BEACH FORMATIONS AT BOTANY BAY. 163 



A whole series of bay bars below low water mark occur 

 from 200 to 1,000 yards away from the present beach. 

 During the great storm of July 1912 these bars appeared 

 to be disposed parallel to the present beach, as evidenced 

 by the parallel lines of heavy breakers. To the casual 

 observer such bars are only apparent during great storms 

 such as those of 1889 and 1912. 



The accompanying transverse section is an attempt to 

 explain the character of the bars and swamps. 



Fig. 1. — Section across old Bay Bars along section EF on Plate VII 



E — Sand dune on old shoreline. NN — Swampy ground drained by Muddy 

 Creek. O— Small bay bar (AB on Plate VII). P—Pat Moore's Swamp. 

 Q—Long high bar (CD on Plate VII). B 1 B' 2 R 3 B i —Old bay bars. S— 

 Present line of sand dunes. P — Sea level. 



History of Area immediately prior to Formation of Present 



Beach. 



It would appear that the site of the present Botany Bay 

 was occupied in early and middle Tertiary time by hori- 

 zontally-bedded Trias-Jura sandstones and shales. In late 

 geological time a wide shallow valley was excavated therein 

 by the conjoint action of George's and Cook's Rivers, 

 which effected a junction somewhere within the area now 

 occupied by the bay. It would appear also that for some 

 reason the ocean overflowed into this stream-formed valley, 

 submerging it in places to a depth of 200 or 250 feet, as 

 suggested by analogy with neighbouring areas. 1 An 

 enormous amount of silting was then accomplished by the 



1 One of the Hawkesbury Bridge piers is sunken about 200 feet in the 

 river silt only about seven miles above the stream mouth. 



T. W. E. David and G. H. Halligan. Evidence of recent submergence 

 of Coast at Narrabeen. This Journal, 1908, pp. 229-237. T. W. E. 

 David. Anniversary Address to the Eoyal Society. This Journal 1896, 

 p. 57. 



