SOILS. 777 



j)laces where the imdei-lying silt has been eroded. The siu-face soil of that 

 region is mainly on the lowan silt, while the Sangamon soil that was 

 formed between the lUinoian and lowan stages of glaciation has been 

 buried beneath that silt. The earlj^ Wisconsin drift within this region has 

 a somewhat limited exposure. The remaining part of the drift surface, 

 comprising a large area, is therefore of late Wisconsin age. 



The unglaciated portion of the Ohio River Basin is covered somewhat 

 widely by Pleistocene deposits. There are not only the valley deposits 

 brought down to the Ohio from the glaciated districts by glacial and modern 

 streams, but also deposits on the uplands of a fine silt apparently of lowan 

 age. The soil of the flat portions of uplands in southeastern ,,01iio and 

 even in States south of the Ohio is formed from this silt. Much of the 

 unglaciated part of the Ohio liiver Basin is, however, so broken that the 

 silt has been removed and soil is being formed from the Paleozoic rock for- 

 mations, as it was before the deposition of the silt or the advent of Pleisto- 

 cene glaciation. There are uneroded places in which the residuary clays 

 formed by the disintegration of the rock surface may be clearly distin- 

 guished in color and texture from the overlying silt of Pleistocene age 



cijAsses of soil. 



There are several modes of classification of soils in use, based gener- 

 ally on either chemical constitution or physical texture or characteristics. 

 The classification which seems best to serve oin- purpose is based mainly 

 on physical characteristics. The control which the physical characteristics 

 exert upon moisture and temperature has been found by expei'imentation 

 to be far more important than the mere chemical cornposition of the soil. 

 It is found that under favorable conditions of moisture and temperature the 

 majority of plants can readily gather sufficient food material from almost 

 any soil. 



In the Erie and Ohio basins the following classes of soils are present: 

 (1) Residuary soils, or soils formed from the underlying rock; (2) stony 

 clay soils, derived from the till or bowlder clay; (3) gravelly or stony soils; 

 (4) sandy' soils; (5) silts or clays of fine texture, but more or less per-sdous 

 to water; (6) peaty soils with a large amount of organic matei'ial. A 

 tabular statement is here jjresented which shows the origin or mode of 

 deposition and the areal distribution of the several classes of soils. 



