42 
sive erosion all tend to form a soil of medium to good fertility and 
of a most durable quality under even fair conditions of agricultural 
use. 
In many regions where the Miami clay loam is encountered, 
scattered bowlders and small stones are found locally over the sur- 
face of the type, and in increasing quantities in the deeper subsoil 
and underlying till. In some small areas this accumulation of stone 
may be sufficient to interfere somewhat with cultivation. In such 
cases the stone is usually gathered from the field and used in the 
construction of fences or buildings. In general, however, the surface 
soil is fairly free from any large masses of rock or extensive ac- 
cumulations of stone and gravel. The larger rock masses associated 
with the Miami clay loam roughly indicate the character of the 
finer grained soil-forming material. The bowlders, stone, and gravel 
comprise fragments of practically every known variety of igneous, 
metamorphic, and sedimentary rock occurring within the area occu- 
pied by the type or within the extensive tracts to the north from 
which the glacial ice passed southward to deposit its load. Granites, 
gneisses, schists, sandstone, limestone, and quartzite are all found 
among the glacial bowlders and pebbles. The softer rocks, such as 
shale, have usually been so finely ground by glacial action as to pre- 
vent identification in the majority of the areas. Usually a large part 
of the rock fragments in the deeper subsoil consists of limestone. 
Considering the wide extent of territory over which the Miami 
elay loam is developed and 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 is gently undulating or slightly rolling with local low, 
rounded hills or steep -sided knobs in areas which include distinct 
glacial moraines. The only other hilly or steeply sloping areas of 
the Miami clay loam are those found where postglacial streams have 
cut deeply below the glacial upland surface, and have extended their 
minor branches through the upland areas occupied by the Miami 
clay loam. 
The altitudes at which this type is developed vary from ap- 
proximately 600 feet above tide level in the vicinity of Lakes Erie 
and Michigan to altitudes of a little more than 1.300 feet in south- 
western Ohio and southeastern Indiana. These differences in alti- 
tude arise chiefly from differences in the elevation of the rock floor 
over which the glacial materials were laid down. The rolling surface 
of the soil type itself slopes gently upward from its lower elevations 
to the highest altitudes attained near the southern boundary of gla- 
ciation. 
There is considerable variation in the natural drainage of the 
Miami clay loam. The- more nearly level areas, especially those some- 
