=Lakes.= The Andine lakes in the Patagonia section are of glacial origin, with much scenic beauty. One of these, Nahuel-Huapi, 40 miles long, is said to be 1000 feet deep. Lake Buenos Aires, partly in Chile, is 75 miles long. The lakes number more than 400; at the north are many swampy lagoons. PLAINS The plains, once under the sea, and now for the most part less than 500 feet above it with a very gradual rise from the ocean to the Andes, extend from the Pilcomayo River, the boundary line with Western Paraguay, on the north, to the Rio Negro on the south. The northern part belongs to the Gran Chaco, swampy and partly wooded, with so slight a southeastward slope that large spaces are regularly flooded in the rainy season. South of the Bermejo River which is parallel with the Pilcomayo, the land is higher, some of it 800 feet above the sea, and the forests are heavier; but there are still marshy lagoons. Then come open grassy plains with occasional salt pans. The section between the Paraná and Uruguay Rivers, called the Argentine Mesopotamia, in Corrientes at the north is of somewhat similar character, but has higher land in Entre Rios at the south. The remainder of the plain is the real Pampa, the part west of the Paraná River and below that extending to the ocean, mainly, treeless and grassy. It includes the Provinces of Buenos Aires, Santa Fé, Córdoba, San Luis, Mendoza, and the Territory Pampa Central. In the far west is a depressed region containing some lakes and swamps with no outlet, but with too little rain. RIVERS The rivers of Argentina are of great importance, being navigable for immense distances. Chief among them are those of the System of La Plata, this river being formed by the union of the Paraná and the Uruguay: a great river indeed, the outflow of water being 80 per cent more than that of the Mississippi, and the drainage basin covering 1,500,000 square miles. The Paraguay, Pilcomayo, Bermejo, Salado del Norte, Iguassú, and many others belong to this basin. The Iguassú, though not navigable except for a mile from the Paraná, is world famed for its magnificent waterfall, surpassing Niagara in height, width, and most of the year in volume of water; while it is rendered altogether incomparable by the extraordinary beauty of its setting.