To the northwest and following a direction almost parallel with the northern coast, the Sierra of Lares extends from Aguadilla to the town of Lares, where it divides into two branches, one going north nearly to the coast, near Arecibo harbor, and the other extending to the spurs of the Sierra Grande de Banos; this latter starting from Point Guaniquilla, crosses the island in its entire length, its last third forming the Sierra of Cayey.

The whole island may be said to form a continuous network of sierras, hills, and heights.  Of these the Sierra del Loquillo is distinguished for its great altitude (the highest peak being Yunque, in the northeast corner of the island and visible from the sea, a distance of 120 kilometers), as is also Laivonito Mountain, near the south coast.

The following are the four highest mountains, with their heights above the sea level:  Yunque, in Luquillo, 1,290 yards; Guilarte, in Adjuntas, 1,180 yards; La Somanta, in Aybonito, 1,077 yards; Las Teras de Cerro Gordo, in San German, 860 yards.  All are easily ascended on foot or horseback, and there are coffee plantations near all of them.

Approximate Height of Towns Above the Sea Level.—­Aybonito, with its acclimatization station, 970 yards; Adjuntas, an almost exclusively Spanish town, 810 yards; Cayey, with a very agreeable climate, 750 yards; Lares, with a very agreeable climate, 510 yards; Utuado, with a very agreeable climate, 480 yards; Muricao, an exclusively Spanish town, 480 yards.  To ascend to all these towns there are very good wagon roads.  There are no fortifications of any kind in them, but they are surrounded on all sides by mountains.

Hydrography.—­Few countries of the extent of Porto Rico are watered by so many streams.  Seventeen rivers, taking their rise in the mountains, cross the valleys of the north coast and empty into the sea.  Some of these are navigable 2 or 3 leagues from their mouths for schooners and small coasting vessels.  Those of Manati, Loisa, Trabajo, and Arecibo are very deep and broad, and it is difficult to imagine how such large bodies of water can be collected in so short a course.  Owing to the heavy surf which continually breaks on the north coast, these rivers have bars across their embouchures which do not allow large vessels to enter.  The rivers of Bayamo and Rio Piedras flow into the harbor of the capital, and are also navigable for boats.  At high water small brigs may enter the river of Arecibo with perfect safety and discharge their cargoes, notwithstanding the bar which crosses its mouth.

The rivers of the north coast have a decided advantage over those of the south coast, where the climate is drier and the rains less frequent.  Nevertheless, the south, west, and east coasts are well supplied with water; and, although in some seasons it does not rain for ten, and sometimes twelve months on the south coast, the rivers are never entirely dried up.

From the Cabeza de San Juan, which is the northeast extremity of the island, to the cape of Mala Pascua, which lies to the southeast, 9 rivers fall into the sea.