1130 
MANGANESE DEPOSITS OF INDIA : DESCRIPTIVE. [ PaRT IV : 
The best proof that the Mysore deposits are, almost without excep- 
tion, of this origin, is the evidence to be seen in almost every working 
of a gradual impoverishment of the deposits in depth, with the appear- 
ance of larger and larger quantities of lithomargic rocks and remains 
of quartzite and quartz. The miscroscope shows that it is a case of 
replacement. Even in the best deposit — namely Kumsi, where the 
downward passage has not yet been exposed — there can be little 
doubt that a similar explanation holds. For in one place I found 
remains of quartzite partly replaced by pyrolusite ; at another, 
residual patches of white quartzite filling in the meshes of a sort of 
network of manganese-ore (psilomelane) ; and in a third place, a 
phyllite, probably a talcose one, larg ly impregnated with manganese. 
The first two instances were right in the ore-body, and the third on 
the southern edge. Further evidence at Kumsi is the occurrence in a 
considerable proportion of the ores now being quarried, even from the 
best parts of the deposit, of occasional quartz grains and patches of 
quartzite, which in some parts of the deposits become very important 
in quantity. 
The three chief ores are psilomelane, wad, and pyrolusite. The 
, , , pyrolusite seems to form directly bv the re place- 
Nature of the are.si. _ .... 
ment of quarfczites, with which it is associ- 
ated in preference to lithomarges. The wads on the other hand seem to 
form more readily in the Uthomargic rocks, by the gradual replace- 
ment of which they grow. As in Sandur, the wad gradually passes 
into psilomelane, good examples of the passage being common at many 
of the deposits. The Kumsi deposit seems to be an aggregate of large 
boulders. From the evidence of remains of replaced rocks T do not 
think these boulders are of derivative origin, i.e., rolled to their present 
position. I think rather that their shape is the result of their mode 
of origin and that they have grown in situ. These boulders often 
show an interior composed of psilomelane, sometimes with a few 
tell-tale grains of quartz, and an outer zone, 1 to 2 inches thick, of wad, 
with a zone of passage between the two. Sometimes the conversion 
seems to have been complete, with the result that the boulder is 
composed almost entirely of psilomelane. At other times it has not 
advanced nearly as far, and the boulder shows a mottled mixture 
of wad and psilomelane. 
