Detailed areal mapping in central Camagüey Province and reconnaissance mapping in northern and eastern Oriente Province, Cuba, have revealed two major structural zones: (1) A zone of intense deformation, including thrust faulting, which lies north of the geographic axis of the island; and (2) a belt of domical mountains bounded on the north by Nipe Bay and the coast, and on the south by the Cauto trough and Guantilnamo basin. In Camagüey, extensive masses of serpentine and overlying tuffs have been complexly folded and overridden from the north by a block, at least 25 miles long, of limestones that form the Sierra de Cubitas and Sierra de Camaján. The overthrust carried a northern fades of Cretaceous and Eocene limestones over a southern fades of tuffaceous rocks of similar age, and had a displacement of at least six miles. In places serpentine was thrust over younger formations, and most of the shearing in the serpentine is attributed to diastrophism. A thrust zone exposed in Loma La Vigía, 15 miles north of Holguín, suggests a similar tectonic history for northern Oriente Province. Chaotic giant breccias that include waterlaid debris indicate that the overthrusts moved across the ancient land surface in both Camagüey and Oriente districts. The folding apparently began in the Cretaceous and culminated in overthrusting during early middle Eocene time. Post‐Eocene deformation appears to be limited to warping or doming to maximum angles of about 20 degrees. The zone of domical mountains is somewhat more than 100 miles long from east to west by 25 to 30 miles wide, and comprises three main units: (1) the Sierra de Nipe and (2) Sierra del Cristal domes, principally of serpentine; and (3) the Cuchillas uplift, which includes the Cuchillas de Toar and Sierra de Purlal, composed of serpentine and pre‐serpentine rocks. These uplifts are overlapped progressively on all sides by sediments ranging in age from Upper Cretaceous to Oligocene and Miocene, the older beds in places being highly folded. The mountains owe their present relief of 2000 to 4000 feet to the doming of an extensive erosion surface in the late Pliocene or early Pleistocene. The north and east flanks of the Cuchillas uplift extend below sea level, and drowned streams and elevated coral reefs show regional instability since the last major doming. ©1947. American Geophysical Union. All Rights Reserved.