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



fragments of andesitic lava. However, the majority also contain 

 numerous fragments of quartz, some of which occur as isolated 

 angular grains in the cement, others embedded in a very fine-grained 

 siliceous rock, and sometimes showing rounded outlines and even 

 bays, invaded by the siliceous aggregate. Tuffs which occur in certain 

 localities, e.g. at Kuala Tekal, Tembeling, and Sibah near Kuala 

 Lipis on the Pahang railway, contain the usual fragments of 

 andesite-lava, with numerous fragments of quartz like those just 

 described, and in addition fragments of rhyolite-lava or quartz- 

 porphyry. It is probable that the great majority of the Pahang 

 Volcanic Series of tuffs are formed of an admixture of andesitic, 

 rhyolitic, and sedimentary material. 



The first type to be described is an andesite-rhyolite-breccia 1 

 from the Benta-Kuantan road, at the 47th mile from Benta. There 

 is no hand-specimen of this rock in the collection, but judging from 

 the slide (PI. XXIX, 2 Fig. 4) it is a dark-green rock, fairly fine- 

 grained, with occasional red spots, made up of abundant fragments of 

 andesite-lava and quartz, with occasional crystals of felspar and 

 fragments of quartzite, set in a cement of quartz and calcite. In 

 addition there are numerous pieces of altered rock, consisting of a fine- 

 grained siliceous aggregate with large included quartz grains, and in 

 one case enclosing a rectangular pseudomorph of magnetite, probably 

 after felspar. Also there are some fragments of a highly altered 

 rock, composed of a rather coarser quartz mosaic, with a little black 

 iron-ore evenly distributed throughout the mass, and comparatively 

 large irregular flakes of white mica. 



The andesite-lava fragments are made up of felspar laths, usually 

 untwinned and with a low extinction angle, set in a dark-green 

 isotropic material which often includes large grains of magnetite. 

 There is a greater quantity of glass in these lava fragments than in 

 any of the andesite-lavas which have been noticed in situ. The 

 felspar laths are bent, suggesting that the andesite fragments were 

 hot plastic masses when they were detached from the parent body. 

 Some of the lava fragments contain numerous cavities filled with 

 a green chloritic mineral which is arranged in radiating fibres. 



The quartz grains vary considerably in size and appearance, some 

 being angular while others are rounded and have a corroded 

 appearance. The quartzite fragments are stained red with haematite, 

 and magnetite and haematite are widespread, both in the lava 

 fragments and in the cement. The few felspar crystals which are 

 contained in the tuff are usually broken, and in composition correspond 

 to oligoclase-andesine. 



Breccias similar to this occur outside Pahang in the south of 

 Negri Sembilan* 3 and north of Johore*, but the rhyolite admixture 

 cannot here be recognized definitely, and the numerous angular 



1 Described by Mr. Scrivenor in The Geology and Mining Industries of 

 Ulu Pahang, Kuala Lumpur, 1911, p. 43, No. 1851, pi. xi. 



2 Plate XXIX of rock-sections, also explanation, appeared with the earlier 

 part of this paper in the October Number, facing p. 462. 



3 An asterisk marks the names of all those places in Malaya mentioned 

 in the text which are outside the area shown on the accompanying Map, 

 Plate XXX. 



