BOTTOM SAMPLES, MURRAY ISLAND, THE BAHAMAS, AND FLORIDA. 265 



Precipitation of CaC0 3 in the Ocean and the Possibility of its 



Solution in the Sea. 



In the foregoing paragraph I have expressed it as my opinion that the 

 small percentage of particles of silt and clay size in both the Murray Island 

 and Cocoanut Point samples is due to the washing away of the fine material — 

 that is, to mechanical sorting. The only other possible explanation is that 

 its removal is due to solution by sea-water. The latter hypothesis will be 

 briefly discussed. 



My personal experience with the problem of the chemical precipitation 

 of CaC0 3 from sea-water and the consideration of the reverse of the process 

 of precipitation, that of solution of CaC0 3 by sea-water, began in the winter 

 of 1907-08, when I first examined the exposures of the oolitic limestones 

 in the vicinity of Miami, Florida. There were associated in this work 

 Messrs. Samuel Sanford, G. C. Matson, and F. G. Clapp. All of us agreed 

 that the origin of the oolites could not be explained on the "wind-blown 

 coral sand" hypothesis of Mr. A. Agassiz. Because the oolites are not of 

 detrital origin, but are zonal in structure, showing outward growth from a 

 central nucleus, and because embedded in them there are marine fossils 

 which have not suffered notable attrition, we interpreted the deposits as 

 marine formations due partly to chemical processes which we did not under- 

 stand. 1 As it seemed to me that oolite might be found forming in the bays 

 and sounds behind the Florida keys, I began in 1908, in connection with the 

 Tortugas Laboratory, a systematic study of the shoal-water bottom deposits 

 of southern Florida. The result of the first season's field work, in 1908, 

 was stated in the following words: 



"In the shallow waters near the shore the opportunity for re-solution as the 

 material settles to the bottom is not afforded and the accumulation on the sea 

 bottom of largequantities of amorphous calcium carbonate apparentlynot of detrital 

 orgin, is undeniable." 2 



Although an attempt was made to explain the precipitation of the CaC0 3 

 by suggesting processes whereby the C0 2 content of the water might be 

 reduced {op. cit., p. 135), it was said in the introduction (p. 106): "The 

 chemical processes of precipitation have not been sufficiently studied." 

 The work of Drew, 191 1-12, extended by Kellerman after the former's unfor- 

 tunate death, as it showed that denitrifying bacteria evolve ammonia, 

 resulted in knowledge of one factor capable of producing precipitation of 

 calcium carbonate from sea-water. But as will later be made evident, not- 

 withstanding the great abundance of ammonifying bacteria, they are almost 

 certainly not the only agents. 



Prosecution of the study of the bottom deposits showed that in all areas 

 not swept by relatively strong currents, fine sediment is accumulating, and 

 that a considerable proportion of this material is a chemical precipitate (the 



'See Carnegie Inst. Wash. Pub. 133, pp. 173-177, 1910. 2 Op . cit., p. 136. 



