218 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
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 affords 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 West 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- 
gists of a serics of two or more low benches and escarpments rising above 
the sca. 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. 
3arbuda, 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 
