20 FIELD OPERATIONS OF THE BUREAU OF SOILS, 1919. 



The Epping, Mitchell, and Bridgeport soils have profiles less 

 maturely developed than those of the series named above. As a rule 

 the horizons have been developed far enough for identification, but 

 fall much short of perfection. In the Mitchell soils the stage of 

 development is somewhat more advanced than in the Epping- or 

 Bridgeport, though in a few areas the profile of the Epping is well 

 developed, approaching in character that of the Rosebud. Owing to 

 the fact that the definition of the Epping soils is a geological one, 

 the variation in character of the soil profile is greater in the various 

 members of this series and even in the same type in different places 

 than is the case in the soils of the Bridgeport or Mitchell. The 

 Epping soils are defined on the basis of their derivation from Brule 

 clay material, one of the geological formations of the area, and the 

 mapping has been done on that basis rather than on the basis of the 

 soil profile. In those rather rare areas where the profile of the 

 Epping soils is approximately mature they do not seem to differ 

 esentially from corresponding members of the Rosebud series and 

 in the future will probably be mapped in that series. Since such 

 areas are very small in Banner County no serious error has been 

 committed in not doing this here. 



AYe are not yet in possession of a sufficient amount of chemical data 

 to show whether a maturely developed soil from the Brule clay will 

 differ from a corresponding type in the Rosebud series. Since the 

 mineral elements, including those usually recognized as the necessary 

 constituents of a productive soil, are very abundant in all these soils, 

 it is perfectly legitimate to question the advisability, or even the 

 justification of a differentiation of the soils on the basis of differences 

 in their content of mineral constituents, except where the amounts 

 of the different constituents are very great. Such data as are avail- 

 able show that these soils (in the two surface horizons) have about 

 2 per cent of lime, 2 per cent of potash, and 0.2 to 0.5 per cent of 

 phosphoric acid. These data, which can not be presented here, show 

 a rather imiform percentage of these constituents in all the soils of 

 the region. This being the case, it would seem that there is no justi- 

 fication for differentiating a maturely developed soil derived from 

 the Brule clay from the Rosebud series. When both soils are devel- 

 oped to the same mature stage their colors are essentially identical, 

 and since they have developed under the same climatic and drainage 

 conditions their organic matter must be assumed to be in the same 

 stage of decay. Since, also, the color is due to their content of 

 organic matter, it is legitimate to conclude that the content of both 

 is approximately the same. Typically, the profile of the Epping 

 series should show no differentiation into horizons, except the darken- 

 ing of the surface soil. 



