8 BULLETIN 1311, IT. S. DEPARTMENT OP AGRICULTURE 
hydrous aluminum silicate, free silicic acid and free hydrated oxides 
of iron and aluminum. A few investigators would include a con- 
siderable proportion of quartz and unaltered minerals. 
Other investigators, following Van Bemmelen, considered that the 
main constituent of the finest fractions of soil was not a definite 
chemical compound, but that the silica, alumina, iron oxide, and 
water were present as an indefinite absorption compound, the con- 
stituents of which were held together more feebly than the constitu- 
ents of definite chemical compounds. 
SOILS SELECTED FOR A STUDY OF THE COLLOIDAL MATERIAL 
FIELD DESCRIPTION 
The soils from which the colloids were separated were selected to 
represent the more important soil types, with some range in texture 
and with as even a distribution regarding geographical location and 
varying conditions of soil formation as a comparatively limited 
number of samples would permit. Special soil formations, such as 
peats, mucks, and laterites, were not selected for these studies. 
Thanks are due to J. E. Lapham, W. E. Hearn, W. E. McLendon, 
AY. E. Tharp, M. H. Lapham, W. T. Carter, and J. M. Snyder for 
the collection and description of the soil samples. 
1. Carrington loam. Depth, to 12 inches ; l 1 /' miles . east and north of 
Farmer, Black Hawk County, Iowa ; color, hlack when wet ; texture, fine 
grained, friable, loam, plastic when wet and characteristically gummy. Under 
cultivation the soil works up to a good state of tilth and does not readily form 
clods unless worked when wet. No stones or gravel. Topography gently roll- 
ing; drainage conditions only fair. 
2. Carrington loam. Depth, 15 to 36 inches. Subsoil of No. 1. This sample 
is dull brownish gray in color, in texture more sandy than the surface soil. 
3. Cecil clay loam. Depth, to 7 inches. Two miles northwest of Bethesda, 
Montgomery County, Md. A red clay loam. Small amount of stones and gravel 
present. Clods badly if worked when wet. Topography rolling and drainage 
good. 
4. Cecil clay loam. Depth, to 9 inches ; 2% miles northeast of Washington 
on old Danbury Road, Wilkes County, Ga. A dark-red clay loam having a 
surface horizon of 2 to 3 inches more sandy in texture and more friable. This 
soil is plastic when wet and clods easily. No mottling noticed. Topography 
rolling and surface drainage excellent. 
5. Cecil clay loam. Depth 9 to 36 inches. Subsoil of No. 4; a dark-red 
sticky clay loam. 
6. Chester loam. Depth, to 7 inches; three-fourths mile south of West 
Falls Church, Fairfax County, Va. Yellowish friable loam ; plastic when wet, 
though it does not easily clod; no pebbles, but occasional small stones of 
angular quartz and schist. Topography rolling and surface drainage good. 
7. Chester loam. Depth, to 8 inches ; one-fourth mile northwest of Glen- 
mont, Montgomery County. Md. Light-brown to grayish-yellow loam with a 
relatively high content of silt ; friable, mellow soil which seldom clods. Topog- 
raphy gently rolling and drainage good. 
8. Chester Loam. Depth, 8 to 32 inches. Subsoil of No. 7. This is a yellow- 
ish-brown, firm, compact but brittle clay. 
9. Clarksville silt loam. Depth, to 10 inches; IV2 miles northeast of Pee 
Dee, Christian County, Ky. A light-brown to grayish-brown, smooth, velvety 
silt loam, without large grains of sand, gravel, or stones. A few limestone 
sink holes noticed. Topography moderately rolling, with good surface drainage. 
10. Clarksville silt loam. Depth 10 to 36 inches. Subsoil of No. 9. Grayish 
to reddish-yellow loam grading into a yellowish-red heavy silty clay loam at 
lower depths. Slightly mottled with gray in the lower 6 to 8 inches. 
11. Crowley silt loam. Depth to 15 inches. Crowley, Acadia Parish, La. 
Grayish brown to ashy gray. Topography flat and drainage poor. It has a 
very retentive subsoil. 
