Stebbins Gulch Ripple Marks

Sedimentary structure: Ripple marks in sandstone

This piece of sandstone was originally horizontal before being torn loose from the Bedford Formation or the Berea Sandstone by stream erosion.  It is now propped up vertically on the streambed.  The parallel ridges are fossilized ripple marks formed by swift currents flowing under a sandy bottom about 350 million years ago.  Except for being lithified (turned to rock), these structures are exactly like the ripple marks that form today on sandy creek bottoms and tidal beeches.  Sedimentary structures like these illustrate one of the most basic tenets of geology, the Principle of Uniformitarianism.  It states that the chemical and physical processes acting on the earth have not changed over time, so that the features we see in ancient rocks were formed by the same processes that create them in modern sediments.  Put in another way, the present is the key to the past.

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