Rivers

Rivers are large streams of water flowing over a portion of the earth's surface and discharging themselves into the sea, a lake, or other rivers. They generally ha.ve their source in springs, or from the melting of snow and ice on the summits of the highest mountains. The most rapid movement is at the surface, friction retarding the lower current. A velocity of 3 inches a second at the bottom of a river is sufficient to tear up fine clay, 6 inches a second moves fine sand, 12 inches a second fine gravel, and 3 feet a second stones as large as an egg. When a river is in flood its transporting power is very great. The material carried by it is deposited in the estuary at its mouth, and tends to form a delta (q.v.).