The submarine slope of the southern coast of Cuba is steep and rugged south of Sierra Maestra, Oriente Province; the average slope in one locality between depths of 1000 and 2000 fathoms is 31°. Two major reversals in slope, at about 2000 fathoms and 2800 fathoms, are taken as evidence of fault zones. Below 2800 fathoms the topography is mountainous in an area parallel to the coast and about 15 miles wide; local relief is several hundred fathoms, but the area deepens to its center where there is a nearly flat plain 3–5 miles wide and about 25 miles long, which also parallels the coast. The plain slopes gradually westward from 3530 to 3542 fathoms with local northward slopes (depths are based on sound velocity of 4800 feet per second); it is the deepest known part of Oriente Deep. The plain is surrounded by hills and intervening gorges which have relatively smooth bottoms grading down to it. Details of the topographic relations indicate that the plain is underlain by unconsolidated sediment brought in by turbidity currents flowing down the gorges. Recent coring in a similar near-by plain supports this view. Seismic evidence, though meager, suggests that the sediment is 1200–1500 feet thick.