608 D. W. JOHKSON BEACH CUSPS 



by small waves may be less than 10 feet apart, while those built by large 

 storm waves may be 100 feet apart. 



Jefferson emphasizes the lack of regularity in the spacing of cusps, 

 whereas others have been impressed by their regular recurrence at fairly 

 uniform, intervals. Inasmuch as the matter of spacing is of vital impor- 

 tance in any discussion of the origin of these forms, we may examine it 

 somewhat carefully. Jefferson writes (1899, 238) : "The constant recur- 

 rence of bay (intercusp space) and point (apex) as one walks along the 

 beach suggests that there is a regularity in the width of intervals. This 

 is not so, however, on Lynn Beach, as appears from the diagram, meas- 

 ures from point to point along the beach being 21, 20, 18, 16, 22, 17, 6, 7, 

 and 22 paces. Fainter cusps farther south toward Nahant show similar 

 irregularity. It might be said, however, that on Lynn Beach they are 

 commonly about 20 paces wide." And again (1905, 10) : "In a view 



Figure 5. — Beach Cusps (after Jefferson) showing compound Cusps 



along the beach these unevennesses are foreshortened into the appearance 

 of points of sand or gravel known as beach cusps. They are less even 

 than they look.'^ In still another connection (abstract of paper pre- 

 sented before the Geological Society of America at the Boston meeting, 

 1909) he says: "Perspective foreshortening gives them a fictitious ap- 

 pearance of regularity." On the other hand, Shaler (164) speaks of 

 their "orderly and uniform succession," and it has seemed to me that the 

 degree of regularity in spacing is so great as to be incompatible with cer- 

 tain of the proposed theories of origin. 



It is true that measurements of the spaces do not always give exactly 

 the same figure; that in the early stages of development a greater degree 

 of irregularity prevails than later on, and that even where cusps are very 

 perfectly developed, occasional aberrant features obscure the regularity 

 of spacing. Nevertheless, a large number of observations of beach cusps 

 in all stages of formation and destruction and the production of arti- 

 ficial cusps in the laboratory have convinced me that a fairly high degree 



