428 



ore, beeoiTies surrounded by a kind of' lialo in wiiicli grains of 

 ore ti'avelling ylowly towards llie focus of atlraclion, hefoine more 

 numerous than at a certain distance from tlie growing nodule 

 beyond its sphere of infhience, wliere tiie grains are found equally 

 distributed in the ooze. The grains, it may be safely admitted, 

 travel very slowly towards the larger nodules, and evidently the 

 positiqn of the tests of radiohiria in the ooze is not altered by their 

 slow movement. The radiolaria are just as numerous and are spread 

 in the same irregular manner botii witiiout or within the nodules. 



Althougli the mode of formation of the concretions by the close 

 packing together of grains of manganese fairly well e.xplains the 

 observed facts, it is, however, not quite clear how finally concretions 

 are formed, composed of manganese and tests of radiolaria exclusively 

 without traces of the ooze being enclosed. 



It might be supposed tiiat in the ooze diffusion currents around the 

 growing nodules, carrying manganese in solution towards them are 

 stronger around grains which are larger, and that consequently the 

 latter grow faster, and by their growth may incorporate and absorb 

 the smaller ones, and finally by this process a concretion or nodule 

 may be formed. Also in this case the tests of radiolaria might be 

 surrounded and absorbed by the growing concretions without being 

 shifted from their original position, but it is not possible to explain 

 why in this case halos of higher concentration with minute grains 

 of manganese abundantly in suspension, should be fouiul around the 

 larger grains. 



Probably these two processes collaborate in the mode of formation of 

 the nodules, firstly growth by precipitation of manganese from con- 

 vergent diffusion currents and secondly growth by accumulalion and 

 packing of preexisting minute grains ^). 



The result is the formation of a concretion with fairly well demar- 

 cated outlines, surrounded by a cloud of smaller grains rapidly 

 diminishing in density. The concretion itself is composed almost 



') in the discussion following on the reading of this paper Mr. Wichmann 

 remarked that according to his opinion, the nodules in deep-sea deposits are not 

 formed by anorganic processes, but by biochemical processes caused by bacteria 

 He drew the attention of the members to experiments made by Mr. Beijebinck, 

 who proved the existence of bacteria possessing the quality to precipitate manga- 

 nese as superoxyde from solutions of carbonate of manganese. The author admitted 

 the possibility of such biochemical processes as the cause of the accumulation of 

 manganese in deep-sea ooze, but lie pointed out that liitherto the existence of 

 bacterial life in abysmal depths had not been proved. Compare M. W. Beijerinck. 

 Oxidation of mangaiio carbinate by microbes. Proc. of the section of sciences 

 of the Kon. Akad. det- Wetensch. Amsterdam XVI f. p 397, 1914. 



