GEOLOGY OF THE JENOLAN CAVES DISTRICT. 339 



cherts were lying conformably above the limestones, the 

 intrusive andesites would probably have broken through 

 the downward continuation of the limestone in order to 

 reach its present position in the cherts. No evidence has 

 yet been found that the andesite is intrusive into the lime- 

 stone, and no inclusions of limestone have yet been found 

 in it, whereas inclusions of chert fragments are common. 

 The quartz-porphyrite intrusions lying to the east of the 

 Gave limestone, on the other hand, contain abundant 

 included fragments of limestone, even at considerable 

 distances from the contacts. These facts are difficult 

 of explanation except on the supposition that both cherts 

 and andesites are older than the limestone and have been 

 faulted against it. 



There is still one other factor which has a bearing on 

 this problem. At the eastern leg of the Jenolan anticline 

 (see section), the limestone is overlain by a thick series of 

 argillaceous quartzites, these are at least 1000 feet in 

 thickness. These quartzites therefore occupy the same 

 horizon in the eastern leg of the anticline that the radio- 

 larian cherts would in the western leg if the latter were 

 conformable with the limestone. It is difficult to imagine 

 conditions such as that at two places so near to one another 

 there should be a simultaneous deposition of radiolarian 

 cherts and quartzites, the one a relatively deep-water 

 deposit and the other a shallow- water deposit, particularly 

 in view of the great thickness of both deposits. 



If the black radiolarian cherts are older than the Silurian 

 limestones, what then is their actual geological age? Litho- 

 logically they much resemble the Ordovician strata from 

 such localities as Oadia, Tallong and Berridale ; further, the 

 occurrence of radiolaria in Ordovician strata is common in 

 New South Wales, although it must not be forgotten that 

 radiolaria have been identified by Prof. David in the slates 



