180 A YEAR IN SCIENCE 



First, its bed has a very gentle slope. It has been 

 eroded to base level, the lowest level to which a stream 

 can erode its bed and still leave slope enough for the 

 flow of water. Very few if any streams have reached 

 this condition throughout their entire course. 



Second, it has wide flood-plains. As this erosion 

 in the bed is nearly finished, most of the erosion 

 is on the sides. As a result of this action in some 

 places the flood-plain of the lower Mississippi River is 

 eighty miles wide. The most fertile land is found 

 on flood-plains of rivers. Perhaps the most famous 

 flood-plain of any river is that of the Nile, which for 

 almost 7,000 years has supported a dense population. 

 The floodTplains of the Euphrates and Tigris are almost 

 equally as famous, as it is thought the birth of civili- 

 zation, occurred on the flood-plains of these rivers. 

 The most extensive flood-plains in the world are those 

 of the Ganges in India and the Hoang-Ho in China. 



Third, an old river is very crooked. It meanders 

 to and fro across the flood-plain, because the soft places 

 have eroded more rapidly than the harder, and as a 

 result there are hollows in the bank. .The current is 

 deflected by the hollow across to the opposite side where 

 it cuts into the side. This deflection of the current back 

 and forth across the stream finally, produces a very 

 winding course. 



Fourth, the valley of an old stream is wide, with 

 very gentle slopes. 



