822 GEOGRAPHY OF liLUE MTS. AND SYDNP:Y DISTRICT, 



by the peculiar character of the topography.* During the Lithgovv 

 cycle the rivers had pushed their loads otf-shore, and the sea 

 currents had built them into the smooth continental shelf below 

 wave-attack. A wide sloping shelf was thus brought about at 

 the close of the period, and the sedimentation on that shelf was 

 more deeply buried by the warping. During the period Ijetween 

 the birth of the canon cycle and the recent drowning the rivers 

 sent down huge loads of waste from the highlands, which were 

 redistributed by the sea to furnish another coat to the already 

 smooth ofF-shore deposits of the plateau C3'cle. At the same time 

 the sea rapidly encroached on the coastal strip, the land retreating 

 until huge cliffs were formed. A measure of the amount of this 

 sea-attack is difficult to arrive at, as the land slope is irregular — 

 now gently convex and now concave to the sky — and does not 

 represent an even inclination seawards near Sydney. f In any 

 case a considerable encroachment is indicated by an attempted 

 restoration of the old slopes, probably exceeding 10 miles in width. | 

 A large fault appears to be indicated for the Nowra District. 

 On the south of the Shoalhaven River, the Lithgow Plain rises 



* If we assume that the warping induced elevation over the coast-line of 

 the plateau cycle, then we are forced to one of two conclusions from the 

 evidence of the topography:- — 



(1) Either the cover of marine (off-shore) deposits laid down on the shore 

 of the plateau period and now forming the plateau around Berowra, Sydney, 

 and Illawarra has been completely removed during the caiion cycle, and that 

 too in certain places where such sediment would be particularly favourably 

 situated as regards preservation; and moreover, from a consideration of such 

 presumably stripped areas, the off-shore base must have been very regular. 



(2) Or (assuming that the present coastal plateau is not of marine erosion) 

 marine erosion in the canon cycle has allowed the sea to considerably 

 encroach on the elevated area, eating it back beyond the limits of the 

 " plateau cycle " shore-line. 



t A7ite, p. 789. 



I Consider, for example, the effect of marine erosion in the neighbourhood 

 of Illawarra. Here the waves have cut the land down from nothing at the 

 shore-line in early canon cycle times to escarpments 2,000 feet in height near 

 the present shore-line, the late elevation causing the sea to retreat consider- 

 ably. Here again we have a measure of the great age of the canon cycle. 



