THE NATIONAL GEOGRAPHfC MAGAZINE 



<S U RJ& 



..•*: 



Statute Miles 



Area of Delta from 

 survey of 1872. 

 Recession of shoreline 

 and area of erosion. 

 Extension of shoreline 

 and area of deposit. 



SKETCH MAP OF THE MISSISSIPPI DEl/fA SHOWING FORMATIONS 



hanna, the Potomac, and the James 

 rivers rolled in stately grandeur to the 

 sea. Then there came a subsidence, and 

 the sea rushed in through the reach be- 

 tween Capes Charles and Henry and 

 overwhelmed the land in all that vast 

 area we call Chesapeake Bay. 



The land has not always been with- 

 out an ally to counterbalance this display 

 of strength. Sometimes there come up- 

 heavals of the floor of the sea that drive 

 the water into a retreat which often be- 

 comes a rout. 



The consequences of even a slight up- 

 heaval may be strikingly shown by fol- 

 lowing what is known as the twenty- 

 fathom line off the eastern seaboard. 

 This line divides the sea into two parts, 

 that which is less than 120 feet in depth, 



and that which is deeper. Were the floor 

 of the continental shelf, the vast, under- 

 sea platform upon which the continent 

 rests, to rise 120 feet, Delaware Bay, 

 Chesapeake Bay, Albemarle Sound, and 

 all the other deep indentations of our 

 coast would disappear and the new battle 

 line would be practically without salients. 



WHEN THE LAND SCORES A VICTORY 



When the land is victor, through an 

 upheaval, it always straightens out its 

 battle front. The bed of the sea, being- 

 untouched by the chemical changes of 

 the atmosphere, unharassed by running 

 water, but constantlv graded by deposits 

 of sand in its low places and scoured bv 

 the tides in its high ones, is ever tending- 

 to assume a common level. 



