In the Geneva basin a 127.3 m deep coring was carried out in the plain of Montfleury in order to get information about hydrogeology, lithology and chronology of the quaternary deposits. Palynostratigraphic studies on the so-called "Marnes à lignite" underlying the "Alluvion ancienne" revealed two interglacial sequences (Montfleury and Confignon). The Montfleury sequence belongs to the penultimate interglacial (Holstein sensu Welten 1988), the Confignon sequence must be assigned to a preceding interglacial. The chronostratigraphic position of the "Alluvion ancienne", which until now was believed to correspond to the Early-Würm, must be revised.