742 JOHN JOHNSTON AND E. D. WILLIAMSON 



In the first place, it will gradually lose C0 2 to the air, the residual 

 concentration of free C0 2 being dependent at any moment upon the 

 temperature of the water and the proportion 1 of C0 2 in the air at 

 that place. The consequence of this loss is that the amount of cal- 

 cium in solution will at some point exceed the concentration which 

 the water is able to hold in solution — or, in other words, the product 

 [Ca ++ ] [CO 7] reaches its characteristic precipitation value — where- 

 upon precipitation 2 sets in, and continues thereafter so long as the 

 temperature continues to rise. This process is without doubt taking 

 place now in tropical and subtropical regions wherever and whenever 

 the necessary conditions are fulfilled. It has been correlated 3 with 

 the abundant bacterial and planktonic life found under such cir- 

 cumstances, and there would seem to be little question that the organ- 

 isms are a factor in the process, if only in the sense of catalyzing it. 

 But may it not be, in some cases at least, that the organisms are 

 abundant there because of the abundance of the C0 2 available for 

 their life-processes in such water ? For it is to be borne in mind that 

 the precipitation of CaC0 3 is accompanied by the setting free of an 

 equivalent quantity of C0 2 which, if not used up in the sea, will pass 

 into the atmosphere. Be this as it may, the physico-chemical factors 

 are in themselves competent to account for the precipitation 4 of 

 CaC0 3 on a large scale, and the prerequisite conditions for deposition 

 by this means do not differ materially from the postulates required 

 for precipitation by bacterial action or by organisms generally. 



Buchanan (Proc. Roy. Soc. London, XXIV [1876]) writes: "There is usually more 

 CO2 in waters taken from the bottom and intermediate depths than in surface water; 

 but if regard be had to the temperature of the water, it will be seen that there is but 

 little difference in the amount in waters of the same temperature from whatever depth 

 they have been derived." It is to be observed that these determinations all refer to 

 low latitudes; conditions in the Polar regions may well be different. 



1 All experiments indicate that this proportion departs in general very little from 

 3 parts in 10,000, except in or near large towns. Off the west coast of Greenland, 

 however, amounts up to 7 parts in 10,000 were observed by Krogh (Meddelelser om 

 Gronland, XXVI [1904], 409). 



2 Supersaturation is under these conditions obviously a negligible factor. 



3 G. H. Drew, Carnegie Inst. Publ. No. 182 (1914),^. 7; Kellerman and Smith, 

 Jour. Wash. Acad. Set., IV (1914), 400. See also recent papers by T. Wayland 

 Vaughan. 



4 Likewise for its re-solution. 



