ORINOCO, a great river of South America, flows through Guiana and Venezuela, and reaches the Atlantic ocean s. of Trinidad, in lat. 8° 40' north. The country in which it takes its rise is inhabited by an aboriginal race called the Guaicas, who have hitherto prevented all access by foreigners to its sources; but it is known to rise iu the Sierra Parime, one of the chief mountain chains of Guiana, near lat. 3° 40' n., long. 64° 30' west. It has been explored by Humboldt to the village of Esmeraldas (lat. 3° 8' n., long, 66° 5' w.), and by Sehomburgk to within 30 m. of its source. After flowing w.s.w. 20 m. past Esmeraldas the river bifurcates, the southern branch, the Cassiquiari (q.v.), flowing s.w., joins the Rio Negro, an affluent of the Amazon. From this point the Orinoco flows n.w. to its junction with the Guaviare, then n.n.e. to its junction with the Apure, after which it flows in an eastward direction to its mouth. Length of course 1960 miles. The head of uninterrupted navigation is at the confluence of the Orinoco, with the Apure, 777 in. from the mouth of the river. Above this point the course of the
river is interrupted by " raudals" or cataracts, of which those of and Atures are the most celebrated. Its principal affluents from the left are the Guaviare, the Viehada, the Meta, and the Apure; from the right, the Caura, and Caroni. The Orinoco, which is joined by 436 rivers, and upwards of 2,000 streams, drains an area (usually stated at 250,000 sq. m.) which, according to Wappnu's Republiken von Sitd Amerika, may be estimated at 650,000 sq. miles. It begins to form its delta 130 m. from its mouth, by throwing off a branch which flows northward into the Atlantic. Several of the mouths are navigable, and the main stream, the Boca de Navios, is divided by a line of islands into two channels, each two m. in width. Bolivar, a town upwards of 250 m. from the mouth of the river, marks the head of tide-water, and here the river is 4 m. wide and 390 ft. deep. Below the junction of the Apure the character of the scenery seems to be uniform—forests on the right bank, and llanos on the left,.