Page:Popular Science Monthly Volume 35.djvu/565

Rh and tortuous, and both, run in a general southeast direction, preserving a remarkable parallelism throughout their course, at a distance of about one hundred and eighty miles. Their depths and general characteristics correspond, and they are frequently obstructed by narrow argillaceous beds and fallen trees. The waters of both rivers are drinkable, but hard and unsuited for washing. The Bermejo brings down an enormous amount of sediment, which is deposited with. such, extraordinary rapidity that it must be considered a peculiarly strong feature of the mechanical work of the river, by which its geological formations are made and unmade. This swift precipitation of its detritus, which, it replaces by an increasing abrasion of the banks, goes on in the Bermejo, even when at its height and when in the exercise of its greatest carrying power, with, a speed equal to the square of its normal current. I have seen this river eat away an entire point of land, and by way of compensation deposit, just a turning below, an amount of detritus sufficient to form a similar promontory, which in one season of low water became covered with a thick and luxuriant growth of red willow. The Pilcomayo is to a great extent unknown, and in one section that is quite unknown is invested with a mythical halo in the shape of a tradition that it disappears. An apparent disappearance is a phenomenon which seems to have taken place with some rivers. The upper Paraguay, as I have witnessed, has been known to flow, as if absolutely lost for many miles, beneath a matted covering of living and dead vegetation several feet in depth. In the year 1858 one of these growths, under the influence of an extraordinary inundation, broke loose and drifted two thousand miles, down to Buenos Ayres, where it brought up, with many wild animals and reptiles that had taken refuge there from the almost universal deluge. The Pilcomayo is not affected in this way, and I believe that it not only does not become lost, but that there are no insuperable obstacles to its navigation. At the point where it is supposed to be lost, it begins a very erratic wandering—after running a few miles to the southeast, it suddenly turns to the north, leaving several minor branches looking in the opposite direction. It then returns as rapidly to its general southeast course, and, while subject to overflows, the main body of it flows on in a natural bed uninterruptedly to its mouth.