From the sources of the Ucayale, 17° S. lat., to the most northern branch of the Lauricocha, S. lat. 1°, the strip of land between the sources of the Amazon and the shore of the Pacific Ocean does not amount to an average of one hundred miles, and in many places is less than seventy miles wide.
To give a minute description of this wide spread and important basin would demand an extensive treatise; we must therefore be limited by a general view. If the windings are followed,by the most lengthened constituent branches, the Amazon flows from 3000 to 5000 miles. If we assume the Amazon proper, and Tunguragua, as the main stream, it receives from the north, beside in numerable branches of lesser note, the Pastaca, Piguena, Napo, Jupura, and Negro, advancing from head to mouth ; on the contrary side, and proceeding in a simi lar direction, we find the Ucayale, Javari, Jutay, Jurua, I'urus; the very lengthened Madeira, Tapajos, Xingua, and we may add the Tocantinas.
If the Amazon basin is compared with that of the Mississippi, the great extent of the former becomes more striking. The basin of the Mississippi is a trape zium of 1700 miles diagonal, with a mean breadth of 800 miles, area one million three hundred thousand square miles. The basin of the Amazon approaches a parallelo gram of 2100 miles by 1400 miles, with an area of 2,940,000 square miles, forming by at least one half, the most extended basin on earth, having but one point of discharge, and affording much the most expansive navi gable system of rivers, flowing towards a single recipient.
The great central valley of South America is conti nued southward from the basin of the Amazon, and be tween 13° and 36° S. lat. presents another very extended flyer basin, that of the Plate. The range of the Orinoco and Amazon basins arc nearly at right angles to the chains of mountains, whilst on the contrary, the l'late basin ranges nearly parallel to the Andes and Brazilian systems of mountains.
The principal river of the Plate basin, the Paraguay, or as it is called in the latter part of its course, Parana, rises about S. lat. 13°, between the sources of the Ma deira and Tocantinas, and flowing in an opposite direc tion from those of the Tapajos. Continuing a southern course through twenty degrees of latitude to its junction with the Uraguay, receiving in the intermediate dis tance, from the west, the Pilcomayo, Rio Grande, and Salado, and from the cast, the great tributary branch the Parana, which latter name the united streams assume below their junction.
The whole of these vast arms with their minor branches, drain a navigable basin approaching the form of a square, with a mean of 1140 miles each side, area nearly one million three hundred thousand square miles. There is a remarkable equality of extent between the basins of the Mississippi and Plate, but what is more remarkable, they do not, when taken together, equal that of the Amazon. Again, if we add together the three great central basins of South America, we have a con tinuous valley sweeping over four million five hundred thousand square miles, and comprising within and con tiguous to the torrid zone, more than the one ninth part of the land area of the earth.
The basin of the Plate, between S. lat. 20° and 24°, approaches to within fifty miles from the Pacific coast of Upper Peru ; and on the opposing side of the conti nent, in the Brazilian province of St. Paul, the remote sources of the Parana rise but little more than thirty miles from the Atlantic Ocean. On S. lat. 24°, the con tinent of South America is 25 degrees of longitude, or 1575 statute miles wide,but the Plate basin has its greatest eastern and western extension on S. lat. 21°. Along the latter curve the basin itself is 25 degrees of long. wide, where the degree is 64.42 miles each, consequently it is upwards of sixteen hundred miles from the fountains of the Pilcomayo, in the Andes, to those of the Rio Grande branch of the Parana.
The breadth of the Plate basin varies less perhap9 than does in that respect any other of the great river basins of the earth. From cape St. Antonio, the south ern point of the bay of Rio de la Plate, to the sources of the Pilcomayo, in the vicinity of Potosi, is 1400 miles. A line drawn between these points is nearly the base of the basin, since it leaves the far greater part of the sur face to the north-east. The breadth from the base con tracts in advancing towards the Brazilian provinces, but will average at least 950 miles.