224 



PHYSICAL GEOLOGY 



the Humber) about 290 square miles have been added to the coast, 

 while on another (Fens of Lincolnshire), the area of the land has 

 been increased more than 1000 square miles. It is stated that for 

 every square mile washed away from portions of this coast, three 

 square miles have been added on others. Moreover the sea-built 

 land is, on the whole, richer than that which was destroyed. A tele- 

 graph pole erected at a point on the English coast in 1873 was 300 

 feet inland in 1902. At Atlantic City, New Jersey, portions of the 

 sand reefs are being built out while others are retreating. Hotels 

 have had to be moved forward so as to be kept near the sea. The 

 history of the town of Rye, England, is instructive as showing that 

 the land may be attacked by the sea at one time and later be increased 

 at the same point and by the same agent. This town was once de- 

 stroyed by the sea, but the site is now two miles inland. 



Shores 



The shores of the oceans may, in general, be classed topographi- 

 cally as smooth or rough, or according to origin as those resulting 

 from elevation or from submergence. To understand the configura- 

 tion of a shore one must keep in mind (1) that the effect of deposition 

 on the ocean bottoms is to smooth out all inequalities and to produce 

 a monotonous plain which slopes gently from the beach to the edge 

 of the continental shelf, and (2) that the effect of erosion on high land 

 is first to roughen it. 



Smooth Shores. — When a sea bottom on which sediment has long 

 been accumulating is raised to form land, a smooth, approximately 

 flat plain will be exposed. The low, level plain of Yucatan, which 

 slopes beneath the water so gently that vessels cannot approach 

 in safety nearer than three miles from the coast, so that all freight 

 must be taken to land in shallow boats, is a good example. The land 

 bordering the Atlantic and Gulf coasts of the United States south 

 of New York is a somewhat broken, level plain, through which 

 streams flow sluggishly to the sea. The underlying strata dip gently 

 towards the sea and are composed of unconsolidated sands and clays 

 containing marine shells. This plain varies in width from a fraction 

 of a mile to 500 miles, extending from the Fall Line on the west to 

 the shore on the east. 



The Fall Line marks the boundary between the new, unconsolidated 

 sands and clays of the Coastal Plain and the harder, ancient rocks of 



