DESCENT—ORES. 155 
nomenon which perhaps indicates that the moun- 
tain has been raised by a power applied from below. 
Relinquishing their design of passing the night in 
that valley, and having again found the path which 
they had cut through the wood, they soon arrived 
at the district of resinous shrubs, where they linger- 
ed so long collecting plants that darkness surprised 
them as they entered the savannah. The moon 
was up, but every now and then obscured by clouds. 
The guides who carried the instruments slunk off 
successively to sleep among the cliffs ; and it was not 
until ten that the travellers arrived at the bottom 
of the ravine, overcome by thirst and fatigue. 
During the excursion to the Silla, and in all their 
walks in the valley of Caraccas, they were very at= 
tentive to the indication of ores which they found 
in the gneiss mountains. In America that rock 
has not hitherto been found to be very rich in metals, 
the most celebrated mines of Mexico and Peru be- 
ing in primitive and transition slate, trap, porphyry, 
graywacke, and Alpine limestone. In several parts 
of the region now visited a small quantity of gold 
was found disseminated in veins of quartz, sulphu- 
retted silver, blue copper-ore, and leadglance ; but 
these deposites did not seem of any importance. In 
the group of the western mountains of Venezuela, 
the Spaniards, in 1551, attempted the gold mine of 
Buria, but the works were soon given up. In the vi- 
einity of Caraccas some had also been wrought, but 
to no great extent. In short, the mines here afforded 
little gratification to the cupidity of the conquerors, 
and were almost totally abandoned, those of Arva, 
near San Felipe el Fuerte, being the only ones in 
operation when Humboldt visited the country. 
