by Dion Stewart
The July 27th fossil collecting trip to SW Georgia was a great success with many of the participants making it a family affair. I should start at the beginning; although we had great driving directions from our leader, Dr. John Anderson, to the gathering spot — a back-road bridge — most of the GPS programs we were using showed us driving through an empty field on the outskirts of the Fort Benning Army base. Most of us who turned off our GPS and followed the written directions arrived early. While we waited for those who were relying on modern electronics to find the bridge, we looked down on the stream bed where you could easily see a dozen or more three to six inch fossil oysters just strewn on banks of the stream. Following the rules of good collecting we awaited the official start time before the stampede was released to grab those fossils, but as we entered the stream we realized the fossils were everywhere. The rain Gods had smiled on this trip; the week before heavy rains had caused high water and fast flow along the banks ripping out fossils, but there had been no rain the few days prior to our arrival and stream level had dropped down to wading conditions with large mud bank exposures for picking up the deposited fossils.
This collecting locality is in the Blufftown Formation, which formed during the Cretaceous period when dinosaurs roamed across the Earth. The environment for this rock unit is shallow marine, probably not more than a few miles off shore. Thus, the only dinosaur pieces are those rare fragments that washed down the rivers and into the ocean, however fossils of marine organisms abound.
The most common fossil at this locality is the bivalve called Exogyra, which is an oyster. Oysters do not show the common symmetry of most bivalves where one shell (valve) is attached along a hinge to an identical (but mirror image) second valve. In the oyster group of bivalves one valve is much larger and curved and the second shell is small and flat. Oysters attach themselves to the sea bed and do not move like their burrowing, symmetrical kindred. What is interesting is that when alive, the large curved shell is on the bottom, but when it dies the muscle holding the smaller shell closed gives way and the small top shell pops open, catches the current of the moving water like a sail, and flips the oyster into its death position with the large curved shell on top. Our group collected all types of Exogyra; most were one large curved shell, some with the two shells still closed, and there were plenty of the one smaller flat valve.
One of our seasoned fossil collectors noticed a small opalescent patch on the ground. Having just returned the week before from a dinosaur dig in S. Dakota, he knew how to slowly but surely work the piece until he had uncovered a relatively rare ammonite that was nearly a foot across. Where many of the less experienced collectors may have destroyed the specimen, he carefully dug all around it, wrapped it and bundled it with twine before he made the final extraction. As most of us merely reached down and picked up a small fossil, his extraction of that large ammonite took well over an hour. He said it was a better ammonite than any he had found during the dinosaur dig. Soon many in the group entered the flowing stream and waded in the knee deep water, with occasional holes that got the kids wet up to their waists. One father and son team returned near the end of the trip time with an armload of fossils, tired, and water logged but very excited about their quarter mile excursion in the swift stream.
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