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 Formations Of The Llanos Are, First, A
Sandstone Or Conglomerate, With Rounded Fragments Of Quartz, Lydian
Stone, And Kieselschiefer,
United by a ferruginous clayey cement,
extremely tenacious, olive-brown, sometimes of a vivid red; second, a
compact limestone (between
Tisnao and Calabozo) which, by its smooth
fracture and lithographic aspect, approaches the Jura limestone:
third, alternate strata of marl and lamellar gypsum (Mesa de San
Diego, Ortiz, Cachipo). These three formations appeared to me to
succeed each other in the order I have just described, the sandstone
inclining in a concave position, northward, on the transition-slates
of Malpasso, and southward, on the gneiss-granite of Parime. As the
gypsum often immediately covers the sandstone of Calabozo, which
appeared to me, on the spot, to be identical with our red sandstone, I
am uncertain of the age of its formation. The secondary rocks of the
Llanos of Cumana, Barcelona and Caracas occupy a space of more than
5000 square leagues. Their continuity is the more remarkable, as they
appear to have no existence, at least on the east of the meridian of
Porto Cabello (70 degrees 37 minutes) in the whole basin of the Amazon
not covered by granitic sands. The causes which have favoured the
accumulation of calcareous matter in the eastern region of the coast
chain, in the Llanos of Venezuela (from 10 1/2 to 8 degrees north),
cannot have operated nearer the equator, in the group of the mountains
of the Parime and in the plains of the Rio Negro and the Amazon
(latitude 1 degree north to 1 degree south). The latter plains,
however, furnish some ledges of fragmentary rocks on the south-west of
San Fernando de Atabapo, as well as on the south-east, in the lower
part of the Rio Negro and the Rio Branco.
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