peat, soil material consisting of partially decomposed organic matter; found in swamps and bogs in various parts of the temperate zone. It is formed by the slow decay of successive layers of aquatic and semiaquatic plants, e.g., sedges, reeds, rushes, and mosses. One of the principal types of peat is moss peat, derived primarily from sphagnum moss; it is used in agriculture as poultry and stable litters as well as a mulch, a soil conditioner, and an acidifying agent; it is also used in industry as an insulating material. Another type of peat is fuel peat, which is most widely used in regions where coal and wood are scarce, e.g., Ireland, Scandinavia, and parts of Russia. Peat is the earliest stage of transition from compressed plant growth to the formation of coal. Large deposits of peat in the United States are found in Michigan, California, and the Florida Everglades.