These soils are formed by the sediments brought down by rivers. The rivers deposit very fine particles of soil called alluvium in their plains during the course of their long journey. It is a mixture of sand, clay and silt, called loam. These have been deposited by three important river systems-the Indus, the Ganga, and the Brahmaputra. These soils occupy 40 percent of the land area. The entire Northern Plians are made up of these soils.