THE BAHAMA ISLANDS 43 



MARINE FOSSILS OF THE BAHAMAS. 



Underneath the geolian rock in which, for the most part, the landshells 

 were found, is an older formation which, from its structure and contents, 

 appears to have been formed as a marine sediment in shallow water. This 

 forms the basement rock of the existing Islands. It is sometimes composed 

 of fine calcareous sand, and other portions are composed of a calcareous gravel 

 in which the worn remains of large gastropods, like Strombus, or large bivalves, 

 broken up by the action of the surf and mixed with worn pieces of coral, form 

 a gravel with pebbles of appreciable size. A third variety of this rock is chiefly 

 composed of minute oolitic granules, and from its fossil contents appears to 

 have been deposited in lagoons where the evaporation of the sea water had 

 markedly increased the proportion of salt in the water, forming " salines " or 

 '' salt pans " as in Watlings Island, or Turks Island of the present archipelago. 

 Still another form, usually nearly or quite destitute of recognizable fossils, 

 shows the oolitic structure in nodules of larger size, from a few millimeters to 

 a couple of centimeters in diameter. 



The marine molhisks are those of the present shallow-water fauna of the 

 Bahamas. All of them, so far observed, occur living and unchanged in the 

 present waters of the archipelago. 1 have given under the lieads of the several 

 stations a list of the species found by the expedition at each locality from which 

 material was received. 



The following species may be regarded as characteristic forms of the 

 sedi mental Bahama limestone as collected bv the Expedition. 



Corals. 



Porites. 

 Meandrites. 

 Favia. 

 Agaricia. 



All too imperfectly preserved to be specifically identified but probably 



identical with living species of the present reefs. 



Crustaceans. 



Balanus, fragments. 

 Claw of crab. 



MOLLUSKS. 



Ostrea parasitica Gmelin (Mangrove oyster). 

 Mytilus exustus Linne. 

 Lithophaga antillarum Orb. 

 Margaritiphora radiata Leach. 



