Description: Mudcracks are sedimentary structures that occur when moist mud-bearing sediment dries upon exposure to air and shrinks with the resulting cracks forming a polygonal pattern.

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Figure 1 - Mudcracks in the Kittatiny Limestone. NY/PA. Original cracks caused by dessication are subsequently filled with coarser sediment that forms ridges due to differential erosion. (Photo 1976)

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Figure 2 - Modern day mudcracks. In the fossil record, the cracks are commonly filled in with coarser sediment that is more resistant to erosion than the contiguous muddy sediment. Raindrop impressions are commonly preserved in the sediment.

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IFigure 3 - Logan Pass, Glacier N.P.