Ap - 0-18 cm below surface; Silty Clay Loam; 10YR 2/1; weak fine granular (units are approximately spherical or polyhedral and are bounded by curved or very irregular faces) structure; clear smooth boundary.
A - 19-35 cm below surface; Silty Clay Loam; 10YR 2/1; few fine prominent (contrast strongly) 5Y 5/2 mottles; moderate fine subangular blocky (faces are a mixture of rounded and plane faces and the corners are mostly rounded) structures; clear smooth boundary.
B1 - 36-48 cm below surface; Silty Clay Loam; 10YR 5/6; few (less than 2 percent) fine (smaller than 5 mm) distinct (contrast only moderately) 2.5 Y 6/4 mottles; weak medium subangular blocky (faces are a mixture of rounded and plane faces and the corners are mostly rounded) structures; few fine (< 2 mm) stains and concretions of iron and manganese oxide; gradual (5 to 15 cm thick) boundary.
B2 - 48-71 cm below surface; Silty Clay Loam; 10YR 6/6; moderate (units are well formed and evident in undisturbed soil) fine prismatic (individual units are bounded by flat to rounded vertical faces and are distinctly longer vertically) structure; many medium (2 - 5 mm) stains and concretions of iron and manganese oxide; gradual (5 to 15 cm thick) smooth boundary.
FF - Feature Fill; Silty Clay Loam; 10YR 4/1; few distinct mottles 10 YR 6/8; charcoal, ash, and burned earth.
S - Feature Fill of slumped/redeposited subsoil; Silty Clay Loam; many medium to coarse, distinct to prominent mottles.
Additional operational definitions:
1. Mottling:
Quantity is indicated by three areal percentage classes of the observed surface: Size: Contrast refers to the degree of visual distinction that is evident between associated colors: 2. Excavation difficulty classes:
Low: Can be excavated with a spade using arm- applied pressure only. Neither application of impact energy nor application of pressure with the foot to a spade is necessary. Linguist conventions of soil as defined in:
Natural Resources Conservation Service. USDA NRCS [Stelle: Soils of the farm are identified in the Soil Survey of McLean County, Illinois as Drummer on the fort proper and Plano Silt Loam, 2 -5% slopes, around TU4. Frankly this doesn't make sense to me, having Plano below Drummer.]
--few: less than 2 percent,
--common: 2 to 20 percent, and
--many: more than 20 percent.
--fine: smaller than 5 mm,
--medium: 5 to 15 mm, and
--coarse: larger than 155 mm.
--Faint: Evident only on close examination.
--Distinct: Readily seen but contrast only moderately with the color to which they are compared.
--Prominent: Contrast strongly with the color to which they are compared.
Moderate: Arm-applied pressure to a spade is insufficient. Excavation can be accomplished quite easily by application of impact energy with a spade or by foot pressure on a spade.
High: Excavation with a spade can be accomplished, but with difficulty. Excavation is easily possible with a full length pick using an over-the-head swing.
Soil Survey Manual. Chapter Three.
http://soils.usda.gov/technical/manual/print_version/chapter3.html#39
1998 Soil Survey of McLean County, Illinois. Illinois Agricultural Experiment Station Soil Report 159.