Oh. X.] PRINCIPLES OF CLASSIFICATIOlSr. 109 



CHAPTER X. 



CLASSIFICATION OF TERTIARY FORMATIONS POST-PLIOCENE GROUP. 



General principles of classification of tertiary strata — Detached formations scat- 

 tered over Europe — Strata of Paris and London— More modern groups — 

 Peculiar difficulties in determining the chronology of tertiary formations — In- 

 creasing proportion of living species of shells in strata of newer rigin — Terms 

 Eocene, Miocene, and Pliocene — Post-Pliocene strata — Recent or human period 

 — Older Post-Pliocene formations of JSTaples, LTddevalla, and N"orway — Ancient 

 upraised delta of the Mississippi — Loess of the Rhine. 



Before describing the most modern of the sets of strata enumerated 

 in the tables given at the end of the last chapter, it will be necessary to 

 say something generally of the mode of classifying the formations called 

 tertiary. 



The name of tertiary has been given to them, because they are all 

 posterior in date to the rocks termed " secondary," of which the chalk 

 constitutes the newest group. These tertiary strata were at first con- 

 founded, as before stated, p. 91, with the superficial alluviums of Europe ; 

 and it was long before their real extent and thickness, and the various 

 ages. to which they belong, were fully recognized. They were observed 

 to occur in patches, some of freshwater, others of marine origin, their 

 geographical area being usually small as compared to the secondary 

 formations, and their position often suggesting the idea of their having 

 been deposited in dift'erent bays, lakes, estuaries, or inland seas, after a 

 large portion of the space now occupied by Europe had already been 

 converted into dry land. 



The first deposits of this class, of which the characters were accurately 

 determined, were those occurring in the neighborhood of Paris, described 

 in 1810 by MM. Cuvier and Brongniart. They were ascertained to con- 

 sist of successive sets of strata, some of marine, others of freshwater 

 origin, lying one upon the other. The fossil shells and corals were per- 

 ceived to be almost all of unknown species, and to have in general a 

 near aflSnity to those now inhabiting warmer seas. The bones and skel- 

 etons of land animals, some of them of large size, and belonging to more 

 than forty distinct species, were examined by Cuvier, and declared by him 

 not to agree specifically, nor even for the most part generically, with any 

 hitherto observed in the living creation. 



Strata were soon afterwards brought to light in the vicinity of London, - 

 and in Hampshire, which although dissimilar in mineral composition, 

 were justly inferred by Mr. T. Webster to be of the same age as those of 



