618 D. W. JOHKSON BEACH CUSPS 



the shoreline at every conceivable point. This done, the supposed reason 

 for cnsp formation disappears. 



It has been shown on preceding pages that the physical conditions 

 necessary for cusp formation exist in parallel waves. One might accord- 

 ingly surmise that in intersecting waves the necessary equilibrium would 

 be destroyed and the formation of cusps rendered more difficult, or even 

 impossible. I believe this to be the case. In 1907, while camping near 

 Huletts Landing, opportunity was afforded to make numerous observa- 

 tions during a period of six weeks, on a portion of the lake shore where 

 intersecting waves were usually developed by a sand and gravel bar off- 

 shore. At no time were cusps observed on the portion of the beaqh 

 where intersecting waves arrived, although they were frequently found 

 on adjacent portions. These observations led to the belief that inter- 

 secting waves tend to prevent rather than to cause the formation of beach 

 cusps. 



WILSON'S THEORY 



Inasmuch as the "cusplets" described by Wilson appear to be true 

 beach cusps of somewhat unusual form, it is proper to consider the 

 hypothesis offered to account for their origin. According to this author, 

 evenly spaced waves striking a straight shoreline at an oblique angle will 

 give evenly spaced points of wave breaking at which cusps will develop. 

 Because at any given instant a series of oblique waves will be breaking 

 at a number of different points along a beach, the author assumes that 

 the points of simultaneous wave-breaking will be nodal points where 

 material will tend to accumulate. It would appear that no account is 

 taken of the fact that every oblique wave of the series breaks not only 

 at the point observed during a given instant, but also at all the other 

 points up and down the beach, so long as the wave exists. The point of 

 breaking of an oblique wave sweeps along the shore until the end of the 

 wave itself is reached. In a series of waves parallel to each other, but 

 oblique to the shoreline, each wave in turn breaks continuously from one 

 end of the beach to the other. Under these conditions no nodal points 

 can develop, and the fact that the waves are a given distance apart, and 

 that at any given instant their points of contact with the shore are evenly 

 spaced, is immaterial so far as the distribution of force of wave attack is 

 concerned. 



In addition to the theoretical objections to Wilson's theory must be 

 added the observed fact that oblique waves appear to be much less favor- 

 able to cusp formation than are waves parallel to the shoreline. Oblique 

 waves have been observed in the process of cliffing the sides of cusps ex- 



