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Show CHAPTER XX. f th e of Vesuvius-Dikes in the recent cone, how D. · a d structure o o con 1 · 1mens1ons n . u Sommo.-V csuvinn lavas ant mmc· ·' S t' on through Vosuvms an formeu- cc 1 • • f 1 -Alluvions callc<l " aqueous lavas"- 1 Efl1 t on uecomllOSihon 0 avn .. ra s- " cc s . . tl ttor enveloping Ilcrculaneum and Pompeu 0 . . u composlhon ou 10 ma . . . ngm nn · . C d' f on anti contents of tho bur1ed c1hcs • 0 1 the subJect- on 1 1 -Conb'OVOl'SIC~ I . ro U b an earthquake-Small number of skcle· -Proofs of thCir havmg ~u ere .Y 1 ld vegetable substances-Rolls of f o 'Vabon of amma at tons-State o pros 1 • : f MSS-Stabiro-Torre del b'l't f futmo UISCOVOllCS 0 ' Po.pyrus-Proba. I 1 y o ks on tho destroying and renovating agency of the Grcco-Concludmg romar Campanian volcanos. te ol! Veswvius.-BETWEEN the end of the Sl·ructure of the co? 'Jl lSflfl the O'rcat crater ofVesu- . 1 tl ntury and t1e year ' o b l cJg Jtecn 1 ce ll £11 d by lava boiling up from e ow, vius had bee? gracl?a yf· c the explosions of minor mouths aml by sconre fallmg . rot m ls on its bottom and sides. In 1 . 1 formed at m erva 1 d w nc 1 were . h £ e there was a roug1 an 1 f regular cavity t ere or ' d t P ace o ~ with' blocks of lava and scorire, an cu rocky plam, covere~ which clouds of vapour were by numerous £s~mes, frofm 1 . was totally changed by the l l B t tlus state o t nngs d . evo vee . u 18~fl ben violent explosions, urmg eruption of October' ' w d b. ke up and threw out the space of more than twenty aysl, IO an immense gulf or 1 t d mass so as to eave b all this accumu a e ' 1 t elliptical shape, a out f . Ilar but somew la chasm' o an Irregt ' h measured along the very three miles in circuml~erencf~t wexetnrerr:le maro·in, but somewhat sinuous an d l· rregu1 ar me o I s'1 . 'ts lon(J'e0s t diameter, w1 1J· C 11 l ·ters of a nn e m 1 o 1 . less than t wee quat W * The depth of t HS tre-was directed from N.E. to. S. 1 . t' ted for from the hour mendous abyss has been van~L~ ~ ~s ~;~he' dilapidation of its of its formation it decrease m d).' to the accounts of some d at first accor mg t of sides. It measure '. d th from the extreme par thors two thousand feet m ep au ' G p Scro1JC, f th Eruption of VesuVI·U S in October, 1822, l>y · ' .:c Account o e 175 ;Esq., Journ. of Sci., &c., vol. :x.v., P· • STRUCTURE OF 'l'llE CONE OF VESUVIUS, 341 the existing summit*; but Mr. Scropc, when he saw it, soon after the eruption, estimated its depth at less than half that quantity. More than eight hundred feet of the cone was carried away by the explosions, so that the mountain was reduced in height from about four thousand two hundred to three thousand four hundred feet t. As we ascend the sloping sides, the volcano appears a mass of loose materials-a mere heap of rubbish, thrown together without ihe slightest order; but on arriving at the brim of the crater, and obtaining a view of the interior, we arc agreeably surprised to discover that the conformation of the whole displays in every part the most perfect symmetry and arrangement. The materials are disposed in regular strata slightly undulating, appearing, when viewed in front, to be disposed in horizontal planes. But as we make the circuit of the edge of the crater, and observe the cliffs by which it is encircled projecting or receding in salient or retiring angles, we behold transverse sections o( the currents of lava and beds of sand and scorioo, and recognise their true dip. We then discover that they incline outwards from the axis of the cone, at angles varying fl'Om 30° to 45°. The whole cone, in fact, is composed of a number of concentric coatings of alternating lavas, sand, and scorire. Every shower of ashes which has fallen from above, and every stream of lava descending from the lips of the crater, have conformed to the outward surface of the hill, so that one conical envelope may be said to have been successively folded round another, until the aggregation of the whole mountain was completed. 'l'he marked separation into distinct beds results from the different colours and degrees of coarseness in the sands, scorire, and lava, and the alternation of these with each other. The greatest difficulty, on the first view, is to con~ eive how so much regularity can be produced, notwithstandmg the unequal distribution of sand and sc01·ire, driven by prevailing winds in particular eruptions, and the small breadth of each sheet of lava as it first flows out from the crater. But on.a closer examination we find that the appearance of extreme Uniformity is delusive, for when a number of beds thin out gradually, and at different points, the eye does not without diffi- •1 ~r. Forbes, Account of Mount Vesuvius, Edin. Journ. of Sci., No. xviii. l>· 9.,, Oct., 1828, t Ibid., p. 194. 1 |