Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 1 - By Alexander Von Humboldt And Aime Bonpland.
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In Our Geognostical Observation Of The Country
Round Caracas We Found Gneiss, And Mica-Slate Containing Beds Of
Primitive Limestone.
The strata are scarcely more fractured or
irregularly inclined than near Freyburg in Saxony, or wherever
mountains of primitive formation rise abruptly to great heights.
I
found at Caracas neither basalt nor dorolite, nor even trachytes or
trap-porphyries; nor in general any trace of an extinguished
volcano, unless we choose to regard the diabases of primitive
grunstein, contained in gneiss, as masses of lava, which have
filled up fissures. These diabases are the same as those of
Bohemia, Saxony, and Franconia;* (* These grunsteins are found in
Bohemia, near Pilsen, in granite; in Saxony, in the mica-slates of
Scheenberg; in Franconia, between Steeben and Lauenstein, in
transition-slates.) and whatever opinion may be entertained
respecting the ancient causes of the oxidation of the globe at its
surface, all those primitive mountains, which contain a mixture of
hornblende and feldspar, either in veins or in balls with
concentric layers, will not, I presume, be called volcanic
formations. Mont Blanc and Mont d'Or will not be ranged in one and
the same class. Even the partisans of the Huttonian or volcanic
theory make a distinction between the lavas melted under the mere
pressure of the atmosphere at the surface of the globe, and those
layers formed by fire beneath the immense weight of the ocean and
superincumbent rocks. They would not confound Auvergne and the
granitic valley of Caracas in the same denomination; that of a
country of extinct volcanoes.
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