144 



ACTION OF THE SEA. 



aware Bay, it was proved by measurement that % 

 from the year 1804 to 1820, the annual encroach- 

 ment of the sea averaged nine feet ; and at Sulli- 

 van's Island, near Charleston, South Carolina, the 

 sea carried away a quarter of a mile of land in three 

 years ending in 1786. 



In relation to Boston Harbour, Professor Hitch 

 cock remarks : " Here are numerous picturesque 

 islands, the inner ones, nearly as far as Boston 

 Light, being composed chiefly of diluvium ; though 

 on their shores, at a low level, not unfrequently we 

 find argillaceous slate and other rocks that occur 

 on the main land. But all the islands outward from 

 the Great Brewster are merely naked masses of 

 rock ; and it would be natural to infer that the di- 

 luvium had been removed from these, even if we 

 did not actually detect the process. But on the 

 Great Brewster the work is going on before our 

 eyes. Its eastern side is a high bank of diluvium, 

 obviously wasting away by the action of the waves 

 that roll in upon it from the wide Atlantic, while 

 the extensive beach along its southern side is com- 

 posed of the materials that have been swept away 

 from its outer coast. The same process is seen 

 going on upon the outer side of several other isl- 

 ands ; and on Deer Island an extensive wall of 

 stone has been erected by the United States gov- 

 ernment to arrest the progress of this degradation ; 

 which, if continued much longer there, would lay 

 open the inner part of Boston Harbour to the fury 

 of the northeasterly storms."* 



Professor H. inclines to the belief that the whole 

 of Boston Harbour, now dotted with small islands, 

 was formerly one piece of solid land; "for," he 

 remarks, " when we see so many islands scattered 

 over its bosom, which seem obviously the wrecks 

 of one continuous diluvial formation, and perceive 

 that the rocks, wherever they occur, are only a con 

 * Report of Geology of Massachusetts, p. 125. 



