THE MIAMI SERIES OF SOILS. 15 
On the other hand, the surface soils of the different types in the 
Miami series are distinctly lacking in lime to a depth of 1 foot or 
more. Whether this condition is due to the original deposition of 
earthy material lacking in lime or is the result of the lime having 
subsequently been removed is not known. 
The textural character of the rock prevailing in the different 
regions where the soils of this series occur has some influence upon 
the texture of the resulting soils. Thus, in the region of western 
Ohio, eastern and central Indiana, and a large part of southeastern 
Wisconsin, the most extensive areas are occupied by the clay loam 
and silt loam members of the series. These regions are also charac- 
terized by the presence of extensive beds of limestone and shale. 
These rocks in their original condition consist of rather finely 
divided mineral particles. Under the influences of glaciation they 
gave rise to fine-grained rock powder, and this was extensively 
worked into the till sheet. Some coarser particles were present, giv- 
ing the material a sandy texture, and the gravel and stone are merely 
large fragments of rock which were not completely ground down by 
ice action. In the Lower Peninsula of Michigan and along the west- 
ern border of the area occupied by soils of this series in Wisconsin, 
sandstones were much more generally exposed, and the loam and fine 
sandy loam types are extensively developed. In some parts of these 
sections the material derived from sandstone is so abundant that 
types of the Coloma series are intricately associated with the soils 
of the Miami series. 
The thickness of the sheet of glacial drift from which the soils of 
the Miami series are chiefly derived varies considerably in different 
sections. It is usually greatest within the interstream areas and least 
where erosion has cut the valleys of the major streams deeply into 
the till plains. The drift is naturally somewhat thinner along the 
outer margins of the different areas than within the main areas of 
glaciation. Over the greater part of the area covered by these soils 
the total thickness of the glacial drift is made up of the combined 
depths of the latest till sheet and of one or more layers of older 
drift, although this condition is not universal. For these reasons the 
depth of the drift varies from a few inches to more than 500 feet. 
Along many of the major streams which flow to the south from the 
glaciated region, such as the Scioto, the Mad, and the Miami Rivers 
of Ohio and the Whitewater and White Rivers in Indiana, ledges 
of rock outcrop along the crests of the slopes from the upland to the 
stream valley. In other instances the rock, whether limestone, shale, 
or sandstone, is only exposed in patches along the bed of the stream 
or in the narrow gorges of tributary brooks. Such exposures are 
usually absent over a large part of the main areas of glaciation. 
Only a few exposures of bedrock occur in southern Michigan, and 
