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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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. From the point where the littoral
Cordillera is linked with the Andes of New Grenada (longitude 71 1/2
degrees) we observe first the granitic mountains of Aroa and San
Felipe, between the rivers Yaracui and Tocuyo; these granitic
formations extend on the east of the two coasts of the basin of the
Valleys of Aragua, in the northern chain, as far as Cape Codera; and
in the southern as far as the mountains (altas savanas) of Ocumare.
After the remarkable interruption of the littoral Cordillera in the
province of Barcelona, granitic rocks begin to appear in the island of
Marguerita and in the isthmus of Araya, and continue, perhaps, towards
the Boca del Drago; but on the east of the meridian of Cape Codera the
northern chain only is granitic (of micaceous slate); the southern
chain is entirely composed of secondary limestone and sandstone.
If, in the granitic series, where a very complex formation, we would
distinguish mineralogically between the rocks of granite, gneiss, and
mica-slate, it must be borne in mind that coarse-grained granite, not
passing to gneiss, is very rare in this country. It belongs peculiarly
to the mountains that bound the basin of the lake of Valencia towards
the north; for in the islands of that lake, in the mountains near the
Villa de Cura, and in the whole northern chain, between the meridian
of Vittoria and Cape Codera, gneiss predominates, sometimes
alternating with granite, or passing to mica-slate. Mica-slate is the
most frequent rock in the peninsula of Araya and the group of Macanao,
which forms the western part of the island of Marguerita. 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.
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