RELATIONS OF DISINTEGRATION AND DECOMPOSITION, 495 



goes on, the surfaces exposed to the action of the chemical agents become 

 larger. If a mass of material, of whatever size, be divided into any 

 number of parts with similar forms, the total area of the new surfaces will 

 be equal to that of the original surfaces multiplied by the square root of 

 the number of parts. For instance, if a given mass of rock be divided into 

 a hundred parts, with forms similar to the original mass, the surface is 

 increased ten times, and therefore the area subjected to chemical action is 

 increased tenfold. Hence, iu so far as the rocks are broken mechanically, 

 they give greater surface of action, and this surface of action increases 

 directly as the comminution increases. It follows that the finely com- 

 minuted material is much more readily decomposed than the coarser mate- 

 rial. Loughridge has shown that the amount of soluble material in soils is, 

 on the average, larger in proportion to the comminution, thus confirming 

 the conclusion that increase in the surface is favorable to chemical action. 11 



But decomposition reacts upon disintegration. In proportion as the 

 material becomes decomposed it is more readily broken up. In so far 

 as the material is chemically altered, and especially in proportion as it 

 is dissolved, the rock is weakened and thus the forces of disintegration 

 rendered more effective. The mechanical and chemical forces therefore 

 act and react upon each other, each one increasing- the effectiveness of the 

 other; hence disintegration greatly accelerates decomposition and solution, 

 and decomposition and solution accelerate disintegration. 



This action and reaction between the mechanical and chemical work is 

 well illustrated by the experiments of Daubree, 6 who found that various 

 minerals and glass when mechanically triturated in a rotating cylinder are 

 very readily acted upon by pure water, carbonated water, and water con- 

 taining sodium chloride. In this way he produced a very fine, impalpable 

 mud, which when dried resembled argillite and contained a high percentage 

 of alkalies. It is clear from the above that the greatest effects in the way 

 of weathering are produced by combination of the mechanical and chemical 

 processes. Where, by the action and reaction of the mechanical and chemical 

 agents, the subdivision has gone to such a stage that the particles are 



"Loughridge, R. H., On the distribution of soil ingredients among the sediments obtained in 

 silt analysis: Am. Jour. Sci., vol. 7, 1874, p. 17. Merrill, George P., Rocks, rock- weathering, and 

 soils, Macmillan Co., New York, 1897, pp. 365-366. 



6 Daubree, A., Geologie Esperimentale, Paris, 1879, pt. 1, pp. 26S-279. Also, Merrill, George 

 P., Rocks, rock weathering, and soils, Macmillan Co., New York, 1897, p. 197. 



