BEACH CUSPS 707 



appearing almost parallel. "The cusps may constitute the serrate 

 seaward side of a prominent beach ridge, or may occur as isolated 

 gravel hillocks separated by fairly uniform spaces of smooth, sandy 

 beach. They may be sharply differentiated from the rest of the 

 beach, or may occur as gentle undulations of the same material as 

 the beach proper, and so be scarcely discernible as independent 

 features." "A cusp may rise from an inch or less to several feet 

 above the general level of the beach. Alany are relatively low and 

 flat, others high and steep-sided. Sometimes the highest part is 

 comparatively near the apex ; at other times the highest part is far 

 back, and from it a long, sloping ridge trails forward toward the 

 water. As a rule, the cusps a])i)ear to point straight out toward 

 the water — that is, the axis of the cusp is at right angles to the 

 shore line — and neither side of a cusp is steeper than the other, ex- 

 cept where oblique, wind-made waves have eroded one side only." 

 (Johnson-i6 : (5o5-(5od.) The material of the cusp varies from the 

 finest sand to the coarsest cobblestone, there being no necessary 

 relationship between the size of the cusp and the size of the material 

 composing it. Gravel cusps are often found on sandy beaches, the 

 cusps being always built of the coarser material of the beach. In 

 size cusps vary from a length of 8 or 12 inches to 30 feet or more. 

 The distance between cusps, measured from crest to crest^ ranges 

 on small ponds from less than a foot to two feet or more. On sea 

 beaches they may be less than 10 feet apart, while those built by 

 large storm waves may be 100 feet apart. The spacing is fairly 

 regular, though in some cases there seems to be irregularity in 

 spacing, as shown by Jefferson. ( Johnson-i6.) Compound cusps 

 are also occasionally formed. 



Various theories have been propounded to explain the origin 

 of beach cusps ; for a review of these the reader is referred to the 

 paper by Johnson, w^here a reference to the bibliography is also 

 found. Johnson's theory, and the one best supported by the facts, 

 is, concisely stated, "that selective erosion by the swash develops 

 from initial, irregular depressions in the beach, shallow troughs of 

 approximately vmiform breadth, whose ultimate size is proportit)nal 

 to the size of the waves, and determines the relative uniform spac- 

 ing of the cusps, wdiich develop on the intertrough elevations." 

 (16: 620.) 



Fossil Beach Cusps. Beach cusps on old shore lines are known 

 especially from the Medina sandstone of western New York. They 

 were described by Gilbert (12) as giant ripples, but, as suggested 

 by Branner (3) and by Fairchild (7), they are undoubted examples 

 of ancient beach cusps. The spacing of these cusps varies from 



