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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In The
Region Of The Littoral Chain Of Venezuela, Where Granite Seems To
Constitute An Independent Formation From 15 To
16 leagues in length, I
saw no foreign or subordinate layers of gneiss, mica-slate or
primitive limestone.* (* Primitive limestone,
Everywhere so common in
mica-slate and gneiss, is found in the granite of the Pyrenees, at
Port d'Oo, and in the mountains of Labourd.)
The Sierra Parime is one of the most extensive granitic strata
existing on the globe;* but the granite, which is seen alike bare on
the flanks of the mountains and in the plains by which they are
joined, often passes into gneiss. (* To prove the extent of the
continuity of this granitic stratum, it will suffice to observe that
M. Leschenault de la Tour collected in the bars of the river Mana, in
French Guiana, the same gneiss-granites (with a little amphibole)
which I observed three hundred leagues more to the west, near the
confluence of the Orinoco and the Guaviare.) Granite is most commonly
found in its granular composition and independent formation, near
Encaramada, at the strait of Baraguan, and in the vicinity of the
mission of the Esmeralda. It often contains, like the granites of the
Rocky Mountains (latitude 38 to 40 degrees), the Pyrenees and Southern
Tyrol, amphibolic crystals,* disseminated in the mass, but without
passing to syenite. (* I did not observe this mixture of amphibole in
the granite of the littoral chain of Venezuela except at the summit of
the Silla of Caracas.) Those modifications are observed on the banks
of the Orinoco, the Cassiquiare, the Atabapo, and the Tuamini.
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