1909-10.] Composition and Character of Oceanic Red Clay. 185 
The hydrous and anhydrous constituents of Red Clay cannot be separated 
by mechanical means, except in so far as undecomposed silicates are present 
in coarse grains ; but a tolerably accurate chemical separation may be 
effected by decomposing and bringing into solution the hydrous portion, 
leaving the anhydrous portion intact. Preliminary treatment of the 
material on these lines renders it possible to furnish dual analyses of Red 
Clay, each of which consists of two complete silicate-analyses. 
Of the twenty-seven analyses of Red Clay hitherto published, twenty- 
one Challenger analyses by Brazier* and one by Harrison and Jukes- 
Brownef are of the dual type, whilst in four Challenger analyses by 
Hornung, Klement, and Renard J the material was dealt with as a single 
silicate, as also in a recent composite analysis, published by Clarke, § of 
twenty-one samples selected by Sir John Murray. It need scarcely be 
pointed out that the true nature of Red Clay is not brought out unless some 
attempt be made to separate it into its primary and secondary constituents. 
Unfortunately the numerous and laborious analyses by Brazier have certain 
imperfections which limit their utility. On the other hand, the analysis of 
an average mixture of Red Clays published by Clarke, even though it takes 
the form of a single silicate-analysis, is invaluable, not only because it was 
carried out with more care than its predecessors, but because it gives in- 
formation as to the several rare and minor elements present in Red Clay : 
no less than twenty-two distinct constituents are enumerated. It is note- 
worthy that qualitatively the same minor oxides were detected by Clarke 
as find a place in Gibson’s || exhaustive analysis of South Pacific manganese 
nodules — viz. Ti0 2 , Cr 2 0 3 , NiO, CoO, SrO, BrO, V 2 0 5 , P 2 0 5 , Mo0 3 , CuO, PbO, 
ZnO. Clarke, in addition, reports As 2 0 5 , and Gibson T1 2 0. Quantitatively 
the percentages present in the nodules are almost throughout higher than 
in Red Clay, and markedly so in the case of NiO, CoO, and CuO. That is, 
manganese nodules have the property of concentrating these oxides out of 
the solid and aqueous surroundings. It should be mentioned that Gibson’s 
nodules were from one single locality, whilst Clarke’s Red Clay was a 
mixture from several places where nodules are scarce or absent. 
In the present re-examination of the chemical composition of Red Clay 
the principle of separating each sample into its two integral parts was 
observed; the alkalies, omitted in the Challenger analyses, were deter- 
mined throughout, but rare and minor elements, with the exception of 
Challenger Reports , “ Deep-Sea Deposits,” pp. 425-433. 
t Quart. Jour. Geol. Soc., li. p. 315, 1895. 
I Challenger Reports , “ Deep-Sea Deposits,” pp. 434, 435. 
§ Proc. Roy. Soc. Edin ., xxvii. p. 170, 1907. 
[| Challenger Reports , “Deep-Sea Deposits,” p. 424. 
