Soil Survey of Murray and Whitfield Counties, Georgia

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The A horizon is a mineral surface layer. It commonly is darkened by humified
organic matter. An Ap horizon is a plow layer commonly darkened by organic matter.
The maximum extent of leaching or eluviation of clay and iron occurs in the A horizon.
If uneroded or plowed and mixed with material from lower horizons, the A horizon
commonly has a granular structure. In an E horizon, considerable leaching has
occurred and organic matter has not darkened the soil material. The E horizon, where
it occurs, commonly is the lightest colored horizon in the profile and is most likely
between the A and B horizons.
The B horizon commonly underlies the A horizon and is called the subsoil. The
maximum extent of accumulation, or illuviation, of clay, iron, aluminum, or other
compounds leached from the surface layer occurs in this horizon. The B horizon
commonly has a blocky structure. It generally is firmer and lighter colored than the A
horizon, but it is darker than the C or E horizons.
The C horizon underlies the A and B horizons. It consists of materials that are little
altered by the soil-forming processes, but it may be modified by weathering. The C
horizon generally is presumed to be the parent material in which the A and B horizons
above it have formed. Young soils, such as those that formed in recent alluvium or in
manmade deposits of fill materials, may have a C horizon that extends nearly to the
surface. In such cases, there may not be a B horizon.
The R layer is continuous, hard bedrock and generally is below the other horizons. It
is commonly the parent rock in which the overlying layer or horizon was formed.
One or more soil-forming processes are involved in the formation of soil horizons.
These processes are the accumulation of organic matter; the chemical weathering,
mainly by hydrolysis, of primary minerals into silicate clay minerals; the translocation of
silicate clay and some silt-sized particles from one horizon to another; and the
reduction and transfer of iron.
These processes have been active in the formation of most of the soils in Murray
and Whitfield Counties. The interaction of the first three processes is indicated by the
strongly expressed horizons in Fullerton and Waynesboro soils. All four processes
have probably been active in the formation of the moderately well drained Shack and
Conasauga soils.
Some organic matter has accumulated in all of the soils in the survey area. Most of
the soils contain moderate amounts of organic matter in the surface layer. The content
of organic matter ranges from low, as in Panama soils, to high, as in Cheoah soils.
Most of the soils in the survey area are acid in the upper layers, unless the surface
layer has been limed, because the bases released during the weathering of the soil
and saprolite have been leached.
The translocation of clay minerals is an important process in the development of
many soils in the survey area. As clay minerals are removed from the A horizon, they
accumulate as clay films on the faces of peds, in pores, and in root channels in the B
horizon.
As silicate clay forms from primary minerals, some iron is commonly released as
hydrated oxides. These oxides are generally red. Even if they occur in small amounts,
they give the soil material a reddish or brownish color. These colors are best
expressed in the subsoil.
The reduction and transfer of iron has occurred in all of the soils that are not
characterized by good natural drainage. This process, known as gleying, is evidenced
by a gray matrix color and by iron or clay depletions. Some of the iron may be
reoxidized and segregated and thus form yellow, brown, red, or other brightly colored
masses of iron accumulation in an essentially gray matrix in the subsoil. Nodules or
concretions of iron ore or manganese also commonly form as a result of this process.
Soil features associated with chemically reduced iron are referred to as redoximorphic
features (Vepraskas, 1992).