UROCOPTID^:. xxi 



of geologists, most extensively by Robert T. Hill and J. W. 

 Spencer. The data as interpreted by Hill indicate extensive 

 Cretaceous land areas, although in the later Cretaceous large 

 portions of the present islands were submerged. There is 

 abundant evidence of erogenic elevation in the early Eocene, 

 and considerable land areas, supplying debris for the forma- 

 tion of thick beds carrying a scanty marine fauna of Cretaceo- 

 Eocene aspect. This was followed in the later Eocene by 

 profound subsidence, culminating at the end of the Eocene, 

 or possibly the early Oligocene (Vicksburgian). This subsi- 

 dence reduced the Antilles to islands smaller and more widely 

 separated than at present. In mid-Oligocene time a great ele- 

 vation is believed to have ensued, indicated chiefly by exten- 

 sive erosion of the preceding deposits. This elevation prob- 

 ably united Jamaica with Haiti ; the latter with eastern Cuba, 

 and with the islands eastward; and at this time there was 

 land in Florida, and probably the Bahamas, carrying an An- 

 tillean fauna, and somewhere connected with the main Antil- 

 lean mass. As the close of Oligocene time approached, there 

 was a subsidence somewhat below the present level, marked 

 by the deposition of the shallow water deposits of late Oli- 

 gocene age at Bowden, Jamaica, and at various places in 

 Cuba, Santo Domingo, and Tampa, Florida. The present 

 general outlines of the islands were assumed at this time, 

 although it is likely that the unification of Cuba did not take 

 place until much later, the eastern, central and western por- 

 tions remaining separate as three or more islands. No move- 

 ments of great magnitude are indicated in later Miocene, 

 Pliocene or Pleistocene time; the evidence adduced for the 

 gigantic elevations and subsidences advocated by Spencer be- 

 ing scanty and of very uncertain meaning, and emphatically 

 negatived by the zoogeographic facts. 



The materials for correlating geological changes with the 

 evolution of land-snail genera in the Antilles are not yet in 

 our possession, owing to the scarcity as yet of fossil land 

 shells ; but what have been found afford some suggestive data. 

 Simpson has shown that the late Oligocene land snails of Bow- 

 den, Jamaica, are of characteristic modern Jamaican types. 



