Vol. 51.] THE CHEMICAL COMPOSITION OF OCEANIC DEPOSITS. 315 



tion of the ' purified pumice,' of which an analysis is given in the 

 ' Challenger ' volume. 1 — April, 1895.] 



The material so separated has the aspect of fine pumiceous sand, 

 and the analysis of it corresponds with that of acidic pumice, 

 though the proportions of soda and potash are unusually large. As 

 a matter of fact, fragments of acidic pumice were actually found in 

 the mass of the deposit brought up by the dredge at this locality, as 

 well as in many other dredgings of red clay. 2 



Besides the ordinary organic and inorganic constituents we find 

 that all the dried oceanic deposits contain a certain proportion of 

 chlorides of sodium and magnesium, together with a smaller amount 

 of calcium sulphate. The presence of these salts is doubtless due to 

 the evaporation of the sea-water with which the ooze was saturated 

 when brought up from the ocean-bottom. Consequently, in grouping 

 the results of an analysis of dried ooze another class of constituents 

 must be admitted, namely, that of adherent sea-salts. 3 



We think, therefore, that the ingredients of a red clay should be 

 arranged under four heads : — 



1. Argillaceous constituents. 



2. Pumiceous matter. 



3. Organic constituents. 



4. Adherent sea-salts. 



Arranged in this way, the result of our analysis of the material, 

 dried at 212° F., is as follows : — 



Argillaceous Constituents. 



Loss on ignition 6'32 



Alumina 12 - 13 



Peroxide of iron 1039 



Peroxide of manganese ... 1*56 



Lime 069 



Magnesia 0'56 



Potash 092 



Soda 1-58 



Silica (combined) 3370 



67-85 



Organic Constituents. 



Colloid silica 4'61 



Calcium carbonate 092 



Calcium phosphate trace. 



Nitrogenous organic matter - 35 



Pumiceous Matter. 



Alumina 3*58 



Peroxide of iron 016 



Lime 032 



Magnesia 0'82 



Potash 0-96 



Soda 1-64 



Silica (combined) 1578 



23 26 



4. Adherent Sea- salts. 



Sodium chloride 184 



Magnesium chloride - 96 



Calcium sulphate 0'80 



5. Quartz 01 



361 



Total... 100-60 



For comparison with the above we append the analysis of part of 

 the same dredging made by Dr. Brazier, and tabulated iu the ' Chal- 



1 ' Challenger ' Eeport on Deep-Sea Deposits, 1891, p. 457. 



2 Ibid. p. 297. 



3 For the suggestion which led us to recognize this point we are indebted to 

 Mr. J. Williams. 



