244 THE RIVER-ROUTES 



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. 1 

 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 

 Parana 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 Fe and 

 Parana, 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. 



But the different scenes of the river region are 

 most of all due to different conditions of erosion and 

 formation. Above Rosario the configuration is due to 

 floods. Each succeeding flood alters it and leaves 

 some trace of itself in the topography. The beds of 

 sand that it lays down are fixed by rushes and float- 

 ing weeds, then by willows (Salix humboldtiana) . 

 This screen of vegetation encourages accretion, and 

 the edges tend to rise higher. In the middle of the 

 island are low, marshy lands. The irregularity of the 

 alluvial deposits causes marked undulations in the 

 whole region of the river, and everywhere gives rise 



1 The district on the right bank of the ParanA, above Santa Fe 

 and Paran, seems to be due to a recent subsidence. The river is, 

 on the other hand, compelled to effect active erosion in crossing the 

 high lands between Santa Fe and Buenos Aires. It is curious that 

 the break or fall at Villa Urquiza occurs precisely above the bend 

 of the Parana. A less marked break has been recognized further 

 north, in the latitude of Lavalle, above the Goya bend. It seems 

 that the diminution in the excavation of the valley is due to the erosion 

 which the current effects laterally on the cliffs of the left bank. 



