THE MIAMI CLAY LOAM. 5 



on account of the fact that these are chiefly formed by the glaciation 

 of easily disintegrated sandstone. They also differ from the light- 

 colored silty soils of the Knox series and the black silty soils of the 

 Marshall series in that both of the latter series are almost without 

 exception stone free and lack even pebbles or small bowlders. The 

 materials from which the soils of the Miami series are derived are 

 chiefly unstratified and massive, while the materials giving rise to 

 the soils of the Plainfield and Waukesha series are formed by the 

 action of outflowing glacial waters and by modification through 

 subsequent wind action. 



SURFACE FEATURES AND DRAINAGE. 



Considering the wide extent of territory over which the Miami clay 

 loam is developed and also holding in mind its derivation from ice- 

 laid materials, the surface configuration of the type is unusually 

 uniform, or at least varies within reasonably narrow limits. In 

 general, the surface of the type consists of gently undulating or slightly 

 rolling surface features which only become accentuated locally into 

 the form of low, rounded hills or steep-sided knobs in such locations 

 as are occupied by distinct glacial moraines. The only other hilly 

 or steeply sloping portions of the Miami clay loam are those found 

 where postglacial streams have cut deeply below the glaciated upland 

 surface, and have extended their minor branches through the area 

 occupied by the Miami clay loam. Such regions are occasionally 

 found even farther west than the territory principally occupied by the 

 ,type and constitute the greater proportion of the Miami clay loam to 

 be found in Iowa and other west-central States. 



The altitudes at which the type has been developed vary from 

 approximately 600 feet above tide level in the vicinity of Lakes Erie 

 and Michigan to altitudes of a little more than 1,000 feet in more 

 southern locations. These differences in altitude arise chiefly from 

 differences in the elevation of the rock floor over which the glacial 

 materials have been laid down. The surface of the soil type itself 

 rolls gently upward from its lower elevations to the highest altitudes 

 attained near the southern boundary of glaciation in central and 

 southwestern Ohio. 



There is considerable variation in the natural drainage features of 

 the Miami clay loam: the more level areas, and especially those some- 

 what remote from lines of pronounced stream drainage, are inclined 

 to be wet and poorly drained. This arises both from the level surface 

 condition of the soil and from the considerable depth of the massive, 

 stiff glacial clay from which the soil itself has been formed. Thus, 

 both surface drainage and the internal soil and subsoil drainage are 

 deficient over such areas. In the more rolling portions, such as com- 

 prise extensive areas in southern Michigan, west-central Ohio, and 



