162 ENTRANCE OF THE LLANOS. 



and mica-slate, which are auriferous. At San Juan 

 some of the rocks were gneiss passing into mica- 

 slate. On the south of this place the gneiss is con- 

 cealed beneath a deposit of serpentine, which, far- 

 ther south, passes into or alternates with green- 

 stone. This rock is now the principal one, and in 

 the midst of it rise the Morros of San Juan, com- 

 posed of crystalline limestone of a greenish-gray 

 .colour, and containing masses of dark-blue indurated 

 clay. Behind the Morros is another compact lime- 

 stone containing shells. The valley that descends 

 from San Juan to the llanos is filled with trap-rocks 

 lying upon green-slate. Lower down the rocks take 

 a basaltic aspect. Farther south the slates disap- 

 pear, being concealed under a trap-deposit of varied 

 appearance, but assuming an amygdaloidal charac- 

 ter, and on the margin of the plainis seen a forma- 

 tion of clinkstone or porphyry-slate. 



The travellers now entered the basin of the llanos. 

 The sun was almost in the zenith, the ground was 

 at the temperature of ] 18° or 123°, and the suffo- 

 cating heat was augmented by the whirls of dust 

 which incessantly arose from the surface of the 

 steril soil. All around the plains seemed to ascend 

 into the sky. The horizon in some parts was clear 

 and distinct, while in others it seemed undulating or 

 blended with the atmosphere. The trunks of palm- 

 trees, stripped of their foliage, and seen from afar 

 through the haze, resembled the masts of ships dis- 

 covered on the verge of the ocean. 



In order to give some interest to the narrative of 

 a journey across a tract of so monotonous an aspect, 

 Humboldt presents a general view of the plains of 

 America, contrasted with the deserts of Africa, and 

 the fertile steppes of Asia ; of which, however, the 

 most striking points alone can be here taken. There 

 is something awful and melancholy, he says, in the 

 uniform aspect of these savannas, where everything 

 seems motiojilcss, and v/hcre the shadow of a cloud 



