Geology of the County

In Hardin County, water is obtained from consolidated sedimentary rocks of Devonian and Mississippian age and from unconsolidated sediments of Quaternary age. Geologists call the oldest rocks found at the surface in Hardin County the New Albany Shale. This formation is from the Devonian Period, and was deposited in warm seas 400 million years ago. The New Albany Shale was formed when the deep sea floor became covered with an organic black muck. The muck is now hard black shale (an oil shale) and is one of the most distinctive of all geologic formations in Kentucky. The Mississippian sandstones and siltstones are the result of a great influx of mud, silts, and sands brought in by rivers and streams from uplands many miles away and deposited as a great delta. The most common rock types in Hardin County are Mississippian limestones, which were deposited 350 million years ago in the bottom of a warm, shallow sea. Over the last million years, unconsolidated Quaternary sediments have been deposited along the larger streams and rivers.

Geologic Formations in the County
Unconsolidated deposits
Alluvium (Qa)

Ste. Genevieve Limestone (Mgl)
St. Louis Limestone (Mgl)
Salem, Harrodsburg Limestones (Msh)
Borden Formation (Muldraugh (Mbf)

Girkin Formation (Reelsville Limestone, Sample Sandstone, Beaver Bend and Paoli Limestone) (Mcl) (Bethel Sandstone of the Mooretown Formation) (Mms)

Interbedded clay shales, siltstones, and sandstones
Borden Formation (Halls Gap, Nancy, New Providence Members) (MDbb)

Fractured shales
New Albany Shale (MDnb)

Interbedded limestones, sandstones, and shales
Girkin Formation (Reelsville Limestone, Sample Sandstone, Beaver Bend and Paoli Limestone) (Mcl)

For more information, see the definitions of geologic terms and rock descriptions, a geologic map of Hardin County, a summary of the geology of Kentucky, and a discussion of fossils and prehistoric life in Kentucky.

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