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ELEMENTARY AGRICULTURE 
by ice and are found principally in states that are 
north of the Ohio and east of the Missouri Rivers. 
Glacial soil is one of our oldest soils and is very fertile. 
It composes the soil of the North Central states, which 
is commonly known as the great corn belt. Aeolian 
soil or wind formed soil is a fine, deep, fertile soil of 
our western prairies. The “bluff” soils along the Mis¬ 
sissippi River are also of wind formation. Colluvial 
soils are soils that are formed at the foot of hills or 
mountains. After the weathering agencies have com¬ 
pleted their work, gravity transports the material to 
the lower areas. This type of soil is very coarse in 
structure and lacking in organic matter. Colluvial 
soils are well adapted to the growing of fruits. 
Soils Classified as to Properties.—The practical 
farmer classifies soils according to the properties that 
are related to crop production. These properties are 
largely controlled by the amount of sand, clay, silt, 
and humus which enter into the composition of soils. 
If the percent of sand in a soil is greater than the 
amount of silt, clay, or humus, we have a sandy soil. 
If the percent of clay is greater we have a clay soil. 
Other kinds of soils are named in similar manner. 
Loam soil, consisting of a mixture of sand, silt, clay, 
and humus, is one of our best Agricultural soils. There 
are several classes of loam such as heavy clay loam, 
clay loam, sandy clay loam, and light sandy loam. The 
percent of sand in loam may vary from ten percent 
in heavy clay loam to ninety percent in light sandy 
loams. 
Size of Soil Particles Important.—The size of the 
soil particles governs the air circulation, heating, water 
holding power, drainage, and fertility of soils. If the 
