Vol. 51.] THE CHEMICAL COMPOSITION OF OCEANIC DEPOSITS. 317 



of alkalies present to be 6-07 per cent., whilst a separate determi- 

 nation of them made for the purpose of control by the Lawrence 

 Smith method gave 6-17 per cent., and we therefore consider 

 that the omission of this determination is a matter of considerable 

 importance. 



The chlorine also was not estimated, and in consequence the 

 presence of sodium and magnesium chlorides was not detected, the 

 amount of magnesia really present in a soluble form being included 

 among that calculated as carbonate. 



With regard to the alumina, Dr. Murray says ('Challenger' Report 

 on the Deep-Sea Deposits, p. 199) : — 'After such a treatment [as that 

 adopted by Dr. Brazier] the clayey matter should pass entirely into 

 solution, and to estimate the quantity of this substance we have 

 merely to take account of the data given in the columns showing 

 the substances soluble in hydrochloric acid. It must be remembered, 

 however, that a certain part of the alumina indicated in the soluble 

 portion does not exist as argillaceous matter in the deposit, but 

 comes from the action of the acid and caustic potash upon the alu- 

 minous silicates and rocks present in the Red Clay.' 



In this Dr. Murray appears to be mistaken ; the alumina rendered 

 soluble by Dr. Brazier's method (6 per cent.), and derived from 

 both sources, is only half as much as we find to exist as argillaceous 

 matter set free from the aluminous silicates by the action of 

 sulphuric acid. 



The fact is that Dr. Brazier's analyses of Red Clay do not afford 

 any reliable basis for discussing the mineralogical constituents of 

 the deposit. 



To return to the analysis which we now publish, and in making 

 which it has been our object to isolate the argillaceous matter as 

 completely as possible, we are aware that our estimate of it as 

 forming 67*85 per cent, of the deposit must include all the minute 

 crystals of phillipsite which Dr. Murray says are always scattered 

 through the Red Clay ; but, as Dr. Murray believes these to be actually 

 in process of formation out of the argillaceous constituent of the 

 clay by the chemical action of the sea- water, we think the inclusion 

 of these minute crystals is not a matter of much importance ; for, if 

 it were not for the action of the sea- water, the constituent elements 

 of these crystals would not have been separated out of the clay. 



"With regard to the nature of this argillaceous ingredient, it is 

 evidently a more highly silicated compound than a pure clay or 

 hydrated ortho-silicate of alumina ; for, if the substance were only a 

 mixture of ordinary hydrated silicate of alumina and free hydrated 

 peroxide of iron, the proportions of silica and alumina would be as 

 14 to 12, whereas they are actually as 33 to 12. 



If, howevei', we calculate the percentage composition of this 

 argillaceous matter, we can compare it with other known substances. 

 When this is done, it is seen to bear a strong resemblance to the 

 ferruginous clays and earths which are the product of the decom- 

 position of certain basic igneous rocks, and especially to the palago- 

 nites derived from basic volcanic glass. 



