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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It May Be Said In General That The Granitic Zone
(Including Under That Denomination The Rocks Of Granite, Gneiss And
Mica-slate) follows the direction of the Cordillera of the shore of
Venezuela, and belongs exclusively to that Cordillera and
The group of
the Parime mountains; since it nowhere pierces the secondary and
tertiary strata in the Llanos or basin of the Lower Orinoco. Thence it
results that the same formations do not constitute the region of
plains and that of mountains.
If we may be allowed to judge of the structure of the whole Sierra
Parime, from the part which I examined in 6 degrees of longitude, and
4 degrees of latitude, we may believe it to be entirely composed of
gneiss-granite; I saw some beds of greenstone and amphibolic slate,
but neither mica-slate, clay-slate, nor banks of green limestone,
although many phenomena render the presence of mica-slate probable on
the east of the Maypures and in the chain of Pacaraina. The geological
formation of the Parime group is consequently still more simple than
that of the Brazilian group, in which granites, gneiss and mica-slate
are covered with thonschiefer, chloritic quartz (Itacolumite),
grauwacke and transition-limestone; but those two groups exhibit in
common the absence of a real system of secondary rocks; we find in
both only some fragments of sandstone or silicious conglomerate. In
the littoral Cordillera of Venezuela the granitic formations
predominate; but they are wanting towards the east, and especially in
the southern chain, where we observe (in the missions of Caripe and
around the gulf of Cariaco) a great accumulation of secondary and
tertiary calcareous rocks.
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