CLASSIFICATION OF SOILS

Soil materials and soils are classified as follows:

_Stones._--Coarse, irregular or rounded rock fragments or pieces of
rock.

_Gravel._--Coarse fragments and pebbles ranging in size from several
inches in diameter down to 1/25 inch.

_Sand._--Soil particles ranging from 1/25 of an inch down to 1/500 of
an inch in diameter. Sand is divided into several grades or sizes.

Coarse sand 1/25 to 1/50 of an inch.
Medium sand 1/50 to 1/100 of an inch.
Fine sand 1/100 to 1/250 of an inch.
Very fine sand 1/250 to 1/500 of an inch.

These grades of sand correspond very nearly with the grains of
granulated and soft sugar and fine table salt.

_Silt._--Fine soil particles ranging from 1/500 to 1/5000 of an inch
in diameter. It feels very fine and smooth when rubbed between the
fingers, especially when moist. A good illustration of silt is the
silicon used for cleaning knives, a small amount of which can be
obtained at most any grocery store. By rubbing some of this between
the fingers, both dry and wet, one can get a fair idea of how a silty
soil should feel. Silt when wet is sticky like clay.