ANNIVERSARY ADDRESS. 55 
fossil fish have already been described Paleoniscus, Cleithrolepis. 
Mr. John Mitchell of Narellan has recorded the occurrence of the 
elytron of a fossil Buprestid, from the Wianamatta Shales near 
Campbelltown. The Rev. W. B. Clarke states that Lntomostraca 
are also met within the shales. Fossil plants are tolerably abun- 
dant, and comprise chiefly the following forms :—T7hinnfeldia 
odontopteroides, Macroteniopteris Wianamatte, and Phyllotheca. 
d. Cretaceous or Tertiary (?). At the top of the monoclinal 
fold, between Lucasville and Glenbrook, a deposit of coarse river 
gravel rests on an eroded surface of Hawkesbury Sandstone, just 
below the horizon of the junction line of the Hawkesbury Sand- 
stone with the Wianamatta Shale. The position of this river 
gravel is shewn on a geological map by the Rev. W. B. Clarke at 
the commencement of the fourth edition of his work, “Sedimentary 
Formations etc. of N.S. Wales.” Its trend follows approximately 
that of the modern valley of the Nepean, and it may probably be 
correlated with the somewhat similar gravel seen in the railway 
cutting east of and close to St. Mary’s. This gravel deposit, 
together with the old river channel in which it is reposing, follows 
the bends of the monoclinal folds in such a way as to prove that 
the fold did not exist at the time when this gravel deposit was 
formed. This is a very significant fact in the history of the 
physiography of the Blue Mountains, inasmuch as it proves that 
at the time this river was flowing, the deep gorges, such as those 
of the Grose and Cox’s Rivers, did not exist, as the surface of the 
Hawkesbury Sandstone at this time had been eroded to a depth 
of only a few feet. Had they existed, it would obviously have 
been impossible for such a river to have co-existed and crossed 
these gorges at right angles, at an altitude of over five hundred 
feet above their present beds. This single fact at once disposes 
of the surmise of Darwin, that the valleys of the Blue Mountains 
occupy the sites of original depressions in the sandstone platform. 
The river gravel, at the spot where the tunnel of the western 
railway runs beneath it, is about one hundred and fifty yards 
wide and fifteen to twenty feet thick ; the shingle varies from a 
