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Show 192 OLDER PLIOCENE PERIOD. (Ch. XlV. necess~li'Y to fill it up with earth and stones, in order to form a sure foundation for the new edifice. 'l'he annihilation of the ancient Olot may, perhaps, be ascribed, not to the extraordinary violence of the ~ovement on that spot, but to the cavernous nature of the subJacent rocks; for Catalonia is beyond the line of those modern European earthquakes which destroy towns throughout e~tensiv.e areas, As we have no historical records, then, to gmde us m regard to the extinct volcanos, we must appeal to geological monuments. We have little doubt that some fossil land-shells, and bones of quadrupeds, will hereafter reward the industt·y of collectors. If such remains are found imbedded in volcanic ejections, the period of the eruptions may be inferred; but at present we have no evidence beyond that afforded by superposition, in regard to which the annexed diagram will present to the reader, in a synaptical form, the results obtained from numerous sections. No.47. Sup~rposition of roc11s in the t!Olcanic clutrict of Catalonia. a, Sandstone and nummulitic limestone. h, Older alluvium with volcanie pebbles. c, Cones of scorire and lava. d, Newer alluvium. The more modern alluvium d is partial, and has been formed by the action of rivers and floods upon the lava; whereas the older gravel, b, was strewed over the countr~ before. the volcanic eruptions. In neither have any orgamc remams been discovered, so that we can merely affirm, as yet, that the volcanos broke out after the elevation of some of the newest rocks of the secondary series, and before the formation of an alluvimn, d, of unknown date. The integrity of the cones merely shows that the country has not been agitated by violent earth· Ch. XIV.] VOLCANOS OF 1'IIE J~tF~L. 193 quakes, nor subjected to the action of any great transient flood since their origin. East of Olot, on the Catalonian coast, marine tertiary strata occur, which, near Barcelona, attain the height of about 500 feet. It appears probable, from a small number of shells which I collected, that these strata may correspond with the Subapennine beds, so that if the volcanic district had extended thus far, we might be able to determine the age of the igneous products, by observing their relation to these older Pliocene formations*. Sa·rdinian volcanos.-The line of extinct volcanos in Sardinia, described by Captain Smyth t, is also of uncertain date, as, notwithstanding the freshness of some of the cones and lavas, they may be of high antiquity. They rest, however, on a tertiary formation, supposed by some to correspond to the Subapennine strata, but of which the fossil remains have not been fully described. VOLCANIC ROCKS OF THE EIFEL. The volcanos of the Lower Rhine and the Eifel arc of no less uncertain date than those of Catalonia; but we are desirous of pointing out some of their peculiar characters, and shall, therefore, treat of them in this chapter, trusting that future investigations will determine their chronological relations more accurately. For the geographical details of this volcanic region, \ve refer the reader to the annexed map, for which r am indebted to Mr. Leonard Horner, whose residence in the country has enabled him to verify the maps of MM. Noeggerath and Von Oyenhausen, from which that now given has been principalJy compiled. * For some account of the Olot volcanos see' Noticia de Los Estinguidos Volcanes dtl Ia Villa de Olot,' by Francisco Bolos. Barcelona, No date,- but tbe observations, I am told, preceded those of Dr. Maclure. t Present state of Saruinia, &c., pp. 6!), 70. VoL, III, 0 |