72 TUCUMAN AND MENDOZA 



and the rareness of frost. The mists which develop 

 at the foot of Aconcagua form a protecting mantle 

 above Tucuman which prevents nocturnal radiation. 

 The nearer one gets to the mountain, the later, rarer, 

 and lighter the frosts are. If, on the contrary, one 

 goes out some distance westward toward the plain, 

 the frost becomes more severe, and it is impossible 

 to grow sugar-cane. Not only the humidity, but the 

 contour also, has some influence on the changes of 

 temperature and the distribution of frost. The de- 

 pressions in which the cold air accumulates, in virtue 

 of the well-known meteorological phenomenon of inver- 

 sion of temperature, are more exposed than sloping 

 districts, where the air circulates regularly and freely. 

 The eastern limit of the zone spared by the frosts 

 passes about thirty-five miles from the foot of Acon- 

 cagua. It has only been made clear by experiment, 

 and one can still see there the traces of abandoned 

 plantations. 



The water-supply in the Tucuman district consists, 

 primarily, of numerous evenly flowing streams which 

 come down the eastern flank of Aconcagua (Lules, 

 Famailla, Angostura, Gastona, Medinas, etc.). They 

 join the Sali to the south of Tucuman. The Sali is 

 an irregular torrent which rises in the sub-Andean 

 depression to the north and Tucuman, and, after squeez- 

 ing Aguadita between the north-eastern extremity of 

 Aconcagua and the sub-Andean chain of Burruyacu, 

 enters the plain at Tucuman. It then flows southward, 

 meandering over a large bed of shingle in which it has 

 not had force enough to excavate a valley, and the 

 inclination of the land on its left bank (to the east) 

 is toward the east and south-east. The lands on the 

 right bank of the Sali are consequently better provided 

 with water than those on the left bank. The difference 

 is so marked that, as the estates on the right bank get 

 most of their supply elsewhere, the water of the Sali 

 nearly all goes to the left bank. In 1912 a siphon 



