 Black soils, associated with subhumid climates and tall-grass native vegetation, have a black A horizon which is usually thicker than that of Brown or Dark Brown soils.Dark Gray soils are transitional between grassland Chernozemic soils and the more strongly leached soils of forested regions.These soils have eluvial horizons from which clay has been leached after snowmelt or heavy rains and illuvial horizons in which clay has been deposited; these horizons are designated Ae and Bt respectively.