Page:The fairy tales of science.djvu/351

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305
PLUTO'S KINGDOM.

Some of these volcanic islands are of a more permanent character ; as, for instance, the island of New Kaineni, near Santorin, in the Grecian Archipelago, which was raised up by a submarine volcanic eruption in 1707, and continues to the present day above water.

There are many mountains whose summits and depressions, though now covered with herbage, and, in some instances, the sites of villages and cities, bear a close resemblance to the cones and craters of active volcanoes; and whose constituent rocks are decidedly volcanic. Geologists apply to such mountains the term "extinct volcanoes" which, however, is intended to signify simply that no eruption has taken place from them for ages; but by no means implies that they will never be active again. Mount Vesuvius, which at some geological era had clearly been an active volcano, had slumbered for ages in a state of apparent extinction, when the terrible eruption that buried Herculaneum and Pompeii under a sea of volcanic ashes, revealed once more the true nature of the mountain.

In certain localities are found vents which emit only gaseous exhalations and aqueous vapour. Such vents or solfataras, as they are usually called, are properly looked upon in the light of half-extinct volcanoes, which may at any time suddenly burst forth again with all the terrific violence of true volcanic eruptions.

Extinct volcanoes are found not only in volcanic