To the first group belong all the rivers which water the Provinces of Corrientès, Entre Rios, Chaco, Jujuy, and Salta, a portion of those of Santa Fé, Córdoba, and Buenos Ayres, and the Territories of Chaco and Misionès. To the second group belong all the water-courses of the Provinces of Tucuman, Catamarca, Santiago de l’Estero, La Rioja, San Juan, Mendoza, San Luis, the greater part of those of Córdoba, and part of those of Buenos Ayres. To the third group belong also a portion of the rivers of Buenos Ayres, and all the rivers of Patagonia. As we have seen, the waterways of the Province of Buenos Ayres come under all three headings. The best-known river of the Republic, and that which gives the Argentine its name, is the Rio de la Plata, formed by the junction of two rivers no less important, the Parana and the Uruguay. It forms an immense estuary, which pours into the ocean the waters of a whole hydrographic system, a vast basin occupying nearly 1,540,000 square miles, or a fourth part of South America. This estuary is 25 miles wide at its head, and where its waters reach the ocean attains a width of no less than 217 miles, its average width being 111 miles; and its superficial area covers 13,475 square miles. Apart from certain hindrances of the nature of islands or sandbanks, the Rio de la Plata offers relatively easy access to vessels of the highest tonnage making for Buenos Ayres or towards the interior. Its level is influenced by the tides of the ocean, and also suffers very violent changes when the easterly or south-easterly winds pile up the waters of the sea in the estuary. The river which is the continuation of the Rio de la Plata towards the north, and with it forms the vital artery of the Argentine, is the Parana; its length is 2980 miles, of which about one-half flows through Argentine territory. Its width varies from 22 to 31 miles, and its average annual flow is estimated at nearly 39,000 cubic yards per second, which represents one and a half times that of the Mississippi, twice that of the Ganges, four times that of the Danube, five times that of the Nile, and nearly a hundred times that of the Seine. It receives, in its turn, as an affluent, the Paraguay, a river which traverses the country of the same name, and thus places it in communication with the sea, by way of the Parana and the Rio de la Plata. This network of rivers forms a magnificent series of waterways. Rising from the central provinces of Brazil, the Parana passes through the rich afforested regions of Chaco, communicates by means of its affluent with Paraguay and South Brazil, and then flows through the Provinces of Corrientès, Entre Rios, and Santa Fé; that is, through the regions of great forests and wide holdings, and then empties itself into the inland sea of the Rio de la Plata, where it mingles with the Uruguay, another means of communication between the Provinces of the East and the Atlantic Ocean.