MARANON, or Orellana, a river of South America, and the largest in the world. Its proper and most remote source is the Ucayale, a branch of which rises near La Paz, in 18° of south latitude. The Marañon, a more northern branch, rises in a lake north-eastward of Lima, and, after a course of many miles to the north, is joined by the Chinchipe at Jaen. From this point, which is only about 200 miles from the Pacific Ocean, the river continues navigable to its embouchure in the Atlantic, a distance of 2100 miles in a direct line, or 3000 miles by the course of the stream. Humboldt measured the height of this spot by the barometer, and found it to be 194 toises, or 1240 English feet; and hence it appears that the fall in the bed of the river is on an average about five inches per mile; but the inclination is of course greater in the upper than in the lower part of the stream. Condamine found the width of the river at some distance below Jaen to be 135 toises, or 860 feet, and the depth to exceed 180 feet. The Marañon is joined by the Ucayale in west longitude 73°, by the Napo at 71°, by the Jagura at 65°. The other most considerable branches are the Negro on the north side, and the Juruary, the Madeira, and the Tapajos, on the south. Many of the tributaries of the Amazon greatly surpass in size the Rhine or the Danube; and their number is very great. It flows through 22° of longitude, near the equator. The country, watered by the river and all its branches, embraces an area of 2,100,000 square English miles, and includes one third part of South America. At a pass called the Pongo, about 140 miles below Jaen, the bed of the stream is suddenly contracted from 250 fathoms to 25, the Amazon having here cut its way through the rocks, which rise like perpendicular walls to a great height. At the junction with the Napo, in longitude 71°, its breadth is 900 fathoms, and its depth was found to exceed 100 fathoms. Between the Negro and the Madeira it has the breadth of a league, which extends to two leagues at those parts where islands abound; but during the annual swell of the water it covers a great part of the adjoining country, and has then no determinate limits. At Pauxis, 200 miles from the sea, the tides are sensibly felt every ten hours; and Mr Condamine infers, from the time which the swell of the waters requires to travel this distance, that there must be a succession of tides in the river at all times, and that its surface of course presents an undulating line. This traveller computes that the water passes from Jaen to the sea in 45 days, flowing about 66 miles per day, or 2½ miles in the hour. But the influence of the tides is felt 400 miles from the embouchure. In the rainy season the rapidity of this river is four miles an hour; and where it meets the ocean its breadth is fully thirty miles. The sea retreats before this mighty mass of rushing water, which causes a very agitated swell; and the river current is said to be still perceptible at more than 400 miles from the shore. Some reckon the Rio Tunguragua the source of the Marañon, which would give it a course of 3300 English miles; but if we consider the Rio Ucayale as its source, its course cannot be less than 3700 English miles.

It receives enormous tributaries—from the north the Rio Napo and Rio Putumayo, each about 700 miles long; the Yapura, 900 miles; the Rio Negro, 1400—from the south, the Yavari, the Yutia, the Tefe, the Puru, and above all, the Rio Madeira, that joins the Marañon after a course of 1800 miles; besides the Topayos of 900, and the Xingu of 1000 miles.

It is a remarkable fact that the great South American rivers, the Marañon and Orinoco join, by a large branch, the Rio Cassiquiare. The Amazon traverses a region thickly covered with lofty forests, which are the haunts of the jaguar, bear, panther, and many other wild animals, and are inhabited by numerous small tribes of savages, among whom the Spaniards and Portuguese have established missionaries. The river abounds in fish, many of which are of the most delicious kinds; and turtles of an excellent quality are numerous. Large alligators are seen stretched motionless in the mud, like trunks of trees. Nearly all the branches of this noble stream are navigable to a great distance from their junction with the main trunk; and collectively, the whole afford an extent of water communication unparalleled in any other part of the globe. What adds to this advantage is, that as the wind and the current are always opposed to each other, a vessel can make her way either up or down with great facility, by availing herself of her sails in the one case, and committing herself to the force of the current in the other.