At Santarem the Amazon receives another great tributary, the Tapajos (or Rio Preto, as the Portuguese call it), a thousand miles long, and, for the last eighty miles, from four to twelve miles in breadth. It rises amid the glittering mines of Matto Grosso, only twenty miles from the headwaters of the Rio Plata, and flows rapidly down through a magnificent hilly country to the last cataract, which is one hundred and sixty miles above Santarem, and is the end of navigation to sailing vessels. Thence to the Amazon it has little current and no great depth. From Santarem to Diamantino it is about twenty-six days' travel. Large quantities of sarsaparilla, rubber, tonka beans, mandioca, and guarana are brought down this river.
Parallel to the Tapajos, and about two hundred miles distant, flows the Xingú. It rises in the heart of the empire, has the length of the Ohio and Monongahela, and can be navigated one hundred and fifty miles. This is the last great tributary of the Amazon proper; if, however, we consider the Pará as only one of the outlets of the great river, we may then add to the list the grand Tocantíns.[153] This splendid river has its source in the rich province of Minas (the source, also, of the San Francisco and Uruguay), not six hundred miles from Rio Janeiro—a region possessing the finest climate in Brazil, and yielding diamonds and rubies, the sapphire, topaz and opal, gold, silver, and petroleum. The Tocantíns is sixteen hundred miles long, and ten miles broad at its mouth; but, unfortunately, rapids commence one hundred and twenty miles above Cametá. The Araguaia, its main branch, is, according to Castelnau, one mile wide, with a current of three fourths of a mile an hour.
Here are six tributaries, all of them superior to any river in Europe, outside of Russia, save the Danube, and ten times greater than any stream on the west slope of the Andes. While the Arkansas joins the Mississippi four hundred miles above New Orleans, the Madeira, of equal length, enters the Amazon nine hundred miles from Pará. But, vast as are these tributary streams, they seem to make no impression on the Amazon; they are lost like brooks in the ocean. Our ideas of the magnitude of the great river are wonderfully increased when we see the Madeira coming down two thousand miles, yet its enormous contribution imperceptible half way across the giant river; or the dark waters of the Negro creeping along the shore, and becoming undistinguishable five miles from its mouth. Though the Amazon carries a larger amount of sediment than any other river, it has no true delta, the archipelago in its mouth (for, like our own St. Lawrence, it has its Bay of a Thousand Isles) not being an alluvial formation, but having a rocky base. The great island of Marajó, in physical configuration, resembles the mainland of Guiana. The deltoid outlet is confined to the tributaries, nearly all of them, like "the disembogning Nile," emptying themselves by innumerable embouchures. To several tributaries the Amazon gives water before it receives their tribute. Thus, by ascending the Negro sixty miles, we have the singular spectacle of water pouring in from the Amazon through the Guariba Channel.
The waters of this great river system are of divers tints. The Amazon, as it leaps from the Andes, and as far down as the Ucayali, is blue, passing into a clear olive-green; likewise the Pastassa, Huallaga, Tapajos, Xingú, and Tocantíns. Below the Ucayali it is of a pale, yellowish olive; the Madeira,[154] Purus, Juruá, Jutahí, Javarí, Ucayali, Napo, Iça, and Japurá are of similar color. The Negro, Coary, and Teffé are black. Humboldt observes that "a cooler atmosphere, fewer musquitoes, greater salubrity, and absence of crocodiles, as also of fish, mark the region of these black rivers." This is not altogether true. The Amazon throughout is healthy, being swept by the trade-winds. The branches, which are not so constantly refreshed by the ocean breezes, are occasionally malarious; the "white-water" tributaries, except when they have a slack current in the dry season, have the best reputation, while intermittent fevers are nearly confined to the dark-colored streams. Much of the sickness on these tropical waters, however, is due to exposure and want of proper food rather than to the climate. The river system of South America will favorably compare, in point of salubrity, with the river system of its continental neighbor.[155]
As we might expect, the volume of the Amazon is beyond all parallel. Half a million cubic feet of water pour through the narrows of Obidos every second, and fresh water may be taken up from the Atlantic far out of sight of land. The fall of the main easterly trunk of the Amazon is about six and a half inches per mile, equivalent to a slope of 21'—the same as that of the Nile, and one third that of the Mississippi. Below Jaen there are thirty cataracts and rapids; at the Pongo de Manseriche, at the altitude of 1164 feet (according to Humboldt), it bids adieu to mountain scenery. Between Tabatinga and the ocean the average current is three miles an hour. It diminishes toward Pará, and is every where at a minimum in the dry season; but it always has the "swing" of an ocean current.
