180 TRANSFORMATION OF MINERAL SUBSTANCES 



the activities of these primitive organisms, considerable amounts 

 of organic matter might have been formed. The acids, especially 

 nitrous, nitric, and sulfuric, would cause dissolution of the rocks 

 and aid in the weathering processes. Some of the minerals thus 

 brought into solution might have been appropriated by the organ- 

 isms for the synthesis of their cell substance. The rest of the min- 

 erals might be washed away by streams, or accumulate, giving rise 

 to the beginning of the inorganic part of the disintegrated surface 

 layer of the earth. The two processes of dissolution of rock con- 

 stituents and synthesis of organic matter were the beginnings of 

 the origin of the soil. 



To these reactions might be added the activities of the nitrogen- 

 fixing bacteria, both alone and in symbiosis with algae, which could 

 have contributed to increases in the supply of fixed nitrogen on the 

 surface of the earth. Algae themselves are known to have a corrod- 

 ing effect upon stones, and, in association with various bacteria, the 

 extraction of mineral substances from rocks is further increased. 



The general phenomena considered in these pages should quite 

 definitely indicate that microbes have played parts of major 

 importance in rock disintegration and in soil formation. Although 

 the climatic factors exert regulating influences on the decomposi- 

 tion processes brought about in the soil, an inquiry into the 

 activities of microbes reveals a great diversity of action and the 

 indispensable nature of their roles in soil formation. In some 

 cases they assist the purely chemical, physical, and mechanical 

 transformations; in some cases they take an active part in the 

 transformation processes; and in other cases they play the domi- 

 nant role, as in the case of formation of forest soils and peat soils. 



LITERATURE 



1. Bavendamm, W. Die farblosen und roten Schwefelbakterien. Gustav 



Fischer. Jena, 1924. 



2. Buchanan, R. E., and Fulmer, E. I. Physiology and biochemistry of 



bacteria. Vol. 2, Chapter 11; Vol. 3, Chapter 17. The WilUams & 

 Wilkins Co. Baltimore, 1930. 



3. Cholodny, N. Die Eisenbakterien. Gustav Fischer. Jena, 1926. 



4. Harder, E. C. Iron-depositing bacteria and their geologic relations. 



U. S. Geol. Survey, Professional Paper 113. Washington, 1919. 



5. Stoklasa, .T. Biochemischer Kreislauf des Phosphat-ions im Boden. 



Gustav Fischer. Jena, 1911. 



6. Waksman, S. a. Principles of soil microbiology. Chapters 7, 23, 25. 



The Williams & Wilkins Co. Baltimore, 1927. 



