Preliminary Remarks on the Geology of the Bahamas. 51 



Dall, so far as I am aware, was the first to suggest that "much of the limy 

 deposit of the area behind the reefs and defended by them is probably the 

 result of the deposition of lime originally in solution and precipitated 

 by chemical action rather than of mechanically transported sediment."^ 

 Later, Samuel Sanford became convinced that the flocculent oozes in some 

 of the Florida bays and sounds were chemically precipitated, and so ex- 

 pressed himself.^ The most careful study as yet made of the shoal-water 

 bottom deposits of south Florida was the one initiated by me in 1908 and 

 conducted in conjunction with George C. Matson.^ 



This investigation led to the conviction that the flocculent, so-called 

 amorphous, calcium carbonate is neither of detrital nor of organic origin, and 

 therefore must be a chemical precipitate. In 191 1, G. H. Drew came to the 

 Tortugas Laboratory for the purpose of studying denitrifying bacteria. As 

 he discovered that ammonia was a product of the metabolism of these organ- 

 isms he was led to conduct experiments to ascertain the effect they might 

 have in precipitating calcium carbonate. They were found to be active in 

 Florida; and investigations he subsequently made in the Bahamas showed 

 160,000,000 of these bacteria to the cubic centimeter of surface mud on the 

 west side of Andros Island. Drew says:* 



A consideration of these observations shows firstly that B. calcis is found in enormous 

 numbers in the chalky mud flats of the Great Bahama Bank, and secondly that this bac- 

 terium is capable of precipitating calcium carbonate from fluid media containing soluble 

 calcium salts. It would seem a fair deduction that these mud flats have been precipitated 

 by the action of B. calcis on the soluble calcium salts carried into the sea by drainage from 

 the land, where extensive and rapid weathering of the limestone rock is in progress. 



Drew has shown what we may be confident is the major agency in pro- 

 ducing the precipitation of the calcium carbonate ooze. 



Every geologist who has studied the Florida oolites, except Alexander 

 Agassiz, has considered them marine deposits; and Louis Agassiz, Sanford, 

 and myself considered them associated with or derived from the fine cal- 

 careous muds. My opinion^ was more definitely expressed than those of the 

 other investigators. 



Rainey, as early as 1858, showed, in a remarkable book entitled "On 

 the mode of formation of shells of animals, of bone, and of several other 

 structures, by a process of molecular coalescence, demonstrated in certain 

 artificially formed products," that calcium carbonate precipitated from 

 water-soluble salts of calcium in a viscid solution form spherulites and not 

 crystals. In 1871, Harting, in a memoir, "Recherches de morphologic 

 synthdtique sur la production artificielle de quelques formations calcaires 

 organiques,"^ showed that calcium carbonate precipitated from a solution of 

 a water-soluble calcium salt by the addition of the carbonate of potassium 



>U. S. Geological Survey Bull. No. 84, p. loi. 1S92. 

 * Second Annual Report Florida Geological Survey, p. 228. 1910. 



» A contribution to the geologic historj- of the Floridian Plateau. Carnegie Institution of Washington 

 Pub. No. 133. pp. 114-145. 1910. 



< Carnegie Institution of Washington, Year Book No. 11, p. 144. 191 2. 

 5 Carnegie Institution of Washington Pub. No. 133. PP- i73-i77. 1910. 

 ^Verh. Kon. Akad. Wetensk., Amsterdam, vol. 13, PP- 84. 4 Pls- 1871. 