Though not so rapid as the Mississippi, the Amazon is deeper. There are seven fathoms of water at Nauta (2200 miles from the Atlantic), eleven at Tabatinga, and twenty-seven on the average below Mandáos.[156]
The Amazon and its branches are subject to an annual rise of great regularity. It does not take place simultaneously over the whole river, but there is a succession of freshets. At the foot of the Andes the rise commences in January; at Ega it begins about the end of February. Coinciding with this contribution from the west, the October rains on the highlands of Bolivia and Brazil swell the southern tributaries, whose accumulated floods reach the main stream in February; and the latter, unable to discharge the avalanche of waters, inundates a vast area, and even crowds up the northern tributaries. As the Madeira, Tapajos, and Purus subside, the Negro, fed by the spring rains in Guiana and Venezuela, presses downward till the central stream rolls back the now sluggish affluents from the south. There is, therefore, a rhythmical correspondence in the rise and fall of the arms of the Amazon, so that this great fresh-water sea sways alternately north and south; while the onward swell in the grand trunk is a progressive undulation eastward. As the Cambridge Professor well says: "In this oceanic river the tidal action has an annual instead of a daily ebb and flow; it obeys a larger orb, and is ruled by the sun and not the moon." As the southern affluents have the greatest volume, the Amazon receives its largest accession after the sun has been in the southern hemisphere. The rise is gradual, increasing to one foot per day. One lowland after another sinks beneath the flood; the forest stands up to its middle in the water, and shady dells are transformed into navigable creeks.[157] Swarms of turtles leave the river for the inland lakes; flocks of wading birds migrate to the banks of the Negro and Orinoco to enjoy the cloudless sky of the dry season; alligators swim where a short time before the jaguar lay in wait for the tapir; and the natives, unable to fish, huddle in their villages to spend the "winter of their discontent." The Lower Amazon is at its minimum in September or October. The rise above this lowest level is between seven and eight fathoms. If we consider the average width of the Amazon two miles, we shall have a surface of at least five thousand square miles raised fifty feet by the inundation. An extraordinary freshet is expected every sixth year.
The Atlantic tide is perceptible at Obidos, four hundred and fifty miles above Pará, and Bates observed it up the Tapajos, five hundred and thirty miles distant. The tide, however, does not flow up; there is only a rising and falling of the waters—the momentary check of the great river in its conflict with the ocean. The "bore," or piroróco, is a colossal wave at spring tide, rising suddenly along the whole width of the Amazon to a height of twelve or fifteen feet, and then collapsing with a frightful roar.
The Amazon presents an unparalleled extent of water communication. So many and far reaching are its tributaries, it touches every country on the continent except Chile and Patagonia. South America is well nigh quartered by its river system: the Amazon starts within sixty miles of the Pacific; the Tapajos and Madeira reach down to the La Plata; while the Negro mingles its waters with those of the Orinoco. The tributaries also communicate with each other by intersecting canals, so numerous that central Amazonia is truly a cluster of islands. Wagons and railroads will be out of the question for ages hence in this aquatic basin. No other river runs in so deep a channel to so great a distance. For two thousand miles from its month there are not less than seven fathoms of water. Not a fall interrupts navigation on the main stream for two thousand five hundred miles; and it so happens that while the current is ever east (for even the ocean can not send up its tide against it), there is a constant trade-wind westward, so that navigation up or down has always something in its favor. As a general rule, the breeze is not so strong during the rise of the river. There are at least six thousand miles of navigation for large vessels. It was lately said that the Mississippi carries more vessels in a month, and the Yang-tse-Kiang in a day, than the Amazon all the year round. But this is no longer true. Steamers already ascend regularly to the port of Moyabamba, which is less than twenty days' travel from the Pacific coast. The Amazon was opened to the world September 7, 1867; and the time can not be far distant when the exhaustless wealth of the great valley—its timber, fruit, medicinal plants, gums, and dye-stuffs—will be emptied by this great highway into the commercial lap of the Atlantic; when crowded steamers will plow all these waters—yellow, black, and blue—and the sloths and alligators, monkeys and jaguars, toucans and turtles, will have a bad time of it.
Officially free to the world, the great river is, however, for the present practically closed to foreign shipping, as it is difficult to compete with the Brazilian steamers. For, by the contract which lasts till 1877, the company is allowed an annual subsidy of $4,000,000, which has since been increased by 250 milreys per voyage. In 1867 the steamers and sailing vessels on the Amazon were divided as follows, though it must be remembered that few of the foreign ships, excepting Portuguese, ascended beyond Pará: