The geological unit called Charentes basin is composed of Eocene and Oligocene deposits, laid above karstic limestone formations of the Campanian, in the north of the Aquitaine Basin. The Charentes basin is named after the departments of Charente and Charente-Maritime. The kaolin clays of Charentes belong to this mainly continental formation often referred as "siderolithic", of which the principal outcrop is situated in the South of the Charente-Maritime department, going north-east from Bordeaux city. The quarries are scattered along a long, wide, north - south band.