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Page:Popular Science Monthly Volume 24.djvu/36

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THE POPULAR SCIENCE MONTHLY.

sistency, the lava-flows have always been produced upon the slope or at the base of the mountain. At each of the orifices of issue the projections forced out by tumultuous jets of gas have formed adventitious cones of dimensions often considerable, like those of il Toppo, il Trippiti, and il Garifoli; and we may count some ten such cones around Epomeo, all of which have been centers of activity and furnished large flows.

The appearance of Ischia was relatively of recent date; it is not placed farther back than the older quaternary. The foundation of the island was begun by submarine eruptions, above which opened the crater of Epomeo, at first appearing above the surface of the sea as an annular reef, from which were thrown out jets of trachytic scoria. The island was raised up in successive stages by the accumulation of the projected matter around the orifice of issue. The proof of this is drawn from the fact that we may still find on the sides of Mount Epomeo, carried to a height of four hundred and seventy metres, masses of marine shells of species yet living in the Mediterranean, encased in clays that have resulted from the decomposition of trachytic tufas under water. The whole of this trachytic mass is itself established on marls and clays, including numerous remains of Mediterranean shells, and has evidently acquired its present relief within the historical epoch.

The most ancient of the recorded eruptions in Ischia was that of Montagnone, to which is ascribed the origin of the vast crater of regular form that still existed before the recent earthquake, in a state of perfect preservation, in the northwestern part of Ischia. About 470 B. C., successive eruptions at Point Comacchia gave rise to the vast flows of Manecoco and Bale, which extended far into the sea and prolonged the point to the north. Numerous efforts have been made since these ancient times to plant colonies on this unstable land, even then fertile and covered with a luxuriant vegetation.

Lyell, who made a long exploration of the island in 1828, relates that first the Erythreans and afterward the Chalcideans, who had settled in the island before the Christian era, were driven away by the incessant earthquakes and the mephitic exhalations escaping from every point. At a later time, 280 B. C., Hiero, king of Syracuse, tried to found a colony there, but it was soon driven away by a formidable explosion preceding the great flows of lava which gave rise to the masses now forming the promontories of Zaro and Camso.

The same fate befell the Grecian colonies which afterward tried at different times to occupy the island. The eruption that forced the retreat of the first Grecian colony gave rise to Monte Rosato, that cone of projections the sudden formation of which is comparable to that of Monte Nuovo. The last-named mountain was raised in September, 1538, in forty-eight hours, at Puzzuoli, after a succession of formidable shocks which occasioned great disasters in the Phlegrean