The History of Cuba. Willis Fletcher Johnson

Чтение книги онлайн.

СКАЧАТЬ of the pre-cretaceous rocks, the granites, diorites and other granular rocks which appear on the surface because of this erosion, were originally formed deep within the crust of the earth, and therefore furnish a reason for believing that this period of erosion was exceedingly long.

      It has been suggested that during the Jurassic times, the southeastern coast of the United States was connected by a long isthmus, following the line of the Antilles, to the northeastern coast of South America. The data presented would seem to indicate that at least the eastern half of Cuba stood high above the level during this period of the earth's history, and although data concerning the western half are less definite, it too was probably composed of high land masses.

      The elevation, and long period of erosion just described, were followed by subsidence, and on the surface of these old rocks the cretaceous formations were deposited. The lowest cretaceous rocks yet found are composed of an arkose, derived in large part from the original igneous mass. The main body of the strata is composed of limestones, and such fossils as they contain belong to the genera similar to those of the cretaceous rocks of Jamaica—Radiolites, Barrettra, Requienia, etc.

      During this time the whole of the Island of Cuba was probably submerged below the level of the sea. The cretaceous rocks in Santa Clara province occur in the bottoms of synclines, and the projected dips appear sufficiently to carry the beds over the tops of the dividing anti-clinal axis. It is believed, however, that the depth of the cretaceous sea over the island was probably never very great.

      Owing to a lack of paleontological data, the history of the island during the Eocene time is vague, but it is probable that a large part of it was submerged. This is certainly true of the province of Oriente, where Eocene fossils have been collected. During, and possibly previous to that period, volcanic agencies were active in Oriente, since volcanic rocks are found interbedded with sediments of the Eocene age. The same forces were probably active in other sections of the island, and the intrusion of Diorite porphyries in Santa Clara and other provinces probably took place during that period.

      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.

      The existence of marine Pliocene in Cuba has not been proved. There may be pliocene rocks in the vicinity of Havana some 60 feet above the sea level. If these are true Pliocene, it would indicate a subsidence during that time of from ISO to 180 feet. The character of the fauna found in the quarry on Calle Infanta does not indicate a greater depth than from SO to 70 feet for the water in which the limestone was deposited.

      Subsequent to this deposition, there was an elevation which caused the land to stand some forty or fifty feet higher than it does to-day. This probably took place in early Pleistocene times, at which time the Isle of Pines and Cuba were connected. One reason for the belief in this elevation is the existence of an old, deep and comparatively narrow cut in the bed of the present channel leading out of Havana harbor. There is further evidence of a general elevation found in borings for water, three miles southeast of the city of Santiago.

      At a depth of some 70 feet below the sea level, in the Rio San Juan Valley, stream-carried pebbles were found. This would indicate that the bottom of this valley once stood at least 70 feet or more above sea level. Subsequent to this elevation, there was a subsidence varying from 40 to 70 feet. There were doubtless other slight oscillations during the Pleistocene period, and these may be going on at the present time, although we have no evidence from records of actually measured monuments established since the Spanish occupation of the island.

      Paleontologic, biologic and physiographic research seems to indicate that there has been no land connection between Cuba and North America at any time since the beginning of the Tertiary, unless perhaps during the Oligocene period, and it seems probable there was no connection whatever during cretaceous times.

      Cuba furnishes a very interesting field, not only for geologic research, but for a far more extended study and survey of its many important mineral zones both for scientific and for economic reasons.

      Topographically the surface of Cuba may be divided into five rather distinct zones, three of which are essentially mountainous. The first includes the entire eastern third of the province of Oriente, together with the greater part of its coast line, where the highest mountains of the island are found. The second includes the greater part of the province of Camaguey, made up of gently rolling plains broken by occasional hills or low mountains, that along the northern coast, and again in the southeast center of the province, rise to a height of approximately 1,500 feet above the general level.

      The next is a mountainous district including the greater part of eastern Santa Clara. The fourth comprises the western portion of this province together with all of Matanzas and Havana. The surface of this middle section is largely made up of rolling plains, broken here and there by hills that rise a few hundred feet above the sea level.

      The fifth includes the province of Pinar del Rio, the northern half of which is traversed from one end to the other by several more or less parallel ranges of sierras, with mean altitudes ranging from 1,000 to 2,000 feet, leaving the southern half of the province a flat plain, into which, along its northern edge, project spurs and foot hills of the main range.

      The highest mountains of Cuba are located in the province of Oriente, where their general elevation is somewhat higher than that of the Allegheny or eastern ranges of the United States. The mountainous area of this province is greater than that of the combined mountain areas of all other parts of the island. The mountains occur in groups, composed of different kinds of rock, and have diverse structures, more or less connected with one another.

      The principal range is the Sierra Maestra, extending from Cabo Cruz to the Bay of Guantanamo, forty miles east of Santiago. This chain is continuous and of fairly uniform altitude, with the exception of a break in the vicinity СКАЧАТЬ