Journal of the Federated Malay States museums - Sabrizain.org

V. NOTE ON A COLLECTION OF ROCK
SPECIMENS FROM PULAU PISANG, WEST COAST
OF JOHORE.
By J. B. Sckivenor, Geologist, F.M.S.
In May igi6 Mr. C. Boden Kloss sent me a collection of
rock specimens from the small island, Pulau Pisang, off the
southern part of the west coast of Johore. Mr. Kloss stated
that only two of the specimens represent rock that he saw
exposed in situ and that the remainder came from a shingle
beach. All the specimens are from the north side of the
island.
These specimens are of sufficient interest to warrant a note
on them and their relations to other rocks in the Malay
Peninsula. On glancing over the collection one had the
impression that they were largely rocks of the " Chert Series"
indurated by metamorphism, and thin sections prepared for
the microscope support this view, while a pebble of granite in
the collection shows how the metamorphism was effected, but
on the other hand they show that volcanic ashes are also
represented on the island. The following is a brief description
of the rocks.
i. Granite. This pebble is too small to say what type of
granite it was derived from. The slide contains only one mica,
biotite, but a larger specimen might very likely show muscovite
as well. There is nothing unusual about the rock.
2.. Qua/rtz-mica-syenite-porphyry. Nothing exactly corresponding
to this rock has been found before in the Peninsula
and it is unfortunate that it is only represented by a pebble.
Hornblende is common and there is an equal quantity of
altered biotite also in fairly large flakes. There are numerous
porphyntic crystals of felspar full of finely divided decomposition
products. Some of them appear to be kaolinized
orthoclase but others show traces of polysthenic twinning.
The felspar crystals are generally bordered by a very delicate
growth which in some cases looks like a radial arrangement of
minute fibres of felspar, but with a high power much of it is
resolved into a micropegmatitic intergrowth of quartz and
felspar. Quartz is confined to this intergrowth and to the
base, which does not form a large proportion of the rock and is
of felspai and quartz in small grains. The quartz is a minor
constituent, and the rock is a porphyry of same composition
as quartz-mica-syenite. The nearest approach to this rock
known as yet in the Peninsula are certain svenitic rocks found
in the Benom Range of Pahang (vide "The Geology and
August, 1916,