GMS Field Trip November 2025

GMS Field Trip
Marine Fossils and Geodes in Tennessee
Saturday, November 15, 2025

It’s a great trip when you get to collect in three different places and get three distinctly different things: fossilized coral, crinoid fossils, and geodes. Start it off with an evening of grilling out and rockhound camaraderie and it’s an awesome trip!

The night before the trip, members gathered at a local inn where our group had a number of rooms booked. Outside, there is a patio with a grill and picnic tables surrounded by a privacy fence. Lawrence Parker started up the grill for us, then grilled up a pile o’ hotdogs. Susanne brought tablecloths, plates, cups (which we forgot to bring!), as well as napkins and some camping lights – definitely appreciated as it got very dark, very early. Members enjoyed some of the best brownies and cinnamon bread ever, as well as pimento cheese with pita chips, and bananas. We roasted marshmallows over the fading embers, devoured the gooey goodness, then had “s’more”. It was fun to catch up with old friends, meet new members, and chat about rockhounding.

We started the next morning by standing in sticky red clay, looking for fossilized coral. The type of coral we were collecting is a colonial coral in the genus Lithostrotionella from the Mississippian Period/Subperiod, so they are 325 to 350 million years old. We didn’t have much time to look because we were facing an early sunset, but members found several nice pieces before we moved on to the next site.

Note: Click the diagrams below for larger images.

The second location we visited had Mississippian age material too. The most abundant fossils there are crinoids, marine invertebrates that resemble plants. Much of the terminology used to describe crinoid anatomy is typically used to describe plants. At the top, there are feathery arms that filter plankton from the water into a cup-like structure called the calyx (KAY-licks), often incorrectly referred to as a head. Attached to the bottom of the calyx is a stalk, also called a stem, composed of multiple discs called ossicles (AH-sick-ulz) or columnals (kahl-UM-nulz). The center of the stem, called the lumen (LOO-men), contains nerves and ligaments.

As of this writing, over 6,000 extinct species of crinoids have been identified worldwide, and there are approximately 700 living species, including feather stars and sea lilies. Feather stars are free-swimming crinoids that only anchor themselves when they are juveniles. Sea lilies are stalked crinoids that anchor themselves by using a structure called a holdfast. The type of holdfast fossils we were more likely to find on this trip are root-like structures called cirri (SIRR-eye) that can be straight or encrusting, and like stems, are composed of ossicles. Some species have holdfast cirri that coil too, though I am not sure any of those species are represented where we were collecting.

Calyxes are only a small portion of the animal and they are easily crushed or broken, so fossilized calyxes are rare. Only one full calyx was found on this trip. Crinoid stems can be long, with some extinct species documented as having stems up to 130 feet long. Because they represent a larger percentage of a crinoid’s body, and because they tend to fossilize well, disarticulated stems are the most common crinoid fossils found.

Members noticed there were more stacks of columnals versus individual columnals, and they saw “broken branches” and tiny indentations on columnal stacks. To understand the stacks and the other features, we need to learn a bit more about crinoid anatomy. There are two kinds of columnals – nodal and internodal. Nodal columnals can have cirri useful for temporary gripping, and are often thicker than internodal columnals. The little branch bits are cirri that broke, before or after fossilization. The belly buttons are scars where cirri detached while the animal was alive and able to heal. Internodal columnals do not have cirri, so those features would not be present. There are several internodals attached to a nodal. Within the lumen, thinner ligaments connect internodals, and thicker ligaments connect a set of internodals to a nodal. The nodal is connected to the next set of internodals only by the thinner ligaments, so the stem is more likely to break at that junction. This is why we find so many stacks of columnals versus whole stems or individual columnals.

Members marveled at ridges and interesting patterns in the center of stems, so there is a little more stem anatomy for us to learn. The stems we find often have detailed preservation of columnal ridges similar to the ridges on poker chips. Where the ridges interlock between two columnals is called a suture or symplexy (sim-PLEX-ee). The ridges prevent twisting and help the crinoid return to its original position as it bends and sways. Most of the stems have a round lumen, i.e., the channel in the center of the stem, but juniors (and adults!) enjoy looking for flower shapes and “star-bellied sneeches”, our nickname for stems with star-shaped centers. Members also found interesting rocks in the area. Masses of stems become cemented together to form clusters and a sedimentary rock called encrinite (en-CRY-nite). Many crinoid stem clusters and encrinite rocks went home with us that day.

At the third and last location, members collected geodes and coral with quartz crystals inside. Often, what looks like a geode is actually a solid nodule. The geodes there do not feel lighter than the nodules, so Charles recommends breaking rocks open on the spot. Also, the geodes do not have colorful banding and look better broken instead of sawed, so there is no need to bring them home to cut them open. I like to collect geodes that are already broken open. It saves the trouble of breaking them, and you already know you have a geode. The coral there is not Lithostrotionella, and I do not know the species other than that it can be found in large groups, perhaps reefs. They don’t look like coral at first, but their somewhat angular shape is easy to spot, and there are often quartz crystals inside, so they are fun to collect too. Once members were happy with their geodes and coral, they returned for another night of grilling and gabbing. Before we started up the grill, the group decided to savor some local fare, and gathered at a nearby restaurant instead. I couldn’t go, so a member gave me a big slice of the best pound cake I have ever had. The crusty bit on the outside was perfection!

There was so much to do on this trip that there was never a dull moment. Everyone got plenty of goodies, learned a little, and had a lot of fun. Many thanks to property owners, the hotel owners and staff, as well as members who spent their weekend with us at this beautiful place. Thanks as always to Charles Carter for arranging yet another fun and successful trip!

Lori Carter on behalf of Charles Carter
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