JHINEUALOGTCAL DESCRIPTION OF THE ISLAND OF BANKA, 413 
regular sides and angles, and exhibit a sample of crystallization oh 
a large scale. In the site of the stockade, I observed several sepa¬ 
rate rocks with uncommonly regular sides and angles. A most ex¬ 
tensive group is placed almost directly before the mouth of the ri¬ 
ver : it consists of a high pile of huge rocks forming a longitudinal 
series, in which masses of a variety of configurations are thrown on 
each other, with so much regularity as to exhibit the appearance of 
art having assisted in their arrangement. 
The colour of the rocks is almost entirely derived from the fels¬ 
par which enters into their composition : this substance is observed 
on the surface or often projecting beyond it, in regular foursided 
crystals or in rhomboidal plains : the form of both however is consi¬ 
derably diversified. In some instances these crystals have the length 
of several inches and arc nearly one inch wide ; they shew themselves 
still more distinctly on the fracture of the stone. The quartz is like¬ 
wise observed on the surface, but is distributed, on the whole, itt 
much smaller proportion than the felspar : both contribute to give 
the granite the white appearance above mentioned, which varies how¬ 
ever from almost pure milky white to that of grey. In all the rocks 
which I examined and of which I collected specimens, the mica was, 
upon the whole, sparingly distributed, and the only occasional ad¬ 
mixture was schorl in very small proportion. 
The mines of Mampang have been opened within the last two 
years near a small river called - Tengalow , which discharges itself in¬ 
to the ocean, a little east of Seka : they are situated in the granite 
district, about one mile from the northern shore of the island. The 
miners (at the mine SunwadJ had met the layer of ore about 10 
feet below' the surface, it was situated in a valley, and pursued nearly 
the same direction as the bed of the river, which w T as directed from 
its course, and employed for the purpose of washing the ore, as an 
aqueduct. 
• I noticed the following strata: 
1. Soil... 2i feet 
2. A mixture of fine particles of quartz and clay,. 4 „ 
3. Detached coarse particles of quartz and felspar 
G 
