DUAL NOMENCLATURE. 147 



recorded in the stratigraphical formations" (p. 197). It is the 

 carrying out of this thought which requires the adoption of a 

 dual nomenclature in the classification. 



Perhaps the best thing that can be said in favor of such a 

 proposition is, that it will enable us to record the facts of our 

 science with greater precision, accuracy, and truthfulness ; and 

 nothing worse, I think, can be said against it than that it will 

 cause confusion and difficulty in mapping and in the estimating 

 of the relations and values of the old terms and system of class- 

 ification, this simply because it is not the old system. Evolution 

 has worked the same difificulty in the classifying of organisms, 

 because, it has suggested that species are changing and not fixed 

 quantities, and in the early part of this century the principle of 

 identification of rocks by their fossils upset, in a similar way, 

 the elaborate classification of the Wernerian school based upon 

 the supposed natural sequence of particular kinds of rocks. 



Where new geology is being elaborated, the application of 

 the dual method may be easily attained, and the adoption of the 

 method by the United States Geological Survey has therefore 

 been found possible and practicable. But the greatest difificulty, 

 and hence the real retardation of progress, is found in applying 

 the method where standards have been established and used on 

 the old basis. The New York rocks constitute, for North 

 America, the standard section of Paleozoic geology. They were 

 classified on the basis of unity and integrity of geological for- 

 mations. 



By unity, I refer to the notion that a geological formation is 

 an integral unit in the single geological stratigraphical column, 

 which may be identified in distinct geographical regions by its 

 fossils ; and by integrity, I mean the notion that a formation is 

 the same in its position in this column, wherever found, thicken- 

 ing and thinning, and even changing somewhat in the character 

 of its material from place to place, but always the same in its 

 relation to other formations. 



Therefore, in discussing geology in North America, it has 

 become a practice to use such terms as Oriskany, or Niagara, or 



