hill: geology of Jamaica. 2.I0 



ill the now quiescent regions of the North Mexican and Trans-Pecos 

 Cordilleras, 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 pla^au 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 atfected 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 paleontologic 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 : — 



