366 THE WORK OF RUNNING WATER 



Mississippi River by swift streams which flow into it and the 

 sediment dropped by the slow-moving river is so large that the 



FIG. 233. River deposits. The river breaks up into numerous small and 

 shallow streams. 



channel of the river fills up quickly and in places must be 

 dredged yearly. 



When a river flows into a gulf or sea, its speed is suddenly 

 checked and its load is quickly dropped. The Mississippi 

 River deposits in the Gulf of Mexico about 1,000,000 tons 

 of sediment a day. Some of this enormous mass is swept 

 far out to sea by waves and tides ; the rest of it accumulates 

 where it drops and builds up new lands called deltas. So 

 great have been the past deposits of the Mississippi River at 

 its mouth in the Gulf of Mexico that a delta has been formed 

 covering as much area as Massachusetts and Connecticut. 

 So large are the present deposits of the river that the delta is 

 enlarging at the rate of one mile in six years. Deltas are fertile 

 and yield good harvests but they are low and are frequently 

 flooded, and crops on them are lost and people are drowned. 

 In many places dikes and embankments are built around deltas 

 as safeguards against floods. 



