38 THE OASES OF THE NORTH-WEST 



the sense of hollows made by erosion by running water. 

 They owe their formation to tectonic movements, 

 subsidences of the surface. The scanty rivers of the 

 arid Anacs are not capable of doing work of that kind. 

 When they enter the already formed bed of a valle, 

 they seem to be lost in the immense space. Often 

 they dry up in it, leaving behind the sediment and salts 

 with which the water was laden. In other places they 

 cut at right angles across the valle, escaping by narrow 

 breaches in it, while the depression continues its course 

 on either side, taking in sections of a number of in- 

 dependent streams. 



Opposed to the valle is the eroded ravine, carved 

 out by water, the quebrada. It opens upon a valle 

 with a V-shaped mouth, which widens out at the top, 

 and one can recognise at sight the various slopes and 

 the successive stages of erosion. Narrow and winding, 

 a level bed of shingle filling the entire base of the valley, 

 it rises rapidly toward the mountains and provides a 

 route from the valle to the puna. These valles, quebradas 

 and puna are the three inhabited zones of the Andes. 

 The first is the richest. The inhabitant of the valle, 

 proud of his comparative comfort, has for his neighbour 

 in the quebrada or the puna the coyada a contempt 

 such as one finds the inhabitants of the good land in 

 Europe feeling for the people in poorer districts. 



The narrower the valle, the less rain there is. The 

 observations give 112 millimetres of rain per year at 

 Tinogasta, 290 at Andalgala, and 200 at Santa Maria. 

 Salta and Jujuy have a much moister climate, and 

 have no less than 570 and 740 millimetres of rain 

 annually. This is because the eastern chain of the 

 Andes, which stretches from the Sierra de Santa Victoria 

 on the Bolivian frontier to Aconcagua, sinks lower 

 at the latitude of Salta, and lets in the moisture of the 

 Chaco to the heart of the zone of the Andes. The 

 rains of Salta and Jujuy are suspended during the winter, 

 but they are so heavy during the summer months 



