The Devonian System, in Iowa, is exposed in a belt about 50 miles wide extending along a line from Mason City to Muscatine. With the exception of the Shell Rock Formation the Upper Devonian is essentially elastic, dominantly shale. The Middle Devonian is dominantly carbonate, and the lower Devonian, known only from subsurface, appears to be dominantly chert with minor amounts of carbonate (Parker, 1967).
Proceedings of the Iowa Academy of Science
©1970 Iowa Academy of Science, Inc.
Dorheim, Fred H.
"The Economic Geology of The Iowa Devonian,"
Proceedings of the Iowa Academy of Science, 77(1), 257-265.
Available at: https://scholarworks.uni.edu/pias/vol77/iss1/38