Commonly, running water gathers into streams and corrades channels; exceptionally, running water spreads into sheets of limited or unlimited width, and, by a combination of erosion and deposition, produces plains.
Pure water flowing over a smooth indestructible surface does not move as a uniform film : if the surface is broad the sheet differentiates into parallel streams of greater depth and relatively rapid flow, separated by shallower bands of relatively sluggish flow; and at the same time both streams and intervening bands differentiate into series of transverse waves which move forward more rapidly than the body of the differentiated sheet. The tendency of flowing water to divide into streams is well known; it is undoubtedly by reason of this tendency that running waters commonly flow in streams which cut channels and eventually fashion most of the lands of the earth. The tendency of flowing water to break up into . . .