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 



