At the state quarries, or North Bend quarries, in sections 5 and 8 of Penn township, Johnson County, Iowa, there is a body of limestone of Devonian age, possessing marked characteristics which set it off sharply from the rest of the Devonian in the upper Mississippi Valley. The formation has a thickness of about forty feet. At present there is some uncertainty as to its exact taxonomic relations.
Proceedings of the Iowa Academy of Sciences
©1896 Iowa Academy of Science, Inc.
"The State Quarry Limestone,"
Proceedings of the Iowa Academy of Science, 4(1), 16-21.
Available at: https://scholarworks.uni.edu/pias/vol4/iss1/5