AMAZON - TRIBUTARIES The TocANTINs is not really a branch of the Amazon. It is the central fluvial artery of Brazil, running from south to north for a distance of about 1,50o miles. It rises in the mountainous dis trict of Pyrenopolis, but its more ambitious western affluent, the Araguay, has its extreme southern headwaters on the slopes of the Sierra Cayapo, and flows I,o8om. before its junction with the par ent stream, which it appears almost to equal in volume. Besides its main tributary, the Rio das Mortes, it has 20 smaller branches, offering many miles of canoe navigation. The Para river, generally called one of the mouths of the Amazon, is only the lower reach of the Tocantins.
The the next large river west of the Tocantins, was first explored by Karl von den Steinen in 1884-87. The river is formed at about 12° S. lat., by the union of three large head water streams, the Ronuro, the Tamitatoala, and the Kuluene, all of which, together with their more important tributaries, rise in an area only about 8om. long from west to east and some zoom. N.E. of Cuyaba. From a point about 75m. from the union of these streams the Xingu enters a 400-mile stretch of rapids that are serious obstacles even to canoe navigation.
The TAPAJOS, running through a humid, hot and unhealthy valley, pours into the Amazon zoom. above Para and is about I , 200m. long. It rises on the lofty Brazilian plateau near Diaman tino in 14° 25' S. lat. Near this place a number of streams unite to form the river Arinos. The Arinos, the Alto Tapajos and the Tapajos to the last rapid, the Maranhao Grande, is a continuous series of formidable cataracts and rapids ; but from the Maranhao Grande to its mouth, about 188m., the river can be navigated by large vessels.
The MADEIRA has its junction with the Amazon 87om. by river above Para, and almost rivals it in the volume of its waters. It rises more than soft. during the rainy season, and the largest ocean steamers may ascend it to the Fall of San Antonio, 663m. above its mouth ; but in the dry months, from June to November, it is only navigable for the same distance for craft drawing from 5 to 6f t. of water. According to the Treaty of San Ildefonso, the Madeira begins at the confluence of the Guapore with the Ma more. The Guapore has its headwaters almost in contact with those of the Paraguay River, but the idea of a connecting canal is based on ignorance of local conditions. San Antonio is the first of a formidable series of cataracts and rapids, 19 in number, which, for a river distance of 263m., obstruct the upper course of the Madeira until the last rapid, called Guajara, Mirim (small pebble), is reached, about I tom. below the union of the Guapore with the Mamore. The Beni River joins the Madeira at the Madeira Rapids, a stretch of nearly 5 miles of reefs, whirlpools and rapids, about 4om. below the Guajara Mirim Rapids. From the Guapore, Mamore and Beni rivers the Madeira receives the drainage from the whole of the eastern and north-eastern slopes of the Andes from the southernmost sources of the Rio Grande (a tributary of the Mamore) at about 2o° S. lat. to the northern most sources of the Madre de Dios River (a tributary of the Beni) at about 12° S. lat., the whole of the south-western slope of the Brazilian Matto Grosso, and the northern slope of the Sierra de Chiquitos in the Gran Chaco. All of the upper branches of the Madeira flow across open, almost level plains, which, al though some 3 5,00o sq.m. of them are yearly flooded to an average depth of 3 f t. for a period of from three to four months, form an agricultural and grazing region that is probably the most healthful and most inviting of the whole Amazon Basin.
The PURds, a very sluggish river, enters the Amazon about 23om. west of the Madeira, which it parallels as far as the falls of the latter stream. It is practically only a drainage ditch for the half-submerged, lake-flooded district it traverses. Chand less found its elevation above sea-level to be only Io7ft. 590 miles from its mouth. It is due to this extremely gentle gradient that the river, although a young stream, exhibits the meandering character of a mature stream. It is one of the most crooked rivers in the world, its length in a straight line being less than half that by its meanders. One of its marked characteristics is the five parallel furos, side channels to the main stream, by which its lower course is connected with the Amazon ; the largest and most westerly one connecting with the Purus about 15om. above its mouth. Its width is very uniform for I,000m. up, and for Boom. its depth is never less than 45 feet. It is navigable by steamers for 1,648m. as far as the little stream, the Curumaha, but only by light-draught craft. Chandless ascended it 1,866 miles. At 1,792m. it forks into two small streams.
