the age of Tertiary Deposits. Ill 



per Parisian formation, referred by M. M. de Beaumont and 

 Dufrenoy to the middle tertiary period ? 



I might also point out, in support of my opinion, which 

 tends to regard the faluns and the crag as contemporaneous, 

 that this latter deposit, whether upon the eastern side of Eng- 

 land, or upon the opposite coast of the low countries, repre- 

 sents there the middle tertiary formation ; the seas of which, 

 according to the contrary opinion held by M. Deshayes and 

 Mr. Lyell, did not penetrate into this part of Europe. We 

 follow the formation of the faluns, from the basin of the low- 

 er Loire, to the sides of the channel, into Cotentin, across 

 central Bretagne, to Chateaubriand, Rennes, Dinan, and from 

 the other side of the channel, to Carentan, &c. By degrees, 

 in proportion as the deposits are more northern, we see a 

 great part of the larger species of the faluns of the Loire and 

 the Gironde, disappear ; while there remains, notwithstand- 

 ing, a great number of smaller species, common to both the 

 faluns and the crag ; so that the identity between the faluns 

 of Carentan, and the crag of Suffolk, is almost incontestable, 

 and is greater than with the faluns of the Loire. How then 

 can we separate them so completely as has been proposed ? 

 Must we not, on the contrary, admit their differences to be 

 simply topographical, in one and the same period ? 



But without insisting much upon this geographical argu- 

 ment, which is not without importance, and would be render- 

 ed more evident by a distinction of colour, upon a map of the 

 distribution of the different tertiary formations of Europe, I 

 shall confine myself to calling once more to this question, the 

 scrupulous examination of those zoologists and geologists, 

 who have particularly applied themselves to the study of the 

 tertiary formations. 



[We have been led to give the above observations of M. Desnoyers, a 

 place in the Magazine of Natural History, from a conviction that the at- 

 tention of those who may be interested in the advancement of tertiary geo- 

 logy, cannot be too frequently, or too forcibly, directed to the unlimited 

 extent of error which must inevitably result from an implicit belief in the 

 merits of the per-centage test of M. Deshayes and Mr. Lyell ; and also, be- 

 cause we feel called upon to notice the circumstances under which M. Des- 

 noyers comes forward as the expounder of the fallacies likely to arise, in 

 forming a chronological classification of fossiliferous rocks, by "the law of 

 the proportional number of species analogous to species now in existence. " 



In the original memoir, (p. 207), we find the following remark. — " M. 

 Charlesworth, qui parait s'etre beaucoup occupe, dans ces derniers temps, 

 de l'examen du crag, et qui a presente aussi, a ce sujet, plusieurs objec- 

 tions sur Pemploi du nombre proportionnel des especes analogues, pour de- 

 terminer l'age des terrains tertiaires, entre autres, celle du melange possible 

 des fossiles d'un terrain, dans le terrain adjacent." Then in a note at the 

 bottom of the page, a reference is given to the English journals in which 

 these objections have appeared. Now as it was clearly the intention of M. 



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