CUM U LOSE SOILS 41 



occurrences of these refractory materials in layers may 

 exercise a very unfavorable effect on the agricultural 

 value of such land. 



Further, residual soils are seldom uniform in texture. 

 The clays are usually gritty, especially when derived 

 from igneous rocks. It has been suggested that this is 

 due to the accumulation of silica set free from the silicic 

 minerals in their loss of alkaline materials. In this state 

 much of it passes into solution and is removed, which 

 probably explains some of the large losses of this ele- 

 ment. But, where the decay is rapid, not all of the 

 silica can be so removed, and it combines with oxygen, 

 to form quartz particles. 



All of these considerations should be kept in mind 

 in the study of residual soils, as they assist in under- 

 standing their characteristics. 



13. Cumulose soils. Cumulose soils consist of 

 years and even centuries of accumulations of plant 

 remains. They occur in every section of the coun- 

 try in areas of from a fraction of an acre to thou- 

 sands of acres, known as peat bogs and muck swamps. 

 The one condition which always accompanies these 

 deposits, and is most largely responsible for their 

 existence, is poor drainage. Such a condition may 

 result from a variety of circumstances. In the North 

 Central states of the glacial section, scattered over the 

 undulating country, are numerous small depressions 

 where water accumulates during much of the year, 

 together with a small amount of sediment from the 

 surrounding hills. These conditions favor the large 

 growth of vegetation which, upon its death, is slowly 



