Federated Malay States. 509 



Raub cberts for them to undergo veining before being eroded shows 

 that the unconformity was an important one. This theory was 

 explained in full in 1911 by Mr. Scrivenor, 1 but at that time it was 

 thought that the chert beds formed a single separate series between 

 the Raub and Gondwana rocks, whereas it is now known that many 

 of the chert beds of the Peninsula are inter stratified with Gondwana 

 quartzites. 



If the deposits of boulders and pebbles in tuff occur at the boundary 

 of Raub and. Gondwana rocks, it is fairly clear that they were formed 

 during the period between them, i.e. in the period of terrestrial 

 conditions. 



Mr. Scrivenor said in 1911, that they bear resemblance to the 

 "ashy conglomerate" of the Mendips, described by Professor S. H. 

 Reynolds, 2 but added that after examining Mr. Scrivenor's photograph 

 of the Pulau Guai beds (plate ix, Ulu Pahang memoir) Professor 

 Reynolds thought that the two deposits do not agree. The bedding 

 observed in the Pahang deposits is a point of difference from the 

 Mendip "ashy conglomerate". Professor Reynolds gives four 

 possibilities as to the nature and origin of the Mendip deposit, and 

 one of them, slightly amended, is now suggested as accounting for 

 the Pahang deposit. 



The deposit of boulders and pebbles in tuff was laid down during 

 the latter part of the unconformity which followed the Raub period, 

 and during the subsidence when the Gondwana rocks were formed. 

 The line from Kuala Tekai on the River Tembeling to Kuala Tekal 

 on the River Pahang marks the position of the coastline during 

 a pause in the depression, in which beach deposits were formed 

 in sheltered parts of the coastline, and were mixed with volcanic 

 ash which all this time was being deposited on the sea-floor by 

 active volcanoes. Sufficient time must have elapsed between the 

 beginning of the terrestrial conditions and the end of the period of 

 formation of the beach-deposit to allow for the denudation of the 

 considerable thickness of sedimentary rocks which must have covered 

 the quartz-porphyry, granophyre, and other intrusions, for boulders 

 of these intrusive rocks are common in the beach-deposit. 



This theory explains the heterogeneous nature of the boulders and 

 pebbles and their well-rounded appearance. It also explains the 

 bedded nature of the deposit and its association at Lubok Plang 

 with a band of chert, for it has been suggested before that chert can 

 be formed in shallow water if the growth of Radiolaria is favoured 

 by abundant silicates being supplied to the sea-water 3 by gases from 



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

 p. 56. 



2 Quart. Journ. Geol. Soc, vol. lxiii, p. 227. 



3 J. B. Scrivenor, " Radiolarian-bearing Rocks in the East Indies " : Geol. 

 Mag., Dec. V, Vol. IX, No. VI, June, 1912, pp. 241-8. Mr. Scrivenor 

 discusses the origin of the Peninsula chert, and points out that in Kedah the 

 chert is not associated with volcanic rocks. He suggests that large quantities 

 of silica in solution, supplied by tropical weathering of siliceous rocks, may 

 have promoted, or helped to promote, the abundant growth of Radiolaria in 

 shallow seas. 



