24 SOILS: PROPERTIES AND MANAGEMENT 



space and the greater the encouragement to physical 

 agencies. As physical changes open the way for chemical 

 decay, coarse texture will ultimately encourage decomposi- 

 tion as well as disintegration. 



Lastly, the disruptive forces of the rock will be in- 

 fluenced by the chemical composition of the minerals 

 and the mineral composition of the rock. A rock made 

 up of minerals that offer but little resistance to decay 

 will naturally reduce readily and quickly to a soil. 

 Rocks that very largely bear minerals which are re- 

 fractory in their nature, however, may never decompose 

 far enough or rapidly enough to give a soil of any agri- 

 cultural significance. The next step, then, in the study 

 of soil formation is a consideration of the relative resistance 

 of the minerals and the rocks. 



22. The law of mineral and rock decay. Considerable 

 work has been done on the comparative solubility of 

 minerals both in pure and carbonated water, but in most 

 cases it has proved somewhat inconclusive. Neverthe- 

 less we are able, by consulting the work of Mtiller, 1 Clark, 2 

 Daubree, 3 and others, to arrange some of the commoner 

 minerals in the order of their solubility, the most resistant 

 minerals heading the list : 



1. Quartz 6. Epidote 11. Apatite 



2. Muscovite 7. Serpentine 12. Olivine 



3. Biotite 8. Talc 13. Calcite 



4. Orthoclase 9. Hornblende 



5. Plagioclase 10. Augite 



1 Miiller, R. Solution of Rocks in Carbonated Water. Jahrb. 

 k-k Geol. Reichsanstalt, Vol. XXVII, p. 25. 1877. 



2 Clark, F. W. Data of Geochemistry. U. S. Geol. Survey, 

 Bui. 330, p. 401. 1908. 



3 Daubree, A. Solubility of Orthoclase. Etudes de Geol. 

 Experimental, pp. 27 and 252. Paris, 1847. 



