On Mr. Ly ell's Classification of Tertiary Deposits, 537 



Art. VII. Abstract of a Paper read before the Members of the 

 British Association at Bristol, August 26. 1836, entitled " On 

 some Fallacies involved in the Results (relating to the compara- 

 tive Age of Tertiary Deposits) obtained from the Application of 

 the Test recently introduced by Mr. Lyell and M. Deshayes." 

 By Edward Charlesworth, Esq., F.G.S. 



During the author's investigation of the fossiliferous strata 

 above the London clay in Suffolk and Norfolk, some facts 

 have come under his observation, which appear to him to 

 point out sources of error to a considerable extent in the 

 application of the test recently proposed by M. Deshayes and 

 Mr. Lyell, and which is now so generally made use of in the 

 classification of tertiary formations. 



The crag has been referred by Mr. Lyell to his older 

 pliocene period, on the authority of Deshayes, who identified, 

 among the fossil Testacea of that deposit, 40 per cent with 

 existing species. The correctness of this result has been 

 called in question by other eminent conchologists, particularly 

 by Dr. Beck of Copenhagen, who has examined the crag 

 fossils in the author's collection, and considers that the whole 

 of them are extinct. In this opinion Dr. Beck is supported 

 by Mr. G. B. Sowerby, who states that he has only met with 

 two or three crag shells which may, perhaps, be identified 

 with existing species. Professor Agassis has inspected an 

 extensive series of ichthyological remains, collected from the 

 crag by the author, and pronounces them all to belong to 

 extinct genera or species; while a precisely similar result has 

 attended Dr. Milne Edwards's examination of the corals. 



Professor Phillips, in his introduction to geology, has 

 placed the crag in the miocene division ; while Dr. Fleming, 

 who, for more than a quarter of a century, has been an in- 

 defatigable collector of British shells, considers that the pro- 

 portion of recent species in the fossils of that formation has 

 been rather under than over rated by Deshayes; and, among 

 the corals of the crag, he has detected a large proportion of 

 living forms. 



The particular one of Mr. Lyell's divisions to which a geolo- 

 gist will refer any given deposit must, therefore, depend upon 

 his own estimate of the characters which constitute specific 

 distinctions, and which is evidently liable to the greatest 

 possible amount of variation. 



The author next enters upon an enquiry respecting the 

 course which should be adopted, in obtaining the relations of 

 analogy presented by the fossils of different deposits to one 

 another, or to the races in existence at the present period. 

 The effect of the method now made use of is, to class as con- 



Vol. IX. — No. 66. r r 



