Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 1 - By Alexander Von Humboldt And Aime Bonpland.
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At Cumana It
Constantly Precedes Them, While At Quito, And Recently At Caracas,
And In The West India Islands, A Noise Like The Discharge Of A
Battery Was Heard A Long Time After The Shocks Had Ceased.
A third
kind of phenomenon, the most remarkable of the whole, is the
rolling of those subterranean thunders, which last several months,
without being accompanied by the least oscillatory motion of the
ground.* (* The subterranean thunders (bramidos y truenos
subterraneos) of Guanaxuato.
The phenomenon of a noise without
shocks was observed by the ancients. - Aristot. Meteor. lib. 2 (ed.
Duval page 802). Pliny lib. 2 c. 80.)
In every country subject to earthquakes, the point at which,
probably owing to a particular disposition of the stony strata, the
effects are most sensibly felt, is considered as the cause and the
focus of the shocks. Thus, at Cumana, the hill of the castle of San
Antonio, and particularly the eminence on which stands the convent
of St. Francis, are believed to contain an enormous quantity of
sulphur and other inflammable matter. We forget that the rapidity
with which the undulations are propagated to great distances, even
across the basin of the ocean, proves that the centre of action is
very remote from the surface of the globe. From this same cause no
doubt earthquakes are not confined to certain species of rocks, as
some naturalists suppose, but all are fitted to propagate the
movement. Keeping within the limits of my own experience I may here
cite the granites of Lima and Acapulco; the gneiss of Caracas; the
mica-slate of the peninsula of Araya; the primitive thonschiefer of
Tepecuacuilco, in Mexico; the secondary limestones of the
Apennines, Spain, and New Andalusia; and finally, the trappean
porphyries of the provinces of Quito and Popayan.* (* I might add
to the list of secondary rocks, the gypsum of the newest formation,
for instance, that of Montmartre, situated on a marine calcareous
rock, which is posterior to the chalk.
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