Up from the ocean into this valley an immense tidal wave rolls, with a bore, twice a day, forcing back the current of the Amazon 500 miles and inundating a portion of the flood-plain.
In the early autumn the equatorial rise commences in the headwaters of its tributaries, far south of the equator. The rains and melting snow raise the streams, and these the waters of the Amazon. As the sun crosses the equator and moves to the north the rain follows its course, and the branches that have their source in the east and northeast add their flood to the waters of the southerly branches. The flood in the Amazon is thus continued for nearly six months, raising its waters from 30 to 50 feet. The channels are filled, and the flood-plains are overflowed. The whole valley becomes a net-work of navigable waters, with islands and channels and lakes innumerable, forming a great inland sea, which the Brazilians call the Mediterranean of America. The upland, though only a little above the flood-plain, is rarely overflowed.
The plants and animals of the flood-plain were formerly considered as distinct from those of the upland as are the plants and animals of Europe from those of America; but later investigations show that there is but little difference between the species.
The sea breeze blows up the valley about a thousand miles. Then for 1500 miles the atmosphere is stagnant and sultry; the climate is that of a permanent vapor bath. The dense foliage forms dark, lofty vaults which the sunlight never penetrates, and over all hangs a perpetual mist. The abundance and beauty of vegetation increases, and the trees which at the mouth of the river blossom only once a year, here bloom and bear fruit all the year round.
Many great rivers run into the Amazon from the north and the south, most of them navigable, for many hundred miles. The Madeira, its greatest tributary, after running 2000 miles, empties into the king of rivers, without making any perceptible difference in its width or depth.
This mighty current, rushing into the ocean, meets the equatorial current and for over one hundred miles keeps on nearly a straight course, when the stronger and mightier oceanic current deflects it to the north. At from 200 to 300 miles from land, the sea is strongly tinged, and in April and May has nearly the clay-yellow hue of the Amazon. And even further north, about 400 miles from its mouth, the naturalist on the Amazon tells us, "we passed numerous patches of floating grass mingled with tree trunks and withered foliage; among these I espied many fruits of the Amazonian palm. And this was the last I saw of the Amazon."
The Rio de la Plata.
The La Plata, the outlet of the waters of central South America, is formed by the union of the Uruguay and Parana, about 150 miles from the ocean; a little lower down, at Montevideo, it is 62 miles wide and widens rapidly to the Atlantic, where it discharges more water than all the rivers of Europe. The tributaries of the Parana are fan-shaped. Its most eastern branches rise in the mountains of Brazil, within seventy miles of the Atlantic ocean; and 1500 miles away, on the other side of the continent, its most western tributaries rise only 125 miles from the Pacific.
Steamers ascend the Parana, Paraguay and Cuyaba, 2100 miles to Cuyaba, and the river with its branches is navigable for 5000 miles.