156 THE OCEAN 



All these changes of the shore are caused 

 by the action of wind and waves alone, but 

 strange as it may seem the land itself is grad- 

 ually rising or falling in many places and this 

 also greatly affects the shores of the sea. If 

 the coast is high and precipitous the rise or 

 fall of a few inches in centuries may make no 

 appreciable difference, but if the shore is low 

 and sandy or muddy even an inch or two in 

 the rise or fall of the coast land may result in 

 vast changes, for in many places the wide 

 mud-flats and extensive sand-bars are only an 

 inch or two beneath the surface of the 

 water. 



As you walked along the smooth beach or 

 across the mud-flats at low water, you noted 

 the wrinkly lines left by the waves, and the ir- 

 regular trails of shells and small animals, and, 

 if you glanced behind you, no doubt you saw 

 the deep imprints of your own feet, while if a 

 sudden shower passed over, the large drops of 

 rain made queer little bowl-shaped impres- 

 sions on the sand and mud. Afterwards the 

 tide slowly rose and covered the flat or beach 

 with water and when the tide again fell, — if 



