54 IOWA ACADEMY OF SCIENCES. 



THE ACCRETION OF FLOOD PLAINS BY MEANS OF 



SAND BARS. 



BY HOWARD E. SIMPSON. 



About one-half mile above the confluence of the Iowa 

 and Cedar rivers, the Iowa makes a great bend from a 

 southwesterly to a southeasterly direction. The river 

 on the outerside of this curve is rapidly cutting at the base 

 of a high bluff for a distance of about one-third of a mile. 

 The bluff extends beyond at each end, bounding the flood 

 plain, but at some distance from the stream. The bluff' is 

 composed chiefly of Kansan drift overlain by lowan loess, 

 which creeps rapidly riverward when saturated with 

 water. 



Opposite the bluff the broad flood-plain and level "bot- 

 toms" extend away eastward to the drift hills beyond the 

 Cedar and to the northward merge into the sandy floor of 

 ancient Lake Calvin. 



The work of the river in cutting down the higher land 

 and widening its flood plain is plainly shown on the face 

 of the bluff where the process has been very rapid during 

 the past season. Many yellow scars indicate the creep of 

 land rapid enough to cause landslips, and at intervals 

 masses of soil fall into the water and are carried away by 

 the current, a single mass having carried four oak trees 

 rooted in it. 



Farther evidence of the retreat of the bluff may be 

 found at the summit, where the very edge forms the divide 

 between the river and its tributary. Short creek, so great 

 has been the shifting. An Indian burial mound known in 

 local tradition as "The Crave of Osceola's Queen," has 

 practically disappeared within the memory of living set- 



