And the coincidence between distant volcanic
eruptions and those noises which the inhabitants of the Andes very
expressively term subterraneous thunders, or roarings.* (* Bramidos
y truenos subterraneos.) All these objects are comprehended in the
domain of the history of nature.
Though the narrow circle within which all certain traditions are
confined, does not present any of those general revolutions which
have heaved up the Cordilleras and buried myriads of pelagian
animals; yet Nature, acting under our eyes, nevertheless exhibits
violent though partial changes, the study of which may throw light
on the most remote epochs. In the interior of the earth those
mysterious powers exist, the effects of which are manifested at the
surface by the production of vapours, of incandescent scoriae, of
new volcanic rocks and thermal springs, by the appearance of new
islands and mountains, by commotions propagated with the rapidity
of an electric shock, finally by those subterranean thunders,*
heard during whole months, without shaking the earth, in regions
far distant from active volcanoes. (* In the town of Guanaxuato, in
Mexico, these thunders lasted from the 9th of January till the 12th
of February, 1784. Guanaxuato is situated forty leagues north of
the volcano of Jorullo, and sixty leagues north west of the volcano
of Popocatepetl. In places nearer these two volcanoes, three
leagues distant from Guanaxuato, the subterranean thunders were not
heard. The noise was circumscribed within a very narrow space, in
the region of a primitive schist, which approaches a
transition-schist, containing the richest silver mines of the known
world, and on which rest trap-porphyries, slates, and diabasis
(grunstein.))
In proportion as equinoctial America shall increase in culture and
population, and the system of volcanoes of the central table-land
of Mexico, of the Caribbee Islands, of Popayan, of los Pastos, and
Quito, shall be more attentively observed, the connection of
eruptions and of earthquakes, which precede and sometimes accompany
those eruptions, will be more generally recognized. The volcanoes
just mentioned, particularly those of the Andes, which rise above
the enormous height of two thousand five hundred toises, present
great advantages for observation. The periods of their eruptions
are singularly regular. They remain thirty or forty years without
emitting scoriae, ashes, or even vapours. I could not perceive the
smallest trace of smoke on the summit of Tunguragua or Cotopaxi. A
gust of vapour issuing from the crater of Mount Vesuvius scarcely
attracts the attention of the inhabitants of Naples, accustomed to
the movements of that little volcano, which throws out scoriae
sometimes during two or three years successively. Thence it becomes
difficult to judge whether the emission of scoriae may have been
more frequent at the time when an earthquake has been felt in the
Apennines. On the ridge of the Cordilleras everything assumes a
more decided character. An eruption of ashes, which lasts only a
few minutes, is often followed by a calm of ten years. In such
circumstances it is easy to mark the periods, and to observe the
coincidence of phenomena.
If, as there appears to be little reason to doubt, that the
destruction of Cumana in 1797, and of Caracas in 1812, indicate the
influence of the volcanoes of the West India Islands* on the
commotions felt on the coasts of Terra Firma, it may be desirable,
before we close this chapter, to take a cursory view of this
Mediterranean archipelago.
(* The following is the series of the phenomena: -
27th of September, 1796. Eruption in the West India Islands.
(Volcano of Guadaloupe).
November, 1796. The volcano of Pasto began to emit smoke.
14th of December, 1796. Destruction of Cumana.
4th of February, 1797. Destruction of Riobamba.
30th of January, 1811. Appearance of Sabrina Island, in the Azores.
The island enlarged very considerably on the 15th of June, 1811.
May, 1811. Commencement of the earthquakes in the island of St.
Vincent, which lasted till May 1812.
16th of December, 1811. Commencement of the commotions in the
valley of the Mississippi and the Ohio, which lasted till 1813.
December, 1811. Earthquake at Caracas.
26th of March, 1811. Destruction of Caracas. Earthquakes, which
continued till 1813.
30th of April, 1811. Eruption of the volcano in St. Vincent; and
the same day subterranean noises at Caracas, and on the banks of
the Apure.)
The volcanic islands form one-fifth of that great arc extending
from the coast of Paria to the peninsula of Florida. Running from
south to north, they close the Caribbean Sea on the eastern side,
while the greater West India Islands appear like the remains of a
group of primitive mountains, the summit of which seems to have
been between Cape Abacou, Point Morant, and the Copper Mountains,
in that part where the islands of St. Domingo, Cuba, and Jamaica,
are nearest to each other. Considering the basin of the Atlantic as
an immense valley* which separates the two continents, and where,
from 20 degrees south to 30 degrees north, the salient angles
(Brazil and Senegambia) correspond to the receding angles (the gulf
of Guinea and the Caribbean Sea), we are led to think that the
latter sea owes its formation to the action of currents, which,
like the current of rotation now existing, have flowed from east to
west; and have given the southern coast of Porto Rico, St. Domingo,
and the island of Cuba their uniform configuration. (* The valley
is narrowest (300 leagues) between Cape St. Roque and Sierra Leone.
Proceeding toward the north along the Coasts of the New Continent,
from its pyramidal extremity, or the Straits of Magellan, we
imagine we recognise the effects of a repulsion directed first
toward the north-east, then toward the north-west, and finally
again to the north-east.) This supposition of an oceanic irruption
has been the source of two other hypotheses on the origin of the
smaller West India Islands.
