BOTTOM SAMPLES, MURRAY ISLAND, THE BAHAMAS, AND FLORIDA. 279 



(d) Globigerina ooze, which covers the bottom of the Tongue of the 

 Ocean. 



(2) Although the areas covered by the three classes of shoal-water 

 sediments have not been accurately determined, it can be said that the 

 coral reefs off the east side of Andros Island are narrow and interrupted. 

 Figure 4 shows diagramniatically the relations. If all the living corals and 

 the dead coral skeletons forming the modern reefs were put together, I 

 doubt if they would make a continuous ridge loo feet wide and 12 feet thick 

 the entire length of the east face of the island. The barrier stands from 

 about 0.5 mile to about 2 miles offshore; and the sands form a thin veneer 

 over the oolitic rock which passes below sea-level. Solution wells occur in 

 the oolite beneath sea-level as well as along shore above sea-level. I have 

 already published the estimate "that on Andros Island, Bahamas, the 



Old oolite 

 dune ridge 



Solution wells 6~7/^fathoms 

 deep Through oolite 



Solution well 31-33 fathoms deep 



.9°1^-??J. _5ea level. 



ibmerged Terrace i^fma 



Diagrammatic Section 



From Mangrove Cay across The barrier reef 



Andros Island, Bahamas 



Horizontal Scale in feet 



I — I I — I I I ■ 



zooo 



100 fms. 



Fig. 4. 



ratio of the constructive work of the present reef to that of agencies that 

 previously resulted in the formation of the Pleistocene oolite is approx- 

 imately as I to several thousand, or, as a constructive agent, chemical 

 precipitation has been several thousand times more effective in forming 

 limestone than corals."^ The classes designated (b) and (c) are the deposits 

 now forming which are of most importance in shoal water. The growing reef 

 and the sands forming behind it are decidedly subordinate in amount. 

 The area of the deep-water Globigerina ooze has not been ascertained, but 

 it appears safe to assume that it covers the bottom at all depths beyond 

 somewhat less than 800 fathoms. 



(3) Examination of the evidence bearing upon the precipitation of 

 CaCOs in the ocean and the possibility of the solution of CaCOa leads to the 

 conclusion that in the shoal waters of tropical and subtropical regions 

 precipitation is caused by both organic (bacterial) and inorganic agen- 

 cies which reduce the CO2 content of the sea-water; and that no solution 

 of CaCOs by sea-water is taking place. More detailed studies of the salinity, 

 the temperature, and the CO2 relations in the ocean are greatly needed. 



'Jour. Wash. Acad. Sci., vol. 4, pp. 26, 27, Jan. 19, 1914. 



