THE NAME ^'NEWARK'' IN AMERICAN STRA TIGRAPHY. 5 7 



Richmond coal, which are not in New Jersey. The unit is pecul- 

 iarly definite in that its lower and upper limits are marked by 

 conspicuous unconformities, while its strata are everywhere con- 

 formable with one another. Its composition, though not uni- 

 form, is so little varied that attempts to unravel its stratigraphy 

 and structure have been successful in but few districts. 



2. The name should include a local geographic terjn. — In the 

 nomenclature of historic geology there are two parallel sets of 

 terms, the one representing larger or smaller bodies of strata, the 

 other representing larger or smaller divisions of geologic time. 

 As the divisions of geologic time are based upon the classifica- 

 tion of strata, their names have been mostly derived from 

 stratigraphy, and there are many circumstances under which it is 

 a matter of indifference whether a given term be construed in its 

 stratigraphic or in its chronologic sense. Partly in this way 

 there has arisen a widely prevalent habit of confusing strata and 

 time. This confusion has an unfortunate influence on the treat- 

 ment of problems of correlation, as it leads to language implying 

 that the stratigraphic units of distant lands, for example, Europe 

 and America, are the same. As I understand the case each por- 

 tion of the general geologic time scale was based upon the strati- 

 graphy of some district, usually in Europe. Correlation at a 

 distance, for example, in America, does not determine the exist- 

 ence in America of the European formations, but only the exist- 

 ence of local formations deposited (in whole or part) in the 

 same portions of geologic time. Or, in other words, correlation 

 arranges the formations of a country in accordance with a 

 standard time scale. 



When the time relations of a formation or other stratigraphic 

 unit are unknown or are imperfectly known, a name derived from 

 the time scale can be employed only provisionally. As knowl- 

 edge of fauna and flora increases, opinions change as to time 

 relations, and experience shows that at any stage in the accumu- 

 lation of paleontologic data conflicting opinions may be held by 

 different students. Time names are thus unstable ; but a geo- 

 graphic name, depending as it does on simple relations readily. 



