The oldest rock formations in South America are found in the complex basement of the Guyanas highlands and in the crystalline line of the Maritime and Cordillera massifs in Venezuela. The Venezuelan part of the Guyanas Altiplano consists of a large granite block of gneiss and other crystalline Archean rocks, with underlying layers of sandstone and shale clay. The core of granite and Cordillera is, to a large extent, flanked by sedimentary layers from the Cretaceous, folded in an anticline structure. Between these orographic systems there are plains covered with tertiary and quaternary layers of gravels, sands and clayey marls. The depression in which are lagoons and lakes, among which is that of Maracaibo, presents, on the surface, alluvial deposits from the Quaternary, on layers of the Cretaceous and Tertiary particularly important, because of them oil infiltrations emerge.