192 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
1. There is no evidence that vuleanism has in any way affected the 
Atlantic Coastal Plain east of the Sabine within the periods of geologic 
history bearing upon our problems, and hence the northern border region 
of the American Mediterranean may be considered as having been be- 
yond the zones of volcanic disturbances affecting the Caribbean region. 
9. Vulcanism in Cretaceous time undoubtedly affected all the periph- 
eral regions of the American Mediterranean except the Coastal Plain 
of the Gulf, including the Great Antilles and Virgin Islands, in which 
detrital igneous rocks similar to those we have described as constituting 
the oldest formations of Jamaica occur under similar conditions. I have 
scen these old Cretaceous igneous rocks in Cuba, Gabb has described 
them from San Domingo, and Cleve has pointed out their wide extent 
in Porto Rico, the Virgin Islands, and St. Bartholomew. In all these 
Antillean localities, as in Jamaica, the rocks are of a hornblendic nature, 
occurring largely as conglomerate and tuffs. In fact, the closing days 
of the Cretaceous were essentially marked by vulcanism in the Great 
Antilles. In my report upon Panama I have shown that an old rhyolitic 
or andesitic tuff of probable Cretaceous age, but not hornblendic, there 
constitutes the oldest discovered formation. 
The occurrence of vulcanism in Cretaceous time in the Andean and 
Central American region has been shown by many writers. In the 
Cordilleras and plateaux of Northern Mexico the closing days of the 
Cretaceous were marked by vast extrusions of volcanic rocks, while 
volcanic action also sparsely occurred in Trans-Pecos, Texas, and perhaps 
as far north as Little Rock, along the interior margin of the Coastal 
Plain during this epoch. 
In Eocene time vulcanism was especially violent in the Isthmian, 
Central American, and Colombian regions, and along the south margin 
of the Mexican Plateau. The volcanoes of the Caribbee Islands were 
also most probably active in this period. 
There is no evidence that vulcanism occurred in the Antilles or Virgin 
Islands during the Eocene epoch. On the other hand, all data tend to 
show that the great eruptive activity of Cretaceous time in the Antilles 
was followed by epochs essentially marked by placid sedimentation. 
The chief Panamie eruptions ceased at or soon after the close of the 
Eocene, although vulcanism continued in the adjacent Costa Rican and 
Andean provinces, and along the Mexican volcanic belt, until the present 
time. On the eastern slope of Costa Rica the Vicksburg fossils of the 
Guallava formation are interbedded with contemporaneous basic eruptive 
débris. 
