1909-10.] Composition and Character of Oceanic Red Clay. 191 
contents of iron, calcium, and magnesium. Their composition thus approxi- 
mates to that of white liparitic pumice, and in so far confirms the accepted 
view that Red Clays are produced by the degradation of such pumice. 
But it is clear that the original substance or mixture of substances 
from which Red Clay originates must have been rather differently com- 
posed, since we find in the hydrous portion considerable percentages of 
iron. Now much, if not all, of this constituent must have been derived 
either from more highly basic (basaltic) pumices or from ferruginous 
minerals accompanying or enclosed in acid pumice. Iron having in most 
cases disappeared from the residues, it may be concluded that basic 
volcanic glasses and pumices, and such individuals as augite, hornblende, 
biotite, and magnetite, are less resistant to submarine decomposition than 
liparitic pumice. This view is supported by the peculiarities of No. 7 
(between Australia and Japan) and No. 11 (South Seas), where the residues 
are not only abnormally high in amount, but abnormally basic and fer- 
ruginous in composition ; here the Red Clay would appear to be of more 
recent formation than in the other examples. The residue of No. 13 (off 
Madagascar) presents similarly abnormal features, but it is possible that 
there may be terrigenous admixtures in this instance. Again, the two Red 
Clays (Nos. 8 and 9) from the open South Pacific, where pumices of a basic 
habit are known to predominate, illustrate the effects of sufficiently pro- 
longed action of sea- water : the proportion of residue is very small — less 
than 20 per cent. — but its composition is much the same as that of Red Clay 
residues from the North Pacific, where the volcanic silicates supplied are 
predominantly acid. 
Quartz, supposed to be wind-blown, had been detected microscopically 
in the Red Clays Nos. 1 and 10; its presence is reflected by the residue- 
analyses, which show unusually high silica contents. 
In general, chemically separated residues, once the coarse minerals have 
been removed by washing, yield little additional information to the 
microscope. The particles are for the most part under 0005 mm. in 
diameter, and too small to react with polarised light or to show vesicles ; 
sometimes, however, a few scattered units are large enough to be recognised 
as felspar, 'or, by their areolar structure, as pumice. Contours are invari- 
ably very much rounded. The undecomposed minerals isolated by chemical 
treatment (compared with which the mechanically separable coarse 
minerals are insignificant in amount) cannot, differences in density notwith- 
standing, be separated from the secondary constituents by elutriation, and 
it appears probable that they exist as cores within envelopes of argillaceous 
secondary matter. 
