PLATA, RIO DE LA, is the name applied to the wide :estuary formed by the confluence of the rivers Parand and Uruguay, in South America. Where the Rio de In Plata enters the sea, between Punta del Este and Cape San Antonio, its width is about 130 miles ; and between Punta de las l'edras and the Barrancas de Santa Lucia above Monte Video, it is still 53 miles wide; but above these places the shores gradually approach nearer, and opposite Colonia they are only 20 miles apart ; this width continues to the confluence of the two large rivers which fall into it. The Rio do in Plata is very shallow ; at its mouth it is only 10 fathoms deep on an average, and this depth gradually decreases. Between Monte Video and Buonoa Ayres the average depth is not more than 3 fathoms ; but vessels drawing 16 feet of water can, except when the water is very low, ascend the Parend as high as San Juan (30' 30' S. lat.), and those drawing 12 feet can go up to Corrientes (27' SO' S. late). The deep part of the Plata opposite Buenos Ayres, called the outer rtarls, is from 7 to S miles from that town • and between the outer and the inner roads there is a sand.bank. Smaller vessels anchor in the inner roads, at from one to two miles from the shore. The navigation of the Rio de la Plata is very difficult, owing to the dangerous shoals, the strong and irregular currents, and the sudden tempests to which it is subject. The strength and irregularity of the currents are easily accounted for, when it is considered that the larger of the two tributaries, the Parana, rises within the tropics, and during the rainy season brings down an immense volume of water, and that the wide expanse of the ;estuary, being bounded either by low and level or very slightly elevated ground, is subject to be influenced by every strong wind which drives a great volume of water to the point of the compass opposite to that from which it blows. The 'pamperos,' or south-western gales, which fre quently blow with inconceivable fury, cause very remarkable fluctua tions in the depth of water. The extremely difficult and dangerous navigation of this seatnary has obtained for it the designation of El Inflerno de las Marineros; but Captain Fitzroy mentions as very redeeming qualities, that it affords anchoring-ground everywhere, and soundings where the indications are certain if the vessel is approaching danger. Little or no tide has been hitherto noticed in this wide ex panse of water, but Captain Fitzroy thinks that " this anomaly may be more apparent than real ; for where the depth of water is so fluc tuating, and the currents are so variable, it is difficult to distinguish the precise effect of tides, except by a series of observations far longer than Las yet been made." Mr. Darwin, when off the coast, noticed
the slowness with which the waters of the Rio de In Plata mingled with those of the sea; the muddy and discoloured river-water, from Re less specific gravity, floating for a great distance on the surface of the salt-water, and producing a very singular effect where the vessel crossed it. dther observers have found that the current occasioned by the discharge of the Plata preserves an easterly direction, and is still found to have a velocity of a mile an hour, and a breadth of more than 800 mile., at a distance of not less than 600 miles from the mouth of the river. (Sabine, 'Notes to Humboldt's Cosmos.') The vast body of water which issues from the Plata may be readily con ceived when it is stated that the basin drained by the rivers which flow into it is estimated at 1,200,000 square miles.
Through the Rio de In Plata the commercial produce of about one fourth of South America is brought to the market of the world. It is thert fore a great advantage to the countries from which the matuary of the Plata receives lie water!, that the rivers which flow into it offer less obstruction to navigation than Is usual in large streams. The largest of these rivers, the Pamnd, as alrea-ly mentioned, is navigable for vessels drawing 12 feet of water as far as Corrientes, a distance of 800 miles from its mouth. The Rio Paraguay, the largest affluent of the Parand, may be navigated by large boats more than 1000 miles above its confluence with the Parand. The Rio Vermejo, another affluent of the Paraguay, is navigable up to the confluence of its two principal branches, the Lavayen and Rio de Tarija, a distance of snore than 400 miles. The Salado, which joins the Parand in its lower course, is navigable to the town of Matara, 350 miles from the mouth of the river. The navigation of the Uruguay is obstructed by two cataracts, which occur about 180 miles above its mouth.
(Fitzroy and King, Surveying Voyages of the Adventure and Beagle; Parish, Buenos Ayres and the Provinces of the Rio de is Plata; Ignacio NuEez, Account of the United Provinces of the Rio de la Plata ; Mackinnon, Steam Warfare on the Parana.)