Southern Extension of the Cretaceous in Iowa

The Cretaceous deposits of Iowa, from time to time, have received the attention of a number of geologists. The most important researches were made by Marcou, Meek, Heer, White and Calvin. Their investigations were carried on chiefly in the vicinity of Sioux City. The formation elsewhere in the State has, with a few exceptions, received no consideration. Its exact extent is yet to be determined; its vertical thickness is yet unknown; the relative ages of some of its beds remain to be established