THEORIES OF ORIGIN 623 



the number or position of the cusps and their intervening spaces, but the 

 importance of initial depressions in the cusp-making process seemed 

 clearly indicated. 



On "VYestquage Beach, lihode Island, the writer has watched a series 

 of parallel "creases," or rill lines, without an}- associated cusps, develop 

 into channels or intercusp spaces with fairly good associated sand cusps. 

 Such observations are relativel}^ rare, however, probably because the 

 initial irregularities are often indistinct undulations in the beach surface 

 or are soon transformed into such undulations, and because the succes- 

 sive changes in the form of broad, shallow channels on a gravel or sand 

 and gravel beach are difficult to trace. The "ribbed" structure occasion- 

 ally reported by observers looking for cusps probably represents an early 

 stage of cusp formation. 



The tendency of intersecting or crisscross waves would be continually 

 to shift the sands first in one direction and then in another obliquely 

 over the beach, and thus to prevent the formation of systematic channels. 

 This would account for the observed failure of such waves to form beach 

 cusps, although they might attack cusps previously formed, or leave a 

 beach with irregularities which might affect the formation of later cusps. 



In a similar wa}^, to a less extent, a single series of oblique waves 

 would not seem favorable to cusp formation, because of the lateral ele- 

 ment in the movement of the water, which would continually tend to 

 wash the interchannel elevations into the channels, and so to fill them up. 



It is not necessary to review all the details of beach cusp character- 

 istics in connection with the theory set forth above. It is sufficient to 

 state that the writer has found no feature of beach cusps which is in- 

 compatible with the theor}^, while the conditions of wave action hypotheti- 

 cated appear to rest on a reasonable basis. 



Eeferences 



J. C. Beanner : The Origin of Beacli Cusps. Journal of Geology, vol. 8, 190U, 



pp. 481-484. 



: Editorial Note. Journal of Geology, vol. 9, 1901, pp. 535-536. 



Yaughan Cornish : Progressive Waves in Rivers. Geographical Journal, vol. 



29, 1907, pp. 23-31. 



: On Sea-beaches and Sand-banks. Geographical .Journal, vol. 11, 1898, 



pp. 528-543 and 628-651. 



M. S. W. Jefferson: Beach Cusps. Journal of Geology, vol. 7, 1899, pp. 237- 

 246. 



: Shore Phenomena on Lake Huron. Abstract. Journal of Geology, 



vol. 11, 1903, pp. 123-124. 



: On the Lake Shore. Normal College News, vol. 3, October, 1905. 



