Page:The Journal of geology (IA journalofgeology21894univers).pdf/172

not alike for different sections which are geographically not greatly separated from each other.

The Catskill formation is primarily a local formation exhibited in the Catskill mountain region of New York, distinguished physically as a series of sandstones and shales with greater or less red-color, and by the absence of marine fossils, and the occasional presence of shells and fish believed to have been of fresh or brackish water habitats. It is the local expression of the broadening shore condition of the continental elevation which brought in the coal-making, or Carboniferous age of eastern North America. As a formation, it is separated from what went before by the reddening, or graying of the sandstones and shales, their coarser, more irregular structure, the departure of marine organisms, and the occasional appearance of brackish water shells, fishes, and some fossil drift-wood and plants. In relation to the time scale, the period of beginning of this formation varies with the regions in which it is exposed. At its extreme eastern extension, on the peninsula of Gaspe, and in eastern New England, it began in the Eodevonian Period. Along the Hudson River, it began at the beginning of the Neodevonian, or perhaps before the termination of the Mesodevonian. In the region of Oneonta and westward it began soon after the beginning of the Neodevonian Period, and then withdrew eastward, the marine conditions returning over the region leaving the Oneonta formation as its record, and later in the middle of the Neodevonian, it returned and continued on to the close of the Devonian era. In the region of Bradford County, Pennsylvania, it did not begin to be deposited till near the close of the Neodevonian Period. Farther west the Olean Conglomerate marks the final close of the Devonian Era, and the formation in question did not begin till after the close of the Devonian. In the eastern Pennsylvania and more southern sections, its age varies with the locality. In general, it is terminated above by indications of the presence of permanent land conditions, either massive beds of rounded pebbles or conglomerates, or thin beds of coal or carbonaceous shales, or, in the absence of actual change in formation, the line is arbitrarily set by the supposed tracing of