Loess << LOH ihs or lehs >> is a kind of silt that forms a fertile topsoil in some parts of the world. Loess consists of tiny mineral particles brought by wind to the places where they now lie. These mineral particles are finer than sand but coarser than clay. Topsoils that are made up of loess are found in the central and northwestern parts of the United States, in central and eastern Europe, in central Asia and east-central China, and in Argentina.
Two great sources have provided most of the world’s loess. One source is the area that once bordered the great ice sheets of the Pleistocene Epoch, a time marked by a succession of ice ages (see Ice age). These lands were dry and barren, so winds easily blew the soil to the grasslands farther south. The other source of loess is the great deserts of central Asia. These deserts furnished the loess now in eastern China.
