SOIL-FORMING PROCESSES 



27 



23. Special cases of weathering. — The weathering of 

 granite and .limestone under different climatic conditions 

 has already been compared. The changes that take 

 place in these rocks as they are evolved to residual clays 

 may now be considered. The following analyses serve 

 to show on what elements the losses are likely to be most 

 serious during the process: — 



Fresh Granite and its Resultant Clay 1 



Si0 2 . 

 A1 2 3 . 

 Fe 2 3 . 

 CaO . 

 MgO. 

 K 2 . 

 Na 2 0. 

 P 2 5 . 

 Ignition 



Rock 



60.69 



16.89 



9.06 



4.44 



1.06 



4.25 



2.82 



.25 



.62 



Clay 



45.31 



26.55 



12.18 



00.00 



.40 



1.10 



.22 



.47 



13.75 



Percentage 

 Lost 



52.45 

 00.00 

 14.35 

 100.00 

 74.70 

 83.52 

 95.03 

 00.00 

 Gain 



Virginia Limestone and its Residual Clay 2 



Si0 2 



A1 2 3 



Fe 2 3 



CaO 



MgO 



K 2 



Na 2 



p 2 o 5 

 co 2 



H 2 



Rock 



7.41 

 1.91 



.98 



28.29 



18.17 



1.08 



.09 



.03 

 41.57 



.57 



Clay 



57.57 

 20.44 



7.93 

 .51 



1.21 



4.91 

 .23 

 .10 

 .38 



6.69 



Percentage 

 Lost 



27.30 

 00.00 

 24.89 

 99.83 

 99.38 

 57.49 

 76.04 

 68.78 

 99.15 

 Gain 



1 Merrill, G. P. Bui. Geol. Soc. Araer., Vol. 8, p. 160. 1879. 

 2 Diller, J. S. U. S. Geol. Survey, Bui. 150, p. 385. 1898. 



