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Show 20 ORIGIN OF TilE EUROPEAN 'fERTIARY (Ch. II. strata*, placed the crag as the uppermost of. the Bri~is~ series, and several geologists began soon to ent.ertam an opm10~ that this newest of our tertiary formations m1ght correspond m age to the Italian strata described by Brocchi. r.Pertia·ry Stmta of Tou·raine.-The next step towards establishing a succession of tertiary periods was the evidence adduced to prove that certain formations, more recent than the uppermost members of the Parisian series, ;vere also old.er than the Subapennine beds, so that they constituted deposits of an age intermediate between the two types above alluded to. M. Desnoyers, for example, ascertained that a group of marine strata in 'romaine, in the basin of the Loire ( e, diagram No. 3), rest upon the uppermost subdivision of the c C, Chalk and other secondary furmations. d, Tertiary furmation of Paris basin. No.3. e, SuperimiJosed marine tertiary beds of the Loire. Parisian group d, which consists of a lacustrine formation, extending continuously throughout a platform which intervenes between the basin of the Seine and that of the Loire. These overlying marine strata, M. Desnoyers assimilated to the English crag, to which they bear some analogy, although their organic remains diffet· considerably, as will be afterwards shown. A large tertiary deposit had already been observed in the south-west of France, around Bordeaux and Dax, and a description of its fossils had been published by M. de Basteroti·· Many of the species were peculiar, and differed from those of the strata now called Subapennine ; yet these same peculiar and characteristic fo~sils reappeared in Piedmont, in a series of * Outlines of the Geology of Euglaucl and Vir ales, 1822. t 1\Iem. de la Soc. d'Hist. Nat. de Paris, tome ii., 1825. Ch. II.] STRATA A'l' SUCCESSIVE PERIODS. 21 strata inferior in position to the Subapennines (as e underlies f, diagram No. 4). C, Chalk and older formations. d, London clay (older tertiary). e, Tertiary strata of same age as beds of the Loire. f, Crag and Subapennine tertiary deposits. · No.4. c This inferior group, e, composed principally of green sand, occurs in the hills of Mont Fen·at, and beds of the same age are seen in the valley of the Bormida. They also form the hill of the Superga, near ':rurin, where M. Bonelli formed a large col· lection of their fossils, and identified them with those discovered near Bordeaux and in the basin of the Gironde. But we are indebted to M. Deshayes for having proved, by a careful comparison of the entire assemblage of shells found in the above-mentioned localities, in Touraine, in the south-east of France, and in Piedmont, that the whole of these three groups possess the same zoological characters, and belong to the same epoch, as also do the shells described by M. Constant Prevost, as occurring in the basin of Vienna*. Now the reader will perceive, by reference to the observa· tions above made, and to the accompanying diagrams, that one of the formations of this intervening period, e, has been found superimposed upon the highest member of the Parisian series, d j while another of the same set has been observed to underlie the Subapennine beds, f. Thus the chronological series, d, e, f, is made out, in which the deposits, originally called tertiary, those of the Paris and London basins, for example, occupy the lowest position, and the beds called ' the Crag,' and' the Subapennines,' the highest. Tertiary Strata newer than the Subapennine.-The fossil 1< Sur lu Constitution, &c:. <lu bassin de Vienne, Jow-n. de Phys., Nov, 1820. |