The study of the sedimentology of three cores from the occidental part of the Lake of Geneva (Switzerland) shows the physical constitution of the sediments and their stratigraphic repartition. The general clay composition is: illite 50%, chlorite 30%, kaolinite 10% and montmorillonite and/or mixed layer 10%. The presence of well cristallised montmorillonite in the Tardiglacial formations can be used in stratigraphy. At this period the sediments are a ratio √Q3/Ql higher and are coarser. The superficial sediments show a chemical pollution by Copper, Zinc and Barium.