350 km of seismic profiles have been realized on the lake Geneva and have made possible the geological and structural study of the "Petit Lac". This prospection, performed with the help of a "boomer" disposal, 1,000 joules, has been made in order to admit the importance of glacial and postglacial formations which cover the molass and to mark the limits of homogenous wholes of those moraines and lake deposits. Furthermore, this study supplies interesting informations on the structure, as well as of the origin, of the "Petit Lac". The continuation of the Ivoire anticline could be followed beneath the lake and informations on the thickness and distribution of various formations have been obtained.