28 BULLETIN 142/ U. S. DEPARTMENT OE AGRICULTURE. 
the material of the deeper subsoil is derived from calcareous rocks. 
In Michigan a much larger proportion of granites, schists, and other 
crystalline rocks has been mixed with the soil-forming material. - 
Field determinations indicate that the surface soil of the Miami 
loam is generally acid to a depth of 9 to 12 inches, even where the 
subsoil contains large quantities of limestone fragments. 
All of the areas of the Miami loam thus far mapped are derived 
from the broad till plains and rolling morainic areas of glacial 
drift formed during the last stage of the Wisconsin ice invasion. 
While a large part of the material entering into the composition of 
the soil is derived from the local rock of each region where it is 
mapped, there has been added a varying amount of material brought 
by the glacial ice from distant localities. The crystalline rocks in 
the form of bowlders and gravel are of such origin, and it is prob- 
able that a large part of the finer-grained material of the soil and 
subsoil was similarly contributed. Consequently the Miami loam 
consists of a heterogenous mixture of mineral matter from a wide 
variety of rocks, and it is partly due to this fact that this soil is 
highly productive and durable under continued cultivation. 
All of this derivative material was brought to its present posi- 
tion by the glacial ice which overspread the region. It was depos- 
ited as a thick sheet of till over the more nearly level areas, and 
accumulated in ridged and hilly tracts where the front of the ice 
stood temporarily during the retreat of the glacier. Usually such 
areas are marked by accumulations of bowlders at the surface and 
within the soil and subsoil, while occasional gravel beds and some 
sand occur in the deeper subsoil. Over the till plains the entire mass 
is a rather uniform compact, gritty, and gravelly bowlder clay. 
The topography of the greater part of the Miami loam is undu- 
lating to gently rolling. There are large areas within which the 
surface is hilly or ridged and where the elevations rise 75 to 100 
feet above the general level of the upland. These ridged areas are 
interspersed by large and small kettle-shaped depressions, so that the 
surface is decidedly irregular. Such areas are encountered where 
the type occurs on the morainal ridges. In southeastern Wisconsin 
the type is gently undulating to rolling. It occurs to some extent as 
long, low, gently sloping ridges, with large areas of nearly level land 
intervening. In general, there is sufficient slope to insure good sur- 
face drainage over the type, although in the more nearly level tracts 
and in local depressions the installation of tile underdrains is bene- 
ficial. 
Probably over three-fourths of the total area of the Miami loam 
encountered in the progress of soil-survey work is under cultivation. 
The remainder of the type consists of broken or hilly tracts which 
are either forested or are utilized as permanent pasture. The type 
