SCULPTURE BY WIND 173 



parallel valleys, with few ramifications, generally lying 

 south-west to north-east, open to the east upon the 

 Pampean plain about the frontier of the Buenos Aires 

 province. On the other hand, the southernmost of 

 them begin at the foot of the Ventana, and seem to blend 

 in the south-west with a general depression that is 

 still little known, though it appears to end at the 

 bottom of the estuary of Bahia Blanca. None of 

 them has permanent running water. ^ The origin 

 of the dry valleys of the tosca is one of the most obscure 

 problems of the morphology of the Pampean plain. 

 Perhaps they are due to aeolian erosion, like the depres- 

 sions which are found on the plateau of the Colorado 

 and the Rio Negro further south. 



The action of the wind in shaping the landscape is 

 more clearly seen in the formation of the dunes. When 

 one starts from Buenos Aires or Rosario, and gets 

 beyond the region of the level Pampas, the dunes are 

 the first feature to meet the eye on the surface of the 

 plain. The first fresh dunes are encountered at Carlota, 

 on the line from the Rio Cuarto ; at Lavalle on the line 

 from Villa Mercedes ; and at Trenque Lauquen on the 

 line from Toay. The dunes spread northward as far 

 as the latitude of Mar Chiquita, but do not enter the 

 Chaco. They are also found in parts of the scrub on 

 the west, but their proper domain is the western border 

 of the steppe, the upper part of the plain at the foot of 

 the Sierra de Cordoba, the south of the San Luis province, 

 and the central Pampa. 



Any accident that causes the vegetal covering to 

 disappear, such as the tread of cattle near a drinking 

 place or an enclosure, is enough to set aeolian erosion 

 at work. The wind raises the sand in a sort of tossing 

 sea. Then the dune assumes a circular shape. A 



' The surface of the tosca tableland is further punctuated by a 

 great number of closed depressions of various depths : long tunnels 

 (dolines) which can only be explained, apparently, as an effect of 

 the dissolving of the limestone by water. 



