Cataract, in hydrography, is occasioned by a precipice in the channel of a river, caused by rocks or other obstacles stopping the course of the stream, from whence the water falls with great noise and rapidity. Such are the cataracts of the Nile, the Danube, the Rhine, etc. In that of Niagara, the perpendicular fall of the water is 137 feet, and in that of Pistell Rhaiadr, in North Wales, the fall of water is nearly 240 feet from the mountain to the lower pool.