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MANGANESE DEPOSITS OP INDIA : GEOLOGY. [PaRT II : 
of manganese-ore ; except at their peripheries, where they are separated 
Formation of man- from the practically non-manganiferoiis ' country ' 
ganese silicate* at the by an envelope of gneiss, schist or quartzite. con- 
dep sits. taining silicates more or less rich in manganese. 
These silicates have in some cases, no doubt, been formed by the 
interaction of the manganese of the ore-body with the surrounding 
'coimtry'; but in many cases the formation of these manganese-silicates 
must have been due to the fact that the sediments immediately over- 
and underlying the ore-body were mixed ^vith manganese oxide at the 
time of their deposition, owing to a more or less gradual change from the 
deposition of manganese oxide to that of sand or clay, or vice versa. As 
examples of such border products due to one of the causes outlined above 
mention may be made of the spessartite-bearing gneisses and 
quartzites occurring on either side of the ore-bodies at Kandri and 
Mansar in the Xagpur district ; whilst the formation of the schist con- 
taining the manganiferous variety of amphibole to which the name of 
winchite has been given, at the Kajlidongri mine in Jhabua State, and 
of the schist containing manganiferous micas as one wall of the Sita- 
pathur deposit, are instances of this same phenomenon of the formation 
of manganese silicates at the periphery of a deposit, although neither 
deposits can be cited as an example of a solid mass of manganese-ore 
free from appreciable quantities of foreign material. 
On the other hand, those ore-bodies that contained intercalated layers 
The banded struc of sand or clay have suffered great alteration. In 
ture of the ore-bodies, cases where the alternating layers of ore and silt were 
thin, averaging, say, 1 to 3 inches each in thickness, the temperature and 
pressure to which they were subjected has often been sufficiently high 
to cause such a complete interaction between the ore-layers and silt 
that aU the ore has been converted into spessartite or spessartite-quartz- 
rock ; the resultant rock has a banded appearance owing to the alter- 
nation of bands of spessartiferous rock \\4th bands of vitreous quartzite, 
roughly corresponding to the layers of manganese oxide and silt, respec- 
tively. When these layers were originally somewhat thicker the 
reaction may not have extended right to the centre of the ore-layer, 
so the central zone of a layer may consist of manganese-ore with, on 
each side of it, a layer of spessartiferous rock separating the ore-layer 
from other bands corresponding to the original layers of silt. In some 
cases the alternating layers of ore and silt may have been so fine that the 
whole mass of rock has passed into a more or less homogeneous mass 
of spessartite-quartz-rock, or of spessartite-rock practically free 
