504 THE JOURNAL OF GEOLOGY. 



bonic acid, was led to make a series of experiments on the effect 

 of shaking with air an artificial sea-water, containing a known 

 amount of carbonic acid. He found that he shook out 27 per 

 cent of the carbonic acid originally present, and this did not 

 represent the greatest possible loss. After describing the experi- 

 ments he says : x 



" The experiments reported in this chapter . . . are sufficient 

 to prove . . . that, supposing a sea-water which contains its 

 carbonic acid as bicarbonate, associated or not with free carbonic 

 acid, to be exposed to the air even at ordinary temperature, such 

 a water will soon lose not only its free but part at least of the 

 loose carbonic acid of the bicarbonate [i. e., of what is present 

 over and above that existing in the form of normal carbonates)." 

 Dittmar also discusses the dissociation tension of bicarbonates in 

 sea-water and suggests that the water of the tropics constantly 

 gives out carbonic acid to the air, and water of cooler and of 

 arctic zones constantly absorbs it. 2 



Thus the chemists describe two conditions under which bicar- 

 bonate of lime may be decomposed into neutral carbonate and 

 carbonic acid : 1st, by diminution of the tension of the carbonic 

 acid in the atmosphere ; 2d, by agitation of the solution. 



Theoretically, either one of three things may occur to the 

 neutral carbonate of lime if it be thrown out of solution by either 

 one of these processes, which we may admit are active on some 

 portions of the salt water surface. The carbonate may be redis- 

 solved, or deposited as a calcareous mud, or built into organic 

 structures. We may discuss these alternatives in turn. 



The solvent action of sea-water has been the subject of direct 

 observation in the ocean and of experimental determination. 

 Deep-sea shells, dredged from the bottom of the Pacific and now 

 in the Smithsonian collection 3 are corroded, some of them on the 

 outside only, some of them through and through. In the former 



1 Report on the Scientific Results of the Voyage of H. M. S. Challenger. " Physics 

 and Chemistry," Prof. Wm. Dittmar, F. R. S. Vol. I, p. 115. 



2 Op. cit., pp. 212-213. 



3 For an opportunity to examine these my thanks are due to Dr. Dall, B. W. 



