This study embraces the stratigraphy, tectonics, and paleogeography of the stratigraphic interval between the Globigerina tapuriensis and Globigerinoides quadrilobatus primordius Zones (Oligocene and basal Miocene) above the older eugeosynclinal facies in the Republic of Cuba. The area studied has been divided into four lithofacies complexes. Lithofacies complex A occupies the Los Palacios basin in Pinar del Rio, where it consists of a carbonate-terrigenous sequence of neritic-bathyal deposits up to 250 m thick. Lithofacies complex B extends from Bahia Honda on the north to Mariel-Carraguao on the south, and is found in Las Villas Province (in part), where a 460-m carbonate-terrigenous sequence ranging from deep water to neritic is developed. Lithofacies complex C involve only the Central basin, where the carbonate-terrigenous sequence ranges from neritic in the northeast to pelagic in the southwest. Its thickness likewise increases in the same direction from zero to 370 m. Lithofacies complex D is present in the Cauto, Nipe, and Guantanamo basins; its facies range from deep-water to neritic carbonate and terrigenous sedimentary rocks. Another complex of Oligocene rocks was deposited north of the medial elevation (welt) of the pre-middle Eocene orthogeosyncline, and is found in the Cayo Frances well off the north coast, and in the Moron basin.

In the course of the study, consideration was given to the validity of some formations and their members, and the names "Banos Formation" and "Bitiri Formation" are proposed.

In the discussion of the paleogeography, tectonics, and geologic evolution during this interval, the en echelon geologic structure of the island is noted. There is a feature which is repeated in the Neogene and other times, and which suggests strongly the necessity for a new tectonic interpretation of Cuban structure.