BEACH FOKMATIONS AT BOTANY BAY. 179 



curves sheltered by the small cuspate forelands, well marked 

 cusps were formed. 



August 4th. — After and during period of westerly winds. 

 Smooth to glassy sea inshore. Strong pulsing movement 

 of water on beach. Low ledge (12 to 18 inches high) formed 

 at low tide mark. Pulses formed here by breaking move- 

 ment. Undulations thence carried out seaward by inter- 

 ference of backwash and of advancing pulse. No cusps 

 noted on beach at low tide and middle tide marks. High 

 water mark on beach marked by poorly defined cusps 

 becoming less defined each day, while beach profiles 

 becoming gradually more even. 



August 10th and 11th. — Very calm weather. Westerly 

 wind. Bank of sand just under water at low water mark 

 with front slightly convex and indented on the seaward 

 aspect, matching the weak cuspate forms of high tide mark 

 on beach. Beach cuspless, except at upper limit of waves. 

 Oily water of bay fell or broke on the edge of this sand- 

 bank or ledge (at low water mark) and advanced in pulse 

 fashion up beach. Pulses interfered with each other and 

 at their upward limit on the low tide beach, the wave front 

 presented appearance of countless small sets of interfering 

 wavelets in plan like so many overlapping circular arcs of 

 equal size. These small interfering pulses formed sets 

 which again interfered with each other at spots approxi- 

 mately on same axes as those of the imperfect cuspate 

 forms higher up the beach. 



August 12th - 16th. — Fairly strong winds from south-east 

 quadrant. Large cusps produced. Broad hard beach. Two 

 sets of cusps formed later, one seaward of the other. 

 Between these forms cuspate depressions formed which 

 gradually became filled by waves under heavier weather 

 conditions. 



