Journal of the Federated Malay States museums - Sabrizain.org
Journal of the Federated Malay States museums - Sabrizain.org
Journal of the Federated Malay States museums - Sabrizain.org
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fgifi.l ScRIVENOR on Pulau Pisang Rocks. 33<br />
There can be no doubt that <strong>the</strong>se rocks are from a junction<br />
<strong>of</strong> Chert Series rocks and granite and <strong>the</strong>re are two points<br />
concerning <strong>the</strong>m that are worth attention. The first <strong>of</strong> <strong>the</strong>se<br />
is <strong>the</strong> association <strong>of</strong> volcanic ash.<br />
The coarser specimens cannot be distinguished from some<br />
<strong>of</strong> <strong>the</strong> ashes <strong>of</strong> <strong>the</strong> Pahang' Volcanic Series, and this is <strong>the</strong><br />
third instance in which <strong>the</strong>se volcanic rocks have been found<br />
associated with chert. Ano<strong>the</strong>r instance is at Lubok Plang, on<br />
<strong>the</strong> Pahang River, where a bed <strong>of</strong> chert was found between a<br />
flow <strong>of</strong> lava and a layer <strong>of</strong> ash. Epidote occurs in <strong>the</strong> chert<br />
and in <strong>the</strong> volcanic rocks but in <strong>the</strong> Pulau Pisang chert it is<br />
more abundant. Radiolaria are more abundant in <strong>the</strong> Lubok<br />
Plang chert.<br />
The second known instance <strong>of</strong> <strong>the</strong> association <strong>of</strong> volcanic<br />
ash and chert was afforded by specimens taken from a stoneheap<br />
in Singapore. The radiolaria in <strong>the</strong> chert are in some<br />
cases at any rate preserved as casts <strong>of</strong> chlorite and <strong>the</strong> same<br />
mineral occurs in <strong>the</strong> ash. Nothing definite could be learned<br />
about <strong>the</strong> locality whence <strong>the</strong>se rocks came. One statement<br />
was to <strong>the</strong> effect that <strong>the</strong>y might have come as ballast from<br />
Mauritius, but that is very unlikely, and in view <strong>of</strong> <strong>the</strong> nature<br />
<strong>of</strong> <strong>the</strong> Pulau Pisang rocks, <strong>the</strong>y may have come from a neighbouring<br />
island.*<br />
Generally <strong>the</strong> radiolarian cherts are found close to thick<br />
beds <strong>of</strong> quartzite and shale, and in <strong>the</strong> coarser quartzites<br />
pebbles <strong>of</strong> chert are abundant. Lately Mr. E. S. Willbourn<br />
has reported chert and quartzite to be interbedded in certain<br />
sections in Negri Sembilan. These three cases <strong>of</strong> ns^ociation<br />
with igneous rocks suggest that in some cases <strong>the</strong>ir origin may<br />
be <strong>the</strong> same as that put forward in <strong>the</strong> Geological Magazine<br />
for 191 1 (British Pillow Lavas and <strong>the</strong> rocks associated with<br />
<strong>the</strong>m—loc. cit. pp. 202-209 and 241-248) by Messrs. Dewey<br />
and Flett, who think that silicate <strong>of</strong> soda from volcanic<br />
eruptions was dissolved in sea-water and created conditions<br />
favourable for siliceous protozoa such as radiolaria. A^ <strong>the</strong><br />
eruptions that formed <strong>the</strong> Pahang Volcanic series were in part<br />
submarine, this may be a case <strong>of</strong> similar conditions ami similar<br />
results.<br />
The o<strong>the</strong>r point <strong>of</strong> interest is <strong>the</strong> resemblance <strong>of</strong> <strong>the</strong> pale<br />
grey rock (Nos. 7 & 10) to some <strong>of</strong> <strong>the</strong> boulders and pebbles<br />
found in Kinta with <strong>the</strong> boulders <strong>of</strong> tourmaline-corundum<br />
rock. These are light colored, sometimes oolitic, and some-<br />
times contain a little corundum and tourmaline. In a description<br />
-<br />
!" <strong>of</strong> <strong>the</strong> tourmaline-corundum rocks it was suggested that<br />
certain bodies in <strong>the</strong>m may be replacements <strong>of</strong> casts <strong>of</strong><br />
radiolaria, and a rock was found in Kinta actually showing<br />
• A fourth occurrence <strong>of</strong> chert associated with an igneus rock fs known<br />
on <strong>the</strong> Ginteng Sempah Road, Selangor.<br />
t Quart Journ Geol Soc. Ixvi 1910, pp. 435-449.