HILL: GEOLOGY OF JAMAICA. 223 
in the now quiescent regions of the North Mexican and Trans-Pecos 
Cordiileras, the Coastal Plain of Texas, the Isthmus of Panama, and 
the Great Antilles, Jamaica then being a volcanic island. The late 
Cretaceous limestones of Costa Rica contain angular specks of volcanic 
material intermixed with them, as also do the late Eocene sediments of 
Panama, which facts lead us to believe that the present Central Ameri- 
can volcanic plateau has been an intermittent locus of volcanic activity 
from the Cretaceous to the present, as also has the volcanic region of 
Mexico. 
The volcanoes of the Windward Islands, in my opinion, date back to 
at least the Eocene. In Mid-Tertiary time granitoid intrusions were 
pushed upward into the sediments of the Great Antilles, the Carribischen, 
Costa Rican, and Panamic regions. How extensively this remarkable 
event affected the Andean and Cordilleran regions we cannot say, except 
that we have fragmental data which lead us to conclude that it cer- 
tainly extended to the Mexican Plateau, while Cross reports that the 
rocks of this epoch from Jamaica are singularly like the material of cer- 
tain laccoliths of Mid-Tertiary age in Colorado. 
After the Miocene vulcanism became quiescent in the Great Antilles, 
and the Coastal Plain of Texas, but has continued to the present in the 
four great loci: of present activity, — Southern Mexico, the Northern 
Andes, Central America, and the Windward Islands. In the last two 
regions mentioned, the greater masses of the present volcanic heights 
were piled up before the Pliocene, and the present craters are merely 
Secondary and expiring phenomena. 
The wide occurrence of benches and terrace levels in the Tropical 
region is as conspicuous and important a topographic feature as the 
folded and volcanic mountains. Whether made by degradational or 
Constructive processes, they record with unusual clearness the later 
regional movements, and in a manner corroborate the history recorded 
by sedimentary and paleontologie evidence. The three distinct groups 
of these phenomena of late Tertiary, Post-Pliocene, and Post-Pleistocene 
epochs respectively, having their typical development in the Antilles, 
around the Windward passage, are traceable, with local modifications on 
both sides of the Costa Rican divide. In the Windward Islands only 
those of the two later groups are positively defined as yet, while in 
Barbados only those of the last epoch occur under entirely anomalous 
conditions, 
With the date presented we can summarize the known history of the 
Antillean region as follows : — 
