 Vast areas of Gray Luvisols in the Boreal Forest Zone of the Interior Plains have thick, light grey eluvial horizons underlying the forest litter and thick Bt horizons with clay coating the surface of aggregates.This order includes all soils that have developed B horizons but do not meet the requirements of any of the orders described previously.Many Brunisolic soils have brownish B horizons without much evidence of clay accumulation, as in Luvisolic soils, or of amorphous materials, as in Podzolic soils.