222 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



On closer study this system presents several interesting minor trends, 

 and its history reveals a complexity of movements. In Jamaica, fur 

 instance, and those islands around the Windward passage in the very 

 heart of the region, two movements of different epochs and axial direc- 

 tions can be traced. The oldest of these produced the intense folds of 

 higher summits of eastern Cuba, Jamaica, and western Haiti, com- 

 posed of terrigenous and volcanic debris of Eocene 'and Cretaceous 

 age. A subsequent subsidence destroyed the pre-existing continuity, 

 and coated the lower slopes of these mountains with 3,000 feet of 

 purely oceanic deposits. This was followed by another uplift of Mid- 

 Tertiary time, which was produced or accompanied by the vast igneous 

 intrusions. The trends produced by these two events are quite distinct. 

 Those of the older uplift are northwest and southeast in Jamaica and 

 Haiti, and continued with the Sierra Maestra of Cuba, and constitute 

 an almost closed amphiteatre of summits, broken only in the west by 

 the Bartlett Deep. 



The trends of the later Miocene uplift, which added the present white 

 limestone areas to the Antilles, are strictly east and west, and the struc- 

 ture is that of simple open anticlinal folds. 



In the Panama and Honduras trends active vulcanism was in opera- 

 tion during the earliest of these mountain making epochs, the chief 

 erupted material being augite-porphyrites. The second orogenic epoch 

 in the Antilles was accompanied in the Panamic, Costa Rican, and 

 Carribischen ranges by intrusions of a different nature. 



The foregoing facts all lead to the conclusion that the orogenic 

 growth of the cross ranges of the Tropical region was a series of inter- 

 mittent processes. These were probably initiated back or before the 

 early Mesozoic, as shown by the uplifts of the Segovian ranges which 

 fire concentric with the southern margin of the older Appalachian 

 trends. This may have been followed by movements in the later 

 Mesozoic not yet deciphered. The chief revolutionary movement ef- 

 fective in producing the present configuration occurred in the Miocene 

 Tertiary. The Post-Eocene age of these uplifts is undoubtedly attested 

 by the fact that in all the regions mentioned, including the Segovian, 

 where older rocks also occur, the ranges are composed of intensely 

 folded Eocene and Oligocene strata which have been cut through by 

 granitoid and basic intrusives. 



Concerning the origin and succession of volcanic events, the follow- 

 ing facts can be stated. In late Cretaceous time vulcanism was active 



