APPENDIX. 169 



It 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 lied 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 volcanic 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 jd/ms 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 palagonitie 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 dis.seminated in Glohigerlna 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 difi'erent 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 aud pass, in decomposing, through a palagonitie stage. These differences 

 explain, at least to some extent, the differences in the respective Red Clays. 



