ON THE ACTION OF WAVES. 449 



not abrade the surface when it acts by itself. We see this 

 surface, on rocks and the sides of piers and dikes, per- 

 petually beaten by the waves, covered with fuci, con- 

 fervse, byssi, and other delicate vegetables* without roots, 

 which the waves have not prevented from contracting 

 a first and feeble adherence, and which they do not 

 hinder from growing. But, if the waves carry with them 

 pebbles, or even sand, it is those hard bodies which act ; 

 the surface of the rocks is abraded, and all vegetation 

 ceases. 



The same effect takes place, and is even augmented 

 by the real degradation of the coasts, if the sea acts up- 

 on friable rocks, capable of mixing with water, such as 

 argillaceous or calcareous marl, or chalk, or upon rocks 

 which are hard, but naturally fissured, or partly disag- 

 gregated, such as certain granites ; it then easily removes 

 the crumbled or previously detached parts, scoops out 

 the foot of the rock or steep coast, and causes the upper 

 part, which is deprived of support, to fall. But, in con- 

 sequence of this fall, it forms a slope, which, by its in- 

 clination, deadens the violence of the shock, and even 

 protects the foot of the cliff, for some time only, if it be 

 friable, or capable of disintegration ; and for ever, if, 

 being compact, it does not carry in it the causes of de- 

 struction. The action of the waves ceasing, the slope is 

 covered with vegetation ; and if the coast continues, ne- 

 vertheless, to be worn, the changes are then owing to 

 causes unconnected with the action of water. 



Such is, in few words, the ordinary action of the wa- 

 ter of the sea upon steep coasts, and even that of great 

 masses of water in a state of agitation. M. De Luc, in 

 his various works, has estimated this action with a cor- 



Ff 



