124 G. H. HALLIGAN. 



why it assumed its present form, and what is going on in 

 the way of sand movement at the present time. 



Plate VI shows the general trend of the ocean currents 

 on the Australian coast, compiled from the latest reports 

 and charts of the British Admiralty. A very large number 

 of observations by the author, of the southerly current on 

 the New South Wales coast, show it to have a mean 

 velocity of from one to two nautical miles per hour from 

 the shore line to at least twenty miles out. This velocity 

 varies very little with the seasons. The surface water is 

 accelerated by the north-easterly winds in the summer, 

 and slightly retarded by the strong southerly winds at 

 other seasons, but such puny forces must be practically 

 ineffectual on a stream many hundreds of feet deep, many 

 miles in width, and thousands of miles long. 



At all the salient points on the coast, from the Tweed 

 River to Jervis Bay, the littoral current is flowing to the 

 southward all the year round, and is conveying sand in 

 suspension in large quantities. 1 When this current meets 

 with an obstruction in the form of an island, a vortex is 

 formed on the lee side, and the sand is here deposited in 

 the form technically known as a banner reef. The land 

 now known as Kurnell, the historic landing place of Captain 

 Cook, was originally such an island, and the sand accu- 

 mulated on the south-western or lee side of it until it joined 

 the main land again at Oronulla. The sand having been 

 brought in by the currents was heaped up by the wind into 

 dunes varying from 20 - 130 feet in height, thus closing 

 up the southern outlet of Botany Bay, and completing the 

 first stage in the filling-up process of this area. 



1 G. H. Halligan, f.g.s., " Sand Movement on the Coast of New South 

 Wales/' Proc. Linn. Soc. N.S.W., 1906 ; also " The Bar Harbours of New- 

 South Wales," Min. and Proc. Inst. C.E., Vols, clxxxiv and clxxxv. 



