Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 2 - By Alexander Von Humboldt And Aime Bonpland.
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Sometimes It Is Very Pure, Very Homogeneous, Of A
Dusky Olive-Green, And Of A Conchoidal Fracture:
Sometimes it is
veined, mixed with bluish steatite, of an unequal fracture, and
containing spangles of mica.
In both these states I could not discover
in it either garnets, hornblende, or diallage. Advancing farther to
the south (and we always passed over this ground in that direction)
the green of the serpentine grows deeper, and feldspar and hornblende
are recognised in it: it is difficult to determine whether it passes
into diabasis or alternates with it. There is, however, no doubt of
its containing veins of copper-ore.* (* One of these veins, on which
two shafts have been sunk, was directed hor. 2.1, and dipped 80
degrees east. The strata of the serpentine, where it is stratified
with some regularity, run hor. 8, and dip almost perpendicularly. I
found malachite disseminated in this serpentine, where it passes into
grunstein.) At the foot of this mountain two fine springs gush out
from the serpentine. Near the village of San Juan, the granular
diabasis appears alone uncovered, and takes a greenish black hue. The
feldspar intimately mixed with the mass, may be separated into
distinct crystals. The mica is very rare, and there is no quartz. The
mass assumes at the surface a yellowish crust like dolerite and
basalt.
In the midst of this tract of trap-formation, the Morros of San Juan
rise like two castles in ruins. They appear linked to the mornes of
St. Sebastian, and to La Galera which bounds the Llanos like a rocky
wall.
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