The Geology of Greene County, Iowa

A layer of Wisconsin drift ranging up to 150 feet in thickness mantles the better part of the bedrock surface of Greene County. The shales and coals of the Pennsylvanian Des Moines series are limited to three townships in the southeastern part of the county. The sections are small and difficult to place in the stratigraphic column, due to the absence of key horizons. Access to strip pits and test hole records has aided in an interpretation of Cherokee sedimentation. The absence of limestones and marine shales indicates that conditions were continental; typical cyclothems are absent. Difficulty in tracing individual units points toward a ·basin or lagoon type of deposition. The eastern half of the county has been mapped as Cretaceous, and 20- to 40-foot exposures of Dakota sandstone may be found in the northeastern part, especially along the upper part of the Raccoon River