DEPTH OF THE VALLEYS. 317 



The first is so encompassed that no drop of water can escape 

 except by evaporation ; it is like the enclosed valley of 

 Mexico,* and of those numerous circular basins which have 

 been discerned in the moon, and which are surrounded by 

 lofty mountains. An immense alpine lake characterizes the 

 basin of Tiahuanaco or Titicaca ; this phenomenon is the 

 more worthy of attention, as in South America there are 

 scarcely any of those reservoirs of fresh water which are 

 found at the foot of the European Alps, on the northern and 

 southern slopes, and which are permanent during the season 

 of drought. The other basins of the Andes, for instance, those 

 of Jauja, the Upper Maranon, and Cauca, pour their waters 

 into natural canals, which may be considered as so many 

 crevices situated either at one of the extremities of the basin, 

 or on its banks, nearly in the middle of the lateral chain. I 

 dwell on this articulated form of the Andes, on those knots 

 or transverse ridges, because, in the continuation of the Andes 

 called the Cordilleras of the shore of Venezuela, we shall 

 find the same transverse dykes, and the same phenomena. 



The ramification of the Andes and of all the great masses 

 of mountains into several chains, merits particular considera- 

 tion in reference to the height more or less considerable of 

 the bottom of the enclosed basins, or longitudinal valleys. 

 Geologists have hitherto directed more attention to the suc- 

 cessive narrowing of these basins, their depth com pared with 

 the walls of rock that surround them, and the correspondence 

 between the re-entering and the salient angles, than to the 

 level of the bottom of the valleys. No precise measure has 

 yet fixed the absolute height of the three basins of Titicaca, 



occupy 23,300 square leagues of this surface, and the three basins con- 

 tained between lat. 6 and 20 south measure 7200 square leagues. De- 

 ducting 33,200 square leagues for the whole of the enclosed basins and 

 spnrs, we find, in latitude 65, the area of the Cordilleras elevated in 

 the form of walls, to be 25,700 square leagues, whence results (compre- 

 hending the knots, and allowing for the inflexion of the chains) an average 

 breadth of the Andes of 18 to 20 leagues. The valleys of Huallaga and 

 the Rio Magdalena are not comprehended in these 58,900 square leagues, 

 on account of the diverging direction of the chain, east of Cipoplaya and 

 Santa Fe de Bogota. 



* We consider it in its primitive state, without respect to the gap or 

 cleft of the mountains, known by the name of Desaghue de Hue* 

 huetoca. 



