RELATION OF BIOLOGY TO GEOLOGICAL INVESTIGATION. 261 



Besides the facts already indicated fclie following liave special signifi- 

 cance in this connection. All fossil remains are more or less imperfect 

 as such because of the destructive natural conditions f<> which they 

 inevitably have been subjected, and the firm consolidation of most of 

 the rocks containing them lias rendered impossible the recovery of the 

 greater part of those which have really been preserved. Tin 1 successive 

 displacements which have taken place in the crust of the earth have so 

 exposed the sedimentary formations to erosion that during the succes- 

 sive epochs large portions of all of them have been destroyed, together 

 with their fossil contents, thus reducing the paleontological record to 

 that extent. Other large portions of those formations have been so 

 completely covered by succeeding deposits, by debris resulting from 

 their erosion, and by the waters of present lakes and seas that they are 

 inaccessible for study, and the avadable paleontological record has been 

 thereby still further reduced. 



An additional reduction has doubtless been accomplished by meta- 

 morphism — that is, in view of many important facts, both physical and 

 biological, it is not unreasonable to conclude that the various series of 

 pre-Canibrian stratified formations which are found in different parts of 

 the world were once fossiliferous, and that the fossils they then con- 

 tained have been destroyed as such by the metamorphic action which 

 changed the mineral character of the strata. 



If fossils were to be treated only as mere tokens of the respective 

 formations in which they are found, their biological classification would 

 be a matter of little consequence, but their broad significance in his- 

 torical geology as well as in systematic biology renders it necessary that 

 they should be classified as nearly as possible in the same manner that 

 living animals and plants are classified. Considering the imperfection 

 of all fossil remains, the question arises, Can they be classified upon the 

 same general plans and by the same systematic methods that are used 

 for living animals and plants? The answer is mainly in the affirmative, 

 because structural characteristics are possessed by the fossilizable parts 

 of animals and plants which are cognate, coincident, and of a similar 

 classificatory character with those of the unfossilizable parts, although 

 the latter, being more complete and convenient, are mainly relied upon 

 in the classification of living forms. 



As regards the classification of animal fossil remains, precisely the 

 same system is available that is used for living animals, the former 

 classification being in fact, only an extension of the latter. In the 

 former case, however, the methods and details depend more fully than 

 in the latter upon the well established principles of comparative anat- 

 omy, because the direct and complete anatomical study of fossil animals 

 is for obvious reasons impracticable. Indeed, it is upon comparative 

 anatomy that most of the real scientific value of fossils depends, and 

 without its aid they would always remain little more than mere curios 



