Delta

Delta, so named from the resemblance in form of that of the Nile to the triangular Greek capital letter D, A, is a tract of flat land of alluvial origin, formed by the advance of the fan-like cones of sediment carried down by a river into a lake or the sea. These accumulations cause the stream to subdivide repeatedly, so that the triangular plain with its apex pointing up-stream is traversed by innumerable tortuous water-channels. These are constantly silting up, while new ones are cut through the soft earth. The delta of the Nile is the whole of Lower Egypt below Cairo; that of the Rhine includes all Holland: the Rhone has two deltas, one at the head of the Lake of Geneva and the other below Avignon: the delta of the Tiber advances 10 feet annually; and that of the Mississippi, covering 40,000 square miles, gains 86 yards a year.