WATERING THE VINEYARDS 83 



north-west hardly know — the problem of drainage — is 

 of paramount importance at San Juan and Mendoza, 

 as far as a large part of the irrigated surface is con- 

 cerned. The water infiltrating into the soil forms a 

 subterranean sheet which approaches more or less 

 to the surface according to the topography. It comes 

 to the surface at the foot of the cone, where the slope 

 diminishes and the cone gradually passes into the 

 plain. Hence the cone has, at its base, a belt of marshes 

 (cienagas), and sometimes a line of good springs [bar- 

 bollon). At San Juan, if you move far enough away 

 to get a comprehensive view of the whole of the estates, 

 you see that they occupy the middle belt, half-way 

 down the cone, the top of which is composed of coarse 

 shingle, while the bottom is too wet. The advance 

 of the plots upward and the steadily increasing 

 use of the available water tends to raise the level 

 of the underground sheet and enlarge the area of 

 marsh. 



There is a fine black soil, very fertile when it is 

 drained, and no irrigation is needed ; as it is possible, 

 according to the depth of the drainage-trenches, to 

 regulate the level of the underground water so as to 

 make it reach and feed the roots. The draining of the 

 marshes, again, opens up a field for the further expansion 

 of the estates, especially at San Juan, where it has 

 scarcely begun. Moreover, the water that is obtained 

 by draining the marshes enables them to create new 

 irrigated estates further on. At Mendoza there is 

 already a considerable area irrigated by drainage-canals 

 {desagile). 



The level of the water m the marshes sinks in the 

 summer and rises in winter, at the time when the 

 irrigation of the upper districts is suspended or greatly 

 reduced, and when the surplus of the acequias, which 

 the fields no longer take, flows or infiltrates downward 

 in any way that it can. Thus, contrary to the torrent 

 itself, it is in winter that the drainage-canals are at 



