Preliminary Remarks on the Geology of the Bahamas. 53 



calcium carbonate, alcyonarian spicules, shoal-water foraminifera, and other 



micro-organisms were present.^ 



Dr. Fred. Eugene Wright has examined some of the bottom samples for 



me and reports that the particles large enough for ascertaining their optical 



properties are calcite, but the fine material can not be optically determined. 



A series of the muds and several powdered specimens of Pleistocene oolites 



from Florida and the Bahamas were tested with the cobalt nitrate reaction; 



and as all of these upon heating gave the purple color characteristic of 



aragonite, this form of calcium carbonate was shown also to be present. 



The muds and the Pleistocene oolites, therefore, are composed of a mixture 



of aragonite and calcite. 



The grains of the Bahama and Florida oolites range in size from o.io 

 to 0.80 mm., and occasionally a grain perhaps exceeds i mm. in diameter. 



The spherulites or spheroid aggregates in the muds range from 0.004 or 

 0.006 mm. to oolite grains of ordinary size. 



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 diameter, and the fine material that passed through the bolting- 

 cloth was put into bottles containing sea-water. These bottles were per- 

 mitted to stand from about November 25 until the first week in March, 

 over three months, when a small portion of each sample was again strained 

 through No. 10 bolting-cloth, and the portion retained on the cloth studied. 

 The formation of oolite grains was found to be in progress in every sample, 

 and numerous grains had apparently grown to such a size as to preclude 

 their passing through the mesh of bolting-cloth. The grains showed the 

 usual forms of oolite grains: spheroids, ovoids, and ellipsoids. The larger 

 grains had smaller diameters of 0.17 mm.; longer diameters up to 0.23 mm. 

 Those newly formed are soft and easily crushed by any kind of pressure. 

 The experiments indicate increase both in number and in size of grains. 



The precipitated calcium carbonate may segregate around a variety of 

 nuclei, for instance, spherulites or round aggregates formed of the precipi- 

 tated material, small grains of sands, shells of foraminifera, and gas bubbles.^ 

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

 retard, or inhibit the formation of spherulites and initial round aggregates 

 and the subsequent growth of the grains, the empirical facts in the process 

 of the formation of the Floridian and Bahaman oolites are clear. They 

 are as follows: 



1. Denitrifying 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 

 or small balls which by accretion may become oolite grains of the usual 

 size, or it may accumulate around a va riety of nuclei to build such grains. 



1 The investigation of these muds is still in progress [June 1913I and wUl not be finished for some months. 

 The completed results will appear in a subsequent pubhcation. 



2 See the papers by Linck. Drew, and Vaughan, already cited. 



