BEACH FORMATIONS AT BOTANY BAY. 185 



regular beach markings. Such beaches have ledges for 

 their upper limits. 



Summary. 



Lady Robinson's Beach appears to be of recent age (say 

 several hundreds of years) and has been developed upon 

 the seaward aspect of older and elevated bay bars which 

 were formed by storm wave action in an old river valley 

 after the transgression of the sea into the valley during a 

 period of rapid land submergence in late Pleistocene time. 

 During record storm action the interaction of alongshore 

 currents, waves, tides and river flood activities, determined 

 several small salients along the present beach. In periods 

 of heavy storms the beach is wide, smooth, of gentle 

 inclination and raised as to its central portion. With 

 decreasing wave strength the beach is cut into cusps by 

 the interference of undulations produced at the breaking 

 line and such cusps are a temporary phase in the production 

 of one regular beach form out of another. 



A study of the beach and the associated beaches and 

 cliffs (as also those of more northern portions of the Eastern 

 Australian Coast) suggests that the present shoreline is in 

 a condition of fairly stable equilibrium, such equilibrium 

 not appearing to have been upset for perhaps several 

 hundreds of years. 



