BY E. C. ANDREWS. 815 



Heads were also converted into islands by the sinking, sea 

 passages existing at Manly and Bondi. Brisbane Water, Broken 

 Bay, Botany Bay and Port Hacking (Plate xliii.) were also 

 formed by the drowning of the Hawkesbury, George's, and 

 Hacking Rivers. The tiny canons excavated in the weak coast 

 spots by the streams were also converted into such inlets as 

 Bronte and Maroubra. 



This movement of subsidence is very youthful, since the main 

 streams present the same appearance as they possessed imme- 

 diately prior to the sinking, all the salient features of the valleys 

 being determined in the earlier stages of the canon cycle. 



The movement appears to have been completed for a consider- 

 able period, as is evidenced by the characteristic hay bars of the 

 coast between Port Hacking and Broken Bay. These hay bars 

 will be more fully described when discussing the vibration of 

 elevation which succeeded the oscillation of subsidence. 



The rivers, however, still sent down their loads of sand and 

 mud, and thus commenced to fill up the magnificent series of 

 harbours formed by the drowning. The floods of the Hawkes- 

 bury silted up the lower salt-water channel, probably possessing, 

 in the earlier stages of drowning, over a hundred feet of water. 

 The dominant currents also swept the river loads and clifT' debris 

 into sheltered spots to form wide shoals. 



The sinking of the shore-line allowed the sea to advance and 

 rapidly undermine the cliffs. The movement is still youthful, as 

 may be seen by a study of the cliffs between Port Jackson and 

 Botan}'- Bay, where the 250 feet walls end abruptly in 8 to 10 

 fathoms of water, thus showing that the formation of forelands 

 and beaches in that locality is still distant in point of time. 



Recent Elevation. 



After the partial shoaling up of salt-water arms like Broken 

 and Botany Bays a slight movement or vibration of elevation 

 ensued for the coast. In the Sydney district its vertical range 

 along the shore-line probably did not exceed 10 or 15 feet. Its 

 ejQPect was to convert into dry land the shoals formed by the tide 



