4 SOILS OF THE EASTERN UNITED STATES. 



The Wabash silt loam is easily distinguishable from the other 

 alluvial bottom land soils of the same region through its character- 

 istic black to dark-brown surface soil, and through the fact that it 

 lies at the lower levels, where it is frequently subject to overflow. 

 It is always associated with the streams which have their head- 

 waters or a considerable part of their course within the region oc- 

 cupied by the brown or black upland prairies of the Central States. 



SURFACE FEATURES AND DRAINAGE. 



The surface of the Wabash silt loam is almost absolutely level, 

 forming the broad first bottoms or overflow lands which occupy one 

 or both sides of the larger streams of the Central Prairie States and 

 of the region immediately to the south. It very often happens that 

 the frequent overflows of the different streams have built up the 

 areas of this soil type which lie immediately adjacent to the stream 

 channel to elevations somewhat higher than the more remote portions 

 of the same bottoms. This arises from the fact that a large part of 

 the suspended sediments are deposited where the force of the current 

 is first checked when the streams overflow their banks. Consequently 

 the larger proportion, particularly of the coarser materials held in 

 suspension, is first deposited and the finer materials in less quantity 

 are carried to the region of quiet water farther from the main stream 

 channel. This continual upbuilding along the course of the stream 

 frequently gives rise to low broad bars or natural levees, which con- 

 stitute the highest elevations to be found within the areas of the 

 Wabash silt loam. In such locations the material is apt to be some- 

 what coarser than the general average of the type, and even small 

 areas of fine sandy surface soil of a somewhat lighter color than that 

 which characterizes the type may be found in such positions. These 

 low elevations rarely rise more than 5 or 10 feet above the general 

 altitude of the bottoms and they usually slope sharply down to the 

 stream channel on one side, and gradually and gently out to the 

 general level upon the landward side. The only other departure 

 from an almost absolutely level surface within the area of the Wabash 

 silt loam occurs in the case of the abandoned stream channels or old 

 bayous which are frequently found within all areas of the type. 

 These abandoned channels are usually narrow, crooked, and of shal- 

 low depth. They constitute the most serious topographic obstruction 

 to the cultivation of the land which occurs ajiywhere within the 

 Wabash silt loam area. Their chief utility to agriculture lies in the 

 fact that they usually furnish a fair outlet for the drainage of ad- 

 jacent fields, thus avoiding the necessity, in some cases, of digging 

 open ditches to cany oflf surplus water. 



The natural drainage of the Wabash silt loam, owing to its bottom- 

 land position and its rather fine texture, is normally very poor. In 



