proceedings: geological society 303 



bonate oozes so abundant in Florida waters are chemical precipitates. 

 Drew showed in 1911 that denitrifying bacteria are an important agent 

 in effecting this precipitation in Florida waters; and in 1912 h6 extended 

 his researches to the Bahamas, where he found them enormously abun- 

 dant and active, as many as 160,000,000 being found in 1 cc. of surface 

 mud on the west side of Andros Island. Rainey in 1858, Harting in 

 1871, and Linck in 1903 (and perhaps others), showed that calcium 

 carbonate precipitated by an alkali forms spherulites; and Drew noted 

 a similar tendency of the calcium carbonate precipitated on his cul- 

 tures. Murray and Irvine showed that at higher temperature chemi- 

 cally precipitated calcium carbonate is of the aragonite form. 



Bahaman shoal water bottom muds were collected at many stations, 

 especially through South Bight and off its west end. The muds when 

 collected were not observed to contain oolite grains, altho these may 

 have ])een present and may have escaped notice, but all the muds when 

 examined at the end of November did contain such grains, which ranged 

 from spherulites 0.004 or 0.006 mm. in diameter, to grains of ordinary 

 size, 0.10 to 0.80 mm. in diameter. The muds are composed of a 

 mixture of aragonite and calcite. In order to test the growth of the 

 grains, samples of a number of muds were strained through No. 10 

 bolting cloth, which has a mesh of about 0.13 mm. in size, and the fine 

 material was put into bottles containing sea-water. During the first 

 half of March a portion of each sample was studied. The formation 

 of oolite grains was found to be in progress in every sample, and numer- 

 ous grains were so large as manifestly to preclude their having passed 

 thru the mesh of the bolting cloth. The experiments demonstrated 

 both the increase in the number of spherulites and the increase in the 

 size of the grains. The precipitated calcium carbonate may segregate 

 around a variety of nuclei, for instance, spherulites formed of precipi- 

 tated calcium carbonate, small grains of sand, shells of foraminifera, 

 and gas-bubbles. 



Altho there is need for additional study of the factors that accelerate, 

 retard, or inhibit the formation of spherulites and the growth of the 

 grains, the empirical facts in the process of the formation of the Floridian 

 and Bahaman oolites are demonstrated. They are as follows: (1) De- 

 nitrifying bacteria are very active in the shoal waters of both regions 

 and are precipitating enormous quantities of calcium carbonate which 

 is largely aragonite; (2) this chemically precipitated calcium carbonate 

 may form spherulites which by accretion may become oolite grains of 

 the usual size, or it may accumulate around a variety of nuclei to build 

 such grains. 



Two 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 construc- 

 tional geologic agent. The material composing the land masses and 

 much of the submarine platforms of the Bahamas are thus removed 



