484 G. H. DREW. 



Calcium salts in their culture solutions in order to obviate the great 

 increase in alkalinity that resulted if Potassium or Sodium salts were 

 used, but they have not called attention to, or apparently realized, the 

 probable significance of this precipitation of Calcium carbonate by 

 bacterial agency as an important factor in the formation of various 

 sedimentary calcareous rocks in Tropical seas. 



The subject of the precipitation of Calcium carbonate in sea-water 

 has been dealt with by Murray and Irvine (14) in 1889, and again by 

 Murray and Hjort (13) in 1912, and they ascribe the precipitation 

 to the interaction of Ammonium carbonate, derived as an ultimate 

 product of the decomposition of nitrogenous organic matter, with the 

 Calcium sulphate present in sea- water, according to the equation 



(NHJo C03 + CaS04 = CaC03-f (NH,)2 SO^. 

 Expressed in the terms of the Ionic Hypothesis, this reaction can be 

 explained by the statement that CaCOg must be precipitated when 

 the product of the concentration of its ions Ca" and CO'j exceeds a 

 certain limit ; an increase in the concentration of CO" ions is pro- 

 duced by the advent of (NHJoCOg, which is partially ionized into 

 NHi and COy, and hence the product of the concentrations of Ca** 

 and CO." ions is increased, and CaCOg is thrown out of solution. 



Though this reaction has been shown conclusively to occur under 

 experimental conditions, where nitrogenous organic matter has been 

 allowed to putrefy for some time in f^^a-water, yet it is obvious that 

 its effect must be purely local, and must be confined to the immediate 

 neighbourhood of the decaying organic body, which gives rise to the 

 formation of (NH4)2 COg. 



In this paper the precipitation of CaCOs in an unorganized state alone 

 is dealt with. The formation of the calcareous skeletons, tests, and 

 shells of animals, and the skeletons and platelets of algae, which 

 play an immensely important part in the constitution of marine 

 bottom deposits, is beyond the scope of these investigations. 



DESCEIPTION OF APPARATUS. 



In 1911 the apparatus at my disposal was of a somewhat primitive 

 nature, as it is difficult when on the first expedition in a new field of 

 work to know beforehand exactly what gear will be necessary. In 

 1912 a more complete outfit was available, and the Carnegie Institute 

 yacht Anton Dohrn was especially fitted for my requirements. 



For deep-sea work the motor trawl winch was modified so as to 

 carry fine sounding wire, and a derrick was rigged aft, projecting over 

 the stern of the boat, over which the wire was led. The motor winch 

 is sunk below the level of the deck, an arrangement which is to be 



