Exploradio Origins: A French Connection Unearthed in Millstones

Oct 10, 2019

“Cultural geology in my eye is the interface of geology and human culture,” Joe Hannibal said.

Joe Hannibal is curator of invertebrate paleontology at the Cleveland Museum of Natural History. He’s a fossil expert, but he’s also used his fossil and rock identification skills to track the movements of cultural materials.

"When the Euro-Americans came into different parts of the country, they would first establish mills. Well, a lot of those mills have then burned down,” Hannibal said. "But millstones, well, they're made out of stone."

Hannibal was examining some historic millstones in Ohio when he noticed they contained tiny spheres of fossilized algae, called charophytes.

“So I wrote in my notebook, 'charophyte?' and came back and realized, oh my galoshes, these are charophytes and they must mean something and they're telling me something,” Hannibal said. 

Both Ohioans and Europeans made millstones out of a type of stone called chert, but only millstones from the Paris Basin contained charophytes.

“So while people said they were looking at millstones made out of French material, they didn't really know,” said Hannibal.

Hannibal says millers in Ohio apparently preferred the French millstones because they ground a finer flour than the local stones. And so tiny algae fossils unique to French quarries lead Hannibal to unlock a mostly forgotten chapter of trans-Atlantic trade.