BY E. C. ANDREWS. 817 



(b) Bondi. — During the Post-Tertiary oscillation of subsidence 

 South Head was converted into an island, a long passage con- 

 necting sea and harbour by way of Bondi and Rose Bay. The 

 dominant along-shore current brought sand and waste lost to the 

 Waverley clitts into the gap; and a bar was quickly formed in 

 the passage. The dominant wind has free play at Bondi, and the 

 bar was quickly piled up above the waves by the heavy wind. 

 Several old shore-lines were formed in this way as the bar grew 

 seawards, with shallow troughs between the old beaches. Silting 

 took place in the blocked passage on the harbour side, and in 

 course of time a shoal whs formed above water at low tide. The 

 recent movement of elevation converted the shoals and shore- 

 lines into dry land, and the dominant southerly wind piled up 

 huge sand dunes on the former beach-lines and shoals. 



It is probable that the sea is even now encroaching on its 

 former work. In that case peat or allied material which once 

 grew in the troughs between the successive shore-lines will be 

 exposed on the beach during storms. 



An interesting problem in structure is suggested by a study of 

 Bondi. 'J'he underlying sand masses represent tide and marine 

 current action; the long curving and now buried beach-lines 

 represent wind-action; while the present masses of sand dunes 

 under which the marine sediments are buried also are wind- 

 blown. It may be possible that many areas in the Hawkesbury 

 Sandstone may represent closely related sea and wind action. 

 The writer intends to present a short note in the near future on 

 the structure of the Triassic Sandstones of Sydney. 



(c) Manly. — North Head also was converted into an island 

 during the recent movement of subsidence. As for the present 

 flat on which Manly is situated, it will be evident at once that 

 its seaward aspect does not face the dominant wind, and that it 

 is screened also in great measure from it as it sweeps across the 

 harbour. 



The heavy waves battered North Head, and produced great 

 quantities of sand, which were swept northwards by the dominant 

 current. In a minor degree also the gentler current from the 



