16 SOIL COMPOSITION, CLASSES AND TYPES 



Residual soils are underlaid by the rocks from which they were 

 formed — such as granite, Hmestone, sandstone, shale and others. 

 Wherever such soils are found the graduation of rock into soil may 

 easily be observed. These soils are widely distributed in the 

 United States — ^including the Great Western Plains and the larger 

 portion of the Southern States, excluding the river valleys and the 

 Atlantic and Gulf Coastal Plains. 



If all the soils could have remained where they were formed then 

 all the soils in the world derived from rocks would be residual. But 

 this has been impossible because of the forces which have been and 

 are still at work effecting changes on the earth. 



Cumulose soils are deposits of vegetable matter accumulated 

 most commonly in what used to be shallow bays, lakes and ponds, 

 and preserved because they were covered or saturated with water. 

 It is common to see water plants such as flags, mosses, reeds and 



Fig 7 — Diagram showing peat formation and a floating bog, cc^ vegetable growth, 

 on surface of poijid, ddy partially decayed organic matter accumulating on bottom, ee, 

 chmbmg bog (Shaler ) 



sedges, growing, for example, along the shores of a pond. These 

 plants die, sink to the bottom and are wholly or partially preserved 

 by stagnant water which prevents or inhibits their decay. Some- 

 times ^^ floating bogs'^ are formed which become thicker and thicker, 

 and as they thicken gradually sink to the bottom (Fig. 7). In either 

 case there comes a time when the shallow body of water becomes 

 filled with a soft, spongy mass — ^the final stage in the formation 

 of peat," 



Peat when dry is the hghtest of soils, and may be black, brown 

 or reddish in color. It is commonly described as ^'raw" when the 

 plant remains can be easily recognized, and "well decomposed" 

 when the plant remains have lost their identity. Peat is a material 

 much used for fuel m countries of the Old World. 



Muck. — ^When considerable sediment is mixed with peat the 

 resulting soil is called "muck. " It is more decomposed, firmer and 

 heavier in weight than peat. 



Occurrence and Value of Peat and Muck Soils. — ^Peat and 

 muck soils occupy local areas ranging from a few to thousands of 

 acres in extent, and they may vary in depth from a few inches to 



