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islands, of Mexico, of Guatimala, and of the table-land of Quito; when we examine either the reactions of
these different systems of volcanoes on one another, or the distance to which, by subterranean
communications, they at the same moment shake the Earth.
The study of volcanoes presents two very distinct branches; the object of one, simply
mineralogical, is the examination of the stony strata, altered or produced by the action of fire; from the
formation of the trachytes or trap porphyries, of basalts, phonolites, and dolerites,
since the sixteenth century, has made its appearance alternately in Palma, Teneriffe, and
Lancerota. Auvergne presents us with a whole system of volcanoes, the action of which has ceased;
but in the middle of a system of active volcanoes, for instance, in that of Quito, we must not
consider as an extinguished volcano a mountain, the crater of which is obstructed, and through
which the subterraneous fire has not issued for ages. Etna, the Eolian isles, Vesuvius, and Epomeo;
the peak of Teyde, Palma, and Lancerota; St. Michael, la Caldiera de Fayal, and Pico; St. Vincent,
St. Lucia, and Guadaloupe; Orizava, Popocatepec, Jorullo, and la Colima; Bombacho, the volcano
of Granada, Telica, Momotombo, Isalco, and the volcano of Guatimala; Cotopaxi, Tunguragua,
Pichincha, Antisana, and Sangay, belong to the same system of burning volcanoes; they are
generally ranged in rows, as if they had issued from a crevice, or vein not filled up; and, what is
very remarkable, their position is in some parts in the general direction of the Cordilleras, and in
others in a contrary direction. (Essai politique sur le Mexique, tom. 1, p. 253.