B ain~b ridge, Ga., and of Alum Bluff, Fla. 245 



tical with or closely allied to Miocene forms of regions border- 

 ing on the Caribbean Sea. The Chesapeake fauna, as its name 

 was intended to imply, has however a decidedly northern 

 facies, though the species are chiefly such as have long been 

 known to exist in the South Carolina and North Carolina 

 Miocene. 



Alexander Agassiz has shown that in later Mesozoic times 

 the Gulf of Mexico was probably connected with the Pacific 

 across Central American regions, and the paleontological evi- 

 dence favors the idea that this connection was not terminated 

 until the close of the Eocene. The subsequent rise of the 

 Central American ranges must have shut off a western outlet 

 to sub-equatorial currents, and such currents as then entered 

 the present Gulf region were obliged to find an outlet by curv- 

 ing along the western and northern shores until they found an 

 exit, as does the Gulf Stream of to-day. This early Miocene 

 return-current, however, is shown by Mr. W. H. Dall* not to 

 have passed to the south of the peninsular portion of Florida, 

 but to the north of it, between present peninsular Florida and 

 Georgia. For convenience in terminology the return-current 

 may be called the Okefenokee current, and the passage, the 

 Okefenokee straits. 



Mr. Dall* shows that towards the end of the Eocene a part 

 of peninsular Florida had already been raised above the sea, 

 and that during the deposition of the Nummulitic or very late 

 Eocene beds, " this elevation (probably in the form of a chain 

 of islands), had continued long enough for these islets to 

 acquire a landshell fauna, as far south as about latitude 29° 

 north." This group of islets of central Florida having a sim- 

 ilar geological history may be conveniently termed the Ocala 

 islands. The area occupied by these islands was increased dur- 

 ing the earlier Miocene, and their continuous history is sug- 

 gested by the presence of forms in the upper part of the 

 Orthaulax beds, identical with those already mentioned as 

 occurring in the late Eocene of this region. North of the 

 Ocala islands the very wide Okefenokee passage must have 

 been shallow at first, as is suggested by the fact that the Chat- 

 tahoochee does not immediately introduce as southern a type 

 of fauna as is contained in the later or Chipola beds, when the 

 passage was probably deeper and the return current more vig- 

 orous. The Chipola fauna with its decidedly sub-tropical, 

 Antillean or Caribbean facies, extended all along this passage 

 as far as the Atlantic, and thence some distance northward. 



A great deflection of currents took place at the close of the 

 Chipola." Instead of the eastward flowing warm water Okefe- 

 nokee current, the southwestward-running Chesapeake or cold 



* Correlation Papers. Neocene. See also publications of Mr. L. C. Johnson. 



