MARINE INDENTATIONS 15 



into a pebble. With each backward mo\e of the rctreatiiT''- 

 splash it is drawn away from the sea-marg-in, to return with 

 the next surge. With every successive advance and retreat 

 it may journey onward for the chstance of a few feet, and 

 so. wearing at every stroke of the wave, it moves on. A 

 large part of these rolling- stones wear out before they attain 

 the greater beaches. 



Before we follow the waste from the point where it is 

 made into pebbles and sand to the part of the shore where 

 we have characteristic beaches, we must return to the cliff 

 section to consider many interesting details of the work which 

 is done there by the waves, tides, and the many other elements 

 of activity which operate in this singular part of the great 

 laboratory of nature. All who are familiar with the rock- 

 bound coasts which are much worn by the waves, have noticed 

 the fact that the materials are very irregularly eaten away ; 

 rarely indeed is the escarpment of the cliff anywhere near 

 a straight line : it is generally deeply indented by sharply 

 re-entering little bays, and not infrequently presents cavern- 

 like openings which penetrate a considerable distance into the 

 clifT. By carefully noticing the conditions exhibited by the 

 face of the precipice at the level where the waves attack it, 

 or, if occasion favors, by examining what takes place in times 

 of storm, we may see how these depressions are formed. At 

 each of these sea-caves, or other indentations, we generally 

 find that there is some structural feature which weakens the 

 rock, so that it is more easily worn out by the waves. Some- 

 times there are several lines of open joints which part the 

 rock and enable the surees to lift the frafjments from their 

 bedding places. Again, where the strata have been turned 

 on edge, there may be here and there soft beds which yield 



