KUSSIAN SOIL INVESTIGATIONS. 705 



scientists of WestoiMi Europo have been at a disadvantage regarding 

 this question, since tiiey have for the most part had to deal with soils 

 only slightly developed, shallow or easily washed away, mixed with 

 various geological deposits, and at the same time strongly altered bj^ 

 cultivation. In reality the ''tilled layer of the soil'' of Western 

 Europe, under the influence of the intensive and deep cultivation there 

 practiced, is an artificial mixture of natural soil and of the underlying 

 primitive rock. This accounts for the geo-petrographic and the 

 physico-chemical classification of soils in vogue among the scientists 

 of Western Europe. 



America, with its virgin soils, vast, frequently still untilled plains, 

 prairies, forests, deserts, and barren alkali lands, and clearly defined 

 climatic, physico-geographical and geo-botanical zones oflers an excel- 

 lent field for the study of natural soils. As a matter of fact the 

 American investigators of the soil, especially Hilgard. have already 

 come to a clear recognition of the soil as an independent formation 

 and have established natural soil types. 



The study of soils which has been so industriouslv carried on in 

 Russia the last 20 to 30 years under the leadership of Dokouchayev and 

 Kostichev has for its starting point the idea of the soil as a natural 

 body which occupies an independent place in the series of formations 

 of the earth's crust. 



According to the definition of Professor Dokouchayev, under the 

 term '\soir' must be understood the surface horizons of the rocks, 

 more or less altered luider the simultaneous influence of water, air. 

 and various organisms, living as well as dead. In other words, the soil 

 is the superficial horizon of rocks in which the general processes and 

 phenomena of weathering, transportation of particles, etc. , combine with 

 the biological processes and phenomena due to the influence of plants, 

 animals, and micro-organisms. Weathering of rocks which takes 

 place independently of the action of organisms yields products which 

 must be considered as rocks, and the study of such products belongs to 

 petrography. These products may replace and may be converted by 

 cultivation and fertilizing into artificial soils, but must be distinguished 

 from natural soils. However, such soils are of rare occurrence. It 

 is well known that many organisms, such as nitrifying bacteria, lichens, 

 alpine plants, etc., play an important part even in the first stages of 

 the disintegration of the massive and sedimentary rocks. On the other 

 hand, in the class of natural soils should not be included the mechanical 

 deposits of dead organisms or their excretions (peat beds, guano, 

 and the like) and those derived from rocks of organic origin. 



As a superficial geo-biological formation of the earth's crust, the soil 

 diflfers from the parent rock from which it is derived in composition, 

 complexity of the dynamic factors, and external morphological pecu- 

 liarities. Natural soils vary with (1) the petrographic type of the 



