Remember the Rainforest 1
Passive extra passages are not produced by the impetuosity of the stream, but: a) they are originated by the main river, which, by diverting part of its waters off the main valley, communicates with the tributary; thus, for example, the mouth of the Purus-Coxiuuara, which is reinforced by the arms of the Coiuana and Coiuana and Aruparana; b) or they form, when an arm diverted from the tributary, en route to the deepest valley, is so reinforced by a lake or other affluent waters, that its waters can reach the master river. Of this hydrographical condition, the Amazon basin also offers many examples.
The width of the river, judging from the view, seems less vast than it really is, because the banks are so low.
The measurements are sometimes hampered by the frequently changing state of the shorelines, in which it is rare to be able to draw a baseline because they are sometimes plumb and impractical gullies, sometimes they are covered with woods, or they are without the necessary free view of the river. I believe that the river, in all the extent that I navigated, did not appear to me without islands,
An Amazon island
except for three or four times. An island-less river appears, for example, to the east of the mouth of the Xingu; there it looks more like a sea-arm than a river,
not permitting measurement and it can only be crossed by a safe boat, in two to three hours; and later, in the Strait of Obidos, which is 869 Portuguese bracos wide, and then, between Coari and Ega.
La Condamine gave the width of 150 toises to the Maranon river, at the point where it is navigable; in Pongo de Manseriche, that of 25 toises, at the narrowest point; in the mouth of the Pastaza, more than 400; and, above Sao Paulo de Olivenca, found the main channel to be 800 to 900 toises wide. The measurement of Mr. von Humboldt in Pongo de Rentema gave 217 toises. Lister Maw ("Journal of a passage from the Pacific to the Atlantic, down the Amazon River", London, 1829, the first voyage that was made in the Amazon, after ours) evaluated the width at the Guallaga junction with the Maranon, (English); the one of the main channel between Ourarinas and Omaguas sometimes in toises, sometimes in maritime miles; the one of the mouth of the Napo, at 1/4, of a marine mile; and that of Maranon, below its meeting on the main channel, in the average, on a sea-mile.
Manaus to border of Peru (Tabatinga)
Between Tabatinga and Fonte Boa, the river is generally widened according to the data of Dr. Spix, and particularly in the latter place, it takes a very considerable extension, as this one also appears in the Portuguese maps. Between Ega and the confluence with the Rio Negro, it is generally estimated a league from one shore to another; and the main channel (Mae do Rio) may be rarely less than 800 wide, and usually 900 to 1,000.
Amazon river, main channel
The view of the river is majestic here; although the terrain is low and uniform, the aspect of such a large volume of busy waters gives the grandiose impression. These proportions grow farther upstream, after the junction of the Negro and Madeira.
Rio Negro and Madeira meet Amazon
In the rapids of Jatauarana, where the waves break high in the steep ravines, the width must be a good league; and, in the same condition, the river extends eastward.
The Brazilians attribute the greatest width to the river in Silves and Faro, and, in fact, both these villages are, the first to five leagues, the other to nine leagues from the southern margin of the river; but the canals, which leave the Amazon and run northward to communicate with the Lakes of Saraca and Nhamunda, should not be considered as the border of their northern banks, since these channels depend almost entirely on those large river basins which are only visible upstream during the flood.
Numerous are the islands, scattered by the freshwater sea of the Amazon. Lopez Aguirre, the tyrant, says in his fabulous letter to King Philip that the river has more than a thousand islands. In this number, however, all the small and moving islands of sand are included. We must, above all, as is customary in the language of the Indians, distinguish the islands in the main body of the river from those which are formed by the deviations of the secondary arms or by the bifurcation of the tributaries: they are the first, in fact, produced by the river; the latter are pieces of solid earth, overlaid by the waters, and modified. As for beaches and dunes, the Indians call them in the Tupi language very expressively, ibi-cui (that is, "plucked earth", or mocui, "eu raspo", this term also appears as a river name in the extreme south of Brazil) ; to islands of higher status, with steady margins, they call, because they are almost always covered with weeds, as well as the forest groves, like islands in the meadows of the south of Brazil, of