Fossils on the beaches may be naturally occurring, either washing up
from offshore deposits or downstream from nearby rivers.  Edisto
Island in South Carolina is well-known for the latter.  Fossils on the
bottom of the Edisto River are probably a bit less worn than the ones
on the beach, but if you don't care for scuba diving in poor
visibility with sharks and alligators, searching the beach after a
storm is probably easier.  There are also a lot of places where beach
renourishment puts fossils onto the beach.

The black shells on the beach are generally due to iron and/or
manganese deposits under reducing conditions.  Similar black crusts
can occur on freshwater shells, too.  Some fossil deposits commonly
show such color, others don't.  However, there are some places,
including parts of the Carolinas, where black phosphatic casts of
fossil mollusks are found.  I even have a phosphatized internal mold
of a pleurotomariid.

--
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"

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