BY E. C. ANDREWS. 809 



The insignificant remnants of these so captured or beheaded 

 streams, determined^' in the previous cycle and modified in the 

 canon period, are known as George's, Port Hacking and Cook's 

 Rivers and the greater number of the streams of the Illawarra 

 coast. 



Although, as was mentioned previously, (a statement to be 

 amplified later) the very gradual uplift of the Lithgow Plain 

 allowed the Hawkesburj^ to entrench itself along its former valley, 

 it is natural to postulate decided stream-modifications for the 

 caiion cycle, the following structures being competent to originate 

 such modifications : — 



ia) The fold and fault passing through Glenbrook and 

 Kurrajong. 



(b) The Wianamatta Shales of the Penrith-Picton area. 



(c) The great warp-like elevation. 



{d) The elevation of soft shales and other strata to a point 

 considerably above sea-level. 

 The fold and associated fault have been described in some 

 detail by Prof. T. W. E. David f. The author, from topographical 

 criteria, is inclined to assign also a considerable age for these 

 movements. By some the fold has been considered as the move- 

 ment which drowned the coastal valleys in late Pleistocene^ time. 

 In these earlier discussions the evidence yielded by canon cycle 

 erosion appears to have been overlooked. Later observations^ 

 prove the plateau to have passed through a great phase of degra- 

 dation since the slow movements resulting in the fold and later 

 fault. A considerable time appears evident for the movement 

 because of the opposite pitches shown, illustrating the slow 



* [a) From a consideration of their present channels, which are suited to 

 their size, {h) Such admirable adjustment of streams to structure as shown 

 here is the work of more than one cycle. 



+ " An Important Geological Fault at Kurrajong Heights, N.S. Wales." 

 Journ. Proc. Roy. Soc. N.S. Wales, xxxvi. pp. 359-370 (and references). 

 \ C. S. Wilkinson. 

 § T. W. E. David, op. cit. p. 365. 



