CADENT, VERGENT, AND PONENT.
The Oriskany sand-rock appears to represent a place in the Ludlow rocks of England, and the base of the Devonian period of the English geologist. It forms a break in the Palfeozoic strata, and forms a change of the ancient life : a new creation begins here.
The Cadent series are made up principally of slates, shales, and lime stones, generally highly bituminous, and range from the Corniferous lime stone to the Genesee slates of New York. These formations may be considered as the lower oil-producing rocks, commencing with the cornife rous lime, which is saturated with oil, wherever found, in New York, Pennsylvania, or Illinois. The following, or Vergent series, comprising the Portage and Chemung groups of New York, are also bituminous in character, and made up of vast beds of gray, blue, and olive-colored shales, and gray and brown sandstones, in thin layers or flags, parted by bands of soft blue slate, and abounding in fossils of fucoids or sea-weeds.
The Ponent rocks are thick masses of red shales and red and gray sandstones, and are represented by the Catskill of New York and the Old Red Sandstone of the English.
All these formations have their maximum thickness along the Atlantic slopes, or the eastern borders of the great Appalachian chain or basin, and they all thin rapidly as they extend westward, with the exception of the limestones, which appear to increase in thickness as they approach the interior of the ancient sea. It is probable, however, that the rocks forming its eastern boundary will also be found to predominate along its western margin and on the eastern slope of the Black Hills and the Rocky Mountains. (?) The old red sandstone is lost in the western basins.