Chap. XX.] 
POND AND RIVER DEPOSITS. 
396 
3. Mangapese that is transported meclianically and deposited on 
the land areas, such as in lake and river bottoms, as for 
example in the form of sands. 
4. Manganese that is transported mechanically to the sea and 
there deposited. 
No case of the last-named sort of recent deposit has yet been recorded 
within the limits of the Indian Empire. The known recent deposits of 
iiianganese-ore in the Indian Empire can thus be divided into three 
groups : — 
1. Deposits in ponds and rivers ; and on the surfaces and in 
the cracks, bedding and joint planes, of rocks, as dendrites. 
2. Deep-sea deposits. 
3. Manganiferous sands and soils. 
Deposits in Ponds and Rivers, etc. 
As has already been mentioned, the rocks of the earth's crust nearly 
all contain manganese in smaller or larger proportions. Although the 
percentage of manganese in most rocks is very small, yet when such 
rocks are exposed at the surface and subjected to the influences of the 
weather this small amount of manganese often passes into solution 
under the solvent action of water containing either organic acids or 
carbon dioxide. Such water usually finds its way into the drainage 
system of the country. The tendency is for the manganese to be 
redeposited at the earliest possible opportunity. The condition for 
this to take place is usually that the water should be subjected to oxid- 
izing influences, although it is sometimes deposited under reducing 
conditions. Rapid motion of the water, as at a waterfall or rapids, 
will sometimes bring about a deposition of the dissolved manganese as 
oxide 1. A good example of this is to be seen in the fine exposure of 
Ppilomelane deposited at Crystalline limestones that occurs in the Pench 
a waterfall on the Pench. river at Ghogara in the Nagpur district (see 
page 961). In one place the river forms a small waterfall down a cleft 
in the limestone, which consists partly of the brownish black manga- 
niferous variety and partly of light- coloured varieties. The mangani- 
ferous limestone is coated with a layer of psilomelane, which has been 
deposited in concentric layers so as to follow all the curves into which 
the limestone had been previously carved by the water of the river. 
1 For foreign examples of this, on the Orinoco, Congo, and Nile, see G. Bertrand. 
Revue GSnerale de Chimie, VIII, pp. 209, 210, (1905). 
