The limits of the Loisa river are: On the east, the sierra of Luquillo (situated near the northeast corner of the island); on the south, the sierra of Cayey, and on the west, ramifications of the latter. It rises in the northern slopes of the sierra of Cayey, and, running in a northwest direction for the first half of its course and turning to northeast in the second half, it arrives at Loisa, a port on the northern coast, where it discharges its waters into the Atlantic. During the first part of its course it is known by the name of Cayagua.
The Sabana river has, to the east and south, the western and southern limits of the preceding river, and on the west the Sierra Grande, or De Barros, which is situated in the center of the general divide, or watershed. It rises in the sierra of Cayey, and, with the name of Pinones river, it flows northwest, passing through Aibonito, Toa Alta, Toa Baja, and Dorado, where it discharges into the Atlantic to the west of the preceding river.
The Manati river is bounded on the cast and south by the Sierra Grande and on the west by the Siales ridge. It rises in the Sierra Grande, and parallel with the preceding river, it flows through Siales and Manati, to the north of which latter town it empties into the Atlantic.
The Arecibo river is bounded on the east by the Siales mountain ridge, on the south by the western extremity of the Sierra Grande, and on the west by the Lares ridge. It rises in the general divide, near Adjuntas, and flows north through the town of Arecibo to the Atlantic, shortly before emptying into which it receives the Tanama river from the left, which proceeds from the Lares Mountains.
The Culebrina river is bounded on the south and east by the Lares mountain ridge, and on the north by small hills of little interest. From the Lares Mountains it flows from east to west and empties on the west coast north of San Francisco de la Aguada, in the center of the bay formed between Point Penas Blancas and Point San Francisco.
The Anasco river is formed by the Lares mountain ridge. It rises in the eastern extremity of the mountains called Tetas de Cerro Gordo, flowing first northwest and then west, through the town of its name and thence to the sea.
The Guanajivo river has to its north the ramifications of the Lares ridge, to the east the Tetas de Cerro Gordo Mountains, and on the south Torre Hill. In the interior of its basin is the mountain called Cerro Montuoso, which separates its waters from those of its affluent from the right, the Rosaria river. It rises in the general divide, flowing from east to west to Nuestra Senora de Montserrat, where it receives the affluent mentioned, the two together then emptying south of Port Mayaguez.
The Coamo river is bounded on the west and north by the Sierra Grande, and on the west by the Coamo ridge. It rises in the former of these sierras, and flowing from north to south it empties east of Coamo Point, after having watered the town of its name.
The Salinas river is bounded on the west by the Coamo ridge, on the north by the general divide, and on the east by the Cayey ridge. It rises in the southern slopes of the Sierra Grande and flowing from north to south through Salinas de Coamo, empties into the sea.
Coasts, Harbors, Bays, and Coves.—The northern coast extends in an almost straight line from east to west, and is high and rugged. The only harbors it has are the following: San Juan de Porto Rico, surrounded by mangrove swamps and protected by the Cabras and the Cabritas islands and some very dangerous banks; the anchoring ground of Arecibo, somewhat unprotected; and the coves of Cangrejos and Condado. During the months of November, December, and January, when the wind blows with violence from the east and northeast, the anchorage is dangerous in all the bays and harbors of this coast, except in the port of San Juan. Vessels are often obliged to put to sea on the menacing aspect of the heavens at this season, to avoid being driven on shore by the heavy squalls and the rolling waves of a boisterous sea, which propel them to destruction. During the remaining months the ports on this coast are safe and commodious, unless when visited by a hurricane, against whose fury no port can offer a shelter, nor any vessel be secure. The excellent port of San Juan is perfectly sheltered from the effects of the north wind. The hill, upon which the town of that name and the fortifications which defend it are built, protects the vessels anchored in the harbor. The entrance of this port is narrow, and requires a pilot; for the canal which leads to the anchorage, although deep enough for vessels of any dimensions, is very narrow, which exposes them to run aground. This port is several miles in extent, and has the advantage of having deep canals to the east, among a wood of mangrove trees, where vessels are perfectly secure during the hurricane months. Vessels of 250 tons can at present unload and take in their cargoes at the wharf. Harbor improvements have been recently made here.