70 Notices of Me^noirs — W. S. Wheek*' — Waves and Tides. 



I. — The Action of Waves and Tides on the Movement of 

 Material on the Sea-coast. By W. H. Wheeler, M.lnst.C.E., 

 Boston, Lincolnsliire.^ 



THE object of this paper is to show the relative effect of waves 

 due to wind and tidal action on littoral drift. It is pointed out 

 that all cliffs that border the sea-coast are doomed to erosion, and 

 the material derived from their destruction, after being sorted and 

 prepared by waves and tidal action, is conveyed to the depths of the 

 sea. The function of wind waves is to break down the cliffs, to sort 

 the material displaced, and to reduce the larger rock fragments into 

 sizes sufficiently small to be acted on by the tides, and to disperse 

 material that has been collected in large masses by tidal action. 

 The function of the tides consists in raising the water of the ocean 

 sufficiently high to enable the waves to attack the cliffs, in assisting 

 in the grinding up of the reduced rock fragments by their perpetual 

 oscillating motion until sufficiently reduced in size, and then in 

 transporting them to the bed of the sea, the latter operation being 

 effected either in solution, suspension, or rolling along the bottom. 



It is shown that all material eroded from the cliffs is ultimately 

 carried seaward, and that the sea yields nothing to the land. The 

 only agents capable of transporting material of greater specific 

 gravity than the water are the waves, and their action, until they 

 break on the shore, is merely one of undulation ; and therefore it is 

 only the stones, shingle, or sand which lie shorewards of the point 

 where the wave breaks that can be carried forward on to the beach. 

 On the other hand, the slope of the beach being seawards, all 

 material has a natural tendency to work downwards under the 

 action of gravity, this downward action being aided by the undertow 

 of the retiring shore waves. 



Material eroded from the cliffs consists of rock fragments, boulders, 

 sand, and alluvium. The alluvium, consisting of particles of 

 sufficient minuteness to remain in suspension for a considei'able time, 

 is diffused by the waves over a very considerable distance, and is 

 finally deposited in the deep part of the ocean ; the sand is gradually 

 "worked down the beach by the action of the waves and tides, and is 

 also spread over the sea bed, but nearer to the shore ; the rock 

 fragments are reduced to shingle small enough to be acted on by the 

 tides, and in this condition are rolled np and down the beach and 

 drifted along the coast until ground into particles sufficiently fine to 

 be transported to the sea. Shingle is generally accumulated in banks 

 in the zone lying between low-water of neap tides and high- water of 

 spring tides, and travels along the coast in one given direction. 

 The heaping up and travel of the shingle is due to tidal action. 

 The effect of wind waves due to gales is principally destructive to 

 shingle banks, cutting out and dispersing the material, the banks 

 being restored by tidal action in calm weather and during offshore 

 winds. The action of waves due to wind is intermittent, variable 

 in direction, and irregular. The travel of shingle, except when acted 



^ Eead before Sect. C (Geology), British Association, Bristol Meeting, Sept. 1898. 



