THE GEOGKAPHIC KELATIONS OF THE WEST INDIES 6 



with the great scarp, or abfall, of the so-called plateau of 

 Mexico, in longitude 97 W., a little south of the capital of 

 that republic, and that the mountains have no orographic 

 continuity or other features in common with those of the 

 Central American region. 



The Andean Cordilleras, which dominate the South 

 American continental area, are largely composed of the old 

 sediments of the Pacific Ocean, and are also accompanied 

 by volcanic intrusions and ejecta now folded into north-and- 

 south mountain trends. They too were pushed up against 

 a preexisting land buttress, but this lay to the east, instead 

 of to the west as in the case of the North American Cordil- 

 leras. The Andean trend, which follows the western side 

 of South America, after crossing north of the equator, 

 bends slightly eastward and abruptly terminates in north- 

 ern Colombia, in longitude 70 W. Only one doubtful 

 spur touches the coast of the American Mediterranean, the 

 Sierra del Marta, lying between the Gulf of Maracaibo and 

 the river Magdalena. The Andes have no genetic connec- 

 tion with the ranges extending east and west along the 

 Venezuelan coast of South America, much less with the 

 mountains of Central America or with the great Rocky 

 Mountain region of Mexico and the United States. The 

 northern end of the Andean system lies entirely east of the 

 Central American region, and is separated from it by the 

 Rio Atrato the most western of the great rivers of Colom- 

 bia. In fact, the deeply eroded drainage valley of this stream 

 nearly severs the Pacific coast of the Republic of Colombia 

 and the isthmian region from the South American continent. 



The trends of the great North and South American 

 Cordilleras, the Rocky Mountain and the Andean systems, 

 if protracted from their termini in southern Mexico and 

 Colombia respectively, would not connect with each other 

 through Central America, but would pass the latitude of 

 the Antilles in parallel lines nearly two thousand miles 

 apart. The Andean trends, if extended, would pass through 

 Jamaica and eastern Cuba, and continue almost east of the 



