CENTRAL AMERICAN GEOLOGICAL WATER WAYS. 579 



Interruptions of the Plateaus corresponding to the Antillean 

 Basins. — In the paper upon The AVest Indian Bridge between iSTorth 

 and South America it was pointed out that the Antillean seas formed 

 three distinct basins — the Gulf of Mexico, the Sea of Honduras (be- 

 tween Cuba, Haiti, and Jamaica), and the Caribbean Sea, although 

 the two latter are united at their surface under the name of the 

 Caribbean Sea. In the investigations of the river valleys, now 

 drowned beneath the West Indian waters, it was found that they 

 were traceable to the floors of the three basins just mentioned. Ac- 

 cordingly, the hypothesis that these three basins were formerly 

 drained into the Pacific Ocean called for corresponding depressions 



Fig. 1. — View of the Mexican Plateau from near Ptiebla, shovvinjir the pliiins out nt" 

 which rise isolated cerros, with tiie volcanic cones of Popocatepetl and Iztaccihuatl in the 



back^Tound. 



across Central America and Mexico; and only such are found to 

 occur (as shown in map. Fig. 2), although the continental barriers 

 are now raised to considerable heights above the level of the sea. 

 Thus the Mexican plateau rapidly narrows to a breadth of only 

 twenty-five miles in the Teliuantepec Isthmus, where for a distance 

 of sixty or eighty miles it is reduced so that the higher points do 

 not exceed four thousand feet, and for a distance of perhaps over 

 twenty-five miles the ridges do not reach an altitude of more than 

 two thousand feet, with a repetition of base levels of erosion only 

 nine hundred or a thousand feet in altitude among them. Indeed, 

 these lower divides are further reduced at seven or eight passes 

 which are only about eight hundred feet above the sea. Beyond 

 these low depressions there are higher passes in the isthmus having 

 an altitude of about twenty-seven hundred feet with accompanying 

 plains. The Tehuantepec depression through the Mexican plateau 



