Niagara, a section of the St. Lawrence River, in N. America, extending between Lakes Erie and Ontario, having a descent throughout its course of 36 m. of 326 ft., the Falls, preceded and succeeded by rapids, being the largest in the world, the Canadian or Horse Shoe Fall being 2640 ft. wide, with a descent of 158 ft., and the American Fall being one-third of the width of the Canadian, and with a descent of over 162 ft.