THE MARSHALL SILT LOAM. 5 



loam one of the most prized of the general farming soils in the central 

 prairie States. 



In general the surface slopes are sufficient to give fairly adequate 

 natural drainage without giving rise to erosion, except over small areas. 

 In consequence the topographic features of the Marshall silt loam are 

 such that fully 90 per cent of its surface may be cultivated with the 

 heaviest and most complete equipments of labor-saving farm imple- 

 ments. This fact alone has placed the type of soil in great demand 

 for agricultural purposes. 



Within the States east of the Mississippi River where the Marshall 

 silt loam is developed, its surface lies at altitudes ranging from 650 

 feet to approximately 1,000 feet above tide level. In northwestern 

 Missouri and in southwestern Iowa the altitude rises gently to approx- 

 imately 1,000 feet and the same altitudes prevail immediately to the 

 west of the Missouri River in Kansas and Nebraska. It is only in the 

 central portions of these latter States that the elevation of the Mar- 

 shall silt loam attains to 2,000 feet or more above sea level. Thus 

 the type extends in a broad east and west belt within the temperate 

 region of the United States at altitudes prevailingly between 650 feet 

 and 1,500 feet above tide. 



The development of the Marshall silt loam east of the Missouri 

 River is entirely within a territory which experiences an adequate 

 rainfall well distributed throughout the growing season, and there 

 is thus no deficiency in the natural moisture supply for the produc- 

 tion even of those crops which make the greatest demand for soil 

 moisture during a long continued period of growth. West of the ninety- 

 eighth meridian, however, the amount of rainfall rapidly decreases, 

 and those areas in the extreme western region of the development of 

 the Marshall silt loam sometimes experience insufficient rainfall for 

 the production of such crops as Indian corn and oats. There is thus 

 within the area occupied by the Marshall silt loam a gradation from 

 a maximum rainfall in its eastern extent to a lighter rainfall, amount- 

 ing to about 25 inches annually, at its extreme western limits. 



In the earlier days when the central portion of the United States 

 was first being opened for settlement the drainage conditions over a 

 considerable part of the area mapped as Marshall silt loam were not 

 adequate. During the months of spring and early summer the 

 almost level prairie lands were frequently covered by standing water, 

 which was only removed by percolation and evaporation during mid- 

 summer. The areas in consequence were occupied by rank growths 

 of prairie grasses in the central States, and these were largely utilized 

 for pasturage by the earlier settlers, who cleared their farms and 

 built their dwellings near the stream courses within the timbered belt. 

 With increases in population, with the opening up of sluggish stream 

 channels, and particularly with the installation of extensive tile under- 



