444 EH. S. Willbourn—Alteration of Granitic Rock. 
with iron-ores and sometimes forming a sagenite web. It is 
practically uniaxial. The ground-mass consists of quartz and 
secondary mica. A slide cut from one specimen showed a wavy line, 
like a crack penetrating the rock, along which occurs some fine- 
grained opaque material and, at one point, a large grain of blue 
tourmaline. A specimen of this rock was crushed in order to examine 
the heavy minerals. Much zircon in small perfect crystals is present 
and also several grains of blue tourmaline. 
This rock resembles an igneous rock which outcrops at the old 
disused gold-mine of Bukit Chindras, which is situated along the 
direction of the Ayer Kuning hill range (namely about N. 60° E.), 
and is between one and two miles distant from it. 
The gold-bearing quartz veins strike in a direction approximately 
north and south. Mr. Scrivenor, the Government Geologist, visited 
the mine in 1904, shortly after it had been shut down, and he then 
noted (Preliminary Report on the Gold Mines of F.M.S., Kuala 
Lumpur, May, 1904) that the country rock is ‘‘ bleached shale. . . 
together with a small quantity of a pale green rock which was not seen 
im situ, composed of fine flakes of colourless and pale green muscovite, 
quartz grains, iron ores, and small prisms of rutile ”’ 
The rock can now be seen forming an outcrop on the hillside 
70 yards long in a direction about N.W. by 8S.E. and about 
20 yards wide. It is much weathered, but slides cut for micro- 
scopic investigation showed phenocrysts of bleached biotite, containing 
needle-shaped inclusions of rutile associated with iron-ores, with 
large corroded quartz phenocrysts, and areas of regular form filled 
with an aggregate of secondary muscovite which may represent 
felspar phenocrysts. The remainder of the rock consists of an 
irregular mass of secondary quartz and mica. The rock shows- 
evidence of having undergone strong shearing, and thin quartz veins 
penetrating the rock have also been subjected to strain. It contains 
a certain amount of iron pyrites, is plentifully stained with iron, and 
has numerous cavities. 
The rocks described above bear a strong resemblance to the 
beresites of the Urals described by G. Rose.! He describes them as 
vein rocks which outcrop in tale and chlorite schists, themselves 
traversed by the gold-bearing quartz veins. Beresite is a very 
uniformly grained rock, nearly always decomposed and impregnated 
with iron pyrites. Itis made up of orthoclase, plagioclase, quartz, 
and primary mica, and these are altered to secondary mica and quartz, 
according to another writer, Arzruni. Some varieties resemble 
sericite schists, others resemble micaceous sandstones. Original 
rutile is present as aggregates and as inclusions in quartz. 
Rosenbusch? and also Zirkel* quote Helmhacker, who wrote a later 
description. He says that beresite is a quartz porphyry, poor in 
quartz, in which the felspars vary in amount, and may disappear 
altogether on account of their alteration to muscovite and quartz. 
1 Zirkel, Petrographie, vol. ii, p. 41, 1894. i 
2-H. Rosenbusch, Mikroskopische Physiographie, II Massige Gesteine, 
p. 462, 1896. 
3 Zirkel, Petrographie, vol. iii, p. 793, 1894. 
