206 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
In the Antilles, instead of subsidence, volcanoes added vast accumu- 
lations of extruded débris 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. j 
The exact loci of the old Antillean volcanic outlets are now lost, but 
their débris 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 voleanoes were on the southern margin of an older Bahaman-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 Rocky 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 em echelon. What phy- 
siographie 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 fect 
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 tho great elevation of this epoch, the shore line of the Gulf of 
Mexico receded with comparative rapidity from the eastern Rocky Moun- 
tain region to the interior margin of the present Coastal Plain, where it 
was located in Eocene time. 
