174 THE PLAIN OF THE PAMPAS 



depression appears in the centre, and it deepens until 

 it reaches the average level of the plain. Frequently 

 there is a little lake in it. From this point onward 

 the deformations are less rapid. The vegetation again 

 creeps over the ground, and the dune falls a prey to 

 the rains, which slowly reduce its mass. 



In the central Pampa, where the elevation is consider- 

 able, the dunes do not form separate circular patches, 

 but stretch in lines parallel to the valleys sometimes 

 in the heart of the valley, at other times backing against 

 one of its slopes. 



Far to the east of the zone of the quick dunes, in 

 the south of the Cordoba province and the centre of 

 the Buenos Aires province, there are certain soft undula- 

 tions, covered with vegetation, with a sandier soil 

 than that of the plain around them. These are dead 

 dunes. The district of the dead dunes is characterized 

 by the extreme irregularity of the surface-soil, the 

 humus, which gains in richness and depth, as a general 

 rule, as one goes eastward, because there it is in some 

 places covered by recent aeolian deposits. 



The distribution of the dead dunes is connected with 

 the stretches of river sand across the Pampa, which 

 have offered an easy victim to the winds. A line of 

 dead dunes follows the upper course of the Salado in 

 the district of Junin and Bragado. On the line from 

 Buenos Aires to San Luis one crosses it between Chaca- 

 buco and Vedia, and then one comes again upon the 

 horizontal plain, which has fresh dunes, only further 

 west, at 120 miles from Villa Mercedes. Its elevation is 

 so conspicuous on the level plain that the first breeders 

 who used its pasturage gave it the emphatic name of 

 the cerillada. D'Azara correctly appreciated the 

 nature of it. "It is, " he says, " only a dune of very 

 fine sand.'* It is only a few yards high. The dead 

 dunes of the Bolivar and Veinte Cinco de Mayo depart- 

 ments, which Parchappe described, have a more con- 

 spicuous relief, and in their disposition sometimes 



