|Geology of the County|
In Union 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 Union 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 form 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, Quaternary sediments have been deposited along the larger streams and rivers.
Geologic Formations in the County
Coals, sandstones, and shales
For more information, see the definitions of geologic terms and rock descriptions, a geologic map of the county, a summary of the geology of Kentucky, and a discussion of fossils and prehistoric life in Kentucky.
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