Reconstruction of the successive mammalian faunas in the Paris basin results in delineation of a stratigraphic sequence that begins with the Cernay-les-Reins conglomerate, containing the oldest Eocene fauna (composed of multituberculate forms) in France. The series continues with the Sparnacian Meudon conglomerate with Coryphodon and Pachaena, the upper Cuisian sands with Lophiodon larteti and the first expansion of artiodactyls, and the Montmartre gypsum in which the first paleotheres appeared. Isolated fossil occurrences give only an indication of other phases--the Sparnacian Soissonnais lignites and the Bartonian Saint-Ouen limestone.