70 



COHESION AND ADHESION. 



cessary to productiveness. This is one reason why 

 the chemical analysis of a soil is not always an in- 

 dex to its value, nor a guide to the quality which it 

 lacks, because in such an experiment its mechani- 

 cal division cannot be considered. The frost is a 

 powerful natural agent in promoting the looseness 

 of land ; but the artificial means of subdivision will 

 be fully considered in the chapter upon Pulver- 

 ization. 



TABLE D. 



The cohesive and adhesive power of soils is, of 

 course, increased when they are wet. Every one 

 knows how difficult it is to separate two wet pieces 

 of glass. Clay soils possess this quality in the 

 greatest degree ; it is, however, lessened by the 

 methods described in the succeeding chapters. Schii- 

 bler called the tenacity of pure clay one hundred, 



