The heavy leaching of iron causes coniferous forest soils to be gray. High water tables in soils cause the reduction of iron, and these soils tend to have greenish and gray-blue hues. Organic matter colors the soil black. The combination of iron oxides and organic content gives many soil types a brown color. Other coloring materials sometimes present include white calcium carbonate, black manganese oxides, and black carbon compounds.
Most soils have a distinctive profile or sequence of horizontal layers.
Generally, these horizons result from the soil processes of eluviation and organic activity. Typical layers found in a soil profile. The O horizon is the topmost layer of most soils. It is composed mainly of plant litter at various levels of decomposition and humus . Below it is the A horizon .