-e sometimes dormant for a series of years, but the vicinity of the former, has been constantever since two hundred and ninety-two years hristian era, being upwards of two thousand llo has continued to emit flames ever since ich time it was elevated from the plain on nds. But Vulcano suffered no eruption for ries, and we have already noticed that Ischia for seventeen hundred years. arances which attend volcanic eruptions, are some instances, flames issue suddenly and the cone, affording only splendid picturesque But in others, the scene is the most terrific g of which the imagination can conceive. For ptions we must, however, refer to particular account of which will follow. tions of Vesuvius and Ætna, these mountains midst of a highly cultivated people, are best Indeed, from the time of Pliny, to the present ve been the subjects of interesting and learned ers, or at other t in the island of B pear PA any lava, We shall descri only those which h entific interest, or fects, either with res or the quantity of 1 Eruptions of Vel this Italian mountai scription, was in A culaneum and Pom that eruption; the eject mud. But it is emitted lava, since t this substance. T any account, wa eruption on record. which have taken described by scienti Some of them pr in the form and app of the the land along the country many villages, and 1, the first appearance of an eruption consists of smoke rising to a great height, and then t in the form which Pliny compared to that e. This is followed by explosions from the rembling of the earth, or perhaps by its alterand falling; the whole being attended by a bterranean sound, forming both an eruption quake. Flame is then seen to issue from the ed by red hot stones, often thrown to the veral hundred feet, producing in the night, t and terrific phenomena, so often described. emission of the black smoke, and before the , there are often the most vivid flashes of hich add greatly to the splendor of the scene. phenomena have existed for a longer or a the melted lava, rising to the edge of the craer it, and runs down the side of the mountain a below. This is in the form of a torrent of ften narrow, but sometimes many miles in ometimes proceeds rapidly, but more often ast portions of lava passing over the first, in les. Sometimes, or from some mountains, h smoke, and but little lava; while from oth cer in other times, the crater vomits rivers of melted ithout smoke or flame. ruption of lava is often followed by showers of ich consist of finely divided particles of lava, and e often wafted by the wind, to the distance of seve. -ed miles. uantity of matter ejected by some volcanoes, is gly great. Brieslak, an Italian geologist, calcuthe quantity of lava which flowed from a volcano and of Bourbon, in 1796, amounted to 45,000,000 eet; and that the quantity from the same, in 1787, 00,000 of cubic feet; and during one eruption Ountain in Iceland, the lava flowed about ninety ing a width of at least twenty miles, and in some depth of several hundred feet. PARTICULAR ERUPTIONS. all describe a few volcanic eruptions, selecting - which have been the subject of peculiar, or scierest, or which have produced extraordinary ef r with respect to the destruction they have caused, ntity of lava they have ejected. ons of Vesuvius. The most ancient eruption of mountain, of which there is any particular dewas in A. D. 79, at which time the cities of Herand Pompeii were destroyed. It does not apany lava, or melted matter was emitted at this the ejected substances being sand, ashes, and t it is certain that this mountain had previously va, since the streets of these cities are paved with nce. The first stream of lava, of which there count, was in 1036, being the sixth or seventh n record. From this period, all the eruptions ve taken place, are recorded, and many of them by scientific men, and at great length. them produced considerable changes, not only and appearance of the mountain itself, but also antry in the vicinity. That of 1538, elevated long the coast of Nex mony fact height. A description and figure of this moungiven hereafter. out the end of the 18th century to 1822, the of Vesuvius had been filling up gradually, hich boiled up from below, so that the bottom y presented a kind of rocky plain covered with s, and hillocks of volcanic matter. But durer year, in the month of October, the form and of the ancient crater was entirely changed. ons at that time were so violent during twenty break up, and throw out the whole of that acmass, leaving an immense gulf, or chasm, about in circumference, and in some parts 2000 feet the same time about 800 feet in height, of the ne or top of the ancient crater, was carried e explosions, so that Vesuvius became reduced rom about 4200 to 3400 feet.