126 G. H. HALLIGAN. 



exist. As time went on, and the sand accumulated on the 

 area now known as the Botany Swamps, the sun dried the 

 surface sand and the winds heaped it into dunes, the rain 

 water filled the hollows, and the floods maintained a tortu- 

 ous channel from lagoon to lagoon. In latter years dams 

 were erected across this channel and the water impounded 

 in them was used for many years as the sole source of 

 supply for the Oity of Sydney. 



The patches of black, indurated sand occasionally met 

 with on this area, are the result of many years of growth 

 and decay of aquatic plants on the swampy areas between 

 the dunes. The carbonaceous soil thus formed consoli- 

 dated, under pressure of the sand blown in from the 

 surrounding dunes to fill up the old swamp, into the familiar 

 indurated black sand which is to be found on similarly 

 formed country from Queensland to Twofold Bay. 1 



As the northern part of the area referred to became 

 filled up, the ratio between the area of the tidal compart- 

 ment and the entrance width became less and the area of 

 still water decreased. The southerly and south-easterly 

 winds still created surface currents in the bay sufficient to 

 convey the sand brought in by the flood tide to the area now 

 known as Sans Souci and Sandringham, but as the amount 

 of sand brought in became less, the rate of filling up has 

 steadily decreased and, at the present time, only a very 

 small amount of sand is moving in Botany Bay below high 

 water. 



The direction of the movement may be clearly seen at 

 the Long Pier near the Botany Tramway Sheds. At this 

 point the sand has heaped up against the stone approach 

 to the Jetty on the eastern side, and has left the beach 



1 For further information on the subject of the origin of these indur- 

 ated sand beds see J. E. Carne, f.g.s., Annual Report, Dept. of Mines, 

 1895, pp. 149 - 160. 



