Chap. XX.] 
POND AND RIVER DEPOSITS 
3S7 
contact with the limestone must have given up a portion of its mangan- 
ese in return for a portion of the calcium carbonate of the limestone. 
The above explanation is given on the supposition that the pyxolusite 
is of recent formation. This, however, cannot be considered as quite 
certain in a region where denudation has in so many places just worked 
its way dowTi to the old land surface of pre-Lameta times. But even 
if the pyrolusite date back to this pre-Lameta time it will probably 
have been formed in much the same way — except as regards the source 
of the manganese — as if, as is almost certain, it has been deposited in 
recent times (see Plate 15). 
The foregoing are examples of manganese-ores deposited recently 
at the surface. There may also be places at small distances 
Dendrites of manganese beneath the surface at which the conditions are 
o^'^les. favourable for the deposition of manganese 
oxides from percolating waters. Thus dendritic growths of black 
manganese oxide are often found on the surfaces of joint and bedding 
planes of rocks when they are imcovered in the course of quarrying 
or mining operations. As would be expected this phenomenon is parti- 
cularly common in manganese quarries. Thus I have seen beautiful 
examples at the Mansar mine on the surface of the fine-grained 
gneiss underlying the ore-body. Equally good examples were seen in 
the manganese-ore quarry at Asalpani II or Karli. Here the den- 
drites were also on the surface of the bedding planes of the underlying 
rock, a fine-grained schistose quartzite. Such dendrites may 
also be found on the surface of rocks in almost any formation. 
Thus very fine examples have been foimd on the bedding planes of 
slabs of Vindhyan sandstone quarried at Panna for building purposes. 
Some fine specimens from this locality are exhibited in the Museum 
of the Geological Survey of India, the fern-like growths being as much 
as 22 inches in length (see Plate 4). 
In sinking weUs for the foundations of the new railway bridge across 
Mnuganese oxide in t^e Ganges at Allahabad some fossil mam- 
pleistocene mamnialiau malian remains were found embedded in a 
reniaias at Allahabad. calcareous conglomerate 80 to 100 feet below 
low water mark^. On examination it was found that these mam : 
malian remains were impregnated with oxide of manganese^. This 
manganese oxide must have been deposited, long after the sealing 
1 Rec. Geol. Sur. Ind., XXXH, p. 136, (1905). 
2 Hcc. Gcol. Sur. Ind., XXXIII, p. 157, (1906). 
