PORTO RICO 105 



cuesta — that is, hills which are the remnants of what was once 

 a steeply slanting summit plain. In this particular case the 

 slant is from the central mountains toward the sea, where the 

 hills are in some places terminated by a steep scarp or sea bluff 

 LOO feet in height. The interior scarp of these hills faces the 

 parting valley lying between them and the cerros and central 

 mountains and is occupied by the lake of Guanica. 



The playa plains are in places very extensive and in others are 

 exceptional features. They 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 Anasco 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 a typical 

 playa plain extending for a short distance back of the city up 

 the valley of the Rio Portugues and widening out to the coast. 

 West of Ponce they are exceptional features, but well defined at 

 the mouths of the principal rivers, the limestone bench being- 

 more continuous and less broken in this direction. 



Similar plains occur at intervals to the eastward of Ponce at 

 Salinas, Guayama, Arroyo, and Jacaboa. Extensive playa plains 

 of this character are also met with on the east coast near Naguabo, 

 ( leiba, and Fajardo, and on the north coast reaching up the val- 

 ley of the Loiza as far as Carolina. 



From San Juan to Camuy, according to Captain Macomb, "the 

 railroad follows the south edge of the coast plain, here and there 

 cutting through a little shoulder. The plain is but a narrow strip 

 until close to Arecibo, when we strike a cane country, the sea to 

 the left one-half mile or more and the mountains some four miles 

 to the south. At Camuy, the railroad terminus from San Juan, 

 the north coast plain is terminated by striking the rising ground 

 of the I'epino hills." 



The name " parting valley " I have given to certain long and 

 narrow valleys which sometimes occur where foothills of the 

 limestone bench abut against the front of an elongated mountain 

 range. Certain streams which come from the mountains and 

 cross the lower country tend either to bend along the mountain 

 front as they pass from it or to send out laterals parallel to the 

 same. The erosion attendant upon such phenomena tends to 

 produce long valleys at the junction of the mountains and foot- 

 hills running parallel to them. Parting valleys of this character 

 are especially well developed on the south side of Porto Rico, 

 such as the plain of Saba Grande and the depression of Guanica 



