| Geology of the County | ||
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In Logan County, water is obtained from consolidated sedimentary rocks of Mississippian through Pennsylvanian age and from unconsolidated sediments of Quaternary age. Geologists call the oldest rocks found at the surface in Logan County the St. Louis Limestone. The most common rocks in Logan County are Mississippian limestones, which were deposited 350 million years ago in the bottom of a warm, shallow sea. At the end of the Mississippian, the seas receded and sediments of the Pennsylvanian Period were deposited 320 million years ago. The warm climate of the Pennsylvanian Period allowed extensive forests and great coastal swamps to grow at the edges of water bodies. Marine waters advances and receded many times, producing many layers of sandstone, shale, and coal. Vegetation of all sorts fell into the water and was buried under blankets of sediments, which over long geologic time were compressed into coal. The nonvegetative sediments such as sand, clay, and silt were compressed into sandstone and shale. Over the last million years, the unconsolidated Quaternary sediments have been deposited along the larger streams and rivers. Geologic Formations in the County Limestones Sandstones Interbedded limestones, sandstones, and shales For more information, see the definitions of geologic terms and rock descriptions, a geologic map of the Logan County, a summary of the geology of Kentucky, and a discussion of fossils and prehistoric life in Kentucky. Previous--Next--Back to "Groundwater Resources in Kentucky"
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