The wide celebrity of the fern-bearing concretions from the Carboniferous beds of Mazon Creek, Illinois, attaches more than passing interest to the occurrence of similar structures in the Coal Measures of Iowa.
Proceedings of the Iowa Academy of Sciences
©1893 Iowa Academy of Science, Inc.
Spencer, Arthur C.
"Occurrence in Iowa of Fossiliferous Concretions Similar to Those of Mazon Creek,"
Proceedings of the Iowa Academy of Science, 1(Pt. 4), 55-55.
Available at: https://scholarworks.uni.edu/pias/vol1/iss4/20