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Curiosities Respecting Earthqakes

this northern coast, which is composed of mica-slate, built their huts on a motionless earth; a gulf three or four thousand fathoms in breadth separated them from a plain covered with ruins, and overturned by earthquakes. This security, founded on the experience of several ages, has vanished; and since the fourteenth of December, 1797, new communications appear to have been opened in the interior of the globe. At present the peninsula of Araya is not merely subject to the agitation of the soil of Cumana; the promontory of mica-slate is become in its turn a particular centre of the movements. The earth is sometimes strongly shaken at the village of Marinaquez, when on the coast of Cumana the inhabitants enjoy the most perfect tranquillity. The gulf of Cariaco nevertheless is only sixty or eighty fathoms deep. "It is thought, from observations made both on the continent and in the islands, that the western and southern coasts are most exposed to shocks. This observation is connected with the ideas which geologists have long formed of the position of the high chains of mountains, and the direction of their steepest declivities: the volcanic phenomena of the Cordilleras and Caraccas, and the frequency of the oscillations on the eastern and northern coast of Terra Firma, in the gulf of Paria, at Carupano, at Cariaco, and at Cumana, are proofs of the certainty of this opinion. In New Andalusia, as well as in Chili and Peru, the shocks follow the course of the shore, and extend but little inland. This circumstance, as we shall soon find, indicates an intimate connection between the causes that produce earthquakes and volcanic eruptions. If the earth was most agitated on the coasts, because they are the lowest part of the land, why should not the oscillations be equally strong and frequent on those vast savannas or meadows, which are scarcely eight or ten toises above the level of the ocean? "The earthquakes of Cumana are connected with those of the West India Islands; and it has even been suspected, that they have some connection with the volcanic phenomena of the Cordilleras of the Andes. On the fourth of November, 1797, the soil of the province of Quito underwent such a destructive commotion, that, notwithstanding the extreme thinness of the population of that country, near forty thousand natives perished, buried under the ruins of their houses, swallowed up in the crevices, or drowned in lakes that were suddenly formed. At the same period, the inhabitants of the eastern Antilles were alarmed by shocks, which continued during eight months, when the volcano of Guadaloupe threw out pumice stones, ashes, and gusts of sulphureous vapours This eruption of the twenty-seventh of September, during which very long-continued subterraneous noises were heard, was followed on the fourteenth of December by the great earthquake quake of Cumana. Another volcano of the West India Islands, that of St. Vincent's, has lately given a fresh instance of these extraordinary connections. This volcano had not emitted flames since 1718, when they burst forth anew, in 1812. The total ruin of the city of Caraccas preceded this explosion thirty-five days, and violent oscillations of the ground were felt, both in the islands, and on the coasts of Terra Firma. "It has long been remarked, that the effects of great earthquakes extend much farther than the phenomena arising from burning volcanoes. In studying the physical revolutions of Italy, and carefully examining the series of the eruptions of Vesuvius and Etna, we can scarcely recognize, notwithstanding the proximity of these mountains, any traces of simultaneous action. It is, on the contrary, undeniable, that at the period of the last and preceding destruction of Lisbon, the sea was violently agitated even as far as the New World, for instance, at the island of Barbadoes, more than twelve hundred leagues distant from the coasts of Portugal. "Several facts tend to prove, that the causes which produce earthquakes have a near connection with those that act in volcanic eruptions. We learnt at Pasto, that the column of black and thick smoke, which in 1797 issued for several months from the volcano near this shore, disappeared at the very hour when, sixty leagues to the south, the towns of Riobamba, Hambato, and Tacunga, were overturned by an enormous shock. When, in the interior of a burning crater, we are seated near those hillocks formed by ejections of scoria and ashes, we feel the motion of the ground several seconds before each partial eruption takes place. We observed this phenomenon at Vesuvius in 1805, while the mountain threw out scoria; we were witnesses of it in 1812, on the brink of the immense crater of Pichincha, from which nevertheless at that time clouds of sulphureous acid vapours only issued. "Every thing in earthquakes seems to indicate the action of elastic fluids seeking an outlet to spread themselves in the atmosphere. Often, on the coasts of the South Sea, the action is almost instantaneously communicated from Chili to the gulf of Guayaquil, a distance of six hundred leagues; and, what is very remarkable, the shocks appear to be so much the stronger, as the country is more distant from burning volcanoes. The granitic mountains of Calabria, covered with very recent breccia, the calcareous chain of the Apennines, the country of Pignerol, the coasts of Portugal and Greece, and those of Peru and Terra Firma, afford striking proofs of this assertion. The globe, it may be said, is agitated with greater force, in proportion as the surface has a smaller number of funnels communicating with the caverns of the interior. At Naples and Messina, at the foot of Cotopaxi and of Tunguragua, earthquakes are dreaded only when vapours and flames do not issue from the crater. In the kingdom of Quito, the great catastrophe of Riobamba, which we have before mentioned, has led several well-informed persons to think, that this unfortunate country would be less often desolate, if the subterraneous fire would break the porphyritic dome of Chimborazo; and this colossal mountain should become a burning volcano. At all times analogous facts have led to the same hypothesis. The Greeks, who, like ourselves, attributed the oscillations of the ground to the action of elastic fluids, cited, in favour of their opinion, the total cessation of the shocks at the island of Eubea, by the opening of a crevice in the the Lelantine plain."