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Show 3~8 'l'llEORY OF ELEVATION CRATERS~ cant area, where a certain quantity of volcanic matter happens to lie, while they carefully avoid purely lacustrine and marine strata, although they often lie immediately contiguous? Why on the southern bor<lers of the Limagne d' Auvergne, where several eruptions burst through, and elevated the horizontal marls an<llimestoncs, did these freshwater beds never acquire in any instance a conical and crateriform disposition? But let us proceed to examine some of the most celebrated examples adduced of craters of elevation. The most perfect type of this peculiar configuration is said to be afforded by the Isle of Palma; and while we controvert Von Buch's theoretical opinions, we ought not to forget how much geology is indebted to his talents and zeal, and amongst other works for his clear and accurate description of this isle*· In the middle of Palma rises a mountain to the height of four thousand feet, presenting the general form of a great cone, the upper part of which had been truncated and replaced by an enormous funnel-shaped cavity, about four thousand feet deep; and the surrounding borders of which attain, at their highest point, an elevation of seven thousand feet above the sea. The external flanks of this cone are gently inclined, and, in part, cultivated; but the bottom and the walls of the central cavity, called by the inhabitants the Caldera, present on all sides 1·ngged and uncultivated rocks, almost completely devoid of vegetation. Vltrv oj' the I1lt qf Palma, a11d qf the Calclm.l in i/1 ct lllrt. So steep are the sides of the Caldera, that there is n? path by which they can be descended; and the only entra.nce !s by a gt·eat ravine, which, cutting through the rocks envll'omng the * Physical. Besch. dcr Cnnarischen Inseln. Berlin, 1825. • ISLE OP PAL MA-.BARREN ISLAND. 389 ctrcus, runs down to tl jagged, broken and p. 1~ . • sea. The sides of this gorge are ' 1 ec1p1tous I tl surroundin()' the Calde · n le mural escarpments o ra are seen n tl . b an~ conglomerates composed of b. o ling ut beds of basalt, whiCh dip away with tile tOken fragments of basalt . greatest regul · t f ' the circumference of the N ari y, rom the centre to f . cone. ow ac . r o " elevatwn craters; " we are ca ll ed ' u em ct mg to the theory the first place, a series of 11 0r.i zontal bpedo n °f suppose that, in 1 . accumulated over each oth . h s 0 vo came matter 1 er' to t e enorm ] 1 t 1an four thousand .l!cet • ous c ept 1 of more 11 -a Circumst 1 · 1 imply the proximity at lea t f ancc w 1IC 1 alone would · . ' s ' o a vent from 1 · 1 · qua.n tities of igneous rocl<.s 11 ac1 procee· d ed Awf u c 1 hI mmense gation of the mass, the expans' I! • • . ter t e aggre- . · lVe 1orcc was directed · pomt With such extraordinary on a giVen whole mass, so that it should ~~:rff' as t~ lift up bodily the sand feet above the sea lea . the height of seven thou- • · ' ' VIUO' a great g If · · middle. Yet, notwithstandin()' ~his rodi()'' u or cavity m the explosions, concentrated on so h o.wus effort of gaseous of being shattered contortedo smda ha pm~t, the beds, instead .1 ' ' an t rown mto tl d' oruer, have acc1uired that gen tl e m. el in at1. d1 e 1u tmost ts-and symmetrical arrangement I . 1 1 on, an t 1at regular a large cone of erupti'on l'k 'Ew 1IC 1 c laracterize the flanks of , I e tna 1 "\V d · 1 f}uakes, when they act . · e a tmt t 1at earth- . on extensive tract f elevate and depress them without d . s o ~ountry, may relative position of hills v 11 ..J eran?mg, considerably' the ' a eys ann ravmes B t · · · to conceive that elastic fluids ' ld b. l 1. u IS It possible as it were of the earth's cr t coud h Jea <. t H'ough a mere point not composed of soft . ~~·'an t at to? where the beds were of solid basalt., thous~:a~: o:nf clay,. or Incoherent sand, but inflate them as it . . h eet tluck, and that they could not the rock's twlere, m t e manner of a bladder? "\Vould 'on 1e contrary b f t d into a vertical and ft . ' e rae ure ' fissured, thrown attained the h~ight of en mto t reversed position; and, ere they reduced to a o sfcven t lousand feet, would they not be Th G mere con used and chaotic heap? e reat Canary i · 1 d f · to that.of Palma. Bar~·e:n ;sian o a c~rcular form, analogous proposed as a strik. . s an~, also, m the Bay of Bengal, is and here it is 'd mg ~llustratwn of the same phenomenon. contrast the s?I we ave the advantage of being able t~ eruption . ~ncient crater of elevation with a cone and crater of m Its centre. WI ten seen f rom the ocean, this island |