The JURUA is the next great southern affluent of the Amazon west of the Purus and traverses the same sort of low, half-flooded country as the latter. It has the same character as the Purus as regards gentleness of gradient, meanders and sluggishness. It rises in the highlands east of the Ucayali which carry the Peru Brazil boundary and is navigable for a distance of 1,133 m. above its junction with the Amazon.
The JAVARY, the boundary line between Brazil and Peru, is another Amazon tributary of importance. It is navigable by canoe for 9oom. above its mouth to its sources among the Ucayali high lands, but only 26om. have been found suitable for steam naviga tion. The Brazilian Boundary Commission ascended it in 1866 to the junction of the Shino with its Jaquirana branch. The country it traverses in its extremely sinuous course is very level, similar in character to that of the Jurua.
The UCAYALI is second only in size to the Madeira among the tributaries of the Amazon. Its headwaters drain a great section of the Peruvian plateau from the source of the Vilcanota River only 7o m. N.W. of Lake Titicaca to the sources of the Mantaro west of Cerro de Pasco. The lower zoo m. of the main channel is bordered by large islands formed by numerous side-channels ; the whole being very low and flooded in the rainy season. The Ucayali is navigable for light draft launches as far as the Tambo Urubamba junction but the main Lima—Iquitos route follows the Pichis—Pachitea tributary.
The HUALLAGA which joins the Maranon about midway between the Pongo de Manseriche and the mouth of the Ucayali has its true source in the Yanahuanca River, a stream flowing from a series of glacier-fed lakes which lie north-west of the famous mining centre of Cerro de Pasco on the eastern slope of the main range of the Andes between the sources of the Maranon and Mantaro rivers. The name Huallaga is applied, however, to a more easterly and much less important headwater tributary which rises a short distance east of Cerro de Pasco. The whole stream is deeply entrenched and from the town of Huanuco to the mouth of the river much of its course is impeded by rapids and gorges. Between the Huallaga and the Ucayali lie the famous Pampas de Sacramento, vast plains broken by low outliers of the Andes, forested in part, but said to consist largely of grass covered areas suited to cattle raising.
The MARANON River rises in Lake Lauricocha, the northernmost of a chain of glacier-fed lakes about zoo m. N.N.E. of Lima and flows northward in a deeply eroded valley. It is due to this and other deeply entrenched longitudinal valleys that the tributaries of the Amazon have cut in the Peruvian plateau that the erroneous conception of the Peruvian Andes as three separate mountain ranges has arisen. At about 5 ° 3o' S. lat. the river makes a great bend toward the north-east and, after passing through a succession of narrows or pongos and no less than 35 formidable rapids, it breaks through from the Peruvian plateau to the Amazon Plain by a great canyon known as the Pongo de Manse riche. This canyon is about 2,000ft. deep and narrows in places to a width of only 1 oof t. Through this dark canyon the Maranon flows, at times, at a rate of over I 2m. an hour. Beyond the pongo the river receives several large tributaries from the north and spreads out into a broad stream with numerous channels and islands.
From the north the Amazon receives many tributaries, but their total volume of water is not nearly so great as that contributed to the parent stream by its affluents from the south. The part of Bra zil lying between the Amazon and French, Dutch and British Guiana, and bounded on the west by the Rio Negro, is known as Brazilian Guiana. It is the southern slope, very convolved, of the northern section of the Brazilian Archaean block. Their northern slope, which is occupied by the three Guianas first named, is saturated and river-torn; but their southern one, Brazilian Guiana, is in general thirsty and semi-barren, and the driest region of the Amazon valley. It is an area which has been left almost in the undisturbed possession of nomadic Indian tribes.
The TROMBETAS is the first river of importance we meet on the northern side as we ascend the Amazon. Its confluence with this is just above the town of Obidos. It has its sources in the Guiana highlands, but its long course is frequently interrupted by violent currents, rocky barriers and rapids. The river is navigable for 135m. above its mouth.
