429 



exclusively of manganese but as a rule ^) contains numerous tests of 

 radioiaria, which in the nodules show a lack of any regular arrange- 

 ment jusi as is the case outside the nodules in the surrounding ooze. 



Tlie mutiuil relation between the accumulation of mamjanese 

 and of silica. 



The study of fossil deep-sea deposits reveals that, before these 

 deposits had been converted into rock, the silica in the ooze has 

 been concentrated in the same manner as the manganese, with this 

 difference only, that tlie concretions of silica, as chert, or hornstone 

 have much greater dimensions, and are far more numerous than 

 those of manganese. 



Silica just as well as manganese is accumulated in fossil deep-sea 

 deposits in concretions or nodules of manifold shapes, originally having 

 been formed in an ooze or colloid, which itself by cementation (petri- 

 fication) has been converted later into siliceous clayshale, marl or lime- 

 stone.") The process of aggregation of the silica is, however, posterior 

 to tliat of the manganese. The silica, in concentrating, not only 

 envelops, and encloses, the tests of radioiaria which float suspended in 

 the ooze, but in the same way also the nodules of manganese. Both, 

 the tests of the radioiaria and the nodules of manganese, remain 

 in their places, and, being enveloped by the silica, are not shifted 

 from their original position. 



The radioiarites (radiolarian rocks) from the island of Rotti thus 

 prove that in their origin and development the nodules of manganese 

 are absolutely independent of those formed of silica; they are just 

 as numerous within as without the nodules of hornstone, and frequently 

 one nodide of manganese is found enclosed partially by hornstone, 

 and partially by siliceous clayshale or marl. Radioiaria occur just 

 as plentiful and scattered in the same way in the nodules of man- 

 ganese, in the concretions of hornstone, and in the surrounding clay- 

 shale of marly clayshale. 



It is further obvious that the two processes of the accumulation 

 of manganese and of silica are not only entirely independent of 

 each other, but are also not synchronous; in fact, the process, i.e. 



1) On the island of Rotti the author has found several Jurassic nodules of man- 

 ganese containing hardly any test of radioiaria. 



^) According to the results of an analysis, for which I am indebted to Mr. J. de 

 Vries, in a .siliceous limestone with nodules both of manganese and hornstone, 

 the proportion of silica of the rock outside of the nodules of hornstone amounted 

 to 4.947o, notwithstanding obviously the bulk of the silica in this rock had been 

 concentrated into the nodules of hornstone. 



28* 



