6 BULLETIN" 355, U. S. DEPAETMENT OF AGEICTJLTURE. 



deposits wMch, in the South Atlantic and the Gulf Coast regions, 

 have an average width of over 100 miles and which are not residual 

 soils, but there should be added numerous small areas of residual 

 soils scattered throughout areas of other kinds of soil. 



Cumulose or swamp soils (Ref. No. 3, pp. 35-38). — This type of 

 soil is related to residual soils in that it has been formed largely from 

 materials not transported. When plants gi'ow where water fills the 

 soil most of the time, the lack of air in the land sui"f ace hinders the 

 decay of organic matter to the extent that large deposits of this 

 material finally collect. Such accumulations going on for ages 

 result in what are commonly known as peat bogs or muck swamps. 

 They contain, as a rule, only such mineral matter as has been washed 

 in from adjoining areas. Cumulose soils are widely distributed and 

 vary greatly in area. In this country they are most numerous in 

 the northern United States, while larger areas of shghtly different 

 type, known as seacoast swamps, are common along the Atlantic 

 and Gulf coasts. Such soils are generally useless for agricultural 

 purposes mitil drained. The management of marsh soils, however, 

 is considered in Lesson X. 



While soil in many cases has been derived as above explained from 

 the rock dii'ectly under, or from plant remains in place, there are many 

 Idnds of soil which were formed in other sections of the country and 

 have been brought to their present location by some natural agency. 

 The three most important agencies transporting soil materials are 

 water, ice, and wind. 



Alluvial soils (Ref. No. 2, pp. 43-50). — The action of water as a 

 soil-forming agent is a matter of common observation. Whenever 

 streams flood and overflow their banks they deposit some of the sedi- 

 ment brought down from higher up in their valleys. In this way 

 they frequently form layers of sand or fine gravel when the stream is 

 rapid, and of silt when it is moving very slowly, and in the broadj 

 lakelike floods which occupy the larger valleys of the more important 

 rivers the finest sediment, or clay, is frequently deposited in deep 

 layers. Soils thus transported by water are called alluvial soils. 

 They are always stratified, and the strata frequently vary a great 

 deal in the size of grains, so that a layer of gravel is often found under 

 one of coarse sand, and a layer of coarse sand under one or more of 

 fine silt. For this reason alluvial soUs differ greatly in character, and 

 one must examine the subsoil of any alluvial field if he desires to 

 know its condition and value. i\.lluvial soils include large agricul- 

 tural areas, and when well drained are among the most productive 

 soils of the earths surface. The high percentage of organic matter 

 which they commonly contain and the frequent renewing of fertility 

 by repeated overflows (in case of the low-lying alluvial soils) are 

 reasons why they keep productive. The Nile Valley in Egjrpt is a 



