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A new group name, the Yellow Spring Group, is designated for those formations herein removed from the Kinderhook Series and assigned as the uppermost unit in the Upper Devonian Series. The formations comprising the Yellow Spring Group are, in descending order, the English River Formation, the Maple Mill Shale, the Aplington Formation and the Sheffield Formation. In spite of the gradational English River - Maple Mill contact in southeastern Iowa, and the local absence of English River and Maple Mill in northcentral Iowa, these formations have significant lithologic features in common that justify their recognition as a rock-stratigraphic unit with group status.
Recent work by paleontologists has resulted in raising the Devonian-Mississippian boundary from its previous position at the top of the Lime Creek to its presently, designated position at the base of the North Hill Group.
Iowa Geological Survey
iii, 30 pages, 13 figures
Stratigraphic geology; Devonian Geologic Period
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Dorheim, Fred H.; Koch, Donald L.; and Parker, Mary C.. The Yellow Spring Group of the Upper Devonian in Iowa. Iowa City: Iowa Geological Survey, 1969. (Report of Investigations, 9)