166 



E. C. ANDREWS. 



significance of these and allied features, the writer made 

 a great number of observations on Lady Robinson's Beach 

 during the years 1909, 1910, 1911, and 1912. 



In Johnson's " Beach Cusps" 1 is given a summary of the 

 opinions of previous writers on this subject. Johnson 

 himself explains the origin of the scallops as follows: — 2 

 "Selective action by the swash develops from initial 

 irregular depressions in the beach shallow troughs of 

 approximately uniform width whose ultimate size is pro- 

 portional to the size of waves, and determines the relatively 

 uniform spacing of the cusps which develop on the inter- 

 trough, elevations." 



Fig. 2. — General appearance of Lady Robinson's Beach before gale 



ofJuhj 1912. 



Vaughan Cornish 3 in " Sea-beaches and Sand-banks" 

 discusses the profile of equilibrium for the beach, and 

 mentions that the greater the wave, the greater the 

 strength of the back-flow. " In a given locality, the 

 regimen slope of beach proper to a rough sea is not so steep 

 as that for a quiet sea." 



"As the size of the breakers increases, the wash tends 

 to make the slope less steep. Neither the force nor the 

 resistance are absolutely uniform along the shore, so that 

 this action commences at selected places. From the 

 moment that even the shallowest grove is thus formed, the 

 backwash finds its way to sea almost entirely by this path. 

 The discharge of the breaker continues, however, to send 



1 Bull. Geol. Soc. Am., Dec. 1910, p. 590. 8 Ibid., p. 620. 

 3 Jour. Royal Geol. Soc, 1893, p. 536. 



