Hunt — On the Action of Waves on 8ea-beaches, ^c. 267 



jBnd our fine sand replaced by coarse sand and stones, up to the 

 largest masses the waves can carry forward ; whilst at the same 

 time our mud will be replaced by sand, and stones sufficiently 

 small to remain within the grasp of the water. 



So far we have seen that the plunge, by supplementing the 

 action of the forward current, causes the latter to accumulate sand 

 or stones in front of it ; in other words, to form a sloping beach. 

 But the moment a slope is formed, an opposite or counteracting 

 force is brought into play, viz. gravity, which gravity vdll tend to 

 cause the accumulated material to roll seaward again. We thus 

 see that the beach-slope, so far as we have considered it, is a com- 

 promise between the action of the plunge tending towards the 

 piling up of the beach-material, and the action of gravity which 

 tends to pull it down, the agents being the forward current + plunge, 

 on the one side, versus the backward current + gravity on the other. 

 This is practically the normal state of things on a flat, sandy 

 beach, where the sand is fine and easily saturated. Where the 

 sand is coarse, or the beach-material is shingle, another factor in 

 beach-making is brought into play, viz. the absorption by the shingle 

 of the whole or a portion of the water of the backward current above 

 the level of repose for the time being. In this case we may consider 

 the forces acting on the beach above the level of repose to be : — The 

 forward current + plunge, versus the backward current + gravity 

 - absorption ; or, the forward current + plunge + absorption, versus 

 the backward current + gravity. 



It will be noted that the absorptive power of the shingle in- 

 creases gradually from the margin of repose, where it is nil, owing 

 to the shingle being saturated, to the point of furthest reach, where 

 it may be perfect ; and that absorption alone would suffice to ac- 

 count for a gradually increasing curve in the profile of a beach 

 above the margin of repose. Such a curved profile is often present 

 at and above high -water mark, where the waves attack the shingle 

 at or about the same level for an appreciable time at the turn of 

 the tide ; and more especially is it a feature of spring and neap 

 tides, at both of which times there is not much difference in the high 

 water-level for several successive tides. So far as my observations 

 go, this absorptive action on the part of the beach-material is 

 essential for the formation of the phenomena known as " Fulls," 

 " Eidges," and " Sets-off." With absorption these will occa- 



