Stratigraphic, paleontological and sedimentological study of the lower Lutetian limestones and sands exposed in a railroad cut northwest of Boissy, in the Creil area (France), provides more precise information on the lower Lutetian in the region northwest of the Oise river. The three upper beds in the cut represent the transition from the lower to upper Lutetian and are equivalent to Zone III of R. Abrard. The three lower beds are partially dolomitized and represent Abrard's Zone II. Although the boundary between these two zones is dolomitized, it can be determined on the basis of the microfauna. Granulometry of the quartz sand shows a characteristic coarse grain in the lower Lutetian becoming finer in the upper zone.