278 PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



The strong cross-bedding of the Floridian oolites shows that waves and 

 currents did move the oolite grains, and thereby gave them access to more 

 chemically precipitated material. 1 



This brief review of the status of the investigation of the origin of oolites 

 will be closed with the statement that, notwithstanding the appreciable 

 advance toward explaining the formation of these bodies, considerable work 

 remains to be done before we shall adequately understand all the processes 

 involved. 



SUMMARY ON BOTTOM DEPOSITS OF THE BAHAMAS. 



(i) The foregoing account of the Bahaman bottom deposits shows 

 three prominent classes of shoal-water deposits and one class of deep-water 

 deposits, as follows: 



(a) Sands such as those forming behind the reef off Cocoanut Point. 

 There is but little silt and clay in this deposit, 1.725 per cent; it is com- 

 posed mostly of the remains of organisms, entire or comminuted, which 

 live upon or are associated with coral reefs; the percentage of MgC0 3 is high, 

 5.24 per cent; although coral detritus is present in the sand it constitutes 

 less than 50 per cent of the material. This deposit is essentially the same 

 as that forming behind the reef at Murray Island. 



(b) Lagoon deposits or deposits forming on extensive flats which are 

 protected by land areas on their windward side. These deposits are very 

 fine-grained, the percentage of particles of silt and clay size averaging 60.7 

 and are largely chemical precipitates. Bacteria appear to be the most 

 important known agents in causing the precipitation, but evaporation 

 and high temperature need further consideration as cooperating factors. 

 Oolite is forming in these muds. MgC0 3 constitutes from 2.56 to 2.72 

 per cent of these deposits, only about 50 per cent as much as in the reef 

 sands. A similar deposit, which had been subjected to alternate wetting and 

 drying by the rise and fall of the tide, has the MgC0 3 (hypothetical com- 

 bination) percentage raised as high as 13.36 per cent (see specimen No. 83). 



(c) Oolitic sand derived from the breaking up of indurated oolite 

 through wave action. This class of deposit contains but little material 

 of silt and clay size (2.3 per cent) and is mostly composed of coarse and 

 medium sand, 1 to 0.25 mm. in diameter (54.5 per cent). There are few 

 organic remains, and the percentage of MgC0 3 is low (0.38 per cent). This 

 oolitic sand differs from the oolitic muds in its larger grain and its lower 

 MgC0 3 content. It is identical with the oolite now elevated above sea- 

 level. Comparison of this material with the oolitic muds indicates that, 

 notwithstanding the advance made toward the understanding of the forma- 

 tion of oolite grains, considerable work remains to be done on the processes 

 involved in the formation of the concentric shells of the grains. 



These three appear to be the most important classes of shoal-water 

 deposits; but some beach deposits should be pl aced in a different category. 



'Vaughan, Carnegie Inst. Wash. Pub. 133, p. 177, 1910. 



