274 
MANGANESE DEPOSITS OF INDIA : GEOLOGY. 
[Part H: 
and sometimes sheared, clay-like ' country ' in which the manganese-ore 
bodies occur. 
It \\iU be seen that there is a general analogy between this theory 
and that which is supposed to explain the formation and structure of the 
Vizagapatam deposits of India.' The analogy, however, only applies to 
the processes, i.e., the magmatic segregation of the manganiferous rocks 
from a molten magma, with subsequent chemical changes producing the 
ore-bodies from the manganiferous-rocks and the clays (or hthomarges) 
from the less manganiferous ' country ' — and not to the actual rocks con- 
cerned. For in Brazil the residual rock, left after the segregation from 
the magma of the manganiferous-rocks, was of b^sic character, while in 
Vizagapatam it was either a felspar or felspar-quartz-rock, i.e., a more 
acid rock. The product of segregation in Brazil, moreover, was essen- 
tially a manganese-garnet rock sometimes containing an amphibolic 
(or perhaps pyroxenic) or micaceous mineral, and at other times instead 
of these latter free (original) manganese-oxide ( ? pohanite) with ilmenite 
and rutile as accessories and a very small quantity of apatite, while both 
quartz and graphite, supposed to be subsequent introductions, also occur. 
This type of rock has been denominated queluiite by Derby. As shown 
in Chapter XII, Icodurite, the typical product of segregation in the Vizaga- 
patam area, is a considerably different rock of which the three chief 
constituents, apatite, spandite, and felspar, are all equally important. 
The Depth to which the Manganese-ores extend. 
There remains one very interesting question to discuss in connec- 
tion with the alteration of the masses of kodurite rocks, namely, the 
depth at which this alteration took place. For on this depends the 
depth to which the bodies of manganese-ore may be expected to 
extend. 
This problem is to be solved by a consideration of the depths at 
which the processes of kaoUnization and oxidation occur. Let us deal 
first -with kaoUnization. Two different reagents have been invoked 
,. . ^. to explain this process. These are water contain- 
ing carbon dioxide in solution, and water contain- 
ing sulphuric acid. Waldemar Lindgren^ says : — 
' Apparently the pure aluminic silicate cannot be formed when the generating 
waters contain much carbon dioxide or alkaline carbonates. But it does form 
' Metasomatic Processes in Fissure-Veins rfOJW. .4»wr. Inst. Min. Eng., XXX, 
p. 658, (1900). 
