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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Fact, M. Defrance, In A Work* Full Of New And Ingenious Ideas, Not
Only Recognizes This Preponderance Of The
Univalves in the number of
the species, but also observes that out of 5500 fossil univalve,
bivalve and multivalve shells,
Contained in his rich collections,
there are 3066 univalve, 2108 bivalve, and 326 multivalve; the
univalve fossils are therefore to the bivalve as three to two. (*
Table of Organized Fossil Bodies, 1824.)
13. FORMATION OF PYROXENIC AMYGDALOID AND PHONOLITE, BETWEEN ORTIZ AND
CERRO DE FLORES.
I place pyroxenic amygdaloid and phonolite (porphyrschiefer) at the
end of the formations of Venezuela, not as being the only rocks which
I consider as pyrogenous, but as those of which the volcanic origin is
probably posterior to the tertiary strata. This conclusion is not
deduced from the observations I made at the southern declivity of the
littoral Cordillera, between the Morros of San Juan, Parapara and the
Llanos of Calabozo. In that region local circumstances would possibly
lead us to regard the amygdaloids of Ortiz as linked to a system of
transition rocks (amphibolic serpentine, diorite, and carburetted
slate of Malpasso); but the eruption of the trachytes across rocks
posterior to the chalk (in the Euganean Mountains and other parts of
Europe) joined to the phenomenon of total absence of fragments of
pyroxenic porphyry, trachyte, basalt and phonolite (The fragments of
these rocks appear only in tufas or conglomerates which belong
essentially to basaltic formations or surround the most recent
volcanoes. Every volcanic formation is enveloped in breccia, which is
the effect of the eruption itself.), in the conglomerates or
fragmentary rocks anterior to the recent tertiary strata, renders it
probable that the appearance of trap rocks at the surface of the earth
is the effect of one of the last revolutions of our planet, even where
the eruption has taken place by crevices (veins) which cross
gneiss-granite, or the transition rocks not covered by secondary and
tertiary formations.
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