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



underlying the Cave limestone and which are of Silurian 

 age, although he referred to these as being doubtful. It 

 would appear probable therefore that these Jenolan radio- 

 larian cherts are of Ordovician age. While it cannot yet 

 be said to have been definitely proved, the balance of 

 evidence at present available strongly suggests therefore, 

 that (a) the radiolarian cherts of Jenolan are unconformable 

 with and older than the Silurian strata and (b) that they 

 are probably of Ordovician age. 



(b) The Silurian Strata. 



These include limestones, slates, and quartzites, with what 

 is probably a contemporaneous rhyolite lava flow. The 

 succession of strata in descending order is as follows : — 



Argillaceous quartzites and slates 1000' + ( ac *rtaow? ness ) 



Slates 



... 100' 



Limestones... 



... 550' 



Slates 



... 100' 



Rhyolite lava flow 



... 300 x 



Slates 



1 Ann' _l_ /actual thickness \ 

 ... 1UUU -t{ unknown. ) 



These strata have a general strike of about N. 15° W. to 

 N. 20° W., and in the district mapped form part of a great 

 anticline. This anticline is a symmetrical one, the eastern 

 and western legs both dipping at an angle of about 60°. 

 Extensive intrusions of quartz-porphyrite have taken place 

 along the axis of the anticlines, particularly in the slate* 

 below the limestone, and near the contact of these intru- 

 sives some local irregularities of dip occur in the slate. 



1. The Limestones. — Two belts of limestone occur in the 

 region examined, (a) the one in which the Jenolan Caves 

 occur, and (b) the limestone which outcrops to the east in 

 the banks of Jenolan River about two miles below the 

 Grand Arch. The former will for convenience be referred 

 to as the Cave limestone, the latter as the eastern lime- 

 stone belt. 



