GEOLOGY OF THE JENOLAN CAVES DISTRICT. 335 



typical V-shaped gorges with steep grades, steep walls and 

 narrow bases. So steep are the valley walls that landslips 

 are frequent. The whole region is very rugged and difficult 

 of access, and geological field-work, except along the few 

 roads and pathways, is both difficult and arduous. 



The limestone caves occur where the Jenolan River and 

 its tributary McEwens Creek, have cut their channels 

 across a thick bed of limestone (the Gave limestone), the 

 various cave levels representing successive levels of the 

 streams' channels as they cut their way downwards from 

 the tableland surface. Owing to the extent to which the 

 limestone resists mechanical erosion as compared with the 

 slates and cherts which lie on either side of it, it now 

 stands as a great wall across the course of the stream from 

 one side of the valley to the other, and entirely cutting 

 off the head of the valley from that part below. The drain- 

 age from the upper valley passes through this wall by 

 means of natural tunnels carved out of the limestone by 

 chemical action, such as the Grand Arch and the Devil's 

 Coach-house. This limestone wall, at its lowest part, rises 

 300 feet above the present stream channel. The Gave 

 House is in the upper valley and the road to it from Mount 

 Victoria passes through the Grand Arch (see PI. LV). This 

 great wall of limestone is a most impressive feature, par- 

 ticularly when viewed along the direction of its strike, and 

 from a position where one can see how completely the 

 upper valley is cut off from the lower valley by it. 



In their geological features the Jenolan Oaves do not 

 differ from other limestone caves, and for a detailed 

 description of them the reader is referred to the excellent 

 guide-book written by Mr. O. Trickett, l.s., and published 

 by the Department of Mines. Each of the cave-levels 

 marks the one time channel of the Jenolan River or one of 

 its tributaries, and all of them contain deposits of river- 



