On Volcanoes. 221 



as the extinguished ones are in places that have become dry; and 

 those that are in a state of activity are never far from the sea. 

 The great quantity of caloric that is given out when the compo- 

 nent parts of water are condensed into that liquid is probably the 

 cause, or at least one of the causes. 



Besides the astonishing explosion of flames and smoke, of cin- 

 ders and burning rocks, the eruptions of volcanoes exhibit a dread- 

 ful phenomenon, in prodigious inundations of liquid fire, which 

 bear inevitable destruction with them. The Italians give the name 

 of lava to these fiery streams. This lava consists of a mixture of 

 stones, sand, earth, metallic substances, salt, SfC.., calcined, ren- 

 dered fusible, and vitrified by the fire of the volcanoes; but as the 

 mass of which it originally consists, is yery heterogeneous, the 

 lava, when cold, appears under various forms and colors. The 

 purest sort is. a hard, black, homogeneous, compact glass, and is 

 very abundant in the volcanic parts of Iceland, formed probably 

 of sand and the alkali of sea weed in the bed of the ocean. There 

 is another species which is hard, heavy, and compact, like mar- 

 ble; susceptible of a very fine polish, and converted, at Naples, 

 to a variety of domestic uses. There is another kind, which is a 

 grosser stone, commonly ash-colored, and used both for building, 

 and for paving the streets. That which is found on the surface is 

 still more gross and spongy, resembling the recrements of melted 

 metals. The violent eruption of Vesuvius, in 1767, is reckoned 

 the 27th since that which destroyed the cities of Herculaneum 

 and Pompeii, in the reign of the emperor Titus; and this eruption 

 of 1767, has been succeeded by nine others. Of the eruptions 

 of jJEtna, Mr. Holdenburg has given an historical account in the 

 Philosophical Transactions., No. xlviii. p. 97. A very great 

 eruption of this mountain took place in the year 1669. The 

 progress of the lava, or fiery deluge above described, was at the 

 rate of a furlong a day. It advanced into the sea 600 yards, and 

 was then a mile in breadth. It had destroyed, in forty days, the 

 habitations of 27,000 persons; and of 20,000 inhabitants of the 

 city of Catania, only 3,000 escaped. This inundation of liquid 

 fire, in its progress, met with a lake four miles in compass, and 

 not only filled it up, although it was four fathoms deep, but raised 

 it into a mountain. Borelli, an ingenious Neapolitan, has calcu- 

 lated, that the matter discharged at this eruption was sufficieni to 

 fill a space of 93,838,750 cubit paces. The lava which ran 

 from it, is fourteen miles in length, and in many parts, six in 

 breadth. A mixture of sulphur, filings of iron, and of water, buri- 

 ed at a certain depth below the earth's surface, will exhibit, in 

 miniature, all the appearances of a volcano. 



