David Campbell writes,
"Exogyra is one of the commonest genera in the type Waccamaw section, which
is uppermost Pliocene to perhaps earliest Pleistocene.  The Exogyra are
reworked from underlying Peedee deposits."

The Peedee is a Cretaceous formation in the Carolinas. I've seen similar
reworking of Cretaceous fossils in Alabama, but only in the lowermost
Tertiary beds, e.g., at Moscow Landing on the Tombigbee River, from the
Cretaceous Prairie Bluff Chalk into the Paleocene (lowest Tertiary) Clayton
Formation. In beds like these, the stratigrapher has to tread carefully lest
the age of the strata be misinterpreted. Generally, the most robust shells
and molds may include some reworked older material. The fragile shells,
which could not be transported far without breaking, represent the true age
of the rock layer.

We see this kind of thing happening at other erosional contacts between
formations, notably, at the contact between the Gosport Sand (middle Eocene)
and the Moodys Branch Formation (upper Eocene), where it has caused
considerable confusion among researchers over the dating of the basal
Moodys. Robust bivalves like Bathytormus scream "GOSPORT!" while fragile
species of Nucula and even more fragile lunulitid bryozoans whisper "m o o d
y s".

Out west, dinosaur bones may be reworked into Paleocene river deposits --
dated as Paleocene by their pollen. That has caused some confusion, let me
tell you!

Generally, the reworked fossils are in the next formation up from their
source. Exogyra is unusually thick-shelled and might be expected to travel a
little farther, or even survive more than one bout of reworking, as some
amber is thought to have done in the Baltic. What do the rocks say in the
Carolinas, "Old Seashells"?

Andrew K. Rindsberg
Geological Survey of Alabama

P.S. I sure hope that my little satire didn't give James any strange ideas.
Black widow spiders? Do keep us posted on the results, James.