30 



SOIL PHYSICS AND MANAGEMENT 



A wet woods swamp is where a forest area with a slope of less 

 than five degrees has heen transformed into a swamp through the 

 accumulation of vegetable material and the consequent increase of 

 moisture. The original forest may be entirely destroyed and re- 

 placed by plants adapted to swamp conditions. 



An ablation swamp is produced by the solution and carrying 

 away of certain more soluble strata, such as gypsum, salt or even 

 limestone, between less soluble strata, thus causing a lowering of 

 the surface and bringing about swamp conditions. 



II. TRANSPORTED FORMATIONS 



Various agencies are engaged in the movement of soil material, 

 namely: gravity, water, ice, and wind, and the deposits formed by 



Fio. 20. Hummocks 6 to 12 inches high, found in swampy places produced by trampling of 

 stock. Commonly called "bogs." (R. W. Dickenson.) 



these are known as colluvial, sedimental, glacial, and eolial. During 

 the transportation of these materials many particles are reduced 

 in size and other changes brought about. Over ninety per cent of 

 the soils surveyed by the Bureau of Soils * in the United States are 

 formed from transported material. 



1. Colluvial or Gravity-laid Soils. Gravity might be said to 

 be the active agent in the formation of all of the above, but gravity, 

 unaided, is very limited in its work, being confined to areas of 

 vertical cliffs or very steep slopes. The material transported by 

 gravity and deposited at the base of cliffs consists of a heterogeneous 

 mixture of detritus that has been loosened by the processes of 

 weathering and carried downward by gravity. This accumulation 

 is commonly designated as talus or cliff debris (Figs. 21 and 22). 



