POPTTLA.TI P71E.TTTDIC\K. 
2 1C 
Eio 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 roc Ins ? 
1 shall content myself with observing, in general, that 
neither the granitic masses remote from the ancient bed or 
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 liio 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 hare 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 ta 
sleep on granite near the river; and many examples are 
cited of persons, who, after having passed the night oo 
these black and naked rocks, have awakened in the lnornii'o 
with a strong paroxysm of fever. Without entirely lending 
faith to the assertions of the missionaries and natives, me 
generally avoided the taxas nearas, and stretched ourseh' 1 ’- 
on the beach covered with white sand, when we found n° 
tree from which to suspend our hammocks. At Carichaum 
the village is intended to be destroyed, and its place changed 
merely to remove it from the ‘black rocks,’ or from a sim 
where, for a space of more than ten thousand square toise=> 
banks of bare granite form the surface. From sinm ar 
motives, which must appear very chimerical to the natu- 
ralists of Europe, the Jesuits Cilmo, Forneri, and Mel'"” 
removed a village of Jaruros to three different spots, be- 
tween the Eaudal of Tabaje and the Eio Anaveni. I mere y 
state these facts as they were related to me, because we « r 
almost wholly ignorant of the nature of the gaseous mixture 
