VESUVIUS, a volcanic mountain, situated in the kingdom of Naples, about six miles to the eastward of the capital. By the ancients it was called Mons Vesevus, or Vesbius, and in the earlier ages of an tiquity, it was famed for the luxuriance of the ve getation with which its sloping sides were covered, as it also is in modern times, except in those spots laid waste by recent streams of erupted lava. On three sides, the mountain overlooks the rich plain, termed from its exquisite cultivation, and the dili gence of its peasantry, with equal propriety the Terra di Lavoro, and the Campo Felice, while on the fourth, it descends more abruptly to be washed by the waves of that splendid expanse of water, to which it adds so high a charm, the Bay of Naples, its base here being covered by a connected chain of large villages, forming a stretch, perhaps almost unexampled, of many miles.
In regard to geological position, several impor tant facts are to be noticed; and in the first place, the whole tract of country, within several miles in every direction landward of Naples, which has all the same general constitution as that small portion called the Phlegrxan fields, must be considered as a formation subordinate to its main feature, Mount Vesuvius, as owing its existence to essentially the same phenomena, and as an actual superposition of a tract of country upon the pre-existent chain of the Apennines, which probably was at one period washed by the sea. The western limit of the Bay must then have been the Monte Massico, not far from Mola, instead of the island of Ischia, which now terminates it, the eastern limit or the promon tory of Minerva remaining constant, which gives an opening more than double the present one, and the extreme depth of the bay, full fourteen miles greater. The whole volcanic formation of which Vesuvius forms the focus, reposes therefore upon the secondary limestone of which the Apennine range is here formed; and of this we have various direct proofs, the most remarkable of which is the frequent projection of calcareous masses from the crater of Vesuvius, either in an unaltered or a mo dified state; we have therefore the conclusive cer tainty, that between the volcanic focus and the point of eruption, there exist calcareous strata. The proximity of this volcano to the sea likewise de serves notice, as following the general law pointed out in the article PHYSICAL GEOGRAPI1Y. " Volca noes," it is there remarked, " seem in general to be situated near the sea-coast, and rarely or never in the interior of large continents. Catopaxi, in
South America, is perhaps, of all volcanic moun tains, the most distant from the ocean, and yet it is only 140 miles distant from the shores of the Pa cific." This is one of the few general facts recog nised in connexion with the theory of volcanoes, and ought therefore to hold a place commensurate with its importance in hypothetical reasoning on this subject.
In taking a general view of the external features of Vesuvius, we are in the first place struck by its remarkable separation into two very dissimilar parts; Vesuvius, properly so called, a cinerous cone rising from an irregular plain, situated at no less than 2400 feet above the sea, and Monte Somma, a craggy range of rocks, the precipitous side of which is formed into the segment of a circle, and presents its concavity towards the cone of Vesuvius, which it flanks to the northward for a considerable extent, its own north side sloping gradually down to the plain of the Campo Felice. It is similar, in many respects, to the remarkable hill of Salisbury Crags near Edinburgh, if we conceive the perpendicular face of the latter to have a concave instead of con vex horizontal projection, and instead of the debris which form the steep slope to the westward, a plain be conceived to extend from the base of the precipi tous rock till it joins the cone already mentioned.
Monte Somma appears undoubtedly to have been the primeval point of ejection, though the conjec ture of some authors, that the present concavity formed the wall of a part of the original crater, seems extravagant, as the circle of which it is a segment would have had a circumference of many miles. Some traces of what may have been the ori ginal crater may be observed in the course of this precipitous range near its western extremity. The face of rock there presents a remarkable section, the main body being traversed by dykes which pur sue contorted courses, and frequently merge into or cross one another; they arc of a different species of rock from the basis, and may probably owe their origin to fissures made by the subsidence of the upheaved pre-existent rock, and filled up by a new species of lava at the next eruption. See Saussure in the Geneva Transactions, vol. ii.; Sir James Hall in the Edinburgh Transactions, vol. vii.; Hamil ton's Carnpi Phlcgrmi, and the Edinburgh Journal of Science, vol. ix. p. 191. The extreme height of the Somma is 3703 feet.