460 E. S. Willbourn — The Pahang Volcanic Series — 



groundrnass which, contains scattered fibres of hornblende and large 

 patches of augite and secondary quartz. A similar rock occurs 

 in situ iu the belt of schists fringing the Kuala Lumpur plain, 

 associated with gneisses made up for the most part of secondary 

 micas and quartz in which remain "eyes" of felspar or quartz 

 phenocrysts that have resisted shearing. It is not proposed to do 

 more than mention these rocks, though they are certainly older than 

 the granite and are probably members of the Pahang Volcanic Series. 



PoRPHYKITE. 



Near the 101st mile on the Pahang railway there is a good 

 exposure of an intrusive rock which is markedly porphyritic, no 

 quartz however occurring as phenocrysts. In one exposure the 

 rock has a pink-white colour, with light-green phenocrysts of 

 felspar ranging up to l # 5cm. in length, and in a neighbouring 

 exposure the rock is grey in colour with white phenocrysts. The 

 specific gravity of the first rock is 2*55, whilst that of the second is 

 2 - 62 — the increase probably being solely due to the large amount of 

 iron-pyrites which is present in the grey rock. 



The phenocrysts are of basic oligoclase or andesine with a very 

 ragged outline, and lie in a granitic groundrnass of oligoclase- 

 andesine, felspar, and quartz. 



The groundrnass consists of a fairly cross-grained mosaic of badly 

 formed crystals of plagioclase and possibly too of orthoclase, of 

 length averaging 0*5 mm., with some finer-grained mosaic. Quartz 

 is present, some of it perhaps being primary, and there is abundant 

 secondary mica with also a little chlorite. 



Doi/erites. 



Intrusions of dolerite were seen in only two cuttings of the 

 Pahang Railway, namely at the 101st mile, where the rock is a fine- 

 grained quartz-dolerite like a lava, and at the 104A- mile, while none 

 were seen on the Pahang River between Kuala Lipisand Mengkarak. 

 However, they are known to occur at several places along the Benta- 

 Kuantan road, in the zone of the Pahang Volcanic Series. 



At the 101st mile the quartz-dolerite is in contact with quartz- 

 porphyry. The relations of the two rocks were not determined, 

 but it was clear that the quartz-porphyry was intruded into inter- 

 bedded ashes and shales. 



At the 104J mile the dolerite is associated with shales, tuffs, and 

 andesitic lava, and some of the tuffs near here contain water-worn 

 boulders of volcanic rocks which will be described later. The 

 dolerite at the 104J mile is considerably altered, the hand-specimen 

 being a dark-green rock containing occasional phenocrysts of augite 

 up to J cm. or more in length with prisms of altered plagioclase, 

 some of which has extinction angle corresponding to oligoclase- 

 andesine. The felspars have ophitic structure with regard to 

 a green mineral which has been formed as a result of the alteration 

 of augite, and there are some fragments of augite still remaining. 

 A little of the green mineral is chlorite, but most of it is an 

 amphibole, some of it of a fibrous habit, and some of it replacing the 

 augite crystal for crystal. There is a considerable quantity of 

 ilmenite present. 



