706 EXPERIMENT STATION RECORD. 



parent rock; (2) the nature and intensity of ttie processes of disintegra- 

 tion, in connection with the local climatic and topographic conditions; 

 (3) the quantity and quality of that complexity of organisms which 

 participate in the formation of the soil and incorporate their remains in 

 it; (4) the nature of the changes to which these remains are subjected 

 in the soil, under the local climatic conditions and physico-chemical 

 properties of the soil medium; (5) the mechanical displacement of the 

 particles of the soil, provided this displacement does not destroy the 

 fundamental properties of the soil, its geo-biological character, and 

 does not remove the soil from the parent rock;^ and (6) the duration 

 of the processes of soil formation. 



All those may be termed genetic conditions of formation of natural 

 soils. Such existing types of natural soils always correspond to a defi- 

 nite combination of the soil-forming factors. The parent rocks, the 

 organisms (with their subsequent transformations), and the physico- 

 geographical conditions of the country, including climate (humidity, 

 temperature), recent geo-physical history and relief, are the chief 

 agents of soil formation. The correlation among these factors may 

 assume various forms, a certain connection or parallelism being observed 

 either among all or only a part of them. Thus, the composition and 

 distribution of the ancient sedimentary and crystalline rocks do not, 

 of course, depend on those conditions (even climatic) of the country to 

 which the formation of the existing soils is subject. But the weather- 

 ing of the rocks and, in general, all the physical and chemical processes 

 which take place in the soil are influenced by climatic conditions. 

 Climates in which wet and dry seasons alternate produce laterites, the 

 climatic conditions governing the biological processes which result in 

 the formation of lateritic soils. Eolian loess and pulverulent rocks 

 which resem))le it are characteristic of continental regions with a dry 

 climate. From this point of view the nature of a given soil type pre- 

 sents, in a certain measure, a function of the climate. 



The soils of a given territorj^ are also influenced by the life activities 

 and the dead remains of plant and other organisms. The soils influence 

 the development and the life activity of these organisms and their 

 decomposition after death. On the other hand, the character of the 

 plant growth, for example, plays not only a direct, but an intermediate 

 role in the formation of the soil. The relief of the soil has an impor- 

 tant influence in determining the drainage, temperature, etc. And 

 lastly, the relative duration of the soil-forming processes which have 

 gone on since the removal of the glacial or water cover, as for example, 

 the successive changes which have taken place in the climate, the en- 

 croachments of the forests upon the prairies, the spread of marshes, 

 the drying up of the soil, etc., must in their turn influence the character 



^Otherwise the soil is converted into alluvium, diluvium, etc., or, in general, into 

 mechanical deposits of secondary formation. 



