WATERFALL is a break in the continuity of slope of the channel of a river or stream, so abrupt that the body of water falls from the higher to the lower level. Waterfalls occur most frequently in mountainous countries, where the streams from the mountain sides enter the valleys. It is only when the side of the valley is composed of hard rock that there can be a waterfall; in friable strata the stream wears out a ravine or side-valley. These mountain waterfalls, however, are generally rather curious and picturesque than grand, the volume of water being in most cases comparatively insignificant, though the height of fall is occasionally very great. All mountain waterfalls necessarily change their aspect from season to season—in winter, a roaring torrent plunging headlong into the abyss; in summer,' often a mere film of water trickling down the face of the preci pice. Waterfalls in comparatively level districts are not nearly so common, and their height of fall is 'insignificant compared with that of mountain cataracts; but the much greater volume of water, its steady and even flow to the head of the precipice over which, in solid column, it descends with a thundering plunge, place such waterfalls among the grandest of nature's phenomena. It is where the course of a large river passes from a higher to a lower plateau, and where the upper plateau is edged with rock, that the grander cataracts are formed. If the rocks are of the same hardness from top
to bottom, the edge of the escarpment, supposing it to be perpendicular at first, becomes worn off, and a slope or rapid is formed. But when the upper edge is hard and the under strata soft and friable, the reverberation of the spray wears away the softer parts below, leaving a projecting ledge at the top, which breaks off, piece by piece, as it becomes too much undermined, so that the fall is constantly receding. The question of, the rate of regression of waterfalls has not hitherto occupied much attention, and has only been estimated in the case of Niagara, Bakewell giving its annual value at one yard, while Lyell limits it to about a third of this. Some of the most remarkable water falls of the world are the Yosemite, California, in a valley of the same name; a fall 2,530 ft. in entire height, but broken into three leaps; the Orco falls at Monte Rosa, 2.400 ft.; Gavarnie (Pyrenees), 1400 ft.; Staubbach (Switzerland), 1000 ft.; Maanelvan (Norway), 940 ft.; Niagara (q.v.); Zambezi (q.v.); Missouri; the great Kaietur fall in British Deme rara, over 700 ft. The cataracts of the Velino and Anio, in Italy, are beautiful artificial imitations.