144 H. S. WILLIAMS — NOMENCLATURE AND CLASSIFICATION 



throughout that portion of the sections where the former faunas are 

 expected. 



This interpretation of the facts is associated with other evidence point- 

 ing to no unconformity or culling out of parts of the stratigraphic 

 series, but rather to a continuous, uninterrupted sedimentation, in which 

 the fossils so prominent at several particular horizons in New York are 

 actually wanting, and their place in the stratigraphic series u occupied 

 by other faunas, which in New York occupy intermediate positions. 



INTERPRETATIONS AND CONCLUSIONS 



Thus, if we interpret like faunas into equivalence of formation we are 

 obliged to say that in central and southern Virginia the Genesee and 

 Portage faunas range through the main part of the Romney and part of 

 the Jennings formations, and the Jennings holds a pure Chemung fauna 

 only in its upper or central part; but in no case do the fossil contents 

 give a basis for saying that the Romney is the exact equivalent of the 

 Hamilton or Marcellus, or both, nor that the Jennings is the exact equiv- 

 alent of the Chemung, when by equivalence is meant the same fauna or 

 fossil contents. Equivalence is therefore a correct term to apply to the 

 formation names united by a hyphen only when the inference is drawn 

 that the beds were deposited at the same period of time (contemporane- 

 ity), since the lithology, stratigraphy, and fossils are all diverse for each 

 couplet. Therefore it can not be claimed that there is either lithologic, 

 stratigraphic, or paleontologic equivalence. Of course, it is to be ex- 

 pected that at any particular epoch of geologic time in different regions 

 of the earth formations, were being made which present no agree- 

 ment in lithology or in fossils ; but when we come to deal with such 

 formations as geologic units, define them in scientific terms, and rep- 

 resent their outcrops on geologic maps, it is all-important to restrict 

 the terms of definition to observable facts, and to classify and name for- 

 mations as the same only when the terms of their definition agree. In 

 the case before us the terms of definition disagree. This fact alone is 

 sufficient reason for applying different names to the stratigraphic divis- 

 ions in Virginia (Romney, Jennings, and Hampshire) which are corre- 

 lated in a general way with divisions called Marcellus, Hamilton, Che- 

 mung, etcetera, in New York. It also follows from what has been said 

 that equivalence, when used in a chronologic sense, may or may not 

 mean equivalence of all or any of the criteria used in defining the for- 

 mation. A formation may be said to be equivalent in the chronologic 

 sense (that is, formed at the same time) when the lithology and paleon- 

 tology are entirely discordant, and it may be true, but the evidence of 

 the truth of the statement is complex and not discernible by simple 



