Nature
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In Ohio, nearly 500 million years are recorded in sedimentary bedrock laid down on the floors of ancient seas that periodically covered the state, with changing conditions producing sandstone, shale, limestone, and, when seas receded and swamp vegetation grew, coal measures later layered with sand and mud as waters alternately flooded and withdrew. These rock layers, oldest at the bottom, form a broad arch with older strata exposed near the center and younger layers in the southeast and northwest. At John Bryan, Clifton Gorge of the Little Miami River contrasts sharply with the flatter landscape of most of western Ohio because continental ice blocked preglacial stream routes during the Pleistocene Ice Age, and glacial meltwaters rapidly cut a spectacular 70 foot deep gorge through middle Silurian dolomite. That bedrock formed about 420 million years ago when most of Ohio lay under life-filled water, where shells and lime precipitates accumulated, hardened into limestone, and later changed into magnesium-rich dolomite visible in the park today.
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Ohio · United States
