hill: geology of JAMAICA. 213 



This orogenic elevation most probably united the Antillean lands, 

 constructing bridges for the wide distribution of the ancestral forms of 

 the wonderful land shell faunas of the Antilles from Central America 

 to Guadeloupe, which are first found fossil in the succeeding Bowden 

 formation. It also brought the submerged bottoms up to a height 

 sufficient for the habitation of littoral MoUusca, and permitted them 

 to migrate for the first time from the continental margins to the 

 islands, and to attain wide West Indian distribution. The preceding 

 marine faunas of Jamaica, at least of the Antilles, had been all insular 

 and unlike that of the continental margins. 



There are no geologic data to prove or disprove connection between 

 the expanded mountainous Antillean lands with the main continent 

 other than that a marine passage between the Gulf and the Atlantic 

 continued across northern Florida. The absence in the Antilles of 

 remains of continental vertebrates of this period, or living descendants 

 thereof, would indicate that no such connection existed. Furthermore, 

 the distribution of the land shells show that the Equatorial current was 

 flowing into the Caribbean through breaks in the windward rims. 



During this epoch the Caribbee volcanoes, persisting from the previ- 

 ous Eocene epoch, were in superb activity and undergoing their maxi- 

 mum development along the western border of the eastern limb of the 

 submerged plateau which may have been the remnant of the probable 

 bridge or Archipelago of Jurassic time. 



The history of the western Gulf region during this epoch of Antillean 

 uplift is obscure. Hilgard ^ has noted the absence, west of the Missis- 

 sippi, of Tertiary deposits of later age than the Vicksburg, and con- 

 cluded that the Gulf must have been closed on the eastern side. The 

 probable absence from the surface west of Eed River of marine deposits 

 of late Oligocene and Miocene age,^ and the presence of apparently 

 fresh water formations in their place along the Texas coast, may seem 

 favorable to this conclusion, but further study is much needed. 



The evidence supporting a contrary hypothesis is of a few alleged old 

 Miocene Gasteropods from a depth of some 3,000 feet, in the borings of a 

 well at Galveston, which Harris alleges have Pacific affinities. No out- 

 cropping strata have as yet been discovered to support this purely pale- 

 ontologic hypothesis. 



However deficient may be our knowledge of the extent and details of 



1 Geological History of the Gulf of Mexico, pp. 6, 7. 



2 The late Tertiary and Pleistocene history of the Texas Coastal Plain has not 

 as yet been fully studied or interpreted. 



