SUGGESTIONS CONCERNING NOMENCLATURE 385 



vician, than are the much less understood older formations which recent 

 studies have shown to be equally important in their physical and organic . 

 histories and therefore worthy of being classed in systems of their own. 

 In my judgment it would be of distinct advantage if the boundaries of 

 stratigraphic divisions comprising two or more formational units were 

 elastic. Indeed, the advantage of elasticity is apparent even in the case 

 of many of the formational units. In recognizing stratigraphic divisions 

 the rule in the past ten or fifteen years has been to adhere strictly to the 

 original definition with particular reference to the type section. In its 

 essence this rule is unquestionably a good one, but its strict enforcement 

 often leads to unnecessary duplication of names and to difficulties in the 

 exact determination and the graphic expression of correlations. 



Many of the formations, and in recent years most of the larger ones, 

 have been established without sufficient regard to subsequent necessary 

 correlations with some well established standard. Often because of diffi- 

 culties in cartographic representation, or it may be for no other reason 

 than lack of time for detailed work, formational units have been so 

 broadly drawn that they include one or more important and sometimes 

 easily discriminated natural boundaries. Besides obscuring or ignoring 

 the full history of the beds, it is an unnecessary burdening of stratigraphic 

 nomenclature to apply definite names to such arbitrary divisions of the 

 stratigraphic column. In subsequent exact and detailed stratigraphic 

 work these names must be either dropped into the limbo of the useless or 

 be redefined and restricted to some natural part of the mass originally 

 included under it. Obviously there are weighty objections to the latter 

 disposition of such names. But considering the difficulties frequently at- 

 tending the selections of suitable names, also the fact that usually the 

 later more detailed and presumably improved account practically relegates 

 the now inadequate original work to the "scrap heap," it may well be 

 questioned if the generally but slight confusion incident to such restric- 

 tion should be regarded as prohibitory. To insure exact understanding it 

 is suggested that subsequent usage of a redefined term should be ac- 

 companied by the name of the authority for the particular meaning 

 intended. 



It seems to me that stratigraphic terms, especially those of a higher 

 rank than formations, might well be regarded as subject to modifications 

 similar to those allowed in the definition of zoological names. In defining 

 a genus, which may be compared with a- system or group, the first es- 

 sential is the selection of a genotype — theoretically the species affording 

 the best expression of the generic characters. All species regarded as more 

 nearly related to this typical species than to any other generic type then 



