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237 



CHAPTER XVII. 



ON THE RECENT TERTIARY STRATA, OR WHAT ARE CALLED BY 

 SOME GEOLOGISTS Q,UATERNARY. 



The Methods for determining the relative Age of Formations explained, and their 

 Value examined. — Evidence from Position. — Evidence from Organic Remains. 

 — System of M. Deshayes founded on Fossil Shells. — Uncertainty attending the 

 Evidence from Organic Remains. — Arbitrary Classifications of Naturalists. — 

 Supposed Limits to the Transmutation of Species of Molluscous Animals exa- 

 mined. — System of M. Elie de Beaumont. — Geological Age of Palaeotheria — of 

 Mastodons — of Elephants. — Recent Tertiary Strata of the Basin of the Loire. — 

 Of the Subappennine Ranges. — Of the Freshwater Formations in the Appennine 

 Valleys. — Remarkable Intermixture of the Skeletons of Whales, EJephants, &c. 

 at Castello Arquata explained by what has taken place iu England. — Freshwa- 

 ter Limestone of CEningen, one of the most recent Tertiary Formations. — Hu- 

 man Skeletons erroneously supposed to have been found there. — Observations 

 on the relative Age of the Strata of CEningen. 



After the discovery of the true character of the tertiary strata of 

 the Paris basin, and of England, it was, for some time, believed that 

 the former was a complete representation of the whole tertiary form- 

 ations in every country ; and that the strata of the London basin, and 

 of the Isle of Wight, represented a portion of the strata of the Paris 

 basin. It is now, however, ascertained, that in the central and south- 

 ern parts of France, and in many other countries, there are exten- 

 sive tertiary formations which contain organic remains, very different 

 from those in the Paris basin. 



These strata are, with much probability, believed to have been 

 deposited in detached lakes or estuaries, at a subsequent period to 

 that in which the Paris basin was laid dry. 



It appears also probable, that these newer tertiary strata are of dif- 

 ferent ages ; and that some of them approach in their characters to 

 the depositions at present forming on the shores of the ocean, or in 

 the deltas of great rivers, or in freshwater lakes. 



The relative antiquity of these recent tertiary formations, is a sub- 

 ject of high geological interest, as it is connected with the history of 

 the latest revolutions of the globe, and the catastrophes that have de- 

 stroyed the ancient races of its inhabitants. 



But how are the relative ages of the strata in different tertiary ba- 

 sins to be ascertained ? The relative ages of two groups or forma- 

 tions of strata, or of two strata in distant parts of the same series, 

 may be determined by two methods : one founded upon the evidence 

 of position, the other upon that of organic remains. As the compar- 

 ative value of these two kinds of evidence, and their relations to each 

 other, has nowhere, that I know of, been briefly and clearly stated, 

 for the benefit of the geological student, I trust I shall be excused for 

 attempting to give a siniple and familiar explanation of each method. 



