273 



AMAZONAS. 



AMAZONAS. 



274 



and then by the Pastaxja, Tigre, Napo, I9a or Putumayo, Yapura, Rio 

 Negro, and Oximina or Trombetas. From the south it receives, pro- 

 ceeding from west to east, the waters of the Huallaga, Ucayali, Yavari, 

 Jutai, Jurua, Teffe", Coary, Purvis, Madera (the largest of its affluents, 

 little short of 2000 miles in length), Tapajos, Xingu, and Tocantins. 

 Most of these rivers pour their water into the Amazonas by several 

 mouths, which frequently are at great distances from one another. Thus 

 the four or five mouths of the Yapura fall into the Amazonas between 

 65 and 67 40' W. long., and the two most distant are more than 

 200 miles apart. The four embouchures of the Purus lie between 61 

 and 62 20' W. long., and the two outer ones are about 100 miles apart. 

 The immense deposits of alluvial soil, through which the lower course 

 of these rivers lies, united to the great volume of water which they 

 bring down during the rainy season, must be considered as the cause 

 of this peculiarity, by which the affluents of the Amazonas are distin- 

 guished from all other rivers in the world. 



The width of the river of course increases as it proceeds eastward. 

 It is however by no means easy to determine its breadth, on account 

 of the great number of islands which lie within the bed of the river 

 and divide its waters into several channels. Between Peru and 

 Ecuador the width varies from half a mile to a mile ; farther down it 

 increases to two miles, and after it has been joined by the Madera it 

 is nearly three miles. Below Faro the width decreases somewhat, 

 and at Obydos, near 55 W. long., the river is only 1738 yards across. 

 To this place, which is about 400 miles from the mouth of the river, 

 the tide ascends when the river is low, but it is. not sensible many 

 miles farther down, when the stream is swollen by freshets. Below 

 Obydos the width again increases, and after the junction of the 

 Tapajoa it is hardly at any place less than seven miles. The Canal de 

 Bragauza. opposite the island of Marajo and as far north as the island 

 of Cavinna, is 30 miles wide, which breadth is at its mouth increased 

 to above 50 miles, the island of Caviana included, which lies in the 

 middle of it. 



The attempts to determine the depth of the river have been only 

 partially successful, on account of the rapidity of the current, and 

 the difficulty of determining in which of the several channels the 

 main current flows. Smyth found in all places where he made the 

 experiment no bottom with 20 fathoms, even above the mouth of the 

 Rio Negro. The depth is supposed to increase considerably after the 

 confluence with the Madera, and still more after the Amazonas 

 has been joined by the Tapajos. It is thought that it cannot be leas 

 than from 50 to 60 fathoms. In the Narrow of Obydoa the depth of 

 the Amazonas exceeds 100 fathoms. 



The velocity of the current varies, greatly. It is of course much 

 greater when the river is swollen by freshets than when its waters 

 are low, and lees along the banks than in the middle of the current. 

 Smyth, who descended the river in the months of March and April, 

 when the water is highest, found that near the mouth the velocity of 

 the current varies between three and four miles per hour, which 

 shows with what a force the water is impelled by the great maaa that 

 presses it forward. For the fall of the river is by no means consider- 

 able. At Tabatinga, near the mouth of the Yavari it is only 673 feet 

 above the sea, and at the mouth of the Madera it is reasonably 

 supposed not to be more than 500 feet. In a course considerably 

 exceeding 900 miles it falls only 178 feet. At some places the current 

 runs only two miles and a half in an hour. In the Narrow of Obydos 

 the current runs more than five miles an hour when the river is full. 

 Lower down its current is hardly anywhere more than two miles, but 

 is never much less. 



There occurs no impediment to navigation as far as the river flows 

 through the plains. Vessels of any size may ascend it to the mouth 

 of the Ucayali, and even to that of the Huallaga, but farther up the 

 depth must be much less, as, according to Maw, only vessels drawing 

 five or six feet of water can advance to S. Borja. The ascent of 

 the river is easiest from July to December. In this season the ventoi 

 geraa, or general winds, blow always from east to west. They seem 

 to be the continuation of the south-eastern trade-wind, which in this 

 season advances to 3 and 4 N. lat. These winds blow strong during 

 the day, and always against the current of the river. In navigating 

 up the river, vessels keep close to either bank, where the current 

 is less rapid. The vessels used on this river have large square sails, 

 and their decks are covered in with a thatched roof to ward off the 

 almost incessant rainx. Descending the river they rarely use their 

 sail, but generally drift with the stream. From the beginning of 

 January to July, when the winds are variable, the navigation up 

 the river is very tedious, and it takes eight months to come up from 

 Gram Para to Tabatinga, whilst the voyage down does not take more 

 than two. 



The islands in the middle of the river are low, flat, and surrounded 

 by sand-banks, which are covered with water during the freshets. 

