184 E. C. ANDREWS. 



the waves break, nevertheless, upon the smoothest beach 

 known such undulatory movement of breaking waves must 

 give rise to fairly evenly spaced cusps if only such beach 

 profile be not adjusted to the wave strength, and if there 

 be not present a heavy on-shore wind coming obliquely on 

 to tbe beach and driving the waves alongshore. Once the 

 operation is started the interfering waves in their return 

 down the beach cut out slight depressions. After a time 

 such action brings about an aggradation of that portion of 

 the shallow water opposite to the intercuspate hollow or 

 furrow, and from this material built up under the water 

 the breaking waves are deflected to right and left, where 

 again, by the onrush of the deeper water opposite the cusp, 

 it is swirled into the furrows and thence in part reflected 

 on to the cusps. At the heads of such interfering pulses 

 in the furrows the water, at a later stage of cusp formation, 

 is again pulsed either straight ahead to spread out like a 

 fan or it is pulsed right and left along the beach both in 

 front of, and across, the advance of the main wave front so 

 as gradually to shift the cusp axes. A common feature 

 associated with decreasing wave-strength at this stage is 

 the partial aggradation of an intercuspate space and the 

 reflection of the undulations on to a cusp so as first to 

 reduce the cusp to a broad triangular facet and secondly 

 to a double cusp. 



Cusps will be formed by waves of all descriptions except 

 those which determine the main beach outlines. This 

 reasoning is really only appreciable to the case of waves 

 known as swells. With very heavy crosswinds evenly 

 sloping but cuspless beaches are commonly formed because 

 the regular undulatory nature of the movement is over- 

 come on the beach by the action of the crosswinds (and the 

 currents thus induced), the cross waves from which chase 

 each other irregularly along the beach and obliterate any 



