DUAL NOMENCLATURE IN GEOLOGICAL 

 CLASSIFICATION.' 



At the meeting of the American Association for the Advance- 

 ment of Science, at Rochester, in 1892, while discussing a paper 

 of Professor James Hall, read by Mr. Merrill, on the classifica- 

 tion of the Devonian rocks in eastern New York, I ventured to 

 express the opinion that the time was ripe for the recognition of 

 the duality of the group of facts which geologists attempt to 

 classify in what we call the geological column or scale of 

 formations. 



Since that meeting, Mr. Darton has published a paper ^ restat- 

 ing and commenting upon substantially the same facts reported 

 by Hall and proposing a special use of the name Catskill. Still 

 later papers have appeared by Professors Stephenson 3 and 

 Prosser^ discussing the proposition made by Mr. Darton, the 

 one from the stratigraphical, the other from the paleontological 

 point of view. There is also now going on the preparation of a 

 revised geological map of New York state, containing the typi- 

 cal paleozoic section for North America. These and other rea- 

 sons have led me to think it not inopportune to ask the serious 

 attention of geologists to the adoption of a dual method of 

 nomenclature in the classification of the facts of historical 

 geology. 



There is nothing novel in the proposition that there are both 

 stratigraphical and chronological divisions in the geological 

 classification, but it is only recently that practical geologists 



' Presented to the Geological Society at its meeting in Boston, December, 1893. 



^ Oneonta and Chemung formation in Eastern Central New York, Am. Jour. Sci., 

 III., Vol. XLV., p. 203. 



3 J. J. Stevenson : On the Use of the Name Catskill, Am. Jour. Sci. III., XLVI., 

 330. 



■* C. S. Prosser : The Upper Hamilton and Portage Stages of Central and Eastern 

 New York, Am. Jour. Sci., III., XLVI., p. 212. 



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