"L'Argile des Milles" is middle oligocene in age. It is made up of detrital elements of south western origin, set free by the destruction of soils and, later, by the erosion of the andalosite bearing cristalline continent still located south west of the "Golfe du Lyon". This formation is missing in the "bassin de Marseille" ; this fact probably demonstrates that this basin did not exist during this period. The subsidence must have starting progressively at the beginning of the upper Oligocene, and must have become major movements during the middle Chattian. A relationship may be tentatively proposed between these facts and the drift of Sardaigne.