Chap. XIV.] dharwar series : metamorphism. 
291 
The rock then formed would be a spessartite-rhodonite-braunite-rock, 
or a spessartite-braunite-rock, according as there had or had not been 
sufficient quartz to form rhodonite. In the event of the silts not con- 
taining anv appreciable quantity of clay or other aluminous matter, 
no spessartite would be formed and the product would be rhodonite- 
rock, rhodonite-quartz-rock, or rhodonite-braunite-rock, according to the 
relative proportions of the manganese oxides and the silica. It will 
be noticed that in all the equations given above, except that for the 
formation of braunite, the manganese has been assumed to be in the 
Liberation of protoxide form ; but as has been already explained 
water, oxygen, and ^j^^ manganese was in all probabilitv originally 
rarely, of carbon ° r . o y 
dioiide. deposited as the result of the oxidation of man- 
ganese-bearing solutions, and therefore presumably as the hydrated 
peroxide, H2Mn03. This simply means that during the changes 
described above oxygen must have been set free in the formation of 
spessartite and rhodonite, whilst in the formation of the manganese- 
garnet water must have also been liberated. If any appreciable 
quantity of the manganese was deposited as carbonate, then in the 
majority of cases this must have been broken up by interaction with 
other substances to form either oxide-ores of manganese or silicates of 
manganese, such as spessartite and rhodonite. In any case this breaking 
up can only have been accomplished with the evolution of carbon 
dioxide, as in the following equation showing the change by which 
rhodonite may have been formed from manganese carbonate : — 
MnCOg + SiOa = MnSiOs + COo 
In a few cases manganese carbonate, in the form of the mineral rhodo- 
chrosite, has been found : but these are very few, the only cases known to 
me being the deposits of Gaimukh and Devi in the Chhindwara district, 
Central Provinces, and doubtfidiy the deposit of Parsioni in the Xagpur 
district, Central Provinces. But whether this rhodochrosite is to be 
considered as a remnant of that originally deposited at the time of deposi- 
tion of the Dharwar sediments, or whether it has been subsequently 
formed under the influence of waters charged with carbon dioxide 
percolating through the deposits, it is not possible to say. 
As the result of the series of changes described above those bodies 
of manganese- ore that were originally deposited as solid masses of 
manganese oxides, without any large quantity of admixed sUt, and free 
from interlami nations of sand or clay, are still found as solid masses 
