842 



VOLCANOES. 



water, and, occasionally flames. The ashes fell in 

 immense quantities, even at Naples. The sea re- 

 tired suddenly for '200 yards, and a portion of its 

 bed was left dry ; and the whole coast from Monte 

 Nuovo to beyond Pozzuoli was upraised to the 

 height of many feet above the bed of the Mediter- 

 ranean, and has ever since remained permanently 

 elevated. On the third of October, the eruption 

 ceased, so that the hill Monte Nuovo, which is 440 

 feet above the level of the bay, and a mile and a 

 half in circumference at its base, and which was 

 chiefly thrown up in a day and a night, was acces- 

 sible. The depth of its crater is 421 feet from the 

 summit of the hill, so that its bottom is only nine- 

 teen feet above the level of the sea. For nearly a 

 century after the birth of Monte Nuovo, Vesuvius 

 still continued in a state of tranquillity. Bracini, 

 who visited Vesuvius not long before the eruption 

 of 1631, gives the following description of its in- 

 terior. The crater was five miles in circumference, 

 and about 1000 paces deep. Its sides were covered 

 with brush wood, and at the bottom there was a 

 plain on which cattle grazed. In the woody parts, 

 wild boars frequently harboured. But at length 

 these forests and grassy plains were suddenly con- 

 sumed blown into the air, and their ashes scattered 

 to the winds. In December, 1631, seven streams 

 of lava poured at once from the crater, and over- 

 flowed several villages on the sides and at the foot 

 of the mountain. Great floods of mud were as de- 

 structive as the lava itself; for such (as often hap- 

 pens during these catastrophes) was the violence of 

 the rains produced by the evolution of aqueous va- 

 pour, ttiat torrents of water descended the cone, 

 and, becoming charged with impalpable volcanic 

 dust, rolled along loose ashes, acquiring such con- 

 sistency as to deserve the appellation of aqueous 

 lava. A brief period of repose ensued, which lasted 

 only until the year 1666, from which time to the 

 present, there has been a constant, series of erup- 

 tions, with rarely an interval of rest exceeding ten 

 years. The modern lavas of Vesuvius are charac- 

 terized by a large proportion of augite. When 

 they are composed of this mineral and feldspar, they 

 differ in composition but slightly from many of the 

 trap-rocks. (See Trap.) They are often porphy- 

 ritic, containing disseminated crystals of augite, 

 leucite, or some other mineral, imbedded in a more 

 earthy base. These porphyritic lavas are often ex- 

 tremely compact. In the lava currents of central 

 France (those of Viverais), the uppermost portion, 

 often forty feet or more in thickness, is an amor- 

 phous mass passing downwards into lava, irregularly 

 prismatic ; and under this there is a foundation of 

 regular and vertical columns, in that part of the 

 current which must have cooled most slowly. A 

 great variety of minerals are found in the lavas of 

 Vesuvius and Somma. Augite, leucite, feldspar, 

 mica, olivine, specular iron, idocrase, garnet and 

 sulphur are mos-t abundant. It is an extraordinary 

 tact, that, in an area of three square miles round 

 Vesuvius, a greater number of mineral species have 

 been found than in any spot, of the same dimen- 

 sions, on the surface of the globe. Many of these 

 are peculiar to this locab'ty. A small part of the 

 ejected matter, however, remains so near to the 

 Tolcanic orifice. A large portion of sand and scoriae 

 is borne by the winds and scattered over the sur- 

 roundiirg plains, or falls into the sea ; and much 

 more is swept down by torrents into the deep dur- 

 ing the intervals, often protracted for many cen- 

 turies, between eruptions. These horizontal de- 



posits of tufaceous matter become intermixed with 

 sediment of other kinds, and with shells and corals, 

 and, when afterwards raised, form rocks of a mixed 

 character, such as tufas, peperinos and volcanic 

 conglomerates. Besides the ejections which fall 

 on the cone, and that much greater mass which 

 finds its way gradually to the neighbouring sea, 

 there is a third portion, often of no inconsiderable 

 thickness, composed of alluvions, spread over flic 

 valleys and plains, at small distances from the vol- 

 cano. Immense volumes of aqueous vapour are 

 evolved from a crater during eruptions, and often 

 for a long time subsequently to the discharge of 

 scoriae and lava. These vapours are condensed in 

 the cold atmosphere surrounding the high volcanic 

 peak ; and heavy rains are caused sometimes even 

 in countries where, under other circumstances, such 

 a phenomenon is entirely unknown. The floods 

 thus occasioned sweep along impalpable dust and 

 light scoriae, till a current of mud is produced, which 

 is often more dreaded than an igneous stream, from 

 the greater velocity with which it moves. 



After Vesuvius, the most authentic records relate 

 to JEtna, which rises, near the sea, in solitary gran- 



deur, to the height of nearly 15,000 feet, the mass 

 consisting chiefly of volcanic matter ejected above 

 the surface of the water. The base of the cone is 

 eighty-seven miles, JEtna appears to have been in 

 activity from the earliest times of tradition. Thucy- 

 dides informs us that between the colonization of 

 Sicily by the Greeks and the commencement of the 

 Peloponnesian war (B. C. 431), three eruptions had 

 occurred. A great eruption occurred in the year 

 1669. The lava, after having overflowed fourteen 

 towns and villages, some having a population of 

 between 3000 and 4000 inhabitants, arrived, at 

 length, at the walls of Catania. These had been 

 purposely raised to protect the city ; but the burn- 

 ing flood accumulated till it rose to the top of the 

 rampart, which was sixty feet in height, and then 

 fell in a fiery cascade, and overwhelmed part of the 

 city. The wall, however, was not thrown down, 

 but was discovered long afterwards by excavations 

 made in the rock by the prince of Biscari ; so that 

 the traveller may now see the solid lava curling 

 over the top of the rampart, as if still in the very 

 act of falling. This great current had performed a 

 course of fifteen miles, before it entered the sea, 

 where it was still 600 yards broad and 40 feet deep. 

 A gentleman of Catania, named Pappalardo, desir- 

 ing to secure the city from the approach of the 

 threatening torrent, went out with a party of fifty 

 men, whom he had dressed in skins to protect them 

 from the heat, and armed them with iron crows and 

 hooks. They broke open one of the solid walls 

 which flanked the current near Belpasso, and im. 

 mediately forth issued a rivulet of melted matter, 

 which took the direction of Paterno ; but the inha- 

 bitants of that town being alarmed for their safety, 

 took up arms, and put a stop to further operations. 

 In 1811, the great crater testified, by its violent 

 detonations, that the lava had ascended to near the 

 summit of the mountain, by its central duct. A 



