20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 69 



The general land surface is hilly and irregular, but the only very 

 high mountains are in the extreme western part, where an extension 

 of the highlands of Costa Rica crosses the international boundary 

 about midway between the two oceans and culminates at about 11,500 

 feet in the volcano of Chiriqui. The higher areas to the east are little 

 known, but the continental divide evidently follows a tortuous course 

 owing to echelon arrangement or other irregularities in the con- 

 tinuity of the principal mountain ranges. It approaches the Pacific 

 side in the vicinity of the Canal Zone and bearing thence diagonally 

 northeastward across the Isthmus continues eastward close to the 

 Atlantic coast, finally curving strongly southward and again ap- 

 proaching the Pacific coast west of the Atrato River Valley. 



The rather ill-defined backbone of the Isthmus is divided by com- 

 paratively low passes into several irregular sections in which steep, 

 but not usually precipitous, mountain ranges reach varying eleva- 

 tions, in few places exceeding 5,000 feet. One of these, the Serrania 

 de la Capira, lies between the Canal Zone and the slightly elevated 

 region separating the drainage areas of the Rio Code del Norte and 

 the Rio Grande de Nata, near the boundary between the provinces of 

 Code and Colon. The Serrania del Brujo, beginning near the 

 Atlantic coast a few miles east of Colon, rises near Porto Bello to 

 3,000 or 4,000 feet, and partially encircling the Chagres River Valley 

 joins the continental axis near Cerro Azul, a mountain about 3,000 

 feet high on the crest between the Chagres and Pacora river valleys. 

 A short distance east of Cerro Azul are trajiscontinental gaps prob- 

 ably less than 1,000 feet in altitude where the headwaters of the Rio 

 Mamoni interdigitate with those of streams flowing north into the 

 Gulf of San Bias. Farther east the long, narrow, curved Isthmian 

 backbone, generally known as the Serrania del Darien, reaches. in 

 many places an altitude of 3,000 to 5,000 feet,, but the crest is inter- 

 rupted at various points by passes less than i.ooo feet high. Among 

 the lowest gaps known are those near the heads of the Rio Membrillo. 

 the Rio Sucubti and other tributaries of the Rio Chucunaque, whose 

 sources are within a few miles of the Atlantic Ocean. Farther east 

 is Paya Pass where, except at the dry est season, only a few miles 

 separate canoe navigation on the Rio Paya, a Panama tributary of 

 the Rio Tuyra, and the Rio Cacarica, a Colombian affluent of the 

 Rio Atrato. Mount Pirre is the name applied to a dominant spur. 

 slightly exceeding 5,000 feet in altitude and projecting northward 

 into the Tuyra basin in a crescentic curve with the axial trend of the 

 continent along the Panama-Colombian frontier. The Serrania del 



