Page:The Journal of geology (IA journalofgeology21894univers).pdf/166

In the discussion of Professor Hall's paper at the Rochester meeting, the question came definitely before us as to the relative value of fossils and structure as means of determining or tracing equivalency of age of formations. In that discussion I maintained that fossils are always the only certain means of carrying from one geological basin to another the evidence of time-relations of the deposits, that structure was indicative of equivalency only when actual continuity of a formation can be traced. Both of Mr. Stevenson's^[1] papers recognize the physical features of the formation to be of great importance in determining its position in the time-scale, and in his use of terms he appears to be classifying formations and yet using the language of the time-scale. In his presidential address he maintained, as quoted by himself, that the series of beds included within the Catskill and Chemung Periods should be grouped into one period, the Chemung, with three epochs, the Portage, the Chemung and the Catskill (page 320), and in his paper in 1893, he insists that the Chemung, and not the Catskill, is the epoch whose name should be applied to designate the whole group, while Catskill must be retained in its original signification only.

Mr. Darton, on the other hand, is discussing the formation-scale alone. The principal purpose of his investigation is said to be to determine the relations and distribution of the Oneonta and Chemung formations (p. 203). In the passage on the status of the name "Catskill" the author proposes to discontinue the use of Catskill as a coördinate formation term, and use the term "Catskill group," to include the Portage and Chemung formations (p. 209). He maintains, correctly, I think, that the term Catskill has been applied in the past to beds of a certain lithologic character—the hard sandstones and red shales—and it has had no definite stratigraphic significance. The rocks of the Catskill Mountains and westward have no distinctive fauna of stratigraphic significance, and they cannot be correlated on paleontologic grounds (p. 208).