TIDAL CUSPS. 411 



The type of current cuspate forelands has been given as the Carolina 

 case where the cuspate form is so marked and well known. The hy- 

 pothesis of backset eddies from the Gulf stream, here presented as the 

 mode of origin, may not be so well known and may require confirmatory 

 proof. This hypothesis is not given as the only one for the origin of all 

 current cuspate forelands, though it is the only one here considered in 

 extenso. Two other possible combinations of currents have been pointed 

 out, and several different causes may originate the currents in different 

 places. 



Tidal Cusps. 

 location and description. 



In regions of drowned valleys, long inlets, or narrow sounds, where the 

 two opposite shorelines are roughly parallel to each other, cuspate de- 

 posits of sand frequently occur when shore evolution has reached an 

 adolescent stage of development and transportation alongshore has begun. 



These forelands usually project from one-quarter to three-quarters of a 

 mile into the sea and vary in breadth between the same limits. In some 

 cases the cusps are long and narrow, while in others they are short and 

 broad. Frequently the}^ inclose, more or less completely, lagoons but in 

 some instances there is no included water body or if there was one it 

 has become filled. The curve of the two outer edges of these deposits 

 is concave toward the water and is a continuation of the curve at the 

 base of a shore cliff. These two concave curves intersect in a marked 

 cusp which is sometimes typically pointed, though in other cases the 

 tip is rounded. The axis of these forelands projects approximately at 

 right angles to the shoreline and also at right angles to the general direc- 

 tion of the tidal currents in the inlets. 



TYPE. 



West point, north of Seattle, Washington (figure 5), will be taken as 

 the type, and, after giving its description and discussing the method of 

 its formation, others difi^ering in details of form will be considered. Mag- 

 nolia bluff, two miles northwest of the city of Seattle, has a gently swing- 

 ing curve doubtless quite satisfactory to the current here prevailing. 

 This curve continued forms the right boundary of the West point cusp. 

 The curve on the left side of the foreland is in like manner a continuation 

 of the curve of another cliff (C. S., 658 ; G. S., Seattle). On the inside of 

 the cusp there is a faint cliff where the coast was nipped after the initial 

 drowning. The central lagoon is nearly all converted into marsh, a small 

 tidal inlet remaining on the left side with a few small ramifying branches. 



