|Geology of the County|
In Clark County, water is obtained from consolidated sedimentary rocks from Ordovician, Silurian, and Devonian ages, and from unconsolidated sediments of Quaternary age. The oldest rocks exposed on the surface in Clark County were deposited in shallow seas 490 million years ago during the Ordovician. Lying on top of the Ordovician rocks are rocks of the Devonian, which includes the New Albany shale. The New Albany shale, also called the black shale, is 400 million years old and was formed when the deep sea floor became covered with an organic black muck. The muck is now hard black shale (an oil shale) which is one of the most distinctive of all geologic formations in Kentucky. Over the last million years, unconsolidated Quaternary sediments have been deposited along the larger streams and rivers.
Geologic Formations in the County
Interbedded clay shales, siltstones, and sandstones
Interbedded limestones and shales
Interbedded shales and limestones
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.