Page:The Journal of geology (IA journalofgeology21894univers).pdf/164
cation of the dual system of nomenclature needs to be insisted upon. And when the occasion for revision of an accepted standard, 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 closing. It was a bold step when, over fifty years ago, the New York state geologists, Emmons, Mather, Vanuxem and Hall, discarded the then standard Wernerian classification to which McClure and Eaton had, with great pains, adjusted our American 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 stratigraphy 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 developed in western New York, and becomes insignificant or is wanting 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-