BY E. C. ANDREWS. 819 



entrance to the Harbour would have been speed il}^ Ijlocked up as 

 the Manly Channel has already become. 



(2). The products of marine erosion will in time to come be 

 borne along shore from the cliffs between Sydney Harbour and 

 Botany Bay, and distributed to form a huge wing-like bar curving 

 north and west from South Head. Beaches also will probably 

 then exist under the cliffs. 



(3). The streams which flow into Port Jackson are insignificant 

 (owing to the former piracy by the Hawkesbury), and possess 

 very little loads in time of flood. The action of these tiny 

 streams will be to gradually silt up their own salt-water channels 

 first, the time being far away when they can seriously affect 

 harbour navigation. 



(4). It will be remembered that the Hawkesbur}^ developed a 

 lengthwise course which,- running north and south but a short 

 distance west of Sydney, captured the headwaters of the other 

 consequent streams. Here then we see the beneficial effects of 

 this stream piracy on the commercial aspect of Sydney Harbour, 

 since otherwise its streams would be possessed of considerable 

 loads, the action of which would be to rapidly silt up the water- 

 way. 



Thus, briefly, it owes its importance to its steep off-shores, and 

 the absence of considerable streams discharging either into it or 

 into the sea immediately to the south. 



(e) Botany Bay. — The huge sand flats and dunes skirting this 

 bay are additional instances of the operation of forces discussed 

 in connection with Sydney Harbour. 



1. Kronulla Beach faces the dominant wind, and encroachment 

 on the bay is shown by the rapid accumulation of huge sand 

 dunes during south-east storms. 



2. Lady Robinson's Beach is a magnificent example of a series 

 of parallel bay-bars formed at the head of the bay. During the 

 movement of subsidence the waste brought down by George's and 

 Cook's Rivers, as also in large measure that swept into the bay 

 by along-shore transportation, silted up the bay in part, and 



