Geology of the County

In Mason County, water is obtained from consolidated sedimentary rocks ranging in age from Ordovician to Silurian and from unconsolidated sediments of Quaternary age. The oldest rocks found on the surface in Lewis County were deposited in shallow seas 490 million years ago during the Ordovician Period. In the Late Ordovician, the seas became relatively shallow, as indicated by the amounts of mud (shale) in the sediments. When the waters were clear and warm, a profusion of animal life developed, particularly brachiopods and bryozoa. 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)/Glacial deposits (Qg)

Clay shales
Crab Orchard Formation (Scb)
Brassfield Dolomite (Scb)

Interbedded limestones and shales
Drakes Formation (Od)/Bull Fork Formation (Ob)
Grant Lake Limestone/Fairview Formation(Oaf)
Clays Ferry Formation and its Point Pleasant Tongue (Okc)

Interbedded shales and limestones
Kope Formation (Ok)

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

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