Chap. XXIX.] singhbhum district. 
The rocks with which these deposits are associated are what Ball 
^ J calls sub-metaniorphics, and are shown on the map 
° accompanying Mr. Maclaren's paper on ' The Auri- 
ferous Occurrences of Chota Nagpur, Bengal,' as Dharwars.i As seen 
just to the south of Chaibasa, where the majority of the deposits are 
situated, these rocks consist of unctuous clay-slates and sericite-phyl- 
lites ; purplish sandstones, quartzites, and grits, which are often of the 
nature of greywackes ; together with red and pink jaspers and jaspery 
quartzites. These rocks are traversed by abundant veins of white 
quartz, which often appear to form irregular masses, and frequently 
show druses lined with quartz crystals. These rocks have a strike aver- 
aging north-east, with a gentle to steep dip to the north-west side ; but 
in many places where the greywacke sandstones and grits — which 
seem to be here the bottom beds of the group — rest on the underlying 
granite, they are either gently rolling or quite horizontal. Consequently 
the bottom beds of the Dharwars often occur as outlying patches on 
the underlying granite.^ 
The granite is a whitish rather fine-grained rock containing a bronze- 
brown mica. It is in places of much coarser grain and occasionally tra- 
versed by pegmatite veins, and seems itself to be a true igneous granite. 
A series of well marked epidiorite dykes traverses the granite in various 
directions, but usually in a N. 30° E. direction in this neighbourhood. 
The manganese, and iron-ores are found in a number of irregular 
Mode of occurrence ridgy hillocks Composed of limonite and psilomelane, 
of the ores. ^j^j^ Sometimes pyrolusite and red ochre. The 
limonite is the commonest of these minerals and is usually ocbreous 
and soft, with abundant scattered remains of jasper, quartz, or sericite ; 
but it is sometimes hard and compact ; whilst it often occurs as layers of 
radiate structure coating cavities, and having an outer shining, black, 
pimply, or botryoidal, surface. Some of these limonitic outcrops seem 
to be practically free from visible manganese oxides, but others show 
scattered patches and veins of psilomelane, which in some places pre- 
dominates over the iron-ore ; in one outcrop near Matkamhatu, to be 
noticed below, the rock is practically all psilomelane, with some pyro- 
lusit ', and with limonite in places. The psilomelane that occurs thus 
1 Bee. G. S. I., XXXI, PI. 5, (1904). 
2 The but slightly metamorphosed character of these sandstones and grits and 
their gently rolling disposition would be more consistent with a Kadapah than a 
Dharwar age for them ; but I think that in this case we have to deal with some 
Dharwar sediments that have escaped being much folded and have therefore been but 
slightly metamorphosed. 
