136 THE GEOLOGY OF PEINCE GEORGE' S COUNTY 



rial has a local character, while in the vicinity of a river mouth the 

 terraces are composed of debris contributed from the entire river 

 basin. 



Besides building a terrace, the waves of the ocean and bay are 

 cutting a sea cliff along their coast line, the height of the cliif depend- 

 ing not so much on the force of the breakers as on the relief of the 

 land against which the waves beat. A low coast line yields a low 

 sea cliff and a high coast line the reverse, and the one passes into the 

 other as often and as abruptly as the topography changes, so that 

 along the shore of Chesapeake Bay, high cliffs and low depressions 

 occur in succession. 



In addition to these features, bars, spits, and other shore forma- 

 tions of this character are being produced. If the present coast line 

 were elevated slightly, the subaqueous platform which is now in 

 process of building would appear as a well-defined terrace of variable 

 width, with a surface either flat or gently sloping toward the water. 

 This surface would everywhere fringe the shores of the ocean and 

 bay, as well as those of the estuaries. The sea cliff would at first be 

 sharp and easily distinguished, but with the lapse of time the less 

 conspicuous portions would gradually yield to the leveling influences 

 of erosion and might finally disappear altogether. Erosion would 

 also destroy, in large measure, the continuity of the terrace, but as 

 long as portions of it remained intact, the old surface could be recon- 

 structed and the history of its origin determined. 



