J. B. Scrivenor — Radiolarian Rocks, East Indie-". 247 



rocks in the field. The Peninsuhir clierts on the other hand, and 

 probably the Billiton chert also, were laid down in a comparatively 

 shallow sea, not out of the reach of terrigenous material. The oceanic 

 Radiolarian rocks are not stated to contain any carbon; the shallow- 

 water Radiolarian rocks are rich in carbon. 



Dr. Hinde has also described Radiolaria from Triassic and other 

 rocks in Timor, Rotti, Savu, Coram, Celebes, Burn, and Mangoli. 

 They are not stated to contain carbon, being light-grey and reddish 

 cherts. Very little is known of their field relations.' Dr. Verbeek 

 mentions, however, on p. 320, '■'■ roclies triasiques, des calcaires 

 a halohies, des gres et de la lydite a radiolaires^^'' as occurring on 

 Savu, and on p. 325 says, " /es argiles renferment des radiolaires''\ 

 These clays are between marls. This association of rocks certainly 

 points to shallow- water conditions, and it would be interesting to 

 know, in the event of extensive exposures of the Radiolarian cherts 

 being found, if they contain carbon in any quantity. 



Origin of the Peninsular Cakbonaceous Radiolarian Cherts. 



Two suggestions have been put forward to account for the formation 

 of Radiolarian cherts near a coastline : Messrs. Dewey & Flett's 

 suggestion that favourable condition were caused by emanations from 

 a volcanic source, and Mr. Dixon's 'lagoon-phase'. The former 

 cannot be applied to every case ; it cannot, for instance, be applied to 

 the Gower cherts. The latter, valuable though it is, lacks, as far as 

 I am awai-e, the support of known modern examples where Radiolarian 

 beds are being formed. 



Messrs. Dewey & Flett have put forward an explanation for some 

 cases, and it remains to find for other cases, such as the Peninsular 

 carbonaceous cherts, where not associated with igneous rocks, a reason 

 for the change from calcareous to siliceous deposits. Whether this 

 change is connected with a lagoon-phase or not, the key to the 

 problem seems to be how sea-water became so charged with silica in 

 solution as to diminish the growth of calcareous organisms forming 

 beds of limestone, and to promote the growth of siliceous organisms. 

 In the absence of volcanic emanations it is just possible that such 

 a condition may be brought about by tropical weathering and rivers 

 discharging into closed or nearly closed seas. 



Certain researches that arose out of a question concerning ' laterite ', 

 now nearing completion, coupled with previous observations, have 

 emphasized the fact that the most remarkable result of weathering in 

 tlie Peninsula, as far as widespread effects are concerned, is the 

 removal of silica in solution in enormous quantities. The power of 

 ground-water to dissolve silica is such that quai'tzite, of which rock 

 there are extensive outcrops, weathers back to sandstone for a con- 

 siderable depth, and granitic rocks are rendered clayey b}" the removal 

 of the finer quartz particles and the breaking down of the felspars. 

 There is no evidence to show that the bulk of this dissolved silica does 

 not find its way out to sea, but with it there must go quantities of 



•^ Yid& " Eapport sur les Moluques ", E. D. M. Verbeek : edition frangaise du 

 Jaarb. v. h. Mijnwezen in Neder. Oost-Indie, vol. xxxvii, partie scientifique, 

 p. 709, 1908. 



