|Geology of the County|
In Jefferson County, water is obtained from consolidated sedimentary
rocks of Ordovician, Silurian, Devonian, and Mississippian ages, and
unconsolidated sediments of Quaternary age. The oldest rocks found on
the surface in Jefferson County, the Calloway Creek Limestones, were
deposited in shallow seas 490 million years ago during the Ordovician.
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. Above the Ordovician rocks are the Silurian rocks, which
were deposited in warm seas 430 million years ago. In Kentucky the Silurian
seas were commonly warm and clear, although the presence of some shale
beds suggest that muddy conditions prevailed at times. Locally, numerous
corals and brachiopods can be found in the Silurian limestones and dolomites.
The Devonian New Albany shale, also called the black shale, was formed
400 million years ago 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 the County
Interbedded clay shales, siltstones, and sandstones
Interbedded limestones and shales
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.