The cretaceous deposits of Woodbury and Plymouth Counties are composed of sandstones, shales and certain calcareous deposits. The heavier beds of sandstone belong to the basal portion of the series, barely rising higher than forty feet above the level of the water in the Big Sioux River. The part of the column to which these heavier sandstones are confined is, however, not all sandstone, but consists of arenaceous beds alternating with beds of argillaceous shales. Above the more massive sandstones the beds, for a vertical distance of fifty to sixty feet, contain streaks and thin layers of sand, but shales preponderate. In certain typical exposures these alternating beds are followed by from thirty to forty beds of pure shales, dark in color, smooth and unctuous to the feel, and containing the remains of saurian related to Plesiosaurus, teleost fishes, and in the uppermost beds, impression of Inoceramus. The summit of the column, overtopping shales and sandstones alike, are the calcareous beds to which allusion has been made. These consist, in part, of soft, chalky material and in part of more indurated, though still soft, beds of fissile limestone that divides under the hammer or on exposure to the weather, into relatively thin laminae crowded with detached valves of Inoceramus problematicus Schlot.
Proceedings of the Iowa Academy of Sciences
©1892 Iowa Academy of Science, Inc.
"The Relation of the Cretaceous Deposits of Iowa to the Sub-Divisions of the Cretaceous Proposed by Meek and Hayden,"
Proceedings of the Iowa Academy of Science, 1(Pt. 3), 7-12.
Available at: https://scholarworks.uni.edu/pias/vol1/iss3/4