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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The Rock On This Road Presents A Geological Phenomenon, The More
Remarkable As The Existence Of Real Stratified Granite Has Long Been
Disputed.
Between La Trinchera and the Hato de Cambury a
coarse-grained granite appears, which, from the disposition of the
spangles of mica, collected in small groups, scarcely admits of
confounding with gneiss, or with rocks of a schistose texture.
This
granite, divided into ledges of two or three feet thick, is directed
52 degrees north-east, and slopes to the north-west regularly at an
angle of from 30 or 40 degrees. The feldspar, crystallized in prisms
with four unequal sides, about an inch long, passes through every
variety of tint from a flesh-red to yellowish white. The mica, united
in hexagonal plates, is black, and sometimes green. The quartz
predominates in the mass; and is generally of a milky white. I
observed neither hornblende, black schorl, nor rutile titanite, in
this granite. In some ledges we recognised round masses, of a blackish
gray, very quartzose, and almost destitute of mica. They are from one
to two inches diameter; and are found in every zone, in all granite
mountains. These are not imbedded fragments, as at Greiffenstein in
Saxony, but aggregations of particles which seem to have been
subjected to partial attractions. I could not follow the line of
junction of the gneiss and granitic formations. According to angles
taken in the valleys of Aragua, the gneiss appears to descend below
the granite, which must consequently be of a more recent formation.
The appearance of a stratified granite excited my attention the more,
because, having had the direction of the mines of Fichtelberg in
Franconia for several years, I was accustomed to see granites divided
into ledges of three or four feet thick, but little inclined, and
forming masses like towers, or old ruins, at the summit of the highest
mountains.* (* At Ochsenkopf, at Rudolphstein, at Epprechtstein, at
Luxburg, and at Schneeberg.
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