796 GEOGRAPHY OF BLUE MTS. AND SYDNEY DISTRICT, 



the earliest tme, indicates an enormous period of time, and as 

 must be obvious at once, each pronounced cycle such as we have 

 evidence of in this area must be associated with a distinct period 

 of sedimentation such as Tertiary (or Lower and Upper Tertiary), 

 Lower and Upper Cretaceous, Jurassic, etc. Undoubted pahieon, 

 tological criteria of age are absent even for the latest movement 

 of elevation resulting in the Lithgow peneplain, although a 

 Miocene* age has been ascribed to the lower high-level plain of 

 Eastern Victoria, which is probably co-extensive through Monaro 

 with the Lithgow peneplain. The evidence as to the age of the 

 Victorian plateau does not, however, appear satisfactory on 

 biological grounds.! 



It is possible, however, that the Lithgow peneplain was elevated 

 by the diastrophic movement which initiated the earlier Tertiary 

 sedimentation. The writer is inclined to assign this age to the 

 uplift from a consideration of the advanced stage of canon 

 formation obtaining at present in the plateau surface. No plains 

 have had time to form along the lower river courses, the Hawkes- 

 bury being confined to a narrow canon even near its point of 

 discharge into the sea. Nevertheless wide valleys have been 

 excavated in still more western areas of weakness, while north of 

 Sydney great valley-making is shown as along the lower and 

 middle Hunter River, and the time necessary to excavate caiions 

 in the resistant sandstone of Sydney is very great, and the amount 

 of waste carried into the sea by the wholesale degradation of the 

 Wianamatta Shales farther west is very considerable, being 

 sufficient for the production of thick offshore deposits. The 

 aspect of the Lithgow peneplain at the shore-line also evidences 

 the far-reaching importance of marine erosion, to which a paper 

 will be devoted in the near future. No movement of note has 

 occurred since. Therefore an early Tertiar}^ age for the last 

 great uplift is very probable. 



* K. F. Murray, Progress Kep. Geol. Survey, Victoria, No. 5, pp. 96-111. 

 t H. Deane, Presidential Address, Proc. Linn. Soc. N.S. Wales, 1895, 

 pp. 652-666. 



