Federated Malay States. 507 



3. They are sometimes arranged in definite strata where they 

 occur as pebbles of small size, e.g. at Tanjong Lindong. 



4. In composition they coincide with the Pahang Yolcanic Series 

 rocks found in situ, including andesite-lava, rhyolite-lava, andesite- 

 rhyolite tuffs and breccias, quartz-porphyry, and granophyre. No 

 dolerite boulders have yet been found in these deposits. In addition to 

 these volcanic rocks, one boulder of reticulating quartz veins was found 

 in the Kuala Tekal section, and at Batu Redap many of the pebbles 

 consist of a rock which should be described as a slightly felspathic 

 grit — though it may be a fine-grained rhyolite-tuff. There is no 

 distinction between the mode of occurrence of the sedimentary rock 

 and the vein-quartz as boulders in the tuff, and the much more 

 numerous boulders of igneous rocks. 



The table on p. 508 gives the different localities in which the 

 boulder deposits are found and the nature of the boulders. 



Some of the boulders in tuff at Pulau Guai (see Map, Plate XXX) 

 are of a rhyolite with numerous dark angular shale-inclusions, some 

 of which contain crystals of chiastolite. This rock contains a good 

 deal of calcite mixed with it. 



It is very like a rhyolite-lava with shale-inclusions which occurs 

 in situ at Pulau Chengai. Unfortunately, in the field the Pulau 

 Chengai rock was mistaken for a conglomerate belonging to the 

 Gondwana series, and certain other exposures near here which were 

 named as coarse-grained quartzites may be really this same rhyolite- 

 lava with inclusions of shale, so nothing can be said with certainty 

 as to whether the boulder deposits of Pulau Chengai occur near the 

 boundary of the Gondwanas and Raubs. This cannot be taken as 

 evidence, but it will be seen from the third column of the following 

 table that there is evidence to show that the boulder deposits occur 

 always at a boundary of an outcrop of Gondwana rocks with Raub 

 rocks. 



The tentative theory as to their origin, 1 put forward by 

 Mr. Scrivenor, the Government Geologist, was " that they were 

 derived from already consolidated sheets of lava and ash, and masses 

 of igneous rock consolidated below the surface, and that they became 

 rounded by attrition in some way we cannot explain before they 

 were shot up into the sea and fell back on ash being deposited on 

 the sea-bottom ". 



Owing to the infrequency of exposures the field relationships of 

 the deposit are very little known, but, in the nine districts where the 

 deposit has been examined, the small amount of evidence that can be 

 collected indicates that the deposit lies at the junction of Raub and 

 Gondwana rocks. It is probable that there was an important 

 unconformity between the Raub Series and the deposition of the 

 Gondwana rocks, and evidence for this is afforded by the occurrence 

 of pebbles of veined chert and Pahang Volcanic Series rocks in the 

 Gondwana conglomerates. It seems likely that the pebbles were 

 derived from cherts and Pahang Volcanic Series rocks of Raub age, 

 and the fact that sufficient time elapsed after the formation of the 



1 The Geology and Mining Industries of Ulu Pahang, Kuala Lumpur, 1911, 

 p. 47. 



