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Show 136 NEWER PLIOCENE PERIOD· [Ch.X. these shells, which will be found in Appendix II.* The v~lcano of Gabel Tor, situate at the entrance of the Arabian If . h t lcanic region known to us at present. O'U , IS t e neares vo 0 We should guard the reader against inferring, ~rom the f~cts a b ove d eta t·1 ed , th.".. t marine strata of the newer Phocene penod have been produced exclusively in countries of earthquakes. If we have drawn our illustrations exclusively from modern volcanic regions, it is simply for this reason, that these formations have been made visible to us in those districts only where the conversion of sea into land has taken place in times comparatively modern. Other continents have, during the newer Pliocene period, suffered degradation, and rivers and currents }1ave deposited sediment in other seas, but the new strata remain concealed wherever no subsequent alterations of level have taken place. We believe, however, that to a certain limited extent the growth of new subaqueous deposits has been greatest where igneous and aqueous causes have co-operated. It is there, as we have explained in former chapters, that the degradation of land is most rapid, and it is there only that materials ejected from below, by volcanic explosions, are added to the sediment transported by running water t. • These fossils are now in the museum of Mr. Greenough, in London, and du· plicates, presented by him, in the cabinets of the Geological Society. t See vol. i. chap. xxiv.; and vol. ii. chap. xviii, CHAPTER XI. NewPr Pliocene fresh-water formations-Valley of the Elsa-Travertins of Rome -Osseous breccias-Sicily-Caves near Palermo-Extinct animals in newer Pliocene breccias-Fossil bones of Marsupial animals in Australian cavesFormation of osseous bl'eccias in the Morea-Newer Pliocene alluviumsDifference between alluviums and regular subaqueous strata-The former of various ages-Marine alluvium-Grooved surface of rocks-Erratic blocks of the Alps-Theory of deluges caused by paroxysmal elentions untenableHow ice may have contributed to transport large blocks from the Alps-Euro· pean alluviums chiefly tertiary-Newer Pliocene in Sicily-Loss of the Valley of the Rhine-Its origin-Contains recent shells. FRESH-WATER FORMATIONS. IN this chapter we shall treat of the fresh-water formationsJ and of the cave breccias and alluviums of the newer Pliocene period. In regard to the first of these, they must have been formed, in greater or less quantity, in nearly all the existing lakes of the world, in those, at least, of which the basins were formed before the earth was tenanted by man. If the great lakes of North America originated before that era, the sedimentary strata deposited therein, in the ages immediately antecedent, would, according to the terms of our definition, belong to the newer Pliocene period. Valley of the Elsa.-As an example of the strata of this age, which have been exposed to view in consequence of the drainage of a lake, we may mention those of the valley of the Elsa, in 'l'uscany, between Florence and Sienna, where we meet with fresh-water marls and travertins full of shells, belonging to species which now live in the lakes and rivers of Italy. Valleys several hundred feet deep have been excavated through the lacustrine bedsJ and the ancient town of Colle stands on a hill composed of them. 'l~he subjacent formation consists of rna. rine Subapennine beds, in which more than half the shells are |
