El Gran The Great Chaco (Chaco), a vast and for the most part unexplored region of South America, extending along the centre of the continent from the left bank of the Rio Salado N. to about lat. 20° S., where it is lost in the Chi-quito plains in Bolivia; and from the banks of the Paraguay W. to the E. limits of the mountain region of the Argentine Republic.

It thus forms the continuation of the great pampnsan plains which begin far south in Patagonia, and reach N. to the Salado. Owing to the nature of its climate and soil, the Chaco is naturally divided into two distinct portions, northern and southern. The northern, watered by plenteous rains and traversed by a river of considerable magnitude, the Pilcomayo, presents the usual features of intertropical countries; it is densely wooded, and clothed in immense tracts with a luxuriant growth of grass, with here and there wide-spreading marshes, which rarely become entirely dry between the periodical floods. Here almost all kinds of spontaneous tropical vegetation are represented. The southern division may be considered as one vast desert, generally unfavorable to vegetable growth, and presenting here and there some rare specimens of dwarfish spiny plants; but the aridity of the soil is due to the lack of moisture so common in all South America below lat. 24° S. and W. of the Plata and Paraguay. This may be overcome by artificial irrigation, and several prosperous colonies have of late years been formed in that region.

The whole of the northern portion, which belongs to Bolivia, is, with the exception of a settlement established in 1872 in the N. W. corner of the territory by the Bolivian government, the undisputed home of uncivilized Indians; while the southern, besides the colonies of whites already mentioned, is divided between nomadic and semi-civilized Indians, the latter having abandoned their predatory habits and established themselves by families in determined localities in imitation of the whites. The animal life in the Chaco differs in few respects from that of the neighboring portions of the Argentine and Bolivian republics. Ca-pybaras or carpinchos, and the various other larger mammals, abound on the banks of the rivers; there are numerous species of serpents and hideous venomous spiders of immense size; and myriads of small birds of endlessly varying plumage enliven the forests.