510 E. S. Willboum — The Pahang Volcanic Series — 



volcanic effusions. 1 The absence of any great quantity of sedimentary 

 material can readily be understood, as also the fact that the boulder- 

 in-tuff deposit often passes into a tuff devoid of pebbly material. 



The theory that the boulders were deposited in water near a shore- 

 line helps to explain a peculiar circumstance noticed with regard to 

 the tuffs near Pulau Guai. There is a series ef exposures of 

 granophyre over a distance of 4 miles to the north of Pulau Guai, 

 one occurring only about a hundred } r ards up-stream from the first 

 boulder deposit, and all the tuffs between Pulau Guai and Kuala 

 Tembeling contain fragments of granophyre, whilst of the many 

 specimens of tuffs examined from Pulau Guai only one contained 

 what might be regarded as a fragment of granophyre. At the 

 102nd mile on the railway there is an intrusion of granophyre, while 

 3 miles further north is a boulder deposit in tuff. One of the 

 boulders consists of granophyre, and fragments of granophyre occur 

 in the tuff at the 105th mile and in tuffs between there and the 

 intrusion. 



The granophyre was exposed by the action of denudation during 

 the period of unconformity, and fragments of it were carried down 

 by stream action and deposited with tuffs which were being formed 

 by active volcanoes at the time. Evidently the shore-line moved 

 from west to east or a little north of west to a little south of east, 

 and this explains the change from tuffs with granophyre fragments 

 to tuffs without granophyre fragments when going down-stream at 

 Pulau Guai, for as soon as the outcrop of granophyre became sub- 

 merged below low-tide mark it would no longer be subject to 

 denudation. 



It was hoped to include in this paper a comparison of the Pahang 

 Volcanic Series with the older volcanic rocks of the Malay Archi- 

 pelago, as described in various Dutch and German publications, but 

 the process of translation has proved so laborious and slow that it 

 has not been possible to compare them with the volcanic rocks of any 

 other districts but the Goemaigebergte of South Sumatra, which are 

 described by Dr. Emil Gutzwiller in Mijnwezen, 1912, Verhandelingen. 



Comparison op the Pahang Volcanic Series with the Permo- 

 Carboniferous Volcanic Pocks of the Goemaigebergte, South 

 Sumatra. 

 There are no older acid intrusive rocks in Sumatra which correspond 



to the quartz-porphyries and granophyres of Pahang, nor are there 



any rhyolitic lavas or trachytes. 



Dolerites. 



Those rocks of the Goemaigebergte which typically have an 

 ophitic structure are divided by Dr. Emil Gutzwiller into two groups, 

 the diabase-porphyrites and the diabases; the former group containing 

 no olivine or diallage, while the second group usually contain one or 

 other of them. 



Very few specimens of dolerite of the period of the Pahang 

 Volcanic Series have been collected in Pahang, so a detailed comparison 



1 E. E. L. Dixon, Quart. Journ. Geol. Soc, vol. lxvii, pp. 511-31, 1911. 



