HYDROGRAPHY. Aside from, a few inclosed basins in the interior, the entire area is drained by easterly flowing rivers into the Atlantic. The great river system of the Plata, formed by the confluence of the Uruguay and the Parand, belongs only partly to Argentina, as both its branches rise in the interior of Brazil, and for a large part of their course flow along the frontiers of Brazil, Paraguay, and Uruguay. The Parand is of great importance to Argentina as a commercial highway. With the Paraguay, it drains the Gran Chaco, through the channels of the Pileomayo, Bermejo, and Salado, and also the northern pampas, where in past times there were several important tributaries that are now represented by smaller streams with intermittent flow. The Parana is navigable by steamers for a distance of about 1200 miles, and by light-draught boats for nearly its whole length. From the continence of the Paraguay to the sea, the fall amounts only to about 225 feet, so that a slight depression would separate the Plata system into three independent branches— the Parand, the Paraguay, and the Uruguay.
In the central Provinces of Argentina, between the Rio Salado on the north and the Rio Colo rado on the south, there is an area of inclosed drainage, with extensive saline marshes, which deposit alkaline salts during the dry season. South Argentina is drained by the Colorado and Negro, both rising on the slopes of the Andes. The drainage basin of the Colorado formerly covered a much larger territory, as the prov inces of San Juan, San Luis, and Mendoza were drained by a northern tributary that now ends in a swampy reservoir. Patagonia has several large streams, including the Chubut, Deseado, Salado, and Chico, which receive their water sup plies from the slopes of the Andes. where there are numerous glacial lakes. See the articles on PLA TA, RIO DE LA; PARANA, etc.