176 



WORK OF THE OCEAN 



ments to which they give rise (i) wear the shores, (2) transport 

 the products of wear, and (3) deposit the transported materials. 



Erosion. In the dash of the waves against the shore, the wear 

 is effected chiefly by the impact of the water and of the debris which 

 the water carries, but lesser results are accomplished in other ways. 



When the land at the margin of the water consists of uncon- 

 solidated material, or of fragmental material but slightly cemented, 

 the dash of the water is sufficient to displace or erode it. If weak 

 rock is associated with resistant rock within the zone of wave-work, 

 the removal of the former may lead to the disruption and fall of the 

 latter, especially when weak rock is washed out from beneath strong. 

 The impact of the water is competent also to break up and remove 

 rock which was once resistant, but which has been weakened by 

 weathering. Rock affected by joints is attacked with success, for 

 the blocks bounded by joints may be loosened and quarried out. 

 Waves of clear water, even when their force is very great, have little 

 effect on rock which is thoroughly solid. 



The effect of the impact of the waves is generally increased by 

 the detritus they carry. The sand, the pebbles, and such stones 



Fig. 1 79. Angular blocks of rock, fallen from the cliff above, as a result of under- 

 cutting by waves; Grand Island, Lake Champlain. 



