46 TRANS. ST. LOUIS ACAD. SCIENCE. 



In 1S3S (the lowest water ever known in the lower Ohio — 9 

 inches at Rockport, Puppy creek, and Cumberland Island) there 

 was not less than 7 feet at Plum Point, the shallowest place be- 

 low Cairo. 



In 1848 the shallowest water below Cairo was 6 feet, and there 

 were three places of that depth, viz., Plum Point, head of Island 

 60, and foot of Island 65. 



In 1858 the shoal water had decreased to 4 J at Helena and 5 

 feet at Plum Point and Paw-paw, and less than 6 feet at several 

 other places. 



In 1868, 5 feet was all that could be found at Phillips', Point 

 Pleasant, Island 21, Plum Point, Island 40, President's Island, 

 St. Francis Island, Helena, Horseshoe cut-off, Island 69, Jersey 

 Point, Paw-paw, and Glascox Island. 



*In 1878 the low water was more extensive, but hardly so shal- 

 low, except at Plum Point. 



This constant decrease in depth can only be imputed to one 

 single cause, namely, the clearing of the banks and country. 



The clearing of the banks affects the river as follows : When 

 the timber is cleared, the decaying roots become channels to con- 

 vey the water into and soften the banks, and when a cave takes 

 place it is no longer a slide, but a tumble over and breaking up 

 of the mass, that is soon swept away by the current, and the 

 undermining again goes on. Thus the widening goes on much 

 faster than the filling on the opposite shore, and the shoaling or 

 filling up of the channel follows the widening. 



The clearing of the country above afiects the rivers by opening 

 the outlets of the swamps. These swainps were formerly reser- 

 voirs that held a large portion of the rain and melted snow in the 

 spring and wet seasons, and during the dry weather they supplied 

 a large portion of moisture to the atmosphere, and also, oozing 

 through the soil, supplied numerous springs along the different 

 water-courses, where now there is nothing but dry sand. Thus 

 the clearing of the country increases the overflow in the wet sea- 

 son, and, aided by the widening of the river, is gradually reducing 

 the depth in the dry season. The rapid destruction of the banks, 

 consequent on the destruction of the timber, is still greater where 

 the caving is at banks of recent formation, as they have no soli- 

 dity, being only sand mixed with alluvium ; and, as the filling is 



