786 MINERALOGICAL DESCRIPTION OP THE ISLAND OF BANKA. 
Most of the fragments here have, upon the whole, a plain or ta¬ 
bular form which is more or less regular ; some have an even sur¬ 
face, determinate thickness and regular sides, resembling in some 
degree slabs or planes prepared by art; others are curved or con- 
choidal. Among these are dispersed huge irregular masses or 
blocks from the thickness of a few inches to that of several feet. 
Their diversity of form and colour scarcely admits of a definite des¬ 
cription, and the detached masses and planes afford here a spectacle 
approaching to the grotesque or whimsical. The fragments resem¬ 
ble in some degree the rude Breccias of Tshengfil, above described, 
but they are both more numerous in one spot and more regular, 
besides, being washed by the sea at high water, the varieties of co¬ 
lour always appear distinctly on the surface. A lively brown forms 
the basis, which is spotted with white, yellow and grey, of different 
shades. 
The uniting medium or cement of those Breccias is ferruginous, 
with varying proportions of admixture of clay and silex ; it is a mo¬ 
dification of the Iron-ore which forms so large a part of the basis 
of Banka, and which in the previous descriptions has been called 
Red-Iron-stone. It is mostly of a dark brown colour, compact, 
and even where apparently most pure or unmixed, enclosing nu¬ 
merous particles of a minute siliceous sand. Some fragments con¬ 
sist entirely of this combination, while in others it forms the cement 
uniting those substances, which are also found detached in the allu¬ 
vial ranges of the neighbourhood. 
The most common substances which enter into the composition of 
these Breccias are 
1st. Sandstone of different degrees of minuteness of grain, and 
highly diversified in colour and compactness. 
2nd. Portions of the siliceous rock ahove described viz. No. 152 
of the descriptive catalogue. 
3rd. Iron-stone, red, brown and black in almost every form in 
which they occur on the Island. 
4th. Nodules of clay, often consisting of layers of alternating 
colours. 
5th. Fragments of pure quartz. 
6th. Nodules of clay and sand united in different degrees of 
compactness, often resembling in their fracture the masses of these 
substances found at the mines. 
7th, In one instance only I found a fragment of granite, it was 
