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Show 154 NEWER PLIOCENE PERIOD· [Ch.XI. and Lorraine, which were previously composed of barren sand and gravel. f preservation of the 1a n d h 11 • h The perfect state o f~l s e ds m· t e loess may have ari·s en f.r om their having been . oate m. . the turbi.d water m· w 1n ·c 1 1 there were no hard particles to ln.J ure them by f r1· et1· 0n. The occurrence of fresh-water shells Is so rare as b y no mea· ns to wal'l'ant the th.e ory adopted b. y some, that the 1o.. ss was 1~0 1· med in a lake mstead of havmg been thrown d own f rom a tra' nsient flood of m.u ddy . water. A few t.n di.v i' du a1 s1 1 e ll s of aquatic species, the mhab1tants, perhaps, of ri·v ers or sma 11 ponds ' may easily have been was.h ed away an d ·m termm· g1 e d W'It h the rest during the inundatwn. The names of fift een sp ec.1es of recent shells, which I collected from the lOss, are given in Appendix II.* "' M. Bronn of Heidelberg possesses o. more extensive collection. CHAPTER XII. Geological monuments of the older Pliocene period-Subapenniue formationsOpinions of Brocchi-Diffcrent groups te1·rned by him Subapennine are not all of the same age-Mineral composition of the Subaponnine formationsMarls- Yellow sand and gravel-Subapeuniue beds how formed-Illustration derived from the Upper Val d'Arno-Organic remains of Subapeunine hills-Older Pliocene strata at the base of the Maritime Alps-Genoa-Savona -Albenga-Nice-Conglomerate of Valley of Magnan-Its origin-Tertiary strata at the eastern extremity of the Pyrenees. OLDER PLIOCENE FORMATIONS. WE must now carry back our retrospect one step farther, and treat of the monuments of the era immediately antecedent to that last considered. '\V e defined in the fifth chapter >K:, the zoological characters by which the strata of the older Pliocene period may be distinguished, and we shall now proceed at once to describe some of the principal groups which answer to those characters. Subapennine strata.-The Apennines, it is well known, are composed chiefly of secondary rocks, forming a chain which branches off from the Ligurian Alps and passes down the middle of the Italian peninsula. At the foot of these mountains, on the side both of the Adriatic and the Mediterranean, are found a series of tertiary strata, which form, for the most part, a line of low hills occupying the "space between the older chain and the sea. Brocchi, the first Italian geologist who described this newer group in detail, gave it the name of the Subapennines, and he classed all the tertiary strata of Italy, from Piedmont to Calabria, as parts of the same system. Certain mineral characters, he observed, were common to the whole, for the strata consist generally of light brown or blue marl, covered by yellow calcareous sand and gravel. There are also, * Above, p. 54. |