National Geographic : 1899 Mar
PORTO RICO other Great Antilles, notably a few interior mountain valleys, the bordering benches of elevated coral reef, the coast lagoons or lakes, and the mangrove swamps. The interior mountain valleys are not conspicuous or abundant features, nor are they completely closed (without drainage out lets) like those of Jamaica, but are local widenings of the stream valleys which formerly reached slack water a considerable dis tance within the marginal area of the mountain mass, when the present coast bench was submerged beneath the sea. The valley of Caguas is the most conspicuous example of this type. This is a wide amphitheater, a considerable distance within the moun tain area, and its bottom is filled with old alluvium. It stands at present about 250 feet above the sea. WEATHERED MOUNTAIN ROCK Elevated reef benches or soborucco, so abundant in Cuba and forming the narrow coast rim of hard rock protecting a softer interior, thereby producing the excellent pouch-shaped harbors of that island, are but faintly developed in Porto Rico. 1 saw this material only at the entrance of San Juan harbor, but my studies of the littoral were not extensive. San Juan, Jabos, and Guanica, however, are the only pouch-shaped harbors of Porto Rico, and I believe that their general absence is largely due to the lack of the elevated reef formation. The coast lagoons or lakes are collections of water in swales of the coastal plain on the north and in parting valleys of the type of that of Guanica, previously described. Mangrove swamps are extensively developed around the in terior margin of San Juan harbor.