784 M1NERAL0G1CAL DESCRIPTION OF THE ISLAND OF BANKA. 
8. Masses of apparently pure felspar of a white or reddish co¬ 
lour appearing spongy from the progress of decomposition. 
2. Sandstone, compact, intersected by veins of a white siliceous 
substance. 
The pit which has last been worked is situated near the village 
of Rangam: a river of the same name rises from the eastern append¬ 
age of the Manumbing and discharges itself into the sea about qne 
fourth of a mile west of the village. Between this and the next ri¬ 
ver, Sungie Fait, a vein of granite rocks descends from the Gunong 
Kukus to the south and forms the point called Tanjong Pahit. In 
my excursions, I crossed the teimination of one of the rocks near 
the sea. The granite consisted here chiefly of quartz and felspar c . 
the latter had acquired a yellow colour from its long exposure to 
sea water: mica and schorl were irregularly dispersed through the 
other substances. 
In the same tract (between the rivers of Rangdm and Fait) I 
discovered near the declivities of one of the hills an extensive vein 
of a rock of a peculiar kind. It must be considered as an aggre¬ 
gate rock and resembles in a small degree the siliceous rocks of 
Kampak and the pile of rocks near Lampur, but it is essentially 
different from both. 
The basis of the stone, as it shews itself on the fracture, consists 
of a substance of a blueish colour approaching the nature of Horn¬ 
blende or Basalt; this is crossed or intersected by white veins of 
substances of two different kinds. The substance of one is semi¬ 
transparent, crystallized and evidently of the nature of pure quartz, 
that of the other is of a somewhat dull or pearly white and resem¬ 
bles felspar. The breadth of the veins is very variable, increasing 
and decreasing during their course, from less than one-fourth of a 
line to more than half an inch in thickness: their distribution 
through the blueish mass is also highly irregular, and strikingly dif¬ 
ferent from that of the intersecting veins of the rocks above men¬ 
tioned, in no instance circumscribing figures of winch the form can 
be regularly defined. 
This vein consists of a number of separate rocks projecting about 
3 or 4 feet beyond the surface and covering a space of nearly 100 
yards in circumference. Their external form is as irregular as 
their internal structure. The surface is marked with numerous deep 
excavations, the substance of the white intersecting lines has remained 
while the blueish mass which composes the stone has been dissolved, 
