The fine grained sandstones and siltstones lying on the creek bed often display raised marks and straight ridges that defy identification. They appear to be the tracks of dense objects dragged along a soft muddy bottom by a swift current. The resulting grooves are later filled by fine sand or slit. Eventually the mud with the tracks, and the silt that filled the tracks, solidify into shale and siltstone, respectively. The underlying shale erodes first, leaving casts of the grooves or furrows preserved on the underside of the siltstone bed. These features have been called drag marks, striation casts or groove casts by various authorities.
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