| Geology of the County | ||
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In Grayson 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 Grayson County the St. Louis Limestone. The most common rock types in Grayson 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 Period, 320 million years ago, the seas receded and sediments of the Pennsylvanian Period were deposited. The warm climate of the Pennsylvanian allowed extensive forests 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, unconsolidated Quaternary sediments have been deposited along the larger streams and rivers. Geologic Formations in the County Limestones 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 Grayson 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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