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Three views of rocks from miles below the surface of the earth.

Anhydrite replacing limestone and filling fracture in Smackover Formation, south Alabama. Thin section photomicrograph. Image about 1 mm across.

Light-colored dolomite, which partially replaced red-stained limestone, is being in turn replaced by limestone. Smackover Formation, south Alabama. Thin section photomicrograph. Image about 1 mm across.

Wormy-looking sponge in the upper part of image, Smackover Formation, south Alabama Slabbed and polished core. Core 4 inches wide.