In Jefferson County the Pella beds of the Saint Louis formation have a thickness of about twenty feet. They consist of heavy ledges of calcareous limestones, interbedded with seams of marly shales, the latter being best developed in the upper part of the section. The several seams and ledges appear quite persistent and some have been identified at different points a few miles apart. They have evidently been laid down at some considerable distance from the shore. Occasionally there are ledges of limestone which are very fine-grained, almost lithographic in texture. Here as elsewhere in the south part of the state, the fauna of the formation is meager in species but quite prolific in individuals. Pugnax ottumwa, Spirifer keokuk, Zaphrentis pallaensis, Anisotrypa fistulosa, and stems of crinoids appear everywhere, especially in the marls. This has long been known.
Proceedings of the Iowa Academy of Sciences
©1901 Iowa Academy of Science, Inc.
Udden, J. A.
"On the Occurrence of Rhizopods in the Pella Beds in Iowa,"
Proceedings of the Iowa Academy of Science, 9(1), 120-120.
Available at: https://scholarworks.uni.edu/pias/vol9/iss1/20