SOILS OF THE EASTERN UNITED STATES AND THEIR USE X. 



THE MARSHALL SILT LOAM. 



GEOGRAPHICAL DISTRIBUTION. 



The Marshall silt loam is without doubt the most extensive single 

 type of soil to be found within the limits of the United States. Exten- 

 sive areas of this type have been encountered in 20 soil surveys dis- 

 tributed through seven different States, and an aggregate area of 

 4,084,230 acres of the type has thus far been mapped. The region 

 within which this soil dominates practically all others extends from 

 west-central Indiana through central and western Illinois across 

 northern Missouri and southern Iowa and into central Nebraska and 

 northern Kansas. Throughout this entire region the upland, brown 

 prairies consist chiefly of this single soil type, and in certain counties 

 of which soil surveys have been made within this prairie belt from 65 

 to 80 per cent of the total area has consisted of the Marshall silt loam 

 alone. Sufficient soil surveys have been made through this section 

 to outline the general region within which it may be expected that 

 additional extensive areas of the Marshall silt loam will be encoun- 

 tered, and it may be predicted with safety that fuUy one-half of the 

 total soil area within the region designated will ultimately be found 

 to consist of this one type. 



CHARACTERISTICS OF SOIL AND SUBSOIL. 



The surface soil of the MarshaU silt loam consists of a dark-brown, 

 chocolate-brown, or almost black silt loam, which is evidently rich 

 in organic matter. This surface soil varies in depth from 7 or 8 inches 

 in the more rolling areas to 18 or 20 inches on the more level prairies. 

 The average depth of the soil material is probably in the vicinity of 

 15 inches. The surface soil grades into a lighter colored, sometimes 

 mottled, silty loam or silty clay, whose prevailing colors are yellow, 

 gray, or drab, depending to some degree upon the completeness of 

 subsoil drainage. This same class of material usually extends to a 

 depth of 6 or 8 feet, in the more shallow deposits, to depths of 20 or 30 

 feet or even more, where the deposits are fully developed. Both 

 surface soil and subsoil are unusually free from stone or gravel of any 

 description, and even the coarser grades of sand are almost entirely 



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