162 MISSOrUI HOTANH'AI, .ARDEN. 



since subsided, or, as Bell suggests (The Naturalist in 

 Nicaragua, p. 266 et seq, with references), the water may 



have been withdrawn to form the great ice-cap at the north 

 during the Glacial Epoch. But, in the latter ease, the 

 estimated lowering of 1,000 feet (166 fathoms) would lay 

 hare the banks, but would not make any important con- 

 nections. 



The Greater Antilles are of ancient formation and may 

 have been connected with Mexico and Central America, at 

 some remote period. But the Bahamas, the Windward 

 Islands and the southern extremity of Florida are of recent 

 origin. The whole area seems now to be in a process of 

 elevation as shown by the elevated reefs of Cuba and other 

 islands, and by the present growth of the submarine banks 

 as the Yucatan and Bahama banks. From the number of 

 endemic species of Phenogams in the larger islands it is 

 probable that they have been separated from the mainland 

 for some time. 



According to Agassiz,* at the time of the elevation of 

 the Isthmus of Panama, the Gulf Stream turned north be- 

 tween Mexico and Cuba and passed around Florida through 

 a much wider channel than now. The Bahama banks and 

 the submarine plateau to the east of the South Atlantic 

 States had already been gradually built up by the lime 

 deposits from the animal life supported by the northern 

 trend of the Equatorial Current. The Gulf Stream now 

 began to build a similar bank to the west of Florida and 

 was active in the southward extension of this peninsula, 

 thus gradually narrowing its channel as it swept through 

 the Straits of Florida. As the channel narrowed the cur- 

 rent became swifter and the erosion at the bottom became 

 greater. In this way the plateau was again cut down along 

 the line of the stream, especially between Florida and the 

 Bahama banks. 



* Three Cruises of the U. S. Coast and Geodetic Survey Steamer 

 u Blake." 



