APPENDIX. 169 
Tt is seen that both the absolute percentage of ferric oxide and its ratio to alumina are 
remarkably high, as also is the magnesia-content. The alkalies, perhaps, are rather higher 
than one would expect in the truly argillaceous portion of a northern Red Clay. The ex- 
traction test shows how loosely the bases are combined with silica; an argillaceous Red 
Clay would retain its bases, and especially its iron, more tenaciously under acid attack. 
The appearance of the deposit suggests comminuted palagonite rather than true clay. 
In chemical composition it differs slightly from palagonite by excess of magnesia and de- 
fect of alkalies. If we take it, then, that the deposit is not argillaceous, we have two 
alternative views of its nature, between which it is difficult to decide. 
On the one hand, the deposit may be palagonite in the process of breaking down to 
clay, that is in a post-palagonitic stage. The complete disappearance of minerals, and the 
structureless condition of the deposit favor this view. 
On the other hand, it follows from the analysis that the deposit is less like palagonite 
than the basic voleanic glass from which palagonite is derived (cf. Murray and Renard, 
Challenger Report on Deep-Sea Deposits, page 307); in fact, it markedly resembles this 
glass plus water. Doubtless the first stage of decomposition of basic glass is simply hydra- 
tion without exchange of bases with the surrounding sea-water. Thus the deposit may be 
a not fully developed palagonite. If this were the case, we should expect to find remnants 
of original glass and palagonitic pseudomorphs of the glass fragments. The absence of 
these may perhaps be accounted for by a fine state of subdivision of the mother-substance, 
and further by trituration of the deposit through volcanic movements. 
In general, the Red Clays from this region of the Pacific seem to be of a different 
character from North Pacific and North Atlantic Red Clays, apart from the circumstance 
that they are richer in manganese and therefore of a darker color. It was observed, for 
instance, that the Red Clay from Station 4701 (2265 fathoms), and the Red Clays which 
are disseminated in Globigerina Oozes, Station 4705 (2031 fathoms) and Station 4707 (2120 
fathoms), behave towards dilute acid like the Red Clay from Station 4719 under discussion. 
It is almost possible to differentiate North and South Pacific specimens by boiling a small 
quantity with dilute hydrochloric acid in a test-tube. The South Pacific variety leaves a 
white residue in large flakes; the North Pacific variety a light grayish- or pinkish-brown 
residue in finer flakes; the residue from North Atlantic Red Clay, again, has a decided 
reddish-brown color. In chemical composition, the most striking point of difference lies 
in the higher contents of magnesia and alkalies in the South Pacific variety. The great 
predominance of iron at Station 4719 is probably a local peculiarity. 
That Red Clay should vary so considerably in character need cause no surprise when 
we remember what very different mother-substances it is derived from. It is a product 
mainly of acid volcanic glasses (pumice) in the North Pacific, and of basic volcanic glasses 
in the South Pacific. The former materials decompose slowly, so that much finely-divided 
undecomposed pumice is found intimately mixed with the Red Clay; the latter contain 
more manganese and pass, in decomposing, through a palagonitic stage. These differences 
explain, at least to some extent, the differences in the respective Red Clays. 
