246 POPITLAE PREJUDICE. 



Rio Congo, and an examination of the circumstances atten- 

 dant on this phenomenon of coloration, could alone "lead to 

 the complete solution of the problem we have discussed. 

 Is this phenomenon independent of the nature of the rocks ? 

 I shall content myself with observing, in general, that 

 neither the granitic masses remote from the ancient bed of 

 the Orinoco, but exposed during the rainy season to the 

 alternations of heat and moisture, nor the granitic rocks 

 bathed by the brownish waters of the Eio Negro, assume 

 the appearance of meteoric stones. The Indians say, " that 

 the rocks are black only where the waters are white." They 

 ought, perhaps, to add, " where the waters acquire great swift- 

 ness, and strike with force against the rocks of the banks." 

 Cementation seems to explain why the crusts augment so 

 little in thickness. 



I know not whether it be an error, but in the Missions 

 ef the Orinoco, the neighbourhood of bare rocks, and espe- 

 cially of the masses that have crusts of carbon, oxide of 

 iron, and manganese, are considered injurious to health. 

 In the torrid zone, still more than in others, the people 

 multiply pathogenic causes at will. They are afraid to 

 sleep in the open air, if forced to expose the face to the 

 rays of the full moon. They also think it dangerous to 

 sleep on granite near the river ; and many examples are 

 cited of persons, who, after having passed the night on 

 these black and naked rocks, have awakened in the morning 

 with a strong paroxysm of fever. Without entirely lending 

 faith to the assertions of the missionaries and natives, we 

 generally avoided the laxas negras, and stretched ourselves 

 on the beach covered with white sand, when we found no 

 tree from which to suspend our hammocks. At Carichana, 

 the village is intended to be destroyed, and its place changed, 

 merely to remove it from the ' black rocks,' or from a site 

 where, for a space of more than ten thousand square toises, 

 banks of bare granite form the surface. From similar 

 motives, which must appear very chimerical to the natu- 

 ralists of Europe, the Jesuits Olmo, Forneri, and Mellis, 

 removed a village of Jaruros to three different spots, be- 

 tween the Raudal of Tabaje and the Eio Anaveni. I merely 

 atate these facts as they were related to me, because we are 

 almost wholly ignorant of the nature of the gaseous mixtures 



