19G Geological Society. 



The fourth area of radiolarian rocks is at the well-known Jenolan 

 Caves, about 67 miles due west of Sydney and about 200 miles 

 south-by-west of Tamworth. It is probable that the Jenolan rocks 

 may be on a somewhat different, perhaps lower, horizon than those 

 of the northern district. 



At Bingara and Barraba the radiolarian rocks consist of red 

 jaspers and fino-grained jointed claystones, accompanied by thick 

 coral -limestones and numerous beds of interstratified tufaceous 

 materials. The radiolaria occur as casts in chalcedony in the 

 jaspers and claystones. The rocks dip at a high angle. No macro- 

 scopic fossils are known with certainty from these districts. 



In the Jenolan Cave district the radiolarian rocks consist of black 

 cherts and clay-shales overlying the Cave Coral Limestone, and of 

 greenish-grey shales underlying this rock. The series is traversed 

 by felsitic dykes, and the hardness of the cherts is attributed to 

 silica derived from the acidic dykes, rather than to that derived from 

 the tests of the siliceous organisms. 



It is at Tamworth that the radiolarian rocks are developed on a 

 grand scale ; their measured thickness amounts to 9267 feet, after 

 allowing for an immense fault, and neither upward nor downward 

 limit is shown. The rocks consist of jointed claystones, black 

 cherts, lenticular siliceous radiolarian limestones, and coral-lime- 

 atones. Numerous beds of submarine tuff also occur. The claystones 

 are largely formed of radiolaria. In certain beds of the claystones, 

 and in some of the tuffs as well, impressions of Lepidodendron 

 australe are not uncommon ; and beds of radiolarian limestone 

 occur in close proximity to the beds with these plant-remains, and 

 radiolaria moreover abound even in the same rock with the Lepido- 

 dendron-impressions. 



At the eastern end of the Tamworth section, and also near the 

 westerly portion, there are limestones containing corals, which 

 have been determined by Mr. II. Etheridge, jun. They are similar 

 to those of the Burdekin Limestones of Queensland which belong to 

 the Middle Devonian, and the radiolarian rocks are thus shown 

 to belong to this period. 



Analyses of the radiolarian chert, chorty shale, shale, and 

 siliceous limestone prepared by Mr. J. C. H. Mingaye, F.C.S., are 

 given ; and from these it appears that, while the amount of silica in 

 the chert and shale ranges between 68 and 91 per cent., there is 

 only 18 per cent, in the siliceous limestone. 



Descriptions of numerous micro-sections both of the sedimentary 

 and of the tufaceous rocks are appended, and in their conclusions 

 the Authors point to the remarkably fine-grained character of the 

 materials forming the base of the radiolarian cherts, jaspers, and 

 shales, the constituent particles not being more than 0-05-0-025 

 mm. (7^5- to yoVrr inch) in diameter. They are of opinion that the 

 radiolaria were deposited in clear sea-water, which, though suffi- 

 ciently far from laud to be beyond the reach of any but the finest 

 sediment, was nevertheless probably not of very considerable depth. 



