SUGGESTIONS CONCERNING NOMENCLATURE 387 



have been separately designated the giving of a new name at the third 

 locally would be unnecessary. When two or more of the members have 

 thus become separately recognized the original formation name takes on 

 the rank of a group term, while the members become formations on the 

 ground of being either lithologic units or stratigraphic units separated 

 by physical and faunal criteria indicating interruptions of the process of 

 deposition. A great variety of conditions depending on overlap of de- 

 posits, irregularities in distribution, erosion of upper members, lateral 

 change in character of sediments, etc., and each requiring some corres- 

 ponding modification of the rules of nomenclature may be imagined and 

 indeed are encountered in daily practice. The really very rare condition 

 of a tangential basal deposit thick enough to be worthy of a separate 

 name will be discussed later on. 



Local stratigraphic terms. — No local section contains within itself the 

 data required for anything approaching a final classification of its com- 

 ponent parts. This becomes possible only when exhaustive comparisons 

 with many other near and far sections have been made. It is for this 

 reason chiefly that the indiscriminate and irresponsible naming of litho- 

 logical units is objectionable. The divisions are seldom drawn with due 

 regard to the organic and diastrophic histories of the several beds. The 

 practice is defensible only on the ground of expediency, but it is a ques- 

 tion if the good gained through it ever balances the evil done to the 

 science as a whole. Still, I am willing to admit that hitherto it has been a 

 necessary evil ; but is it so today ? The evil, too, would be much less if the 

 suggestion on a preceding page concerning elasticity of boundaries were 

 adopted. Many of these local names, originally perhaps given in ignor- 

 ance, may with slight emendation be made to serve a good purpose. 



I should not be misunderstood as saying that the need for new names 

 has been satisfied. On the contrary, a great many more are required to 

 properly classify the stratigraphic units already known. I do not "there- 

 fore wish to discourage the naming of formations that have been proved 

 to differ in one or another valid respect from all related formations ; but 

 I do object to names proposed solely because of admitted ignorance re- 

 specting the relations of the beds in hand to some standardized section. 

 This knowledge should be acquired before the new section is classified and 

 supplied with a nomenclature ; or if it is necessary to publish before this 

 can be done purely temporary designations will serve the purpose of the 

 author quite as well as a new set of formal names. There can be no 

 valid excuse for a "formation" name like the "Shenandoah limestone ;" 

 nor is there a sufficient reason for applying two distinct sets of names for 

 the Paleozoic formations in the Black Hills and the Big Horn Mountains, 



