Abstract
THE paper read at Monday's meeting of the Royal Geographical Society was on the Gran Chaco of the Argentine Republic and its rivers, by Captain John Page, of the Argentine Navy. The Gran Chaco, Captain Page said, is a vast central tract of country lying between the southern tropic and 29° S. lat., bounded on the north by Brazil and Bolivia, on the south by the Argentine province of Santa Fé, on the east by the Paraná and Paraguay Rivers, and on the west by Santiago del Estero and Salta. It contains about 180,000 square miles, or considerably more than the superficies of Great Britain and Ireland. About one-third part of this vast area belongs to Paraguay. The Gran Chaco has been called, particularly in allusion to the low-lying Paraguay section, the oceano firme, or solid ocean. This section and the central section of the Argentine rise from the Paraguay River towards Bolivia almost imperceptibly, having numerous and very extensive marshes and jungle, which are drained by many small streams likely to become, as the country progresses, important local waterways. The monotonous level of these sections is relieved by various prominent points of great beauty along the Paraguay River. Both are well wooded, although the predominating woodland feature is the great and almost interminable palm forests, which, singularly enough, in the Chaco are a sure indication of marshy lands subject to inundation, although in the province of Entre Rios, and other parts of the world, they are the exact contrary. On the northern and eastern borders of the River Bermejo the Central Chaco rises sensibly, as if to form a barrier to the waters of that river in their easterly progress. The Chaco Austral of the Argentine is the most favoured in natural riches of the three great sections. Its surface rises gradually from the Paraná River, and is intersected by several small streams, which are even now useful as a means of water-carriage to the many colonists settled along their courses; after rising thus up to the parallel of 25° 40′ S., the ground dips towards the valley of the San Francisco, sending its waters with those of that river to the Bermejo, sometimes in untimely floods. This depression extends across the Central into the Paraguayan Chaco, taking in the sections of the two rivers that are subject to yearly overflows between long. 61° and 62° W. of Greenwich, thus making a point of analogy between the two. The Austral is favoured with extensive primaeval forests, notably that on the north-western border extending into Salta and covering a superficies of many hundreds of miles, quite unexplored, and sometimes designated by the name of “impenetrable.” The principal water-courses of these territories are the Pilcomayo and Bermejo, which are undoubtedly destined to become highways of commerce. The waters of these rivers differ in colour, those of the Pilcomayo being dark and sometimes brownish, and those of the Bermejo red, as its name indicates; both are long, narrow, and tortuous, as are most of the interior rivers of the La Plata system; both run in a general south-east direction, preserving a remarkable parallelism throughout their entire course, running distant from each other as nearly as possible 180 miles. Neither of these streams receives tributaries of any kind over the greater part of their course, and their waters are consequently subjected to a great and constant drain from evaporation, in a climate whose average temperature is 80° F., as well as from absorption by the deep alluvial covering overlying the compact argillaceous bed, which is a geological characteristic of the whole Chaco subsoil. The impermeability of this bed probably arrests the effect of absorption, and in a great measure accounts for the non-diminution of the wealth of waters delivered into the Paraguay; such a geological formation may also account for the saline properties of the waters found in the Chaco, wherever wells have been made. The density of the Bermejo water is greater than that of the Pilcomayo; the amount of sediment it brings down is enormous, and it is deposited with such extraordinary rapidity that it cannot but be considered a peculiarly strong feature of the mechanical work of this river, by which its geological formations are rapidly made, and, indeed, unmade as well; this swift precipitation of its detritus, which it replaces by an increas ing abrasion of the banks, may be caused, to some extent, by the quantity of salt contained in its water. This constant precipitation goes on in the Bermejo, even when at its height, and when in the exercise of its greatest carrying power, with a speed quite equal to the square of its normal current; a fact which would seem to say that its currents are swifter on the surface than over its bed. Captain Page has 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—the Piscumayu, as it is called in the Quichua tongue, signifying Bird River—is to a great extent unknown. The section that is quite unknown, and that is surrounded by a certain mythical halo which it will be a geographical triumph to dispel, is that comprised between long. 61° and 62° W., and the parallels of 22° and 23° S.; the river at this point was said, by theorists who forgot to account for its reappearance immediately below, to disappear altogether. Captain Page then gave an historical sketch of the various expeditions which have explored the Gran Chaco, concluding with an account of an expedition in a steamer up the River Bermejo, which he himself led, amidst many dangers from banks, and snags, and wrecks, as well as from the widespread flood that suddenly overtook him.
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Geographical Notes . Nature 39, 328–329 (1889). https://doi.org/10.1038/039328c0
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DOI: https://doi.org/10.1038/039328c0