18 ORIGIN OF THE EUROPEAN TERTIARY [Ch. II. 



set of strata overlap another, in such a manner that the 

 geologist might be enabled to determine the difference 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 conviction of the necessity of 

 referring the European tertiary formations to distinct periods, 

 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, those of 

 Hampshire and of the basin of the Thames were examined in 

 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 Wight, an alter- 

 nation 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 dis- 

 cordance, 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 ter- 

 tiary 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 EnglefielU's Isle of Wight and Geol. Trans., vol. ii. p. 161. 

 f Conch. Foss. Subap., 1814. 



