A first geological submarine map of the Sill of the Gibraltar Strait has been established as a result of the geological and geophysical research of the several oceanographic campaigns covering this area and by the integration of the information collected in the different samplings taken through «gravity cores». The outcrops offlyschs and their probable structure have been recognized (a continuity of the units that form geologically both sides of the Strait exists). Quaternary deposits are mainly composed of non consolidated sediments (sands and bioclastic gravels) in the continental platforms and in deep basins, and the development of calcareous crusts (biocalcarenites) in the central area of the Sill of the Strait, which does not seem very thick, covering and hiding the substrate of the flyschs