Dry Dredgers Field Trip
May 26, 2012
Mt Orab Trilobite Farm, Ohio

The Famous Mt. Orab Trilobite Farm, Ohio
Trilobite Farm
Mt. Orab, Ohio
Arnheim Formation

We were graced with an invitation from the land owner to come out to to the Mt. Orab trilobite farm and collect fossils. Not only is this by invitation only, but it's not every year we get to go to the best trilobite locality in the Cincinnati tristate area. This is because the site is privately owned for the purpose of mining trilobites.

We gathered at an offsite meeting location so we would not have to publish directions to this site. Since this site has limited parking we had to car pool to fit the cars on the lot.

The trip was led by Bob Bross, who arranged the caravan, and trailed by Bill Heimbrock, to ensure all were present.  

Once on the site, we were treated to a surprise. We were allowed to dig! This means we can find fresh trilobites like in the old days. But with limited tools available, most were assigned to split the shale that Bob and a few others extracted from the layer.

Here are some pictures of the fun. Enjoy.

Fossils Found and Dug That day

Trilobites: Isotelus

Trilobites: Flexicalymene

Here's a group shot of 3 Flexicalymene and one Isotelus.

Nautiloid Cephalopods


Here is an articulate brachiopod named Rafinesquina with many inarticulate brachiopod epibonts. The inarticulates (not a disability at all) look to be Petrocrania scabiosa.

Another inarticulate brachiopod commonly found while digging at Mt. Orab is Pseudolingula. They are uncommon at other sites because they are very fragile and fragment easily. But because we dig at Mt. Orab, we found large numbers in the Arnheim formation.

Pelecypods (clams or bivalves)

Many different kinds of Pelecypods can be found on this site - while digging and while surface collecting. Here's an example of Caritodens.

This clam is an internal mold with some black surface that may reveal the microstructure of the shell. It's likely the genus is Modiolopsis.

Gastropods (snails)


As is true for all Cincinnatian Series sites, a wide variety of common bryozoans were found. This first one is a cyclostomate bryozoan.

I can't identify the encrusting bryzoan, but it is clearly encrusting a gastropod in its entirety.


This is an unusual Graptolite that is commonly found while digging at Mt. Orab in the Arnheim formation. According to Rich Fuchs, it is likely to be Mastigograptus strictus, but it could be the same species as Mastigograptus tenuiramosus

Non-Ordovician fossils 

Every time we visit Mt. Orab, we find fossils that are not from the Upper Ordovician strata. These were brought in as gravel at some time or perhaps other ways. Here are some non-Ordovician brachiopods.

That's all for this field trip.

Now let's look at the multitude of photos from our very successful June field trip to Penn Dixie, NY and points north.

Here are the previous trips to Mt. Orab.

May 2009
May 2005
May 2004

May 2003

May 2002

May 2001
Sept. 2000


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