MINERALOGICAL DESCRIPTION OF THE ISLAND OF BANKA, 399 
ly distributed and occurs in situations of secondary elevation, in 
single rocks, or in veins of many united together, and covering ex¬ 
tensive tracts of country. The red colour universally predominates, 
and it contains a large proportion of Iron in its composition, but a 
more particular accounts of its distribution and conjunction with 
other parts of the Island, is one of the chief subjects of the following 
description: the analysis will be added separately. 
4. In many parts of the Island, these tracts of country, which 
are composed of Red-Iron-stone, are bounded by the alluvial dis¬ 
tricts which are again subdivided into such as are formed of range!? 
of waving hills, gradually rising on each other, apparently of prior 
formation, and of such as are completely low and level, of recent 
origin, and confining the discharge of the large rivers. 
5. In conjunction and often within the alluvial tracts are found 
sand-stones, breccias (or amygdaloids) and various mixed stones, 
bearing marks of a comparatively late origin. The former is gener¬ 
ally distributed in extensive veins or low ridges; the breccias or 
amygdaloids occur in a great variety of form and disposition. Im¬ 
mense conchoidal or tabular masses, in some instances, cover exten¬ 
sive portions of the ground. 
0. Those districts which occur in juxtaposition to the primitive 
portions, filling the space between these and the fixed veins of Red- 
Iron-stone (Iron-rock), or again between these and the alluvial parts, 
are stratified: the strata are uniformly horizontally arranged, and 
characteristic of the tracts above mentioned which form the basis of 
the Island. 
7. The ore of tin is disseminated through these horizontal stra¬ 
ta, and, as far as has hitherto been remarked, either immediately 
under the surface or at no great distance below it: they are most¬ 
ly found in low situations or near the primitive ridges: The process 
of mining has greatly contributed to illustrate their composition, arul 
It is one chief object in the following details to give a clear account 
of the component parts of the strata, in as far as these were illustrated 
by the various fragments of stone found at the aqueducts of the mines. 
8. Forming part of these strata and distributed through the more 
