THEORY AS TO ORIGIN OF CURRENT CUSPS. 403 



stnaller currents revolve in the reverse direction to that of the great cir- 

 culation. Eddies of this kind are appropriately called backset eddies. 

 When more waste is supplied than the on and offshore components of 

 the total sea action can spread over the bottom, the alongshore compo- 

 nent will deposit it where it encounters dead water or water moving with 

 less velocity than the current itself. In a backset eddy system of circula- 

 tion such comj)aratively dead water will occur where the alongshore 

 currents curve from the shore toward the deep sea. Slight inequalities 

 of outline in the newly born land may break the backset current into 

 eddies of varying radius of curvature. Between such eddies there would 

 be formed a triangular space of comparatively dead water, in which the 

 growth of a cusp might be expected. Given the backset eddies and the 

 inequalities, or even a straight shoreline, and cuspate forelands at least in 

 outline could be formed, for a detritus- laden current must deposit the 

 surplus of its load along its margin where it comes in contact with quiet 

 water. 



COMBINATIONS OF CURRENTS. 



There are three possible pairs of currents which might produce cuspate 

 forelands upon the outer shoreline : First, both currents flow toward the 

 land ; second, both currents flow toward the water ; third, one current 

 flows toward the land and the other toAvard the water. 



The first will not cause a cusp unless the currents come to the land 

 laden with detritus, or else one or both of the currents be reversed for a 

 portion of the time, bringing out waste from the land. 



Mr Gilbert figures a V-bar on the Bonneville shoreline, where both the 

 currents seem to have flowed from the land.* He says : 



"All that I could observe in the case of the fossil shores was the direction of the 

 net movement, and where I found no evidence on that point I drew no arrows. The 

 evidence consisted of difference in size of pebbles, difference in amount of round- 

 ing, and difference in height of embankment. I remember that in case of figure 4, 

 for example, the right-hand Umb of the V is a foot or two higher than the left-hand, 

 and this feature was so often found associated with other evidence of transportation 

 in the direction indicated by the arrows that I may possibly have used it in some 

 cases without the other evidence.'' f 



There is probably movement in both directions along all forelands at 

 different times and the form shows in which direction the dominant 

 movement has taken place. The dominant movement may not always 

 correspond to the prevailing movement alongshore. A few severe storms 

 causing a strong current from the right during one month might deter- 



* Monograph I., U. S. Geological Survey, p. 58, pi. vii, figure 2. 

 t Letter to writer. 



