I 5 O THE JO URN A L OF GEO LOG V. 



cation of the dual system of nomenclature needs to be insisted 

 upon. And when the occasion for revision of an accepted stand- 

 ard, such as the geology of New York state, appears, it is more 

 important to adapt the classification to the needs of the coming 

 century than to preserve the imperfections of the one now clos- 

 ing. It was a bold step when, over fifty years ago, the New 

 York state geologists, Emmons, Mather, Vanuxem and Hall, dis- 

 carded the then standard Wernerian classification to which 

 McClure and Eaton had, with great pains, adjusted our Ameri- 

 can geology, and, describing the New York rocks just as they 

 found them, with new names and a new classification, formed 

 the New York system. This New York system has become the 

 standard formation-scale for American geology. 



But since the New York system was described, the fossils, 

 which were then looked upon as mere marks by which to identify 

 the formations, have come to be known as the evidences of the 

 gradual evolution of species, each one holding its definite place 

 in a continuous history of organism. As stratigraphy replaced 

 the Wernerian lithology in classifying formations in 1840, so 

 now paleontology comes forward to take the place of strati- 

 graphy as the true means of classifying geological periods. 



The case of the Catskill formation is in point. It has been 

 a recognized fact, since the New York State Survey Reports 

 were published, that the Catskill formation of New York was 

 peculiar to the eastern parts of the state, and that it thins out on 

 passing westward, and that the Chemung formation is well devel- 

 oped in western New York, and becomes insignificant or is want- 

 ing in the east. According to the single method of geological 

 classification, it is necessary to call one above or below the 

 other, and in our geological columns we have been accustomed 

 to see the Catskill as the upper member of the Devonian lying 

 above the Chemung, and because usage has vacillated between 

 the time-scale and the formation-scale the confusion has been 

 very difficult to formulate, or to bring to the minds of geologists. 



If we are discussing the formation-scale, it is true to the 

 facts. to speak of the Catskill formation as lying above the Che- 



