466 Scientific Intelligence, Sfc. 



crag in the miocene division ; while Dr. Fleming, who, for more 

 than a quarter of a century, has been an indefatigable collector of 

 British shells, considers that the proportion 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 geologist 

 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 pre- 

 sented 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 contemporaneous those deposits which 

 respectively furnish the same per-centage of extinct forms, without 

 the slightest reference to the greater or less degrees of approximation 

 which these forms exhibit, when compared with living types. The 

 conchologists who agree with Dr. Beck cannot, by means of the 

 per-centage test, express the difference in the amount of approxi- 

 mation presented by the testacea of the crag and London clay to 

 those now existing, because they would consider all the fossils of 

 both these formations extinct, and, consequently, refer them both to 

 the eocene division. 



In this instance, the relations of analogy can only be obtained by 

 a general estimate of the amount of resemblance borne to existing 

 species by the entire series of crag or London clay fossils, taken 

 collectively. This mode of procedure may, at first, appear only a 

 different adaptation of the numerical plan adopted by Mr. Lyell. 

 It will, however, be found an important modification of his principle; 

 for, when applied to the fossils of those formations which, from the 

 presence of living species, can also be subjected to the per-centage 

 test, it will, under some circumstances, furnish results that clearly 

 establish a fallacy in one of the two methods. For instance, the 

 red and coralline crag are supposed by Deshayes to contain the 

 same number of extinct species ; and, by the per-centage test, they, 

 therefore, present an equal approximation to the existing organization. 

 But if the shells, which Deshayes thinks he can identify with those 

 now inhabiting the German Ocean, are rejected, and the extinct 

 testacea alone compared with living types, the forms most remote 

 from existing species will be found to occur in that series which has 

 been derived from the coralline crag. 



The author then changes his line of argument, and, assuming that 

 there is a general agreement among conchologists as to the characters 

 which should be depended upon in discriminating species, and also, 

 that the per-centage test is the true method of obtaining relations 

 of analogy, he proceeds to inquire whether the association of organic 

 remains in fossiliferous deposits implies their previous contempor- 

 aneous existence. The evidence drawn from this source appears to 

 the author to be by no means so conclusive as it has been generally 

 considered ; and his opinions have been formed principally from an 

 attention to the causes now in operation upon the earth's surface. 



