400 
MANGANESE DEPOSITS OF INDIA : GEOLOGY. [PaET. II 
it has never been determined ; chemists seem to have considered it unne- 
cessary to take it into account, even in analyses carried to six figures^ 
The question then arises as to what has become of that portion of the 
manganese that should be present in the sea-water, and is not. The 
obvious answer is that it must have given rise to at least a portion of the 
manganese-ores known to occur at the bottom of the sea. For, during 
deep-sea exploration work, nodules of manganese-ore are frequently 
dredged up from the sea floor. In fact, in some places, according to 
Murray, the sea bottom and everything on it is coated with manganese 
oxide — shark's teeth, shells, corals, sponges, and other remains, both 
organic and inorganic, being encrusted with this substance. 
The way in which the manganese is deposited, and also its source, is a 
matter of some doubt, and for a full discussion of tliis subject the reader 
may be referred to the excellent work of R. A. F. Penrose, Jr.^, and to 
the Challenger Reports, Volume on Deep-sea Deposits, pp. 372-8, (1891), 
by John Murray and A. F. Rcnard. The various views held on each 
of these points can be seen from the follomng list^ of the opinions of 
different authorities as to the mode of origin of manganese 
nodules : — 
' 1. The manganese of the nodules is chiefly derived from the decomposition 
of the more basic volcanic rocks and minerals with which the nodules are nearly 
always associated in deep-sea deposits. The manganese and iron of these rocks 
and minerals are at first transformed into carbonates, and subsequently into 
oxides, which, on depositing from solution in the watery ooze, take a concre- 
tionary form around various kinds of nuclei (Murray)*. 
2. They are formed under the reducing influence of organic matters on the 
sulphates of sea-water, sulphides being produced and subsequentl}' oxidi.sed 
(Buchanan). 
.3. They arise from the precipitation of manganese contained in the waters 
of submarine springs at the bottom of the ocean (Giimbel). 
4. They are formed from the compounds of manganese dissolved in sea- 
water in the form of bicarbonates, and transformed at the surface of the sea' into 
oxides, which are precipitated in a permanent form on the bottom of the ocean 
(Boussingault, Dieulafait)'. 
Penrose further considers the possibilities that marine plants such as 
sea- weeds may segregate manganese in their tissues, this being deposited 
1 Thorpe's Inorganic Chemistry, I, p. 208, (1902). 
2 An. Rep. Geol. Surv. Arkansas for 1800, Vol. I, pp. 559-569. 
•3 Taken from the abovc-incntioned vohnne of the f'liall. Rep., p. lil'.i. 
1 In a footnote at this point Rcnard says: — 
' While admitting ' hat a j)art of the manganese accumulated at the bottom of the 
ocean may be derived from the decomposition of volcanic rocks, in the 
manner described above (No. 1), it appears to me that the greater part must 
have been derived fron\ the manganese in solution in the sea-water '. 
