A portion of the island, at least in the vicinity of Baracoa, was deeply submerged during the lower Oligocene times, as is proved by the occurrence of radiolarian earth beneath the upper oligocene limestones near the above town. Radiolarian oozes are at present being formed on the sea bottom at depths of between 2,000 and 4,000 fathoms. This, of course, does not prove that the deposits of Baracoa were laid down at so great a depth as present day dredging would indicate, but we can at least feel confident that they were formed in very deep water. This does not imply however that the whole island was sunken to the abysmal depths.
During the upper Oligocene time very nearly the whole island was undoubtedly submerged. Previous to this volcanic agencies had been very active throughout the larger portion of the island. Mountain building in Oriente had begun before the deposition of upper Oligocene strata, and the Sierra Maestra had already been elevated to a considerable height above the sea. It is probable that the sea at this time covered the whole of the island, with the exception of portions of Oriente province along its north and south coast, and occasional high peaks along the axis of the provinces further west.
The Miocene period was one of general uplift. The whole of the island as we at present know it, was above the level of the ocean's waters. There were foldings and uplifts during this period, and volcanic elevation along the axial line being greater than at the sides. It is probable that the folding of the Oligocene strata noted in the vicinity of Havana and Matanzas took place during this time. It may be inferred that the central portion of the province of Oriente was more highly elevated than the coastal portions, since upper Oligocene limestones occur in this section at considerably higher elevations than along either the north or south coast.
It is furthermore very probable that the terracing of the Oligocene coral reefs, such as may be seen in the vicinity of the city of Santiago, was taking place during that time. All the evidence goes to show that these are wave-cut terraces. It may be added here that all of the elevated Pleistocene coral reefs recorded are plastered on the surface of the upper Oligocene formations, or in some instances older geologic rocks. This applies to every later coral terrace that has been described, beginning with Cabanas and extending entirely around the island to the City of Santiago.