Abstract: Rivers are both the means and the routes by which the products of continental weathering are carried to the oceans of the world. Except in the most arid areas, more water falls as precipitation than is lost by evaporation and transpiration from the land surface to the atmosphere. Thus there is an excess of water, which must flow to the ocean. Rivers, then are the routes by which this excess water flows to the ultimate base level. Originally published: American scientist ; v. 50, no. 4 (December 1962).