1 909-1 0.] Composition and Character of Oceanic Red Clay. 197 
Whilst, therefore, it is not at all improbable that colloidal hydrated alumina 
and silica are present as such in the argillaceous portion of Red Clay, one 
may incline to the belief that the dominant molecular species in the 
argillaceous portion of Red Clay is an “absorption -compound” (the expression 
is Van Bemmelen’s) Si0 2 . mAl 2 0 3 . nFe 2 0 3 . pH 2 0, where on the average 
m = 0'20, n = 0T0, and p = 069. 
The ultimate physical structure of the simpler gelatinous and flocculent 
inorganic colloids is now known * to consist of a reticulated or honey- 
combed framework of no great elasticity, filled with colloidal liquid matter. 
No dhubt the particles of clay-substance are similarly constituted. The 
extremely variable behaviour of a given colloid according to its mode of 
preparation, previous history, etc., may be set down to variations in the 
shape, dimensions, and elasticity of this framework. Similar considerations 
may well apply to Red Clay. Thus Red Clays produced mainly from basic 
glasses (Southern Hemisphere) might be expected to differ physically from 
such as are derived mainly from acid pumice (Northern Hemisphere) ; and 
indeed the No. 9 type, as brought up from the bottom, is much more 
gelatinous and unctuous than the No. 1 or No. 4 type, and is relatively 
more easily decomposed by dilute acid. Differences in ultimate physical 
structure may also account for the rather wide differences in hydration, 
expressed as ignition loss, which appear from Table B. 
It has been established, as was mentioned above, that Red Clays 
originate in the main from the degradation of acid and basic volcanic 
glasses. The chemical processes involved cannot differ in essence from 
those associated with the subaerial weathering of silicates. A peculiarity 
of vitreous silicates is that their decomposition begins with an absorption 
of water without loss of coherence on the part of the substance. This 
admits of direct proof in the case of basic glasses (South Pacific), which 
pass first into a hydrated hyaline mineral, palagonite. Acid pumices 
doubtless behave similarly, though the existence of an intermediate hyaline 
stage has not been observed in deep-sea deposits, probably because acid 
glass, having more material (silica) to lose in its passage towards clay, 
cannot long remain in a coherent hydrated form. Laboratory experiments 
by Lemberg -f- and by Barus J have shown that glasses in general have a 
marked tendency to take up water, and that silicates in vitreous form are 
consequently more easily decomposed than the same silicates as crystals. It 
* Biitschli, Untersuchungen iiber Struhturen, Leipzig, 1898 ; Hardy, Journ. of Physiol ., 
xxiv. p. 158, 1899. 
t Zeitschr. deutsch. geol. Ges ., xxxix. p. 594, 1887 ; xl. p. 637, 1888. 
X Amer. Journ. Sci ., vi. p. 270, 1898 ; Phil. Mag., xlvii. p. 461, 1899. 
