dominantly from organic deposits .The majority are saturated for most of the year unless artificially drained .Organic matter, soil - The organic fraction of the soil : includes plant and anima lresidues at various stages of decomposition, cells and tissues of soil organism sand substances synthesized by the soil population . It is usually determine don soils that have been sieved through a 2 mm sieve .Orthic - A term used in soil classification to denote the Subgroup that typifies th ecentral concept of the Great Group .Outwash - Sediments "washed out" by flowing water beyond the glacier and lai ddown in beds as stratified drift . Particle size may range from boulders t osilt .Outcrop - That part of a geologic formation or structure that appears at the surfac eof the earth .Paleosol (fossil soil) - A soil of the geologic past that was buried subsequent to it sformation .Parent material - The unconsolidated and more or less chemically weathered minera lor organic matter from which the solum of a soil is developed by pedogenicprocesses .Particles size analyses - The determination of the various amounts of the differen tseparates in a soil sample, usually by sedimentation, sieving, micrometryor combinations of these methods .Peat - Unconsolidated soil material consisting largely of undecomposed, or onl yslightly decomposed, organic matter .Ped, soil - A unit of soil structure such as a prism, block, or granule, formed b ynatural processes (in contrast to a clod, which is formed artificially) .Pedology - Those aspects of soil science dealing with the origin, morphology ,genesis, mapping and taxonomy of soils, and classification in terms o ftheir use .Pedon - The smallest volume of soil which we should describe and sample to represen tthe nature and arrangement of its horizons and variability in the other propertie sthat are preserved in samples . A pedon is comparable in some ways to the unitcell of a crystal (Soil Survey Staff, 1975) :Percolation, soil water - The downward movement of water through soil ; specificallythe downward flow of water in saturated or nearly saturated soil at hydrauli cgradients of 1 .0 or less .