Page:Popular Science Monthly Volume 22.djvu/841

Rh During these years the New York geologists had accumulated a vast amount of material and of facts regarding the geological formations within the State, proving conclusively that they could not be parallelized with any of the described and well-determined formations of Europe. The Silurian system of Murchison, as described and illustrated in the "Edinburgh Review," in 1838, and as finally published in 1839, although covering a portion of similar ground, was not broad enough to meet the requirements of the geology of New York. Thus failing to find the means of comparison and identification, the term "New York System" was proposed, to embrace the sedimentary formations from the Potsdam sandstone to the base of the carboniferous system; or, as the formations were developed in New York and southerly into Pennsylvania, the upward extension of this term reached to the base of the coal-measures. This term, "New York System," includes the formations ordinarily embraced in the names Cambrian, Silurian, and Devonian of England and the Continent of Europe. The geological series in New York is so complete that the succession leaves no lines or breaks for the establishment of "systems," the whole being but a single system; and had the older rocks of the globe been first studied in this State, no such terms or subdivisions would ever have found their way into geological nomenclature. The strongest line of demarkation, however, or the most marked interruption of continuity in the succession, occurs at the termination of the Hudson River group, where a great conglomerate or a heavy-bedded and well-marked sandstone terminates the physical and biological conditions of the preceding period. This break in the continuity, which is the proposed limit of the Cambrian system, is, however, only of local importance.

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 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