|Geology of the County|
In Shelby County, water is obtained from consolidated sedimentary rocks of Ordovician and Silurian ages, and from unconsolidated sediments of Quaternary age. The oldest rocks found on the surface in Shelby County, the Lexington Limestone, 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. Lying on top of Ordovician rocks are Silurian rocks, which were also deposited in warm seas, 430 million years ago. In Kentucky, the Silurian seas were generally warm and clear, although the presence of some shale beds suggests that muddy conditions prevailed at times. Locally, numerous corals and brachiopods can be found in the Silurian limestones and dolomites. Over the last million years unconsolidated Quaternary sediments have been deposited along the larger streams and rivers.
Geologic Formations in the County
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.
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