Vol. 51.] THE CHEMICAL COMPOSITION OE OCEANIC DEPOSITS. 



323 



Argillaceous and Earthy Constituents. 



Iron peroxide 3'41 



B. 



C. (cont.). 



Alumina 

 Manganese peroxide 

 Lime 



Potash . 



Soda 



Combined silica 

 Quartz . 



Adherent Sea-salts. 



Sodium chloride 



Magnesium chloride 1*17 



Calcium sulphate 



Potassium sulphate 



3-41 



1-23 



1-22 



■42 



•44 



•79 



•35 



•38 



•38 



1-65 



•25 



•42 



•81 



•12 



•04 



•28 



•17 



•17 



•35 



•04 



•25 



2 - 27 



119 



1-27 



•17 



•04 



•55 



2-67 



1-79 



2-11 



1-17 



•27 



•27 



•73 



•42 



•32 



— 



traces 



traces 



Totals 100-00 100-37 99'87 



On referring to the ' Challenger ' Report, we find that analyses 

 were made by Dr. Brazier of the samples A and B, but that in the 

 case of A it was the coarser part only that was analysed, ' after 

 the finer parts had been washed away (op. cit. p. 441).' The 

 following is Dr. Brazier's analysis of this coarser part : — 



Soluble in 

 hydrochloric 



acid. 

 9757 p. c. 



Loss on ignition 1*50 ") 



f Alumina 125 



Ferric oxide "47 



Calcium phosphate - 28 



Calcium sulphate "29 



Calcium carbonate 93'14 



Magnesium carbonate '57 



Silica 1-57 



Alumina, ferric oxide, and silica *93 



= 10000 



Insoluble 



On comparing this with our analysis it is evident that the com- 

 position of the coarser part is very different from that of the mass. 

 The coarser part contains 93'71 per cent, of carbonates, while the 

 amount in the whole mass according to our analysis is about 80 '; 

 consequently in the part which was washed away there must have 

 been much less than 80 per cent. 



It is true that in Dr. Brazier's analysis the adherent sea-salts 

 were almost entirely removed in the washing process, and that if 

 we had removed them from our sample before analysis the amount 

 of carbonate of lime would have come out higher, namely, 83*61 

 per cent. But to obtain a mean of 83*61 per cent, when one portion 

 has 93*71, the other, i. e. the finer part, must have had only 73*51 

 per cent, of carbonate of lime. 



A glance at the microscopical structure of the material (see p. 327) 

 will explain this difference, for the coarser part consists almost 

 entirely of Globigerina-testB, and is therefore highly calcareous, 

 while the finer part would naturally be less calcareous and more 

 siliceous. Thus the amount of siliceous and earthy matters in 



1 Dr. Murray's determination was 79'20 per cent. 

 Deep-Sea Deposits, p. 108. 



: Challenger ' Reports, 



