ORINOCO, a river in the north of South America, which falls into the Atlantic on the north-east seaboard between 60° 20' and 62° 30' W. long., after draining an area of at least 366,000 square miles (belonging to Venezuela and Colombia) in a course of about 1500 miles. Between the source of its westmost affluent, the Guaviare, and that of its eastmost, the Caroni, there is a difference of 14 degrees of longitude. The head-waters of the main stream rise on the southern slope of the Sierre Parime; but the branch which keeps the name Orinoco has not yet been traced by any European, and the position of the lake from which, according to native report, it issues can only be vaguely fixed. Michelena y Rôjas, who ascended the Orinoco as far as the mouth of the Mawaca (itself about 30 feet deep), found it even there a deep and navigable river; and a little way lower down it receives no inconsiderable accession from the Ocamo and Padamo. Below Esmeralda, a settlement in 65° 50' W. long., long known as the limit of definite exploration, occurs one of the most remarkable bifurcations in the world; while the main stream holds on in a north-west direction, a branch called the Casiquiare turns south and, increased by numerous small tributaries, runs for about 180 miles to the Rio Negro (an affluent of the Amazons) with so rapid a current that, while a boat takes only four natural days to descend, the return voyage requires twenty to thirty days. In the neighbourhood of San Fernando de Atabapo (in 4° 2' N. lat. and 68° 10' W. long., a miserable village, but officially the capital of the Venezuelan province of the Amazons, and famous in the history of the river) the Orinoco is joined by the united waters of the Atabapo, the Ynirida, and the Guaviare,—the Guaviare receiving the ...Ynirida about 10 or 15 miles west of San Fernando and then meeting the Atabapo opposite the village. The Guaviare is the first of the great rivers which bring down the waters of the Andes to the Orinoco, and is fit for steamboat traffic a long way up. From its junction with the Guaviare to the great rapid of Mariapiri (a distance of about 180 miles) the Ynirida, which was explored in 1872 by Frédéric Montolieu, hastens through a rugged country with a swift and frequently interrupted stream; above Mariapiri, and as far as Guacamayo (Montolieu’s farthest), it forms, on the other hand, a succession of lakes and lagoons with hardly any current {Bull. Soc. Gêogr., Paris, 1880). Though smaller than either the Guaviare, the Ynirida, or the Orinoco, the Atabapo gives its northward direction to the united river, which below the confluence widens out into a noble flood several miles broad, but before long has its channel contracted and twisted and broken by the rough granitic rocks of the country through which it has to force its way. About 80 miles bring the river to the great cataracts of Maypures, and a few miles more to that of Atures; both are complete barriers to upward navigation, and, since Humboldt’s glowing description, have been ranked among the most striking pieces of river scenery in South America (Humboldt and Bonpland, Voy. au Nouv. Continent, vol. ii. pp. 360-363). Some distance below Atures is the confluence of the Meta, a powerful many-watered affluent from the Andes, which has been ascended by steamer within 60 miles of Bogota; but the Orinoco still continues northward till, meeting the Apure, which drains the whole Merida Cordillera, it turns westwards through the great Venezuelan valley. In its onward course it receives a great many tributaries from both north and south, the former being comparatively short, but the latter, especially the Caura and Caroni, rising in the highlands hundreds of miles away. About 50 miles below the mouth of the Caroni and 120 miles from the sea begins the enormous delta, embracing 200 miles of coast. The southmost branch, Boca de Navios or Boca de Varime, continues in the line of the river; the Manamo or Vagre branch strikes off almost at right angles northward to the Gulf of Paria or Golfo Triste. The annual inundation of the Orinoco, which makes a kind of false start in April, and, gradually increasing in May, June, and July, reaches its height in September, is extensive enough to lay the country under water in some places for scores of miles inland. As most of the regions through which it passes are in a state of nature, and there is hardly, with the exception of Angostura (⅛.v.), a town of any considerable size on the banks of either main stream or affluents, this noble river-system is but little turned to account for commerce. Not only, however, is it easily navigable for steamers for nearly 800 miles, but, as the lower part of its course lies in the line of the trade-winds, sailing craft are able to make their way slowly upwards against the current. Even at the junction of the Guaviare the height above the sea is only 744 feet.
In 1498 Columbus entered Golfo Triste, and probably observed the northern mouths of the Orinoco, and in 1499 the main channel appears to have been noted by Ojeda. The first to attempt the ascent of the river was Diego de Ordaz in 1535, who reached the mouth of the Meta. For its scientific exploration we are mainly indebted to José Γturriaga and José Solano (1756), Humboldt (1800), and Michelena y Rojas (1855-1856).
See Gumilia, EZ Orinoco ilustrado (Madrid, 1741); Michelena y Rojas, Exploration oficial (Brussels, 1867).
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