THE PARTING VALLEYS. 



13 



Ceiba, and Fajardo, and on the north coast reaching up the valley of 

 the Loiza as far as Carolina (fig. 3). 



From San Juan to Camuy, according- to Captain Macomb, the rail- 

 road 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 a cane country begins, the sea to the left one-half 

 mile or more and the mountains some 4 miles to the south. At Camuy, 

 the railroad terminus from San Juan, the north coast plain is termi- 

 nated by the rising ground of the pepino hills. 



THE PARTING VALLEYS. 



The name "parting valley" the writer has given to certain long and 

 narrow valleys which sometimes occur between the foothills and the 

 front of the central mountains. Some of the streams, as they emerge 

 from the mountains and cross the lower country, tend either to bend 



Fig. 3.— Rio Loiza, near Carolina. 



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

 parallel to the same. The erosion attendant upon such phenomena 

 produces long parallel valleys at the junction of the mountains and 

 foothills. Parting valleys of this character are especially well devel- 

 oped on the south side of Porto Rico, such as the plain of Saba Grande 

 and the depression of Guanica lagoon. The former is a long valley 

 extending east and west between the cerro and the interior mountains, 

 threaded by the Eio Grande of Mayaguez. This particular valley is 

 almost entirely given up to the extensive cultivation of indian corn. 

 The latter, separated from the former by the cerros, is the parting valley 

 of the Laguna de Guanica, extending from near Guayanilla to the port 

 of Cabo Rojo. This is a narrow east-and-west valley nearly at sea level, 

 lying between the cerro hills and the narrow rim of coast hills, the 

 latter separating it from the sea. The Laguna de Guanica occupies the 

 east end of this valley, and has outlet to the sea by a narrow passage 



