BEACH FORMATIONS AT BOTANY BAY. 



171 



profile convex to sky. This lower convex portion beauti- 

 fully scalloped with cusps. 



During the night a heavier wind had sprung up and piled 

 up the sand seaward of the ledge especially near low water 

 mark. Towards morning the cusps had then been developed 

 under a falling wind. 



January 12th. — Tides decreasing, wind moderating, 25 

 miles an hour from S.S.E. Ledge of erosion cut in the 

 erosion bench of January 11th. This ledge front in plan 

 was notched with slight cuspate indentations possessing 

 successive widths of 20, 20, 20, 25, 25, 25, 25 paces. Cusps 

 almost absent. Breaking wave travelled along-shore from 

 N. to S. at about four or five miles an hour, while each 

 wave instead of continuously breaking approached the shore 

 line in a manner somewhat en echelon (Pig. 6), and chased 

 each other along the beach before the wind in a direction 

 as from south-east to north-west. The backwash traversed 

 the beach in successive ridges or waves running from 

 W.S.W. to E.N.E. or N.E. forming cusps in the beginning. 



Fig. 6. — Method of wave approach on Lady Robinson' ] s Beach during 

 heavy cross winds. 

 ABC — Wave front. AB' C — Breaking line. 00 — Travel along shore of 

 breaking woive ABC. R — General direction of wave motion. B' — Direction 

 of small cross waves. R" — Direction of wind. Small cross bars along ABC 

 represent cross waves into vihich ABC vms divided. 



January 12th -24th. — About January 16th a "black 

 nor'easter" (gale) obliterated all cusps. Breakers travelled 



