“The depressions occupied by the water forming these harbors appear to be due to erosion by streams flowing into the sea during a recent geologic period when the land stood somewhat higher than now. In other words, drowned drainage basins. Their peculiar shape, a narrow seaward channel and a broad landward expansion, is due to the relation of hard and soft rocks which generally prevail along the coast. Wherever the conditions are favorable for the growth of corals, a fringing reef is built upon whatever rocks happen to be at sea level, and as the land rises or sinks this rock reef forms a veneer of varying thickness upon the seaward land surface. The rocks on which this veneer rests are generally limestones and marls, much softer and more easily eroded than coral rock. Hence several small streams, instead of each flowing directly to the sea by its own channel, are diverted to a single narrow channel through the hard coral rock, while they excavate a basin of greater or less extent in the softer rocks back from the coast. “The fact that the land has recently stood at a sufficiently higher level to enable the streams to excavate such basins is proven by the sandfilled channel in the Habana harbor entrance and by borings made near the mouth of the Rio San Juan at Santiago, showing that the present rock floor lies below the level of the sea. Doubtless similar filled channels would be discovered in the other harbors of this class if they were properly sounded. “It is interesting to note that along the Cuban coast precisely similar basins are now being excavated which would form pouch-shaped harbors if the land should be slightly depressed. Several such basins were observed eastward from Santiago. If the coast at Matanzas were to sink thirty feet or more, a portion of the Yumuri valley would be flooded, forming a broad basin connected with the sea by a narrow entrance, the present Yumuri Gorge.” The chief harbors of the type in question are those of Habana, Cienfuegos, and Santiago de Cuba. Other important harbors, more or less of the same formation, are Bahia Honda, Nuevitas, Gibara, Nipe Bay and Baracoa. Matanzas and Cardenas are exceptions. By far the greater number of good harbors are on the north coast. On the south, aside from those which have already been mentioned, Guantanamo Bay is the only one of consequence. Other harbors on this side of the Island, such as Manzanillo and Batabano are merely open roadsteads, generally lacking in depth, and securing more or less shelter from outlying keys and reefs. Cuba was reclaimed from the sea by a great mountain-making movement in late tertiary time. During the Pliocene and Pleistocene epochs the Island underwent a series of subsidences and elevations which affected the coastal borders, and the margin of elevated rock-reef which borders the coast in parts, as [Illustration: A STREET IN SANTIAGO DE CUBA.]