i38 H. S. WILLIAMS — NOMENCLATURE AND CLASSIFICATION 



classifying formations. In papers recently completed and now being 

 published as Bulletin 244 of the United States Geological Survey the 

 application of these principles and rules to certain specific cases is set 

 forth in detail. 



Suggested Modification of Rule 14 



In all these various papers the attempt was made to employ common 

 nomenclature, as far as practicable, in describing the intricate relation- 

 ships existing between the fossil faunas and the geological formations 

 under discussion. While revising the proofsheets of Bulletin 244, how- 

 ever, the conviction became positive to the writer that one of the chief 

 difficulties presented by this whole problem of classification and nomen- 

 clature of geologic formations arises from the very vague and uncertain 

 use of the word " contemporaneity." In the revised " rules " referred to, 

 although the word " contemporaneity " is dispensed with, the idea is. 

 still perpetuated in the phrase " chronologic equivalences." Rule 14 

 reads as follows : 



11 The fundamental data of geologic history are (1) the local sequences of forma- 

 tions and (2) the chronologic equivalences of formations in different provinces' 

 Through correlation all formations are referred to a general time scale, of which 

 the units are periods. The formations made during a period are collectively 

 designated a system." 



The purpose of the present paper is to raise the question as to whether 

 " chronologic equivalences of formations " are fundamental data of geo- 

 logic history, and, if not, whether the " fundamental data " indicated by 

 that expression are not in reality the similarities in the fossil faunas of 

 formations of different provinces. In practice is it not also true that 

 formations are not referred to a "general time scale," but to a strati- 

 graphic scale, of which not " periods," but systems, are the units ? Con- 

 sidering these queries as answered in the affirmative, why should not 

 rule 14 read as follows : 



The fundamental data of geologic history are (i) the local sequences of 

 formations and (2) the similarity of the fossil faunas of the formations of dif- 

 ferent provinces. Through correlation all formations are referred to a standard 

 stratigraphic scale, of which the units are systems. 



Views of Huxley and Geikie 



Before discussing the facts of the particular case or bearing on this 

 proposition, the exact point in issue may be emphasized by referring to 

 the argument used by Huxley in 1862 for the substitution of " homataxis " 

 for " contemporaneity." 



