100 THE GEOLOGY OF ST. ilARY'S COUNTY 



the land along their shores and in depositing the detritus on a submarine 

 platform or terrace. This terrace is everywhere present and may be 

 found not only along the exposed shores but also passing up the estuaries 

 to their heads. The materials are extremely variable. Along the un- 

 broken coast the detritus has a local character, while near river mouths, 

 the terrace is composed of the debris contributed from the river basin. 



In addition to building a terrace, the waves of the Atlantic and the 

 Chesapeake are cutting a sea-cliff along their coast line. The height of 

 this cliff depends not only on the force of the breakers but also on the 

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

 a low sea-cliff, and a bold coast line, a high one, and each passes into 

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

 one travels along the shore of Chesapeake Bay high cliffs and low de- 

 pressions are passed successively. The wave-built terraces and the wave- 

 cut cliffs are important features along the entire extent of the Bay 

 shore, and should be sought for wherever other terrace surfaces are 

 studied. It must, however, be borne in mind that there are places 

 along the Bay shore where the sea-cliff is absent, or so low that it does 

 not form a conspicuous feature in the topography. In addition to these 

 features, bars, spits, and other wave and current-built formations of a 

 similar character are frequently met with. 



If the present coast line should be elevated, the submerged platform 

 which is now forming would appear as a well-defined terrace of variable 

 width with a surface sloping gently toward the water. This surface 

 would fringe the entire Atlantic and Bay shores as well as those of all 

 the estuaries. The sea-cliff would at first be sharp and easily distin- 

 guished, but as time passed, the least conspicuous portions would gradu- 

 ally yield to the levelling influences of erosion, and might gradually dis- 

 appear altogether. Erosion would also destroy in large measure the 

 original continuity of the formation, biit as long as portions of it re- 

 mained, the old surface could be reconstnicted and the history of its origin 

 determined. 



If the topographic and geologic features which are associated with the 

 terrace now forming are compared with those which accompany the 



