The rivers of Buenos Ayres are innumerable, but the largest and the most noted is the RIO DE LA PLATA, which may be termed the great channel by which the south-eastern part of America is drained. This noble stream is the conjunct flood of the _Paraguay_, the _Pilcomayo_, the _Parana_, the _Uruguay_, and a multitude of minor rivers which rise either in the Andes or the mountains of Brazil. It was first discovered by Juan de Salis in 1515, who sailed up as far as an island in 34° 40' south latitude. The distance from the confluence of the Parana and Paraguay to the mouth of the La Plata is 600 miles; but if the length of any of the three great streams is added, the La Plata will not yield in magnitude of course to the Amazons or to the Orinoco. The _Paraguay_ is generally supposed to be the original river; this stream rises in 13° south latitude in the mountains, forty leagues north of the Portuguese town of Cuyaba, and on the opposite side of the chain in which rises the Arinos, a broad navigable river flowing into the Maranon. The sources of the Paraguay are very numerous, forming, soon after their issue, large rivers, and successively joining into one stream, under the name of the Paraguay. In 16° 24' south latitude, seven leagues from Villa Bella, the _Jauru_ flows into this river, and is noted as being the point where a fine marble pyramid is erected, which was brought from Lisbon, and denotes, by several inscriptions, that this place is the boundary of Brazil and Spanish America. From its sources to this point the Paraguay has a navigation interrupted only by one fall; and the lofty chain of mountains in which this river rises, are terminated seven leagues below the pyramid, in south latitude 16° 43' by a point called Morro Excalvado. East of this cape all is marsh; nine leagues further south, the _Rio Nuevo_ joins the Paraguay; this river was only discovered in 1786. In 17° 33' the west or Spanish banks of the great river again become mountainous, and three leagues to the south of his parallel there is a deep break in the chain which forms the mouth of lake _Gaiba_, which is connected with another named _Uberava_; six leagues and a half below the mouth of the Gaiba, and opposite the mountain bank the St. _Lourenço_ or Porrudos enters the Paraguay from Brazil. This river receives several very large ones, such as the Cuyaba, the Paraiba, the Jaquari, and the Itaquiri. The _Itaquiri_ rises near the great Parana in Brazil, and allowing only for a short portage, canoes actually circumnavigate the country included between the Parana and the Paraguay.