354 
MANGANESE DEPOSITS OF INDIA : GEOLOGY. [PaRT II : 
m icroscope. On Plate 12, figure 2, is shown a photo-micrograpli of 
a section of this partially altered spessartite-rock. A reference to 
this will show that there are irregular patches and veinlets of 
Association of mauganese-ore spreading thoroughout the spessar- 
manganese-ore and tite. Xow there are three possible ways of 
spessartite. explaining this association of manganese -ore and 
spessartite with each other. They are as follows : — 
1. The manganese-ore and the spessartite were formed at the 
same time, during the metamorphism of the original 
sediments. 
2. The manganese-ore, under the influence of metamorphic 
agencies accompanied by an influx of sihca in solution, 
has been partially converted into spessartite. 
3. The spessartite has been partially altered into manganese- 
ore, the original rock having been composed entirely of 
spessartite. 
The relations of the two minerals one to another in the section, show 
that the first explanation cannot be correct. For if it were, one of 
the minerals should be idiomorphic with regard to the other ; or if the two 
minerals crvstallized at the same time they should be Lntcrgrown in a 
more or less poikilitic manner, or mixed together as a granular 
aggregate. 
If the second explanation were true we should expect to see veins of 
spessartite traversing the manganese-ore rather than the reverse rela- 
tion shown by the figure. 
By the process of eUmination we arrive at the conclusion that the 
Spessartite changes third explanation is probably the correct one. 
to manganese -ore. According to this, we should expect to see irregular 
patches of manganese-ore encroaching on the spessartite, and small 
veinlets traversing it. The photomicrograph shows that such is the 
case. The exAmination of a large nimiber of field exposures and thin 
sections of rocks has convinced me this is not an isolated example, but 
that the direction of change is really from garnet to ore and not the 
reverse. This explains the numerous cases of manganese-ores with 
irregular patches of spessartiferous rock, often disposed more or less 
centrally in a block of ore bounded by joint planes. If the change were 
the reverse, one would expect the manganese-ore patches to be central, 
and the spessartite being formed by alteration to be peripheral. 
