295 



Facts like these prove, if I mistake not, the impossibility of insti- 

 tuting any rigid comparison between all the successive groups in the 

 basins of Paris and the Isle of Wight. But discrepancies in minute 

 details militate in no respect against Mr. Webster's leading gene- 

 ralizations, which have received such a striking and unlooked-for 

 illustration in the fossil mammalia of Binstead. If the hints now 

 thrown out should induce him to lay before the public some part of 

 his valuable observations on our different tertiary deposits, or to 

 hasten the publication of his long-promised work on the Isle of 

 Wight, my present purpose will be completely answered. 



In these papers, a brief analysis of which I have now placed before 

 you, we have some new and striking proofs of the great importance 

 of organic remains in determining the comparative age of remote 

 and discontinuous formations. And we have seen that in cases where 

 we have few examples of specific agreement, we can, from the aspect 

 of large groups of fossils and the general resemblance of their generic 

 types, form at least a probable estimate of the age of the deposits to 

 which they are subordinate. Inferences of this kind would be alto- 

 gether worthless were they invalidated by the direct evidence of 

 geological sections. But we deny that this is in any respect the case ; 

 and our conclusions are the more certain, because they are not only 

 founded upon a wide induction of particulars, but are consistent 

 among themselves. 



There can be no doubt that in the ancient ocean, as well as in the 

 present, the distribution of organized beings was affected by many 

 causes— by the temperature and depth of the waters — by the nature 

 of the soundings — by the action of tidal currents — and by other unap- 

 preciable disturbing forces. Even among the old secondary groups 

 we can sometimes separate littoral formations from those of deep seas, 

 not merely by their mineral structure, but also by their fossils : and 

 in all geological periods of the history of the earth, formations on the 

 shores and formations in deep seas must have gone on together. 



Again, our great formations may be subdivided into many dis- 

 tinct mineralogical groups of strata ; and the large suites of organic 

 remains, characteristic of the formations as a whole, may also be sub- 

 divided into many groups, the species being defined by the mineral 

 structure of the beds to which they are subordinate. 



All this is in harmony with the distribution of the animal kingdom 

 in the existing seas. Some animals may be found almost indifferently 

 on a calcareous, a sandy, or a muddy bottom (for example, the float- 

 ing cephalopods) ; and the remains of ancient animals of kindred 

 organization occur indifferently in calcareous, siliceous, and argilla- 

 ceous groups of strata. Some animals have lived and propagated 

 under the waters of a muddy shore ; the remains of these occur 

 abundantly in our secondary beds of shale. To the very existence of 

 some shells calcareous rocks are necessary ; and on banks of mud or 

 moveable sand, corals and attached zoophytes could find no proper 

 resting place. Hence it is that many species of shells and zoophytes 

 are chiefly characteristic of limestone strata j and if they exist at all 



