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Show 112 NEWER PLIOCENE PERIOD· [Ch. IX. but are usually t.n c1 m. e d at a very sl 1' g ht anOo 'le '· they are s.e en to exten d unm. t errup t e dly fi·om the base of the escar. pment mto the platform, showing distinctly that the lofty cliff was not produced by a fault or vertical shift of the beds, but by the removal of a considerable mass of rock. Hence we must con~ elude that the sea, which is now undermining the cliff::; of the Sicilian coast, reached at some former period the ·base of the • 1prec1p ·ce a , b, at which time the surface .o f the terrace c, b, must have constituted the bottom of the Mediterranean. Here, then, we have proofs of at least two elevations, but there may have been -fifty others, for the encroachment of the sea tends to ob~ literate all signs of a succession of cliffs. Suppose, for example, that a series of escarpments, e, f, g, h, once existed, and that during a long interval, free from subtet· .. ranean movements, the sea had time to advance along the line c b all those ancient cliffs must then have been swept away one ~ft;r the other, and reduced to the single precipice a, b. There may have been an antecedent period when the sea advanced along the line h, l, substituting the single cliff e, l, for the series e,f, g. We may also imagine that the present cliffs may be the result of the union of several lines of smaller cliffs and terraces, which may once have been produced by a succession of elevatory movements. For example, the waves may have carried away the cliffs k, i, in advancing to c, d. In the same manner they may ultimately remove the mass c, b, m, d, and then the platform c, b, will disappear, and the precipice a, m, will be substituted for a, b. We have stated, in the -first volume, that the waves washed the base of the inland cliff near Puzzuoli, in the Bay of Baire, within the historical era, and that the retiring of the sea was caused, in the sixteenth century, by an upheaving of the land to an elevation of twenty feet above its original level. At that period, a terrace twenty feet high in some parts, was laid dry between the sea and the cliff, but the Mediterranean is hastening to resume its former position, when the terrace will be Ch. IX.] PROOFS OF SUCCESSIVE ELEVATION. 113 destroyed, and every trace of the successi·ve rise of the land will be obliterated. We have been led into these observations, in order to show that the principal features in the physical geography of Sicily are by no means inconsistent with the hypothesis of the successive elevation of the country by the intermittent action of ordinary earthquakes *. On the other hand, we consider the magnitude of the valleys, and their correspondence in form with those of other parts of the globe, to lend countenance to the theory of the slow and gt·adnal rise of subaqueous strata. We have remarked in the :first volume t, that the excavation of valleys must always proceed with the greatest rapidity when the levels of a country are undergoing alteration from time to time by earthquakes, and that it is principally when a country is rising or sinking by successive movements, that the power of aqueous causes, such as tides, currents, rivers, and land-floods, is exerted with the fullest energy. In order to explain the present appearance of the surface, we must first go back to the time when the Sicilian formations were mere shoals at the bottom of the sea, in which the currents may have scooped out channels here and thet·e. We must next suppose these shoals to have become small islands of which the cliffs were thrown down from time to time>, as were those of Gian Greco, in Calabria, during the earthquake of 1783. The waves and currents would then continue their denuding action during the emergence of these islands, until at length, when the intervening channels were laid dry, and rivers began to flow, the deepening and widening of the val- * Since writing the above I have read the excellent memoir of M. Boblaye, on the alterations produced by the sea on calcareous rocks on the shores of Greece. By examining the line of littoral cavems worn by the waves in cliffs composed of the harder limestones, together with the modes of decomposition of the rock, acted upon by the spray and sea air, as well as lithodomous perfomtions and other m.arkings, he has proved that there are four or five distinct ranges of 1 ancient sea chff.-;, one above the otht>r, at various elevations in the Morea, which attest as ~~~~successive elevations of the country. Journal de Geologie, No. 10. Feb. Vor .. III. t Chap. xxiv. I |