132 ACTION OF THE WAVES AND OF TIDES. 



parts of the world : we have famous examples from the mouths of the Scheld 

 to the canal of Jutland, where the Bies-Bosch, the Harlem sea, the Zuyder- 

 Zet, the Dolhirt, have been produced in the extraordinary irruptions of the 

 ocean ; where numerous changes have taken place in the islands, from the 

 Texel to the mouths of the Elbe, in the windings of Lymfiord, or on the 

 coasts of the Cuttegat and of the Baltic : immense cuts, bays, and deep 

 gulf*! are formed during tempests, and these are still daily forming by the 

 ordinary action of the waves, which sometimes carry away banks of sand, 

 and sometimes destroy the dykes they had already formed. 



22. The action of waves is not confined to moveable soils, but 

 takes place on the most solid rocks ; and hence those daily modi- 

 fications in the enormous precipices found on the coasts of France, 

 England, and almost all parts of the world. The more abrupt the 

 coast, the more it is exposed to denudation from the waves, because 

 directly breaking them, the shock is felt in all its force. On flat 

 coasts, on the contrary, the wave meeting with no obstacle, ad- 

 vances as long as its force lasts, and until its rapidity is sensibly 

 lost ; and it carries up in sand and pebbles much more than it 

 destroys, even on the most moveable soils. The natural disposi- 

 tion of solid beds is sometimes opposed,' and at others favourable 

 to the action of waves ; it is opposed when the beds, being uniform 

 and homoge"neous, incline towards the sea ; because the return of 

 the wave along the slope or ta'lus diminishes the action of the suc- 

 ceeding wave, the remaining force of which is spent in merely 

 ascending the plane: the waters are spattered only by the crevices 

 and fissures that may exist in the rock. But the same is not the 

 case when the soil presents an escarpment to the action of the 

 waters (Jigs. 211, 212): the lower parts, continually attacked by 



*''*2S^??=^ 



Fig. 211. Fig. 



Action of waves on abrupt rocks. 



reiterated shocks of waves, which nothing contributes to diminish, 

 are degraded and excavated successively, and with a rapidity in 

 proportion to the facility with which the substance is disaggregated ; 

 the upper beds being soon undermined, are not long in being pre- 

 cipitated into the sea. In this way considerable portions of coast 

 have been overturned at different times, promontories have disap- 



22. Are all coasts equally subject to the action of waves. What circuia- 

 lances diminish the effects of the action of waves ? 



