b CUBA AND PORTO RICO 



blending into one another, the volcanic areas of the tropics 



are of two distinct kinds, which we may call the quiescent 

 and the active. 



The active volcanic group occurs in four widely sepa- 

 rated localities: 1. The Andean group of volcanoes of 

 the equatorial region of western South America, which 

 rise above the corrugated folds of the northern termination 

 of the dominant South American Cordilleras. 2. The 

 chain of some twenty-five great cinder-cones which stretch 

 east and west across the south end of the Mexican Pla- 

 teau, protruding on the terminal ranges of the North 

 American Cordilleras. 3. The Central American group, 

 with its thirty-one active craters, occurs diagonally across 

 the western ends of the east-and-west folds of the Antil- 

 lean corrugations, and fringes the Pacific side of Guate- 

 mala, San Salvador, and Costa Rica. This is separated 

 from the Mexican group on the north by a quiescent 

 volcanic area, the Isthmus of Tehuantepec, and on the 

 south from the Andean volcanoes by the Isthmus of 

 Panama, where no active volcanoes are found. 4. The 

 volcanoes of the Windward chain of islands, which mark 

 the eastern gate of the Caribbean Sea in a line directly 

 across the eastern terminus of the Antillean Mountains. 

 These are parallel to the Central American group, and 

 together these two groups constitute the eastern and west- 

 ern borders of the Caribbean Sea. 



Other regions in which volcanic activity has been quiet 

 in recent geologic epochs are the Great Antilles, the 

 Isthmus of Panama, the Pacific coast of South America 

 west of the Atrato, and the Venezuelan coast of South 

 America. Thus the Caribbean is bordered on the east and 

 west by volcanic chains, and on the north and south by 

 mountain folds. 



