THE PHYSIOGRAPHY OF BOTANY BAY. 123 



Second, all borings taken on the stippled area shown on 

 the maps show clean white sand from the present shore- 

 line to the original highwater mark, and this obviously 

 could not have been carried down the rivers during flood 

 time, for, had it been so carried, traces of alluvium would 

 appear, and the flats would consist of good soil in place of 

 the present hungry sand, which supports only the hardiest 

 vegetation. 



Third, the disposition of the sand is not such as would 

 indicate the deposits of sluggish streams in salt water, as 

 will presently be shown. 



In this the author is at variance with the views expressed 

 in a paper recently presented to this Society 1 in which it 

 is stated that this accumulation of sand is due to the 

 "enormous amount of silting accomplished by the action of 

 George's and Cook's Rivers when in flood." 



It is obvious that the sandy deposits in any estuary must 

 be due to one of two causes. Either they must have been 

 brought down from the watershed area of the inflowing 

 rivers during floods, or they must have come in from the 

 sea shore by the action of currents. If the sand comes 

 from the uplands it will be mixed with alluvium and will 

 tend to form flats more or less muddy, and such flats do 

 not exist on the shores of Botany Bay except near the 

 mouth of George's River. In this particular locality, the 

 mud is due to the flood waters of the river depositing its 

 small load of alluvium, washed down from the hills in the 

 immediate vicinity, where the current is checked by meet- 

 ing the still waters of the bay. The deposit is compara- 

 tively small and is largely mixed with sea sand. 



It now remains to be shown how the sand, indicated by 

 the stippled area on Plate V, was brought in from the sea, 



1 E. C. Andrews, b.a., p.g.s., "Beach Formations at Botany Bay/' this 

 Journal, Vol. xlvi, p. 163. 



