Samples of carbonaceous material from several exposures of the Cedar Valley formation have been studied in order to establish a basis for calling the material a coal. Examination has shown that the material is a "cannel'' coal, and it is believed to be one of the earliest known coals in North America.
Proceedings of the Iowa Academy of Science
©1960 Iowa Academy of Science, Inc.
Dow, Verne E.
"Some Notes on the Occurrence of a Coal Seam in the Cedar Valley Formation of Johnson County, Iowa,"
Proceedings of the Iowa Academy of Science, 67(1), 253-259.
Available at: https://scholarworks.uni.edu/pias/vol67/iss1/37