176 GEOGRAPHIC RELATION OF THE THREE AMERICAS 
lying between the gulf of Maracaibo and Rio ^lagdalena. This 
northern end of the Andes lies entirely west of the Isthmian 
region and is separated from it by Rio Atrato. Minute study 
shows that the Andean system has no genetic connection with 
the mountains of the northern coast of South America, much 
less with the mountains of Central America or the great Rocky 
Mountain region of Mexico and the United States; in fact, the 
deeply eroded valley of this stream nearly severs the Isthmian 
region and the Pacific coast of the Republic of Colombia from 
the South American continent. 
The studies of many geographers, especially those recently 
conducted by Felix and Lenk, have shown that the main cor- 
dilleran system of Mexico, which is the southern continuation 
of the R(^cky Mountain region of the United States, abruptly 
terminates with the great scarp or “abfall” of the so-called 
plateau a little south of the capital of the Republic, and that 
these mountains have no orographic features in common with 
those of the Central American region lying further southward. 
The axes of the two great North American and South American 
cordilleras, the Rocky mountains and the Andean sy.stem, if 
projected from their termini in Colombia and southern Mexico, 
respectively, would not connect through Central America, but 
would pa.ss each other in parallel lines many hundred miles 
apart. The projected Andes would pass through Jamaica and 
ea.stern Cuba and continue east of the longitude of the whole 
Appalachian system in the direction of Nova Scotia ; the south- 
ward continuation of the North American cordilleras would cross 
the equator in the Pacific, far west of Central America and the 
South American continent. 
Between the widely separated termini of the main North 
American and South American cordilleras as above defined, and 
extending directly across their trend at right angles to them, lies 
another great orogenic system of folds, to which the term An- 
tillean has been applied. Collectively they constitute a great 
orogenic system which has been of the utmost importance in 
giving to the Caribbean region its predominant outline.s — a 
system composed of corrugations having an east-west trend, 
which has never been appreciated by the geologist or geog- 
rapher owing to the overwhelming proportions of the adjacent 
mountains built up by volcanic ejecta. They extend along the 
Venezuelan and Colombian coast of South America, north of the 
Orinoco, the isthmus of Panama, Costa Rica, and the eastern 
