WA VES. 43 



of open material, such as shingle, a large proportion of the run 

 of the waves must be absorbed by filtration, so that stones being 

 borne along or thrown forward by the waves are deposited 

 as the water recedes, the volume, and consequently the power, 

 of the drawback being greatly diminished. Possibly this may, 

 in some measure, account for the slopes of shingle beaches, 

 especially near the top, being so steep as they often are. 



