Some of the shells on the berms were living in the canals when they were
deepened, so are not fossils at all (generally still colorful fresh water
species.)  Many of them are late Pleistocene (less than 1 million years
old) and represent mostly species that are still alive, so although they
are fossils, they look just like Recent beach shells, or like the
freshwater shells that now live in the canal (both marine and freshwater
and land fossils are present.)  The early Pleistocene and late Pliocene
fossils (going back a few million years) are less commonly available but
they are often still living or very closely related to living species,
and require a good knowlege of the living faunas to see the difference.
As was noted, do not expect recrystalization or other obvious
modifications of the shell beyond bleaching.  Most recrystalized shells
are poorly preserved.  Many areas have all the shells leached out,
forming empty molds.  Age does not directly affect preservation.  It is
more a matter of the chemistry of the water that surrounded the fossils,
and that is regional.

Allen Aigen  NYC
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On Mon, 20 Nov 2006 16:27:54 -0500 Mike Gray <[log in to unmask]>
writes:
> All my collecting is on scuba on a single stretch of local reef
> (about
> 130 species so far) here in SoFla.
>
> I also spend some time bicycling the berms in the Everglades. At my
> age,
> I spend a lot of time on the ground
> resting. The berms are dredged from the canals alongside, then
> topped
> and filled with stuff from wherever
> they could get it. Both the fill and the dredged stuff are full of
> shells, all of which are the same shade of white.
> I've started crunching  some and most are obviously not fossils but
> a
> few appear to be.
>
> I'm sure you fossil hunters don't crunch stuff, so...  How does one
> tell
> a fossil from a very old shell?
>
> tia
> m
>
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