QUATERNARY LAKES IN THE MISSISSIPPI BASIN 491 



When the Mississippi and Ohio finally became not only able to 

 carry all the load delivered to them but a little more, they began 

 to cut down again. Perhaps even before this time the lakes had 

 become intermittent, being drained except at times of high water, 

 for they were almost filled with sediment. The great flat lake 

 bottoms became swamps, and channels began to deepen again at 

 the former outlets. At the same time the swamps themselves 

 began to be drained at the lower ends. The process of swamp 

 draining has continued to the present time, and on medium-sized 

 streams there now remain only 10-20 miles of swamp, the lower 

 20-50 miles having been drained (see Fig 4). 



