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recorded in the stratigraphical formations" (p. 197). It is the carrying out of this thought which requires the adoption of a dual nomenclature in the classification.

Perhaps the best thing that can be said in favor of such a proposition is, that it will enable us to record the facts of our science with greater precision, accuracy, and truthfulness; and nothing worse, I think, can be said against it than that it will cause confusion and difficulty in mapping and in the estimating of the relations and values of the old terms and system of classification, this simply because it is not the old system. Evolution has worked the same difficulty in the classifying of organisms, because it has suggested that species are changing and not fixed quantities, and in the early part of this century the principle of identification of rocks by their fossils upset, in a similar way, the elaborate classification of the Wernerian school based upon the supposed natural sequence of particular kinds of rocks.

Where new geology is being elaborated, the application of the dual method may be easily attained, and the adoption of the method by the United States Geological Survey has therefore been found possible and practicable. But the greatest difficulty, and hence the real retardation of progress, is found in applying the method where standards have been established and used on the old basis. The New York rocks constitute, for North America, the standard section of Paleozoic geology. They were classified on the basis of unity and integrity of geological formations.

By unity, I refer to the notion that a geological formation is an integral unit in the single geological stratigraphical column, which may be identified in distinct geographical regions by its fossils; and by integrity, I mean the notion that a formation is the same in its position in this column, wherever found, thickening and thinning, and even changing somewhat in the character of its material from place to place, but always the same in its relation to other formations.

Therefore, in discussing geology in North America, it has become a practice to use such terms as Oriskany, or Niagara, or