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



observed. Some pyrites is present. Veins of fibrous serpentine or 

 cblorite penetrate the rock and there are also veins of calcite. 



The evidence is all in favour of the volcanic rocks at the 17£ 

 and 21st miles being identical, the one near the 21st mile having 

 suffered considerable alteration. The felspars in both rocks are 

 partially obscured by an opaque dust, but the extinction angles can 

 be measured in many cases, and there is no doubt that these 

 correspond to oligoclase. There is no sign that the felspar was 

 originally a more basic variety that has undergone albitization, but 

 the association of the volcanic rock with chert at once suggests that 

 the latter owed its origin to the fact that the sea-water was highly 

 charged with silica derived from pneumatolytic gases which were 

 given off by the volcanic rocks. These same gases may have 

 attacked the basic felspar of the volcanic rocks, turning it into 

 a more alkaline variety, and at the same time releasing some of the 

 calcium as calcium carbonate. Under these conditions radiolarian 

 organisms flourished and their siliceous remains dropped to the sea- 

 bottom and there formed beds of chert. However, no proof has yet 

 been obtained that the felspar of the rocks was originally more basic. 



Greenstones. 



In early reports 1 certain "greenstones" were often referred to 

 which are probably all members of the Pahang Yolcanic Series, in 

 which chlorite, epidote, and calcite have been developed by 

 weathering. It is sometimes difficult to distinguish whether they 

 are tuffs, lavas, or intrusive rocks, and probably all three occur, but 

 their relationship with the series as a whole is easily recognized. 



Serpentine. 



Serpentine occurs in Perak*, Pahang, and also in Negri Sembilan*, 

 but its relation to the Pahang Volcanic Series is not yet known, 

 though, as it is known to be strongly sheared in Pahang and in one of 

 the Negri Sembilan* outcrops, it is probably of pre-granitic age. An 

 outcrop at Bersiah * in Upper Perak * contains olivine, but the 

 indications are that the serpentine of all the other outcrops was 

 formed by the alteration of amphibole. The four known outcrops in 

 Negri Sembilan * seem to occur at the boundary of llaub and 

 Grondwana rocks, but as this fact has not been definitely proved it is 

 useless to theorize about its significance. There is little doubt that 

 the serpentine is an altered lava or intrusion of Pahang Volcanic 

 Series age. 2 



EXPLANATION OF PLATES XXIX AND XXX. 

 FlG- Plate XXIX. 



1. Augite-andesite, 41st mile, Benta-Kuantan road. X 30 diam. 



2. Olivine-andesite, Kuala Teh, Pahang Railway. x 30 diam. 



3. Quartz-porphyry with flow-structure, Ginting-Sempak. X 25 diam. 



4. Andesite-rhyolite breccia, 47th mile, Benta-Kuantan road. X 25 diam. 



[Photographs by J. B. Scrivenor.) 

 Plate XXX. 

 Map 3 of Pahang Volcanic Series, Federated Malay States. 



1 These are alluded to in the Ulu Pahang Memoir, p. 41. 



2 This article is published by permission of the Geologist, F.M.S. 



3 The Map (Plate XXX) will appear with the second part of this paper in 

 the November Number. 



[To be concluded in our next Number.) 



