the relative Age of Tertiary Deposita, S 



Such then was the condition of the inquiry up to the time 

 of a small series of shells from Ramsholt being placed by Mr. 

 Lyell in the hands of M.Deshayes, and the result attending his 

 examination of these fossils has been appealed to as one which 

 must necessarily prOve fatal to the views which I entertain 

 as to the relative antiquity of the coralline crag *. A fellow- 

 labourer in the field of geological research, presuming that all 

 other sources of evidence must yield to the deductions arising 

 from a concho-geological investigation, has been led, perhaps 

 rather too precipitately, to exclaim, " If such be the fact, there 

 is an end of the question between my opponent and myself." 

 I trust, however, that without subjecting myself to the impu- 

 tation of obstinately adhering to preconceived opinions, I shall 

 be able to show that this question is not to be decided by 

 quite so summary a proceeding. A critical examination into 

 the real merits of the per-centage test, as a general rule for 

 determining the comparative ages of tertiary deposits, will be 

 found to exhibit such extensive limits of error in its practical 

 application, that so far as the present inquiry is concerned, I am 

 confident that no impartial observer would feel justified in en- 

 deavouring to form a conclusion, either on one side or the other, 

 from the evidence which has yet been obtained from this source. 



Before I proceed to discuss the value which should be at- 

 tached to certain numerical calculations, I must briefly digress 

 for the purpose of offering a few remarks upon the real nature 

 of the discussion now pending, and its abstract geological 

 importance. 



There are doubtless some to whom it may appear a matter 

 of little or no moment, whether we speak of these inferior 

 beds as forming the lower part of the crag formation, so long 

 as that geological distinction is made, or whether we consider 

 them altogether as a distinct deposit. Here I would observe, 

 in passing, that there is no a priori reason whatever why 

 a distinct deposit should not be found between the beds called 

 crag and the London clay. In fact, if we adopt Mr. LyelFs 

 present classification of the British and Continental tertiary 

 series, such a discovery would seem to be in every respect a 

 desideratum, for the crag being placed in the pliocene period 

 and the London clay in the eocene, a dc posit of an inter- 

 mediate age would lessen the hiatus between these two forma- 

 tions. Now among some of the important results which have 

 arisen from the accumulated observations of geologists are 

 certain general deductions, involving points of a physiological 

 or general philosophical nature which possess an extreme 

 degree of interest, apart from any connexion with geology as a 



See a paper by Mc^S^WoodwarJ in Lond. and Edinb. Phil. Mag., 

 vol. viii. p. 139; ajj^^a^so Mr. Lycll's address to the Geological Society, 

 Ibid., p. ox?7. 



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