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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Nowhere Can They Be Confounded
With The Grauwackes (Fragmentary Transition-Rocks) Which MM.
Boussingault And Rivero Found Along The Cordilleras Of New Grenada,
Bordering The Steppes On The West.
Does the want of fragments of
granite, gneiss and porphyry, and the frequency of petrified wood,* (*
The people of the country attribute those woods to the Alcornoco,
Bowdichia virgilioides (See Nova Gen.
Et Spec. Plant. volume 3 page
377), and to the Chaparro bovo, Rhopala complicata. It is believed in
Venezuela as in Egypt that petrified wood is formed in our times. I
found this dicotyledonous petrified wood only at the surface of the
soil and not inclosed in the sandstone of the Llanos. M. Caillaud made
the same observation on going to the Oasis of Siwa. The trunks of
trees, ninety feet long, inclosed in the red sandstone of Kifhauser
(in Saxony), are, according to the recent researches of Von Buch,
divided into joints, and are certainly monocotyledonous.) sometimes
dicotyledonous, indicate that those sandstones belong to the more
recent formations which fill the plains between the Cordillera of the
Parime and the coast Cordillera, as the molassus of Switzerland fills
the space between the Jura and the Alps? It is not easy, when several
formations are not perfectly developed, to determine the age of
arenaceous rocks. The most able geologists do not concur in opinion
respecting the sandstone of the Black Forest and of the whole country
south-west of the Thuringer Waldgebirge. M. Boussingault, who passed
through a part of the steppes of Venezuela long after me, is of
opinion that the sandstone of the Llanos of San Carlos, that of the
valley of San Antonio de Cucuta and the table-lands of Barquisimeto,
Tocuyo, Merida and Truxillo belong to a formation of old red sandstone
or coal. There is in fact real coal near Carache, south-west of the
Paramo de las Rosas.
Before a part of the immense plains of America was geologically
examined, it might have been supposed that their uniform and continued
horizontality was caused by alluvial soils, or at least by arenaceous
tertiary strata. The sands which in the Baltic provinces and in all
the north of Germany, cover coarse limestone and chalk, seem to
justify these systematic ideas, which have been extended to the Sahara
and the steppes of Asia. But the observations which we have been able
to collect sufficiently prove that both in the Old and the New World,
both plains, steppes, and deserts contain numerous formations of
different eras, and that these formations often appear without being
covered by alluvial deposits. Jura limestone, gem-salt (plains of the
Meta and Patagonia) and coal-sandstone are found in the Llanos of
South America; quadersandstein,* (* The forms of these rocks in walls
and pyramids, or divided in rhomboid blocks, seems no doubt to
indicate quadersandstein; but the sandstone of the eastern declivity
of the Rocky Mountains in which the learned traveller Mr. James found
salt-springs (licks), strata of gypsum and no coal, appear rather to
belong to variegated sandstone (buntersandstein).) a saliferous soil,
beds of coal,* (* This coal immediately covers, as in Belgium, the
grauwacke, or transition-sandstone.) and limestone with trilobites,*
(* In the plains of the Upper Missouri the limestone is immediately
covered by a secondary limestone with turritulites, believed to be
Jurassic, while a limestone with grypheae, rich in lead-ore and which
I should have believed to be still more ancient than oolitic
limestone, and analogous to lias, is described by Mr. James as lying
above the most recent formation of sandstone.
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