284 



ALEUVIUM. 



eiy &c. In many places the alluvial deposites are 

 from 20 to 50 feet deep, and logs, leaves, and other 

 vegetable and animal relics are dug up from that 

 depth. The banks, however, are so much elevated 

 by the gradual deposition of these deposites, that it 

 is only during a time of flood or an unusual accu- 

 mulation of water that they are overflowed. In 

 some of them, as the Mississippi, the beds of the 

 streams are also elevated by the same cause, so 

 that the river is considerahly higher than the adja- 

 cent country. This is not always the case ; for 

 Professor Hitchcock states that, since the Connec- 

 ticut and its tributaries began to flow, they have 

 excavated their beds nearly 100 feet, though the 

 Connecticut at Northampton is still more than 100 

 feet above tide-water at New-Haven; so that its 

 descent to the ocean is only at the rate of about a 

 foot per mile. Where the descent, and, consequent- 

 ly, the velocity of the water, is greater than this, the 

 bed of the stream will be excavated ; where it is 

 slower, it will fill up. 



We have, in a former chapter, briefly described 

 the action of the sea upon its shores, and alluded 

 to the rapid wearing away of some portions of the 

 coast, wiiile on others there was as rapid increase 

 of land. This process is going on along our whole 

 Atlantic border; but in no place, perhaps, is it ex- 

 hibited in a more striking manner than on the shores 

 of Long Island. The materials which form these 

 extensive alluvial deposites are transported coast- 

 wise by tidal, marine currents, and by the action of 

 the waves, in the direction of the prevailing winds 

 and storms. 



The winds which produce the greatest transport 

 of alluvial matter on the coast of Long Island come 

 from the northeast, bringing in a heavy sea, which 

 sweeps the sand along in a westerly direction. In 

 this manner, outlets of small bays are more or less 

 obstructed by bars and shoals, formed by the cur- 



