Page:The Journal of geology (IA journalofgeology21894univers).pdf/159

At the meeting of the American Association for the Advancement of Science, at Rochester, in 1892, while discussing a paper of Professor James Hall, read by Mr. Merrill, on the classification 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^[2] restating 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^[4] 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 typical paleozoic section for North America. These and other reasons 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