Orino'co, one of the great rivers of South America, has its origin on the slopes of the Sierra Parima, in the extreme south-east of Venezuela. Flowing at first W. by N., a mountain-stream, it divides, a little below Esmeralda (65° 50' W. long.), and sends off to the south an arm, the Cassiquiare, 180 miles to the Rio Negro, a tributary of the Amazon. The other branch on reaching San Fernando (68° 10' long, and 4° 2' N. lat.) is met by the strong current of the Guaviare; the united stream then turns due north, and, after passing over the magnificent cataracts of Maypures and Atures, and picking up the Meta and the Apure, turns east and traverses the llanos of Venezuela, its waters being here 4 miles broad. About 120 miles from the Atlantic, into which it rolls its milk-white flood, its delta (8500 sq. m.) begins. Of the numerous mouths seven are navigable. The waterway principally used by ocean-going vessels, which penetrate 240 miles up to Ciudad Bolivar (Angostura), is the Boca de Navios, 3 3/4 to 23 miles wide. The total length of the river is some 1550 miles, of which 900, up to the cataracts of Atures, are navigable, besides a farther stretch of 500 miles above the cataracts of Maypures. Most of the larger affluents are also navigable - the Meta, for instance, to within 60 miles of Bogota in Colombia. See lives of Raleigh for his last voyage hither; and works by Humboldt, Bonpland, and Schomburgk.