54 Papers from the Marine Biological Laboratory at Tortugas. 



The deduction may be made that all marine oolites, originally composed 

 of calcium carbonate, of whatever geologic age, may confidently be attrib- 

 uted to this process. 



Two other important deductions may be made from the knowledge of 

 this process, viz: 



1. Neither the Bahamas nor the oolitic keys of southern Florida are 

 coral islands, but they have been formed by this other process. Elevated 

 coral rock is exceedingly scarce in the Bahamas and the Recent reef of 

 Andros is comparatively insignificant as a constructional geologic agent. 

 The material composing the land masses and much or most of the submarine 

 platforms of the Bahamas is thus removed from the category of "coral rock " 

 and the living reef reduced to a subordinate ratio as a builder of limestone. 



2. Drew's studies (unfortunately incomplete) of the distribution of 

 denitrifying bacteria have shown them to be most prevalent in the shoal 

 waters of the tropics. They therefore conform to the temperature relations 

 enunciated by Murray^ for the distribution of lime-secreting organisms. By 

 combining the results of Drew and Murray, the deduction seems warranted 

 that great limestone formations, whether they be composed of organic or of 

 chemically precipitated calcium carbonate, were laid down in waters of 

 which at least the surface temperatures were warm, if not actually tropical. 



This brief paper may be closed with the following statement and tenta- 

 tive outline of the geologic history of the Bahamas, with special reference to 

 the eastern part of Andros Island : 



The presence of oolite containing Pleistocene marine fossils above sea- 

 level indicates elevation in the Bahamas; the presence of submerged solution 

 pot-holes, not filled with sediment, indicates that the last movement was 

 downward. 



TENTATIVE OUTLINE OF THE PLEISTOCENE AND RECENT GEOLOGIC HISTORY 

 OF THE BAHAMAS, AND ESPECIALLY OF ANDROS ISLAND. 



(i) During Pleistocene, perhaps earlier Pleistocene time, numerous shal- 

 low submarine banks existed, on which calcium carbonate was chemically 

 precipitated mostly as aragonite, and this was converted into oolite. 



(2) This submergence was followed by uplift with the production by 

 marine erosion of a platform and a margining shore cliflf, and the formation 

 of shore dunes paralleling the windward sea-front. 



(3) Apparently there wat. further uplift and pot-holes were subaerially 

 formed by solution on the platform between the dunes and the sea-front. 

 At this time the land on the east side of Andros Island stood about 40 feet 

 higher than now. 



(4) The last event was a subsidence of about 40 feet, admitting the sea 

 back to the edge of the previously cut low scarp, and the present barrier 

 reef developed on the off-shore margin of the submerged platform. 



' Natural Science, vol. 2, pp. 25-27. 1897. 



