Professor Hall himself says of the rationale of the system of nomenclature under which the New York surveys were conducted, and which has served as the basis of the Western surveys: "Since there was no possibility of identifying the individual rocks and groups of strata with those of Europe, as described, the New York geologists were compelled to give names to the different members of the series; and since the sandstones, limestones, slates, and shales are so similar in different and successive groups, it was impossible to give descriptive names which would discriminate the one from the other. Therefore, local names were proposed and adopted; as, for example, Potsdam sandstone, Trenton limestone, Niagara limestone, and Niagara shale (the two latter, with subordinate beds, making up the Niagara group), the Medina sandstone, the Onondaga salt group, the Hamilton, Portage, and Chemung groups, thus giving typical localities of the rock instead of descriptive names. This method or system of nomenclature leaves no possibility of mistake or confusion which might arise from a different appreciation of descriptive terms. The typical locality always remains for study, comparison, and reference, and there need be no difference of opinion or discussion as to what was intended by the use of any one of the terms. The progress of geological science in the country is greatly indebted to this system of nomenclature, and to the absolute working out of the succession of the groups, and the members of the same, to which it has been applied." The system was adopted by a vote of the Geological Board.
The geologists of the survey were accustomed to meet once a year in the Capitol of the State, to compare notes. "The comparison of observations and interchange of views led to the opening of correspondence, by a formal resolution of the New York Board, with other geologists, especially with those engaged in State surveys, of which several were then in progress. This correspondence led to an agreement for a meeting of geologists in Philadelphia in the spring of 1840, and this assemblage, of less than a score of persons, led to the organization of the Association of American Geologists, which, at a later period, on the occasion of its third meeting, added the term Naturalists; and, finally, by expanding its title, it became the American Association for the Advancement of Science." Professor Hall was president of this association, under its present title, at its Albany meeting in 1856.
The general results of Professor Hall's comparative studies in the West are given in the third volume of the "Paleontology," and more fully in the first volume of the "Report on the Geology of Iowa," where he was engaged in the survey, with Whitney and Worthen. To this survey he contributed a memoir on the paleontology of the State, as he did to the survey of Wisconsin; and some of the fruits of his paleontological labors may be found embodied in the geological reports of several other States. He declined to take the direction of the
