294 
MANGANESE DEPOSITS OF INDIA : GEOLOaY. 
[Paet II 
chemical alteration of manganese silicates, such as spessartite and 
rhodonite, the question at once arises as to what proportion of the ore- 
bodies as we now see them consists of the original manganese oxides 
simply compressed and to a certain extent recrystalUzed and what 
proportion of them consists of ores formed by the chemical alteration 
of manganese sUicates. I have not yet found sufficient evidence to 
settle this question, but it seems possible to specify certain instances 
of either. Thus the solidity of the portion of the Kandri deposit in 
South Hill is such that it seems difficult to imagine that it has been formed 
solely by the chemical alteration and replacement of masses of spessart- 
iferous or rhodoniferous rock ; so that it seems n.ore rational to suppose 
that this is an example of a mass of manganese oxide deposited as such 
and since compacted and recrystaUized ; but, considering that the saddle 
separating North from South HOI contains a large quantity of spessar- 
tite, it is possible that this deposit may after all have been formed 
by the alteration of manganese-silicate- rocks. The Balaghat deposit 
may, however, be cited as an undoubted example of a deposit that 
has not passed through the silicate stage, because it contains in it numer- 
ous bands of quartzite that have not been sufficiently metamorphosed 
to have even given rise to spessartite or rhodonite. As a good example 
of a deposit the ore of which has probably been derived, perhaps almost 
entirely, by the alteration of spessartiferous rock, the Mandri deposit 
may be cited, whilst the Manegaon deposit, also in the Nagpur district, 
is a good example of a deposit in which the ore has been derived from 
both spessartite and rhodonite. 
The question next arises as to when this alteration of the manganese 
silicates took place. It has already been shown that during the 
Time of alteration metamorphism of the manganese-ore deposits, water, 
of the manganese oxygen, and probably, in some cases, carbon dioxide, 
sihcates. must have been liberated. These substances would 
then have probablv been available to act on the deposits as soon as the 
pressure was somewhat released, remaining in the meanwhile in 
the form of waters containing, as a portion of their burden, oxygen, 
and a certain proportion of carbon dioxide. Hence it seems 
probable that, as soon as the pressure became locally lessened, 
the percolating waters would begin to attack the manganese 
silicates. This attack must probably have continued for a considerable 
time after the cessation of the movements that folded and metamor- 
phosed the Dharwars, probably in fact as long as the temperature was 
at any considerable elevation above that of water at the surface of the 
