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constantly accumulated in the upper part of the 

 cavern. May we attribute the insalubrity of 

 the atmosphere to the same causes as in the 

 plains between Tivoli and Rome, to disengage- 

 ments of sulphuretted hydrogen*? Perhaps 

 also the mountainous lands, that are near the 

 Llanos of Monai, have a baneful influence on 

 the surrounding plains. The South-East winds 

 may bring to them the putrid exhalations, that 

 rise from the ravine of Viilegas, and from La 

 Sienega de Cabra, between Carora and Carache. 

 I am desirous of collecting every circumstance, 

 which has a relation to the salubrity of the air ; 

 for, in a matter so obscure, it is only by the 

 comparison of a great number of phenomena, 

 that we can hope to discover the truth. 



The barren yet feverous savannahs, that ex- 

 tend from Barquesimeto to the eastern shore of 

 the lake of Maracaybo, are partly covered with 

 cactus ; but the good Silvester cochineal, known 

 by the vague name of grana de Carora, comes 

 from a more temperate region, between Carora 

 and Truxillo, and particularly from the valley 



* Don Carlos del Pozo has discovered in this district, at 

 the bottom of the Quebrada de Moroturo, a stratum of clayey 

 earth, black, strongly soiling the fingers, emitting a strong 

 smell of sulphur, and inflaming spontaneously, when slightly 

 moistened and exposed for a long time to the rays of the 

 tropical Sun; the detonation of this muddy substance is 

 very violent. 



