WATER ON THE PAMPA 169 



When we confine ourselves to studying the actual 

 conditions in which the deposits were formed, we are 

 first struck by the poverty of the hydrographic network 

 of the Pampa. It is slight except in the vicinity of 

 the sierras, where the slope of the ground is pronounced, 

 and in the eastern area, on the right bank of the Parana 

 and Entre Rios, where the climate is more humid, and 

 the streams flowing over an impermeable soil more 

 numerous. The only one of the streams born in the 

 Pampean sierras that reaches the Parana is the Rio 

 Tercero or Carcarana. All the others dwindle as they 

 descend, and disappear in a low-lying district marked 

 by lagoons which they only reach in time of flood. 

 The floods themselves never bring the Rio Cuarto 

 and the Rio Quinto and the Salado de Buenos Aires 

 into touch with each other. The waters of the northern 

 slope of the Sierra de Tandil, and even those of the 

 Sierra de Curumalal, on the other hand, reach the 

 Salado after the rains, either by way of streams which 

 drain the strings of lagoons, or by flood-sheets, which 

 spread over large areas. 



The watercourses of the plain are unstable in their 

 direction. The traces of their wanderings remain 

 in the form of stretches of alluvial sand crossing the 

 fine aeolian clays. These river sands sometimes spread 

 over extensive areas, the distribution depending upon 

 a hydrographic scheme which is now partially effaced. 

 The sands of the departments of General Lopez (south 

 of the Santa Fe province) and General Arenales (Buenos 

 Aires province), where the Salado is now developed, 

 were probably brought by the Rio Cuarto, and mark 

 an earlier junction of the Cuarto and the Salado. 

 These sands run along the Salado as far as the con- 

 fluence of the Saladillo, and the contrast between the 

 light soil and the clay of the bank of the Parand is so 



deposits may come next to each other in the same series, according 

 to the particular process of deposition, and that their alternation does 

 not imply a general change in the conditions of erosion. 



