HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 159 



main Cordilleran system of Mexico, which is the southern continuation 

 of the Rocky 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 oro- 

 graphic features in common with those of the Central American region 

 lying to the south thereof. 



The trend of the two great North and South American Cordilleras, 

 the Rocky Mountain and the Andean systems, if protracted from their 

 termini in Colombia and Southern Mexico respectively, would not con- 

 nect through Central America, but would pass each other in parallel 

 lines many hundred miles apart. The protracted Andes would pass 

 through Jamaica and Eastern Cuba, and continue east of the longitude 

 of the whole Appalachian system in the direction of Nova Scotia. A 

 similar southward continuation of the North American Cordilleras would 

 carry them into the waters of the Pacific, crossing the Equator far west 

 of Central America and the South American continent. 



Between the widely separated termini of the main North and South 

 American Cordilleras, as above defined, and extending directly across 

 their trend at right angles to them, lies another great orogenic system 

 of folding to which the term Antillean may be applied, and which has 

 been of the utmost importance in giving to the Caribbean region its 

 configuration. It belongs to a system composed of corrugations hav- 

 ing an east and west trend, which has never been appreciated by the 

 geologist or geographer owing to the overwhelming proportions of the 

 adjacent volcanic mountains. The corrugations extend along the 

 Venezuelan and Colombian coast of South America, north of the Orinoco, 

 the Isthmus of Panama, Costa Rica, and the eastern parts of Nicaragua, 

 Guatemala, Honduras, Yucatan, Chiapas and Southern Oaxaca, and 

 through the Great Antilles. The mountains trending east and west are 

 made up of granites, eruptives, and folded sedimentary rocks of Paleozoic, 

 Mesozoic, and Czenozoic age in Guatemala and Southern Mexico ; 1 of 

 Mesozoic and Czenozoic age in the Antilles, Costa Rica, Venezuela, and 

 Colombia, and of Czenozoic age in Panama. 



The two elongated submarine ridges stretching across the Cai'ibbean 

 from the Antilles to the Central American coast, between the Sierra 

 Maestra range of Cuba and the Gulf of Honduras, and from Jamaica to 

 Cape Gracias a Dios respectively, separated by the deep submarine valley 

 known as " Bartlett Deep," have a suggestive and remarkable resem- 

 blance to these east and west corrugations of the land. 



1 See further details in later pages of this report. 



