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.

Clay.—­The finest of rock particles, 1/5000 to 1/250000 of an inch in diameter, too small to imagine.  Clay when wet is very soft, slippery and very sticky.  Yellow ochre and whiting from the paint shop are good illustrations of clay.

Humus, or decaying vegetable and animal matter.  This is dark brown or almost black in color—­decaying leaves and woods soil are examples.

Soils composed of the above materials: 

Sands or Sandy Soils.—­These soils are mixtures of the different grades of sand and small amounts of silt, clay and organic matter.  They are light, loose and easy to work.  They produce early crops, and are particularly adapted to early truck, fruit and bright tobacco, but are too light for general farm crops.  To this class belongs the so-called Norfolk Sand.  This is a coarse to medium, yellow or brown sand averaging about five-sixths sand and one-sixth silt and clay and is a typical early truck soil found all along the eastern coast of the United States.

“It is a mealy, porous, warm sand, well drained and easily cultivated.  In regions where trucking forms an important part of agriculture, this soil is sought out as best adapted to the production of watermelons, canteloupes, sweet potatoes, early Irish potatoes, strawberries, early tomatoes, early peas, peppers, egg plant, rhubarb and even cabbage and cauliflower, though the latter crops produce better yields on a heavier soil.”

A very similar sand in the central part of the country is called Miami Sand and, on the Pacific Coast, Fresno Sand.  These names are given to these type soils by the Bureau of Soils of the United States Department of Agriculture.