MINERALOtilCAL DESCRIPTION OF THE ISLAND OF BANKA. 401* 
2. Sand mixed witli mould (containing trun ks 
of trees in a recumbent position ; and 
perforated by deep roots). 9 feet. 
3. Yellow clay in small irregular layers al¬ 
ternating with dark coloured sand. . . 1 foot. 
4. White clay, . . 6 in. 
5. Black clay massive . 1 foot. 
0. Coarse sand. 
f Fhe miners were at this time engaged in carrying out these dif¬ 
ferent strata; they had penetrated nearly 14 feet below the surface, 
and from the disposition of the vein of ore, with which they were 
acquainted by the experience of the last pit, they expected to arrive 
at it after having descended about 6 feet more. On the surface re¬ 
maining exposed from the former works. I observed very large frag¬ 
ments of a glistening white stone consisting of quartz and felspar 
mixed nearly in equal proportions. Some of them had more than 
twelve inches in diameter. If force was applied they separated at fis¬ 
sures into fragments with regular sides. They had remained after 
the washing of the ore ; the fragments of stone which remain, after 
this process, at the sides of the canals or aqueducts, demonstrate 
clearly the composition of the stratum in which the ore is found, 
and I made it a rule to examine them in every mine I visited, and 
to collect specimens of the varieties. 
At this place I found, besides the large fragment above mentioned 
smaller particles, diminishing gradually to the weight of a few grains 
of the same kind; they all had a disposition to separate into frag¬ 
ments with regular angles. In some cases the particles of felspar 
were in a state of decomposition and formed a white powder resem¬ 
bling chalk ; it was not in the least affected on the applications of 
the strong acids; Small crystals of pure quartz were mixed with 
this white powder. 
Besides these, I found at the aqueduct, sand-stone in small frag¬ 
ments, resembling that above described. An aggregate stone or 
amygdaloid in laminae, composed of particles of quartz united by a 
yellow, ochreous Iron-earth ; to several of these the particles of tin- 
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