LAKE OF VALENCIA. 149 



Mariara, the Devil's Wall, and the coast chain, these 

 rocky hills were shoals or islets." 



But the Lake of Valencia is remarkable for other 

 circumstances than its beauties. From a careful ex- 

 amination, Humboldt was convinced that in very re- 

 mote times, the whole valley, from the mountains 

 of Cocuyza to those of Torito and Nirgua, and from 

 the Sierra of Mariara to that of Guigue, Guacimo, 

 and La Palma, had been filled with water. The 

 form of the promontories and their abrupt slopes in- 

 dicate the shores of an alpine lake. The same little 

 shells (helicites and valvatae) which occur at the 

 present day in the Lake of Valencia are found in 

 layers three or four feet thick in the heart of the 

 country, as far as Turmero and La Concesion, near 

 Victoria. These facts prove a retreat of the waters ; 

 but no evidence exists that any considerable diminu- 

 tion of them has taken place in recent times, al- 

 though within the thirty years preceding Humboldt's 

 visit the gradual desiccation of this great basin had 

 excited general attention. This, however, is not de-- 

 pendent upon subterranean channels, as some sup-, 

 pose, but upon the effects of evaporation, increased 

 by the changes operated upon the surftice of the 

 country. Forests, by sheltering the soil from the 

 direct action of the sun, diminish the waste of moist- 

 ure ; consequently, when they are imprudently de- 

 stroyed, the springs become less abundant, or are 

 entirely dried up. Till the middle of the last cen- 

 tury the mountains that surround the valleys of 

 Aragua were covered with woods, and the plains with 

 thickets, interspersed with large trees. As cultiva- 

 tion increased, the sylvan vegetation suffered ; and 

 as the evaporation in this district is excessively pow- 

 erful, the httle rivers were dried up in the lower 

 portion of their course during a great part of the 

 year. The land that surrounds the lake being quite 

 flat and even, the decrease of a few inches in the 

 level of the water exposed a vast extent of ground, 



N2 



