It is near Corpus, about forty miles above Posadas, that the upper Paraná escapes from the restraint of the Brazilian tableland, which imprisons its valley, from the falls of the Guayra, in a deep fissure between lofty basalt cliffs. Below Posadas the river leaves the region of hills and red earth. Below Corrientes it flows everywhere over its own alluvia. Even above Corrientes its form has surprising characteristics of youth. The precise survey done on its banks has brought to light a very distinct break of its fall above Villa Urquiza, about 400 miles from Buenos Aires. The fall, which from Corrientes onward remains between sixty and forty millimetres per kilometre, sinks suddenly to thirteen over a stretch of twenty-five miles, and then rises again to thirty to forty-five millimetres.[124] Below Rosario the mean descent is twelve millimetres to the kilometre, below San Pedro only six.

Above Corrientes the width of the main arm of the Paraná varies, as a rule, from 2,600 to 6,500 feet. The width of the river-plain over which the floods spread is still more irregular. Between Santa Fé and Paraná, where it is especially narrow, it is still ten miles wide. Lower down it gradually broadens to a width of sixty-five miles at the head of the estuary. The scenery is not the same in all sections of it. The vegetation on the islands is richer and more varied up river, and tropical essences (laurel-timbo) are found below the Bajada, forming clumps of trees covered with creepers.

THE PARANÁ AT CORRIENTES.

Banks and islands partially fixed by vegetation.

Photograph by Widmayer.

[Click to view larger image.]

THE BARRANCA AT PARANÁ (ENTRE RIOS), LEFT BANK.