Chap. XXXVI.] 
NAGPUR : GHOGARA. 
963 
B 
free limestone. Besides spessartite in the black limestones, there are 
also white limestones containing abundance of spessartite in small yellow 
and orange grains, and at one place there is an indication that the black 
limestones have been formed from the greyish white ones by impreg- 
^ nation with manganese oxide. Figure 74 is 
T a rough sketch of an actual example. It 
! was seen on the upper surface of the rocks 
and is practically equivalent to a section at 
right angles to the dip. AB is the direc- 
tion of bedding of the rocks, and it seems 
as if waters containing manganese salts in 
solutions must have percolated along the 
cracks CD and EF (thpy were not as 
straight as shown in the figure ) and taken 
Fig 74.-Sectiou showing mu.ga- advantage of the bedding planes, such as 
lu'se iniprogniit ions in limestone. AB, by creeping along them, and impreg- 
nating the hmestones by the deposition of oxides of manganese along 
the cleavage and tAvinning planes of the calcite, with consequent black- 
ening of the rock. Where the white and black limestones are inter- 
banded, the latter sometimes occur as bands swelling out — in one 
case from 9 to 18 inches. It only needs an extension of the process to 
account for the formation of masses of such rock 10 to 20 feet thick. 
As these black limestones nearly always contain spessartite, it seems 
probable that this action is purely local and that the manganese oxide 
is derived from the decomposition of spessartite in one part of a bed 
of limest(me, with the re-deposition in another part of the manganese 
thus taken into solution. 
The manganese-ore nodules usually occur arranged in lines, and may 
be of any size up to 6 inches long, but are sometimes in thin bands 
up to 2 or 3 feet long. They weather out with a smooth surface. The 
usual shape is that of a lenticle or flattened lenticular band with the ore 
arranged in layers parallel to the outside of the nodule. But they are often 
strangely contorted into S-shaped forms, and occasionally into curves 
of several turns. In some 
places they are even faulted, 
as shown in the accompany- 
ing sketch, the different parts 
of the nodules being separat- 
ed by limestone. This, of 
course, indicates that the 
limestones have been folded 
V r,K r^- ^- . . . r since the formation of these 
75. — Diagrammatic sk^tf hes of some manga 
manganese-orea. 
2 A 
75. — Diagrammatic skftf hes of some manga 
nese-ore nodules. 
IV 
