620 
MANGANESE DEPOSITS OF INDIA : DESCRIPTIVE. [PaRT IV : 
is cavernous, of irregular shape, and often botryoidal and concretionary : 
in many places it contains rounded patches of pale pink jaspery quartzite 
simulating pebbles, but really the remains of an original band of jasper, 
the larger portion of which has been replaced by oxide of manganese. 
Much of the ore on being broken shows tiny specks of white quartz, while 
other pieces show remains of white silky-looking sericite — looking like 
talc at first sight — and at times fragments of sericitic slate and phyllite. 
Besides the above-mentioned irregular deposits of lateritic aspect, 
the manganese-ore occurs in some places, as at Tekrasai, Tutugutu, 
and Bistampur. in bed-like layers from one to six inches thick, the ore 
then being sometimes very fine-looking compact psilomelane. With these 
layers are also associated the cavernous, botryoidal, or concretionary ores, 
the whole making up a manganiferous layer, which is in places as much 
as two or three feet thick. The ores in this bed often show remains of 
quartz and sericite and invariably I'est on horizontal or nearly horizontal 
purpUsh sandstones and grits. 
Judging from the evidence obtained, both in the field and from the 
^ microscopic examination of the specimens coUect- 
" ' ed, there can be little doubt that these manganese- 
and iron-ores have been formed by the percolation of solutions contain- 
ing manganese and u"on, which have replaced indiscriminately whatever 
rock was at the surface ; the rocks seen to have been thus replaced are 
slates, sericite-phyllites, jasper, vein-quartz, and purpUsh felspathic 
sandstones and quartzites, the two latter to a much less extent than the 
former. Where the rocks he at a moderate or high angle the result of 
this alteration seems to have been a cavernous cindery-looking lateritic 
rock (laterifoid — see page 381) : where the dip is horizontal or very small, 
the manganese has often formed a well-marked bed-like layer, usually 
where a thin layer of slates or phyllites rested on the purplish felspathic 
grits and sandstones ; the latter rocks not being as a rule much affected, 
although they are sometimes limonitized at their outcrops. 
The iron is doubtless in part a concentration product resulting from 
g f th weathering and denudation of the rocks under 
manganese. consideration, but the source of the manganese is 
not so apparent. As none of these rocks when 
unaltered seem to be notably manganiferous, it is probable that the 
manganese has been brought in solution to its present position. 
Considering the complete parallelism between the mode of origin of 
the Chaibasa ores and those of the Jabalpur district, and the fact that 
the associated rocks are in both cases Dharwars, one would expect the 
