276 REPORT OF NATIONAL MUSEUM, 1892. 



tain to the universal chronological classification of the sedimentary 

 formations and to their correlation in different parts of the world. The 

 naturalist studies fossil remains as representatives of the long- succes- 

 sion of progressively and differentially developed organic forms which 

 during geological time have existed and become extinct and of which 

 succession the now existing forms of life constitute only the terminal 

 portion. It is the results of such studies as these that the geologist 

 uses in the philosophical studies referred to. While these questions 

 are discussed in following essays this one is devoted more especially 

 to questions pertaining to the practical study of geology in the field. 



The idea of using fossils as characteristic tokens of formations by 

 means of which they may be distinguished from one another and iden- 

 tified in their geographical extension began to prevail with the earliest 

 studies of structural geology. Originally they were apparently re- 

 garded as of little or no more value in the identification of formations 

 than was their lithological composition, to which, indeed, their use 

 seems at first to have been merely auxiliary. Although the use of 

 fossils soon came to be recognized as indispensable in the characteriza- 

 tion and identification of formations, and their investigation came to 

 constitute a leading feature in geological research, it was long before 

 they began to be studied in a philosophical rather than in an empirical 

 manner. 



That increase in their philosophical use did not diminish their value 

 in other respects, as is apparent from the fact that a large propor- 

 tion of the practical field work of to-day is necessarily based upon the 

 empirical use of fossils as tokens of formations. That is, a large propor- 

 tion of all the field work in structural geology depends upon the specific 

 identification of fossil remains with, necessarily, only incidental refer- 

 ence to their systematic biological classification, and with no necessry 

 reference to their value in other respects. Therefore the empirical use 

 of fossils is even now held to terms as simple as those which were em- 

 ployed by the early geologists. Although it is essential that geological 

 observations of all kinds should always be made with reference to all 

 related physical as well as biological facts which maybe available, it is 

 not to be expected or desired that this primitive empirical use of 

 fossil remains will ever be either discarded or diminished. 



The foregoing remarks are made in defense of even the simple use of 

 fossils just indicated, because it is evident that their value in that re- 

 spect, as well as in others, is often underestimated, even by some 

 geologists. The full measure of their usefulness, however, even in the 

 identification and characterization of formations, can be attained only 

 by a thorough investigation of comprehensive collections, prosecuted 

 with direct reference to, and a rational interpretation of, the biological 

 laws that governed the existence of the respective faunas and floras 

 which they represent, and with equally direct reference to the physical 

 laws which governed the production of the formations which they 

 characterize. 



