210 THE OCEAN 



oozes), along with volcanic glassy fragments 

 more or less completely decomposed into 

 palagonite. The origin of the red clay has 

 been much discussed, but it is now generally 

 admitted that the clayey matter is chiefly 

 derived from the decomposition of volcanic 

 particles in situ. The peroxides of iron and 

 manganese are universally present in red 

 clays, in the form of grains or coatings, or 

 deposited concentrically around a nucleus 

 as nodules of larger or smaller size. Among 

 less frequent constituents found in the red 

 clays are : small magnetic, metallic or chon- 

 dritic, spherules, which are supposed to have 

 formed part of the tails of meteorites and to 

 have fallen from interstellar space ; zeolitic 

 crystals formed in situ from the decomposition- 

 products of basic volcanic debris ; wind-borne 

 particles from desert regions and in some 

 areas ice-borne rock-fragments and minerals 

 from polar regions ; and volcanic ashes 

 derived from both subaerial and submarine 

 eruptions. Traces of many of the rarer 

 metals have been detected in the manganese 

 nodules from the red clay areas. The pro- 

 portion and size of the mineral particles in 

 the red clays vary greatly, but as a general 

 rule (if we except the nodules formed in situ) 

 they are very small, the larger ones usually 

 showing traces of profound alteration. The 



