SOIL SURVEY

-170-GLOSSARY'AASHO classification - The official classification of soil materials and soi laggregate mixtures for highway construction used by the American Associationof State Highway Transportation officials .Accretion - The gradual addition of new land to old by the deposition of sediment scarried by a stream .Adsorption complex - The group of substances in the soil capable of adsorbin gwater and ions (nutrients) .Aeolian (eolian) - Material accumulated through wind action; includes bot hloess and dune sand .Aggregate - A group of soil particles cohering in such a way that they behav emechanically as a unit .Alluvial deposit - Material deposited by running water .Alluvium - A general term for all deposits of modern rivers and streams .Alpine - Areas characterized by polar climates, represented vegetationally byareas that occur above the upper elevational limit of trees, roughly abov e2100 to 2150 m a . s . l .Atterberg limits - See plastic limit, liquid limit .Available soil moisture - The portion of water in a soil that can be readily absorbedby plant roots; generally considered to be that water held in the soil agains ta pressure of up to approximately 15 bars .Base saturation percentage - The extent to which the adsorption complex of asoil is saturated with exchangeable cations other than hydrogen and aluminum .It is expressed as a percentage of the total cation exchange capacity .Bearing capacity - The average load per unit area that is required to rupture asupporting soil mass .Bedrock - The solid rock that underlies soil and the regolith or that is exposed a tthe surface .Blanket - Herein used as a term to describe a mantle of unconsolidated material sthick enough to mask minor irregularities in the underlying unit but whic hstill conforms to the general underlying topography .1 This material is abstracted from several sources and the definition given here i sthe one that corresponds to usage in this report (Agriculture Canada 1976, CSS C1976, Gary, McAfee and Wolf 1972, Hutchinson, 1976) .