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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Its
Height Is Computed At 2500 Toises, And Yet At Some Seasons It Is
Entirely Free From Snow.
An exact measure of this summit, situated in
very frequented latitudes, has for 25 years been desired in vain by
naturalists and geologists.), the culminant points of the whole globe
belong to continuous chains - to the Cordilleras of Central Asia and
South America.
In that part of the Andes with which I am best acquainted, between 8
degrees south latitude and 21 degrees north latitude, all the colossal
summits are of trachyte. It may almost be admitted as a general rule
that whenever the mass of mountains rises in that region of the
tropics much above the limit of perpetual snow (2300 to 2470 toises),
the rocks commonly called primitive (for instance, gneiss-granite or
mica-slate) disappear, and the summits are of trachyte or
trappean-porphyry. I know only a few rare exceptions to this law, and
they occur in the Cordilleras of Quito where the Nevados of Conderasto
and Cuvillan, situated opposite to the trachytic Chimborazo, are
composed of mica-slate and contain veins of sulphuret of silver. Thus
in the groups of detached mountains which rise abruptly from the
plains the loftiest summits, such as Mowna-Roa, the Peak of Teneriffe,
Etna and the Peak of the Azores, present only recent volcanic rocks.
It would, however, be an error to extend that law to every other
continent, and to admit, as a general rule, that, in every zone, the
greatest elevations have produced trachytic domes:
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