Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 3 - By Alexander Von Humboldt And Aime Bonpland.
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Is The Island Of Oruba (In Which Nuggets Of Native Gold Of
Considerable Size Have Been Found) Primitive?); Yet Amidst
This soil
of gneiss, inclosed mica-slate re-appears, often talcous in the Valle
de Caurimare, and in the ancient
Provincia de Los Mariches; at Cabo
Blanco, west of La Guayra; near Caracas and Antimano, and above all,
between the tableland of Buenavista and the valleys of Aragua, in the
Montana de las Cocuyzas, and at Hacienda del Tuy. Between the limits
here assigned to gneiss, as a predominant rock (longitude 68 1/2 to 70
1/2 degrees), gneiss passes sometimes to mica-slate, while the
appearance of a transition to granite is only found on the summit of
the Silla of Caracas.* (* The Silla is a mountain of gneiss like Adams
Peak in the island of Ceylon, and of nearly the same height.) It would
require a more careful examination than I was able to devote to the
subject, to ascertain whether the granite of the peak of St. Gothard,
and of the Silla of Caracas, really lies over mica-slate and gneiss,
or if it has merely pierced those rocks, rising in the form of needles
or domes. The gneiss of the littoral Cordillera, in the province of
Caracas, contains almost exclusively garnets, rutile titanite and
graphite, disseminated in the whole mass of the rock, shelves of
granular limestone, and some metalliferous veins. I shall not decide
whether the granitiferous serpentine of the table-land of Buenavista
is inclosed in gneiss, or whether, superposed upon that rock, it does
not rather belong to a formation of weisstein (heptinite) similar to
that of Penig and Mittweyde in Saxony.
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