SUGGESTIONS CONCERNING NOMENCLATURE 389 



elsewhere for certain important parts of the sedimentary record that 

 happen to be either wanting or not well shown in New York. 



In accepting the New York section as the standard for especially the 

 Ordovician, Silurian, and Devonian systems in southeastern North 

 America, it seems to me we should endeavor to apply the New York 

 nomenclature as far as a liberal interpretation of the facts will permit. 

 Of course we should not go back to the practice of our fathers who re- 

 quired but one set of formation names which they applied with great 

 confidence in all parts of the country. Today we realize that only a few 

 of the names given to lithologic units in New York are strictly applicable 

 to stratigraphic units recognized in the Ohio and Mississippi valleys. 

 The Lowville and Onondaga limestones are the best and perhaps only 

 unquestionable examples, but with some shifting of boundaries a few 

 others would pass. Yet other formations are quite as typically developed 

 in the iVppalachian Valley as in New York, and in these cases it would 

 be a pity if the New York names were not extended southwardly in 

 designating the corresponding beds, whether they are viewed as distinct 

 formations or as members of the larger formational units commonly 

 thought unavoidable in mapping the rocks of folded areas. 



Correlations being established and the lithic characters reasonably 

 uniform, the remaining essential condition on which the applicability of 

 a New York formational designation in other than the typical area is 

 determined is that the deposits should belong to the same continental sea. 

 In other words, when the faunas and waters which laid down a New York 

 formation can be traced to the Gulf of Mexico in one case, the north 

 middle Atlantic in another, or possibly the Arctic in a third, the de- 

 posits of similar age and character in the path of the particular invasion 

 should be known by the same name. This rule implies continuity of 

 Buch formational units and it is doubtless so even when the fact can not 

 be demonstrated by uninterrupted outcrop. Oscillatory movements and 

 consequent irregularities in shifting of strandlines of continental seas 

 were too frequent to render such continuity of crop at all common. 



Many of the stratigraphic units, more particularly of the Ordovician 

 and the upper series of the Silurian, are represented in New York by 

 not only a lesser thickness of deposits, but the accessible marine record 

 there indicates more frequent and longer enduring interruptions of the 

 process of sedimentation than in areas to the south. This is explained 

 by the fact that each of these formations represents a distinct invasion 

 of the sea and that the ensuing deposits overlap to extinction on the 

 sloping surfaces of contemporaneous land projections extending into 

 northeastern New York from Canada. In consequence the eroded edges 



