Clay is the smallest particle that makes up soil. Clay tends to hold a lot of moisture. Clay can be very expansive when wet. There are parts of Texas where clay can expand a foot or more between the wet and dry season. Next comes silt, silt is a sedimentary material consisting of very fine particles of rock.
Most silt comes from the process of erosion of the top layer of earth.
Erosion is the general term given to the process by which the surface of the earth is constantly worn away by wind and water. Clay and silt are called cohesive types of soils. Cohesive means that the particles tend to stick togother. Sand is the slightly bigger than silt. Sand is rock material occurring in the form of loose, round or angular grains, varying in size from 0.06 to 2mm in diameter.