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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Von Buch And Raumer Have So Ably Demonstrated
In Their Excellent Papers On Landeck And The Riesengebirge, Namely,
Granite, Granite-
Gneiss, gneiss, gneiss-mica-slate, and mica-slate.
Geologists whose researches have been confined to a small tract of
land,
Having confounded these formations which nature has separated in
several countries in the most distinct manner, have admitted that the
gneiss and mica-slate alternate everywhere in superimposed beds, or
furnish insensible transitions from one rock to the other. These
transitions and alternating superpositions take place no doubt in
formations of granite-gneiss and gneiss-mica-slate; but because these
phenomena are observed in one region, it does not follow that in other
regions we may not find very distinct circumscribed formations of
granite, gneiss, and mica-slate. The same considerations may be
applied to the formations of serpentine, which are sometimes isolated,
and sometimes belong to the eurite, mica-slate, and grunstein.) Beyond
the town of Villa de Cura and the Cerro de Chacao the aspect of the
country presents greater geognostic variety. There are still eight
leagues of declivity from the table-land of Cura to the entry of the
Llanos; and on the southern slope of the mountains of the coast, four
different formations of rock cover the gneiss. We shall first give the
description of the different strata, without grouping them
systematically.
On the south of the Cerro de Chacao, between the ravine of Tucutunemo
and Piedras Negras, the gneiss is concealed beneath a formation of
serpentine, of which the composition varies in the different
superimposed strata.
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