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Show 18 ORIGIN OF TilE EUROPEAN TERTIARY tch.ll. set of strata over1 a p another ' in s.u ch a m.a nner that the geo I og1. st m1.g · ht be enabled to determme the d1fference of age by direct superposition. ORIGIN OF THE EUROPEAN TERTIARY STRATA AT SUCCESSIVE PERIODS. We shall now very briefly enumerate some of the principal steps which eventually led to a convic.tion of t~1e. necessi~y of referring the European tertiary formatiOns to di.stmct ~er10ds, and the leading data' by which such a chronological series may be established. London and Hampshire Basins.-Very soon after the inves-tigation, before alluded to, of the Parisian strata, t~1ose ?f Hampshire and of the basin of the Thames were exammed m our own country. Mr. Webster found these English tertiary deposits to repose, like those in France, upon the chalk or newest rock of the secondary series. He identified a great variety of the shells occurring in the British and Parisian strata, and ascertained that, in the Isle of '¥ight, an alternation of marine and freshwater beds occurred, very analogous to that observed in the basin of the Seine*. But no two sets of strata could well be more dissimilar in mineral composition, and they were only recognized to belong to the same era, by aid of the specific identity of their organic remains. The discm ·dance, in other respects, was as complete as could well be imagined, for the principal marine formation in the one country consisted of blue clay, in the other of white limestone, and a variety of curious rocks in the neighbourhood of Paris, had no representatives whatever in the south of England. Subapennine Beds.-The next important discovery of tertiary strata was in Italy, where Brocchi traced them along the flanks of the Apennines, from one extremity of the peninsula to the other, usually forming a lower range of hills, called by him the Subapenninesf. These formations, it is true, had • Webster in Englefield's Isle of Wight and Geol. Trans., vol. ii. p.l6l. t Conch. Foss. Subap., 1814. Ch. II.] STRATA AT SUCCESSIVE PERIODS, 19 been pointed out by the older Italian writers, and some correct ideas, as we have seen, had been entertained respecting thei1· recent origin, as compared to the inclined secondary rocks on which they rested*. But accul'ate data were now for the first time collected, for instituting a comparison between them and other members of the great European series of tertiary formations. Drocchi came to the conclusion that nearly one-half of several hundred species of fossil shells procured by him from these Subapem1ine beds were identical with those now living in existing seas, an observation which did not hold true in respect to the organic remains of the Paris basin. It might have been supposed that this important point of discrepancy would at once have engendered great doubt as to the identity, in age, of any part of the Subapennine beds to any one member of the Parisian series ; but, for reasons above alluded to, this objection was not thought of much weight, and it was supposed that a group of strata, called 'the upper marine formation,' in the basin of the Seine, might be represented by all the Subapennine clays and yellow sand. English Crag.-Several years before, an English naturalist, Mr. Parkinson, had observed, that certain shelly strata, in Suffolk, wpich overlaid the blue clay of London, contained distinct fossiJ species of testacea, and that a considerable portion of these might be identified with species now inhabiting the neighbouring sea i·· These overlying beds, which were provincially termed ' Crag,' were of small thickness, and were not regarded as of much geological importance. But when duly considered, they presented a fact worthy of great attention, viz., the superposition of a tertiary group, inclosing, like the Subapennine beds, a great intermixture of recent species of shells, upon beds wherein a very few remains of recent or 1i ving species were entombed. Mr. Conybeare, in his excelJent classification of the English "' See vel. i. p. 51, for opinions ofOdoardi, in 1761. t Geol. Trans., vol. i. p. 324. 1811. c 2 |