C. D. Walcott — The Taconic System of Emmons. 229 



Aet. XX. — The Taconic System of Emmons, and the use of 

 the name Taconic in Geologic nomenclature / by Chas. D. 

 Walcott, of the U. S. Geological Survey. With Plate III. 



The nomenclature employed in classifying geologic forma- 

 tions and terranes should be based upon priority of definition 

 and upon the accuracy of the original observations ; the latter 

 to be judged by the testimony of the formations within the 

 areas where they were first made. If the original proposer of a 

 name bases it upon such errors of observation and interpreta- 

 tion that subsequent observers cannot verify his work, and the 

 name can only be used by dropping a name proposed as the 

 result of accurate observation and definition, the latter should 

 be retained. 



There is another principle that has been frequently over- 

 looked in discussions relating to the nomenclature to be applied 

 to geologic formations and groups of formations forming ter- 

 ranes. It is this : In the evolution of stratigraphic and his- 

 toric geology, stratigraphic geology preceded paleontologic 

 stratigraphy : that is, the succession of strata for a given geolo- 

 gic province was first determined and then the succession of 

 organic remains in the strata. This has been so far perfected 

 that, in most instances, the known succession of life in a 

 geologic terrane in one province can be compared with that in 

 some other not geographically connected with it : also, different 

 sections of strata in the same province may be compared with 

 one another when the continuity of the strata is broken. 

 From this it follows : First : that the unit of geologic nomen- 

 clature is the formation as lithologically determined, and the 

 combination of these units in any given section builds up the 

 greater geologic divisions. Second : that the means of corre- 

 lation of the formations and terranes of one province with 

 those of another, is by the order of succession, as stratigraph- 

 ically determined, of the contained organic remains of the 

 respective formations and terranes. 



A paleontologist should rely largely upon the evidence of 

 geologic age furnished by the fossils ; but. at the same time, as 

 a geologist, he should endeavor to obtain their stratigraphic 

 position and order of succession in each geologic province. 

 An example of the desirability of this is shown by the vertical 

 distribution of the Devonian fauna in central Nevada, where 

 several species of the Lower Devonian fauna of New York oc- 

 cur at the Upper Devonian horizon, in the Eureka district. 

 (Introduction to Monograph viii, U. S. Geol. Survey). 



Am. Jour. Sct.— -Third Series. Vol. XXXV, No. 201.— March, 1888. 

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