There are two areas of Pennsylvanian (325-290 million years ago) rocks in Kentucky, both are shown as dark blue on the geologic map above. Pennsylvanian rocks in Kentucky are composed mostly of interbedded shale, sandstone, conglomerates, and coals. Thin limestone beds may also occur. Coal is Kentucky's leading mineral commodity. Because Kentucky has two areas of of coal-bearing Pennsylvanian strata, it produces a large amount of coal and ranks among the top three states in the Nation in annual coal production (between 160 and 180 million tons annually).
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