oceanic 

 areas. 



IV DEPTHS AND DEPOSITS OF THE OCEAN 175 



muds it seems to be the rule that the upper portion should be 

 thin and watery and reddish-brown in colour, in striking contrast 

 with the stiff compact blue lower portion, and this is apparently 

 due to the ferric oxide or ferric hydrate being transformed into 

 sulphide and ferrous oxide in the deeper layers. Among our 

 records there are seven cases of Red clay overlying Globigerina 

 ooze, eight cases of Globigerina ooze overlying Red clay, thre*e 

 cases of Globigerina ooze overlying Blue mud, two cases of 

 Globigerina ooze overlying Diatom ooze, and four cases of 

 Diatom ooze overlying Blue mud ; in twenty other cases the 

 percentage of calcium carbonate was considerably higher in 

 the upper portion of the deposit- samples than in the lower 

 portion, while in six cases the lower portion was richer in 

 calcareous remains than the upper portion. 



The examples of Red clay overlying Globigerina ooze point Subsidence in 

 to subsidence in the region where they occur, and, indeed, there 

 are many reasons for believing that the great earth-blocks in 

 the oceanic areas for the most part undergo subsidence, while Elevation in 

 similar earth-blocks on the continents are, on the whole, subject continental 



. ' ' J areas. 



to elevation. 



3. Some Chemical Reactions in the Deep Sea 



In Dittmar's well-known analysis of ocean-water^ the acids 

 and bases are arbitrarily combined, but it is now known that 

 the dissolved substances in sea-water are not accurately repre- 

 sented by that table, inasmuch as they are present mainly as 

 ions. The aggregate degree of ionic dissociation may be cal- 

 culated from the freezing and boiling points of sea-water to be 

 about 90 per cent. That is, only one-tenth of the total solids 

 are present as salts pure and simple ; but these must comprise 

 not only those named by Dittmar but all the possible combina- 

 tions of bases with acids, among which calcium and magnesium 

 sulphates will be relatively in largest proportion. The bulk of 

 the solutes, however, consists of ions, and it would be more 

 rational to write the composition of sea-water thus : — 



35- 000 



