Jenolan Caves. 
245 
slate floated bodily upwards by the intrusion of quartz 
and felspar porphyry. The slate rocks will also be 
seen folded, the core of one anticline being easily 
noticed near the Grand Archway. 
When at the Caves the geological student would 
do well to observe : — 
(1.) A mass of intrusive augite-porphyrite in a cutting 
made for the erection of the dining-room at Cave 
House. This interesting rock is altered much in 
places, through the absorption of overlying rocks 
while still in a liquid condition. With a little 
care, specimens may be found showing crystals of 
augite in a quasi-felsitic base or paste. 
(2 ) About Inchman’s Creek, two-and-a-half miles from 
Cave House, towards Mount Victoria, fossil corals 
and crinoids can be found in a matrix that in 
hand specimens can hardly be distinguished from 
an igneous rock. This may be taken as a proof 
that sedimentary rocks, and even limestones, may 
have been absorbed by the underlying igneous 
rocks as they worked their way upwards into the 
solid crust. On the other hand, of course, these 
sediments may have been depressed into the liquid 
magma. A more probable view is that while the 
corals were growing they were buried in a layer 
of coarse volcanic sand, which rained down into 
the clear sea-water. Whatever the explanation 
is, we find casts of marine fossils, such as corals 
in a matrix which has many of the characters of 
an igneous rock. 
(3.) fossil corals may be detected in the limestones on 
