251] W. P. Wo'odring 53 



eral is extended into considerably deeper water. The presence 

 of apparently deeper water elements, such as Tindaria and 

 Bathyarca, may be the result of the action of currents or other 

 extra-limital factors. Since but a single valve of Tindaria is 

 present it is doubtful whether the form was indigenous. It 

 may be suggested that the depth did not exceed 30 or 40 

 fathoms and it is highly probable that the bulk of the fauna 

 lived in water that was considerably shallower. 



The waters were clear and the bottoms free from mud. By 

 far the larger number of the Bowden pelecypods are partial 

 to bottoms of sand or fine gravel; even the burro wers are 

 usually found on sandy bottoms. The absence of Mulinia 

 and related forms that prefer a muddy bottom is not without 

 significance. The meager representation or absence of the 

 Leptonacea and other small forms that usually frequent 

 muddy bottoms in sheltered near-shore positions or are 

 attached to algae indicates an open coast and rather strong 

 current action. Estuaries interrupted the coast line and led 

 back to the streams that supplied the relatively coarse volcanic 

 debris which constituted the bulk of the sediments. From the 

 estuaries valves of Dreissena and the mangrove-oyster were 

 carried down to the coast and mixed with the indigenous beach 

 and off-shore dwellers. 



4. EELATIONS TO THE FAUNAS OF THE NORTH AMERICAN 

 MAINLAND 



The possibility of comparing an Antillean Tertiary fauna 

 with those of the Floridian Peninsula is enhanced by the 

 proximity of the areas and by the succession of tropical or 

 sub-tropical faunas of the mainland. Dall 11 has correlated 

 the Bowden horizon with the top of the Alum Bluff formation 

 which includes the Chipola, Oak Grove and Shoal Eiver mem- 

 bers in ascending order. According to Dall 12 the Chipola 



"Ball, W. H., Trans. Wagner Free Inst. Sci., Philadelphia, vol. 3, 

 pt. 6, pp. 1560, 1582, 1903; Bull. U. 8. Nat. Mus. 90, p. 8, 1916. 

 12 Dall, W. H., loc. tit., p. 1574, 1903. 



