The Venezuelan Andes, considered as a geologic unit, has a special interest structurally as the abrupt and massive bulkwark between the Maracaibo basin and the Orinoco plains, from the lowlands of which, at 100 and 200 meters, respectively, it rises to the maximum of more than 5,000 meters on the snow-capped peaks. Though the bulk of the mountain mass is composed of Paleozoic or older metamorphic rocks, including some fossiliferous Carboniferous, sediments ranging up to Cretaceous are found at 3,000 meters, 4,000 meters, or even higher, and Eocene rocks occupy large areas in the southwestern portion. Topography, areal geology, and structure sections are shown on maps, and serve to indicate broad lines of structure. It is a great geanticline without boundary faults at the resent mountain fronts, cut by cross faults which further work may show to be of greater rather than of less importance. Present evidence indicates that classic Alpine structural concepts are not applicable to the isolated problem of the Venezuelan Andes.

Carboniferous localities not heretofore published are mentioned and further discoveries predicted. Cretaceous rocks are mapped in new areas, and the Cretaceous-Eocene unconformity is shown to be of minor importance as a structural break compared with unconformities at the base of the Cretaceous and in Middle Miocene.