244 MARK S. IV. JEFFERSON 



out on the beach, and only a steady trickle of water draining 

 out of the ridge of stones and seaweed remains, in place of the 

 violent rushing at high water. The contact of the delta cusps 

 with the flat beach is now disclosed, and we see the cobbles 

 already referred to strewn along the margin of the cusps (Fig. 

 5). The view is taken from a point on the edge of the flat beach 

 itself and shows only the delta cusps, the residual cusps lying 

 off farther to the left. The cobbles have probably come down 

 the bays in the rushing streams that build the deltas. They are 

 scattered quite at random at the foot of the delta slopes, as 

 indicated in Fig. 2. The advancing waves of the next tide will 

 doubtless drive some of them up the promontories on which the 

 earlier waves are concentrated by the delta cusps. 



But if the establishment of bays in the ridge of cobbles is 

 to be ascribed to the great waves, the part of the ordinary wave 

 is not therefore to be neglected, nor the waves of lesser tides so 

 long as they send the water at all into the region affected. The 

 ordinary waves intensify the form given by the gaps in the sea- 

 weed. Across the beach below all waves advance in long, even 

 lines. As these come to the delta cusps their front is broken 

 into tongues which are concentrated into the outer bays and 

 made to impinge on the residual cusps in advance of the water 

 which comes to the inner line of bays. Of all the details of the 

 wave-work, this is one of the best established. As the wave 

 thus concentrated on the stony promontories tries to surmount 

 them, it is more and more deflected to right and left by the steep- 

 ness of the cusps. Thus, when the wave recedes, almost all the 

 water runs down the inner bays. This was first seen at Gay 

 Head, where I have a record in photographs. The bays thus 

 have a preponderance of seaward scour. On Lynn Beach this 

 point was studied by gathering bricks along the shore and throw- 

 ing them in front of the points of the stony promontories. Of 

 twenty bricks cast into the sea where the two fans meet in Fig. 

 3, corresponding to the second stony point from the left in Fig. 2, 

 one went across into the bay alongside with the next incoming 

 wave; then a great wave brought all over the ridge of seaweed. 



