The geological location of the Ledges in the state, the kinds of rock found there and their arrangement together with their structural features and some other factors, suggest a number of problems concerning the Pennsylvanian system of rocks in Iowa. Some of these problems are pointed out and discussed in this paper.
Proceedings of the Iowa Academy of Science
©1934 Iowa Academy of Science, Inc.
Smith, John E.
"The Ledges and Pennsylvanian Problems in Iowa,"
Proceedings of the Iowa Academy of Science, 41(1), 239-239.
Available at: https://scholarworks.uni.edu/pias/vol41/iss1/67