BY C. A, SUSSMILCH AND H. I. JENSEN. 171 



4. Age of the Volcanic Rocks, 



No direct evidence has yet been found as to the age of the 

 alkaline lavas of this district. The oldest fossilifeioiis strata 

 observed are of Devonian age, and these had been extensively- 

 folded and denuded before the lavas were deposited upon them. 



The age of the peneplain upon which they rest is also uncertain. 

 Mr. E. C. Andrews, in his published description of this feature 

 in the Blue Mountains, considered that it had been cut out in 

 the Pliocene period, but has since expressed the opinion tliat it 

 may be considerably older. Until the study of the peneplains of 

 Eastern Australia is carried into the marine Tertiary areas of 

 Victoria, it will be difficult to arrive at any satisfactory conclu- 

 sion. As already pointed out by one of us (H. I. Jensen),^ a 

 remarkable similarity occurs in every way between the alkaline 

 rocks of the Canobolas area, and those of the Warrumbungle 

 and Nandewar areas. In all these areas, also, the lavas have 

 been deposited on top of what are, probably, portions of the same 

 peneplain. There is every reason for believing, therefore, that 

 the eruptions in the three areas were contemporaneous. In the 

 Warrumbungle Mountains, fossil leaves have been obtained from 

 a bed of tuff, near the base of the volcanic series. These have 

 been described by Mr. Henry Deane,t who considers that they 

 may be of Eocene age. This determination, if correct, would 

 relegate the beginning of the volcanic series to the Eocene, and 

 would correspondingly jjut back the cutting out of the peneplain 

 to the early Eocene, or even Cretaceous. It is questionable as 

 to how much reliance can be placed upon the evidence of a few 

 Tertiary leaves, as to geological age; so that the age, both of the 

 peneplain, and of the volcanic series, must still remain doubtful, 

 but we can assume that it still lies somewhere between the Upper 

 Cretaceous and the Miocene. 



* The Alkaline Petrographical Province of Eastern Australia. Proc. 

 Linn. Soc. N. S. Wales, 1908, p. 589. 



fNotes on Specimens of Fossil Leaves from the Warrumbungle Mountains. 

 Ree. Geol. Surv. N. S. Whales, Vol. viii., Part 3. 



