Stebbins Gulch Cleveland Shale

Cleveland Shale showing tendency to break into thin plates

Cleveland Shale showing tendency to break into thin plates

Notice the fissile nature of the Cleveland Shale, the uppermost member of the Devonian-age Ohio Formation.  Fissility is the tendency for some rocks to split easily into thin layers along roughly parallel cleavage planes. Shown here is a small rockfall that slipped off a vertical cliff face along joint fractures and landed on the creek bed, shattering the rock.  At first glance, these rocks look like slate, but slate is a much harder metamorphic rock, compressed and baked at depth under great pressure.  Some visitors assume that the thin slivers of shale were used by Native Americans to fashion into arrowheads, but shale is much too weak and brittle for this purpose.  Instead, they used a hard form of quartz called flint to make points for hunting, fishing and warfare.

     
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