712 EXPERIMENT STATION RECORD. 



drainage, the soils may become swampy, and, lu.ce ve)'sa, marshy soils, 

 by dr^'ing and drainage, lose their characteristic peculiarities and 

 approach other local types. If, during the period of formation of 

 chernozem, the steppe or prairie is encroached upon by forests, the 

 latter change the structure and composition of the soil in the direction 

 of soils of wooded steppes and forest soils, etc. 



The genetic t3'pes of soils are large categories which include many 

 subtypes, groups, and subgroups. A detailed classification of soils 

 ma}' be based on two kinds of facts: (1) On the degree or force and 

 on the variation of those d3namic processes which impart to the 

 soil the fundamental features of the given genetic type. Thus, for 

 example, there exist conditions which lead to the formation of cher- 

 nozem soils, but these conditions may vary, ma}' deviate from a certain 

 juean, and, in consequence of these fluctuations, from one and the 

 same or a similar parent rock there may result unlike chernozems with 

 a difl'erent content and quality of humus. (2) On the changes in the 

 composition and structure of the soils in connection with the compo- 

 sition and structure of the parent rocks. The su})divisions of this cate- 

 gory are based upon (a) the physical properties of the soils, / . e. , their 

 skeleton and fine earth; (Jj) the chemical and chemico-petrographic 

 peculiarities of the soils. Chernozem, for instance, may be argilla- 

 ceous, subargillaceous, subarenaceous, marl}', phosphoritic, etc. The 

 division of the genetic types and subtypes of soils into groujxs and 

 subgroups, a division liased on the mechanical, physical, and chemical 

 properties of the soil mass, connects the system here described with 

 the common soil classifications of the German and Russian authors 

 (Mayer, Schiibler, Knop, Senft, Ramann, Feska, Kostichev, and 

 others). It is believed that a soil classification such as that described 

 above, which is based on the quantitative contents in the soil of skele- 

 ton and tine earth and on the particular character of these two con- 

 stituents (mechanico-physical groups and subgroups), is more general 

 than the commonly accepted system. Following these subdivisions, 

 or, more properly, within them, are the chemical sul)divisions based 

 on (1) the chemico-petrographic composition of the soil skeleton, (2) 

 the composition of the siliceous substances of the tine earth of the 

 soil (the chemical nature of the soil clay, of the zeolitic compounds, 

 etc.), and (3) the oxids and salts containing no SiOg, their quantity and 

 nature (carbonates of alkaline earths, of alkalis, ferrous and ferric oxid, 

 phosphates, sulphates, their solubility in water, etc.). 



(Concluded in next number.) 



