| Geology of the County | ||
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In McLean County, water is obtained from consolidated Pennsylvanian sedimentary rocks and from unconsolidated sediments of Quaternary age. Geologists call the oldest rocks found at the surface in McLean County the Caseyville Formation. These Pennsylvanian rocks were deposited 320 million years ago. The warm climate of the Pennsylvanian allowed extensive forests to grow and great coastal swamps to develop at the edges of water bodies. Marine waters advanced and receded many times, which produced 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, unconsolidated Quaternary sediments have been deposited along the larger streams and rivers. Geologic Formations in the County Sandstones Coals, sandstones, and shales Interbedded limestones, sandstones, and shales For more information, see the definitions of geologic terms and rock descriptions, a geologic map of McLean 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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