Bibliogr. p. 291-293

Fossil charophytes belonging ti the genus Gyrona Can be used to distinguish chert millstones made of french burr (pierre meulière) from millstone made of domestic North American cherts. The occurence of the charophytes gyrogona medicaginula Lamarck and Gyrogona cf. G. medicaginula in millstonrs imported from France has been previoulsy documented for Massachusetts, Vermont, and Ohio in the Unated States. Additional localities with millstones containing Gyrogona are documented in this paper for the states of Arkansas, North Carolina, Virginia and Wisconsin in the United States, and in the Province of ONtario on Canada. These widespread occurences demonstrate the utility of charophytes as indicators of provenance of stone used for millstones. The geologic age and depositional environment (marine) of chert-bearing beds known to have used for manufecture of millstones in North America are also noted.
(Source : éditeur)