EUSSIAN SOIL INVESTIGATIONS. 711 



(2) The Avashinji- off of the huinu.s horizon l)y the snow and rain 

 waters (crude soils on hills and slopes). 



(3) The short duration of the processes of soil formation (undevel- 

 oped soils on comparatively recently uncovered or deposited rocks). 



(4) The interference with the soil-forming processes l)y unfavorable 

 climatic influences (especially in deserts and arctic regions). 



The fundamental feature of alluvial soils is their formation with the 

 aid of mechanical transportation and deposition of particles by water. 

 Such are the soils of the river valle3^s. Alluviums, however, must not 

 be confused with alluvial soils. The former are purely mechanical 

 deposits of varying depth — geological formations — while an alluvial 

 soil is the horizon of this deposit which has been subjected to the 

 action of the general dynamic agents of weathering and to the influence 

 of organisms. 



To sum up the above considerations, natural soils may be divided 

 into the following genetic classes and types: 

 Class I. — Zonal soils, complete. 

 Type 1. Lateritic. 



2. Atmospheric eolian. 



3. Soils of the steppe, deserts or dry steppes. 



4. Chernozem. 



5. Soils of wooded steppes and gray forest soils. 



6. Sod soils and podzol soils. 



7. Soils of the tundras. 

 Class II. — Intrazonal soils. 



Type 1. Alkali lands. 



2. Humus-calcareous soils. 



3. Marshy soils, etc. 



Class III. — Incomplete or azonal soils. 

 Soils formed in situ. 



(a) Crude ) . . 



(h) Skeleton r* "^^"^"^ ^'"^''P'- 

 Alluvial soils (of different types). 

 In nature transitional forms are found among the soils of the various 

 genetic types. These transition types may result (1) from the fact that 

 the soil-forming agents (e. g., the climatic conditions) do not change 

 suddenly, but more or less graduall}^, and thus can produce interme- 

 diate results; or (2) from the changes which take place in the soils 

 themselves in the course of their formation and development. Soils 

 may pass through various phases and forms of development in corre- 

 spondence with the external influences which act upon them. Thus, 

 some alkali soils, losing little l)y little their salts by leaching, are con- 

 verted into soils of dry steppes or even into chernozem. Alluvial soils, 

 having passed out of the sphere of river inundations, approach the 

 local zonal types. If a locality, for one reason or another, loses its 

 16466— No. 8—01 2 



