402 MANGANESE DEPOSITS OF INDIA : GEOLOGY. [ PaRT II : 
of calcareous matter thus available does not seem to be adequate to 
account for the deposition of all the manganese-ore ; although it 
must be remembered that the greater the amoimt of replacement of 
calcareous matter that has taken place, the smaller will be the amount 
of this material now left to be dredged up. The paucity of calcareous 
matter in these red clays, however, is probably due not to its having 
been nearly all used up in precipitating manganese oxide, but to the 
solution on their way to the bottom of the thin-shelled or calcareous 
organisms that in places where the ocean is less deep give rise to calcare- 
ous oozes. Xow considering the fact that there is as a rule no excess of 
carbon dioxide in sea- water over that required to hold all the calcium 
carbonate in solution in the form of bicarbonate, it seems probable that 
when this solution of calcium carbonate takes place corresponding 
amounts of oxides of manganese and iron are thro%vn out of solution, 
according, in the case of manganese, to the following equation : — 
MnH2(C03)2 i- 2CaC03 + 2H2O -1- O - 2C aH2(C03)2 + H2Mn03. 
Any such precipitated particles of hydrated peroxide of manganese and 
iron would gradually sink to the bottom, which they would probably 
reach without solution owing to the absence of free carbon dioxide ; even 
if they suffered solution before reaching the bottom their precipitation 
would lead to the transference of a portion of the manganese to a lower 
stratum of the sea, and, if larger calcareous organisms passing this point 
did not bring about another precipitation of this dissolved manganese and 
iron, the slow circulation of the sea-water would finally bring it within 
reach of the sea-bottom. The falling particles, on reaching the bottom, 
would act as nuclei round which further portions of manganese oxide 
would be deposited by concretionary action : whilst if no particles actually 
reached the bottom in this way, but only water with manganese in solu. 
tion, then the oxygen dissolved in the water would lead to the deposition 
of the dissolved manganese round any already-deposited portions of 
manganese oxide, and round other nuclei. 
I have given the foregoing brief outline of a possible way in which 
these deep-sea deposits may have been formed, and are still forming, 
to show that it is not necessary to suppose that all the manganese, or 
even the larger portion of it, has been derived from volcanic rocks 
or cosmic dust, as some previous writers have imagined. It has, 
moreover, the advantage of accounting for the disappearance of 
the large amounts of manganese salts that are constantly being carried 
