MlNEItALOGICAL DESCRIPTION OF THE ISLAND OF BANKA. 7^0 
or less pure; to some of these masses, Poudingue or sand-stone are 
agglutinated. After an interruption of several hundred yards the 
continuation of the lower stratum appears again before and a little 
westward of the mouth of the liver Teluk-Robiya. A plain more ex¬ 
tensive than the one last mentioned is here covered with Black-Iron¬ 
stone, masses of a great variety of configuration are spread over it: 
the external colour is dark brown or black of a blueisli or steel-grey 
hue. Their form is highly irregular, tuberous or rudely botryoidal, 
many of the portions are excavated, resembling broken vessels or af¬ 
fording various grotesque figures arid representations. In one in¬ 
stance a large mass resembling the trunk of a tree is covered with 
it: the fracture of several fragments which I separated indicates a 
vegetable substance, some portions are excavated or tubular. The 
Black-Iron-stone, here, is rarely pure, it is in most instances united 
to the masses of Poudingue in the neighbourhood. The fracture is 
compact or striped with bands of different colours, it is mostly va¬ 
riegated with quartz, and nodules of ochre often appear on it. 
With tins Black-Iron-stone, pyrites is plentifully mixed : it ap¬ 
pears in the form of nodules on or below the surface; these are in 
general, globular, compressed or reniform ; many are often united to¬ 
gether and form botryoidal masses. They frequently adhere by in¬ 
tervening particles of quartz. The fracture represents a dark, steel- 
grey ground, spangled with numerous minute metallic particles. On 
being preserved some time most of the nodules decompose sponta¬ 
neously like other pyrites; they burst in many places, an efflores¬ 
cence of slender delicate crystals protrudes, and finally the whole 
mass crumbles to pieces. 
Many of the masses which I examined to the west of the discharge 
of the river of Teluk Robiya exemplify the manner in which the 
Black-Iron-stone passes into Poudingues. It appdhrs as a cement 
uniting the various substances above mentioned but particularly par¬ 
ticles of quartz. Some of the Poudingues consist of regularly alter¬ 
nating, dark coloured, striae of various shades; the sand-stone and 
ochre are observed in large proportion. 
This compound district of Iron-ores and Poudingues is here in¬ 
tersected by a branch of the stratum of Tin-ore following the course 
of the Teluk Robiya. "Quantities of ore have been carried down 
the river by the current, and being mixed with the sand along the 
shore have been collected by the natives. The termination of this 
stratum is indicated by the substances usually found at the mines. 
o 3 
