PORTO RICO 



107 



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 the}' 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. 



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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. 



Thr 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. 



