336 C. A. SUSSMILCH AND W. G. STONE. 



gravel, some of the pebbles of which reach a foot or more 

 in diameter; the rivers themselves still flow through the 

 lowest cave-levels. 



A word might be said here about the probable age of the 

 Oaves; observations have been made of the present rate of 

 growth of some of the stalactites and stalagmites in the 

 caves, and assuming that the rate of growth so obtained to 

 have been the same ever since the caves first began to form, 

 estimates of many million years have been made as to the 

 age even of some of the stalactites. It is obvious that the 

 Jenolan Oaves could not have been formed before the valley 

 in which they occur was formed, and this cannot date back 

 beyond the end of the Tertiary Period, when the tableland 

 was uplifted to its present height. The most liberal esti- 

 mates of the length of time which has elapsed since the 

 end of the Tertiary Period do not exceed 1,000,000 years, 

 while many estimates do not exceed 500,000 years. The 

 present caves occur more than 1000 feet below the tableland 

 level, so their age must be considerably less than that of the 

 valley as a whole; it is therefore quite improbable that the 

 age, even of the oldest of the caves can exceed 500,000 

 years. 



D. General Geology. 



The various rock formations met with in travelling from 



Mount Victoria to the Jenolan Caves may be classified, 



according to geological age, as follows: — 



Mesozoic Triassic Hawkesbury Series. 



^ ~ , .„ f Upper Goal Measures. 



Permo-Oarbomferous \ ^ Marine geries _ 



f Granites, quartz porphyrites, 

 Upper Devonian] felsites, Mount Lambie Beds, 

 Iquartzites, etc. 



«» . f Jenolan Series — Slates, quartzites, 

 biiunan <j limestones and r t]yolite lavas. 



(?) Ordovician — Jenolan radiolarian cherts. 



Palaeozoic 



