THE GEOSPHERES 233 



Ordinary detritus from the continents cannot 

 be detected, while volcanic ash and punaice 

 are present. 



It seems evident that very little of the 

 ordinary deposit-forming materials reach these 

 deep red-clay areas, and that in consequence 

 rare and unusual constituents come into prom- 

 inence. The materials have all been for a very 

 long time exposed to the action of sea-water. 

 The manganese nodules and zeolites are 

 secondary products formed in situ. The vol- 

 canic materials are all profoundly altered or 

 disintegrated ; only the hard dentine of the 

 sharks' teeth and only the densest of the 

 cetacean bones remain. The cosmic spherules 

 have fallen from interstellar space, and 

 they are found more abundantly here than 

 elsewhere simply because they are not covered 

 up by any large amount of other materials. 

 In an area such as has just been pictured the 

 rate of deposition is at a minimum — a foot 

 of deposit may not have been laid down since 

 the early Tertiary period. All the materials 

 we have mentioned may occasionally be met 

 with in the other varieties of deep-sea deposits, 

 but never in such abundance as on the red- 

 clay areas. The composition of these red 

 clays warrants the belief that they would, 

 when consolidated, form rock with a relatively 

 high specific gravity. The animals dredged 



