124 ALFRED W. G. WTLSON 



spine of the cusplet and up to the main beach by the more pow- 

 erful, less retarded portion of the waves — there to be rolled 

 slowly or rapidly along the long slope of the next cusplet, where 

 the process was repeated. 



The size of the cusplet in some cases seemed to be increasing, 

 but several seemed to have reached a maximum stage. Given a 

 constant material, the limit of size seems to depend upon the size 

 of the waves and their periodicity. 



These little cusps are formed during the period of a single 

 storm, or series of storms, when the waves advance in an oblique 

 direction on a previously evenly curved shore. Their forma- 

 tion and their symmetrical arrangement seem to be due to 

 two factors. In the first place, very frequently the undertow is 

 able to carry material down the slope of the beach a little farther 

 than the front of the wave can move it up, within certain limits. 

 Consequently, although some of the material moved up the slope 

 by the front of the wave lodges, some of it moves down with the 

 undertow, and a small percentage of this latter material may 

 move out beyond the zone at which the next oncoming waves 

 can move it up the beach. Hence there will be a slow but 

 gradual accumulation just beyond this line, which in time will 

 even modify the direction of the long shore currents. A 

 second and more important factor in the production of these 

 serrations along the shore is the development of nodal lines along 

 which material tends to accumulate. Where the waves are 

 advancing at an angle to the shore there will be a number of 

 waves breaking at the same time at different points along the 

 shore. As the spacing of the waves is nearly uniform, if the 

 shore line were perfectly straight, these points of simultaneous 

 wave-breaking would be equidistant from one another. On a 

 curved shore the spacing will be systematic, but the distances 

 between breaking points will not necessarily be equal. Now, the 

 undertow which flows out from one wave as it breaks will inter- 

 fere with the advance of the next following wave, if it meets that 

 wave on that part of the shore where the orbital motion is nearly 

 a straight line up the' beach. This happens very frequently 

 where part of a wave is retarded by a cusplet while the other 



