568 RADIOLAEIA IN PALAEOZOIC ROCKS, 



Casts of the inner and outer shells are well preserved in the 

 form of a nucleus of translucent chalcedony separated by a zone 

 of the grey liase from an outer ring of clear chalcedony. 



Radial sjiines are indistinctl}'- A-isihle in many of the specimens, 

 and can be seen best under crossed Nicols. Most of the casts are 

 spherical, and vary in diameter from -05 mm. to '2 mm. 



Internal casts of the medullary shell are more frequent than 

 casts of the outer shell. 



Sponge sjDicules were not observed. 



4. Summary. 



The radiolarian rocks, as yet discovered in ISTew South Wales, 

 range for at least 285 miles, from the Jenolan Caves on the south 

 to Bingera on the north. Their total thickness has not yet been 

 ascertained, but at Tamworth it appears to amount to at least 

 2,000 feet, and at Jenolan to not less than 1,000 feet. The 

 radiolarian rocks consist of red jaspers, black cherts, thin siliceous 

 limestones, and thin bedded argillites. The radiolaria hitherto 

 discovered are in the best state of preservation when enclosed in 

 the siliceous limestone. For the most part, however, they are 

 represented merely by chalcedonic casts, the casts of the medullary 

 shell being more frequently preserved than those of the outer 

 shell. In the thin siliceous limestones of Tamworth the radiolarian 

 shells frequently have the original substance of the skeleton fairl}'' 

 well preserved in the form of sub-translucent to translucent silica. 

 llarely the original siliceous skeleton is found to be replaced by 

 iron pyrites. In the Jenolan Cave Cherts the radiolarian skeletons 

 show obscure traces of latticing in the form of fragments of oj^aque 

 black nets. 



At Tamworth and Jenolan the radiolarian rocks ha^'e beds of 

 coralline limestone interstratified with them, probably over 1,(00 

 feet thick at the former, and over 400 feet thick at the latter 

 locality. 



At the Jenolan Caves a volcanic agglomerate containing blocks 

 of coral is associated with the radiolarian shales. 



