160 E. C. ANDREWS. 



during the period mentioned could scarcely have been 

 deduced from a mere knowledge of wave and current action 

 as contained in the text-books. It is also evident that he 

 who would understand the origin of the so-called beach 

 " cusp" or scallop must understand the origin of the beach 

 itself. 



Thesis. 

 The beach cusp is a form due to the interference of water 

 undulations or pulses, and is a temporary feature illustrating 

 the methods adopted by water undulations either in excav- 

 ating or in building one beach adjusted to their own strength 

 out of another beach not adjusted to their strength. 



Physical Features of Botany Bay Locality. 



The main features of Botany Bay and district are shown 

 on the accompanying map (Plate VII). The maximum 

 width of the bay is between five and six miles, and the 

 maximum length is about eight miles. The heads connect- 

 ing the inlet with the South Pacific Ocean are about 1,500 

 yards wide at the narrowest point. Lady Robinson's Beach 

 has a length of five miles. It consists of several large flat 

 curves facing the heads. Sandy forelands compose the 

 northern and southern extremities of the beach and the 

 beach itself stretches uninterruptedly from the two tidal 

 streams of George's and Cook's Rivers which discharge 

 into Botany Bay. Of these, the former is by far the larger 

 stream, but each for miles above its point of discharge into 

 the bay is tidal, and it is doubtful whether the fresh-water 

 content of these streams is ever as important as that of 

 the tidal stream. 



The bay is shallow, a maximum depth of about fourteen 

 fathoms occurring between Oape Banks and Point Solander. 

 About three fathoms is the average depth. The spring 

 and neap tides have vertical ranges of 5 feet 6 inches and 

 3 feet 8 inches respectively, with a maximum and minimum 



