§ 19. SUBMARINE VOLCANOES. 837 



celebrated for its beauty and extreme fertility. In June 

 1759, alarming subterranean sounds were beard, and these 

 were accompanied by frequent earthquakes, which were 

 succeeded by others for several weeks, to the great conster- 

 nation of the neighbouring inhabitants. In September 

 tranquillity appeared to be re-established, when in the 

 night of the 28th the subterranean noise was again heard, 

 and part of the plain of the Malpays, from three to four 

 miles in extent, rose up like a mass of viscid fluid, in the 

 shape of a bladder or dome, to a height of nearly 1,700 

 feet ; flames issued forth, fragments of red-hot stones were 

 thrown to prodigious heights, and through a thick cloud of 

 ashes, illumined by volcanic fire, the softened surface of 

 the earth was seen to swell up like an agitated sea.* A 

 huge cone, above 500 feet high, with five smaller conical 

 mounds, suddenly appeared, and thousands of lesser cones 

 (called by the natives hornitos, or ovens) issued forth from 

 the upraised plain (Lign. 187). These consist of clay 

 intermingled with decomposed basalt, each cone being a 

 fumarole, or gaseous vent, from which issues thick vapour. 

 The central cone of Jurullo is still burning, and on one 

 side has thrown up an immense quantity of scorified and 

 basaltic lavas, containing fragments of primary rocks. Two 

 streams of the temperature of 186° of Fahrenheit, have 

 since burst through the argillaceous vault of the hornitos, 

 and now flow into the neighbouring plains. For many years 

 after the first eruption, the plains of Jorullo were uninha- 

 bitable from the intense heat that prevailed. 



19. Submarine Volcanoes. — Volcanic eruptions take 

 place alike indiscriminately, either on the land or beneath 

 the waters of the ocean. The igneous foci of southern 

 Italy are certainly not confined to the land, but extend 

 beneath the bed of the Mediterranean, of which the appear- 

 ance of new shoals and islands affords conclusive evidence. 

 * The tract consisted of porphyritic rocks. 

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