Dry Dredgers Field Trip
May 2009
Mt Orab, Ohio, Trilobite Farm

In May, the Dry Dredgers returned to the famous Mt. Orab Trilobite farm. We have not been there since our 2005 trip. This is a privately owned dig site for which visitation is by unsolicited invitation only. The Dry Dredgers are privileged and fortunate to have been invited back for surface collecting. Even though trilobites are extracted from a ditch on this site, the discard piles over the years weather out, producing good quantities of trilobites on the surface.

We gathered at the rest stop and proceeded to the secret location. Parking is extremely limited at the site, compared to the number of people who wish to attend, so car pooling to the site was mandatory this time.

 Bob did an excellent job of organizing people into groups by car to get everyone to the site.

Once at the site, parking was still not easy, as these pictures show, and because the driveway out is blocked by cars, everyone must stay until everyone is done for the day.
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This site exposes the Arnheim Formation, which is at the bottom of the Richmondian Stage. The rocks and fossils on this site are somewhere in the range of 430 to 445 million years old.

Here are some photos of the surface collecting.
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Fossils Found That day.

Perhaps the most exciting find was a whole crinoid calyx that was fragmenting on needed to be carefully extracted from the surface. Here are some photos of that extraction. The crinoid appears to be either Pycnocrinus dyeri or a variety of Glyptocrinus.
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Non-Ordovician Fossils

As seems to always be true, we find a few fossils that are not from the Ordovician rocks. Here's one rock that was found in a pile of material that was dumped on the site which has a number of nice non-Ordovician fossils on it.

One one site of the rock is a nice pygidium (tail section) a non-Cincinnatian trilobite. Near it are parts that are likely from the same type of trilobite.

On another part of the same rock is a fossil that appears to be an Edrioasteroid. It might not be that, however for two reasons. 1-Edrios are only common in the Cincinnatian. They are found elsewhere, but are rare finds in those cases. 2-The plates do not look entirely like Edrio plates. This could be a pile of trilobite parts instead.

Trilobite: Isotelus

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Prone Flexicalymene retrorsa


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Enrolled Flexicalymene retrorsa

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Crinoids Found


Pelecypods (bivalves/clams) Found





Nautiloid Cephalopods Found


Gastropods (snails) Found

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Here's a recent snail that was found, showing the coloration. (not a fossil)

Brachiopods Found

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Bryozoans Found


Trace Fossils Found


Now lets move on to the June events around town in which the Dry Dredgers participated.

Here are the previous trips to Mt. Orab.

May 2005
May 2004

May 2003

May 2002

May 2001
Sept. 2000

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