The central mountainous region of the Island is located in the province of Santa Clara, where a belt of mountains and hills following approximately northeast and southwest lines, passes through the cities of Sancti Spiritus and Santa Clara. Four groups are found here, one of which lies southwest of Sancti Spiritus, and east of the Rio Agabama. A second group is included between the valleys of the Agabama and the Rio Arimao. The highest peak of Santa Clara is known as Potrerillo, located seven miles north of Trinidad, with an altitude of 2,900 feet. A third group lies southeast of the city of Santa Clara, and includes the Sierra del Escambray and the Alta de Agabama. The rounded hills of this region have an altitude of about 1,000 feet although a few of the summits are somewhat higher. The fourth group consists of a line of hills, beginning 25 miles east of Sagua la Grande, and extending into the province of Camaguey. The trend of this range is transverse to the central mountain zone as a whole, but it conforms in direction with the general geological structure of the region. East of the city of Santa Clara the hills of this last group merge with those of the central portion of the province. The summits in the northern line reach an altitude of only a thousand feet. The principal members are known as the Sierra Morena, west of Sagua la Grande, Lomas de Santa Fe, near Camaguani, the Sierra de Bamburanao, near Yaguajay, and the Lomas of the Savanas, south of the last mentioned town. In the province of Pinar del Rio, we find another system, or chain of mountains, dominated by the Sierra de los Organos or Organ mountains. These begin a little west of Guardiana Bay, with a chain of “magotes,” known as the “Pena Blanca,” composed of tertiary limestone. These are the result of a seismic upheaval running from north to south, almost at right angles with the main axis of the chains that form the mountainous vertebrae of the Island. Between the city of Pinar del Rio and the north coast at La Esperanza, the Organos are broken up into four or five parallel ridges, two of which are composed of limestone, while the others are of slate, sandstones and schists. The term “magote,” in Cuba, is applied to one of the most interesting and strikingly beautiful mountain formations in the world. They are evidently remnants of high ranges running usually from east to west, and have resulted from the upheaval of tertiary strata that dates back probably to the Jurassic period.