244 J. B. Scrivenor — Radiolarian Rocks, East Indies. 



experience elsewhere there are good reasons for supposing that the 

 arenaceous rocks are separated from the cherts by an important 

 unconformity. The evidence for this is as follows : The con- 

 glomerates contain abundant pebbles of chert identical •with that in 

 the Chert Series. It might be argued that these pebbles come from 

 still older chert beds that are not visible on the surface now, but 

 pebbles of the volcanic rocks with which the cherts are known to be 

 associated on the Pahang River have also been found in the 

 conglomerate. This points to the Chert Series as the source of 

 the pebbles ; and not only had the chert time to consolidate before it 

 was included in the conglomerate, but some of the chert became 

 traversed by veins before being denuded and rolled into pebbles. 

 These facts indicate a considerable break in the record unless we 

 assume, against all available information, that Radiolarian cherts can 

 be deposited and consolidated with great rapidity. There is, more- 

 over, a piece of negative evidence against a close connexion between 

 chert and quartzite, which is that in the biggest outcrop of the 

 quartzites and conglomerates, namely that stretching through the 

 centre of Pahang, no chert has been seen in situ. Of course, it 

 may be there nevertheless, but its apparent absence is worth 

 mentioning. 



The connexion of the Pahang cherts with volcanic rocks is 

 interesting when one considers the arguments put forward lately by 

 Mr. Dewey and Dr. Flett to supply a possible explanation of the 

 association of Radiolarian cherts and spilites.' No evidence has been 

 noticed yet of the albitization of the Pahang lavas, but it is con- 

 ceivable that emanations from these eruptions, wliich were mostly 

 submarine, supplied sufficient silica for a flourishing growth of 

 Radiolaria without producing albitization. In Kedah, however, 

 I cannot point to volcanic rocks associated with the chert as a possible 

 explanation of the formation. 



In Sarawak the Radiolaria-bearing rocks that I have seen are 

 associated with Middle Oolite limestones and marls, '^ and also with 

 shales that are probably not far removed in age from the limestones 

 and marls. The Radiolaria were found in chert nodules in the 

 limestone, in chert from a calcai'eous conglomerate, in indurated 

 shales, and in a nodule in shale. The chert occurs in much the same 

 way as flint in chalk, and contains but few recognizable Radiolaria. 

 Some of the indurated shales, found as included fragments in an 

 igneous rock, contain calcite and were probably calcareous shales or 

 marl originally. Radiolaria are common in these fragments. At 

 Santubong, however, on the coast, a few Radiolaria were found in 

 beds of indurated shale associated with beds of sandstone and an 

 occasional bed of ash. Thin sections do not show any reason for 

 supposing that the indurated beds were originally ash of very fine 

 grain. 



The nodule containing Radiolaria was found in shale on the Sarawak 

 River at the landing-place for the Bau gold-mines (Bau penkalan). 



^ " British Pillow-lavas and the Rocks associated with them " : Geol. Mag., 

 1911, pp. 244-6. 

 •^ R. B. Newton, Geol. Mag., 1897, p. 415. 



