the relative Age of Tertiary Deposits. 9 



the characters which its fossils, considered collectively, present, 

 it would appear much older than the superjacent tertiary 

 beds, but if the numerical test be made use of, the apparent 

 age of both these deposits would be equal. Some remarks by 

 Professor Phillips which have appeared in the Encyclopcedia 

 Metropolitana, and which were probably written bef()re 1 had 

 described the conditions under which the organic remains of 

 the crag are deposited, bear very strongly upon the above 

 statement. The passage is as follows ; " Upon comparing 

 them [that is, the crag fossils,] with recent kinds, we are pre- 

 sented with very curious and striking results. There are se- 

 veral of the crag shells so exceedingly similar to recent shells 

 of the German Ocean that it is impossible to distinguish them. 

 Turbo littoreus retains its colour, many others are with dif- 

 ficulty separated by minute discrimination ; but some, as the 

 corals of Orford^ Pecten Princeps, Terebratula iJalei, and 

 others^ are evidently unlike anything now existing in the Ger- 

 man Ocean, and indeed not now to be paralleled in any part of 

 the world" — Encyc. Metrop., Geology, p. 674. 



Now the Corals, Pecten and Terebratida, spoken of by Pro- 

 fessor Phillips as so utterly unlike anything now existing, are 

 fossils of the lower or coralline crag. The Turbo littoreus re- 

 taining even its colour, so far as my own experience has gone, 

 occurs only in that bed where we meet with existing species 

 of Mammifera, and the more recent origin of which I have 

 from the first endeavoured to establish. 



From what 1 have advanced it will be seen that I am dis- 

 posed to regard the source of error now under consideration 

 as involved in the application of the per-centage test, and if 

 the history of the crag be ever thoroughly worked out, 

 I think this view will be confirmed. The fallacy probably 

 consists in supposing that by number we can obtain a true 

 expression of relations of affinity, when being totally ignorant 

 of the characters which constitute species, we have really no- 

 thing upon which to found our numerical calculations. 



I pass on from the consideration of this rather intricate 

 question to another stage of the inquiry; and here for the sake 

 of argument I must assume that there is a general agreement 

 among conchologists as to the characters upon which specific 

 distinctions are founded, and also that the true method of ob- 

 taining relations of affinity is the one which has been adopted 

 by Mr. Lyell and M. Deshayes. 



[To be continued.] 



Third Series. Vol.10. No. 58. Jan, 1837. 



