218 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



epoch the Antilles were restricted to a fraction less than their present 

 dimensions. 



This subsidence of late Pliocene or early Pleistocene time did not 

 lower the Isthmian barriers sufficiently to permit the commingling of the 

 two oceans across them, or to divert the Gulf Stream across it in Pleis- 

 tocene time, as has been frequently asserted, nor is there a single fact in 

 the geology or geomorphology of the Isthmus of Panama to warrant this 

 conclusion. How long this subsidence persisted in the Tropical regions 

 cannot be stated with accuracy. 



There is one point in this history which seems to present a hiatus. 

 There should be some record of a subsidence in early Pleistocene time 

 corresponding with the great Columbian depression of the North Amer- 

 ican coast in the Glacial epoch. We must confess, however, that the 

 structure of the islands affi^rds no data whereby it can be exactly estab- 

 lished in the islands, although the Isthmian and Texan coasts clearly 

 record traces of such an episode. 



Following this Pliocene expansion were a number of pseudo epeiro- 

 genic elevations which probably continued from Pleistocene time to -the 

 present, marked by a series of interrupted uplifts of a large portion of 

 the AVest Indian region, bringing the pre-submerged plateaux, ridges, 

 and benches to altitudes sufficiently near the surface (fifteen fathoms) to 

 permit the growth of modern coral reefs, which as the elevation pro- 

 gressed were elevated above the water, while other slopes of the sub- 

 merged lands were brought successively within the limits of the reef 

 coral growth, by which they are now inhabited. 



These later elevations of the West Indian region are recorded in the 

 elevated reef and wave-cut bench and bluff topography or newer terraces 

 of all the islands except the Leeward side of the Windward Islands. 

 The topography, whether seen against the margins of the older moun- 

 tainous islands of the Great Antilles, or in isolated islands like Barbuda, 

 Desirade, Alta Viela, Navassa, or a dozen other examples that might be 

 quoted, is the most striking modern feature of the West Indies, and con- 

 sists of a series of two or more low benches and escarpments rising above 

 the sea. In Jamaica, besides the higher benches of older origin, they 

 comprise four benches, the oldest and highest of which is composed of 

 elevated Pliocene marls, and the three lowest of elevated coral reef rock. 

 Barbuda, Sombrero, Navassa, and others, show a double terrace, consist- 

 ing of a low coastal bench surmounted by a higher mesa summit. 



The newer group of terraces is traceable and recognizable throughout 

 the islands and margins of the whole West Indies, with the exception of 



