

206 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY". 



In the Antilles, instead of subsidence, volcanoes added vast accumu- 

 lations of extruded debris to the pre-existing land masses, or built up 

 islands in the sea like Jamaica, around which peculiar colonies of marine 

 life separated from that of the continental borders by great depths were 

 segregated. 



The exact loci of the old Antillean volcanic outlets are now lost, but 

 their debris constitutes the oldest known rocks of all the Antilles and 

 Virgin Islands, with the exception of the few doubtful Paleozoic rocks of 

 Cuba and Haiti previously mentioned. It is a possible hypothesis that 

 these volcanoes were on the southern margin of an older Baharaan- Antil- 

 lean land. 



The close of the Cretaceous and initiation of the Tertiary was marked 

 in both the North and South American continents by great orogenic 

 revolutions in the Andean and E/Ocky Mountain regions. This is known 

 to have affected the North American Cordilleras as far south as the south 

 end of the Mexican Plateau, and elevated the Cretaceous sediments of 

 the preceding northwestern extension of the Gulf of Mexico to heights of 

 15,000 feet or more. 



In North America the material thus folded was the pre-existing Atlantic 

 (Gulf) sediments, — and the land buttress was on the Pacific side. In 

 South America the sea sediments folded were of Pacific origin, and the 

 land buttress was the eastern or Atlantic side of South America. Some- 

 where between north latitudes 10° and 25° and longitudes 75° and 100°, 

 including the Central American and West Indian regions, the axes of 

 these two mighty uplifts passed each other en echelon. "What phy- 

 siographic changes occurred in the Mediterranean region between the 

 termini of the stupendous orogenic uplifts acting upon it with tortional 

 stress cannot readily be conceived, but changes of a most revolutionary 

 nature undoubtedly took place. 



Two of the principal events of Eocene time were faulting and vulcan- 

 ism. According to Felix and Lenk, great faults of at least 12,000 feet 

 downthrow to the southward, along which the present east and west 

 series of living Mexican volcanoes are situated, developed along the south 

 and east of the Mexican Cordilleras, at the great " Abfall" of the Plateau. 

 Perhaps other faults, as described by these writers, extended in a com- 

 plemental direction up the east side of the Plateau. Faulting of this 

 epoch certainly influenced the southern part of Texas. 



With tlie great elevation of this epoch, the shore line of the Gulf of 

 Mexico receded with comparative rapidity from the eastern Ivocky Moun- 

 tain region to the interior margin of the present Coastal Plain, where it 

 was located in Eocene time. 



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