-Forbes in Ed. d Scrope in Jour. of Science. ding the mountain, its sloping sides are found d with loose materials intermixed with each ut the slighest order, and just as they fell from But on arriving at the crater itself, the beprised to find that every thing is there arranged perfect symmetry, and that the materials are regular undulating strata. These consist of yers, composed of lava, sand, ashes, and scoria, stinct beds, and alternating with each other. resulted from the different colors, and coarsee materials, and which severally remain in the on and succession as they fell from the air durrent eruptions. parts of the crater, are seen dykes, or veins of ct matter intersecting the above described strata. on the outside of the cone, and being harder canic matter through which they have passed, resisted decomposition, and therefore project rface. ve undoubtedly been formed by the filling up res with liquid matter forced up from below. iod they were formed is unknown, but if such formed by the cooling, and consequent shrinkrater, after an eruption, it is probable that at uption, these are filled with the fused matter, so that some eruption. In the adjoinin These vapors, bei 1. some of these veins may be formed at every Fig. 5. d adjoining diagram, fig. 5, from Lyell's Geology, ns or dykes, are represented, as also is the cone r of Vesuvius, and a part of the ancient Somma, ppeared in 1828. a, Mount Somma, or the rethe ancient cone of Vesuvius; b, the Pedamentina, like projection, enclosing the base of the recent esuvius on the south side; c, Atrio del Cavallo, because travellers leave their mules there, when are to ascend to the cone, on foot; de, the crater us left by the eruption of 1822; f, a small cone ttom of the crater, thrown up in 1828. In the many craters there are several of these small ich are constantly emitting steam, or smoke, imes throw up lava; gg, dykes intersecting the ata of Somma; h h, dykes intersecting the reof Vesuvius. se volumes of steam, or aqueous vapor, are om the craters of volcanoes, during eruptions. pors, being condensed by the surrounding atoften fall down in torrents of rain. The rain s the volcanic dust from the air, and sweeps which had fallen on the declivity of the mouna torrent of mud is produced. Such torrents ich to be dreaded as the inundations of mud sometimes thrown from the volcano, and with ion of the heat, are more disastrous than burnbeing much more rapid in their descent. In of these mud streams descended from Vesuvius, ed into the villages of St. Sebastian, and Massa, ng the streets, and some of the houses, it sufen persons. ion of Pompeii and Herculaneum. These cities whelmed, and destroyed in the year A. D. 79, robably either by an alluvion of mud, such as ust described, or by an emission of the same tter from the mouth of the volcano. een supposed, that it was by an eruption of lava cities were destroyed; but Lippi, an Italian wriown that many facts presented by their ruins patible with this opinion. Thus the casts, or s of persons which still remain, especially of a und in a vault at Pompeii, cannot be accounted supposition of flowing melted lava, nor of fallc ashes, for the first would have utterly destroyn of the body, and the second could not have rough the roofs of the buildings. Herculaneum circumstance of upon the theatre patra were found authors, as being Campania; they nies. Both at Hercu found with inscri rebuilding after h This earthquake three years after t the catastrophe by It is supposed t ered, presenting st ments of art, many nearly 2000 uge of mud, even the wood remains the walls of the bu quake which happ edifices chiefly rem Circumstances of where indicated am found lying upon th is decisive evidence," says Mr. Lyell, "that no ava ever reached Pompeii since it was first built, he foundations of the town stand upon the old unt Somma, several streams of which have been -h in making excavations. At Herculaneum, different, although the substance which fills the the houses and vaults, must have been introstate of mud, like that found in similar situampeii: the superincumbent strata differ wholly tion and thickness. Herculaneum was situated les nearer to the volcano, and has, therefore, ys more exposed to be covered, not only by ashes, but by alluvions, and streams of lava. y, masses of both have accumulated on each e the city, to a depth of nowhere less than ad in some places 112 feet. The tuff or mud, elops the buildings, consists comminuted volmixed with pumice. A mask imbedded in this left a cast, the small lines and angles of which erfect, nor did the mask present the least indieat." were the workmen were ple for which they some places the pa but, in general, it re of lava, in which t the constant passage ness of this stone is from one end of the markable, for there ments of modern cit Only a very sm found in either city, of the inhabitants h with them most of th of Pompeii, were the the stocks; and in were the bones of se fled there to escape found enclosed in in ities were both seaports, and Herculaneum is ne shore, but Pompeii is at some distance from vening land having been made, at various times, c matter. 10 |