141 



grammes. 



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cent 



35 



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7i 



>> 



289 



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62J 



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COMPOSITION OF OCEANIC AND LITTORAL MANGANESE NODULES. 465 



anchor was brought up. There can, therefore, be no longer any doubt that it is 

 really in the deep trough that the nodules occur, and only in a very limited area 

 of it. 



The mud of 21st September 1878 was divided in two equal portions, one of which was 

 preserved and the other was analysed mechanically. It was separated into three consti- 

 tuents, the nodules, the shells, and the residue, a sandy clay. The number of nodules thus 

 obtained was 83, and they weighed 142*7 grammes, whence the mean weight of a nodule 

 was 1*7 gramme. Packed as closely as possible in a graduated cylinder of 37 millimetres 

 internal diameter, they occupied a length of 130 millimetres, reaching to 146 c.c. on the 

 graduation. I then poured in 100 c.c. water, which stood at 158 c.c. Hence the 

 volume of the nodules was 58 c.c, and the average volume of one was 0*7 c.c, and their 

 density 2*46. The shells were all dead, and principally Pecten ; they weighed 35 grammes. 

 The following was the mechanical composition of the mud : — 



Nodules, 

 Shells, 

 Sandy Clay, . 



465 „ 100 



Of twenty-two nodules which were split open, sixteen contained soft nuclei of about the 

 size of a pea, and apparently very rich in manganese. One of these nuclei was so 

 slightly attached to the rind as to fall out when the nodule was split. The rind is 

 always very hard and gritty, and when the oxides of iron and manganese are removed 

 by hydrochloric acid, it falls into a mass of sand, similar to that which makes up a large 

 proportion of the rind. This agrees with the idea that the nodules are agglomerations 

 of the mud found in situ, and cemented by the ochreous oxides. One nodule (No. 24) 

 was interesting, as showing the complete soft kernel, loose, in a cavity of mud, the rind 

 not having as yet formed, although it was evidently forming, the mud being stained from 

 the inner wall of the shell outwards. No. 25 was a similar nodule, only the kernel had 

 no free space round it. The mud round it was stained yellow. This seems to be very 

 general with the growing nodule ; the oxide of iron spreads itself in front of the oxide 

 of manganese. A little of the yellow shell gives no manganese reaction with hydro- 

 chloric acid. A nodule of the size of a pea was found, resembling the others perfectly, 

 except that it contained Fe 2 3 , and no Mn0 2 . Very careful examination of the mud 

 from which the nodules and shells had been removed showed that perfect nodules exist 

 down to the size of a pin-head, and all through the mud there were specks showing where 

 probably nodules had begun to form. Although so near the shore, the mud contains 

 hardly any pebbles larger than a grain of sand. This shows conclusively that the nodules 

 have not been washed down into their present position ; and that they have been formed 

 in situ is further shown by the fact that the mud round them is generally stained 

 yellow with ferric oxide. A number of nodules were picked out for illustration and 

 analysis. 



