The presence of great numbers of geodes of varying size and degree of development in the Keokuk beds of the Central Mississippi Valley has long been known to geologists, but their origin has been, from the earliest times, a disputed question, and, although there has been considerable speculation upon the subject, no theory of their formation has been, as yet, widely held.
Proceedings of the Iowa Academy of Science
©1912 Iowa Academy of Science, Inc.
Van Tuyl, Francis M.
"The Origin of the Geodes of the Keokuk Beds,"
Proceedings of the Iowa Academy of Science, 19(1), 169-172.
Available at: https://scholarworks.uni.edu/pias/vol19/iss1/29