The Marine-Life Era on Urantia · The Crustal-Shifting Stage - The Fern-Forest Carboniferous Period - The Age of Frogs
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The coal layers alternate with shale, stone, and conglomerate. These coal beds over central and eastern United States vary in thickness from forty to fifty feet. But many of these deposits were washed away during subsequent land elevations. In some parts of North America and Europe the coal-bearing strata are 18,000 feet in thickness.