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Show 102 NEWER PLIOCENE PERIOD. [Ch, VIII. trees and herbaO'e which protect them from waste; and in 0 ' • rerrard to the newer ones such is the porosity of their compo-o ' .. nent materials that the rain which falls upon them Is Instantly ' . absorbed and for the same reason that the rivers on Etna have a subterr~nca1~ course, there are none descending the sides of the minor cones. No sensible alteration has been observed in the form of these cones since the earliest periods of which there are memorials; and we see no reason for anticipating, that in the comse of the next ten thousand or twenty thousand years they will undergo any great alteration in their appearance, unless they should be shattered by earthquakes, or covered by volcanic ejections. We shall afterwards point out, that, in other parts of Eul'ope, similar loose cones of scorioo, which we believe to be of higher antiquity than the whole mass of Etna, stand uninjured at inferior elevations above the level of the sea. CHAPTER IX. Origin of the newer Pliocene strata of Sicily-Growth of submarine formations gradual-Rise of the same above the level of the sea probably caused by subterranean lava-Igneous newer Pliocene rocks, formed at great depths, exceed in volume the lavas of Etna-Probable structure of these recent subterranean 1·ocks-Changes which they may have superinduced upon strata in contactAlterations of the surface during and since the emergence of the newer Pliocene &trata-Forms of the Sicilian valleys-Sea cliffs-P1·oofs of successive elevation- Why the valleys in the newer Pliocene districts corresponu in form to those in regions of higher antiquity-Migrations of animals and plants since the emergence of the ne\ver Pliocene strata-Some species newer than the stations they inhabit-Recapitulation. ORIGIN OF THE NEWER PLIOCENE STRATA OF SICILY. HAVING in the last two chapters described the tertiary forma4 tions of the Val di Noto and Valdemone, both igneous and aqueous, we shall now proceed more fu1ly to consider their origin, and the manner in which they may be supposed to have assumed their present position, The consideration of this subject may be naturally divided into three parts: first, we shall inquire in what manner the submarine formations were accumulated beneath the waters; secondly, whether they emerged slowly or suddenly, and what modifications in the earth's crust, at considerable depths below the surface, may be indicated by their rise; thirdly, the mutations which the surface and its inhabitants have undergone during and since the period of emergence. Growth of Submarine formations.-First, then, we are to inquire in what manner the subaqueous masses, whether volcanic or sedimentary, may have been formed. On this subject we have but few observations to make,~ for by reference to our former volumes, the reader will learn how a single stratum, whether of sand, clay, or limestone, may be thrown down at the bottom of the sea, and how shells and other organic remains |
