SUMMARY AND CONCLUSIONS 149 



In the use of fossils, for determining the geologic horizon of the 

 formations containing them, the essential fact open to investigation is 

 the presence or absence of the fossils themselves. The presence of in- 

 dividual fossils indicates, not some narrowly limited horizon, but a gen- 

 eral portion of the stratigraphic scale represented by the system or by a 

 large subdivision of it. By close discrimination characters of narrower 

 vertical range can be detected, but up to the present time very few char- 

 acters of fossils are known whose vertical range-limits are so narrow as to 

 indicate an horizon of less than about a third of a standard system. 



Certain modifications of current usage are suggested by the facts here 

 presented, which may be expressed by the following recommendations : 



In seeking to perfect the rules governing nomenclature and classifica- 

 tion of sedimentary geologic formations should not the following prin- 

 ciples be applied : 



1. The abolition from the nomenclature, definition, and classification 

 of geologic sedimentary formations of all reference to time or time rela- 

 tions. 



The application of this rule would result in the rewording of rule 14 

 of the " Revised Rules," as suggested at the opening of this paper. 



2. The adoption of lithologic characters, stratigraphic position, and 

 paleontologic contents as three (at least) chief means for. discriminating 

 and defining sedimentary formations. 



3. The revision of technical nomenclature in the following particulars : 

 In the place of time scale use the term stratigraphic scale ; in place of 

 contemporaneity use homotaxy ; in place of age, in its general sense, 

 apply the term horizon'with the definite and technical meaning of posi- 

 tion in the vertical stratigraphic scale ; in place of period use the term 

 system ; it has already become common practice to speak of group, 

 series, and formation on this general principle ; in the place of earlier or 

 older adopt the terms inferior, lower, subjacent, or underlying ; in place 

 of younger or later adopt the terms superior, superjacent, overlying ; 

 and in general in the selection of descriptive terms to apply to sedi- 

 mentary formations, both in definition and correlation, employ physical 

 characters (such as composition, texture, structure), special dimensions, 

 and position in a vertical stratigraphic column in place of any chrono- 

 logic terms, these latter, so far as formations are concerned, being infer- 

 ential, not observable, and incapable of accurate application on account 

 of the wide divergence of opinion as to the modes of their determination. 



In proposing these changes in usage it should be stated that it is not 

 intended in any sense to exclude the consideration of time relations in 

 geological discussions, but rather to remove from the definition and dis- 

 crimination of formations any reference to their supposed time relations 



