WIDESPREAD NORTH AMERICAN (UNITED STATES AND CANADA) OCCURRENCE OF MILLSTONES MADE OF IMPORTED FRENCH CHERT (MEULIÈRE, FRENCH BUHR) CONTAINING CHAROPHYTES

Fossil charophytes belonging to the genus Gyrogona are useful in distinguishing chert millstones made of stone imported from France (meulière; French buhr) from millstones made of domestic North American cherts. The charophytes Gyrogona medicaginula and Gyrogona cf. G. medicaginula have been well documented in millstones or millstone segments located in Massachusetts, Vermont, and Ohio. Additional localities with millstones containing Gyrogona include sites in the states of Arkansas, California, Colorado (originally used in a mill in Nebraska, but now in a Colorado museum repository), Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Nebraska, New York, North Carolina, and Wisconsin in the United States, and in the province of Ontario in Canada. Chert-bearing beds known to have been used for manufacture of millstones in North America are marine, whereas the charophyte species Gyrogona medicaginula and cf. G. medicaginula are freshwater. The widespread occurrences of millstones containing Gyrogona medicaginula and cf. G. medicaginula in North America confirm the utility of these charophytes as indicators of the provenance of stone used for chert millstones.

The widespread occurrence of certain French buhr across North America supports a potential designation of the meulière as a Global Heritage Stone Resource.