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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On The West
Of Maniquarez The Mica-Slate Of The Peninsula Of Araya Loses By
Degrees Its Semi-Metallic Lustre;
It is charged with carbon, and
becomes a clay-slate (thonschiefer) even an ampelite (alaunschiefer).
Beds of granular limestone are
Most common in the primitive northern
chain; and it is somewhat remarkable that they are found in gneiss,
and not in mica-slate.
We find at the back of this granitic, or rather mica-slate-gneiss soil
of the southern chain, on the south of the Villa de Cura, a transition
stratum, composed of greenstone, amphibolic serpentine, micaceous
limestone, and green and carburetted slate. The most southern limit of
this district is marked by volcanic rocks. Between Parapara, Ortiz and
the Cerro de Flores (latitude 9 degrees 28 minutes to 9 degrees 34
minutes; longitude 70 degrees 2 minutes to 70 degrees 15 minutes)
phonolites and amygdaloids are found on the very border of the basin
of the Llanos, that vast inland sea which once filled the whole space
between the Cordilleras of Venezuela and Parime. According to the
observations of Major Long and Dr. James, trap-formations (bulleuses
dolerites and amygdaloids with pyroxene) also border the plains or
basin of the Mississippi, towards the west, at the declivity of the
Rocky Mountains. The ancient pyrogenic rocks which I found near
Parapara where they rise in mounds with rounded summits, are the more
remarkable as no others have hitherto been discovered in the whole
eastern part of South America. The close connection observed in the
strata of Parapara, between greenstone, amphibolic serpentine, and
amygdaloids containing crystals of pyroxene; the form of the Morros of
San Juan, which rise like cylinders above the table-land; the granular
texture of their limestone, surrounded by trap rocks, are objects
worthy the attention of the geologist who has studied in the southern
Tyrol the effects produced by the contact of poroxenic porphyries.* (*
Leopold von Buch.
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