AQUEOUS AGENCIES. 



43 



down the land a little below the sea-level. Hence,, along 

 a shore-line which has suffered much from beating waves, 

 we are apt to find first a steep, perhaps overhanging cliff ; 

 then a level, submarine plateau ; and then, as we go far- 

 ther, a sudden falling off to deep water. In Fig. 21, the 



FIG. 21. Ideal section view of submarine plateau and shore-cliff : I, sea-level ; a, &, 

 submarine plateau ; s, present, and #', the original, shore-line. 



dotted line shows the original configuration of land and 

 position of the shore-line. Such level plateaus, termi- 

 nated by cliffs, are often found far inland. In some cases, 

 though not in all, they indicate old sea-cliffs. 



Nearly all shore-lines are receding under the incessant 

 action of waves and tides, but the rate is very different 

 in different places. As rain-erosion is concentrated on 

 certain lines, giving rise to surface inequalities, such as 

 gorges, ravines, canons, etc., so wave and tide erosion 

 give rise to nearly all the inequalities of coast-line. The 

 general form of continents, and their largest inequalities, 

 are doubtless due to other (i. e., continent-making and 

 mountain-making) causes ; but all the promontories, har- 

 bors, bays, etc., are due to ocean-erosion. As land scen- 

 ery is due mainly to rain and river erosion, so sea-shore 

 scenery is due mainly to sea-erosion. Every projecting 

 promontory will usually be found to consist of hard rock, 

 and every indentation is determined either by the soft- 

 ness of the rock or else by the mouth of a river giving 

 entrance to powerful tidal currents. 



Examples are found on every coast. In our own coun- 

 try the rocky shores of New England everywhere show 

 the wasting action of waves. Farther south the coast is 



