246 THE RIVER-ROUTES 



are replaced by granitic red sandstone.^ On the 

 right bank the height of the cliffs gradually diminishes 

 up river. They are still conspicuous at the confluence 

 of the Carcarafia, but at Santa Fe they rise only about 

 thirty-four feet. North of 31° S. lat., and for some 

 distance beyond Pilcomayo, the plain of the Chaco is 

 very low, and it is impossible to define exactly the limit 

 of the alluvial zone of the Parana. The fine clays, 

 grey and white, which form the soil of the Chaco, 

 reach the left bank north of Corrientes, in the esteros 

 of Neembucu. The red sandstone hills of the Asuncion 

 district rise like an archipelago out of this level bed 

 of lacustrine deposits. 



There is no obstacle to navigation in the entire 

 stretch from Posadas to the falls of the Guayra on 

 the Parana and the Salto Grande on the Yguassa. 

 Sixteen miles below Posadas the Parana passes through 

 a series of graduated rapids for about sixty miles 

 (1,467 kil. to 1,558 kil. from Buenos Aires) wrongly 

 called the Salto de Apipe. The current then rises to 

 a speed of eight knots, and the depth is three feet at 

 low water. These rapids are due to beds of mela- 

 phyre, which emerge amongst the granitic sandstone, 

 and the water makes its way between large rocky 

 islands. At Ituzaingo (1,455 kil.) the current loses 

 force. There is, however, still a rocky bottom lower 

 down, for ninety miles, at a depth of five feet. Below 

 this the rock only appears on the left bank, and in 

 a few ridges near the bank, or in isolated reefs which 

 it has been easy to mark with buoys. 



From Corrientes to La Paz the river flows from 

 north to south at the feet of the Corrientes cliffs. 

 These line the main stream between Corrientes and 

 Empedrado, and for thirty-five miles south of Bella- 



' In the space between the frontier of Entre Rios and the Rio 

 Empedrado, south of Corrientes, the clifts expose, above the red sand- 

 stone, beds of sand and clay, iiuvial alluvia left by former beds of 

 the Parana, the traces of which can be followed from the north-east 

 to the south-west diagonally across the province of Corrientes. 



