Page:The fairy tales of science.djvu/336

 the beds snap, and rest in highly inclined planes about the mouth of the fissure.

It occurs also occasionally that both kinds of craters are found in one mountain.

The lava in a crater may be burning and boiling for years, without either an eruption of scoriæ or an overflow of lava taking place; a multitude of small conical vents are formed, however, in such cases, which rise out of the cooled surface of the melted lava, and incessantly emit volumes of smoke and sulphurous vapour. A vent of this kind is called in Europe a Fumerole or Moffet, and in Mexico a Hornito, or small oven. Other vents also are produced occasionally on the walls of the crater, or on the sides of the mountain, by the jets of scoriæ thrown up accumulating in falling round the mouth of the vent.

The number of volcanoes is very great, more than 300 of them being known to exist in the world at the present time, of which 24 are in Europe, 11 in Africa, 46 in Asia, 114 in America, and 108 in Oceania. Most of the islands of the Pacific, and many isles of the Atlantic and Indian Oceans, are also volcanic, or else composed of volcanic rocks.

The most ancient volcanoes known are Mount Vesuvius in Italy, Mount Ætna in Sicily, and Stromboli, one of the Lipari Islands, near Sicily. Stromboli is always burning, which has gained it the name of "the great lighthouse of the Mediterranean."