THE OCEAN AND ITS WORK 



213 



Striking Examples of 

 Marine Erosion. — The 

 almost complete destruc- 

 tion by the sea of the 

 village of Dunwich, Eng- 

 land, within historic times, 

 affords an excellent ex- 

 ample of rapid marine 

 erosion under favorable 

 conditions. The village 

 was built upon sand and 

 gravel which formed at 

 the shore a cliff 50 feet 

 high. In the time of 

 Henry II the village is 

 described as " of good note 

 and abounding with much 

 riches," but in Queen 





Fig. 203. — Map of 

 Sharp's Island, Chesa- 

 peake Bay. In 1848 it 

 contained 438 acres and 

 supported a summer re- 

 sort and a number of 

 people throughout the 

 year; in 1900 (lines) the 

 area was 91 acres, and 

 in 1910 (solid black) 54 

 acres. If the rate of 

 erosion continues, the 

 island will disappear be- 

 fore 1930. (U. S. Geol. 

 Surv.) 



Fig. 202. — Map showing how rapidly the island of 

 Helgoland has been destroyed by the sea. The length of 

 the shore line at different times is given. This island is 

 used by Germany as a naval base, and its shores are 

 artificially protected. (After Hobbs.) 



Elizabeth's time it was reduced to one fourth of its former 

 size. Records show that " at one time a monastery, at 

 another several churches, then the old port, then four 

 hundred houses at once, and gradually the jail, the town 

 hall, the high roads, and even the ancient cemeteries, the 

 coffins of which were for some time exposed in the cliff, were 

 all swept away by the devouring sea." The erosion of the 

 cliff has now ceased, as it is protected by a bank of shingle. 



The port of Ravenspur, England, where Henry Boling- 

 broke landed in 1399 to depose Richard II, has entirely 

 disappeared, and no one knows exactly where it stood. 

 Portions of the English coast, where the cliffs are from 200 

 to 250 feet high, have receded at an annual rate of 14 feet. 



In 183 1 a volcanic island — called Graham's Island — 

 composed of volcanic ash, appeared above the Mediter- 

 ranean Sea near Sicily. After reaching a height of 200 feet 

 above the sea and a diameter of a mile, the volcano became 

 extinct, and so rapidly and thoroughly have the waves worn 

 it down, that not even a shoal remains to indicate its 

 former position. 



On Cape Charles, Virginia, it has been necessary to build 

 three successive lighthouses on account of the encroach- 

 ment of the sea. The .irst was built in 1827, 700 feet 

 from the shore line of that time; this was abandoned- in 

 1863, and the whole site has now been washed into the sea 



