12 FOREST CONDITIONS OF PORTO RICO. 



occupied by the lake of Guanica, separated by still another row of hills 

 called the cerros from the central mountains. 



The cerros. — On the southwest end of the island there are two 

 parallel rows of hills separated from each other and the interior moun- 

 tains by long and fertile valleys. The interior chain of hills, which 

 extends from north of Gabo Rojo to within 3 miles of Yauco, passing 

 west of San German, is of a peculiar type not seen elsewhere on the 

 island. It is a single chain of highly rounded wooded hills of the type 

 called " knobs " in this country, and "cerros 7 ' by the Spaniards. They 

 owe their configuration to a thick cap stratum of hard mountain lime- 

 stone, the lower portion being composed of the softer decomposing 

 rock. Where the cap has been removed erosion has widened the val- 

 leys into great elongated plains or vegas. 



THE PLATA PLAINS. 



For want of a better, the term "play a plains" is used for the wide 

 alluvial plains found at more or less frequent intervals along the entire 

 coast between the hills which limit them. The word "playa" means 

 literally the shore or strand. Many cities of Porto Eico are situated 

 upon the interior border of such plains where they meet the foothills, 

 several miles from the port of entry, which is located at the immediate 

 seashore, and which is usually designated "playa," in order to distin- 

 guish it from the city proper. These playa plains are usually fan-shaped 

 in area, with their broader base next to the sea, where they are often 

 many miles in width, and stand only a few feet above the ocean. They 

 are bordered by escarpments composed of the sharp rise of the coast 

 hills, and extend with constantly decreasing width backward up the 

 stream valleys toward the central mountains. 



These plains were formerly old alluvial river estuaries, which in late 

 geologic time constituted bays indenting the laud, and have been 

 reclaimed by the general elevation of the island. The playa plains are 

 in many cases so extensive that they now far exceed the area of the 

 limestone bench out of which they were original!} 7 carved, and in places 

 the surviving hills of the bench are almost entirely removed. 



The playa plains are notably wide along the entire north coast from 

 Arecibo via San Juan to the northeast cape, on the west at the mouth 

 of the Afiasco north of Mayaguez and south of the same city (the plain 

 of Hormigueras), and along the south coast east of Ponce. Ponce is 

 situated upon atypical playa plain, which extends a short distance back 

 of the city up the valley of the Rio Portugues. West of Ponce the 

 playa plains arc exceptional, the limestone bench being more continu- 

 ous and less broken in this direction. They are, however, well defined 

 at the mouths of the principal rivers. Similar plains occur at inter- 

 vals cast of Ponce at Salinas, (iuayama, Arroyo, and Jacaboa. Exten- 

 sive playa plains are also met with on the east coast near Naguabo, 



