38 



THE PRINCIPLES OF SOIL MANAGEMENT 



tion of loss of the different elements calculated to the 

 amount of the element originally present, and to the 

 proportion the loss bears to the original rock. This 

 exhibits some of the reasons for the difference between 



"ft? -vx-fc 





Fig. 13. Residual soil from limestone. Showing relation to underlying rock 



many soils and the rocks from which they were derived. 

 Assuming that there is any element which is constant 

 in amount, these figures show that the total loss suffered 

 by different rocks ranges from 97.64 per cent for the 

 limestone to 13.47 for the granite. In other words, a 

 limestone soil represents the supplementary materials 

 in the original rock, the main constituent having been 



