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Show 104 NEWER PLIOCENE PERIOD, [Ch. IX. may become imbedded therem. . H c will also u. ndersdt and hobw one sheet of lava, or bed of scorioo and volcamc san ' rna~ e spread out over a w.i de area, an d how ' at a subsequent dp elr wd, a second bed of san d , cIa y, or limestone' or a secon ava-cs: tream may be supen•m posed , so that in the lapse of ages a mountain mass may be produced. . It is enoug1l t h at we s1I ou ld behold a sin.O0 'le course of bncks or stones lai' d b y t 11 e mason upon another, m order to comprc- hend how a massi.v e ed 'l.ll!lc e • such as the Colo. sseum a. t . Rome, was erecte d ; an d we ca n have no difficulty m conce1vm. g that a sea, three Il Ull d re d or. four hundred fathoms d. eep, .m ight .b e filled up 1> y se dI.m en t and lava ' provided we adm. it an mdefimte I apse of ages for the accumulation of the materials. PI' The sedimentary and volcanic masses of the newer Iocene era, w1 1 ·1 c1 1 , I' n the Val di Noto' attain the thickness of two thou-sand feet, are subdivided into a vast number of strata and lava-streams, each Of Which were orh'"r" inally formed on the sub. aqueous stl rface , J. ust as the tuffs and lavas whereof sections are laid open in the Val del Bove, were each in their turn external additions to the Etnean cone. It is also clear, that before any part of the mass of submarine or1·g 1: n beO0 'an to rise above the wate• rs, the upperm. ost stratum of the whole must have been deposited; so that If the date of the origin of these masses be comparatively recent, still more so is the period of their rise above the level of the sea. Subaqueous formations how raised.-In what manner, then, and by what agency, did this rise of the subaqueous formations take place? We have seen that since the commencement of the present century, an immense tract of country in Cutch, more than fifty miles long and sixteen broad, was permanently upraised to the height of ten feet a.bove ~ts former positi~n, and the earthquake which accompamed this wonderful variation of level, is reported to have terminated by a volcanic eruption at Bhooi. We have also seen*, that when the Monte N uovo was thrown up, in the year 1538, a large fissure a1J-Ch. IX.] SUBAQUEOUS .FOR1f'ATIONS HOW RAISED, 105 proached the small town of Tripergola, emitting a vivid light, and throwing out ignited sand and scorire. At length this opening reached a shallow part of the sea close to the shore, and then widened into a large chasm, out of which were discharged b]ocks of lava, pumice, and ashes. But no current of melted matter flowed from the orifice, although it is perfectly evident that lava existed below in a fluid state, since so many portions of it were cast up in the form of scorire into the air. We have shown that the coast near Puzzuoli rose, at that time, to the height of more than twenty feet above its former level, and that it has remained permanently upheaved to this day*. On a review of the whole phenomena, it appears most probable that the elevated country was forced upwards by lava which did not escape, but which, after causing violent earthquakes, during several preceding months, produced at length a fissure from whence it discharged gaseous fluids, together with sand and scorire. The intruded mass then cooled down at a certain distance below the uplifted surface, and constituted a solid and permanent foundation. If an habitual vent had previously existed near Puzzuoli, such as we may suppose to remain always open in the principal ducts of Vesuvius or Etna, the lava might, perhaps, have :flowed over upon the surface, instead of heaving upwards the superficial strata. In that case, there might have been the same conversion of sea into land, the only difference being, that the lava would have been uppermost, instead of the tufaceous strata containing shells, now seen in the plain of La Starza, and on the site of the Temple of Serapis. Subterranean lava the upheaving cause.-'rhe only feasible theory, indeed, that has yet been proposed, respecting the causes of the permanent rise of the bed of the sea, is that which refers the phenomenon to the generation of subterranean lava. We have stated, in the first volume, that the regions now habitually convulsed by earthquakes, include within them the site of all the active volcanos. We know that the expan- .* Vol, i, chap. xx..v. |
