ON THE PRECIPITATION OF CALCIUM CARBONATE IN THE SEA BY 

 MARINE BACTERIA, AND ON THE ACTION OF DENITRI- 

 FYING BACTERIA IN TROPICAL AND TEMPERATE SEAS. 



By G. Harold Drew. 



INTRODUCTION. 



The investigations described in this paper were made in the summers of 

 191 1 and 1912 under the auspices of the Carnegie Institution of Washington. 

 The original intention was to study the action of marine denitrifying bacteria 

 in tropical seas. The discovery, during the course of the experiments, that 

 these denitrifying bacteria also possess the power of precipitating calcium 

 carbonate from soluble calcium salts present in sea-water has perhaps, by its 

 geological significance, somewhat overshadowed the interest of the primary 

 object of the work. The main contentions raised in this paper are: 



(i) That in the seas of the American tropics bacteria exist which are 

 actively precipitating calcium carbonate from the calcium salts 

 present in solution in sea-water. It is suggested that this bacterial 

 action has been a very considerable factor in the formation of 

 chalk and many other varieties of sedimentary rock, chiefly or in 

 part composed of calcium carbonate. It is also contended that 

 the vast deposits of chalky mud now being formed to the west of 

 the Bahamas and in the neighborhood of some of the Florida Keys 

 are precipitated by bacterial agency and that a similar process 

 plays an important part in the cementation of fragments of coral 

 and other detritus into compact coralline rock. 



(2) That the destruction of nitrates by bacterial action in the seas of the 

 American tropics is far in excess of that occurring in temperate 

 waters. Hence an explanation is afforded of the relative scarcity 

 of plant life (and consequently of animal life) in tropical as corn- 

 pared to temperate seas, in accordance with the terms of Brandt's 

 (2 and 3)^ hypothesis. 



Preliminary notes on this work have already been published in the 

 Tortugas Laboratory Reports^ for 191 1 and 1912. The chronological 

 sequence of the investigations will be followed in the account given here of 

 the experimental work. 



' The figures in parentheses refer to the bibliography, p. 45. „ . »- 



2 Carnegie Institution of Washington, Year Book No. lo, 1911. pp. 136-141; \ear Book No. 11, 1912. PP- 

 136-144. 