The NEGRO, the great northern tributary of the Amazon, has its sources along the watershed between the Orinoco and the Amazon basins, and also connects with the Orinoco by way of the Casiquiare Canal. The Negro is navigable in dry season for m. above its mouth for vessels of 4 ft. draft; but it has many sandbanks and minor obstructions. In the wet season it over flows its banks, in places to a width of 20 miles. Its lower course is very wide and full of long islands and intricate channels. The main headwater affluent of the Negro is the Uaupes. Its principal affluent from the north is the Branco formed by the union of the Uraricuera and Takatu which, with their tributaries drain a large section of the southerly slopes of the Guiana Highlands which separate Brazil from Venezuela and British Guiana. The Branco flows nearly straight south for 35o miles to the Negro which it enters by numerous channels similar to those of the lower course of the latter.
The Casiquiare Canal which connects the upper Orinoco, about 18 m. below the old mission site of Esmeraldas, with the Rio Negro affluent of the Amazon near the village of San Carlos, is a natural waterway, the only one of its kind known in the world. The existence of the canal was first reported by Father Acuna in 1639 but was not confirmed until 1744, when the Jesuit Father Roman, ascending the Orinoco, met Portuguese slave-traders from settlements on the Rio Negro, accompanied them on their return by way of the Casiquiare Canal and returned to the Orinoco by the same route. According to data obtained by the Rice Expedi tion which made a survey of the canal in 1919, the length of the canal is 227 m. Its width at its beginning in the Orinoco is 758 ft.; but this rapidly narrows down to 15o ft. and widens again to 2,15o ft. at its mouth in the Negro. The level of the water at the Orinoco end was found to be 283 ft. and, at the Rio Negro end, 212 ft. giving the canal an average slope toward the Negro of 7.2 in. per mile. The banks of the canal are heavily forested. The chief inhabitants of the region are Indians of the Maquiratares tribe although there are some whites engaged in rubber gathering. There are several small settlements at the lower end of the canal of which Solano was founded while the Scientific Expedition of the Boundary Commission of 1756 was at work in the region.
The YAPURA. West of the Negro the Amazon receives three imposing streams from the north-west—the Yapura, the Ica or Putumayo and the Napo. The first was formerly known as the Hyapora, but its Brazilian part is now called the Yapura, and its Colombian portion the Caqueta. Barao de Marajo gives it 600m. of navigable stretches. Jules Crevaux, who descended it, describes it as full of obstacles to navigation, the current very strong and the stream frequently interrupted by rapids and cataracts. It rises in the Colombian Andes, nearly in touch with the sources of the Magdalena, and augments its volume from many branches as it courses through Colombia.
The IcA or PUTUMAYO, west of and parallel to the Yapura, was found much more easily navigated by Crevaux. He ascended it in a steamer drawing 6f t. of water, and running day and night. He reached Cuemby, 800m. above its mouth, without finding a single rapid. Cuemby is only Zoom. from the Pacific ocean, in a straight line.
The NAPO rises among the volcanoes of the eastern border of the Andes in northern Ecuador. Its headwater tributaries in the Ecuadorian Oriente flow through one of the least known areas of the eastern border of the Andes. The course of only its south ernmost headwater tributary, the Anzu, is definitely known. The Coca which is believed to have its source on the slopes of Cayambe Volcano close to the equator, and the Aguarico, an important river with headwaters between Cayambe and the Colombian frontier, join it from the north. The Curaray, a tributary of secondary importance, joins it from the south some 200 miles from its mouth. The Napo is navigable for river craft to this point and by canoes to the mouth of the Coca. The Curaray–Coca section of the river is little-known.
The NANAY is the next Amazon tributary of importance west of the Napo. It belongs entirely to the lowlands, and is very crooked, has a slow current and divides much into canos and strings of lagoons which flood the flat, low areas of country on either side.
The TIGRE is the next west of the Nanay, and is navigable for 125m. from its confluence with the Amazon. Like the Nanay, it belongs wholly to the plains. Its mouth is 42m. west of the junction of the Ucayali with the Amazon.
The PASTAZA (the ancient River Sumatara) is the next large river we meet. It rises on the Ecuadorian tableland, where a branch from the valley of Riobamba unites with one from the Latacunga basin.
The MORONA flows parallel to the Pastaza and immediately to the west of it, and is the last stream of any importance on the northern side of the Amazon before reaching the Pongo de Manseriche. Above the Pongo de Manseriche two important tributaries, the Santiago and the Chinchipe join the Maranon from the north.