 They are without trees, but covered with thick bushes. Many of 

 them are above 10 miles long, but commonly not wide. They are 

 rarely swampy, and some of them are of importance from the number 

 of turtles' eggs collected on them. The islands which occur along 

 the banks of the river are much higher and of a different description, 

 being covered in all their extent by thick forests of high trees. They 

 are divided from the mainland either by arms of the Amazonas itself, 

 or by a branch of one of its affluents. Some of these islands are of great 



GEOG. DIV. VOL. I. 



extent. The island of Tupinamba is about 200 miles long, and about 

 30 miles wide. It lies between 56 and 59 W. long., and is separated 

 from the mainland by the Furo de Uraria, an arm of the Madera, 

 which, about 50 miles above the confluence of the two rivers, branches 

 off from the Madera and runs parallel to the Amazonas. The area 

 of this island is more than 5500 square miles. The island of Paricatiba 

 occurs on the western side of the mouth of the Tapajos, and is divided 

 from the mainland by the Lago das Campinas and two channels which 

 connect the lake with the two rivers. The island is about 60 miles 

 long and more than 15 miles wide. It is remarkable for its extensive 

 plantations of cotton. The largest of the islands is that of Maraj6 or 

 Ilha dos Joannes, which lies in the mouth of the Amazonas, and is 

 150 miles long from east to west, and about the same from north to 

 south ; its area exceeds 10,500 square miles. The island of Caviana, 

 in the Canal de Bragauza del Norte, is about 40 miles long and 25 

 miles wide. 



The basin of the Amazonas is by far the largest river-basin on the 

 globe. According to Humboldt, its area exceeds 3,000,000 square 

 miles, or somewhat more than one-half of South America. The Oby, 

 one of the largest rivers of the Old Continent, drains, according to 

 Ritter, an extent which falls somewhat short of 2,000,000 square miles, 

 and the basin of the Mississippi contains about 1,000,000 square miles. 

 The Amazonas is the only large river in the world whose basin 

 comprehends countries lying on both sides of the equator. The 

 northern edge of the basin extends only to about 7 N. lat., but the 

 southern edge reaches in one part to near 19" S. lat. 



The Amazonas is in no other respect so remarkable as for the 

 immense volume of water which it brings to the ocean. According to 

 a calculation of Remiel, the principal branch of the Ganges in the 

 dry season discharges in one second 80,000 cubic feet of water. 

 Wilcox states, that below the mouth of the Bonash, near Goyalpura, 

 the Brahmapootra pours down in one second 176,188 cubic feet. 

 Martins calculates that the volume of water passing in one second 

 through the Narrow of Obydos exceeds 550,000 cubic feet. 



With such resistless force does the wide deep current of the 

 Amazonas enter the Atlantic, that its vast mass of waters sweeps on 

 unbroken and unmixed with the ocean for above 200 miles to the 

 eastward of the embouchure. A remarkable phenomenon is witnessed 

 in the Amazonas at the time of spring tides. The wide mouth of 

 the river receives the broad swell of the Atlantic tide-wave ; but as 

 the channel becomes narrower by the islands and the gradual approxi- 

 mation of the banks, the tide has not room to move up the stream, 

 and the continuous pressure of successive waves prevents it from 

 rushing back to the ocean. The consequence is that the tide becomes 

 heaped up in the embouchure of the river, until at length a wall of 

 water from 12 to 16 feet high, followed rapidly by a second, a third, and 

 sometimes a fourth enormous wave, sweeps with irresistible force and 

 incredible velocity up the river and over its banks, carrying every- 

 thing before it, and accompanied with a tremendous roar, which is 

 heard to a distance of four or five miles. This enormous wave which 

 causes instantaneous high water in the river is called by the Indians 

 prororoco. 



The Amazonaa is indebted for its abundance of water to its position 

 between the tropics, and to the extent of its tributaries. Whilst 

 the sun passes from one tropic to the other it is preceded, attended, 

 and followed by heavy and nearly continual rains ; and all the 

 countries constituting the basin of the Amazonas are successively, 

 for five or six months together, drenched by an excess of moisture. 

 A considerable portion of the rains descending on South America, 

 whilst the sun is in the northern hemisphere, runs southward to the 

 Amazonas, and perhaps seven-eighths of the intertropical rains, which 

 pour down on that continent whilst the sun is in the southern 

 hemisphere, are brought to its channel by its numerous large southern 

 tributaries. It may almost be said that the river is never at low water, 

 properly so called; for when its northern affluents during the dry 

 season bring down a comparatively small volume of water, the southern 

 rivers are filled by the rains, and pour into it an overwhelming mass of 

 water. When the latter begin to subside, the former are already on 

 the increase. 



As the quantity of water brought down by the northern rivers ia 

 but small in comparison with the volume which the southern rivers 

 pour into it, the Amazonas has least water whilst the sun is in the 

 northern hemisphere. But the rains do not commence in the same 

 month, even in the countries which are situated under the same parallel. 

 On the banks of the Amazonaa the intertropical rains begin on the 

 eastern declivities of the Andes in the month of November, and at 

 Gram ParJi they do not set in before the end of the year. The effect 

 of the rains on the swelling of the rivers becomes apparent only after 

 a period of from four to six weeks. The waters of the Marauon begin to 

 rise perceptibly at the end of December, those of the Solimoes at the 

 end of January, and those of the Amazonas in February. The Amaze man 

 rises for about 120 days. Its northern affluents, the largest of which 

 are the Rio Negro and Yapura, are highest in August, September, 

 and October, but in the southern affluents the freshets do not occur 

 in the same months. The Tocantins, Xingu, and Tapujos, begin to 

 rise in November, and attain their greatest height in February and 

 March, whilst the Madera, by far the largest of the affluents of the 

 Amazonas, has its freshets simultaneously with the Amazonas, the 



